Browsing by Author "Vijay, Dilip P."

Now showing 1 - 8 of 8
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    Comparison of lead zirconate titanate thin films on ruthenium oxide and platinum electrodes
    Bursill, Les A.; Reaney, Ian M.; Vijay, Dilip P.; Desu, Seshu B. (American Institute of Physics, 1994-02-01)
    High-resolution and bright- and dark-field transmission electron microscopy are used to characterize and compare the interface structures and microstructure of PZT/RuO2/SiO2/Si and PZT/Pt/Ti/SiO2/Si ferroelectric thin films, with a view to understanding the improved fatigue characteristics of PZT thin films with RuO2 electrodes. The RuO2/PZT interface consists of a curved pseudoperiodic minimal surface. The interface is chemically sharp with virtually no intermixing of RuO2 and PZT, as evidenced by the atomic resolution images as well as energy dispersive x-ray analysis. A nanocrystalline pyrochlore phase Pb2ZrTiO7-x, x not equal 1, was found on the top surface of the PZT layer. The PZT/Pt/Ti/SiO2/Si thin film was well crystallized and showed sharp interfaces throughout. Possible reasons for the improved fatigue characteristics of PZT/RuO2/SiO2/Si thin films are discussed.
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    High temperature electrode-barriers for ferroelectric and other capacitor structures
    (United States Patent and Trademark Office, 1998-08-04)
    A capacitor for use on silicon or other substrate has a multilayer electrode structure. In a preferred embodiment, a bottom electrode situated on the substrate has a bottom layer of Pt--Rh--O.sub.x, an intermediate layer of Pt--Rh, and a top layer of Pt--Rh--O.sub.x. A ferroelectric material such as PZT (or other material) is situated on the bottom electrode. A top electrode, preferably of identical composition as the bottom electrode, is situated on the opposite side of the ferroelectric from the bottom electrode.
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    Method of forming multilayered electrodes for ferroelectric devices consisting of conductive layers and interlayers formed by chemical reaction
    (United States Patent and Trademark Office, 1996-02-13)
    A ferroelectric device is constructed using a bottom electrode composed of a conducting oxide such as RuO.sub.x, on a substrate such as silicon or silicon dioxide. A ferroelectric material such as lead zirconate titanate (PZT) is deposited on the bottom electrode, and a conducting interlayer is formed at the interface between the ferroelectric and the electrode. This interlayer is created by reaction between the materials of the ferroelectric and electrode, and in this case would be Pb.sub.2 Ru.sub.2 O.sub.7-x. A conductive top layer is deposited over the ferroelectric. This top layer may be a metal, or it may be the same type of materials as the bottom electrode, in which case another interlayer can be formed at the interface. A device constructed in this manner has the property of lower degradation due to fatigue, breakdown, and aging.
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    Novel high temperature multilayer electrode-barrier structure for high-density ferroelectric memories
    Bhatt, H. D.; Desu, Seshu B.; Vijay, Dilip P.; Hwang, Y. S.; Zhang, X.; Nagata, M.; Grill, A. (AIP Publishing, 1997-08-01)
    This has been accomplished in the past using four/five separate electrode- and diffusion-barrier layers. In this letter, we report a novel Pt-Rh-O-x/Pt-Rh/Pt-Rh-O-x electrode-barrier structure which acts as an electrode as well as a diffusion barrier for integration of the ferroelectric capacitors directly onto silicon deposited using an in situ reactive rf sputtering process. The electrodes have a smooth and fine grained microstructure and are excellent diffusion barriers between the PbZr0.53Ti0.47O3 (PZT) and Si substrate and exhibit good thermal stability up to very high processing temperatures of 700 degrees C. The ferroelectric (PZT) test capacitors using these electrode barriers grown directly on Si, show well saturated hysteresis loops with P-r and E-c of 16 mu C/cm(2) and 30-40 kV/cm, respectively. The capacitors exhibit no significant fatigue loss (<5%) up to 10(11) cycles and have low leakage currents (2X10(-8) A/cm(2) at 100 kV/cm). These electrode barriers can be used to directly integrate the thin film capacitors on the source/drain of the transistors of the memory cell structure for accomplishing large scale integration. (C) 1997 American Institute of Physics.
