Panagiotis Dimitrakis, National Center of Scientific Research ''Demokritos"
Yoshihisha Fujisaki, Hitachi Ltd
Guohan Hu, IBM T.J. Watson Research Center
Eisuke Tokumitsu, Japan Advanced Institute of Science and Technology
M2: Polymer Memories
Monday PM, December 01, 2014
Hynes, Level 3, Room 309
2:30 AM - M2.01
High Density Au Nanoclusters for Highly Efficient Non-Volatile Memories
Dimitris Tsoukalas 1 Emanuele Verrelli 1 Panagiotis Bousoulas 1 Nikolaos Boukos 2
1National Technical University of Athens Zografou Greece2NCSR Demokritos Aghia Paraskevi GreeceShow Abstract
In this work we present results concerning the deposition at room temperature of Au nanoparticles of 1.3 nm average diameter on oxidized silicon substrates and with areal densities approaching 10^13 cm^-2 using a physical process based on DC sputtering and inert gaz condensation. The formation and growth of Au nanoclusters occurs through nucleation and coalescence of the 1,3 nm nanoparticles soft-landing on the substrate at room temperatre, which allows the fine tuning of the cluster size and density, is investigated by TEM analysis of samples with increasing Au load, in the range 0-1 mu;g/cm2. These conditions give average gold nanocluster diameter sizes in the range 1,5 - 3,5 nm according the deposition conditions. Taking advantage of the above phenomenon, the nanocluster density and size have been optimized in such a way to attain highly efficient (e.g. in terms of charges/NP and total areal charge density) non-volatile memory devices based on a mixed dielectric stack, 3,5 nm SiO2 tunneling oxide and 20 nm HfO2 control oxide deposited following a low thermal budget RF sputtering process using high purity HfO2 target, with Au NPs used as storage nodes. The above optimization process highlighted the clear correlation existing between the efficiency of the charging process and the mean nearest neighbor distance of the nanocluster film, the latter being a particularly important parameter when the density of nanoclusters is extremely high i.e. above 10^12 cm^-2. The conditions discussed in the paper drive to very large memory windows, as large as 10V for write/erase pulses of 10V height, and excellent charge retention characteristics. The estimated charge loss after a 10 years retention period is less than 40%.
2:45 AM - M2.02
MOS Charge Trapping Memory with Graphene Nanoplatelets Embedded in ZnO Charge Trapping Layer
Nazek El-Atab 1 Furkan Cimen 2 3 Sabri Alkis 3 4 Ali K. Okyay 2 3 4 Ammar Nayfeh 1
1Masdar Institute Of Science and Technology Abu Dhabi United Arab Emirates2Bilkent University Ankara Turkey3Bilkent University Ankara Turkey4Bilkent University Ankara TurkeyShow Abstract
Recently, graphene has attracted great efforts and research due to its exceptional characteristics such as high carrier mobility, large work-function, and optical transparency.1 Based on these unique properties, graphene seems to be a promising material in nonvolatile memory devices. In this work, the effect of embedding graphene nanoplatelets (GNs) in atomic layer deposited (ALD) ZnO charge trapping layer on the MOS charge trapping memory performance is demonstrated. The MOS charge trapping memory cells are fabricated on an n+-type (111) (Antimony doped, 15-20 m#8486;-cm) Si wafer. First, 3.6-nm-thick tunnel oxide Al2O3 followed by 2-nm-thick ZnO are deposited at 250°C using ALD. Pristine GNs are deposited by drop-casting technique. Samples are placed on hot-plate at 110°C and 2-2.5 ml of 0.05 mg/ml graphene solution is drop-casted slowly by using plastic pipette then samples are left to dry for 5 minutes on hot-plate. Then, a 2-nm-thick ZnO followed by a 15-nm-thick Al2O3 blocking oxide are ALD deposited at 250°C. Finally, a 400-nm-thick Al layer with a diameter of 1 mm is sputtered using a shadow mask for the gate contact. The charging effect in the fabricated memory cells is analyzed by studying the high frequency (1 MHz) C-Vgate curves of the programmed and erased states. The gate voltage of the memory cells is swept at -12/12 V backward and forward. The obtained memory hysteresis shows a 6.5 V window. The direction of the programmed state shows that the memory is programmed by trapping only electrons in the storage media. Also, the measured memory hysteresis at different operating voltages is studied and a large memory window (4 V) is obtained at a reduced operating voltage (6 V) and the charge trap states density of the GNs is calculated2 to be roughly 1.08×1012 cm-2. Without GNs, the obtained threshold voltage shift (ΔVt) is negligible indicating that GNs behave as charge trapping centers. Moreover, the retention of the memory is analyzed by programming/erasing the memory at 10/-10 V and measuring the ΔVt in time at room temperature. The memory showed an excellent retention characteristic where the extrapolation to 10 years indicates a 25% loss of the initial stored charge. The remarkable retention characteristic indicates that using GNs in the charge storage media allows further scaling the tunnel oxide thickness and consequently the gate length; thus increasing the memory density without degrading the retention property of the memory. Also, the endurance characteristic of the memory is studied by measuring the memory cell hysteresis at 10/-10 V forward and backward at room temperature up to 104 cycles where the ΔVt is reduced by 13.3% indicating a good endurance of such memory structure. Finally, the results indicate that graphene nanoplatelets have great potential for future low-cost/low-power memory devices. 1- F. Schwierz, Nat. Nanotechnol. 5, 487-496 (2010). 2- N. El-Atab, et al, Appl. Phys. Lett 104, 013112 (2014).
