Guohan Hu, IBM T. J. Watson Research Center
Hyunsang Hwang, Pohang University of Science and Technology
Gabriel Molas, LETI-CEA
Eisuke Tokumitsu, Japan Advanced Institute of Science and Technology
Symposium Support Kojundo Chemical Laboratory Co. Ltd. of Japan
Tuesday PM, December 01, 2015
Hynes, Level 2, Room 202
2:30 AM - *KK2.01
Magnetization Reversal and Thermal Stability of Perpendicular Spin-Transfer-Torque Magnetic Random Access Memory Devices
Luc Thomas 1
1TDK- Headway Technologies Milpitas United StatesShow Abstract
The combination of high speed and non-volatility of perpendicular Spin-Transfer-Torque Magnetic Random Access Memories (pSTT-MRAMs) promises a significant reduction of computing power, making this technology particularly attractive for mobile and Internet-of-Things applications .
In this talk, we will present recent advances in the development of perpendicular Magnetic Tunnel Junctions (pMTJs) at TDK-Headway Technologies , which have enabled the demonstration of fully functional 8Mb pSTT-MRAM chips with sub-5ns writing . Furthermore, we will discuss the physics of current-induced switching and thermal stability in pMTJs devices, in comparison with writing and data retention properties of 8Mb test chips .
3:00 AM - KK2.02
Dictating Magnetic Easy Axis in CoFe2O4 Films with Helium Implantation
T. Zac Ward 1 Andreas Herklotz 1 Anthony T. Wong 1
1Oak Ridge National Laboratory Oak Ridge United StatesShow Abstract
Heteroepitaxial strain engineering is an essential tool in strongly correlated systems for investigating fundamental coupling effects and for more practical control of thin film properties. We demonstrate that the length of a single axis in an epitaxial CoFe2O4 (CFO) film can be controlled by strain doping helium into the lattice which in turn allows fine control over the magnetic easy axis through induced magnetostriction. Compressively strained thin films of CFO are grown coherently on MgO substrates and show pronounced out-of-plane magnetic anisotropy. Successive doping of the CFO films with He using a commercial ion gun results in an expansion of the out-of-plane lattice parameter while maintaining in-plane epitaxial lock to the substrate. We observe a continuous rotation of the magnetic easy axis towards the film plane with increasing unit cell tetragonality. A vacuum anneal above 500 °C is sufficient to evacuate the He from the lattice and return it to the pristine state. The results are in agreement with the strain-induced change of the magnetic anisotropy due to the large negative magnetostriction of CFO and demonstrates that strain doping via He implantation is an elegant path to tune desired characteristics of transition metal oxide thin films.
This work was supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division.
3:15 AM - KK2.03
Tunneling Magnetoresistance and Enhanced Voltage-Controlled Magnetic Anisotropy in Magnetoelectric Tunnel Junctions with MgO/PZT/MgO Tunnel Barrier
Diana Chien 1 Xiang Li 1 Kin Wong 1 Shauna Robbennolt 1 Guoqiang Yu 1 Sarah Tolbert 1 Nick Kioussis 1 Pedram Khalili 1 Kang Wang 1 Jane Chang 1
1University of California, Los Angeles Los Angeles United StatesShow Abstract
As existing memory systems approach fundamental limitations, ultra-thin uniform and conformal PZT films are needed for next-generation ultralow-power voltage-controlled non-volatile magnetoelectric RAM devices. By utilizing the magnetoelectric effect, where an electric field or voltage can be used to control the magnetization switching (instead of current), the writing energy can be reduced, resulting in increased memory density. Previous research has shown that the voltage-controlled magnetic anisotropy (VCMA) effect increases with the capacitance of the stack. Therefore, integrating an ultra-thin PZT film (having a dielectric constant 1-2 orders of magnitudes higher than currently used MgO) into the tunneling oxide layer enhances the VCMA coefficient, allowing for a lower voltage to switch the magnetization of the free magnetic layer and thus decreasing the write energy.
In this work, the growth of MTJ stacks with an MgO/PZT/MgO tunnel barrier using a combination of sputtering and atomic layer deposition (ALD) techniques was shown to be a viable process. First, an 18 nm thick Ta layer was deposited as the MTJ bottom electrode on thermally oxidized Si substrates, and then a Co20Fe60B20 free layer (out-of-plane magnetically anisotropic) was sputtered. For the MgO MTJ, a 2.5 nm thick MgO tunnel barrier was then sputtered. For the PZT MTJ, a 1.5 nm thick PZT film was deposited via ALD with an atomic Zr:Ti ratio of 52/48 between two layers of 1.0 nm thick sputtered MgO to form the MgO/PZT/MgO tunnel barrier. The PZT thin film was deposited by ALD at a substrate temperature of 250°C with Pb(tmhd)2, Zr(tmhd)4, and Ti(O.i-Pr)2(tmhd)2 as metalorganic precursors and deionized H2O vapor as the oxidant. A Co20Fe60B20 fixed layer (in-plane magnetically anisotropic) and capping layers of Ta and Pt were then sputtered on top of the tunnel barrier. The MTJs were annealed at 200-250°C for 30 minutes under vacuum and fabricated using standard photolithography and reactive ion etching techniques.
The perpendicular magnetic anisotropy of the bottom free magnetic Co20Fe60B20 layer was verified via superconducting quantum interference device magnetometry, confirming that the ALD PZT deposition process is a viable method for synthesizing PZT MTJs. The TMR ratio and VCMA effect were measured by sweeping an in-plane magnetic field from 0shy;3000 Oe while varying the applied voltage from -300shy;300 mV. The MgO MTJs were measured to have a tunneling magnetoresistance (TMR) ratio of 61.5% and a VCMA coefficient (xi;average) of 14.32.7 fJ/V-m, whereas the PZT MTJs were measured to have a TMR ratio of 53.1% and a xi;average of 19.81.3 fJ/V-m. The VCMA coefficient of PZT MTJs was 38.5% larger than those of MgO MTJs. In conclusion, PZT MTJs were demonstrated to have tunneling magnetoresistance and an enhanced VCMA effect, making them being potential candidates for future voltage-controlled, ultralow-power, high-density memory devices.
3:30 AM - KK2.04
Etching and Smoothing Process of Materials Used in Magnetic Tunneling Junctions with Gas Cluster Ion Beams
Noriaki Toyoda 1
1Univ of Hyogo Himeji JapanShow Abstract
Etching and smoothing of materials used in magnetic tunneling junctions (MTJ) with gas cluster ion beam (GCIB) were studied. For etching of etch-resistant metals, acetic acid vapor was supply during O2-GCIB irradiation in order to enhance the chemical reactions induced by GCIB. Etching depth of various etch-resistant materials (Pt, Ru, Ta, CoFe) showed 1.8 - 10.7 times higher values than those without acetic acid. High-pressure and high-temperature effects of GCIB enhance chemical reactions between reactive gas and substrate surface at room temperature. Thus, halogen free and room-temperature etching of etch-resistant materials was achieved. In additions, surface smoothing of Ru films under MTJ with GCIB was studied. Surface roughness of Ru film decreased monotonically with increasing the GCIB fluence, and reached 0.2 nm (Ra). After smoothing of Ru films, MTJ was formed. The magnetic properties of MTJ formed on the smoothed Ru showed improvement of inter-layer coupling magnetic field (Hin). Thus, etching and smoothing with GCIB are promising process for MTJ fabrications.
3:45 AM - KK2.05
Dual Field Effects in Spinel Ferrite Field Effect Devices: Volatile Electrostatic Carrier Doping and Nonvolatile Redox Reactions
Hidekazu Tanaka 1 Takashi Ichimura 1 Kohei Fujiwara 1
1Osaka Univ Ibaraki JapanShow Abstract
Controlling the electronic properties of functional oxide materials via external electric fields has attracted increasing attention as a key technology for next-generation electronics. For transition-metal oxides with metallic carrier densities, the electric-field effect with ionic liquid electrolytes has been widely used because of the enormous carrier doping capabilities. The gate-induced redox reactions revealed by recent investigations have, however, highlighted the complex nature of the electric-field effect. Here, we use the gate-induced conductance modulation of spinel ZnxFe3minus;xO4 to demonstrate the dual contributions of volatile and non-volatile field effects arising from electronic carrier doping and redox reactions using field effect device structure with an ionic liquid DEME-TFSI. These two contributions are found to change in opposite senses depending on the Zn content x; virtual electronic and chemical field effects are observed at appropriate Zn compositions. In the (Fe2.5Zn0.5)O4/DEME-TFSIFET EDLT, a large hysteresis observed in the drain current vs gate voltage characteristics is not accounted for solely by electrostatic doping, strongly suggesting the presence of chemical reactions . For the heavily Zn substituted system of (Fe2.2Zn0.8)O4/DEME-TFSIFET EDLT with less carrier concentration, the characteristic hysteresis virtually disappears . These observations revealed the coexistence of two types of field effects in the Fe3minus;xZnxO4 devices, and the tuning of field-effect characteristics via composition engineering should be extremely useful for fabricating high-performance oxide field-effect devices.
References;  Adv. Mater. Interfaces 1 (2014) 1300108,  Sci. Rep. 4 (2014) 581
Present affiliation of Dr. Kohei Fujiwara: The Institute for Materials Research#12289;Tohoku Univ., Japan
4:30 AM - *KK2.06
Thermally-Assisted MRAM for Embedded Applications
Philip Trouilloud 1 Anthony Annunziata 1 Sebastien Bandiera 2 Stephen Brown 1 Erwan Gapihan 2 Eugene Orsquo;Sullivan 1 Lucien Lombard 2 Daniel Worledge 1
1IBM T.J. Watson Research Ctr Yorktown Heights United States2Crocus Technology Grenoble Cedex FranceShow Abstract
Programming of Thermally-Assisted Magnetic Random Access Memories (TA-MRAM) relies on the coincidence of a thermal pulse and a writing pulse. With the thermal pulse, crossing the energy barrier needed to write to a new state can occur with a weaker writing pulse than would be needed in regular MRAM1. The data storage element is a ferromagnetic layer pinned by an antiferromagnetic layer. Materials with stronger pinning improve data retention and make it harder to overwrite. The thermal pulse temporarily reduces the pinning strength by bringing the antiferromagnet to its blocking temperature. TA-MRAM is well suited for small devices, as they can be heated and cooled quickly and efficiently.
In addition to retention, strong pinning in the operating temperature range of the device has another advantage. The devices can be read using a self-reference readout in which the stored state is interrogated non-destructively without the need for a global reference. This makes Read more tolerant to manufacturing spreads of size and resistance inherent in small devices.
We investigated TA-MRAM for embedded applications with devices designed to survive BEOL process temperatures of 400C2. Read and write performance was characterized as a function of TA-MRAM material stack parameters. In the main part of the device population, there is a 3-sigma separation between the write voltage and the breakdown voltage observed for 10^7 pulses. Consistency of the self-reference read was tested for 10^8 write pulses.
 Prejbeanu et al., J. Physics: Condensed Matter 19 (16), 165218 (2007).
 Annunziata et al., J. Appl. Phys. 117, 17B739 (2015).
5:00 AM - KK2.07
Fabrication and Magnetoelectronic Transport of Double Stack FePt Nanodots on Ultrathin SiO2
Seiichi Miyazaki 1 Yuuki Kabeya 1 Yusuke Mitsuyuki 1 Katsunori Makihara 1
1Nagoya Univ Nagoya JapanShow Abstract
Nanodots (NDs) showing a high magnetic anisotropy have received much attention because of their potential application to magnetoelectronic devices. So far, we have demonstrated a spontaneous formation of L10-ordered FePt dots with an areal density as high as ~1011cm-2 by remote H2-plasma (H2-RP) exposure of Pt/Fe bilayers on ultrathin SiO2 without external heating and a unique magnetic-field dependent electron transport through individual FePt dots/ultrathin SiO2 by means of a CoPtCr-coated magnetic tip of atomic force microscopy (AFM) in a contact mode.
