Zvonimir Z. Bandic Hitachi Research Center
Michael Rooks IBM T. J. Watson Research Center
Ruediger Berger Max Planck Institute for Polymer Research
Takashi Ando Hitachi Research Lab #431
O1: Patterned Magnetic Media
Monday AM, November 27, 2006
Room 310 (Hynes)
9:30 AM - **O1.1
The First 12 Years of Patterned Media
Stephen Chou 1 Show Abstract
1 Electrical Eng, Princeton University, Princeton, New Jersey, United States
Since the proposal of “quantum magnetic disks” (now termed “patterned media”) in 1994 , the field has been gone through different phases. Now this new paradigm for magnetic data storage is being pursued aggressively by entire industrial as a key path to increase data storage density. Yet, initially, quantum disks were poorly understood and were considered as academic interest only, until a low-cost, high-throughput, large-area sub-10 nm patterning technology, nanoimprint lithography (NIL), became available . The talk will present author’s bird-eye view of the patterned media developments in the past 12 years, as well as its new directions and potentials in the future. The talk will also address advances in NIL, which has demonstrated 6 nm half-pitch  and 400G dots/in2 and its application in manufacturing of patterned media. S. Y. Chou, M. S. Wei, P. R. Krauss, P. B. Fischer, J. Appl. Phys. 76 (10), 6673 (1994). S. Y. Chou, P. R. Krauss, and P. J. Renstrom, Appl. Phys. Lett, 67 (21), 3114 (1995) and Science, 272, 85 (1996) Austin MD, Zhang W, Ge HX, Wasserman D, Lyon SA, Chou SY, Nanotechnology 16 (8): 1058-1061 AUG 2005.
10:00 AM - **O1.2
Future Trends in Magnetic Recording Media.
Dieter Weller 1 Show Abstract
1 Media Research Center, Seagate Technology, Fremont, California, United States
10:30 AM - O1.3
Novel Methods to Reduce Pattern Size and Pitch for Data Storage Using Electron Beam Writing.
Zhou Lu 1 , Alexander Cartwright 1 Show Abstract
1 Electrical Engineering, University at Buffalo, Buffalo, New York, United States
Pattern size and pitch are two major factors that directly affect the capacity of a data storage unit. As a technique that can be used for direct writing or molding in the nanometer scale, electron beam lithography has been expected to be one of the best candidates to fabricate ultra-fine and ultra-compact patterns for the next generation of data storage media. In the talk, we present novel methods which are used to reduce the pattern size and pitch written by electron beam on positive tone resist Poly(methylmethacrylate) (PMMA).Specifically, the current work uses a very fine writing dose which is much lower than the critical dose of the PMMA. The distance between the adjacent writing spots (which correspond to Gaussian functions) is finely adjusted till the partially overlapping Gaussian functions form a contour with periodic dose peaks higher than the critical dose, which results in a periodic exposure of the PMMA. This writing strategy making use of fine dose Gaussian function overlapping results in patterns with smaller size and pitch compared to the conventional method that use writing dose higher than the critical dose. Additionally, we use ultrasonic development in combination with cold development to greatly increase the resist contrast, which further defines smaller pattern size, and enables smaller pattern pitch, as well as brings higher pattern uniformity and reproducibility. Using a conventional beam voltage of 15kV, with the methods above, we achieve ultra-fine and high density patterns with about 10nm in size and 40nm in pitch, which corresponds to a storage capacity near the range of trillion bits/inch2. In comparison, using dose (slightly higher than the critical dose) and normal development strategy (resist developed at room temperature, without ultrasonic agitation), we can only obtain patterns with size about 20-30nm and pitch about 100nm.
10:45 AM - O1.4
Hierarchical Magnetic Nanodot Array for Multiple States Storage Device.
Qijun Xiao 1 , Robert Krotkov 1 , Thomas Russell 2 , Mark Tuominen 1 Show Abstract
1 Physics, Umass, Amherst, Amherst, Massachusetts, United States, 2 Polymer Science and Engineering, Umass, Amherst, Amherst, Massachusetts, United States
11:30 AM - **O1.5
Patterned Media Technology: How Nanopatterning Will Change Magnetic Recording Media and Hard Disk Drives.
Thomas Albrecht 1 , Z. Bandic 1 , M. Best 1 , E. Dobisz 1 , D. Kercher 1 , T. Thomson 1 , Tsai-Wei Wu 1 , H. Yang 1 Show Abstract
1 San Jose Research Center, Hitachi Global Storage Technologies, San Jose, California, United States
As the superparamagnetic effect continues to make scaling of conventional magnetic recording technology to higher densities more difficult, alternative technologies such as thermally assisted recording (TAR) and patterned media (PM) are being considered as likely routes to terabit per square inch density and beyond. PM solves the thermal stability problem by moving away from the conventional concept of using multiple independent random magnetic grains per bitcell and instead uses a single domain pre-defined magnetic island per bitcell, the island having larger volume than the individual grains in conventional recording media. Creating a workable data recording system based on PM presents multiple challenges, not the least of which is cost-effective high volume fabrication of disk media with ~1012 pre-patterned magnetic islands per surface. The size of these islands (~25 nm diameter and ~35 nm periodicity in 2 dimensions) is generally beyond the capabilities of conventional optical lithography. Advanced e-beam lithography may be used to create a master pattern for PM disks, and nanoimprint lithography shows promise as a practical and low-cost method to replicate e-beam generated patterns over large numbers of disks. Since nanoimprint lithography is itself an emerging technology, it presents its own set of challenges, including resist materials selection, control of resist flow during printing, resist curing methods, mold release strategy, and pattern transfer issues. Other media fabrication challenges include etching of nm-scale features into the surface of disk substrates, planarization of media, and metrology. Integration of PM into a disk drive recording system also creates challenges in head-disk interface, track-following servo, and signal processing. While PM alone can significantly extend recording density, even higher density can be achieved by combining PM and TAR, creating a new set of technical hurdles to overcome in the future.
12:00 PM - O1.6
Annealing Study of Co/Pd Magnetic Multilayers for Applications in Bit-Patterned Magnetic Recording Media
Chunsheng Ee 1 , James Rantschler 1 , Shishan Zhang 1 , Darren Smith 2 , Sakhrat Khizroev 2 , Dieter Weller 3 , Dmitri Litvinov 1 4 Show Abstract
1 Electrical and Computer Engineering, University of Houston, Houston, Texas, United States, 2 Electrical and Computer Engineering, Florida International University, Miami, Florida, United States, 3 , Seagate Technology, Fremont, California, United States, 4 Chemical & Biomolecular Engineering, University of Houston, Houston, Texas, United States
High anisotropy magnetic multilayer thin films such as (Co/Pd)n and (Co/Pt)n have been studied extensively as promising recording layer materials for applications in magneto-optical and perpendicular magnetic recording. These materials are characterized by very large values of magnetic anisotropy resulting from the hybridization of 3d electrons in Co and 4d electrons in Pd at the Co/Pd interfaces and are suitable for ultra-high density recording application beyond the superparamagnetic limit of conventional CoCr alloys. Magnetic multilayer properties are strongly affected by the thicknesses of Co and Pd layers in the bi-layer stack, which can be used as an efficient pathway to achieve material with desirable properties.Recently, the magnetic multilayers have been considered for applications in patterned medium recording, the technology with a promise to advance magnetic recording beyond the areal bit densities achievable with conventional magnetic recording schemes. This work presents an annealing study of Co/Pd magnetic multilayers developed for bit-patterned medium recording applications. The effects of microstructure modifications resulted from multilayer annealing are correlated to the change in magnetic properties. Several samples of Co/Pd magnetic multilayers with qualitatively distinct magnetic properties, achieved by varying Co and Pd layer thicknesses, were deposited by magnetron sputtering. Evolution of the microstructure and magnetic properties under different annealing temperatures was studied. Magnetic properties including M-H loops, DCD and IRM curves, and micromagnetic properties were evaluated using VSM, MOKE, and MFM. Surface morphology and microstructure were characterized using AFM, SEM, and X-ray diffraction. Hybridization of the d-shells was evaluated using XPS.It has been found that for lower annealing temperatures (<200C), the coercivity, Hc, and nucleation field, Hn, increased monotonically with the annealing time. However, for higher annealing temperatures, the initial increase in Hc and Hn was followed by the decrease of these parameters. This transition results in the change of the magnetization reversal modes from a two-stage reversal by domain nucleation and domain wall motion to a single stage reversal by magnetization rotation. XRD showed improved texture before the transition. AFM and SEM imaging showed increased surface roughness - the indication grain growth. XPS spectra reveal a shift in the valence band indicating the alloying of Co and Pd layers. The MFM images of a AC demagnetized multilayers demonstrate a transition from long-range ordered stripe domain patterns to the short range ordered cluster-like domain patterns. The transition from primarily exchange interaction to dipolar-like interaction was observed from DCD and IRM curves.Detailed evaluation of the magnetic properties of the patterned Co/Pd multilayers including the mechanisms of magnetization reversal will be presented as well.
12:15 PM - O1.7
Development of Block Co-Polymers as Self-Assembling Templates for Patterned Media
Martin Bakker 1 2 , Warke Vishal 1 2 , David Nikles 1 2 , Micheal Curry 1 3 , Kunlun Hong 4 , Jimmy Mays 4 , Phillip Britt 4 Show Abstract
1 Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama, United States, 2 Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 3 Physical Sciences, The University of West Alabama, Livingston, Alabama, United States, 4 Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Block Co-polymers that self-organize are of interest as templates for patterned media, as they potentially provide a low cost fabrication route. Poly(styrene)-Poly(methylmethacrylate) block co-polymers (PS-b-PMMA) of appropriate block length and PS to PMMA ratio self-assemble into a 2-D hexagonal phase in which the PS majority phase is continuous and surrounds cylinders of the minority, PMMA phase. For application of this phase to patterned media it is necessary that the cylinders of the minority phase be oriented perpendicular to the substrate surface. This can be achieved by a number of methods, including appropriate choice of substrate and use of a random co-polymer underlayer We report here that Indium Tin oxide surfaces are also capable of inducing a perpendicular orientation in block co-polymers, likely due to the effect of surface roughness of the substrate. By use of an acetic acid wash the minority PMMA component can be induced to rearrange, giving rise to pores perpendicular to the substrate. By using a conducting substrate such as ITO, electrodeposition can be carried out into the open pores to produce arrays of magnetic nanopillars of 18 nm diameter.
12:30 PM - O1.8
Self-assembly of L10 FePt Nanocrytals for Patterned Media
Jiao-Ming Qiu 1 , Byeong-Su Kim 2 , T. Andrew Taton 2 , Jian-Ping Wang 1 Show Abstract
1 The Center for Micromagnetics and Information Technologies (MINT) and Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 2 Department of Chemistry, University of Minnesota, Minneapolis, Minnesota, United States
12:45 PM - O1.9
Patterned Media Based on CoPt/Ni Composite Nanowire Array.
Andrew Gapin 1 , Xiang-Rong Ye 1 , Li-Han Chen 1 , Sungho Jin 1 Show Abstract
1 , University of California San Diego, La Jolla, California, United States
A convenient fabrication of patterned media with discrete magnetic elements and high crystal anisotropy is highly desirable for future ultra-high-density magnetic recording media with terabit/in2 level density. We have fabricated an array of CoPt/Ni composite nanowires using anodized aluminum oxide (AAO) templates by electrochemical deposition and annealing treatment. The array consists of vertically aligned, ~25 nm diameter, composite nanowires with ~80 nm long, magnetically soft Ni at the base and ~20 nm long, magnetically hard, L10 phase CoPt at the top. To see the influence of the composite structure, separate samples with Ni and CoPt nanowires of the same height were prepared and annealed using the same conditions. M-H hysteresis loops perpendicular to the substrate and along the nanowire axis show that the Ni nanowires exhibit relatively soft magnetic coercivity of 242 Oe, while the CoPt nanowires show a very high coercivity of at least 10.97 kOe. The composite CoPt/Ni nanowires exhibit an intermediate coercivity of ~1.96 kOe. The results for further optimization and analysis of materials and processes including guided and patterned anodization, as well as implications for potential patterned media applications will be discussed.