3:00 AM - *M2.03
Recent Effort on Charge Trapping Nonvolatile Memories
Jianlin Liu 1
1University of California Riverside USAShow Abstract
There are tremendous efforts in academia and industry researching various emerging nonvolatile memory technologies. In this presentation, I will only talk about charge trapping memories and focus on reporting some recent effort in my group on nanocrystal-based charge trapping nonvolatile memories and wide bandgap semiconductor memories. Having a goal of extending scaling limit of nanocrystal memories in mind, we explored a few approaches in addition to our earlier silicide nanocrystal approach, such as making vertical nanocrystal memory cells, assembling nanocrystals using di-block co-polymer process, and using parallel-assembled carbon nanotubes and even graphene as channels of the devices. With the purpose of being able to store data for millions of years, we carried out ZnO-based wide bandgap semiconductor memories and preliminary results suggest that this approach is promising.
4:00 AM - *M2.04
Nonvolatile Memory Devices by Exploring the Interface between Metals and Metal Nanoparticles
Jianyong Ouyang 1
1National University of Singapore Singapore SingaporeShow Abstract
Devices with a polymer film blended with metal nanparticles exhibit resistive switches, and they are regarded as the next-generation memory devices. They have advantages of low fabrication cost and high flexibility of the active layer. However, resistive switching devices exploring the interfaces between the active layer and the electrodes have been rarely reported, whereas the interfaces have significant effect on the electrical behavior of many devices. In this talk, I will present resistive switching devices with a polymer film blended with gold nanoparticles capped with conjugated organic ligands. The resistive switches of these devices are sensitive to the electrode materials.
4:30 AM - M2.05
Flexible Organic TFTs Based Memories Integrated with Pressure Sensors for Robotics Applications
Piero Cosseddu 2 1 Giulia Casula 1 Stefano Lai 1 Annalisa Bonfiglio 1 2
1University of Cagliari Cagliari Italy2CNR - Institute of Nanoscience, S3 Centre, Via Campi 213A, 41100, Modena, Italy Modena ItalyShow Abstract
The possibility of developing fully organic electronic circuits is critically dependent on the ability to realize a full set of electronic functionalities based on organic devices. In order to complete the scene, a fundamental element is still missing, i.e. reliable data storage. In this work we introduce an interesting approach consisting in the employment of a Low Voltage Organic Thin Film Transistor (OTFT) realized with a combination of two insulating layers, namely a high-k ultrathin aluminum oxide layer (average thickness around 5-6 nm) and a second, low-k, ultrathin insulating layer (thickness from 25 up to 80 nm), made out of Parylene C and deposited from vapor phase. Thanks to the high capacitance coupling induced by the ultrathin double-layer insulating films, such devices can be operated at ultralow voltages, as low as 1V, showing mobility up to 0.4 cm2/Vs, Ion/Ioff up to 105 and remarkably low leakage currents (100 pA), with a typical breakdown field higher that 5MV/cm. Moreover, these devices were fabricated on a highly flexible (13 um thick) Kapton substrate, and we will demonstrate that their electrical performances are not affected by a continuous mechanical deformation, even after more than 1000 cycles at bending radii as small as 150 um. Very interestingly, we have observed that by applying a pulsed gate voltage, slightly higher than the nominal breakdown voltage, it is possible to induce a pronounced threshold voltage shift in the transistor behavior. A study of the influence of the polarization parameters, such as applied gate field, pulse duration, and number of applied pulses, on the main parameters of the fabricated memory elements (i.e. Ion/Ioff and retention time) will be discussed as well as the physical principle behind the observed behavior. In particular, we observed that, when a high electrical field is applied, the charges injected into the device channel can tunnel and get trapped into the Parylene C low-k dielectric, whereas, the Al2O3 high-k blocking dielectric avoid trapped charges to move all the way through the gate electrode.