In this work, based on size dependence of magnetic properties of FePt nanodots, we designed and fabricated double stack FePt NDs with ultrathin internal SiO2 and characterized their magnetoelectronic transport by using a non-magentic Rh-coated AFM tip at room temperature (RT).
After FePt NDs with an areal density of ~4.5x1011cm-2, an average dot size of ~5.0nm and a RT coercivity as small as 0.5kOe were formed by H2-RP exposure of ultrathin Pt/Fe bilayers on 2nm-thick thermally- grown SiO2 layer/Si(100) without external heating, uniform coverage of the FePt NDs with a 2nm-thick SiO2 layer by a PVD method, a very uniform formation of Pt/Fe bilayers was followed by H2-RP exposure to form a spontaneous formation of FePt nanodots with an areal density of ~2.5x1011cm-2, an average dot size of ~8.0nm and a RT coercivity of ~2.5kOe formed was carried out in a similar way to the 1st formation of FePt NDs. After that, Al back contact was formed to measure the electron transport through the double stack FePt NDs on ultrathin SiO2.
I-V characteristics of the double stacked FePt NDs as a function of magnetic field were measured by using non-magnetic Ph-coated AFM Tip at room temperature. With an increase in magnetic field from 1.5 to 2.5kOe in the direction normal to the sample surface, the current level is increased significantly by over one order of magnitude. Then no further change in the current level was detectable by magnetic field application of 4.5kOe. In addition, such a current level occurred at 2.5kOe remains almost unchanged even in 24hr after removal of external magnetic field, which implies stable magnetization of the double stack FePt NDs. But when the magnetic field of 0.5kOe was applied in the opposite direction to the 1st magnetization, the current level was decreased markedly to the initial low current level. With further increase the magnetic field from 1.5 to 2.5kOe, the switching to a high current level occurred. The observed magnetic field dependence of the current level through the double stack FePt NDs can be interpreted in terms of alignment in the magnetization polarity between staked FePt NDs with different coercivities.
5:15 AM - KK2.08
Magnetoresitance of Nickel Nanoparticles Embedded in High-Quality Single-Crystal Silicon
Girish Malladi 1 Mengbing Huang 1 Hassaram Bakhru 1 Steven Novak 1 Thomas Murray 1 Vincent LaBella 1 Akitomo Matsubayashi 1
1CNSE SUNY Albany Albany United StatesShow Abstract
Integrating magnetic functionalities with Silicon, the dominant semiconductor in microelectronics, holds a promise to realize devices with multiple functionalities such as spin-valves, spinFETs etc. Earlier studies based on the incorporation of transition metal atoms into Silicon have reported ferromagnetism in Silicon but such materials have very low Curie temperature. Additionally, the observed room-temperature ferromagnetism in transition metal implanted Si has been rather associated with the implanatation-related defects. In this work, we developed a novel method based on ion implantation to fabricate a thin layer of ferromagnetic nanostructures embedded within single crystal Si. This is achieved by exploiting the effects of ion implanted hydrogen on the formation of metal nanoparticles in Si. With this approach, we demonstrate the synthesis of a layer of Ni nanoparticles (size: ~10-25 nm; density: ~ 1011/cm2) within a Si environment of a very high crystal quality. Ni nanoparticles encapsulated within such high-quality crystalline Si layer exhibit a high magnetic switching energy barrier of ~ 0.86 eV, an increase by about one order of magnitude as compared to their counterparts on a Si surface or in a highly defective Si environment. Strong ferromagnetism associated with this Ni nanostructure layer is evidenced even at room temperature. These ferromagnetic nanostructures also show enhanced positive or negative magnetoresistance depending on injected carrier types, when an external magnetic field is applied in the transverse direction. Such a thin layer of ferromagnetic nanostructures embedded in Si has a potential to act as an internal spin filter for the generation of spin-polarized carriers in Silicon.
5:30 AM - KK2.09
Thickness Dependent Multiferroic Properties of Nanoscale PZT/LSMO and PZTFT for Multiferroic Tunnel Junction Applications
Danilo G. Barrionuevo Diestra 1 2 Nora Ortega 1 2 Ram S. Katiyar 1 2 Ashok Kumar 3
1University of Puerto Rico San Juan United States2Institute of Functional Nanomaterials San Juan United States3National Physical Laboratory (CSIR), Dr K S Krishnan Road New Delhi IndiaShow Abstract
Multiferroic magnetoelectric materials combine ferromagnetism and ferroelectricity giving the possibility of controlling polarization P with a magnetic field H or magnetization M with an electric field E. Ultrathin films offer the opportunity of combining respective advantages of fast low-power electrical write operation and non-destructive magnetic read operation, resulting in the realization of four-state logic. A way to exploit these properties are to use them in multiferroic tunnel junctions (MFTJs). Pb(Zr0.53Ti0.47)0.60(Fe0.5Ta0.5)0.40O3 (PTZFT) is a single-phase multiferroic material at room temperature. In order to study thickness effect on electrical and magnetic properties from thicker to ultrathin films, we have grown films with thicknesses from 4 to 80 nm of PZTFT on (001) LSMO/(LaAlO3)0.3(Sr2AlTaO6)0.7 (LSMO/LSAT) substrates deposited by pulsed laser deposition (PLD) technique. Well saturated ferroelectric loops were observed for PZTFT films with a remanent polarization of 32, 25 and 10 mu;C/cm2 for films with thicknesses of 80, 50 and 20 nm respectively. An enhanced saturated magnetization (Ms) was observed with increased PZTFT layer thickness in PZTFT/LSMO structures. The average Ms values for PZTFT/LSMO heterostructures were 33, 25, and 15 emu/cm3 for 80, 50, and 20 nm respectively, at 300 K. Piezo force microscopy measurements for 4, 5, and 7 nm ultrathin PZTFT films showed a clear and reversible out-of-plane phase contrast above ± 4 V, which indicates the ferroelectric character of ultra-thin films. Magnetic force microscopy show magnetic stripe domains in ultrathin films. The effect of PZTFT film thickness on temperature dependent dielectric properties will be discussed. We have also studied the effect of polar capping on magnetization in nanoscale PZT(PbZr0.52Ti0.48O3)(5 and 7 nm)/LSMO(30 nm) heterostructures grown by PLD technique. PZT/LSMO heterostructures with thick polar PZT (7 nm) capping showed nearly 100% enhancement in magnetization compared with thin polar PZT (5 nm) films, probably due to excess of hole transfer from the ferroelectric to the ferromagnetic layers. Core-level X-ray photoelectron spectroscopy (XPS) studies revealed the presence of large Mn (3s) spin-orbit hybridization and high Mn3+/Mn4+-ion ratio in the LMSO with 7 nm polar capping. The transport properties for Pt/PZT(7 nm)/LSMO heterostructures shown a significant variation in tunneling electroresistance (TER) ratio when was exposed to magnetic field and its values at zero bias changed from 57 (at 0 G) to 110 under 10 kG of magnetic field. We attributed this enhancement to change in resistance near the PZT/LSMO interface under magnetic field. Ferroelectric polarization reversal and application of magnetic field changed lattice strain, chemical bonding and charge modulation near PZT/LSMO interface which in turn affects the charge carrier density and transmission probability. Our results suggest the possibility to manipulate TER by magnetic field.
5:45 AM - KK2.10
Experimental Realization of Non-Volatile Memory: A Nanodevice Based on the Interplay between Superconducting Ratchet Effect and Out of Plane Magnetization
Jose Luis Vicent 1 2 Javier del Valle 1 Alicia Gomez 1 Elvira Maria Gonzalez 1 2 Manuel R. Osorio 2 Daniel Granados 2
1Univ Complutense Madrid Madrid Spain2IMDEA-Nanociencia Madrid SpainShow Abstract
We have fabricated and tested a nanodevice that works as a non-volatile three-state memory, as well as a reading device (1). The nanodevice is a Si substrate with array of triangular-shaped nanomagnets embedded in a superconducting film. The nanomagnets are made of Co/Pd multilayers with the magnetization perpendicular to the samples plane. This magnetic configuration yields a strong stray magnetic field threading the Nb superconducting film. Consequently superconducting vortices are induced in the film without needing an applied external magnetic field. Applying an ac current in the device triggers a ratchet effect (2), so that an output dc voltage is obtained. The nanomagnet can be easily set in three states upward magnetization (+1), downward magnetization (-1) and demagnetized state (0). These three resilient states are detected by measuring the output dc voltages. We have to point out that the zero state shows a plateau where the output voltages remain constant. So the three states are well defined. In the case an external magnetic field is applied to the device the device turns into a magnetic sensor device, which more outstanding realization is that output voltage signal is zero for a precise value of the applied magnetic field. This value only depends on the fabrication characteristics of the nanodevice.
(1) J. del Valle, A. Gomez, E. M. Gonzalez, M. R. Osorio, D. Granados and J. L. Vicent, arXiv: 1505.04961
(2) J. E. Villegas, S. Savelev, F. Nori, E. M. Gonzalez, J. A. Anguita, R. Garcia, J. L. Vicent,Science 302, 1188 (2003).
KK3: Poster Session I: Advanced Flash, MRAM, Ferroelectric Memory, PCM, Others
Tuesday PM, December 01, 2015
Hynes, Level 1, Hall B
9:00 AM - KK3.02
Improving Electrical Properties of Inter-Poly Dielectric Layer using Atomic Layer Deposition Process in 2D NAND Flash Memory
Jeahoon Lee 1 Byoungjun Park 1 Minho Jeong 1 Jiyul Park 1 Sungpyo Lee 1 Younghwan Choi 1 Myoungkwan Cho 1 Kun-ok Ahn 1 Jinwoong Kim 1
1SK Hynix Cheongju-si Korea (the Republic of)Show Abstract
Recently, the NAND flash memory as a storage media for various mobile devices has been scaled down into sub-20 nm. However, reliability characteristics such as endurance and retention of NAND cells are also degraded as NAND Flash memory cells became smaller and closer. Of those ones, data retention characteristic is strongly related with inter-poly dielectrics (IPD), which consist of oxide-nitride-oxide layers. Because, those ones play an important role in NAND flash memory cell structure to prevent loss of charges in the floating gate. In this study, to improve the electrical properties of IPD layers, we change the way of deposition from conventional low pressure chemical vapor deposition to atomic layer deposition, which shows excellent step coverage and has less trap sites. Electrical properties of IPD layers are characterized with time dependent dielectric breakdown method and current versus voltage curves in the test element groups. Also, we check the data retention characteristic with threshold voltage distributions of NAND cell array.
9:00 AM - KK3.03
Laser Fabricated Nanocrystals for Memory Devices
L Kastanis 2 Jacob Leonard Spear 1 A Aggelou 3 Nikolaos Kalfagiannis 1 Ch Sargentis 2 Demosthenes Koutsogeorgis 1 E.K. Evanglou 3 D. Tsamakis 2
1Nottingham Trent University Nottingham United Kingdom2NTUA Attiki Greece3University of Ioannian Ioannina GreeceShow Abstract
Flash memory is a type of electronic memory most often used in portable electronic devices and floating gate is the primary technology to construct such memories . With downscaling of the device feature size, conventional poly-silicon floating gate flash memories are facing a severe challenge that the thinner tunneling oxide will degenerate retention characteristics due to leakage current . During the last decades nanocrystals (NCs) have been extensively studied as a replacement to the polycrystalline Si layer in the floating gate nonvolatile memories (NVMs) . Among various NC materials, it is well known that nonvolatile memories utilizing metal NCs have the advantages of higher density of states around the Fermi level, stronger coupling with the conduction channel, and smaller energy perturbation due to carrier confinement . Moreover, metal nanoparticles with high work-function, like platinum (Pt), Silver (Ag) and gold (Au) NPs, are promising for the use of nanoparticle type memory due to the deep potential wells they create. At the same time, laser fabrication has been proven to be a versatile and powerful method for fabricating nanoparticle arrays with well controlled characteristics (size and distribution) .