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    Oriented growth of SrBi2Ta2O9 ferroelectric thin films
    Desu, Seshu B.; Vijay, Dilip P.; Zhang, X.; He, B. P. (AIP Publishing, 1996-09-01)
    We report on the ferroelectric properties of c-axis oriented ferroelectric SrBi2Ta2O9 thin films. Pt/SrBi2Ta2O9/Pt capacitors were grown on single crystal MgO (and/or SrTiO3) substrates using pulsed laser ablation. These substrates provide the necessary template for (100) texture in platinum due to their close lattice matching. This in turn facilitates the c-axis orientation in the ferroelectric films. The degree of orientation in the layered structure ferroelectric film was systematically varied from highly c-axis oriented to random polycrystalline by varying the growth conditions of the bottom metal electrode. The polarization and coercive field values were found to decrease with an increasing degree of c-axis orientation; while the randomly oriented films exhibited a remnant polarization of 5 mu C/cm(2), a coercive field of 70 kV/cm, and a dielectric constant of 320, the c-axis oriented films exhibited very low polarization (similar to 1 mu C/cm(2)), coercivity (22 kV/cm), and dielectric constant (similar to 200) values. (C) 1996 American Institute of Physics.
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    Reactive ion etching of lead zirconate titanate and ruthenium oxide thin films
    (United States Patent and Trademark Office, 1996-03-05)
    A method of reactive ion etching both a lead zirconate titanate ferroelectric dielectric and a RuO.sub.2 electrode, and a semiconductor device produced in accordance with such process. The dielectric and electrode are etched in an etching gas of O.sub.2 mixed with either CClF.sub.2 or CHClFCF.sub.3.
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    Reliability and processing of ferroelectric thin film capacitors with emphasis on fatigue and etching
    Vijay, Dilip P. (Virginia Tech, 1995)
    Ferroelectric materials are characterized by a reversible spontaneous polarization in the absence of an electric field. The characteristic polarization response of a ferroelectric material to an applied electric field enables a binary state device in the form of a thin film ferroelectric capacitor that can be used to store digital information. This provides opportunities for the development of high speed, low cost and low power, nonvolatile memory devices. The development of commercial ferroelectric memory devices has however been hampered by (a) several reliability issues including fatigue, leakage current, aging, time dependent dielectric breakdown, retention and imprint and (b) processing problems including the development of a low temperature thin film deposition process and the development of a patterning technology. Lead zirconate titanate (PZT) is now widely considered as the most promising material for ferroelectric memory applications as a result of its excellent ferroelectric properties and wide operating temperature range. However, it is commonly found that metal electroded-PZT capacitors (e.g., Pt/PZT/Pt) show a loss of switchable polarization with cumulative switching cycles. This phenomenon is known as fatigue and is the one of the critical problems affecting the lifetime of ferroelectric memories. This research is primarily focused on the problem of fatigue. On the basis of a quantitative model, various guidelines to minimize the degradation problem have been derived. The model attributes fatigue to domain pinning by space charge that is caused by defect (e.g. oxygen vacancy) entrapment at various interface sites such as electrode-ferroelectric interface, domain boundaries and grain boundaries. Two different approaches to minimize the problem have been outlined : (a) control of the defect density and (b) control of the interface state. The control of interface state was achieved by replacing the metal electrodes with conducting oxide electrodes such as RuO₂. The oxide electrode/PZT capacitors were characterized for their diffusion barrier properties, perovskite phase formation, interface nature and ferroelectric properties. The results indicate that these oxide electroded PZT films are good candidates for nonvolatile memory applications. However, the leakage current levels at the operating voltages are far higher than the metal counterparts. Simultaneous minimization of fatigue and leakage current in PZT films was achieved by using multilayer metal/conducting oxide electrodes (e.g., Pt/RuO₂). The control of defect density was attained by (a) donor doping to compensate for the oxygen vacancies (e.g, Nb doping in PZT) and (b) utilizing ferroelectric materials that have a low intrinsic defect concentration. As a result of the latter approach, novel ferroelectric materials belonging to the layer-structure family of oxides have been identified as excellent candidates for fatigue free nonvolatile memory applications. Laser ablated SrBi₂(TaxNb1 - x)₂O₉ (0
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    Simple method of fabricating ferroelectric capacitors
    (United States Patent and Trademark Office, 1998-09-15)
    A ferroelectric capacitor device and method of manufacture. A substrate supports a bottom electrode structure, with an adhesion/diffusion barrier layer sandwiched therebetween. The electrode layer includes a metal or metal alloy and an oxide of the metal or alloy. The adhesion/diffusion barrier layer is a similar oxide. Ferroelectric material is sandwiched between a top electrode. The top layer includes a metal or metal alloy and an oxide of the same; the metal or metal alloy may be the same as the bottom electrode but need not be. The metal and metal oxide electrodes may be deposited by known deposition techniques, or the metal may be deposited and the oxide formed by annealing in oxygen ambient environment.