Ferroelectric DRAM's

Tuesday, April 11, 2000 1:30 PM in Room Sunrise

Start Invited? Item
1:30 PM H3-1 Synthesis and Characterization of Sol-gel Derived Ferroelectric Thin Films
R.S. Katiyar, S.B. Majumder (University of Puerto Rico)
Ferroelectric thin films are the key elements of a variety of integrated devices including non-volatile memories, pyroelectric infra-red detectors, electro-optic wave guides etc. Among the various thin film deposition techniques, sol-gel processing is emerging as an attractive alternative to yield excellent quality ferroelectric thin films at relatively lower cost. In our laboratory we have synthesized a variety of perovskite (viz. PLT, BST, KTN) and tungsten bronze (SBN) thin films by sol-gel technique and characterize them it terms of their structural, microstructural, optical, and ferroelectric properties. A device quality ferroelectric thin film should be stoichiometric, dense in microstructure, and epitaxially grown for certain applications. In this review article we have demonstrated the effect of several intrinsic ( eg. thickness of the film, electrode materials, process temperature) and extrinsic (addition of dopants) parameters on the growth and properties of the deposited films.
2:10 PM H3-3 Challenges in Mass Production of PZT for Non-volatile Memory, Pyroelectric and Piezoelectric Applications
G.R. Fox, F. Chu, S. Sun, J. Ortega (Ramtron International Corp.); Unknown Trolier-McKinstry (Penn State)
Ferroelectric PbZrxTi1-xO3 (PZT) is the core component of mass produced ferroelectric random access memories (FRAM). In addition to FRAM memories, PZT is also under development for integrated pyroelectric infrared sensor arrays and piezoelectric sensors and actuators. In order to mass produce PZT for reproducible device performance and reliability, there are several materials challenges that must be overcome. Since PZT is a multi-element material that must be crystallized at temperatures between 600 and 700?C, it is necessary to control the stoichiometry throughout the deposition and crystallization processes. Because of the polar nature of PZT, it is necessary to control the crystallographic texture such that the switching and non-switching polarization response is consistent for device performance. Structuring of the PZT and associated electrode films also presents significant challenges to the integration of PZT. Standard photolithography and etching processes can severely degrade the PZT electrical performance even if PZT thin film growth is properly controlled. A review of the factors controlling PZT stoichiometry and texture will be presented along with a description of process control metrics. These factors will be linked to the performance structured devices for memory, pyroelectric and piezoelectric
2:50 PM H3-5 Epitaxial Growth and Characterization of (BaSr)TiO@sub 3@ Thin Films for Tunable Microwave Applications
C.L. Chen, G.P. Luo (University of Houston); Y. Liou (Institute of Physics); S.Y. Chen, Z. Zhang (University of Houston); F.A. Miranda (NASA Glenn Research Center); F. Van Keuls (NASA Glenn Research Lab)
Perovskite ferroelectric Ba@sub1-x@Sr@subx@TiO@sub 3@ (BSTO) thin films with x = 0, 0.50, 0.60, 0.75, and 1.00 have been synthesized on various substrates, such as (001) LaAlO@sub 3@and (001) MgO substrates by pulsed laser ablation. The epitaxial behavior and the microstructures of the as-grown perovskite oxide films have been systematically studied by using extensive X-ray diffraction, rocking curve and pole-figure measurement, selected-area electron diffraction, electron microscopy, and Rutherford Backscattering Spectrometry. The as-grown films exhibit excellent crystalline quality with an ion beam minimum yield of less than 3.0 %. High-resolution electron microscopy studies reveal the interfaces between the film and substrates are atomic sharp. The dielectric property measurements for the BSTO film on LAO by the interdigital technique at 1 MHz show the room temperature values of the relative dielectric constant and loss tangent are 1430 and 0.007 with no bias, and 960 and 0.001 with 35 V bias, respectively, which suggest that the films can be used for development of room-temperature high-frequency tunable elements. Also, the growth mechanisms of these oxide thin films have been studied by UHV- STM and -AFM, suggested that the epitaxial behavior are high dependent on the film growth conditions. Edge dislocations at interfaces were directly revealed in the HREM studies. Details will be presented in the talk.
3:30 PM H3-7 Local Optical Probes of Thin-Film Electro-Optic Materials
J. Levy, C. Hubert, O. Tikhomirov (University of Pittsburgh)
Large dielectric losses still limit the usefulness of ferroelectric thin films for frequency agile microwave devices. Obtaining a physical understanding of the important mechanisms of microwave dielectric loss is important for a number of applications. The linear electro-optic effect, which couples the ferroelectric polarization to reflectivity changes, allows a number of high spatial and temporal resolution optical techniques to be used. They include: quasi-static, dynamic, and temperature-dependent confocal scanning optical microscopy (CSOM), and apertureless near-field scanning optical microscopy (ANSOM). Quasistatic CSOM and ANSOM measurements reveal a spatially inhomogeneous polarization in BaxSr1-xTiO3 thin films that is reminiscent of relaxor ferroelectrics. The phase transition for thin films is broadened out significantly compared to the bulk, due most likely to inhomogeneous strain induced from the substrate and the presence of Oxygen vacancies. Time-resolved CSOM measurements performed at GHz frequencies reveal local regions of large dielectric loss from the ferroelectric mode. A remarkable feature of our results concerns the bias dependence of the local dielectric loss. The distribution of local loss tangents widens significantly as the bias field is increased. We believe this phenomena is due to an uneven growth of in-plane ferroelectric nanodomains, whose dielectric relaxation frequency dpeends strongly on size. CSOM measurements taken as a function of temperature will also be presented. This work is supported by ONR (N00173-98-1-G011) and by NSF (DMR-9701725).
4:10 PM H3-9 Thin Films of Lithium Intercalation Complex Oxides for Cathods
S. Nieto-Ramos, M.S. Tomar, S. Hernandez, F. Aliev (University of Puerto Rico)
Lithium intercalation materials are of special interest for the cathodes of rechargeable battery. We developed a novel chemical route for the synthesis of Li(Mn,Co,Ni) mixed oxides, and thin films were deposited on several substrates by spin coating. Annealed films were analyzed by x-ray diffraction and dielectric spectroscopy. X-rays show single phase polycrystalline films. The temperature dependent dielectric spectroscopy shows ionic conduction. These films can be used in thin film microbattery as cathodes with polymer-ceramic as an electrolyte, and the work is in progress.