O2: Nanoimprinting Lithography I
Monday PM, November 27, 2006
Room 310 (Hynes)
2:30 PM - **O2.1
Room-Temperature Nanoimprint Lithography
Shinji Matsui 1 , Ken-ichiro Nakamatsu 1 Show Abstract
1 , University of Hyogo, Hyogo Japan
Nanoimprint lithography (NIL)1-3, has promise as a simple, high-throughput, low cost process for replicating various nanostructures and is beginning to attract plenty of attention from industries for various applications. Previously, we proposed the use of hydrogen silsesquioxane (HSQ; Dow Corning FOX-16) as a replication material for NIL. HSQ has the unique property of enabling NIL at room temperature (RT), meaning that nanostructures can be replicated without a resist thermal cycle and UV-exposure. In previous experiments on HSQ pattern replication, we formed HSQ resin on a substrate using the conventional spin coating technique. However, the following issues still remain to be addressed in NIL using spin-coated HSQ as the replication material. (1) A high imprinting pressure, ranging from 5 to 40 MPa is required. (2) HSQ imprinted depth often depends on mold linewidth12, which means that complex mold patterns containing structures with various linewidths cannot be precisely imprinted into HSQ thin film. (3) Transferring large-size patterns with linewidths exceeding 10 mm is extremely difficult. (4) After mold pressing, a residual HSQ layer over 100 nm thick remains in recessed areas. We attributed these problems to surface hardening of HSQ resin by evaporation of the solvent contained in HSQ during spin-coating. To overcome the above problems, we developed a new nanoimprint technique using liquid-phase HSQ as an alternative to the conventional HSQ resin spin coating technique. The steps are as follows. (1) HSQ solution was dropped onto the Si substrate. (2) A SiO2/Si mold was pressed to the substrate with 1 MPa press-pressure. (3) The HSQ-coated substrate was heated up to 90oC while the press-pressure was held. (4) After cooling, the mold was removed from the Si substrate, and then the HSQ patterns were completely replicated. HSQ patterns with 150-nm-linewidth and 300-nm-pitch was successfully obtained by the new imprinting. Furthermore, the new imprint technique also generated nano-scale pattern of 25-nm-linewidth and 75-nm-pitch. We also succeeded in reducing the thickness of residual HSQ. The measured thickness of the residual layer was less than 10 nm. Large size patterns of over hundred microns were precisely imprinted into the HSQ resin, which was very difficult to realize using spin-coated HSQ. The new technique enabled us to simultaneously fabricate arbitrary patterns including both nano- and micro-scale structures by one-step process using the SiO2/Si mold with complex patterns. Thus, liquid-phase HSQ enhanced the fidelity of HSQ imprinted patterns, and is more suitable as a replication material for nanoimprinting than spin-coated HSQ resin. We believe that the new imprint technique using liquid phase HSQ developed here will be widely applied to the nano- and micro-structure replications.
3:00 PM - **O2.2
High Resolution Imaging Technology: a View of the Future.
Grant Willson 1 Show Abstract
1 Chemistry and Chemical Engineering, University of Texas, Austin, Texas, United States
The National Nanotechnology Initiative (NNI) has focused hundreds of millions of dollars of research funds into the area of nanoscale structure fabrication. Government agencies have great expectations for the influence of this research on the world economy and on employment. The drive to manufacture semiconductor devices with ever smaller features has inspired amazing improvements in imaging materials science and technology for over 3 decades. Billions of dollars have been spent in efforts to devise methods and materials that enable the printing of ever smaller transistors. The most advanced microelectronic devices in full scale production have minimum features in the range of 60-90nm and fully functional transistors with 10nm gates have been characterized. Continued scaling of CMOS devices is projected to occur by introducing immersion lithography in various forms, adaptation of double exposure processes and ultimately, EUV exposure. The lithographic process used to produce these nanostructures is becoming extremely expensive and the cost of that process threatens the structure and the economics of the semiconductor manufacturing industry and the expectations of the NNI founders. Imprint lithography, a much lower cost, high resolution patterning technology is emerging as a potential adjunct to photolithography. It is now recognized on the ITRS roadmap. Imprint lithography loosely defines a set of techniques that include several forms of embossing; stamping and molding that show great promise as low cost methods for producing nanostructures. These techniques take many different forms, each of which has it’s own special applicability. The technique we call Step and Flash Imprint Lithography (S-FIL) is designed to allow the fabrication of high resolution, high aspect ratio images that can be aligned with precision. The process accurately replicates arbitrary shapes as small as 20nm (below) and structures smaller than 10 nanometers in width have been faithfully reproduced. The state of high resolution imaging processes for production of devices with nanoscale features will be presented with emphasis on the Step and Flash Imprint Lithography Process.
4:30 PM - **O2.3
Template Fabrication Challenges for Patterned Media
Douglas Resnick 1 Show Abstract
1 , Molecular Imprints, Inc., Austin, Texas, United States
Ultra Violet Nanoimprint Imprint Lithography (UV-NIL) and in particular, Step and Flash Imprint Lithography (S-FILTM) are unique methods for printing sub-100 nm geometries. Relative to other imprinting processes, these technologies have the advantage that the template is transparent, thereby facilitating conventional overlay techniques. Further, these imprinting methods provide sub-100 nm feature resolution without the significant expense of multi-element, high quality projection optics or advanced illumination sources. The S-FIL process differentiates itself from other UV imprinting methods through the use of field-to-field drop dispensing of UV curable liquids for step and repeat patterning. Several applications, including patterned media, photonic crystals and wire grid polarizers, are better served by a patterning process that requires full wafer coverage with minimal alignment. In general, the substrates employed in these are markets do not have the stringent flatness specifications needed for silicon integrated circuit fabrication. As a result the imprinting of nano-scale features becomes particularly challenging, especially when imprinting with rigid templates such as those typically in Step and Flash Imprint Lithography. The purpose of this paper is to present methodologies suitable for creating a thin template suitable for full wafer imprinting. Included in this paper are the challenges that are encountered when fabricating both a Master Template and a Replicate (or Daughter) Template.
5:00 PM - O2.4
Wafer-scale Metal Imprint Stamps and their Applications for Perfectly Ordered Anodic Aluminum Oxide (AAO).
Woo Lee 1 , Ran Ji 1 , Caroline Ross 2 , Ulrich Goesele 1 , Kornelius Nielsch 1 Show Abstract
1 Experimental Dept. II, Max Planck Institute of Microstructure Physics, Halle Germany, 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology (MIT), Boston, Massachusetts, United States
5:15 PM - O2.5
Fabrication of Ordered Polymer Structures by Nanoimprinting Using Anodic Porous Alumina
Takashi Yanagishita 1 , Kazuyuki Nishio 1 2 , Hideki Masuda 1 2 Show Abstract
1 , Kanagawa Academy of Science and Technology, Kanagawa Japan, 2 , Tokyo Metropolitan University, Tokyo Japan
Fabrication of nanometer-scale structures is of growing importance for preparing various types of functional nanodevices, such as electronic, optoelectronic, and biological devices. Nanoimprinting is a promising technique for fabricating ordered fine structures of nanometer dimensions with high throughput, because of its high resolution capability. In the present report, we describe the fabrication of large-sized ordered polymer structures by nanoimprinting using anodic porous alumina. Anodic porous alumina, which is a typical self-ordered nanohole array material formed by anodization of Al in an appropriate acidic solution, has recently attracted increasing interest as a key material for fabrication of nanometer structures . Using naturally occurring ordered anodic porous alumina as a mold for nanoimprinting, large-sized fine patterns can be prepared easily. In the experiment, ordered polymer pillar arrays were fabricated by nanoimprinting of photopolymerized polymers using anodic porous alumina as a mold. In addition, ordered polymer nanohole arrays were fabricated using a metal mold prepared from anodic porous alumina template [2,3]. The obtained polymer nanostructures will be applied to several types of functional nanodevices.  H. Masuda et al., Science, 268, 1466 (1995).  H. Masuda et al., Appl. Phys. Lett., 78, 826 (2001).  T. Yanagishita et al., Jpn. J. Appl. Phys., accepted.
5:30 PM - O2.6
Impact of Planarization Layers Stack on Full Wafer Printing Uniformity.
Tanguy Leveder 1 , Stefan Landis 1 , Nicolas Chaix 2 , Laurent Davoust 3 Show Abstract
1 D2NT, CEA/LETI, Grenoble France, 2 , CNRS-LTM, Grenoble France, 3 , LEGI/ENSHMG, Grenoble France
5:45 PM - O2.7
Residual Stresses and Pattern Stability in Nanoimprint Lithography.
Yifu Ding 1 , Hyun Wook Ro 1 , Jack Douglas 1 , Alamgir Karim 1 , Daniel Hines 2 Show Abstract
1 , NIST, Gaithersburg, Maryland, United States, 2 , University of Maryland, College Park, Maryland, United States
Zvonimir Z. Bandic Hitachi Research Center
Michael Rooks IBM T. J. Watson Research Center
Ruediger Berger Max Planck Institute for Polymer Research
Takashi Ando Hitachi Research Lab #431
O3: Cross-Point Memories
Tuesday AM, November 28, 2006
Room 310 (Hynes)
9:30 AM - **O3.1
Nanoimprinting and Fabrication of Crossbar Memories.
Stan Williams 1 Show Abstract
1 , HP Labs, Palo Alto, California, United States
Crossbar memories can have extremely high densities and are conceptually easy to construct. However, there are very few examples of commercial crossbar memories today because of the difficulty of reading from and writing into large arrays of serial/parallel connections with enough voltage margin to clearly distinguish a ONE bit from a ZERO bit, and at the same time not perturb neighboring bits. In the future, as wire sizes shrink into the few nanometer diameter regime, the frequency of broken wires and connections will get much worse. Thus, any strategy to produce a crossbar memory that will successfully scale into the future must consider both the manufacturing process and viable defect tolerance schemes for handling manufacturing mistakes and operating faults. This talk will cover the following issues: fabricating crossbar structures using nanoimprint lithography with half-pitch as small as 17 nm, writing and reading the memory with appropriate multiplexers and demultiplexers, the use of coding theory to improve the manaufacturing yield and the voltage margin of the memory, and finally experimental results from memories in which the individual bits in the memory have an ON to OFF conductance ratio exceeding one hundred thousand.
10:00 AM - O3.2
Resistance-change Memory from Nanoscale Volumes of Metal Sulfides Fabricated Using Self-assembled Di-block Copolymers.