Interestingly, it was found that, by properly designing the double layer gate dielectric, it is possible to achieve threshold voltage shifts higher than 2V, giving rise to a remarkably high Ion/Ioff ratio, usually in the range of 103, measured at -1V, with a retention time up to 5x106s. Finally we have integrated an array of OTFTs memory elements with a piezo-resistive rubber sheet, which was connected in series with the gate electrodes of each singly memory cell. We will show that using such an approach it is possible to trigger the memory element with a mechanical stimulus. This approach represents a very interesting solution for the realization of artificial skin in the human-robot interaction field.
4:45 AM - M2.06
The Resistive Memory Effect in Organic Electronic Devices: Unveiling Its Origin and Emerging Opportunities
Sebastian Nau 1 Christoph Wolf 1 Stefan Sax 1 Emil J.W. List-Kratochvil 1 2
1NanoTecCenter Weiz Forschungsgesellschaft mbH Weiz Austria2Graz University of Technology Graz AustriaShow Abstract
Electrically tunable resistors realized in two terminal structures seem to be one of the most versatile innovations in the semiconductor industry with many possible applications such as logic circuitry or neuromorphic systems. In particular, inorganic resistive switching devices utilized as non-volatile memory are close to commercialization. Hysteretic current-voltage (IV) characteristics have also been observed from a huge manifold of organic devices employing different π-conjugated small molecules or polymers as well as dielectric materials like poly(methyl methacrylate) (PMMA). However, despite vital academic interest no consistent explanation of the working mechanism of resistive switching elements has been given to date. Various mechanisms are usually suggested, including charge-trapping and charge transfer mechanisms, filament formation, coulomb blockade or molecular conformation changes.
Based on our most recent work, we here present a set of experiments (I/V characterization, photovoltaic measurements, impedance spectroscopy) to explain unipolar resistance switching: For the first time we are able to unambiguously rule out all charging based models which were held responsible for the switching in organic devices and show that the memory behaviour can be interpreted as the formation and rupture of a conductive pathway (‘filament&’). We demonstrate that unipolar resistive switching is a universal and largely material independent (electrodes AND organics) property in electrode/organic/electrode thin-film structures.
We also report on the fabrication of organic resistive switches using environmentally friendly inkjet-printing methods and their integration into fully functional hybrid crossbar array structures. Unipolar resistive switches can be integrated into memory arrays by utilizing a diode as selector device. In contrast to a planar transistor, a diode is itself realized as a 2-terminal device allowing for high density '4F2' integration. The requirements to such a diode will be elucidated and a high-performance organic diode, fulfilling all needs, is demonstrated.
We will further present novel and unique applications of organic resistive switching devices like flexible flat-panel image and x-ray detectors.
 S. Nau, S. Sax, E. J. W. List-Kratochvil, #8218;Unravelling the nature of unipolar resistance switching by utilizing the photovoltaic effect‘, Advanced Materials 2014, 26, 2508.
5:00 AM - M2.07
Charge-Storage Memory Based on Solution Processed Zinc-Tin Oxide Thin Film Transistors
Jeng-Ting Li 1 Li-Chih Liu 1 Jen-Sue Chen 1 Jiann-Shing Jeng 2
1National Cheng Kung University Tainan Taiwan2National university of Tainan Tainan TaiwanShow Abstract
Charge-storage memories based on metal-oxide-semiconductor (MOS) structure have been intensively studied using various formats of charge storage media. Instead of using MOS structure with bulk semiconductor, we investigate the charge storage memory based on solution processed zinc-tin oxide (ZTO) thin film transistors (TFTs). The solution processed ZTO film is only 3-5 nm in thickness and the ZTO TFT with SiO2 dielectrics exhibits a good field-effect mobility of ~4 cm2/Vs, small subthreshold slope of ~0.3 V/decade and high on/off ratio of ~108. After introducing a Ni charge storage layer and an AlOx tunneling layer, the ZTO TFT ID-VG transfer characteristics can be horizontally shifted by +6V when applying a positive gate bias of 35V. The shift of ID-VG transfer characteristics can be recovered by applying a negative bias with light illumination. The charge transport between ZTO TFT channel region and Ni charge storage layer will be discussed based on the migration of electrons and charged oxygen vacancies, under the influence of bias and light illumination.