In this work we present the growth of Ag nanocrystals (NCs) on SiO2 surfaces via sputtering followed by post deposition laser annealing (LA) as well as conventional rapid thermal annealing (RTA). Post-annealing treatment was introduced to the fabrication process to optimize device performance. Enhanced performance nanocrystal memory characteristics are shown for the laser annealed MOS devices as compared to RTA ones.
Thermally grown SiO2 with thickness around 2-5nm was prepared on n type Si(1-10 Ohm.cm) wafers. On top of the SiO2 surfaces a thin (5nm) Ag layer was sputtered followed by a blocking Y2O3 layer (around 40 nm sputtered at room temperature). After laser annealing at various fluences with an KrF laser, MOS devices were fabricated by shadow mask evaporation of Al gate contacts.
Capacitance vs Voltage (C-V) and Current vs Voltage (I-V) measurements of n-Si\SiO2\Ag NCs\Y2O3\Al devices show an almost 20% larger memory window, improved retention properties and reduced leakage currents. Fowler-Nordheim tunnelling was found to be the dominant current conduction mechanism at applied gate voltages in the range of 5 to 10 V.
Our results indicate that laser annealing leads to MOHOS-type flash memory devices with improved electrical characteristics due to the creation of superior quality metal nanocrystals.
9:00 AM - KK3.04
A Hybrid Ferroelectric-Flash Memory with Quasi-Single Crystal Pb(Zr,Ti)O3 for Blocking Layer
Jaehyo Park 1 Hyung Yoon Kim 1 Zohreh Kiaee 1 Seung Ki Joo 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
In this work, A novel concept of charge-injection (CI) type ferroelectric-assisted flash memory FET (FAFM-FET) were fabricated. The total structure of the device was Pt/Pb(Zr,Ti)O3(PZT)/ZrTiO4(ZT)/SiO2/Si, where the PZT, ZT, and SiO2 was used for the blocking layer, charge-trapping layer, and tunneling layer, respectively. Strong polarization and high dielectric constant (1500) of PZT layer showed amplification effect, which improves the retention time and P/E switching speed. The ZT layer having a high dielectric constant (45) showed a high charge storage and effective diffusion barrier. As a result, the CI FAFM-TFT exhibited excellent memory characteristics, such as large memory window (9.1 V), fast P/E speed (500 nsec), long retention time and good endurance.
9:00 AM - KK3.05
Magnetoelastic Effect in Multilayer of Ni Nanoparticle and C Film Produced by Pulsed Laser Deposition
Alexsandro dos Santos Evangelista Cruz 1 Fernando Fabris 1 Dante Ferreira Franceschini 1 Yutao Xing 1 Wallace Castro Nunes 1
1Instituto de Fiacute;sica ( Universidade Federal Fluminense) Niteroacute;i BrazilShow Abstract
The research on magnetic nanoparticle(NPs) has increased in recent years due to several potential applications, including recording media, magnetic hyperthermia, drug delivery and others. In this work, we produced multilayer in substrate of Si alternating the deposition of Ni NPs and amorphous carbon film. The film and NPs was deposited by Pulsed Laser Deposition (PLD). Carbon film was deposited in vacuum of about 1.6x10-6 Torr and Ni NPs was grown in Argon atmosphere at pressure of 1.0 Torr. The carbon film causes a mechanical stress in Ni NPs resulting in a magnetic anisotropy of magnetoelastic origin. The results shows that the samples with lower thickness of carbon film have easy axis magnetization parallel to the film surface. On the other hand, the increase of the thickness changes the easy axis to perpendicular direction. In addition, there is a change in blocking temperature of about 15K to near room temperature, respectively. The change is due to the increase of the stress of the carbon film. The energy associated with this anisotropy can be evaluate according to the and is given by E=-(3/2)lambda;σcos2theta;, where lambda; is the magnetostriction coefficient, σ is the induced strain and theta; is the angle between magnetization and deformation axis. It has been reported that anisotropy induced by magnetoelastic effect can be larger than magnetocrystalline anisotropy in Ni NPs system, and thus can define the easy axis of magnetization of the sample. The morphology of the samples were characterized by Transmission Electron Microscopy. To study the details about anisotropy effect we measured M(H) curves and ZFC(Zero Field Cooled) and (Field Cooled) curves for applied magnetic field parallel or perpendicular to the sample surface. The magnetic and structural results of the studied samples are discussed considering the magnetoelastic effect induced by carbon film in Ni NPs and potential application in magnetic recording media.
9:00 AM - KK3.06
Temperature Dependence of Magnetization in Interacting Nanoparticle Systems
Fernando Fabris 2 Oana Pascu 1 Maria Fialho Vaz 1 Wallace Castro Nunes 2
1Universidade Federal Fluminense Niteroacute;i Brazil2Universidade Federal Fluminense Niteroacute;i BrazilShow Abstract
The nanostructured materials have shown large potential applications in many fields of science and technology. In particular, magnetic nanoparticles have been used as high-moment soft magnetic materials, magnetic sensors, improved nanocomposite magnets, and others. Theoretical models describing the magnetic properties of nanoparticle systems usually neglect interaction effects among nanoparticles. However, in rather concentrated systems the nanoparticles are close enough for interactions among them become noticeable, affecting their macroscopic magnetic properties. Is this work we developed a phenomenological model to describe the magnetic behavior of interacting nanoparticle systems. The model is based on a simple modification of the random anisotropy model to take into account the concentration and size of the nanoparticles as well as the field dependence of the correlation length. In addition, we considered that each group of correlated nanoparticles is subjected to the external magnetic field plus a internal mean field generated by dipolar interaction of other groups of nanoparticles. The proposed model leads to a accurate description of the zero-field cooled and field cooled magnetization curve of nanoparticle systems for a wide range of nanoparticle concentration.
9:00 AM - KK3.07
Ferroelectricity in Rare-Earth (Sm, Gd) Doped-HfO2 Thin Films Fabricated by Sequential Pulsed Laser Deposition
Yogesh Sharma 1 Danilo Barrionuevo 1 Radhe Agarwal 1 Shojan Pavunny 1 Ram S. Katiyar 1
1University of Puerto Rico San Juan United StatesShow Abstract
Recently, experimental as well as theoretical studies showed ferroelectricity in aliovalent ions (Si4+, Al3+, Y3+, and Zr4+) doped hafnia (HfO2) thin films which are compatible with existing CMOS technology. Ferroelectric HfO2 films have promising potential for the three-dimensional capacitor structure required for the future field driven and energy efficient ferroelectric random-access-memory (FeRAM) devices. With this motivation, rare-earth doped hafnium oxide (HfO2) thin films are pulsed laser deposited by sequential ablation of individual ceramic binary oxide targets. 6 mol. % of Sm2O3/Gd2O3 doped-HfO2 thin films (Sm:HfO2 and Gd:HfO2) of about 60 nm thickness and crystallized in cubic phase are found to exhibit ferroelectricity. A remnant polarization (Pr) of ~12.5 (11) mu;C/cm2 along with a coercive field (EC) of ~334 (384) kV/cm are observed in Sm:HfO2 (Gd:HfO2) thin films. Piezoresponse force microscopy measurements further confirmed the ferroelectric nature of these thin films by showing phase hysteresis and butterfly amplitude loops. It can be noticed that wake-up cycles improved the remnant polarization and found to be necessary for the forming of a well saturated hysteresis loop. Our results show potential towards realization of densely scaled next generation non-volatile FeRAM devices compatible with silicon technology.
9:00 AM - KK3.08
Probing Multi-Level Ferroelectric States in Multi-Floor P(VDF-TrFE) Nanostructures
Owoong Kwon 1 Seung Hyun 2 Jin Kon Kim 2 Yunseok Kim 1
1Sungkyunkwan University Suwon-si Korea (the Republic of)2Pohang University of Science and Technology Pohang Korea (the Republic of)Show Abstract
Ferroelectric random access memory (FeRAM) is one of next-generation memories which show fast read/write time, low power consumption, high write-erase cycles and etc. However, its actual application is technically limited due to scalability and flexibility of the device. Thus, here, to overcome these limitations on the scalability and flexibility, we demonstrate multi-floor ferroelectric copolymer polyvinylidene fluoride trifluoroethylene [P(VDF-TrFE)] nanostructures for achieving both flexible devices and multi-level polarization states. Since the P(VDF-TrFE) is a well-known flexible ferroelectric material with high dielectric constant and low processing temperature, we have chosen the P(VDT-TrFE) for preparing array of multi-floor cascading of the nanostructures which allows achieving spatially multi-leveled structures. Switching spectroscopy piezoresponse force microscopy (PFM) clearly shows the different switching behavior at each floor indicating spatially varied ferroelectric states. Furthermore, multi-level ferroelectric states on the same floor were examined by first-order reversal curve-type PFM. The obtained results clearly reveal the existence of the multi-level ferroelectric states on the multi-floor P(VDF-TrFE) nanostructures. To further understand the existence of the multi-level ferroelectric states, finite element modeling was performed to visualize the electric field distribution with respect to the location of the conductive probe. These results can provide not only stepwise structural effects of the piezoresponse in the P(VDF-TrFE) but also potential device structures in the FeRAM.
9:00 AM - KK3.10
Differentiating Ferroelectric/Piezoelectric Effects from Electromechanical Response in Strain Based Atomic Force Microscopy
Seongjae Park 1 Daehee Seol 1 Olexandr Varenyk 2 Tricia Meyer 3 Ho-Nyung Lee 3 Anna Morozovska 2 Yunseok Kim 1
1Sungkyunkwan University (SKKU) Suwon Korea (the Republic of)2Institute of Physics of the National Academy of Sciences of Ukraine Kyiv Ukraine3Oak Ridge National Laboratory Oak Ridge United StatesShow Abstract
The ferroelectric materials have been of great interest for multiple applications such as ferroelectric memories and energy harvesting due to its spontaneous polarization and piezoelectricity. In order to probe the exitence of ferroelectric properties at nanoscale, hysteresis loop measurements are typically performed using piezoresponse force microscopy (PFM). However, ferroelectric-like hysteresis loops were recently reported in non-ferroelectric materials and could be resulted from different mechanisms so that it can be misinterpreted as ferroelectric materials. This indicates that an approach for probing ferroelectric effect based on the hysteresis loop measurements can be limited in the interpretation of the ferroelectricity. Here, we suggest a new and facile way to differentiate ferroelectric effects from the other contributions using frequency dependent Vac measurements. Li-ion conductive glass ceramics (LICGC), which have both ionic and piezoelectric phases, and Pb(Zr,Ti)O3, which is a ferroelectric material, have been chosen as model systems to demonstrate our approach. The electromechanical (EM) response originated from piezoresponse is independent with its frequency, whereas that induced by the other contributions shows frequency dependent behavior. In addition, theoretical calculation of the other contributions to the EM response approves its frequency dependence. These results can provide a new and facile approach for differentiating the ferroelectric effects.
