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Clive A Randall - One of the best experts on this subject based on the ideXlab platform.
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Polarity dependent DC Resistance Degradation and electrical breakdown in Nb doped PZT films
APL Materials, 2019Co-Authors: Betul Akkopru-akgun, Clive A Randall, Wanlin Zhu, Michael T. Lanagan, Susan Trolier-mckinstryAbstract:The role of interfacial defect chemistry in time dependent breakdown and associated charge transport mechanisms was investigated for Pb0.99(Zr0.52Ti0.48)0.98Nb0.02O3 (PNZT) films. Electrical Degradation was strongly dependent on the sign of the electric field; a significant increase in the median time to failure from 4.8 ± 0.7 to 7.6 ± 0.4 h was observed when the top electrode was biased negatively compared to the bottom electrode. The improvement in the electrical reliability of Pt/PNZT/Pt films is attributed to (1) a VO•• distribution across the film due to PbO nonstoichiometry and (2) Ti/Zr segregation in PNZT films. Compositional mapping indicates that PbO loss is more severe near the bottom electrode, leading to a VO•• gradient across the film thickness. Upon Degradation, VO•• migration toward the bottom Pt electrode is enhanced. The concentration of VO•• accumulated near the bottom Pt interface (6.2 × 1018/cm3) after Degradation under an electric field of 350 kV/cm for 12 h was two times higher than that near the top Pt/PNZT interface (3.8 × 1018/cm3). The VO•• accumulation near the bottom Pt/PNZT interface causes severe band bending and a decrease in potential barrier height, which in turn accelerates the electron injection, followed by electron trapping by Ti4+. This causes a dramatic increase in the leakage current upon Degradation. In contrast to the bottom Pt/PNZT interface, only a small decrease in potential barrier height for electron injection was observed at the top Pt/PNZT interface following Degradation. It is also possible that a Zr-rich layer near the top interface reduces electron trapping by Ti4+.
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Modification of the Schottky barrier height at the RuO2 cathode during Resistance Degradation of Fe‐doped SrTiO3
Journal of the American Ceramic Society, 2017Co-Authors: Ruth Giesecke, Thorsten J M Bayer, Clive A Randall, Ramis Hertwig, Andreas KleinAbstract:The long‐term stability of electronic devices at high temperatures and electric fields might be strongly influenced by the electronic properties of interfaces. A modification of Schottky barrier heights at electrode interfaces of functional oxides upon changes of the external oxygen partial pressure is well documented in literature. In this work, an experimental approach using X‐ray photoelectron spectroscopy is presented, which enables to study transient changes in the Schottky barrier height induced by electrical Degradation. A rise of the Fermi level at the RuO2 cathode interface of Fe‐doped SrTiO3 single crystals by 0.6 eV is observed in the course of Resistance Degradation. The change of the effective barrier height is associated to the migration of oxygen vacancies towards the cathode and accompanied by the observed reduction of Ti. Different scenarios are discussed to explain the origin of barrier modification and the localization of the reduced Ti.
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the relation of electrical conductivity profiles and modulus data using the example of sto fe single crystals a path to improve the model of Resistance Degradation
Acta Materialia, 2016Co-Authors: Thorsten J M Bayer, Jianjun Wang, Ali Moballegh, Elizabeth C Dickey, Douglas L Irving, Longqing Chen, Jared J Carter, Jonathon N Baker, Clive A RandallAbstract:Abstract Resistance Degradation in perovskites is characterized by an increase in current over time with applied electric field. This behavior can be simulated and spatially resolved conductivity profiles can be measured, but some inconsistencies remain. A new approach to address these problems is presented that utilizes time-resolved impedance spectroscopy with an applied DC voltage to provide new insight into the Resistance Degradation phenomenon. In particular, this method allows the in-situ acquisition of spatio-temporal variations in conductivity. In SrTiO3 a single bulk-dominated maximum of the imaginary part of the modulus M″ transitions to two maxima during Degradation, reflecting the hole conductivity in the anode region and the electron conductivity in the cathode region. To clarify the influence of conductivity profiles on impedance data, the reversed route is presented by using simulated conductivity profiles to calculate impedance data. It will be emphasized that this methodology is not limited to the perovskite system considered here, but can be adapted to any kind of system characterized by a spatially varying conductivity.
