Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session L24: Focus Session: Dielectric, Ferroelectric, and Piezoelectric Oxides -- Applications |
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Sponsoring Units: DMP Chair: Matthew Dawber, Stony Brook University Room: D133-D134 |
Tuesday, March 16, 2010 2:30PM - 2:42PM |
L24.00001: Ferroelectric Tunnel Junctions: Resistive Switching Behavior by Scanning Probe Microscopy A. Stamm, H. Lu, D. Wu, Y. Wang, D. Felker, M. Rzchowski, H. W. Jang, C. W. Bark, C.-B. Eom, E. Y. Tsymbal, A. Gruverman In this work, we demonstrate the reproducible tunneling electroresistance effect in ultrathin epitaxial ferroelectric heterostructures by means of scanning probe microscopy techniques. Ultrathin films of barium titanate (in the range from 2 nm to 10 nm) with microscopically patterned SrRuO3 top electrodes have been grown on the SrRuO3/SrTiO3 substrates by atomic-layer-controlled pulsed-laser deposition. Imaging and control of polarization state in SrRuO3/BaTiO3/SrRuO3 and BaTiO3/SrRuO3 heterostructures have been performed via Piezoresponse Force Microscopy (PFM) along with conductance measurements by Conducting Atomic Force Microscopy (C-AFM). The selected locations have been probed by performing the local I-V measurements using a fixed tip. In parallel, at the same locations local PFM hysteresis loops have been measured. The obtained results show a change in resistance by about two orders of magnitude upon polarization reversal on a lateral scale of 20 nm at room temperature. These results are promising for employing ferroelectric tunnel junctions in non-volatile memory and logic devices. [Preview Abstract] |
Tuesday, March 16, 2010 2:42PM - 2:54PM |
L24.00002: Mechanism for bipolar resistive switching in transition metal oxides Marcelo Rozenberg, Maria Jose Sanchez, Ruben Weht, Carlos Acha, Fernando Gomez-Marlasca, Pablo Levy Resistive andom access memories (RRAM) composed of a transtition metal oxide dielectric in a capacitor-like structure is a candidate technology for next generation non-volatile memory devices. We introduce a model that accounts for the bipolar resistive switching phenomenom observed in many perovskite transition metal oxides. It qualitatively describes the electric field-enhanced migration of oxygen vacancies at the nano-scale. The numerical study of the model predicts that strong electric fields develop in the highly resistive dielectric-electrode interfaces, leading to a spatially inhomogeneous oxygen vacancies distribution and a concomitant resistive switching effect. The theoretical results qualitatively reproduce non-trivial resistance hysteresis loops measured in YBCO and PCLMO samples that we also report, providing key validation to our model. [Preview Abstract] |
Tuesday, March 16, 2010 2:54PM - 3:06PM |
L24.00003: Tunneling Electroresistance in Ferroelectric Tunnel Junctions with a Composite Barrier M. Y. Zhuravlev, Y. Wang, E. Y. Tsymbal, S. Maekawa A ferroelectric tunnel junction (FTJ) is a tunnel junction in which a thin ferroelectric layer serves as a barrier between two metal electrodes.[1] Contrary to ferroelectric capacitors where leakage currents are detrimental to the device performance, the conductance of a FTJ is the functional characteristic of the device. The key property of FTJ is tunneling electroresistance (TER) that is a change in electrical resistance with reversal of ferroelectric polarization. It was predicted that TER in FTJs can be sizable due to the change in the tunneling potential barrier dependent on polarization orientation. [2] In this work we predict that a FTJ with a composite barrier that combines a functional ferroelectric film and a thin non-polar dielectric layer can exhibit a significantly enhanced TER. [3] Due to the change in the electrostatic potential with polarization reversal the non-polar dielectric barrier acts as a switch that changes its barrier height from a low to high value. The predicted values of TER are giant reaching several orders of magnitude. The proposed method of enhancing TER may be practical for device applications. [1] E. Y. Tsymbal and H. Kohlstedt, \textit{Science} \textbf{313}, 181 (2006); [2] M. Y. Zhuravlev et al, \textit{Phys. Rev. Lett.} \textbf{94}, 246802 (2005); [3] M. Y. Zhuravlev et al, \textit{Appl. Phys. Lett.} \textbf{95},~052902 (2009). [Preview Abstract] |