John Jameson 1 , Yoshiaki Fukuzumi 3 , Ho-Cheol Kim 2 , Joy Cheng 2 , Oun-Ho Park 2 , Sung-Woo Kim 1 , Peter Griffin 1 , Yoshio Nishi 1 Show Abstract
1 Center For Integrated Systems, Stanford University, Stanford, 94305-4075, California, United States, 3 , Toshiba Corporation, Yokohama, 235-8522, 8 Shinsugita-cho, Isogo-ku, Japan, 2 Advanced Organic Materials, IBM Almaden Research Center, San Jose, 95120-6099, California, United States
The scaling of current memory technologies beyond the 32nm node of the ITRS poses difficult challenges for the semiconductor industry, and recent years have seen a flurry of activity aimed at finding alternate technologies. One promising idea is to use a material whose electrical resistance can be changed reversibly between two or more values. Such materials include metal sulfides and selenides (e.g., Cu2S, ZnCdS, AgGeSe), binary metal oxides (e.g., NiO, TiO2, WO3), perovskites (e.g., SrTiO3), and others. At the high bit densities of future technology nodes, the area allocated to each bit of a memory circuit will become exceedingly small, so a critical question in gauging the viability of these materials is whether and/or how their electrical properties change when they are reduced to nanoscale volumes. The present work investigates this question for metal sulfides by synthesizing them within the pores of a self-assembled di-block copolymer. The first step in the process is to spin a uniform organosilicate underlayer onto a Pt substrate to control the interfacial energy between the copolymer and substrate. The di-block copolymer is then spun onto the underlayer, self-assembling to form a hexagonal array of columnar pores approximately 20nm in diameter, covering an area of several square centimeters. A plasma etch is used to remove the underlayer from the bottoms of the copolymer pores, and a thin layer of metal (e.g., Cu or Ag) is then electroplated onto the exposed Pt. Finally, the electroplated metal is transformed into a sulfide (e.g., Cu → Cu2S) by anodizing it in a solution of sodium sulfate.The resulting sulfide-filled pores are suitable for probing individually by conductive AFM or STM, or in parallel by patterning a top electrode with conventional lithographic techniques. The present work focuses on the latter approach, with top electrodes formed by a shadow mask. Initial electrical measurements of these devices confirm that metal sulfides retain their ability to switch when confined to nanoscale volumes. It appears, however, that the switching voltages are significantly higher than in comparable devices fabricated in continuous blankets of sulfide.Besides being a test bed for evaluating the properties of sulfides at nanoscale dimensions, the large areas and high pore densities of the present copolymer/sulfide blankets make them suitable for scanning-probe-based memory applications. By altering the chemistry of the anodizing solution or by replacing this step with a gas-phase oxidation, the present technique could also be extended to metal oxides.
10:15 AM - O3.3
Non-volatile Resistance Switching in In-Zn-O/TiOx Bi-layers.
Choong-Rae Cho 1 , Genrikh Stefanovich 1 , DongChul Kim 1 , SeungEon Ahn 1 , Myongjae Lee 1 , Sunae Seo 1 , Eun-Hong Lee 1 , YoungSoo Park 1 , InKyeong Yoo 1 Show Abstract
1 , Samsung Institute of Technology, Suwon Korea (the Republic of)
10:30 AM - O3.4
Observation of Ge2Sb2Te5 Thin Film Phase Transition Behavior According to the Number of Cycles Using Transmission Electron Microscope and Scanning Probe Microscope.
Hyunjung Kim 1 , Sikyung Choi 1 , Sukhoon Kang 2 , Kyuhwan Oh 2 , Soonyong Kweon 3 Show Abstract
1 , Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of), 2 , Seoul National University, Seoul Korea (the Republic of), 3 , Chungju National University, Chungju Korea (the Republic of)
Recently, the development of information technology (IT) increases the demands of memory devices. Phase change random access memory (PRAM), based on the reversible phase change of the chalcogenide alloy, Ge2Sb2Te5, is widely regarded as a favourite candidate for the next generation memory. Because of PRAM has a simple cell structure with high scalability; it is non-volatile, has a relatively high read/write operation speed (≤50ns). The PRAM operation relies on the fact that chalcogenide-based materials can be reversible switched from an amorphous phase to a crystalline state by an external electrical current. It is important to study the electrical property with set/reset cycles, since film thickness shrinkage occurs with the phase transition. In this work, we fabricated the 100nm amorphous Ge2Sb2Te5 thin film on TiN/Ti/Si substrate using dc-magnetron sputtering. The 50X50μm2 isolated Ge2Sb2Te5 cell was lithographed by the lift-off pattern and wet etching. And TiN top electrode was deposited using pattern align process at room temperature after the SiO2 insulator CMP. Phase transition behavior with the set/reset cycle was observed using I-V measurement and transmission electron microscope (TEM) on isolated Ge2Sb2Te5 cell. The set/reset programming was operated using tungsten SPM tip which was fabricated using focused ion beam (FIB) lithography. I-V curve which was observed by the I-V probe clearly showed that the phase transition was occurred by applying the electric field through the I-V probe. The resistivity difference between amorphous and crystal state was more than 102. After the phase transition, it was also demonstrated with transmission electron microscope (TEM) analysis. For the preparation of TEM specimen of the amorphous and crystalline cell, focused ion beam (FIB) lithography was adopted.
10:45 AM - O3.5
General Synthesis of 1-D Phase-Change Chalcogenide Nanowires for Information Storage Application
Xuhui Sun 1 , Bin Yu 1 , Garrick Ng 1 , Meyya Meyyappan 1 Show Abstract
1 Center for Nanotechnology, NASA Ames Research Center, Moffett Field, California, United States
The electrically operated phase-change random access memory (PRAM) features faster write/read, improved endurance, and much simpler fabrication as compared with the traditional transistor-based nonvolatile semiconductor memories. One-dimensional phase-change materials in nanoscale offer advantages over their bulk or thin-film counterpart in several aspects such as reduced programmable volume and reduced thermal energies in phase transition. These features contribute to low power operation, excellent scalability, and fast write/erase time. In this paper we reported a general bottom-up synthesis approach and systematic material analysis study of one-dimensional chalcogenide-based phase-change materials including germanium telluride (GeTe), indium selenide (In2Se3), antimony telluride (Sb2Te3), and germanium antimony telluride (Ge2Sb2Te5) nanowires that are targeted for nonvolatile resistive switching data storage. The phase-change nanowires have been synthesized via thermal evaporation method under vapor-liquid-solid (VLS) mechanism. The physical morphology, chemical composition, and crystal structure of the synthesized nanowires were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HR-TEM) and X-ray photoemission spectroscopy (XPS). The as-synthesized nanowires are structurally uniform with single crystalline structures (i.e., GeTe nanowires with cubic structure and In2Se3 nanowires with hexagonal structure). The 1-D phase-change chalcogenide nanowires exhibit significantly reduced melting points, low activation energy and excellent morphology, making them promising nanomaterials for data storage devices with very low energy consumption and excellent scalability. Prototype data storage devices based on these synthesized 1-D phase-change nanowires are demonstrated.
11:30 AM - **O3.6
Application of Electron Beam Lithography to the Fabrication of Prototype Memory Devices.
Charles Rettner 1 , Luisa Bozano 1 , Geoff Burr 1 , Yi-Chou Chen 1 , Masamitsu Hayashi 1 , Kailash Gopalakrishnan 1 , Jennifer Hou 1 , Xin Jiang 1 , Jean Jordan-Sweet 1 , Robin King 1 , Robert Miller 1 , Rai Moriya 1 , Stuart Parkin 1 , Simone Raoux 1 , Martin Salinga 1 , Jeyaprakash Samuel 1 , Campbell Scott 1 , Robert Shelby 1 , Rohit Shenoy 1 , Luc Thomas 1 Show Abstract
1 Almaden Research Center, IBM Research Division, San Jose, California, United States
12:00 PM - O3.7
Nonvolatile Two-Terminal Molecular Memory.
Jason Snodgrass 1 , Glen Kennedy 1 , Wai-Ning Mei 1 , Renat Sabirianov 1 Show Abstract
1 Physics, University of Nebraska at Omaha, Omaha, Nebraska, United States
A tunnel junction composed of one or few monolayers of polar molecules sandwiched between two electrodes made of materials with different conducting properties is proposed as a nonvolatile two-terminal memory with two resistance states. As a prototype model system we study rare earth endohedral metallofullerene molecule attached to metal and semiconducting electrodes. Such molecule exhibit reversible dipole moment. We use the Thomas-Fermi model to calculate the potential profile across the device and tunneling current through the proposed structure. We have solved this model exactly and show that bi-stable resistance switching occurs upon applied voltage due to the electromigration of Gd atom inside of the cage and different screening in asymmetric electrodes.
12:15 PM - O3.8
Experimental Investigation of Resistive Memory Switching Origin in NiO.
Dong chul Kim 1 , Sunae Seo 1 , Myoung-Jae Lee 1 , Seung-Eon Ahn 1 , Dong-Seok Suh 1 , Ranju Jung 1 , YoungSoo Park 1 , InKyeong Yoo 1 , In-Gyu Baek 2 , Hyun-Jo Kim 2 , Eun-Kyung Yim 2 , JangEun Lee 2 , SoonOh Park 2 , Hee-seok Kim 2 , U-In Chung 2 , Joo-Tae Moon 2 , Byung-Il Ryu 2 Show Abstract
1 Semiconductor Device & Material Lab, Samsung Advanced Institute of Technology, Suwon Korea (the Republic of), 2 Process Development Team, Semiconductor R & D Center, Samsung Electronics, Co. Ltd., Yongin-City, Kyeonggi-Do, Korea (the Republic of)
12:30 PM - O3.9
Filamentary Conduction in Memory Switching NiO Film Observed by Impedance Spectroscopy.
Seung-eon Ahn 1 , Sunae Seo 1 , Myoungjae Lee 1 , Dongchirl Kim 1 , Dongseok Suh 1 , Ranju Jung 1 , YoungSoo Park 1 , InKyeong Yoo 1 , Gyu Tae Kim 2 Show Abstract
1 , Samsung Advanced Institute of Technology, Suwon Korea (the Republic of), 2 Department of Electrical engineering, Korea University, seoul Korea (the Republic of)
12:45 PM - O3.10
An Electronic Nonvolatile Memory Device Based On Electrostatic Deflection of a Bistable Mechanical Beam.
Joshua Rubin 1 , Sandip Tiwari 1 Show Abstract
1 , Cornell University, Ithaca, New York, United States
The speed of memory structures is considerably slower than that of logic permitting a variety of approaches to achieving and using bistability. In this work, we show the use of bistability of an anchored beam to achieving two states that can potentially be used in implementing non-volatile memory. The speed of such structures is in 100’s of MHz, similar to the frequencies achieved by small electromechanical oscillators that have a single anchor. Our non-volatile memory device, in the first form of implementation, is achieved by employing a bistable beam as the gate of an air gap transistor. The bistable beam is obtained by patterning and releasing a compressively stressed thin film with sufficient internal stress to cause buckling upon release. This enables the bistable mechanism - the beam can be deflected either up or down, thus creating two states. In addition to the beam used for the gate, another beam or plate must be suspended above the gate to perform the write function. The write/erase mechanism operates on the principle of electrostatic attraction. Therefore, in order to obtain the “down” state a large bias is applied between the gate and the source/drain, thus attracting the gate towards the channel. Upon removal of the voltage the gate remains in the “down” position due to it being energetically favorable as a result of the bistable mechanism. On the other hand, in order to obtain the “up” state, a large bias is applied between the upper plate and the gate so that the gate is pulled up to the other stable position. The upper plate is rigid, unlike the gate. This establishes the gate as the only deformable element of the device. The read function is executed using small biases between the gate and the substrate. In read mode, the device operates like a MOSFET. The read voltages must be lower than the write voltages in order to prevent any additional deflection of the gate. The device’s electrical characteristics substantially change as the gate is moved between the two stable states. The “down” state corresponds to a lower threshold voltage and sub-threshold slope, whereas the “up” state is described by a higher threshold voltage and sub-threshold slope. In theory, in scaled structures, the threshold voltage shift corresponding to a gate deflection of nanometer dimensions provides sufficient change to provide sensing of the state of the nonvolatile memory cell. The device structure is potentially scalable if mechanical properties maintain expected characteristics, and is thus highly dense. In addition, by removing the need to store charge, the retention time of the device is not limited by electronic defects or leakage paths, but by fatigue and other mechanical failures. By operating the gate such that the material is stressed in its elastic regime, material fatigue can be minimized. Details of the device fabrication and performance will be presented along with the material considerations for the gate and upper plate.