9:00 AM - KK3.11
The Orientation Controlled (Pb,La)(Zr,Ti)O3 Thin Films through PLD and Annealing Conditions for Robust Ferroelectric Capacitor
Takeyasu Saito 1 Taiga Amano 1 Rika Tamano 1 Yoko Takada 1 Naoki Okamoto 1 Kazuo Kondo 1 Takeshi Yoshimura 2 Norifumi Fujimura 2 Koji Higuchi 3 Akira Kitajima 3
1Osaka Prefecture University Sakai Japan2Osaka Prefecture University Sakai Japan3Osaka University Ibaraki JapanShow Abstract
Ferroelectric random access memory (FeRAM) has tremendous potential for future non-volatile memory devices due to its excellent characteristics. Ferroelectric properties were generally influenced by crystal orientation of the films that also determines device performance. Therefore, the orientation control of the ferroelectric films was very crucial for highly integrated and reliable FeRAM devices.
In this study, we fabricated (Pb,La)(Zr,Ti)O3 (PLZT) thin films using pulsed laser deposition (PLD), then, we studied effects of PLD and annealing conditions on ferroelectric properties. Also, we measured crystallographic orientation of the films and discussed the relationship between electrical properties and orientation.
The substrates were highly (111)-oriented sputtered Pt (150-nm-thick) as bottom electrode. PLZT thin films (ca. 300-nm-thick) (Pb:La:Zr:Ti = 1.13~1.27:0.03:0.3:0.7) were deposited on Pt bottom electrode by using PLD. The substrate temperature during PLD was changed from R.T. to 600°C. Then, Pt top electrode was formed on the PLZT thin films using RF sputtering with a 5minus;500-mm-diameter shadow mask. Finally, the fabricated ferroelectric capacitors were annealed using rapid thermal annealing at 650~750°C (3~30 min) in air.
We investigated the effects of substrate temperature during PLD, Pb contents of the target, annealing temperature, and annealing period to improve ferroelectric properties. Lower substrate temperature (R.T.) during PLD, higher Pb contents (Pb = 1.27) of the PLD target, higher annealing temperature (750°C) and appropriate annealing period (10 min) exhibited PLZT(100) well-oriented films. Especially, PLZT(100) originated peaks appeared with increasing annealing temperature up to 750°C, in addition to PLZT(111) peaks. The annealing temperature strongly affects the orientation of PLZT thin films. The best remnant polarization and coercive voltage at an applied voltage of 10 V was 22.0 mu;C/cm2 and 7.1 V, respectively, was obtained.
9:00 AM - KK3.12
Dielectric and Ferroelectric Properties of Lead-Free BTS-BCT Thin Films Processed by Chemical Solution Deposition Method
Berk Akbay 1 Ahmet Macit Ozenbas 1
1Middle East Technical Univ Ankara TurkeyShow Abstract
For a few decades, the piezoelectric materials have been considered as important functional materials for various applications, from the microphones to the high technology scanning electron microscopes, actuators, sonar sensors, cell phones, MEMS and etc. Lead-based phases have dominated almost all these applications. However, lead based materials have been found as toxic and hazardous materials and will be prohibited to use within a short period of time. Among various lead-free piezoelectric materials, BTS-BCT based phases are good candidates instead of Pb-based materials due to having a tricritical point compared to other lead-free alternatives. In this study, lead-free Ba(Ti0.88Sn0.12)O3-0.3(Ba0.7Ca0.3)TiO3 (BTS-BCT) thin films were successfully grown on Pt/TiO2/SiO2/Si substrates using chemical solution deposition method. The effect of sintering temperatures on microstructure, dielectric and ferroelectric properties were studied systematically. Among the various high-quality BTS-BCT thin films with uniform thickness, the optimum room temperature dielectric and ferroelectric responses were observed for the thin films sintered at 850oC for 1 h. The thickness was kept constant for all measurements as 500 nm (13 layered films). Both morphological and structural analyses showed that BaTiO3 based (Ba0.91Ca0.09)(Ti0.92Sn0.08)O3 composition had homogeneously nucleated growth mechanism throughout the film. This type of growth mechanism yields polycrystalline films as observed in structural analyses and dense-small grained morphology as observed in morphological analysis. Optimum dielectric constant and dielectric loss values were obtained as 113.4 and 5.46 % at 600 kHz frequency for the BTS-BCT thin films sintered at 850°C due to perovskite phase showing full crystallization and minimum surface porosity obtained at this temperature. Also, remnant polarization (Pr) and coercive field (Ec) values were determined as 4.1 mu;C/cm2 and 57.8 kV/cm, respectively, for the films sintered at 850°C using 10 V applied voltage. Both ferroelectric and dielectric results were evaluated in the light of morphological and structural information. Thus, process parameter is selected as 850°C which was the optimum sintering temperature for the production of BaTiO3 based BTS-BCT thin films.
9:00 AM - KK3.13
Statics and Dynamics of Ferroelectric Domains in Diisopropylammonium Bromide
Haidong Lu 1 Tao Li 1 Shashi Poddar 1 Om Goit 1 Stephen Ducharme 1 Alexei Gruverman 1
1University of Nebraska-Lincoln Lincoln United StatesShow Abstract
Recent discovery of ferroelectricity in molecular salts has spurred the studies on fundamental ferroelectric ordering and polarization control in these materials in quest for new type of functionality not available in conventional inorganic and polymer ferroelectrics. Uniaxial The uniaxial molecular ferroelectric diisopropylammonium bromide (DIPA-B) is one of the emerging materials of high fundamental and potentially technological importance. Here, we report the results of an investigation of the nanoscale static and dynamic behavior of ferroelectric domains in DIPA-B microcrystals by means of piezoresponse force microscopy (PFM) technique. Effective manipulation of in-plane polarization by electrically-biased PFM tip is demonstrated. We show that stable head-to-head or tail-to-tail domain configurations can be realized in DIPA-B crystals and study the factors determining this stability. In-plane alignment of polarization allows investigation of the forward domain growth along the polar axis - a process that is difficult to attain in conventional ferroelectric switching studies. Using this sample geometry, we have directly measured anisotropy of the domain wall velocity for the forward and lateral growth and demonstrate the effect of the forming charged domain walls on morphology of the growing domains.
9:00 AM - KK3.14
Ferroelectric Retention Free BiFeO3 Mesocrystal
Ying-Hui Hsieh 1 Fei Xue 2 Yen-Chin Huang 3 Yi-Chun Chen 3 Chun-Gang Duan 4 Long-Qing Chen 2 Qing He 5 Ying-Hao Chu 1 6
1National Chiao Tung University Hsinchu Taiwan2Pennsylvania State University University Park United States3National Cheng Kung University Tainan Taiwan4East China Normal University Shanghai China5Durham University Durham United Kingdom6Academia Sinica Taipei TaiwanShow Abstract
Nowadays, one of the focal approaches to pursue next generation low power consumption, multifunctional, and green nanoelectronics is to advance the electric field control of lattice, charge, orbital, and spin degrees of freedom. In order to control these degrees of freedom, a medium possessing the coupling between these degrees needs to be established. Multiferroics that support both strong ferroelectric and magnetic orders are typically insulators with an antiferromagnetic spin arrangement. Among numerous multiferroic systems, BiFeO3 (BFO) is currently the most studied and best understood. Large ferroelectric polarization along <111> directions and G-type antiferromagnetism at room temperature make BFO appealing for applications in non-volatile devices. The orientation of the antiferromagnetism couples to the ferroelastic strain state and is always perpendicular to the ferroelectric polarization. Once the polarization is switched by an electric field, the easy plane of magnetization changes accordingly to reach a stable state, offering an opportunity for controlling spin via the electric field.
Although BFO is an ideal template of manipulating the spin via electric field, some key issues, such as imprint, retention, and fatigue, have to be solved before the realization of new devices. For example, retention can be addressed to thermodynamic instability of the domain. Asymmetric free energy landscapes, mainly due to different out-of-plane electric boundary conditions, result in at least one unstable polarization state. In the metal-ferroelectric-metal capacitor, the problem can be solved by controlling the bottom and top electrodes to ensure the electrostatic boundaries are balanced. However, to reduce the circuit size, the structure of a transistor with ferroelectric/multiferroic is more favorable. The transistor of semiconductor-ferroelectric/multiferroic-metal will form an imbalance of electrostatic boundary conditions, causing severe retention problems. To solve the problem, additional energy term has to be induced into the system to balance the free energy landscape. Although efforts on related studies have shown their ways to reduce the energy difference of the polarization double-well by controlling chemical environment, breaking the out-of-plane compositional symmetry, or using strain gradient, ferroelectric retention is still a key issue to be dealt with. In order to shed light on the retention problem, we intend to use the elastic energy as a key parameter to improve ferroelectric retention of BFO. In this study, self-assembled BFO mesocrystal will serve as a model system. The intimate connection between the mesocrystal and matrix material provides a tunable structure coupling. This elastic energy term may be exploited to improve ferroelectric/multiferroic retention. The achievement of great improvement on the retention in this system will open a new avenue to ferroelectric retention and the possible application in nonvolatile devices.
9:00 AM - KK3.15
Photoelectric Switchable Diode Effect in Semiconducting Sulfur-Based Ferroelectric Materials
Yiping Wang 1 Jian Shi 1
1Rensselaer Polytechnic Institute Troy United StatesShow Abstract
We will present both experimental and theoretical exploration of how ferroelectricity would manipulate the diode behaviors in ferroelectric semiconducting materials. Via van der Waals epitaxy, we will show the growth of high-quality large scale semiconducting ferroelectric SbSI and Sb2S3 sheets. The 3d transition metal-free ferroelectrics will enable greatly increased diffusion lengths of minority carriers, making the high-efficiency light-to-electricity generation process possible. We will show that the ferroelectric polarization effectively regulates the width of depletion region and therefore boosts the quantum efficiency of the sulfur-based materials as light sensitizer. The coupling of ferroelectricity and semiconductivity suggests a new avenue to high-efficient, fast, and endurable ferroelectric photovoltaic nonvolatile memory.
9:00 AM - KK3.16
Multistate Switching in Ferroelectric Multilayer Capacitors
Alexei Grigoriev 1 Pavel Salev 1
1Univ of Tulsa Tulsa United StatesShow Abstract
Ferroelectric materials are successfully used in non-volatile memory applications. Multifunction properties of ferroelectric and multiferroic complex oxides allow researchers to develop new approaches to memory storage and switchable electronic and optical devices. We found double polarization switching and multiple dielectric states in ferroelectric bilayer capacitors of thin BaTiO3 (BTO) and PbZr0.2Ti0.8O3 (PZT) layers. Computational analysis predicts that the multistate switching can be a common feature of ferroelectric multilayer capacitors made of materials with different remnant polarizations. In this work we present experimental results of polarization stability, switching dynamics, and switchable dielectric state analysis of BTO/PZT bilayer capacitors.
9:00 AM - KK3.17
Realization of Flexible Block Copolymer-Incorporated One Diode-One Phase Change Memory Array on Plastic Substrate
Beomho Mun 1 Byoung Kuk You 1 Daniel Juhyung Joe 1 Se Ryeun Yang 1 Hyeon Gyun Yoo 1 You Yin 2 Yeon Sik Jung 1 Keon-Jae Lee 1
1KAIST Daejeon Korea (the Republic of)2Gunma University Gunma JapanShow Abstract
Recently, there has been significant research effort on realization of flexible non-volatile memory, the fundamental component for data processing, storage, and radio frequency communication in flexible electronic systems. Among several emerging non-volatile memory technologies, phase-change random-access memory (PRAM) is one of the strongest candidates for next-generation non-volatile memory devices due to its remarkable characteristics of large cycling endurance, high speed, and excellent scalability. Although there are several approaches for flexible phase-change memory (PCM) devices, high reset current is the biggest obstacle for their practical operation. In this presentation, we show the fabrication of flexible PCMs by incorporating nano-insulators derived from Si-containing block copolymer (BCP) in order to significantly lower the operating current of the memory on a plastic substrate. The reduction of thermal stress by BCP nanostructures enables the reliable operation of the memory devices spatially integrated with ultrathin, single crystal flexible Si-diodes during more than 100 switching cycles and 1000 bending cycles. These results may open up a new opportunity for realizing flexible PRAMs for practical implementation in electronic applications.
