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  • 1
    Electronic Resource
    Electronic Resource
    Thickness dependence of structural and electrical properties in epitaxial lead zirconate titanate films (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 595-602 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the effect of misfit strain on the microstructure and properties of ferroelectric lead zirconate titanate thin films. We have changed the misfit strain by varying the film thickness and studied the thickness effect on the domain formation of epitaxial PbZr0.2Ti0.8O3 (PZT) films grown by pulsed laser deposition on (001) LaAlO3 substrates with La0.5Sr0.5CoO3 (LSCO) electrodes. The nominal thickness of the PZT films was varied from 60 to 400 nm with the LSCO electrode thickness kept constant at 50 nm. X-ray diffraction experiments show that the films relax via the formation of a domains, the fraction of which increase with the ferroelectric film thickness. The c-axis lattice constant of PZT films calculated from the 002 reflection decreases with increasing film thickness and approaches the bulk value of ∼0.413 nm in the films thicker than 300 nm. Cross-sectional transmission electron microscopy images reveal that the a-domain fraction and period increase with increasing film thickness. The relaxation of misfit strain in the film is accompanied by systematic changes in the polarization properties, as well as the switching fields, quantified by the coercive field and the activation field. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370772
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of contact electrodes on leakage characteristics in ferroelectric thin films (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 375-382 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrodes can impact the device performance of ferroelectric capacitors in several ways. The present controlled studies on Pb (Nb, Zr, Ti)O3 with Pt, (La, Sr)CoO3 and SrRuO3 is a clear demonstration of the role of electrodes in impacting the leakage current mechanism of the ferroelectric capacitors and their reliability properties. The oxide electrode capacitors show predominantly nonblocking contact and good fatigue and imprint properties. Pt electrode capacitors show blocking contacts, long term leakage current relaxation, and poor fatigue and imprint properties. The nature of the temperature and voltage dependence of leakage current relaxation in Pt capacitors indicates trapping of charge carriers to be the cause for the observed relaxation. A good correlation between leakage current relaxation and the rate of polarization loss during fatigue and the similarity in their voltage and temperature dependence suggests trapping (of charged carriers/domains, respectively) as common to both phenomena. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1371947
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  • 3
    Electronic Resource
    Electronic Resource
    (Ba,Sr)TiO3 thin films with conducting perovskite electrodes for dynamic random access memory applications (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3194-3196 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Interfaces and hence electrodes determine the performance of (Ba,Sr)TiO3 (BST) capacitors for ultralarge scale integration dynamic random access memories. Electrode materials forming a rectifying contact on BST drastically reduce the dielectric constant and hence the capacitance and charge storage density of the capacitor, when the dielectric thickness is reduced. This can limit the role of Pt as an electrode material for gigabit dynamic random access memories (DRAM). The conducting oxide, La0.5Sr0.5CoO3 (LSCO) with its perovskite structure, has structural and chemical compatibility with BST. Our results in LSCO/BST/LSCO capacitor show that the mechanism of conduction is not interface limited but predominantly bulk limited. A 75 nm BST film with LSCO electrodes shows a leakage current density of 1×10−7 A/cm2 at 1 V, 85 °C. The dielectric constant at 1 V, 105 Hz is 350, making LSCO a potential contact electrode for DRAM memories. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124104
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  • 4
    Electronic Resource
    Electronic Resource
    Activation field of ferroelectric (Pb,La)(Zr,Ti)O3 thin film capacitors (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2211-2213 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report results on the activation field and frequency dependence of the coercive voltage in epitaxial ferroelectric thin film capacitors. Frequency dependent hysteresis loops and pulse width dependent polarization of epitaxial La0.5Sr0.5CoO3/(Pb,La)(Zr,Ti)O3/La0.5Sr0.5CoO3 capacitor structures were measured as a function of La content. The coercive voltages and their frequency dependence vary systematically with increasing La content. We show that the activation field for polarization reversal is directly related to the c/a ratio (tetragonality ratio) of the ferroelectric layer. A larger c/a ratio leads to a larger field to activate the motion of domain walls through the lattice. An important consequence of a larger activation field is a stronger pulse width dependence of the pulse switched polarization. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119383
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of cationic stoichiometry of La1−xSrxCoO3 electrodes on the ferroelectric properties of lead based thin film memory elements (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 1617-1624 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In earlier publications, we have demonstrated that La0.5Sr0.5CoO3 electrodes dramatically improve the phase stability and electrical properties of lead based ferroelectric capacitors. This study evaluates the influence of deviation from the cationic stoichiometry, La/Sr=1, on the ferroelectric properties. Polycrystalline Pb(Nb0.04Zr0.18Ti0.78)O3 based capacitors were fabricated with La0.5Sr0.5CoO3 as the bottom electrode and either La0.5Sr0.5CoO3 or La0.85Sr0.15CoO3 as the top electrode. The as-grown capacitors with La0.85Sr0.15CoO3 as the top electrode were slightly asymmetric about the voltage axis. However, the asymmetry did not increase when the capacitors were subjected to single side pulses and temperature. Both capacitor structures showed good fatigue (no fatigue up to 1011 cycles), retention, and imprint characteristics. Detailed pulse width and voltage dependent measurements were also carried out to further understand the impact of the change in electrode composition. The polarization values at 1 μs pulse width were as large as 13 μC/cm2, though the dependence was steeper for capacitors with asymmetric electrodes. The resistance to switching during polarization reversal, formally termed activation field, α, was measured from the switching current dependence of the applied field. These values were slightly larger for the capacitors with asymmetric electrodes. The data indicate that the ferroelectric properties of the capacitor are almost not influenced by a change of the top electrode from La0.5Sr0.5CoO3 to La0.85Sr0.15CoO3.© 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366874