O4: E-Beam Lithography in Information Storage
Tuesday PM, November 28, 2006
Room 310 (Hynes)
2:30 PM - **O4.1
Electron-beam Mastering with Fine Beam and Precise Positioning for Patterned Disks.
Tetsuya Nishida 1 Show Abstract
1 Central Research Laboratory, Hitachi,Ltd., Tokyo Japan
Patterning disks is one of the most effective techniques to increase data density on hard disk drives (HDDs). Discrete track media can prevent disk noise from an erasure band on the track edge at a narrow track pitch. Patterned media consisting of a dot array can reduce thermal magnetic fluctuation from the superparamagnetic effect in small magnetic domains. While a pre-patterned servo is of course necessary on such patterned disks, high-cost servo track writing is unnecessary.Large-scale electron-beam (e-beam) lithography on a rotatively moving stage should enable fabricating masters for the patterned disks. The e-beam mastering tool needs fine and precise beam positioning. Two types of e-beam mastering tools are introduced: an XY-stage driving e-beam recorder  and a rotary stage driving e-beam recorder . The former has a Y stage moving along a sine oscillation on an X stage moving along a cosine oscillation, allowing a disk on the XY stage to move smoothly along a circular or spiral trajectory in a wide area. The latter has a rotational spindle on a translatory stage.The prototyped XY-stage driving e-beam recorder can precisely draw fine pit patterns by e-beam deflection correction from an accurate detection of stage position error. The electron-optical column provides a fine beam of 20-nm diameter at a 1-nA current. The stage is smoothly driven by friction force transmitted from DC motors. The position of the XY stage is detected with 0.05-nmσ precision by using the moving-average processing of the output signal from the laser interferometer. Residual errors between the controlled stage position and the destination address are less than 4 μm at a stage velocity of 10 mm/s. The errors are eliminated by accurate e-beam deflection with two sets of two parallel electrodes. The recorded pit size was less than 40 nm. The recording accuracy was less than 2 nmσ in the radial & tangential directions and alignment between pits on adjacent tracks.The prototype for a rotary stage driving e-beam recorder can draw fine pit patterns quickly. It has a high-speed turn table at an order of 1 m/s, and its electron-optical column provides a high current of 35 nA at a 50-nm diameter. A rotation stage with a noncontact vacuum seal and a rotation error correction system were applied to improve the recording position accuracy. In addition, an active magnetic shield system and learning compensation for beam displacement were adopted to stabilize the beam position. The recording accuracy was also less than 2 nmσ in the radial & tangential directions and alignment between pits on adjacent tracks.These large-scale e-beam recorders can be applied to master fabrication for high density HDD patterned disks as well as conventional patterned optical disks. T. Nishida, F. Isshiki, et al., Jpn. J. Appl. Phys. 42, 772 (2003) H. Kitahara, T. Nishida, et al., Jpn. J. Appl. Phys. 43, 5068 (2004)
3:00 PM - **O4.2
Nanofabrication for Patterned Media.
Elizabeth Dobisz 1 , Tsai-Wei Wu 1 , Margaret Best 1 , Dan Kercher 1 Show Abstract
1 Research, Hitachi Global Storage Technologies, San Jose, California, United States
Disk drives continue to provide the highest density data storage with over 100 Gb/in2 commercially available and 240 Gb/in2 in laboratory demonstrations. The areal density of magnetic data storage has increased by 100% per year thru the 1990’s and 40% per year since 2001. However, as the storage density increases and the bit size decreases, the energy to flip a bit approaches the thermal stability limit, imposed by the superparamagnetic effect. Patterned media is a leading candidate as a solution to the problem of thermally stable data and is expected to emerge at storage densities between 500 Gb/in2 and 1000 Gb/in2 . In nanofabrication terms, the relevant densities require ~ 15-25 nm diameter magnetically isolated islands spaced 25- 35 nm center-to-center. In addition, disk manufacture is a high volume and high throughput process. UV nano-imprint lithography is a promising technology to pattern disks, because of its high resolution and throughput. Disk patterning requires only one lithographic level per disk side and alignment is not very critical. Disk patterning is likely to be one of the first manufacturing applications of nanoimprint lithography. However imprint lithography requires 1X masters. Presently, e-beam lithography is the only tool with the resolution to make the masters. The required resolution and precision present a formidable challenge to e-beam tool technology and the throughput is low. The e-beam patterning of masters for imprint lithography is discussed in detail. We examine patterning, metrology, and the relationship between the master and the imprinted patterns.
4:00 PM - O4.3
Nano-Phase Change Random Access Memory Fabrication by A Hybrid Technology of E-beam and Optical Lithography
Rong Zhao 1 , Luping Shi 1 , Eng Kuan Yeo 1 , Kianguan Lim 1 , Hockkoon Lee 1 , Weijie Wang 1 , Hongxin Yang 1 , Towchong Chong 1 Show Abstract
1 , Data storage institute, Singapore Singapore
Phase Change Random Access Memory (PCRAM) has a near ideal memory properties, low cost, low power, high speed, high retention, high scalability and non-volatile. It stores data by phase change induced by electrical pulses between the high resistance amorphous and low resistance crystalline states of chalcogenide materials. The performance of PCRAM device is highly dependent on the volume of the material involved in the phase change. Less power consumption is required when the volume of the phase change is reduced. Hence PCRAM has been considered as the best candidate to replace FLASH beyond 45 nm. Therefore, shrinking the device or active area size of the device is the most important activity for PCRAM development. Because the conventional optical lithography encounters the optical diffraction limitation, alternative technologies are required to achieve smaller feature size. In this paper, the fabrication and characterization of PCRAM devices in nano-scale were investigated. A hybrid fabrication process integrating with E-beam lithography (EBL) and optical lithography has been developed. The EBL is mainly used to pattern the active area in nano-scale, while the optical lithography is used to pattern all of the other layers of the device. Thus, not only nano-scale size, but also fast and reproducible fabrication could be achieved using this approach. In this work, the process employed 75 kV EBL to pattern a PMMA-based e-beam resist. PCRAM devices in nano-scale have been successfully designed and fabricated. The testing results of device characteristics showed the scaling effect of the programming current to the memory cell features. The smallest device size achieved is 50 nm. It demonstrated a low programming current in sub-mA. However, although EBL exhibits distinguished performances in creating minimum feature size, the proximity effect due to the forward and backward scatterings makes it difficult to precisely determine the distribution of electron irradiation. This effect becomes more dominant with further reduction in feature size, and thus imposes a severe constraint for creating deterministic geometry. In this work, different geometry shapes of the active area have also been designed and fabricated using EBL. The geometry effect on the device performance is investigated experimentally though the device fabrication and characterization. The detailed results will be presented and discussed in the conference.
4:15 PM - **O4.4
Lithography Strategy and Requirements for Patterned Media.
Kim Lee 1 , Chris Formato 1 , David Kuo 1 , Shuaigang Xiao 2 , XiaoMin Yang 2 , Dorothea Buechel 2 , Dieter Weller. 1 Show Abstract
1 Seagate Technology, RMO , Fremont, California, United States, 2 Seagate Research Center, Seagate , Pittsburgh, Pennsylvania, United States
There is currently great interest in patterned media as a possible solution for magnetic data storage at densities beyond 500Gb/in2. To realize this, tremendous challenges in manufacturability must be overcome. Conventional wisdom envisages a manufacturing process involving fabricating a master template from which tens of thousands of disks are replicated by nanoimprinting. The imprinted patterns are then transferred into disks by either a subtractive or an additive process thus forming periodic arrays of isolated magnetic islands. Besides the requirements for high throughput, high volume, and low cost, very precise printing and pattern transfer are critical. Final disk planarization for head flyability is another key issue.This talk will focus on the lithography for patterning the masters or templates. Key requirements are resolution, placement accuracy, size and shape uniformity, throughput and extendibility. For bit areal density of 500 to 1000Gb/in2, the bit size is between 12.5 and 25nm, and the center-to-center spacing between adjacent bits is between 25 and 50nm. Moreover, for reasonable SNR, the bit size variation must not exceed 6% (1σ), and the periodicity maintained within 6% (1σ)1. Various lithographic options are being considered, the most important being electron-beam lithography at this early developmental stage. Although electron-beam technology possesses both resolution and precision potentials, it suffers from a substantial trade-off between resolution and throughput. Such tools will also require a rotating stage and these are woefully lacking in both selection and sophistication in the market. Guided self assembly may be more practical but the technology is still in its infancy. Other innovative approaches considered are interference lithography, frequency multiplication of periodic structures, and cross-imprint lithography.1Richter et al, APL 88, 222512 (2006)
4:45 PM - O4.5
Development Stopping Characteristics and Multiple Development of the HSQ Resist in the E-beam Lithography.
Hyo-Sung Lee 1 , Jung-Sub Wi 1 , Sung-Wook Nam 1 , Hyun-Mi Kim 1 , Ki-Bum Kim 1 Show Abstract
1 School of Materials Science & Engineering, Seoul national university, Seoul, Seoul, Korea (the Republic of)
5:00 PM - O4.6
Nano-Si-dot Arrays with a Bit and a Track Pitches of 25 nm Formed by EB Writing and Reactive Ion Etching for 1 Tb/in2 Storage.
Sumio Hosaka 1 , Hirotaka Sano 1 , Hayato Sone 1 Show Abstract
1 Nano Material Systems, Gunma University, Kiryu Japan
5:15 PM - O4.7
Combination of Electron Beam Recorders for Mastering with NanoImprint Lithography for HVM-Production of Patterned Magnetic Media and Next Generation Optical Media.
Marc Beck 1 , Torgny Moller 1 , Nicklas Nilsson 1 , Roland Palm 1 , Erik Theander 1 , Anette Lofstrand 1 , Babak Heidari 1 Show Abstract
1 , Obducat AB, Malmo Sweden
O5: Poster Session: Cross-Point Memories II
Tuesday PM, November 28, 2006
Exhibition Hall D (Hynes)
9:00 PM - O5.10
Memory Effects in Manganese Perovskites. Experiment and Theory.
Natalia Noginova 1 , Joseph McClure 1 , Empress Etheridge 1 , Vladimir Gavrilenko 1 , Dmitri Novikov 2 Show Abstract
1 , NSU, Norfolk, Virginia, United States, 2 , TIAX LLC, Cambridge, Massachusetts, United States
Electrically induced quasi-permanent changes in low-field conductivity have been observed in single crystals of LaGa1-xMnxO3 in the broad range of Mn ion concentrations (x= 0.1 – 1). The memory effects can last for a long time at room temperature and can be easily erased by heating up to Tc ~ 300 C. The temperature dependence of the resistivity demonstrated a sharp drop around the phase transformation temperature, pointing to the role of phase transformation processes. We explain our experimental data in terms of thermo induced local phase transition with the oxidation of Mn ions. The results of the ab initio calculations of the electron energy structure in Jahn-Teller-distorted and non distorted cells confirm the mechanism suggested.
9:00 PM - O5.12
Process Integration of Composite High-k Tunneling Dielectric for Nanocrystal Based Carbon Nanotube Memory.