9:00 AM - KK3.18
Electrodeposition of GST phase change memory
Philip Bartlett 1 Sophie Benjamin 1 2 C. H (Kees) de Groot 1 Andrew Lee Hector 1 Ruomeng Huang 1 Andrew Jolleys 1 Gabriela Kissling 1 3 William Levason 1 Gillian Reid 1
1Univ of Southampton Southampton United Kingdom2Nottingham Trent University Nottingham United Kingdom3University of Bath Bath United KingdomShow Abstract
Chalcogenide-based phase change memory (PCM) is a promising candidate for next generation non-volatile memory. Electrodeposition offers several potentially significant advantages for growth of semiconductor alloys for PCM as a fast process with lower cost compared with vapour deposition techniques. It enables excellent control over the composition across ternary phase diagrams in p-block alloys, and is well suited to deposition into patterned substrates.1,2
We have developed a tuneable electrolyte bath that is suitable for the rapid electrodeposition of ternary GexSbyTez phase change materials. Uniform and continuous films were deposited with very low impurity levels. Thin film memory cells are fabricated from these films, displaying good switching performance, stable endurance and an on/off ratio of around 1000.
Uniform filling of nano-patterned electrodes constructed by lithographic or e-beam etching of silica films on titanium nitride provided access to vertical memory devices. TiN top contacts have been applied to these and the resulting microstructured and nanostructured GST-225 devices also displayed good switching performance.
1. P. N. Bartlett, D. Cook, C. H. de Groot, A. L. Hector, R. Huang, A. Jolleys, G.P. Kissling, W. Levason, S. J. Pearce and G. Reid, RSC Adv. 3 (2013) 15645-15654.
2. P. N. Bartlett, S. L. Benjamin, C. H. de Groot, A. L. Hector, R. Huang, A. Jolleys, G.P. Kissling, W. Levason, S. J. Pearce, G. Reid and Y. Wang, Mater. Horiz. (2015) DOI: 10.1039/c5mh00030k.
9:00 AM - KK3.19
Modeling Crystallization and Void Formation in Ge2Sb2Te5 Nanostructures
Adam Cywar 1 Zachary Woods 1 Ali Gokirmak 1
1Univ of Connecticut Storrs United StatesShow Abstract
There is considerable interest in studying and modeling phase transitions in Ge2Sb2Te5 (GST) nanostructures for the development of phase-change memory technology . Typically, the crystallization models in the literature [2-3] examine a rectangular area of material in which the material is being heated uniformly throughout. We present a finite element model for simulating the nucleation and growth of crystal grains within an amorphous domain of GST alongside other physics such as joule heating and solid mechanics, allowing for modelling of crystallization in an arbitrarily shaped structure where a thermal gradient and/or a transient may be present. This approach will allow for the modeling of dynamic crystallization during a set or reset operation, allowing for updates of the electrical, thermal and mechanical properties of the material as it crystallizes.
The current models for the crystallization of GST reported in the literature [2-3] do not account for the ~ 7% volume reduction that occurs upon the as-deposited amorphous to crystalline phase change . Experimental results (STEM) have shown that a confined volume of as-deposited amorphous GST typically exhibits several voids after crystallization during annealing. The locations and sizes of the resulting voids are critically important to the quality of the device performance. Our model captures the volume change during crystallization to predict void locations and sizes based on the local strain and stress of grain boundary locations during the first-time annealing of as-fabricated devices.
 H. Wong et al., "Phase Change Memory," Proc IEEE, vol. 98, pp. 2201-2227, 2010.
 P. Ashwin, et al., "Fast simulation of phase-change processes in chalcogenide alloys using a Gillespie-type cellular automata approach," J. Appl. Phys., vol. 104, pp. 084901, 2008.
 G. W. Burr et al., "Observation and modeling of polycrystalline grain formation in Ge2Sb2Te5," J. Appl. Phys., vol. 111, pp. 104308-104308-12, 2012.
 W. K. Njoroge et al., "Density changes upon crystallization of Ge2Sb2.04Te4.74 films," Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, vol. 20, pp. 230-233, 2002.
9:00 AM - KK3.20
Growth of Crystalline Hexagonal GexSbyTez by Metal Organic Vapour Phase Epitaxy
Martin Schuck 1 2 Sally Riess 1 2 Kristof Keller 1 2 Daniel Wilson 4 5 3 Christoph Schmitz 5 2 Denis Rudolf 1 3 2 Manuel Bornhoefft 6 7 2 Joachim Mayer 6 7 2 Astrid Besmehn 8 Gregor Mussler 1 2 Martina von der Ahe 1 2 Hilde Hardtdegen 1 2 Detlev Gruetzmacher 1 2
1Forschungszentrum Juelich GmbH Juuml;lich Germany2Juelich-Aachen Research Alliance (JARA) Juelich Germany3RWTH Aachen University Juelich Germany4Forschungszentrum Juelich Juelich Germany5Forschungszentrum Juelich Juelich Germany6RWTH Aachen University Aachen Germany7Forschungszentrum Juelich Juelich Germany8Forschungszentrum Juelich Juelich GermanyShow Abstract
Phase change memory (PCM) based on chalcogenides such as the Ge-Sb-Te compounds along the Sb2Te3 - GeTe pseudo-binary line have been widely used for optical data storage and in recent years also as non-volatile resistive memory devices. In these applications, the ultra-fast and reversible phase change between the amorphous and the metastable cubic crystalline phase, associated with a high contrast in reflectivity and resistivity is used for data storage. They are deposited in the amorphous state by atomic layer deposition or physical vapour deposition (sputtering). Due to the lack of applications, the thermodynamically stable crystalline hexagonal phase was not in the centre of attention up to now. However, recently superlattices of highly textured hexagonal Sb2Te3 - GeTe layers have received increasing interest due to an altered switching mechanism with reduced switching energy. Switching is field induced and occurs at the interfaces of the materials between two crystalline states circumventing the melting needed for the phase change. The layered structure of monocrystalline hexagonal Ge-Sb-Te compounds inherently resembles the superlattice structure with respect to atomic stacking and crystal orientation to the substrate. For this reason, the preparation and intense study of epitaxial, hexagonal Ge-Sb-Te can be of fundamental interest for future applications.
In this contribution, we present the growth and characterization of crystalline Ge-Sb-Te films on Si (111) deposited by MOVPE. At a reactor pressure of 50 hPa and growth temperatures around 450°C epitaxial films are grown using nitrogen as the carrier gas to transport the precursors DETe, TESb and digermane to the reactor. Different partial pressures of the precursors were employed to vary the film composition. The morphology of the deposited material was investigated using AFM and SEM, while the structure of the as-grown samples was studied by XPS, XRD and TEM. The chemical composition was determined using EDS.
The two compositions Ge1Sb2Te4 and Ge2Sb2Te5 were controllably achieved. XRD studies indicate, that the 100nm thick Ge-Sb-Te is crystallized in the stable hexagonal structure (P-3m1 or R-3m). TEM investigations reveal that the Ge, Sb and Te atoms form building blocks, consisting of 7 (Ge1Sb2Te4) or 9 (Ge2Sb2Te5) alternating cation and anion layers parallel to the Si (111) substrate surface, stacked along the  axis. These building blocks are separated by van der Waals gaps originating from hexagonal Sb2Te3, where they are naturally present. The samples are monocrystalline and exhibit a low amount of defects. XPS reveals oxidation mainly of Ge and Sb at the surface of the films. Additionally the occupation of the cation sites by Ge and Sb atoms in the hexagonal lattice was investigated by TEM and XPS.
9:00 AM - KK3.21
In-Situ XRD Measurements and Simulations to Determine Grain Sizes in GeSbTe at Various Annealing Temperatures
Kadir Cil 1 Zachary Woods 1 Lhacene Adnane 1 Adam Cywar 1 Faruk Dirisaglik 1 Yu Zhu 2 Chung Lam 2 Ali Gokirmak 1 Helena Silva 1
1University of Connecticut Storrs United States2IBM T. J. Watson Research Center Yorktown Heights United StatesShow Abstract
PCM utilizes the large electrical resistivity contrast between the amorphous (high resistance) and the crystalline (low resistance) phases of chalcogenides -Ge2Sb2Te5 (GST) being the most common - that can be reversibly and rapidly switched between the two phases by self-heating via electric pulses . Understanding the crystallization dynamics during set operation is critically important.
We have performed XRD measurements to characterize grain size distribution in GeSbTe as a function of temperature and test the crystallization numerical models we have constructed using nucleation and growth rates from the literature . The material crystallizes over time as the chuck temperature is increased with 2oC/min heating rate and is monitored by the peaks in the XRD measurements. Peaks start appearing at T ~ 175 oC. The small widening of intensity peaks is attributed to an increase grain size due to temperature dependent nucleation and growth dynamics . When the chuck temperature reaches 300 oC, the material transitions from fcc phase to hcp phase. The X-ray peak width and maximum intensity increase with temperature, showing increasingly larger crystalline grain sizes up to melting temperature. A step-wise change is visible on the average grain size of GST at maximum nucleation rate (~325oC) and the grain sizes tend to saturate as the peak growth rate temperature is approached. However, in these slow measurements, the material goes through an fcc-hcp mixed phase that is not expected to take place during normal device operation as the phase transition to hcp is a very slow process.
Our crystallization model captures transitions between fcc and amorphous phases but does not capture movement of grain-boundaries if the material is not molten. At this point, we are able to compare the simulated grain-size distributions with the experimental data assuming that the simulation is starting from amorphous material. The average grain sizes obtained from these simulations are in good agreement with the experimental ones even though there are important differences such as the temperature ramp rate which is significantly slower in the experiments.
 H. -. P. Wong, S. Raoux, S. B. Kim, J. Liang, J. P. Reifenberg, B. Rajendran, M. Asheghi and K. E. Goodson, "Phase Change Memory," Proc. IEEE, vol. 98, pp. 2201-2227, 2010.
 G. W. Burr, P. Tchoulfian, T. Topuria, C. Nyffeler, K. Virwani, A. Padilla, R. M. Shelby, M. Eskandari, B. Jackson and B. Lee, "Observation and modeling of polycrystalline grain formation in Ge2Sb2Te5," J. Appl. Phys., vol. 111, pp. 104308, 2012.
9:00 AM - KK3.22
Fusing Behavior of Flexible Silver-Fuse Memories Fabricated by Reverse Offset Printing
Nobuko Fukuda 1 Jaakko Leppaeniemi 2 Hirobumi Ushijima 1 Ari Alastalo 2
1AIST Tsukuba Japan2VTT Technical Research Centre of Finland, Ltd. Espoo FinlandShow Abstract
Printed electronics has recently been focused towards low-costs and energy-efficient manufacturing processes. The advantages of printing technology involve the additive and direct patterning of functional materials, as well as manufacturing of flexible devices. Reverse offset printing enables high-resolution patterning and constant thicknesses regardless of the width of the pattern. This printing technique has the potential for producing low-power and high-resolution flexible memory devices.