Tuesday, March 16, 2010 3:06PM - 3:18PM |
L24.00004: An assessment of memristor intrinsic fluctuations: a measurement of single atomic motion Julien Borghetti, J. Joshua Yang, Gilberto Medeiros-Ribeiro, R. Stanley Williams Memristors provides electrically tunable resistance for upcoming non-volatile memory and future neuromorphic computing. One of the key benefits of such a device is its scalability, which can be demonstrated from an architectural perspective as well as from a fundamental physics limit. 4D addressing schemes utilizing cross bar structures that can be stacked several layers high above the chip embodies unlimited addressing space. On the other limit, the basic operating principles of memristive devices allow one to reach storage of information in a single atom. In this report of nanoscale (sub 50nm) devices, we detect single atom fluctuations, which would then represent the ultimate limit for noise sources thus delineating the boundary conditions for circuit design. We show that electrically induced individual atom migrations do not affect the overall device atomic configuration until a critical bias where a single local fluctuation triggers a general atomic reconfiguration. This instability illustrates the robustness of the device non-volatility upon small electrical stress. [Preview Abstract] |
Tuesday, March 16, 2010 3:18PM - 3:30PM |
L24.00005: Interfacial engineering and mechanism of metal oxide memristive switching Hongwu Zhao, Zhaoliang Liao, Ziyu Liu, Yang Meng, Dongmin Chen Resistance switching in metal oxides has drawn growing interest because of its potential applications in high performance nonvolatile resistance random access memory devices. Resistive switching characteristics of a Pr0.7Ca0.3MnO3 (PCMO) film sandwiched between a Pt bottom electrode and top electrodes (TE) made of various metals are found to belong to two categories. Devices with TE made of Al, Ti, and Ta exhibit a large I-V hysteresis loop and bipolar RS, but those with TE made of Pt, Ag, Au, and Cu do not. Transmission electron microscopy reveals that a thin metal-oxide layer formed at the interface between the former group of TE and PCMO, but not for the latter group of TE. Analysis shows that the categorization depends on the Gibbs free energy of oxidation of the TEs with respect to that of PCMO. As an effort to investigate the interfacial layer and its effect on the resistance switching, the thin Ta films with difference thickness were inserted between the PCMO and Au electrodes, and the I-V characteristics will be presented. [Preview Abstract] |
Tuesday, March 16, 2010 3:30PM - 3:42PM |
L24.00006: Resistive Switching in ALD ZnO and TiO2 Films Todd Waggoner, John Co Resistive switching in metal oxide thin films has recently become a major scientific interest due to the possibility of producing low power, non-volatile resistive random access memory (ReRAM). Theories proposed for the switching mechanism typically involve the migration of oxygen vacancies under an applied electric field. Resulting from local increases in vacancy concentration, conducting filaments can form between device electrodes. The process is reversible by either applying a stronger voltage bias across the device to burn out the filaments or by reversing the applied field. This allows for the design of devices with unipolar or bipolar operation. A material comparison of ZnO and TiO2 thin films grown by atomic layer deposition (ALD) demonstrate different switching behavior in our devices. ALD TiO2 films have been prepared in the past but results typically show a wide variance. Here ZnO and TiO2 are directly compared utilizing Al electrodes. So far most work has been done using Pt electrodes on TiO2 thin films. Investigations show that device yield, performance, cycle endurance, and stability appear to differ significantly as a result of the chosen dielectric. [Preview Abstract] |