Udayan Ganguly 1 2 , Tuo-Hung Hou 3 , Edwin Kan 3 Show Abstract
1 Nanotechnology, NASA Ames Research, Moffet Field, California, United States, 2 Dept. of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 3 School of Electrical and Computer Engineering, Cornell University, Ithaca, New York, United States
9:00 PM - O5.3
Molecular Memory Device patterned by Organic Conducting Electrode
Hyoyoung Lee 1 , Nak-Jin Choi 1 , Junghyun Lee 1 , Gyeong Sook Bang 1 , Jonghyurk Park 1 , Kang-Ho Park 1 Show Abstract
1 NCRI, Center for Smart Molecular Memory , ETRI, Daejeon Korea (the Republic of)
For the realization of high density memory device in nanotechnology field, many researchers have applied functional organic memory molecules to molecular electronic device by using self-assembled monolayers (SAMs) with soft lithography such as nano-imprinting technique which is promising for cheap fabrication cost and easy process. However, to implement single organic monolayer device in the vertical structure of metal-molecule-metal electrode, there are fundamental problems, that is, an electrical short. The yield of the molecular device, even in nano-via-hole, is less than 5 %. For the realization of molecular memory device using single mono-layer, here we introduce new way by using organic conducting electrode. The yield of newly developed molecular device is over 95%. In addition, we report the synthesis of novel thiol-terminated organic molecules having memory effect, the characterization of single monolayer formed by self-assembly process (SAM), and device fabrication by using nano-imprinting technique. Finally, we will report the detailed experiments and fabrication process in this talk.
9:00 PM - O5.4
Nanostructural Evolution in Non-epitaxial Growth of Thin Films.
Minghui Hu 1 , Suguru Noda 2 , Hiroshi Komiyama 2 Show Abstract
1 Biology Department, Brookhaven National Laboratory, Upton, New York, United States, 2 Department of Chemical System Engineering, The University of Tokyo, Tokyo Japan
9:00 PM - O5.5
Quantum-Cross Tunneling Junction for High Density Memory
Hideo Kaiju 1 , Kenji Kondo 1 , Akira Ishibashi 1 Show Abstract
1 Research Institute for Electronic Science , Hokkaido University, Sapporo Japan
We have proposed double nano-baumkuchen (DNB) structure, composed of two thin slices of alternating metal/insulator hetero layers, as a candidate to augment or replace the conventional lithography technology. The DNB structure has potential application in a high-density memory device, the cross point of which can scale down to ultimately a few nanometers feature sizes because the pattering resolution is determined by the metal-deposition rate, ranging from, typically, 0.01 nm/s to the order of 0.1 nm/s. Not only memory device but also novel functional phenomenon may emerge from quantum effects arising from the DNB structure having the scale-down active area, corresponding to a small number of molecules sandwiched between the two electrodes. One element of DNB structure having those features mentioned above is called ‘quantum cross’ structure that consists of two metal nano-ribons having edge-to-edge configuration. It differs from face-to-face conventional configuration such as molecular-electronic devices comprising a single molecular monolayer sandwiched between two metal electrodes and magnetic tunneling junctions (MTJs) consisting in ferromagnetic electrodes separated by insulating tunneling barriers, fabricated by today’s production procedures, such as nanoimprint lithography, electron-beam lithography, and optical lithography. In this present study, we derived equations for the transport properties of edge-to-edge quantum cross structure with tunneling barrier and calculated the current-voltage characteristics depending on the metal-ribbon thickness, the barrier height and the barrier thickness. The current-voltage characteristics of face-to-face MTJs consisting Co(10nm)/Al-oxide (2.5nm)/Co(50nm) on glass substrates fabricated by ion-beam mask sputtering are found to be explained by Simmons formula, which is the generalized expression for the leakage-free tunnel effect through the insulating thin barrier. The transport equation extended Simmons formula is, also, derived for the edge-to-edge quantum cross structure with the tunneling barrier. The metal-ribbon thickness is 5 – 30 nm and the barrier height and thickness are 0.5 – 1.5 eV and 0.5 – 1.0 nm, respectively. Interesting behavior of transport properties is that the metal-ribbon thickness affects the current density due to the quantization of nano-ribon and also the tunneling current density, being dependent on the barrier height φ and the barrier thickness d, decreases with high φ and thick d. It indicates that we can precisely obtain the information, such as the barrier height and the barrier thickness, on the material sandwiched between two electrodes, by a fit of experimental data to our derived equation, resulting in a distinction between the sandwiched material and the electrode. These results will play an important role not only to find a novel functional device but also to develop the next-generation high-density memory.
9:00 PM - O5.7
Localized Pressure Induced Ferroelectric Pattern Arrays of Semi-crystalline PVDF by Micro-imprinting
Seok ju Kang 1 , Youn Jung Park 1 , Ho-Cheol Kim 2 , Cheolmin Park 1 Show Abstract
1 Materials science and engineering, Yonsei university, Seoul Korea (the Republic of), 2 Advanced organic Materials, IBM Almaden Research Center, San Jose, California, United States
Information storage devices fabricated from ferroelectric polymers such as poly(vinylidene fluoride) (PVDF) have drawn a great attraction due to their potential use in non-volatile memory technology. Permanent dipole formation between hydrogen and fluorine atom can be rotated around carbon backbone upon application of electric field large enough to induce conformational change of the polymer chain, resulting in bistability. One of the major advantages of ferroelectric polymers is their solution compatibility. The polymers can be dissolved in common organic solvents, and memory unit capacitors are achieved by sandwiching highly uniform thin ferroelectric film prepared through a simple spin-casting process between two electrodes. Several crystalline structures induced by the regular chain packing of the different configuration orders are found in PVDF known as α, β, and γ which correspond to TGTG, TTTT and TTTG, respectively. Among the three crystalline forms, α crystal is primarily produced from the melt, even though β and γ form are the most important polymorph with outstanding intrinsic ferroelectric properties. Therefore, it is critical to find the ways to transform non-polar α crystals into the useful ferroelectric β and γ ones. We investigated the control of pressure driven polymorphic transition of PVDF by using micro/nanoimprint lithography. The localized regions pressed by a patterned PDMS mold turn into polar γ type structure under certain temperature and pressure. The pressure induced polymorphic phase transition was evidenced by the remnant polarization and coercive voltage of approximately 6.0µC/cm2 and 11V, respectively measured in the pressurized PVDF films with 200nm in thickness. Several PDMS patterns such as hexagonal, square and reverse hexagonal were used. The resulting ferroelectric PVDF micropatterns are characterized by both 2D imaging Infrared spectroscope, atomic force and electron microscopes including cross-section Transmission Electron Microscope.
9:00 PM -
O5.1 Transferred to O3.2
O6: Poster Session: Nanoimprinting Lithography II
Tuesday PM, November 28, 2006
Exhibition Hall D (Hynes)
9:00 PM - O6.1
Preparation of Transition Metal Oxides Nano-Array by Imprint Technique using MgO Nano-Mask
Hidekazu Tanaka 1 2 , Naoki Suzuki 2 , Yoshihiko Yanagisawa 1 , Satoru Yamanaka 1 , Kaoru Ojima 2 , BongKuk Lee 2 , JungHyun Seo 3 , Heayeon Lee 1 2 , Masaki Kanai 2 , Tomoji Kawai 1 2 Show Abstract
1 ISIR-Sanken, Osaka University, Osaka Japan, 2 , JST-CREST, Saitama Japan, 3 , POSTECH, Pohang Korea (the Republic of)
We report a new simple technique to prepare transition metal oxide nano scale array over 2cmx2cm large area. Transition metal oxides exhibit a broad spectrum of characteristics including ferromagnetism, ferroelectricity, and metal-insulator transition, leading to application of oxide-MRAM, FeRAM, RRAM, and of various kinds of sensors. Therefore, their nano-pattering would be indispensable to realization highly integrated oxide based devices.We pattered nano-well array with from 500nm×500nm square size to 3μm×3μm square size, with 100nm depth on PMMA organic resist layer on SiOx/Si substrate by quartz mold, and then deposited an amorphous MgO layer on them by Pulsed Laser Depostion (PLD) technique at room temperature. Next, PMMA layer was removed by ultrasonic treatment in acetone to prepare “MgO nano-mask”. Thirdly ferrimagnetic (Fe,Zn,Mn)3O4 spinel oxide film (≈10nm) were deposited by PLD technique at substrate temperature of 300C under oxygen pressure of 10-6mbarr. Finally, the area of (Fe,Zn,Mn)3O4 just above MgO nano-mask were removed by ultrasonic treatment in water, leading to nano-well array with minimum size of 500nmx500nm square within (Fe,Zn,Mn)3O4 film. Superior to conventional organic resist mask, amorphous MgO nano-mask is stable even under metal oxide film formation condition (high temperature and high oxidation atmosphere) and soluble to water, to realize damage-less lift-off. This technique allows us to construct high quality epitaxial, and also, multilayered nano-array systems of transition metal oxides.
9:00 PM - O6.2
Patterning of the Au-nanoparticles onto SiO2 and Flexible Substrates via Langmuir-Schaefer Method Combined with μ-Contact Printing Technique: The Effect of UV Irradiation on the Electrical Conductivity.
Gun-Chul Shin 1 , Jae-Hyun Park 1 , Jeong Sook Ha 1 Show Abstract
1 Department of Chemical and Biological Engineering, Korea University, Seoul Korea (the Republic of)
Gold nanoparticles (Au-NPs) are the most stable metal nanoparticles which have various fascinating characteristics including the size-dependent electronic and optical properties and the applicability to catalysis and biology. In particular, sub-100 nm line patterns of Au on insulating substrates can be used as electrical wires in the nanoelectronic circuits. Here, we introduce a simple method to fabricate Au nanopatterns onto SiO2, polymer and flexible substrates via transferring Au-NPs using Langmuir-Schaefer (LS) technique combined with μ-contact printing (MCP) and subsequent UV-treatment. Well-ordered monolayer of Au-NPs stabilized with alkanethiol molecules were easily formed on water surface. This monolayer of Au-NPs was transferred from the water surface to a polydimethylsiloxane (PDMS) stamp by LS technique and subsequently transferred to SiO2, polymer, and flexible substrates by MCP. Au-NPs line patterns with a width from 40μm to 250nm were successfully fabricated on the various substrates. UV irradiation onto those Au-NPs patterns for about 30 min reduced the height of the pattern from 25nm, 50nm, and 90nm to 7nm, 15nm, and 30nm, respectively. It is attributed to the UV-oxidation of thiol molecules adsorbed on Au-NPs and resultant coagulation of the Au-NPs. The electrical conduction through the Au-NPs lines was enhanced after UV irradiation due to the coagulation of Au-NPs. In this study, we have successfully fabricated Au-NPs patterns with a line width as small as 250 nm on the various substrates, especially on the flexible substrate. This technique can be extended to combine monolayers of different nanoparticles and produce multilayers of nanoparticle with control over the properties of the individual layers. The patterned nanoparticle array can be used as sensing elements in sensor arrays and as functional components in electronic devices.
9:00 PM - O6.3
Toughnening of Dielectric Material by Thermoplastic Polymer
JungWoo Lee 1 , MyeongHo Hong 1 , ChoonKeun Lee 1 , JaeChoon Cho 1 , HyukSu Lee 1 , SeungHyun Ra 1 Show Abstract
1 Central R&D institute, SamSung Electro-Mechanics Co., LTD., Suwon, Gyuggi-Do , Korea (the Republic of)
Recently, high performance microelectronic devices are designed in multi-layer structure in order to make dense wiring of metal conductors in compact size. Imprint lithography have received significant attention due to an alternative technology for photolithography on such devices. In this work, we synthesized dielectric composite materials based on epoxy resin, and investigated their thermal stabilities and dynamic mechanical properties for thermal imprint lithography. In order to enhance the mechanical properties and toughness of dielectric material, various modified polyetherimide(PEI) was applied in the resin system.Curing behaviours, thermal stabilities, and dynamic mechanical properties of the dielectric materials cured with various conditions were studied using dynamic differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Universal Test Method (INSTRON).