Here, we fabricated electrical fuse memories by the reverse offset printing with an ink containing silver nanoparticles on a flexible plastic sheet. After printing, the memories were sintered at 150 °C for 30 min. The resulting memories include 8 different widths of the 500-mu;m-length bits from 3 to 50 mu;m with the average thickness of 95 nm and the each bit has two contact pads. The resistivity of the silver fuse lines is estimated to be ca. 7 × 10-5 Omega; cm by 4-point probe method. The bits are fused within 1 s by applying a voltage except the 50 mu;m-width bit. The current density for fusing of the bits regardless of applying voltage is estimated to be less than 10 mA/mu;m2. This is smaller than that of the bits printed on a glass substrate, as we have reported previously (~ 60 mA/mu;m2). The lower-power fusing of the bits on the plastic sheet is probably caused by the larger thermal expansion and the smaller thermal conductance of the plastic sheet as compared with those of the glass. Observation during fusing with an optical microscope shows a difference between the reflectivities of the bits before and after fusing. The behavior can be explained by scanning electron microscope images. During fusing, bonding of neighboring silver nanoparticles in the bit would be accelerated with the generated Joule heat and formed into plate-like shapes. Then, shrinking of the bit leads to fusing. In addition, thermal expansion of the flexible plastic sheet assists breaking of the bit, resulting in low-power fusing.
9:00 AM - KK3.23
Protecting and Engineering of DNA for Long-Term Information Storage
Robert N Grass 1 Reinhard Heckel 2 Wendelin Jan Stark 1
1ETH Zurich Zurich Switzerland2IBM Research Rueschlikon SwitzerlandShow Abstract
DNA is nature&’s way of storing information - every cell of our body contains about 750 megabytes of genomic information. This information is not only stored on an extremely small space, it can also be read after thousands of years of storage (e.g., from bone and tooth fossils). Both in space requirements (>300&’000 terabytes per gram) and in terms of long-term reliability (thousands of years) DNA outperforms current information storage materials by several orders of magnitude.
In an attempt to mimic these advantages for the storage of non-biological information, we investigated if DNA encapsulated within silica glass spheres (i.e.”synthetic fossils”) can endure for similarly long time-frames, and we compared DNA based information storage with physical (optical/magnetic/semiconductor) storage technologies.
For this we combined  the information theoretic concept of forward error correction with DNA encapsulation, a tool from materials chemistry. In a first experimental validation of the idea 83kB of digital information was encoded by a error correction scheme building on Reed-Solomon codes and translated to DNA sequences (4991 sequences each 117bp long). The DNA sequences were synthesized by a microarray technology and encapsulated into a silica matrix. This encapsulation resulted in very low DNA degradation rates, which were measured by accelerated aging experiments in various atmospheres. Following a simulated 2'000 year storage at ambient conditions, the digital information could be recovered from the DNA without error with the aid of the error correcting scheme . Besides giving an insight into the state of the art of information preservation in DNA we will also discuss future challenges and needs of digital data preservation in the form of chemical information.
 Church et al. Science 2012, 337, 6102.
 Meyer et al. Nature 2014, 505, 403.
 Paunescu et al. Nat. Protoc. 2013, 8, 2440.
 Grass et al. Angew. Chem. Int. Ed. 2015, 54, 2552.
9:00 AM - KK3.24
Development of All-Solid-State Electric-Double-Layer Transistors Using Oxide Ion and Proton Conducting Oxide Thin Films
Takashi Tsuchiya 1 Kazuya Terabe 1 Masakazu Aono 1
1NIMS Ibaraki JapanShow Abstract
Electrostatic carrier doping (ECD) by electric-double-layer (EDL) is an attractive technique for exploring interesting physical properties due to the ability to easily control the high electronic carrier density (1014 cm-2) merely by adjusting the DC bias voltage and in the freedom from the structural disorder inherent in chemical doping. While non-solid-state electrolytes, such as ionic-liquids, enable high carrier density, compatibility with other electronic devices is problematic. The nonuse of liquids is thus beneficial for practical applications. Here, all-solid-state EDLTs with oxide ion and proton conducting oxide thin film are developed.1-3 The device performance and electric properties of electrolyte will be discussed.
 T. Tsuchiya, K. Terabe, M. Aono, Appl. Phys. Lett. 103, 07311010 (2013)
 T. Tsuchiya, K. Terabe, M. Aono, Adv. Mater. 26, 1087-1091 (2014)
 T. Tsuchiya, M. Ochi, T. Higuchi, K. Terabe, M. Aono, ACS Appl. Mater. Interfaces, 7, 12254-12260 (2015)
9:00 AM - KK3.25
Titanium Dioxide Nanorods: Hybrid, Solution Processable and Photocrosslinkable Resistive Switching Materials for Tuneable Organic Electronic Memories
Emanuele Verrelli 1 Fei Cheng 2 Fahad Alharthi 2 Mohammed Ibrahem 1 Neil Kemp 1 Stephen M Kelly 2 Mary O'Neill 1
1University of Hull Hull United Kingdom2University of Hull Hull United KingdomShow Abstract
Titanium dioxide is one of the most investigated resistive switching material and there are many reports on its bipolar or unipolar switching behaviour. Nevertheless, very little has been done on solution processable hybrids, in particular those based on titanium dioxide nanorods. Here we demonstrate the resistive switching of functionalized titanium dioxide nanorods films, which can be processed photolithographically. The material was prepared modifying an existing technique found in the literature which allowed the high yeld production of titanium dioxide nanorods with an average diameter of 5 nm and length of 20 nm. Ligands of different types, including oleic-acid, phosphonic-acid and photocrosslinkable phosphonate terminated coumarin, were successfully used to functionalize the nanorods. The use of photocrosslinkable ligands is particularly attractive because it enables 1) the 3D integration of these organic memories and 2) the fabrication of devices based on stacks of such hybrid thin films allowing thus to further tune the properties of the devices (e.g. bilayer approach). The functionalized nanorods can be solution processed in several common solvents and spin coated producing uniform thin films with RMS surface roughness of the order of 1-2 nm. Crossbar metal-insulator-metal (MIM) devices were used in this work in order to investigate the switching properties of the hybrid materials. In those samples incorporating the crosslinkable material, ultraviolet light irradiation was used to make insoluble films prior to depositing the top electrode. It should be stressed that the material preparation, device fabrication and measurements are all carried out in air showing the huge potential of this approach in the organic memory field. The as spin casted material show bipolar behaviour with set/reset ratios of 100-1000 and high stability under repeated bias sweeps. Switching fields as low as 0.25 MV/cm are needed to set or reset the devices with the set to reset transition always taking place when a positive voltage is applied to the top electrode. A forming step is needed for the as-spin-casted material. The role of the organic component in the switching behaviour of these films will be addressed and discussed in order to show the potential of these materials as tuneable organic resistive switching memories. In the same direction, we will also present results concerning the possibility to tune the switching behaviour of these thin films by processing them further (e.g. O2 plasma, ozone, etc) or by blending them with other compounds. The differences in the switching behaviour of devices based on 1) nanorods functionalized with different ligands, 2) nanorods with anatase or rutile crystalline phase and 3) stacks of hybrid titanium dioxide films (bilayer approach) will also be addressed and discussed.
KK1: Advanced Flash
Tuesday AM, December 01, 2015
Hynes, Level 2, Room 202
11:30 AM - *KK1.01
Split Gate Flash Memory in Embedded NVM Applications
Alexander Kotov 1
1SST-Microchip San Jose United StatesShow Abstract
The tremendous market growth of smart mobile devices, smart cards, wearables, industrial and automotive electronics, and IoT (Internet of Things) has led to a strong demand for high performance and reliability, while low power and cost SoC (System on Chip) devices, where integration with eNVM (embedded Non-Volatile Memory) is an important key. This paper reviews a current landscape of the available eNVM solutions on the market with a particular focus on the most adopted embedded Flash memory cells with a charge storage medium based on floating gate (FG), nitride, nano-crystals. A conventional stacked-gate 1T (single transistor) NOR Flash memory cell technology continues to maintain a good share of eNVM-MCU market in automotive applications. It has been successfully scaled and offered now in 40nm automotive CMOS technology by a large IDM. At the same time 1T NOR Flash memory scaling faces a number of fundamental challenges such as the need for read voltage boost above 1.8V supply voltage, known over-erase issue that requires sophisticated operation algorithms, very limited high voltage scaling, a decreased operation window in terms of stored FG charge that separates ONE and ZERO states.. Power and cell scaling constraints of 1T NOR Flash turned industry to massively adopt 1.5T (one and half transistor: split gate) NOR flash for various eNVM applications. Split gate Flash memories become an established choice on the eNVM roadmaps for many CMOS Foundries and IDMs down to 28nm. The paper reviews pros & cons of different 1T and 1.5T flash cells structures, suitability for various applications, scaling potential. In particular, we present Embedded SuperFlash (ESF) split gate technology scaling roadmap and key features to meet a variety of eNVM applications.
12:00 PM - KK1.02
Effect of Word-Line Air-Gap Process Optimization on sub-20nm NAND Flash Memory Performance and Reliability
Kwanghyun Yang 1 Daehwan Yun 1 Gil-Bok Choi 1 Kyongtaek Lee 1 Byoungjun Park 1 Seongjo Park 1 Kun-ok Ahn 1 Jinwoong Kim 1
1SK hynix Inc. Cheongju Korea (the Republic of)Show Abstract
As the NAND flash memory has been continued to scale down for more productivity, the distance between floating gates has been decreased and the number of cells in a NAND sting increased. These phenomena have led to the degradation of reliability properties which is from widening of distribution of cell&’s threshold voltage (Vth) due to increase in cell-to-cell interference and due to decrease in cell string current. In order to enhance the word line(WL)-to-word line interference, WL air-gap technique has been adopted in NAND flash memory industry. Some researches addressed profile of WL air-gap is important for reliability properties. But these mostly focuses on portion of air-gap in inter layer dielectric. In this work, we optimize the profile of WL air-gap in view of bottom oxide thickness of WL air-gap and fabricate the optimized profile by appling new processes. Through the optimized profile and process, we obtained the enhanced performance and reliability properties in NAND flash memory. The optimized profile of WL air-gap is observed by Transmission Electron Microscope(TEM) images. To evaluate the improvement on reliability properties, electrical characteristics such as cell current, endurance and data retention have also been measured using test wafer. The results indicate that thicker WL air-gap bottom oxide produces higher cell current, narrower cell Vth distribution and better reliability.
12:15 PM - KK1.03
In-Line Monitoring of Grain Size Distribution of Channel Poly Si Used in 3D V-NAND Flash Memory Devices Using Multiwavelength Raman Spectroscopy
Nohyeal Kwak 1 Chul Young Ham 1 Sung Chul Shin 1 Seung Jin Yeom 1 Chun Ho Kang 1 Byung Seok Lee 1 Sung Gi Park 1 Woo Sik Yoo 2
1SK hynix Inc. Icheon-si Korea (the Republic of)2WaferMasters Inc. San Jose United StatesShow Abstract
The NAND Flash business is transitioning from the conventional two dimensional, planar structure to three dimensional(3D), vertical structures to meet storage density requirements. Small scale volume production of 3D V-NAND Flash memory devices has recently begun and V-NAND-based solid-state drives(SSD) have been introduced in the market place.
For 3D V-NAND Flash memory devices, device scaling is being achieved by vertical staking of TFTs in multiple layer configurations, without heavily relying on advances in lithography. 3D V-NAND Flash memory device fabrication involves many processes that have never before been used in mass production of semiconductor devices.