Tuesday, March 16, 2010 3:42PM - 4:18PM |
L24.00007: Lead-free piezoelectrics and mechanisms of high electro-mechanical coupling Invited Speaker: The high electromechanical coupling of the most versatile piezoelectric, Pb(Zr,Ti)O3 (PZT), originates in combination of lattice effects, motion of domain walls and presence of a morphotropic phase boundary (MPB). In search for the lead-free alternatives, it is tempting to look at materials that are structurally and chemically similar to PZT. This approach has so far focused on a number of Bi containing compounds and solid solutions possessing an MPB. Interestingly, evaluation of domain walls motion has so far been largely neglected in lead-free piezoelectrics even though it is known to account for more than half of the response in PZT. In this presentation, relative contributions of domain walls, lattice and MPB to the piezoelectric response of Pb-based and some lead-free materials (K,Na)NbO3, (Na,Bi)TiO3, BiFeO3) are discussed. By using recent reports on direct observation of domain walls motion in polycrystalline ferroelectrics, it is shown how complex boundary conditions on microscopic scale lead to unexpected average behavior and make difficult estimation of the macroscopic properties from lattice and domain walls motion.. [Preview Abstract] |
Tuesday, March 16, 2010 4:18PM - 4:30PM |
L24.00008: Atomic Layer Deposited Ta$_{2}$O$_{5}$/Al$_{2}$O$_{3}$, ZrO$_{2}$/Al$_{2}$O$_{3}$ and ZrO$_{2}$/Ta$_{2}$O$_{5}$ as Dual Dielectric MIIM Diodes for Rectenna Applications Nasir Alimardani, John F. Conley, Stephen Kilpatrick, Madan Dubey A rectenna is an integrated receiving antenna and diode that captures electromagnetic energy and converts it to DC power at high efficiency. Harvesting of energy in the infrared (IR) region requires rectification at $\sim $10 THz frequencies. Because of their high speed of operation, metal/insulator/metal tunnel diodes are a potential candidate for this application. The primary MIM diode requirements for rectenna applications include a highly nonlinear and asymmetrical current-voltage (I-V) characteristic with low ``zero-bias'' resistance. To meet these requirements, Ta$_{2}$O$_{5}$/Al$_{2}$O$_{3}$, ZrO$_{2}$/Al$_{2}$O$_{3}$, and ZrO$_{2}$/Ta$_{2}$O$_{5}$ nanolaminate stacks were deposited using atomic layer deposition (ALD) on Al and Pt electrodes to form MIIM structures. The use of dual dielectrics with different bandgaps and conduction band offsets improves asymmetry of the I-V response. Expected and measured I-V characteristics are compared as a function of insulator material, thickness, and gate metal. [Preview Abstract] |
Tuesday, March 16, 2010 4:30PM - 4:42PM |
L24.00009: Electronic States of Hafnium and Vanadium oxide in Silicon Gate Stack Structure Chiyu Zhu, Fu Tang, Xin Liu, Jialing Yang, Robert Nemanich Vanadium oxide (VO$_{2})$ is a narrow band gap material with a metal-insulator transition (MIT) at less than 100C. Hafnium oxide (HfO$_{2})$ is currently the preferred high-k material for gate dielectrics. To utilize VO$_{2}$ in a charge storage device, it is necessary to understand the band relationships between VO$_{2}$, HfO$_{2}$, and Si substrate. In this study, a 2nm thick VO$_{2}$ layer is embedded in a dielectric stack structure between an oxidized n-type Si(100) surface and a 2nm HfO$_{2}$ layer. The in situ experiments are carried out in an UHV multi-chamber system. After each growth step, the surface is characterized using XPS and UPS. After the initial plasma cleaning and oxidation treatment the Si substrate displayed essentially flat bands at the surface. After deposition of the VO$_{2}$ layer, the Si 2p peak shifted to lower binding energy, and the Si 2p associated with the SiO$_{2}$ layer also was shifted, indicating an internal field in the SiO$_{2}$. The VO$_{2}$ valence band maximum (VBM) was identified at 0.6 eV below the Fermi level (E$_{F})$. This ultra thin VO$_{2}$ exhibits the metal-insulator transition at a temperature higher than thicker films. As a comparison, a 100nm thick film of VO$_{2}$ on Si showed a MIT at 60C. After the HfO$_{2}$ deposition, the Si 2p substrate feature returned to the initial value indicating a return to flat band conditions. The UPS indicated the VBM of HfO$_{2}$ at 4.0 eV below E$_{F}$. This work is supported by the NSF (DMR-0805353). [Preview Abstract] |