9:00 PM - O6.4
Nanofabrications for Information Technology.
Kyung Choi 1 Show Abstract
1 , Bell Labs, Lucent Technologies, Murray Hill, New Jersey, United States
9:00 PM - O6.5
Nanopatterning and Nanomachining with Table-top Extreme Ultraviolet Lasers.
Mario Marconi 1 , Maria Capeluto 2 , Przemyslaw Wachulak 1 , Carmen Menoni 1 , Jorge Rocca 1 , Georgyi Vaschenko 1 , Erik Anderson 3 , Weilun Chao 3 , David Attwood 3 4 , Oscar Hemberg 5 , Bradley Frazer 5 , Scott Bloom 5 Show Abstract
1 Electrical and Computer Engineering, Colorado State University, Fort Collins, Colorado, United States, 2 Departamento de Fisica. FCEyN, Universidad de Buenos Aires, Buenos Aires Argentina, 3 Center for X Ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 Electrical Engineering and Computer Science, University of California Berkeley, Berkeley, California, United States, 5 , JMAR Technologies Inc., San Diego, California, United States
9:00 PM - O6.6
Replication of Grating-Based Optically Variable Devices in Polypropylene
Patrick Leech 1 Show Abstract
1 CMIT, CSIRO, Clayton, Victoria, Australia
Advanced types of document security device have comprised complex arrays of gratings which produce diffractive optically variable images in metallised foil. This paper describes the fabrication of large area arrays of grating-based OVDs using a unique method of electron beam lithography. The 30 x 30 µm pixels which comprised the grating structure in the array were individually assigned a grating pitch (0.7-1.3 µm) and/or groove angle . The grating structure thereby represents a very large amount of encoded data across the area of a device (up to 8 cm square). A switch between two images was achieved by dividing each image into vertical tracks of width 30 µm. One image was defined as columns with a specific grating spacing while the second image corresponded to alternate columns with a different grating spacing. The two images produced first order diffraction at different angles of viewing or tilt to create an image switch effect. This paper also reports on the replication of these grating array structures by hot embossing in biaxially-oriented polypropylene film. Grating-based optically variable devices were hot embossed over an area of 80 x 80 mm in the transparent film. At temperatures significantly above the glass transition temperature, Tg, (>120 °C) at 135 kN force, a high quality diffractive image was achieved over the full embossing area. The novel embossing of several different types of optically variable device has been examined including portrait, non-portrait and 3 dimensional images. Each of the embossed optically variable devices displayed a switch in diffractive images when viewed in transmitted light.  P.W. Leech, B.A. Sexton and R.J. Marnock, Microelectronic Engineering, 60, (2002) 339.
9:00 PM - O6.7
Feature size and Density Tuning in Nanoimprint Lithography.
Li Tan 1 , Zheng Li 1 , Ocelio Lima 1 , Haojing Lin 1 Show Abstract
1 Engineering Mechanics, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Nanoimprint lithography (NIL) has made deep impacts on nanomanufacturing due to its nanometer scale resolution, easiness in operation and compatibility to a variety of materials. In this process, a master stamp is used to transfer topographic features into thin films, such that, either negative or positive replicas are obtained. Attenuation of the replica structures, however, presents great challenges, such as complication in tuning feature density, lack of means for reducing line edge roughness, as well as a much concerned resolution in competing with beam or scanning probe lithography. Recently (2006) Tan and others presented the concept of feature miniaturization through external mechanical deformation upon the substrate, which shed light on addressing part of above challenges. In one of the examples, lateral contraction process, such as uni- or bi-axial contraction, was used to aggressively reduce feature size and increase feature density at the same time. For instance, sub-40 nm protein gratings are revealed after contracting original sub-micrometer features, and correspondingly pattern density has been increased 10 fold.This added process in NIL suggests great flexibility in tuning both feature size and density, thus, suggesting less demand on precision manufacturing of the master stamp from other high-end lithography platforms. To make this miniaturization process controllable with thorough understanding, systematic work on fabrication, modeling and simulation are provided in this discussion. In particular, we discuss the change in pattern profile and density on elastic membrane and hope the investigation provide guidance on relating mechanical deformation to patterned features, and more importantly, to better regulate pattern integrities.
9:00 PM - O6.8
Nanomold of Less than 30 nm Features and High Aspect Ratio for Nanoimprint Fabricated by Electron Beam Lithography.
Fu-Der Lai 1 , Yi-Chiuen Hu 1 , Chih Hsun Lin 1 , Yu Hin Lin 1 Show Abstract
1 , Electro-Optical Engineering, Kaohsiung Taiwan
O7: Poster Session: Patterned Media II
Tuesday PM, November 28, 2006
Exhibition Hall D (Hynes)
9:00 PM - O7.1
Preparation of Magnetic Nanowires with Controlled Anisotropy Using Porous Oxide Matrices
Alexey Lukashin 1 , Andrey Eliseev 1 , Kirill Napolsky 1 , Alexandr Vyacheslavov 1 , Irina Kolesnik 1 , Yuri Tretyakov 1 Show Abstract
1 Dept. of Materials Science, Moscow State University, Moscow Russian Federation
9:00 PM - O7.2
Development of 3-D Magnetic Nano-Arrays by Electrodeposition into Mesoporous Silica Films.
Roger Campbell 2 , Jason Manning 1 2 , Martin Bakker 1 2 , Xuefa Li 3 , Dong Ryeol Lee 3 , Jin Wang 3 Show Abstract
2 Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 1 Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
The development of periodic nanostructures fabricated by self-assembly of surfactants and block co-polymers has opened up the possibility of generating periodic magnetic nanostructures of types not accessible by self-assembly of nanoparticles. The fabrication of mesoporous silica thin films around self-assembled block co-polymers is well established. Common structures for such films are SBA-15 which consists of hexagonal arrays of cylindrical pores and SBA-16 which has face centered arrays of spherical voids. These pores are connected by 1-2 nm thick flaws in the continuous silica phase producing an effectively continuous porous phase. After removal of the block co-polymer template, electrodeposition into the mesoporous silica thin films produces arrays of 5-10 nm diameter nano-wires and nano-particles. We have demonstrated that such materials can be fabricated on a wide range of metal substrates. Characterization by Scanning Electron Microscopies shows that the mesoporous silica is well ordered over micron scale areas. Grazing Incidence Small Angle X-ray Scattering (GISAXS) studies shows diffraction spots, consistent with the entire film being well ordered. GISAXS also shows that the mesoporous silica films survive removal of the template and electrodeposition of nickel and cobalt into the mesoporous silica films. Such films are of interest for their magnetic properties, as the nanophase and scale can be independently varied. Further, the presence of nanowires inside an insulator suggests that these films might also be of interest as the current confining element for Confined Current Path-Current Perpendicular to Plane GMR sensors.
9:00 PM - O7.3
Size and Composition Dependent Magnetic Properties of Co/Pt Nanodot Arrays.
S. Park , J. Bang 1 , C. Bae 2 , S. Park 2 , J. Ha 1 Show Abstract
, 1 Department of Chemical and Biological Engineering, Korea University, Seoul Korea (the Republic of), 2 Department of Chemistry, Kyunghee University, Seoul Korea (the Republic of)
Zvonimir Z. Bandic Hitachi Research Center
Michael Rooks IBM T. J. Watson Research Center
Ruediger Berger Max Planck Institute for Polymer Research
Takashi Ando Hitachi Research Lab #431
O8/P1: Joint Session: Patterned Films
Wednesday AM, November 29, 2006
Room 310 (Hynes)
9:30 AM - **O8.1/P1.1
Magnetic Films on Self-assembled Nanoparticles.
Manfred Albrecht 1 , Till Ulbrich 1 , Ildico Guhr 1 , Olav Hellwig 2 , Sebastiaan Van Dijken 3 , Thomas Schrefl 4 Show Abstract
1 , University of Konstanz, Konstanz Germany, 2 Hitachi San Jose Research Center, HGST, San Jose, California, United States, 3 , Trinity College Nanoscience Lab., Dublin Ireland, 4 , University of Sheffield, Sheffield United Kingdom
In modern magnetic recording materials the ‘superparamagnetic effect’ has become increasingly important as new magnetic hard disk drive products are designed for higher storage densities . In this regard, nanoparticle media , where two-dimensional arrays of monodisperse nanoparticles with high magnetic anisotropy are used, is assumed to be the ideal future magnetic recording material. In this presentation a novel magnetic gradient nanomaterial, which has been created by depositing Co/Pd multilayers onto two-dimensional arrays of self-assembled nanoparticles  will be introduced. The magnetic nanostructures formed on top of the particles are in a magnetically exchange-isolated quasi-single-domain state. This nanoscale system is quite distinct from the classical geometries: Neither extrinsic properties nor the intrinsic properties are uniform in space. The film is extended over a wide region of the sphere and thus shows substantial curvature. The film thickness varies and so do the intrinsic magnetic properties most notable the magneto-crystalline anisotropy, which is a key factor affecting the fundamental nature of the reversal process. The specific magnetic characteristics of such a gradient nanomaterial and in particular its impact on the reversal mechanism will be discussed. Angle-dependent reversal studies were performed for different particle sizes and the experimental results were interpreted using micromagnetic simulations . Moreover, these nanoscale magnetic patterns are used to study the scaling behavior of the exchange bias effect employing antiferromagnetic layers of IrMn and CoO, offering new opportunities in the functionalization of magnetic nanostructures. A. Moser et al., J. Phys. D: Appl. Phys. 35, (2002) R157. S. Sun et al., Science 87, (2000) 1989. M. Albrecht et al., Nature Mater. 4, (2005) 203. T. Ulbrich et al., Phys. Rev. Lett. 96, (2006) 077202.
10:00 AM - **O8.2/P1.2
Magnetic And Structural Roughness In A Multilayer PatternedUsing Self-Assembled Spheres
Sean Langridge 1 , Timothy Charlton 1 , Lisa Michez 2 , Mannan Ali 2 , Christopher Marrows 2 , Bryan Hickey 2 , Ernie Hill 3 , Mike Toohey 3 , Sam McFadzean 4 , John Chapman 4 Show Abstract
1 ISIS, Rutherford Appleton Laboratory, Didcot United Kingdom, 2 School of Physics and Astronomy, University of Leeds, Leeds United Kingdom, 3 Department of Computer Science, University of Manchester, Manchester United Kingdom, 4 Department of Physics and Astronomy, University of Glasgow, Glasgow United Kingdom
The functionality of magnetic multilayers is derived from their interfaces, which may exhibit both structural and magnetic roughness. We have prepared antiferromagnetically coupledCo/Ru multilayers on a nanoscale patterned substrate to study the influence of a controlledsurface morphology on the relationship between these two forms of disorder. The patterningwas realised through nanosphere lithography to prepare a template onto which the magneticmultilayers were deposited, and the internal magnetic microstructure was probed using offspecular neutron reflectometry. Here we show that a quantitative analysis reveals that thepatterning induces a concomitant magnetic roughening of the system which is not observed in the unpatterned system. The results are confirmed by micromagnetic simulation. This effectis particularly prominent for the exposed surface structures. Significantly, the magneticordering is controlled by the structural morphology throughout the entire thickness of thestructure. For the optimisation and understanding of the next generation of spin-electronicdevices, exchange biassed systems and particularly patterned systems, that rely on interfacialmagnetism then measurements such as those presented, which are able to probe inter and intralayer ordering and separate bulk from interfacial phenomena from buried interfaces are particularly useful and extend the information attainable through more conventional magnetometerytechniques.
10:30 AM - O8.3/P1.3
Magnetic Nanostructures by Laser Manipulation of Atoms.