5:15 AM - M2.08
Photo-Controllable Resistive Memory Based on Polymer Materials
Mikhail Dronov 1 2 Maria Kotova 2 Ivan Belogorokhov 2
1Prokhorov General Physics Institute Moscow Russian Federation2M.V. Lomonosov Moscow State University Moscow Russian FederationShow Abstract
Resistive switching, the reversible modulation of electronic conductivity, is of interest for prospective memory devices that could be perfect electronic memory. Despite different types of ReRAM (Resistive Random Access Memory), organic based ReRAM is an object of special interest due to ability to produce high performance devices using relatively simple technology. There is still much uncertainty about mechanisms driving these effects that our work attempts to bring to light.
We have discover, that admixtion of phososensitive organic molecules (different metal phthalocyanines and metal tienoporphyrazines) to polymer materials (e.g. polystyrene, in which electrically induced resistive switching where reported before) results in possibility of adding photo-controllable properties to organic memory devices.
We observed two different effects achievable with such device improvement:
1) Ability to change critical voltage/current parameters for electrically resistive switching effect for illuminated sample (for different materials and illumination sources both upping and lowering of critical switching voltage/current levels were present).
2) The possibility of fully light-induced switching of device nonvolatile resistive state i.e. effect of changing device state without applying electrical voltage in both directions between states with significantly different resistance. The resulting states had same nonvolatile properties as the ones achieved with electrically induced switching.
To clarify, these effects were also present in devices made from organic dyes that were used as photosensitive admixture. The observed effects were tested in coplanar and “sandwich” geometry, and have shown no dependency from contact material (ITO, Ag or Cu were used as contacts).
For the undoped polystyrene, all our results propose the filament formation model as the most possible mechanism of observed effects. In that case, the filaments could be possibly originating from metal particles injected into an organic film from metallic contacts during the initial device electroforming. Observed light-induced effects could be explained only with the charge-storage related resistive switching, thus bringing a requirement to consider crossover between this possible switching mechanisms as an explanation for observable effects.
This demonstrated necessity to consider more than one mechanism of resistive switching could bring better explanation of different results often achieved on the same materials and similar devices under different conditions or different research methods.
From practical point of view, the effect of photo-induced resistive switching could lead to a novel type of organic based devices like light-electrical interfaces, or photo-programmable memory.
5:30 AM - M2.09
Resistive Switching In Hydrogen Silsesquioxane Thin Film
Wing H Ng 1 Mark Buckwell 1 Adnan Mehonic 1 Anthony J Kenyon 1
1University College London London United KingdomShow Abstract
Hydrogen silsesquioxane (HSQ) is commonly used as a dielectric insulating layer in the electronic industry. In this paper, we demonstrate that this material shows resistive switching properties, and it can be potentially used as an active layer in resistive switching memory devices.
The device was fabricated on a p-type silicon substrate with Cr/Au bottom contact. The HSQ active layer was deposited by spin coating and the device region was defined by electron beam exposure. A top aluminium electrode was then evaporated onto the HSQ layer. The thickness of the HSQ layer after the exposure step was 40nm. The switching voltage is in order of several volts, and a greater than six order of magnitude difference in resistance between the high resistive state and low resistive state is observed.
A Metal-Insulator-Metal (MIM) device with ITO bottom contact was also fabricated, and resistive switching behaviour was observed using conductive atomic force microscopy (C-AFM) measurements in which the C-AFM tip acted as the top electrode.
X-ray photoelectron spectroscopy (XPS) data shows the HSQ layer becomes SiOx and SiO2-like upon cross-linking by electron beam exposure. The combination of using HSQ and electron beam lithography allows fabrication of resistive switching memory devices with an endless combination of desired shapes in nanometre-scale.