Tuesday, March 16, 2010 4:42PM - 4:54PM |
L24.00010: ABSTRACT WITHDRAWN |
Tuesday, March 16, 2010 4:54PM - 5:06PM |
L24.00011: Atomic Layer Deposited Aluminum Oxide / Tantalum Oxide Laminate Films Sean W. Smith, John F. Conley Jr. Nanolaminates offer the possibility of tuning the electrical properties of a dielectric film for specific applications. The use of multiple materials can influence the electrical properties of a film stack and spatial confinement, due to the laminate structure, can affect the crystallization. The conformal, self limiting nature of atomic layer deposition (ALD) makes it ideal for producing thin laminates. ALD was used to deposit nanolaminates of Ta2O5 (k about 25, high leakage) and Al2O3 (k about 8, highly insulating). A MOS test structure was used to look at electrical properties such as dielectric constant, leakage, and breakdown. Spectroscopic ellipsometry, x-ray diffraction, electron microprobe and x-ray reflectivity were used to measure film and bilayer thickness, interfacial roughness, composition, and crystallinity in the laminate. The effect of increasing the number of bilayers, reducing the bilayer thickness, and annealing on the electrical properties and crystal structure of Al2O3/Ta2O5 laminates with a fixed overall composition and thickness is reported. [Preview Abstract] |
Tuesday, March 16, 2010 5:06PM - 5:18PM |
L24.00012: Electrical Properties of MOOM Junctions Fabricated by Electrochemical Anodization Wenbin Fan, Jiwei Lu, Stuart Wolf Localized electrochemical anodization has been used to prepare metal-oxide-oxide-metal (MOOM) diode-like junctions based on granular oxide-metal tunnel junctions. The room-temperature I-V characteristics of MOOM junctions fabricated by anodized aluminum and tantalum thin films were studied. The asymmetric nonlinear I-V curves indicate they behave as diodes. The diode characteristics are strongly determined by the details of anodization process and the amount of each oxide. The High Resolution Transmission Electron Microscope (HRTEM) is used to explore the structure of the MOOM near the interface of two different oxides. Low temperature electrical properties of the MOOM will be reported. [Preview Abstract] |
Tuesday, March 16, 2010 5:18PM - 5:30PM |
L24.00013: Annealing temperature dependence of optical properties of SrTiO$_{3}$/BaTiO$_{3}$ multilayered films on indium tin oxide Satreerat Hodak, Thidarat Supasai, Somsak Dangtip, Punyachai Learngarunsri, Narong Boonyopakorn, Anurat Wisitsoraat We have grown SrTiO$_{3}$/BaTiO$_{3}$ thin films with multilayered structures deposited on indium tin oxide (ITO) coated glass by a sol-gel deposition. The annealing temperatures were varied in the range of 300-650\r{ }C to study the change in optical properties of the films. The absorption edge shifts to longer wavelengths with increasing in annealing temperature. The band gap energy of the films increases in the 3.64-4.19 eV range and the grain size becomes smaller when the annealing temperature decreases. The film annealed at 650\r{ }C showed the maximum refractive index of 2.09-1.91 in the 450-750 nm wavelength range while the extinction coefficient was less than 0.05. The Urbach energy obtained from absorbance data for the multilayer films annealed at 500\r{ }C, 550\r{ }C and 600\r{ }C are 0.272 eV, 0.263 eV and 0.220 eV, respectively. [Preview Abstract] |
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