Alternate deposition of ultra-thin films and selective etching are required for successful fabrication of vertically stacked layers used in 3D V-NAND Flash memory devices. Deep trenches are etched to form layers for gate dielectric, charge trapping and tunnel dielectric. Each trench is then filled with a-Si which will be converted to conducting poly-Si to form the channel. As the number of stacked layers increases, poly-Si channel length increases proportionally. Highly homogenous poly-Si channel materials, with uniform grain size, are required for reducing device performance variations within these “strings” of vertically stacked TFTs.
For poly-Si channel fabrication, an amorphous Si film is typically deposited in the channel trench region and then thermally converted to poly-Si by annealing. Depending on the heating mechanisms of the a-Si film, using different annealing techniques, average poly-Si grain size and its distribution pattern yield significantly different results. Variations of channel poly-Si grain size within, and between, “strings” of vertically stacked TFTs can result in device property variations in individual transistors and between “strings”. To achieve the desired properties of the channel poly-Si through process optimization, the average grain size, and its distribution, must be carefully monitored and controlled. Development of proper, in-line poly-Si grain size distribution characterization techniques for 3D V-NAND structures are required for identifying improper annealing techniques in the early stages of process development and for process monitoring during manufacturing.
The grain size distribution in the poly-Si channel, converted from the thin chemical vapor deposited(CVD) a-Si films after various thermal annealing techniques used in the 3D V-NAND Flash memory devices, was monitored using a multiwavelength Raman spectroscopy (MRS-300) system. The grain size distribution characterized by Raman spectroscopy was in good agreement with high resolution cross-sectional transmission electron microscopy (HRXTEM) and showed good correlation with on current(ION) of 3D V-NAND Flash memory devices. The multiwavelengh Raman characterization technique is very promising for in-line monitoring of grain size distribution in the poly-Si channel of 3D V-NAND Flash memory devices.
12:30 PM - KK1.04
Remote Plasma ALD of Silicon Nitride for CTF
Woochool Jang 1 Heeyoung Jeon 1 Hyoseok Song 1 Jingyu Park 1 Hyeongtag Jeon 1 Hyunjung Kim 1 Honggi Kim 1 Jaemin Lee 1
1Hanyang University Seoul Korea (the Republic of)Show Abstract
As the feature size of device shrinks continuously, conventional floating gate (FG) NAND flash memory suffers from reliability problem such as decrease of charge loss tolerance, cell to cell interference, and vulnerability of stress induced leakage current via single defect. To increase memory density without above mentioned problems, NAND flash memory chose a three dimensional (3D) structures for next generation flash memory. In 3D NAND flash memory, stacking up many layers is critical technology because the number of layer is directly related high memory density. However, as more layers stack up, aspect ratio increases. In first generation 3D NAND flash memory, it has 24 layers and its aspect ratio is 40:1. Next generation 3D NAND may have 48 or 64 layers and its aspect ratio goes beyond 60:1. Therefore, there are demands the deposition technology with precise thickness control and high step coverage. In 3D NAND, charge storing type changed from FG to charge trap flash (CTF) memory. Silicon nitride (SiNx) is used as charge trap layer in CTF. To deposit SiNx thin film in semiconductor, low-pressure chemical vapor deposition (LPCVD) conventionally utilized due to its low hydrogen content good step coverage, and thermal stability. However, it is not sufficient to deposit SiNx in very high aspect ratio structure.
Among various deposition methods, atomic layer deposition (ALD) is considered to be the best solution to satisfy above-mentioned requirements. ALD reaction is self-limited and enables to deposit thin film with high step coverage and precise thickness control. Particularly, remote plasma ALD (RPALD) was utilized to enhance the reactivity between precursor and reactant gas for high film density with minimizing plasma damage. In RPALD, the plasma generation section is remotely outside of reaction chamber and the radicals in plasma generation region enter into the reaction chamber for deposition.
In this study, we developed low temperature SiNx with RPALD using trisilylamine (TSA) and NH3 remote plasma as the reactant gas and we investigated correlation between materials properties and trap properties of SiNx thin film. As the stoichiometry of SiNx thin films impacts defect properties, Rutherford back scattering spectroscopy (RBS), Auger electron spectroscopy (AES) was utilized to measure the stoichiometry. As hydrogen contents are influent to the defect density, elastic recoil detection (ERD) and secondary ion mass spectroscopy (SIMS) was utilized to measure hydrogen contents of deposited SiNx film. X-ray photoelectron spectroscopy (XPS) was utilized for chemical binding state. In addition, we fabricated metal-Al2O3-silicon nitride-SiOshy;2-Si (MANOS) device to obtain defect properties which are related with memory performances such as retention and program/erase(PE) characteristics.
Guohan Hu, IBM T. J. Watson Research Center
Hyunsang Hwang, Pohang University of Science and Technology
Gabriel Molas, LETI-CEA
Eisuke Tokumitsu, Japan Advanced Institute of Science and Technology
Symposium Support Kojundo Chemical Laboratory Co. Ltd. of Japan
KK6: Ferroelectric Memory II
Wednesday PM, December 02, 2015
Hynes, Level 2, Room 202
2:30 AM - *KK6.01
Doped Hafnium Oxide for Ferroelectric Memories
Tony Schenk 1 Michael Hoffmann 1 Claudia Richter 1 Milan Pesic 1 Sergei V. Kalinin 2 Alfred Kersch 3 Thomas Mikolajick 1 4 Uwe Schroeder 1
1NaMLab gGmbH Dreseden Germany2Oak Ridge National Laboratory Oak Ridge United States3Munich University of Applied Sciences Munich Germany4TU Dresden Dresden GermanyShow Abstract
Ferroelectricity in HfO2 was first reported in 2011. In the following years, it has been attracting a lot of interest from both theoretical and application oriented groups. From the material point of view, ferroelectric hafnium oxide is interesting since it is lead-free and a simply binary oxide with a non-perovskite structure. From the application perspective, especially the low permittivity, high coercive field and proven compatibility with semiconductor fabrication are appealing. In the last two years, first ab-initio studies were published and the space group originally claimed responsible for the ferroelectricity in HfO2 was recently experimentally verified. Already in 2012, a ferroelectric field effect transistor in 28 nm complementary metal-oxide-semiconductor (CMOS) technology was demonstrated. Consequently, the HfO2 based ferroelectric memories were included in the 2013 edition of the International Technology Roadmap for Semiconductors (ITRS).
This talk starts addressing the requirements for non-volatile memories. From a basic point of view, it is explained why the criteria of speed, data retention and cycling endurance cannot be independently optimized. Next, the two main concepts of ferroelectric memories with either a capacitor or a transistor as the storage element are introduced. Major scaling issues of such devices when based on conventional ferroelectrics are summarized. With the above mentioned boundary conditions in mind, the research on HfO2-based ferroelectrics is motivated. The short “history” of research on this rather new class of ferroelectrics will be described leading to the current status of fundamental material research and the application in ferroelectric memories. Open material and engineering challenges are summarized and next steps on the road towards non-volatile ferroelectric memories are outlined.
 T. S. Böscke, J. Müller, D. Bräuhaus, U. Schröder, and U. Böttger, Appl. Phys. Lett. 99, 102903 (2011).
 J. Müller, E. Yurchuk, T. Schlösser, J. Paul, R. Hoffmann, S. Mueller, D. Martin, S. Slesazeck, P. Polakowski, J. Sundqvist, M. Czernohorsky, K. Seidel, P. Kücher, R. Boschke, M. Trentzsch, K. Gebauer, U. Schröder, T. Mikolajick, “Ferroelectricity in HfO2 enables nonvolatile data storage in 28 nm HKMG”. Symposium on VLSI Technology (VLSIT), June, 2012.
 International Technology Roadmap for Semiconductors - Emerging Research Devices. 2013
 Nanoelectronics and Information Technology: Advanced Electronic Materials and Novel Devices, edited by R. Waser (Wiley-VCH, Weinheim, 2003).
3:00 AM - KK6.02
Effect of Stress on Ferroelectricity of (Hf0.5Zr0.5)O2 Thin Films
Hiroshi Funakubo 1 Takahisa Shiraishi 1 Tatsuhiko Yokouchi 1 Takahiro Oikawa 1 Hiroshi Uchida 2
1Tokyo Inst of Technology Yokohama Japan2Sophia University Tokyo JapanShow Abstract
Ferroelectricity of thin films of HfO2-based materials has been demonstrated by substituting various ions. Most noticeable feature of these films compared to the previous ferroelectric films is the appearance of ferroelectricity less than 10 nm in thickness even in polycrystalline film form. This feature is possible to realize not only low voltage operation of capacitor-type ferroelectric memories due to the very thin film thickness, but also ferroelectric transistor-type one due to the good compatibility of HfO2-based insulators with CMOS. Origin of the ferroelectricity is pointed out to be the noncentrosymmetric orthorhombic phases. This phase is non-equilibrium phase, but is pointed out to be stabilized in thin film form. Two stabilization factors are pointed out from the previous reports; one is the crystallite size and the other is the stress from the substrates. Crystalline size is systematically investigated by Hwan&’s groups, but the stress effect from the substrate has been hardly reported. In the present study, we first investigated the effect of the stress from the substrate by changing the kinds of substrates and film thickness. Ferroelectricity was investigated for 17 and 55 -nm thick (Hf0.5Zr0.5)O2 thin films prepared by Pulsed MOCVD. Ferroelectricity was found to be strongly depended on the film thickness and the kinds of substrates. This suggests that the formation and the volume fraction of ferroelectric orthorhombic phase strongly depended on the stress applied to the films from the substrate.
3:15 AM - KK6.03
Ferroelectricity in Hafnia, and the Role of the Surface Energy
Rohit Batra 1 Huan Doan Tran 1 Ramamurthy Ramprasad 1
1University of Connecticut Willimantic United StatesShow Abstract
Conventional perovskite structure based ferroelectric (FE) materials suffer from various limitations such as poor Si-compatibility, small band gap, and the requirement of large physical thickness. Doped hafnia (HfO2) thin films (<10nm) with high remnant polarization, high bandgap and excellent silicon compatibility offer a strong prospect for future non-volatile memory and FE-Field Effect Transistor applications . However, the origins of the FE behavior in doped hafnia thin films are not well understood as the known equilibrium phases of hafnia display inversion symmetry and hence, are non-polar. Recent work  suggests that two polar, non-equilibrium orthorhombic phases of hafnia, namely Pca21 and Pmn21, are energetically competing with the equilibrium phases, and may be responsible for this FE phenomenon. However, conditions under which these polar orthorhombic phases are stabilized are unknown.
In this study, the role of surface energy in stabilizing the non-equilibrium FE phases was explored using first-principles density functional theory calculations. Two equilibrium phases, i.e., monoclinic P21/c and tetragonal P42/nmc, and the aforementioned two polar phases were included in the present study. Phenomenological (1D) slab, (2D) rod and (3D) box models with different surface plane terminations were constructed to predict the critical thickness, area and volume, respectively, under which the polar phases become thermodynamically more favorable over the equilibrium monoclinic phase. The spontaneous polarization of the stable FE models was computed through evaluating the Born effective charge and was found to be in good agreement with the experimental observations. It is concluded that the surface energy is one of the prominent factors controlling ferroelectricity in hafnia thin films. Pathways for rationally designing FE hafnia thin films are also proposed.