5:45 AM - M2.10
Organic Memory Elements
Klaus Meerholz 1
1University of Cologne Koln GermanyShow Abstract
Photochromic molecules provide an intriguing and relatively untapped alternative to traditional materials utilized in organic memory devices. We have recently reported on a new prototype of a nonvolatile light-emitting organic memory (LE-OMEM) that integrates a layer of crosslinkable dithienylethene photochromes (XDTE) into a solution-processed, multilayer OLED. The XDTE molecules undergo a change in both their UV-visible absorption and energy level position due to a photo- and/or electrically-induced ring-opening/-closing reaction. Exploiting the difference in HOMO and LUMO energies of both isomers and the subsequent change in hole-injection barrier we use this XDTE layer as an electrical switch within our OLED layer stack. Optimized devices have displayed ON/OFF ratios in both current and electroluminescence of greater than 104. We investigate both optical and electrical programming of the OMEM devices and show that precise control of the ratio of both isomers in the active layer enables access to a multitude of intermediate states demonstrating the potential of these devices for future multilevel memory applications. We also discuss the difference in the molecular-scale mechanisms that are responsible for the optically- and electrically-induced switching effect in these devices by in-situ monitoring of the fraction of closed molecules as a function of the external stimulus.
M3: Poster Session I: RRAM I
Monday PM, December 01, 2014
Hynes, Level 1, Hall B
9:00 AM - M3.01
Gap-Fill Performance of Amorphous Carbon Layer Film by the Reactive Ion Deposition Systems for Double-Patterning Trenches in NAND-Flash Memory Process
Jongwook Kim 1 Jaeyoung Yang 1 Keunho Park 1 Ginyung Hur 1 Jaeho Lee 1 Wonjin Ban 2 Donggeun Jung 2
1TES Co. Ltd. Yongin-Si Korea (the Republic of)2Sungkyunkwan University Suwon Korea (the Republic of)Show Abstract
In this paper, the gap-fill performance and behaviors of the amorphous carbon layer (ACL) film processed by reactive ion deposition system using the acetylene as the precursor. The Gap-fill ability of ACL film used as the hard-mask of the double pattering process in semiconductor integration process have significantly change for the reactive oxygen species (ROS) with the variation of the pulsed direct current (DC) bias condition. The gap-fill ability of ACL film used as the hard-mask of the double pattering process in semiconductor integration process have significantly change for the reactive oxygen species (ROS) with the variation of the pulsed direct current (DC) bias condition. The gap-filled profile of a-C:H film deposited on the pattered wafer with the aspect ratio (AR) >4.0 was analyzed by TEM and SEM and the deposited film properties were characterized by Fourier transform infrared (FT-IR) spectroscope, Raman spectroscope, stress gauge, and ellipsometry. In this experiment we processed by reactive ion deposition system with the reactive oxygen species. We had been performed at the process condition test with Acetlyene (C2H2) as the precursor. Reactive oxygen species (ROS) ratio to precursor depended on gap-fill ability of ACL film and then the bottom-up thickness was varied on substrate temperature and applied the pulsed DC power at 20kHz.
9:00 AM - M3.02
Dynamics of Oxygen Vacancies in TiO2
Michael Wehlau 1 Peter Deak 1 Jan M. Knaup 1 Thomas Frauenheim 1
1BCCMS University of Bremen Bremen GermanyShow Abstract
Resistive switching materials like titania (TiO2) are potentially capable for applications in next-generation semiconductor devices or as components of artificial neurons. Resistive switching effect of metal oxides is based on phase-change mechanisms induced by accumulation of oxygen vacancy defects (VO) and following transformation of insulating TiO2 into substoichiometric conductive phases. For this reason the VO migration is a crucial mechanism for resistive switching. In this work we investigate the dynamics of oxygen vacancies in detailed computational studies. We involve thermodynamics in calculations of the free energy surface by metadynamics and obtain accurate minimum energy paths (MEP) for rutile and anatase. We assume the vacancy to be neutral in anatase and double positively charged in rutile, respectively.
We employ the charge self-consistent Density-Functional based Tight-Binding (SCC-DFTB) method implemented in the DFTB+ code, together with the tiorg parameter set. We calculate free energy profiles for the VO diffusion using metadynamics, employing a modified version of the PLUMED code, coupled to DFTB+, which implements a permutation invariant vacancy tracking (PIVOT) collective variable. This method provides a technique for rare event sampling without specifying reaction paths.