Grzegorz Myszkiewicz 1 , Erich Jurdik 1 , Fred Atoneche 1 , Tonnie Toonen 1 , Albert van Etteger 1 , Theo Rasing 1 Show Abstract
1 , Institute for Molecules and Materials/Radboud University Nijmegen, Nijmegen Netherlands
We present a novel way of fabricating periodic structures with areal densities of 1 Tbit/inch2 and possibly beyond. A big advantage of the employed technique – laser-focused deposition – is its extreme parallelism combined with very high accuracy, which allow growing nanostructures on macroscopic sample areas (~mm2). In our experiments we have focused iron atoms and subsequently grown them into nanolines. The nanoscopically corrugated iron surface consists of highly-uniform nanolines with a period of 186 nm, a full-width at half maximum of 95 nm and a height (above the background) of 8 nm. The magnetic measurements performed on the fabricated sample – magnetic force microscopy and magneto-optical Kerr measurements – both revealed a ferromagnetic behavior with in-plane easy axis that was independent from the position on the iron patch (irrespective of the presence of nanolines). This is due to a large background layer of about 25 nm. This drawback could be overcome by nanofabrication of magnetic materials with periodically varying composition and thus magnetic properties. This can be achieved by selective manipulation of iron during simultaneous deposition of a number of other species. In our recent laser-focused experiments with chromium atoms we achieved the extremely high resolution of 16 nm, which, when transferred to magnetic materials, might lead to practical applications (in, for example, magnetic data storage devices). Although there exist other techniques for nanofabrication on a similar scale, like electron beam lithography and self-assembly, the advantage of our method is that it can cover macroscopic surface areas within a single deposition run and, at the same time, maintain the extreme periodicity of the pattern. To the best of our knowledge, no other technique has been able to demonstrate such a result so far and this, in its very spirit simple experimental concept, can potentially have a large impact on industrial developments. The patterned media concept is currently considered as the most promising alternative that will help to overcome the superparamagnetic limit of the magnetic storage technology and thus help the industry to move forward. It is very possible that the technique of laser-focused deposition will enable a new generation of magnetic storage devices. Part of this work was supported by the Dutch nanotechnology R&D initiative NanoNed and the Stichting voor Fundamenteel Onderzoek der Materie (FOM), which is financially supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO).
10:45 AM - O8.4/P1.4
Ripple Induced Modifications of Magnetic Properties.
Maciej Oskar Liedke 1 , Adrian Keller 1 , Stefan Facsko 1 , Jurgen Fassbender 1 Show Abstract
1 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf, Dresden Germany
Self-organized ripple formation during ion erosion of a Si wafer is used to create a template system with a well defined roughness of uniaxial symmetry. By using special buffer layers subsequent thin magnetic film deposition by molecular beam epitaxy leads to a periodically modulated magnetic thin film with drastically modified magnetic properties with respect to a nominally “flat” film of the same thickness. In the case of Permalloy thin films, an enhancement of the uniaxial in-plane anisotropy by approximately a factor of 20 is observed. The enhancement can be explained by a combination of step induced dipolar and magnetocrystalline surface anisotropy contributions. If a ferromagnet/antiferromagnet-bilayer is deposited a superposition of ripple-induced uniaxial anisotropy and exchange coupling induced unidirectional anisotropy is observed. Since the direction of the unidirectional anisotropy depends only on the magnetic field direction during a field cooling procedure any angle between both anisotropy contributions can be set. The observed angular dependence of the magnetization reversal behavior is in perfect agreement with simulations based on the Stoner-Wolfarth coherent rotation model.
11:30 AM - O8.5/P1.5
Patterned Magnetic Nanostructures by Partial Crystallization of Amorphous Alloys on Patterned Catalytic Nanoparticles.
Anup Gangopadhyay 1 3 , Christopher Favazza 1 3 , Lydia Longstreth 1 3 , Clayton Miller 2 , Ronald Indeck 2 3 , Ramki Kalyanaraman 1 3 Show Abstract
1 Dept. of Physics, Washington University, St. Louis, Missouri, United States, 3 Center for materials innovation, Washington University, St. Louis, Missouri, United States, 2 Dept. of Electrical and Systems Engineering, Washington University, St. Louis, Missouri, United States
Because of potential applications in data storage and sensor development, any efficient processing method that can produce a regular array of ferromagnetic nanocrystals is interesting. Here we demonstrate a cost-effective bottom-up processing method that can produce one (1-D) or two dimensional (2-D) Fe-based nanocrystal arrays by partial crystallization of amorphous alloys. The method involves: a) formation of patterned arrays of catalytic nanoparticles (Cu, in the present case) by laser-induced self-assembly; b) deposition of a Fe-Si-B-Nb amorphous alloy on this Cu array by laser ablation; and c) partial crystallization of the amorphous alloy by heat treatment to produce Fe-Si nanocrystals on top of the Cu nanoparticles by heterogeneous nucleation and growth. The diameter, height, and separation of the ferromagnetic nanocrystals, and therefore, their magnetic properties can be controlled. Although demonstrated for a specific system, the method can be applied to a wide variety of materials by using material-specific catalytic nanoparticles, and by exploiting the much wider solubility of elements in the amorphous phase.
O9/P2: Joint Session: Magnetic Nanostructures
Wednesday AM, November 29, 2006
Room 310 (Hynes)
11:45 AM - O9.1/P2.1
Tailoring Ordered and Oriented Inorganic Nanostructures with Molecular-Templated Processing
Michael Hu 1 Show Abstract
1 , Oak Ridge National Laboratory, Knoxville, Tennessee, United States
Molecular templating using block-copolymers, in combination with sol-gel chemistry and processing, could become a powerful scalable, bottom-up approach for chemical manufacturing of diversified organic-inorganic hybrids and nanoporous/mesoporous nanomaterials. However, the production of self-assembled nanostructures is usually limited in achievable sizes of ordered domains and a lack of control in nanopore orientation. This paper will present new paradigms of “engineering nanoprocesses” for controlled production of new material nanostructures having desired pore size and orientation by applying process engineering and molecular engineering principles into several sol-gel synthesis processes. With the achievement of engineered chemical processing of materials at nanoscale, we have created new nanoscale materials, i.e., inorganic membranes and nanowires that contain high ordered arrays of oriented nanoporous channels. Some potential impacts of array-based nanomaterials on applications (e.g., fuel cells, solar cells, gas separations, catalysis, electronics, sensors/detectors) will be discussed.
12:00 PM - O9.2/P2.2
Arrays of Ultrasmall, Small Symmetric and Asymmetric Nanoscopic Ferromagnetic Rings
Deepak Singh 1 , Robert Krotkov 1 , Hongqi Xiang 2 , Thomas Russell 2 , Mark Tuominen 1 Show Abstract
1 Physics, University of Massachusetts, Amherst, Amherst, Massachusetts, United States, 2 Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts, United States
There has been a considerable amount of recent interest in the magnetic properties of nanoscopic ferromagnetic rings. This is largely motivated by the unique stability of the vortex state of magnetization and its relevance in future data storage elements. In this work, we discuss experimental research on ultra-small, small symmetric and asymmetric cobalt nanorings. We fabricate arrays of nanoscopic rings using the techniques involving self-assembled diblock copolymer templates, electron-beam lithography, glancing angle evaporation and ion beam etching. The nanoscopic rings have an outer diameter of 13 nm and inner diameter of 5 nm in the case of ultra-small rings, whereas the small rings have an outer diameter of 150 nm and a wall width that varies from 5 nm to 30 nm. The magnetization properties of these arrays are measured in both parallel and perpendicular field orientations in SQUID magnetometer. We compare these measurements to analytical calculations for different magnetic configurations that take into account the competition between exchange energy, Zeeman energy and magnetostatic energy. Based on analytical calculations and magnetic measurements we find that for the ultrasmall ring structures, only two states are important: single domain states and flux-closure vortex states, depending upon the exchange length for the polycrystalline Co materials used. We have also shown that by creating asymmetry in the ring’s width, one can control the direction of magnetic vortex circulation that is in agreement with the prior research results. Low temperature magnetic measurements for asymmetric ring arrays exhibit interesting exchange bias effects. This work is supported by NSF grants DMR-0306951 and DMI-0531171.
12:15 PM - O9.3/P2.3
Control of the Vortex Chirality in Ring-shaped Magnetic Memory Elements Using Exchange Bias.
Wonjoon Jung 1 , F. Castaño 1 , C. Ross 1 Show Abstract
1 DMSE, M.I.T., Cambridge, Massachusetts, United States
Thin film magnetic rings have attracted a great deal of attention since the ring shape could be an alternative geometry for high-density magnetic storage elements. Ring magnets can support flux-closure or ‘vortex’ states in which magnetization is oriented tangentially and no stray field exists. Data bits can be stored using the chirality of the vortex (clockwise or counterclockwise) and the absence of stray fields in these states allows for increasing storage densities since memory cells can be arranged in close proximity while maintaining magnetostatic interactions negligible. Control of the vortex chirality in ring elements is of importance for applications in magnetic data storage. Most work on the chirality control has been done with geometrical modification such as introducing a notch or flat edge to the ring. In this contribution we demonstrate the control of the chirality using exchange bias, which is a crucial element in the operation of spin valve and magnetic tunnel junction structures.Arrays of elliptical rings with a 3.2/2.0 μm major/minor diameter and widths of 400–500 nm were fabricated with e-beam lithography and lift-off processing. Co (12 nm) and Co (12 nm)/IrMn (5 nm) exchange bias structures were deposited using ion beam or dc-magnetron sputtering. Formation of the vortex state typically occurs as one of the domain walls of the bi-domain or ‘onion’ state, which is attained after saturation, unpins, moves, and finally annihilates the other wall in a reverse field. Therefore the chirality is determined by the direction of domain wall motion during the onion-to-vortex transition. We present a model that analytically describes the onion state domain wall motion in an elliptical ring in a field at an angle α with respect to the major axis. The model allows the change in energy of the system to be calculated as a wall moves from its remanent position, so that the direction of wall motion, e.g. the chirality of the vortex, can be predicted. The calculations show that for single-layer elliptical rings the chirality will be counterclockwise if a reverse field is applied at angle α between 0° and 90°, and clockwise at α between 0° and -90°, that is, the critical field direction αc= 0° (the major axis). Meanwhile, for exchange-biased rings, αc approaches the exchange bias direction β as β deviates from 0°. This prediction was compared with experimental observations of the direction of wall motion by means of magnetic force microcopy (MFM). MFM measurements showed a good agreement with the model. Based on a series of calculations and observations for various angles α and β, a phase diagram of the vortex chirality was determined. This work demonstrates that the desired vortex chirality can be obtained using an appropriate combination of field and exchange bias direction. Vortex states in the free and pinned layer of ring-shaped spin valve structures, which were investigated by magnetotransport measurements, will be discussed.
12:30 PM - O9.4/P2.4
Current-induced Domain Wall Motion in Bar-shaped Pseudo-Spin-Valve Elements.
Irenee Colin 1 , D. Morecroft 1 , F. Castano 1 , C. Ross 1 Show Abstract
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
12:45 PM - O9.5/P2.5
Fabrication of Ring-shaped Magnetic Nanostructures for MRAM using Electron Beam and Focused Ion Beam Exposure of HSQ.