 M. H. Park et al., Adv. Mater. 27(11):1811-31 (2014)
 T. D. Huan, V. Sharma, G. A. Rossetti, Jr., and R. Ramprasad, Phys. Rev. B 90, 064111 (2014)
4:30 AM - KK6.04
Patterned Organic Ferroelectric Memory Diodes by Solution Micromolding
Thomas Lenz 1 2 Frank Simon Benneckendorf 1 Kamal Asadi 1 Paul W. Blom 1 2 Dago de Leeuw 1
1Max Planck Institute for Polymer Research Mainz Germany2Graduate School Materials Science in Mainz Mainz GermanyShow Abstract
The ability to store data is crucial for many of the envisioned applications of flexible electronics. RFID tags for example need to be able to send and receive stored information that is communicated by means of a radio signal. Ferroelectric materials are promising candidates for memory technology, since they provide two bistable non-volatile polarization states corresponding to a Boolean 1 and 0, which can repeatedly be switched by an external field.
Ferroelectric polymers are specifically suited for flexible electronics, as their solution-processed thin films are bendable without compromising their properties. The most widely investigated organic ferroelectric is the copolymer of poly(vinylidene fluoride) and trifluoroethylene (P(VDF-TrFE)). Comprising capacitors exhibit a relatively large remanent polarization, short switching times, and good environmental and thermal stability. Furthermore, the programming cycle endurance is comparable to inorganic ferroelectric capacitors.
However, implementation of capacitors into integrated circuits is hampered by the read-out of the information being destructive. This problem can be overcome by using phase separated blends of P(VDF-TrFE) with a semiconducting polymer. The microstructure consists of semiconducting columns in a ferroelectric matrix. The bi-stable polarization state of the P(VDF-TrFE) yields the binary information that can be read-out non-destructively by the current through the semiconducting columns.
Phase separation however is a random process that yields a spatially undefined microstructure. Here we use solution micromolding to obtain well-defined interfaces between the two polymers. In this technique, a solution of P(VDF-TrFE) is poured onto the substrate and a polydimethylsiloxane stamp with relief structures on its surface is pressed onto the substrate surface using a hot press. After the solvent has fully evaporated, the stamp is removed and a complementary linear grating of P(VDF-TrFE) is obtained. The space in between the lines is backfilled with a semiconducting polymer by hot pressing with a flat stamp. Sandwiching the resulting binary array between two electrodes yields a bistable ferroelectric diode.
The diode can be programmed reversibly in a low resistive on-state and high resistive off-state. When the bias is turned off, the information is retained. Hence, the memory is non-volatile, as confirmed by programming cycle endurance and data retention measurements. Finally, the diode can be designed in such a way that current transport is rectifying. This allows implementation into a crossbar memory array without cross talk. The performance can be optimized by down scaling the lateral dimensions of the binary array. In this contribution we will discuss the prospects for data storage in applications of flexible electronics.
4:45 AM - KK6.05
Well-Ordered, Nanostructured Active Layers in Semiconducting-Ferroelectric Polymer Composites for Organic Memory Devices
Seung Hyun Sung 1 Bryan Boudouris 1
1Purdue University West Lafayette United StatesShow Abstract
Organic non-volatile memory devices based on a phase-separated blend of ferroelectric and semiconducting materials (i.e., ferroelectric diodes) have received growing research interest due to their low-cost fabrication and easy processability. In these systems, the blend film is composed of semiconducting domains surrounded by a ferroelectric matrix. The ferroelectric phase dictates the memory retention functionality while the semiconducting phase serves as the pathway to read-out the memory in a non-destructive manner. The phase-separated structures of the semiconducting and ferroelectric phases play an important role in device performance. In order to evaluate this crucial structure-property relationship, we have fabricated ordered ferroelectric devices (OFeDs) through lithographic techniques to establish systematically the impact of nanoscale structure on the macroscopic performance. To simplify the morphological model, a square grid pattern was used with a continuous and perpendicular semiconducting pathway between two electrodes. After the fabrication of a nanoporous ferroelectric domain, a semiconducting polymer was deposited into the hole pattern arrays to complete the ordered heterojunction. These systematic studies reveal the optimal ferroelectric domain size (~400 nm) with the interpenetrating networks of semiconducting domains; this optimal structure provides a significant improvement in the memory performance of with respect to the ON/OFF current density ratio relative to the blended film fabricated using conventional solution casting. The improved performance originates from a combination of the ordered nanostructure and the interfacial interaction between the ferroelectric-semiconductor composite domains. This facile lithographic approach to create heterojunction arrays helps to quantitatively elucidate the impact of nanostructure with well-ordered active layer domains, and also triggers the enhancement of memory switching performance. As the first demonstration of macroscopic OFeDs, this work offers a new opportunity to investigate the underlying physics of the device operation and establishes a promising route for material design.
5:00 AM - KK6.06
Controlling the Threshold Voltage and Current of Electronic Components Using Organic Ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) Film
Negar Sani 1 Deborah Mirbel 2 Simone Fabiano 1 Georges Hadziioannou 2 Isak Engquist 1 Magnus Berggren 1
1Linkoping Univ Norrkoping Sweden2Universiteacute; de Bordeaux Bordeaux FranceShow Abstract
In many electronic devices and components it is necessary to have control over the current and the threshold voltage which defines the on/off limit of the component. For this purpose, now a days it is very common to use TFTs as switches. TFTs have a settled technology but still a rather complicated fabrication process including several depositing, etching and curing steps. Here we present a method to define a turn-on threshold and control the current of an electronic component simply by depositing a ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDFminus;TrFE) film on one of the electrodes. This is possible due to the fact that the PVDFminus;TrFE film is an insulator except for when the coercive field needed for aligning the dipoles in the film is applied. When the coercive field is applied the number of charges necessary for aligning all the dipoles can pass through the film, which then becomes insulating again. Since the PVDFminus;TrFE film has a defined surface charge density in the poled state, the amount of transferred charges can be adjusted by varying the surface area of the electrode on which the film is deposited. In addition, the threshold voltage can be adjusted by changing the thickness of the PVDFminus;TrFE film.
5:15 AM - KK6.08
Solution Processed Fabrication and Nano-Scale Domain Manipulation in Organic Ferroelectric Microcrystals of Diisopropylammonium Bromide(DIPAB)
Shashi Poddar 1 2 Haidong Lu 1 2 Jingfeng Song 1 2 Om Goit 1 2 Shah Valloppilly 2 Alexei Gruverman 1 2 Stephen Ducharme 1 2
1Univ of Nebraska-Lincoln Lincoln United States2Nebraska Center for Materials and Nanoscience Lincoln United StatesShow Abstract
The recent discovery of ferroelectricity in halogen salts of diisopropylammine has lead to a new family of organic ferroelectric materials exhibiting spontaneous polarization up to 22 µC/cm2 and coercive field of 10 KV/cm, which are comparable to the inorganic perovskite materials like Barium titanate (BTO) and Lead zirconium titanate (PZT). The order-disorder motion of the center nitrogen atom in the amine group about the plane of pseudo symmetry is believed to play a vital role in the ferroelectric behavior of DIPAB. Until now only three-dimensional bulk crystals of DIPAB have been synthesized and it is important to be able to fabricate thin films of these materials to be integrated into future electronic devices.
In the present work we have used a blend of diisopropylammonium bromide and poly vinyl alcohol (DIPAB:PVA) with water as the common solvent to spin coat on a metal substrate. Due to difference in the rate of evaporation of the solvent, the constituent materials of the blend phase-separate resulting in the formation of well-aligned microcrystals of DIPAB with thickness ranging from 100 nm to 500 nm while the polyvinyl alcohol films are deposited in between the interstitial spaces which has been confirmed by scanning electron microscopy analysis and x-ray diffraction. Piezoresponse force microscopy (PFM) was used to study the spatial distribution as well as the electrical property of these microcrystals. The PFM studies revealed the crystals growing on the substrate with the polar b-axis (010) [SD1] along the plane of the substrate resulting in a strong lateral signal that was also supported by x-ray diffraction analysis. The microcrystal films of DIPAB consisted of 180° ferroelectric domains separated by uncharged domain walls. We were able to create and propagate 180° charged domain walls by applying a bias with the tip of the PFM. The ability to create and manipulate charged domain walls provide us a unique possibility of engineering ferroelectric domains in organic molecular systems.
KK4: Ferroelectric Memory I
Wednesday AM, December 02, 2015
Hynes, Level 2, Room 202
9:30 AM - *KK4.01
Hard-Disk-Drive-Type Ferroelectric Data Recording with Memory Density over 1 Tbit/inch2 Based on Scanning Nonlinear Dielectric Microscopy
Tomonori Aoki 1 Yoshiomi Hiranaga 1 Yasuo Cho 1
1Tohoku Univ Sendai JapanShow Abstract
With the recent progress of information society, the importance of high-density data storage systems is increasing. Ferroelectric data storage system records the data bits in the form of the polarization direction of individual domains . The domain wall of typical ferroelectric materials is as thin as a few lattice parameters , which is favorable for high-density data storage. In this system, data bits are reproduced by scanning nonlinear dielectric microscopy (SNDM) . Up to now, real information storage at a density of 4 Tbit/inch2 was achieved by the ferroelectric data storage system based on atomic force microscopy type SNDM with a piezo linear scanner . Moreover, reproduction with a bit rate of 2 Mbps and recording with a bit rate of 20 Mbps were achieved using the hard-disk-drive (HDD)-type data storage system .
However, in the HDD-type ferroelectric data storage system, recording with a density of 1Tbit/inch2 has not yet been achieved.
In this study, experiments were performed to demonstrate recording with a density over 1 Tbit/inch2 by HDD-type ferroelectric data storage system. As a result, we successfully achieved the recording of bits with a density of 3.4 Tbit/inch2.
Next, actual information data writing was conducted using the same equipment. In this demonstration, an ASCII bit array of “S”, “N”, “D” and “M” was recorded on the ferroelectric medium. The bit was written with the bit spacing of 25 nm. The SNDM image of the written bit data showed that all of the bit data was separately recorded and the bit data array could reproduce the original bit array with an appropriate signal processing. Finally, it was confirmed a series of writing and reading operation was possible with a density of 1 Tbit/inch2 using the same HDD-type ferroelectric data storage system.
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10:00 AM - KK4.02
Precise Stoichiometry Control as Key for Room Temperature Ferroelectricity in Strain-Enabled CaTiO3 Thin Films
Ryan Haislmaier 1 Everett D. Grimley 2 Michael David Biegalski 3 James M. LeBeau 2 Susan E. Trolier-McKinstry 1 Venkatraman Gopalan 1 Roman Engel-Herbert 1 Matthew J. Brahlek
1Pennsylvania State Univ University Park United States2North Carolina State University Raleigh United States3Oak Ridge National Laboratory Oak Ridge United StatesShow Abstract
Strain-engineering has proven to be a powerful strategy for unlocking ferroic functionality in ABO3 perovskite oxides. For instance, theory and experiments have shown that epitaxial strain can induce room temperature ferroelectricity in the incipient ferroelectric SrTiO3. However, precise control over composition is also required to realize such strain tuning, although this has received much less attention . In this work, we demonstrate precise control over stoichiometry as key for observing predicted strain-enabled ferroelectricity in CaTiO3  films grown by hybrid molecular beam epitaxy (hMBE) where fluxes are co-supplied using thermal and organometallic sources. This approach enables an adsorption controlled growth window where the Ti:Ca stoichiometry is self-regulating, which has also been demonstrated for SrTiO3 films grown by hMBE. In order to map out the growth window, a series of CaTiO3 films were grown on (001)(LaAlO3)0.3(Sr2AlTaO6)0.7 substrates (+1.23% tensile strain) by systematically adjusting the supplied titanium tetra-isopropoxide flux for each film. We measured the structural and electrical properties using x-ray diffraction, scanning transmissio