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  • 6
    Electronic Resource
    Electronic Resource
    Evaluation of imprint in fully integrated (La,Sr)CoO3/Pb(Nb,Zr,Ti)O3/(La,Sr)CoO3 ferroelectric capacitors (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 2165-2171 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the imprint characteristics of fully integrated ferroelectric lead zirconate titanate based capacitors. These capacitors were fabricated using conducting perovskite La–Sr–Co–O electrodes. We have specifically focused on the effect of several test and capacitor variables, including temperature, unipolar stress amplitude, number of cycles, and device area. Two different figures of merit, one based on coercive voltage changes and the other based on differences in polarization values were used to quantify imprint. The imprint in our capacitors showed a small temperature dependence over the range that we have studied. The unidirectional pulse voltage amplitude had a larger influence on the imprint. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366954
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  • 7
    Electronic Resource
    Electronic Resource
    Oxide electrodes as barriers to hydrogen damage of Pb(Zr,Ti)O3-based ferroelectric capacitors (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3023-3025 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ferroelectric properties of Pb(Zr,Ti)O3 films are known to degrade when subjected to forming gas anneals. In an earlier publication we established that although there may be loss of oxygen and lead during forming gas anneal, the primary mechanism for loss of ferroelectricity is the incorporation of hydrogen and subsequent formation of [OH]−1 bonds between the ionized hydrogen and oxygen ions along the polarization axis in the octahedra. In this study, we show that (La,Sr)CoO3 oxide electrodes can act as a diffusion barrier to hydrogen during forming gas anneals. Forming gas anneal at lower temperatures such as 200 and 300 °C does not lead to a measurable loss of polarization. There is some loss of polarization during forming gas anneals at 450 °C for 〈fraction SHAPE="CASE"〉12 h, however the capacitors still exhibit ferroelectric properties. The capacitors show no fatigue up to 1011 cycles, no imprint, good logic state retention characteristics, and similar slopes for the pulse width dependent polarization values before and after forming gas anneal in the measured range. More importantly, we have demonstrated that even a bare La0.5Sr0.5CoO3 top electrode can prevent the complete loss of ferroelectricity during forming gas treatment. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124052
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  • 8
    Electronic Resource
    Electronic Resource
    Conducting barriers for vertical integration of ferroelectric capacitors on Si (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 230-232 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One of the issues impeding the commercialization of nonvolatile ferroelectric memories is the identification and development of a conducting diffusion barrier for the vertical integration of ferroelectric capacitors on Si-based transistors. We report results on the use of Ti–Al alloys as such a diffusion barrier. Our results indicate that it maintains its structural integrity and electrical conductivity after the deposition of a lead-based ferroelectric stack at 650 °C. The electrical properties of the capacitors were measured through the barrier layer by making direct contact to the diffusion barrier. The properties of the capacitors measured by direct contact to the Ti–Al alloy show clearly the absence of an insulating interfacial layer. Transmission electron microscopy and Rutherford backscattering studies confirm that there is no oxidation of the conducting barrier and no reaction between it and the electrode. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123301
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of hydrogen on Pb(Zr,Ti)O3-based ferroelectric capacitors (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1973-1975 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The properties of ferroelectric films are known to degrade when subjected to hydrogen in forming gas anneals. Earlier studies have attributed this degradation to the loss of oxygen from these films during these anneals. In this study, we show that though oxygen is lost during forming gas annealing, hydrogen incorporation is the primary mechanism for the degradation of ferroelectric properties. Raman spectra obtained from the forming gas-annealed films show evidence of polar hydroxil [OH−] bonds in the films. The most probable site for hydrogen ions is discussed based on ionic radii, crystal structure, electrical properties, and Raman spectra. We propose that the hydrogen ion is bonded with one of the apical oxygen ions and prevents the Ti ion from switching. Pyroelectric measurements on forming gas-annealed capacitors confirm that the capacitors no longer possess spontaneous polarization. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122339
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  • 10
    Electronic Resource
    Electronic Resource
    Dynamics of polarization loss in (Pb, La)(Zr, Ti)O3 thin film capacitors (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 3300-3302 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report results of high-speed polarization relaxation measurements in ferroelectric thin film capacitors. Polarization relaxation has been reported to occur in two distinct time regimes, one for relaxation times in the range of a few milliseconds and a second for longer relaxation times. We find that the polarization relaxation in the first regime is governed by at least two different physical processes, namely depoling fields and the activation field for switching. Using prototypical epitaxial PbZr0.2Ti0.8O3 and Pb0.9La0.1Zr0.2Ti0.8O3 test capacitors, we demonstrate the effect of film microstructure and switching speed on the relaxation dynamics in the first regime. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121630
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