Chen Chen 1 , Michael Cabral 1 , Lloyd Harriott 1 , Robert Hull 2 1 Show Abstract
1 Electricla and Computer Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Material science and engineering, University of Virginia, Charlottesville, Virginia, United States
O10: Novel Nanofabrication Techniques
Wednesday PM, November 29, 2006
Room 310 (Hynes)
2:30 PM - **O10.1
Atsushi Yokoo 1 , Hideo Namatsu 2 Show Abstract
1 , NTT Basic Research Laboratories, Atsugi-shi, Kanagawa Pref., Japan, 2 , NTT Advanced Technology Corporation, Atsugi-shi, Kanagawa Pref., Japan
3:00 PM - **O10.2
Ion Projection Direct Treatment of Surfaces
Wilhelm Bruenger 1 Show Abstract
1 , Fraunhofer-Society, Itzehoe Germany
Ions can be used in a variety of principles to modify sample properties such as sputtering of surfaces, ion implantation, intermixing of multilayers, change of surface potential for subsequent selective deposition or defined crosslinking of polymer materials. Ion projection direct treatment uses an open stencil mask with electrostatic demagnification optics and overcomes the bottleneck of time consuming serial writing . The technique is conducted without a photoresist layer, which saves process steps and avoids possible surface contamination. Here I will give an overview about ion projection direct treatment principles and potential applications for information storage or surface functionalization. Co/Pt multilayers show perpendicular magnetic anisotropy, which can be altered by intermixing of both layers. Large-area Ar+ projection was used to generate planar magnetic nanostructures on a 1”-format hard disk in a single step . The complete recording pattern with data areas and head-positioning structures was transferred. In addition, the magnetic switching behavior of magnetic nano patterns from 170 nm to 57 nm diameters have been investigated by means of magnetic force microscopy in dependence of the ion dose.Irradiation of He+, Ar+, and Xe+ onto p-doped Si results in a change of surface potential. Small Au and Cu dots with a diameter of 200 nm have been fabricated in a subsequent selective electroplating process. Significant differences in the current density of voltage curves between irradiated and non-irradiated areas were recorded by microcapillary measurements . On non-metallic surfaces such as polymers or glass an electrode less selective metal deposition was achieved from supersaturated salt solutions. This process might be applicable for the production of electronic circuitry on polymer foils .A new field is ion projection direct crosslinking (IPDC) of polymers. IPDC is applied as top down method to crosslink polymers locally and a subsequent temperature or solvent treatment  initiates chain relaxation resulting in finer surface morphologies on a nanometer scale (bottom up assembly). The periodicity of the morphology depends on the number and depth of created vacancies in the polymer by the ion projectiles. Ripple type structures <250 nm were observed in locally irradiated stretched polystyrene samples after annealing. This method allows creating organized morphologies, inside the borders of ion-irradiated areas. References H. Loeschner et al., Journal of Microlithography, Microfabrication and Microsystems 2, 34-48 (2003). A. Dietzel, et al., Advanced Materials 15, 1152-1155 (2003). A. Spiegel et al., J.Vac.Sci.Technol.B 20, 2713, (2002). W.H. Bruenger et al., German Patent application 102005028391.8-54. K. Büscher et al., Microelectronic Engineering 83, 819-822 (2006).
4:00 PM - O10.3
Advanced Nano-patterning of Magnetic Media Using a Ultra High Resolution Focused Ion Beam.
Jacques Gierak 1 Show Abstract
1 , LPN-CNRS, Marcoussis France
The development of industrial processes for the patterning of materials in the nanoscale is one of the major challenges of nanotechnology. Lithographic techniques, used at ever-shorter wavelengths in the integrated circuit (IC) manufacturing industry, have clearly identified limitations. As a consequence, next-generation lithographies (NGLs) are being actively developed to take over for highly successful optical lithography. Ion beams are in principle well suited to nanofabrication, because ions suffer very little scattering, have short penetration ranges, and should be compatible with innovative patterning schemes. Additionally focused ion beam technology (FIB) is capable of overcoming some basic limitations of current nanofabrication techniques and allowing innovative patterning schemes. Following this we have developed a very high resolution FIB instrument specifically to meet nanofabrication requirements with an unrivalled patterning capability in the sub 5 nm regime. One key application we have started to explore since many years is the application of the FIB technique in magnetic material nanopatterning. Magnetic nanostructures are of considerable interest for several reasons. Many characteristic lengths (e.g., the exchange length, the domain wall width, the length associated to Barkhausen jumps) have typical nanometer sizes, so that reducing the lateral dimensions of patterns to about that level may lead to new insights into nanomagnetism properties and applications. Ultra-high density recording using nanopatterned magnetic media is obviously a major issue. In this work we aim to present and detail two complementary FIB processing schemes for magnetic media nanopatterning.(i) The top down approach achieved via local defect injection on high quality, ferromagnetic Pt/Co ultra-thin films and multilayer structures will be presented. The samples we use were produced as 2D films by sputtering. The coercivity and perpendicular anisotropy of such materials have been shown to depend much on the nature of the Co/ Pt interfaces. We will show that even under extremely low FIB doses, the magnetic properties of the ultra-thin film structure by intermixing the Co and Pt atoms are modified, especially across interfaces, through collisions with the incoming ion beam.(ii) In a second step we will detail a bottom up approach we propose based on surface defect generation by low dose FIB impacts and followed by the deposition of preformed nanometer-sized clusters on these patterned surfaces. We will analyse and illustrate the trapping potential of these defects, via nanometer and mixed cobalt-platinum (Co50Pt50) clusters, on the functionalised surfaces.These two distinct patterning approaches achieved using unconventional low ion doses and high writing speeds will be detailed and commented in the presentation.
4:15 PM - O10.4
Templated Fabrication of Nanoring Arrays based on Interference Lithography
Ran Ji 1 , Woo Lee 1 , Mato Knez 1 , Roland Scholz 1 , Ulrich Gösele 1 , Kornelius Nielsch 1 Show Abstract
1 , Max Planck Institute of Microstructure Physics, Halle Germany
Lithographically addressable nanoring arrays have attracted considerable attention due to their unique magnetic, optical, or electrical properties. Conventional patterning techniques, such as photo- and e-beam lithography, are limited in spatial resolution and writing speed, respectively. Alternatively, self-assembled nanospheres and nanoporous substrates have been employed as templates for ring-shaped nanostructures, but these alternative approaches are limited in terms of long-range ordering and shape of the nanorings. Especially, elliptical magnetic rings with in-plane magnetic anisotropy are highly attractive for potential applications in magnetic random access memories (MRAMs). In this contribution we present two novel fabrication approaches for wafer-scale, ideally ordered arrays of elliptical and circular nanorings with feature sizes ranging from 30 to 200 nm based on laser interference lithography (LIL). In Method I, templates consisting of periodic Si3N4 nanohole arrays on highly doped Si wafers are generated by LIL and reactive ion etching. The nanoring arrays are prepared by selective electrochemical deposition on the step edges of the Si3N4 holes. In Method II, the developed photoresist generated by LIL is coated by atomic layer deposition (ALD) of TiO2. The top and bottom parts of the TiO2 layer are removed by Ar bombardment in the out-of-plane direction, and the resist is removed in O2–plasma, finally. The TiO2 layer on the sidewall of the resist holes is remaining and forms the TiO2 ring structures. This approach will be extended to other materials, e.g. SiO2, Fe3O4, Ni, and Co.We thank the Federal Ministry of Education and Research (BMBF) for financial support (FKZ 03N8701).
4:30 PM - O10.5
Dot Arrays with density over 500 Gbit/in2 Fabricated by Extreme Ultraviolet Interference Lithography.
Harun Solak 1 2 , Yasin Ekinci 1 , Laura Heyderman 1 , Jens Gobrecht 1 Show Abstract
1 Laboratory for Micro and Nanotechnology, Paul Scherrer Institute, Villigen PSI Switzerland, 2 , EULITHA GmbH, Villigen PSI Switzerland
Lithographic fabrication of patterned data storage media places extreme requirements on the fabrication method which includes high-throughput and resolution below 50 nm in terms of the pattern period. Extreme Ultraviolet Interference Lithography (EUV-IL) has the potential to address these challenges. We have fabricated dot arrays with periods going down to 35.3 nm using EUV-IL. The corresponding aerial density of the arrays is 516 Gbit/in2. In addition, we have fabricated line/space type grating patterns with periods as low as 25 nm. These high resolution dot-array and line-space patterns were obtained in a negative-tone calixarene resist.Diffraction gratings are used to form interfering beams in the EUV-IL technique. The gratings, which are fabricated either with e-beam lithography or laser interference lithography are illuminated with EUV light at a wavelength of ~13 nm from a synchrotron source. The interference pattern has a period that is smaller than the period of the gratings by a factor of 1.4 – 2, depending on the mask design. This demagnification factor between the mask (grating) and the final pattern greatly simplifies the production of the masks and enables the iterative use of the technique to multiply the resolution. By using grating based interference it is possible to form one- and two-dimensional patterns as well as patterns that have circular symmetry, such as bits on circular tracks.The EUV-IL technique has a number of important advantages. The proximity effect caused by photoelectrons generated in the resist and the substrate is practically absent at the used beam energy of 92.5 eV. The interference technique offers practically unlimited depth of focus. The use of photons to define the image means that the technique is insensitive to charging and thus can be used on insulating substrates such as glass. In addition, the aerial image is strictly related to the grating pattern on the mask which greatly helps with the reproducibility of the lithographic process.The ultimate limit of resolution in EUV-IL in terms of the pattern period is λ/2 which corresponds to about 7 nm. The resolution potential combined with the high throughput of this parallel printing method makes EUV-IL a candidate for the production of dense patterns for patterned data storage applications.
4:45 PM - **O10.6
Chemical Mechanical Planarization for Patterned Media and Interconnects.
C. Fred Higgs 1 2 , Elon Terrell 1 2 , David Engel 1 Show Abstract
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 Data Storage Systems Center, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Recently, the growth rate of magnetic storage density has increased to 100% per year. At this rate, the physical limit of areal density, known as the superparamagnetic limit, will be reached in the near future. Patterned media separates the bit domains so that exchange coupling can be limited and thermal stability can be enhanced. The fabrication and manufacturing of reliable patterned media depends on a key issue— the ability to produce highly planarized and thin composite films for slider flight. Chemical mechanical polishing (CMP) is a process originally created to planarize or polish nanoscale oxide or metallic surfaces to produce integrated circuits (ICs) from semiconductor wafers. During polishing, a rotating wafer is mounted face up on a fixture and pressed against a rotating polymeric pad that is flooded with chemically reactive slurry. The slurry has nanoparticle abrasives which act as mechanical removal agents while also serving as the chief catalyst of surface damage. This effort will introduce work being conducted to fabricate patterned media in-house for experimental validation of a novel CMP modeling simulation. Since CMP is largely an unpredictable and costly process, a first principle multi-scale, multi-physics CMP modeling simulation is being developed to explore the feasibility of adopting CMP as a planarization tool for patterned media. This approach involves considerations of the involved (i) contact mechanics, (ii) fluid mechanics, (iii) particle dynamics, and the resulting (iv) material removal.
5:15 PM - O10.7
A Nanodamascene Process to be used as a Building Block for Nanodevices.
Christian Dubuc 1 , Jacques Beauvais 1 , Dominique Drouin 1 Show Abstract
1 , U. of Sherbrooke, Sherbrooke, Quebec, Canada
O12: Poster Session: Magnetic Nanostructures II
Wednesday PM, November 29, 2006
Exhibition Hall D (Hynes)
9:00 PM - O12.1
Grain Size Refinement in Cu bottom lead in CPP GMR Stack
Zeenath Tadisina 1 , Subhadra Gupta 1 , Cristian Papusoi 2 , Hideo Fujiwara 2 , Chandan Srivastava 1 , Gregory B. Thompson 1 Show Abstract
1 Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, Alabama, United States, 2 Center for Materials for Information Technology (MINT), The University of Alabama, Tuscaloosa, Alabama, United States