Furthermore, we also perform nudged elastic band calculations to find the MEP for essential VO transitions using the ab-initio DFT method provided by the vasp code.
We find free energy barriers and MEP in good agreement. Both crystal structures provide three symmetry inequivalent hopping events which enable three-dimensional diffusion. In either case, we identify a highly preferred hopping event. We also find a strong dependency of the activation energy on the crystallographic direction, the crystal structure and the material density. Our results also indicate a high thermal stability of rutile-like structures against vacancy diffusion induced phase-change in contrast to anatase.
9:00 AM - M3.03
Dynamic Mass-Spectrometry Characterization of Oxygen Emission during Operation of SiOx ReRAM Devices
Luca Montesi 1 Manveer Munde 1 Mark Buckwell 1 Leon Garnett 1 Adnan Mehonic 1 Richard Chater 2 Sarah Fearn 3 Steve Hudziak 1 David McPhail 2 Anthony Kenyon 1
1University College London London United Kingdom2Imperial College London United Kingdom3Imperial College London United KingdomShow Abstract
ReRAM devices have shown promising functional results despite controversial models of switching mechanism. It has been well reported that "bubbles" can develop on the surface of devices as a result of the switching process. We see similar behavior in our TiN/SiOx/TiN devices, leading to insulating electrode regions that limit the number of successful switching cycles. Literature relies on material analysis to attribute such defects to oxygen release without certain characterization of any emitted gas. We present results from dynamic RGA mass-spectrometry measurements in high vacuum during in-situ switching, demonstrating positive identification of oxygen species emission from our devices. This will allow for a more certain understanding of switching mechanics and more reliable and long-lasting future devices.
9:00 AM - M3.05
Computational Study of Cu Diffusion and Agglomeration in Silicon Dioxide
David M Guzman 1 2 Sumeet C. Pandey 3 Gurtej S. Sandhu 3 Alejandro Strachan 1 2
1Purdue University West Lafayette USA2Birck Nanotechnology Center West Lafayette USA3Micron Technology Inc. Boise USAShow Abstract
We report results on the activation energy for diffusion of isolated and aggregated copper ions in crystalline and amorphous silicon dioxide based on density functional theory (DFT) and bond order molecular dynamics calculations. The minimum energy pathways for diffusion of copper are studied for the alpha-quartz, alpha-cristobalite, and amorphous phases of silicon dioxide as function of the copper cluster size using the nudged elastic band method. The DFT results provide insight into the operation of conductive-bridging random-access memory (M-RRAM) cells and validation data for the force-fields that can be employed to simulate the dynamical operation of the cells. To investigate the implications of stochastic Cu migration and clustering in SiO2 on the variability and reliability of the devices, we use simulations of metallic filament formation. These results have implications on data retention characteristics allowed by the multiple order of magnitude separation between the resistance states in these devices.
9:00 AM - M3.06
Control of Parameters of In-Plane Resistive Switching in Fe3O4 by Means of Lateral Arrays of Nanodefects Introduced by Stepped Substrate Morphology
Askar Syrlybekov 1 Ozhet Mauit 1 Sumesh Sofin 2 Elisabetta Arca 2 Igor Shvets 1
1Trinity College Dublin Dublin Ireland2College of Science, Sultan Qaboos University Muscat OmanShow Abstract
This report focuses on control of resistive switching (switching voltage) in magnetite (Fe3O4) thin film grown on stepped surfaces. Films were deposited by means of Molecular Beam Epitaxy system on MgO (100) substrates miscut along the <010> axis with miscut angles of 4°. The periodicity of stepped MgO surface can be controlled by the annealing temperature and time. In this way, substrates with different steps densities were prepared. We studied the field-induced switching along two crystallographic identical directions: along- and perpendicular to the steps, i.e. along <001> and perpendicular <010> directions. Resistive switching has been observed bellow Verwey temperature, at 100-80 K. Sharp jump in current was observed when source voltage reached the critical value. As temperature decreased, switching voltage increased. During the electric measurement, current was limited to 1 mA by setting the compliance appropriately in order to protect the devices from breakdown. Crucially, the switching voltage was different along- and perpendicular to the steps, along <001> and <010> in this cubic spinel. Along the steps, a lower switching voltage is required to enable the lower conducting state than that required perpendicular to the steps. This is attributed to the high density of anti-phase boundaries present at step edges. Number of switching cycles has been demonstrated for the electric field applied along the steps. A maximum of 16,000 cycles were performed without damaging the devices or alteration of the switching characteristics. This work demonstrates the way to alter switching parameters in oxides via controlled introduction of defects and substrate morphology.
9:00 AM - M3.08
Formation and Characterization of High Density FePt Nanodots on SiO2 Induced by Remote Hydrogen Plasma
Seiichi Miyazaki 1 Yuuki Kabeya 1 Ryo Fukuoka 1 Hai Zhang 1 Katsunori Makihara 1 Takeshi Kato 1 Satoshi Iwata 1
1Nagoya University Nagoya JapanShow Abstract
Metallic nanodots (NDs) have received much attention because of their potential application to charge storage nodes. In the spintronic application of metallic NDs, high-density formation of magnetic NDs and control of the magnetization change are major concerns.#12288; In this work, we reported recent our achievement of the formation of magnetic NDs made of FePt alloy by exposing a metal bi-layer stack to H2-RP and characterized their magnetization properties.
After conventional wet-chemical cleaning steps of p-type Si(100) wafers, SiO2 layers was grown at 1000 #730;C in dry O2 ambience. Ultrathin Fe layers were first deposited uniformly on the SiO2 layers by electron beam evaporation, and then covered uniformly with an ultrathin Pt layer without air exposure. Subsequently, the metal bi-layer stacks so-prepared were exposed simply to a remote H2 plasma without external heating.
Topographic images taken by AFM observations before and after remote H2 plasma exposure confirm that the ultrathin bi-layers with a uniform surface coverage are drastically changed to NDs with an areal density as high as ~5x1011 cm-2 by exposing to remote H2 plasma as a result of surface migration of metal atoms and their cohesive action promoted with progressive surface recombination of H-radicals on metal surface. The magnetic properties evaluated by measuring in-plane and out-of-plane magnetic field within ±15 kOe show that the FePt-alloy NDs exhibit a large perpendicular anisotropy with an out-of-plane coercivity of ~4.8 kOe while the in-plane and out-of-plane coercivities of Pt/Fe bi-layer are almost zero reflecting the small magneto-crystalline anisotropy of Fe layer. The x-ray diffraction pattern of FePt-alloy NDs confirms the formation of (001) oriented L10-ordering FePt phase. In addition, electron conduction measured through FePt-NDs on ~1.7nm-thick SiO2/c-Si by using a magnetized CoPtCr-coated AFM probe at room temperature confirm a a distinct anisotropic magnetoresistance reflecting characteristic of the L10 FePt phase.
9:00 AM - M3.09
Fast Ultra High-Density Writing of Low-Conductivity Patterns on Semiconducting Polymers
Marco Farina 3 Tengling Ye 4 Guglielmo Lanzani 4 Andrea di Donato 3 Giuseppe Venanzoni 3 Davide Mencarelli 3 Tiziana Pietrangelo 1 Antonio Morini 3 Panagiotis E. Keivanidis 4 2
1Universita amp;#8216;amp;#8216;G. damp;#8217;Annunzio" Chieti Italy2Cyprus University of Technology Limassol Cyprus3Universita` Politecnica delle Marche Ancona Italy4Fondazione Istituto Italiano di Tecnologia Milano ItalyShow Abstract
The realization of high-density, low-cost storage media of high longevity can be enabled by the technological development of programmable and readable nonvolatile organic memory devices. Amid the ongoing efforts for the development of high density nonvolatile memory systems  the use of scanning probe techniques  has emerged as a promising concept for the realization of high capacity and storage density memory devices. Here we show that the mechanical interaction between the electrically unbiased tip of the atomic force microscope and the surface of π-conjugated polymeric films produces a local increase of molecular disorder, inducing a localized lowering of the semiconductor conductivity, not associated to detectable modifications in the surface topography . This phenomenon allows for the swift production of low-conductivity patterns on the film surface at a speed exceeding 20 mm s-1; the patterned paths have a resolution in the order of the tip size (20 nm) and they are clearly detectable in the conductivity maps, as registered by the conducting-atomic force microscopy tip.
 P. Heremans, G. H. Gelinck, R. Müller, K.-J. Baeg, D.-Y. Kim, Y.