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defect chemistry and Resistance Degradation in fe doped srtio3 single crystal
Acta Materialia, 2016Co-Authors: Jianjun Wang, Houbing Huang, Thorsten J M Bayer, Ali Moballegh, Andreas Klein, Elizabeth C Dickey, Douglas L Irving, Clive A Randall, Longqing ChenAbstract:Defect chemistry and transport in Fe-doped SrTiO3 single crystal are studied to understand its Resistance Degradation mechanism. The temporal evolution of electric conductivity under a voltage stress was obtained computationally by solving the transport equations for ionic and electronic defects coupled with the defect reaction equilibrium equations. The computational results are compared to the corresponding experimental measurement under similar conditions. It is shown that the local electron and hole concentrations are controlled by the local electronic defect equilibria rather than by their quasi-steady state diffusional transport. It is the electric field-induced migration of oxygen vacancies and the subsequent instantaneous reestablishment of the local defect equilibria that lead to the Resistance Degradation. The Resistance Degradation behavior and the defect distributions under a long-term voltage stress are strongly influenced by the sample-annealing oxygen partial pressure, degrading electric field, and temperature. The present study contributes to the understanding of Resistance Degradation mechanism and provides guidance to improve the lifetime and reliability of wide band-gap semiconducting capacitors.
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effect of ferroelectric polarization on ionic transport and Resistance Degradation in batio3 by phase field approach
Journal of the American Ceramic Society, 2014Co-Authors: Jie Shen, Clive A Randall, Longqing ChenAbstract:We proposed a model to study the Resistance Degradation behavior of ferroelectric oxides in the presence of ferroelectric spontaneous polarization by combining the phase-field model of ferroelectric domains and nonlinear diffusion equations for ionic/electronic transport. We took into account the nonperiodic boundary conditions for solving the electrochemical transport equations and Ginzburg–Landau equations using the Chebyshev collocation algorithm. We considered a single domain structure relative to a thin film BaTiO3 single crystal orientated to the normal of the electrode plates (Ni) in a single parallel plate capacitor configuration. The capacitor was subjected to a dc bias of 0.5 V either along the polarization direction or opposite to the polarization direction at 25°C. It is shown that the polarization bound charges at the metal/ferroelectric interface play an important role in charge carrier transport and leakage current evolution in BaTiO3 capacitor.
Longqing Chen - One of the best experts on this subject based on the ideXlab platform.
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the relation of electrical conductivity profiles and modulus data using the example of sto fe single crystals a path to improve the model of Resistance Degradation
Acta Materialia, 2016Co-Authors: Thorsten J M Bayer, Jianjun Wang, Ali Moballegh, Elizabeth C Dickey, Douglas L Irving, Longqing Chen, Jared J Carter, Jonathon N Baker, Clive A RandallAbstract:Abstract Resistance Degradation in perovskites is characterized by an increase in current over time with applied electric field. This behavior can be simulated and spatially resolved conductivity profiles can be measured, but some inconsistencies remain. A new approach to address these problems is presented that utilizes time-resolved impedance spectroscopy with an applied DC voltage to provide new insight into the Resistance Degradation phenomenon. In particular, this method allows the in-situ acquisition of spatio-temporal variations in conductivity. In SrTiO3 a single bulk-dominated maximum of the imaginary part of the modulus M″ transitions to two maxima during Degradation, reflecting the hole conductivity in the anode region and the electron conductivity in the cathode region. To clarify the influence of conductivity profiles on impedance data, the reversed route is presented by using simulated conductivity profiles to calculate impedance data. It will be emphasized that this methodology is not limited to the perovskite system considered here, but can be adapted to any kind of system characterized by a spatially varying conductivity.
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defect chemistry and Resistance Degradation in fe doped srtio3 single crystal
Acta Materialia, 2016Co-Authors: Jianjun Wang, Houbing Huang, Thorsten J M Bayer, Ali Moballegh, Andreas Klein, Elizabeth C Dickey, Douglas L Irving, Clive A Randall, Longqing ChenAbstract:Defect chemistry and transport in Fe-doped SrTiO3 single crystal are studied to understand its Resistance Degradation mechanism. The temporal evolution of electric conductivity under a voltage stress was obtained computationally by solving the transport equations for ionic and electronic defects coupled with the defect reaction equilibrium equations. The computational results are compared to the corresponding experimental measurement under similar conditions. It is shown that the local electron and hole concentrations are controlled by the local electronic defect equilibria rather than by their quasi-steady state diffusional transport. It is the electric field-induced migration of oxygen vacancies and the subsequent instantaneous reestablishment of the local defect equilibria that lead to the Resistance Degradation. The Resistance Degradation behavior and the defect distributions under a long-term voltage stress are strongly influenced by the sample-annealing oxygen partial pressure, degrading electric field, and temperature. The present study contributes to the understanding of Resistance Degradation mechanism and provides guidance to improve the lifetime and reliability of wide band-gap semiconducting capacitors.
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effect of ferroelectric polarization on ionic transport and Resistance Degradation in batio3 by phase field approach
Journal of the American Ceramic Society, 2014Co-Authors: Jie Shen, Clive A Randall, Longqing ChenAbstract:We proposed a model to study the Resistance Degradation behavior of ferroelectric oxides in the presence of ferroelectric spontaneous polarization by combining the phase-field model of ferroelectric domains and nonlinear diffusion equations for ionic/electronic transport. We took into account the nonperiodic boundary conditions for solving the electrochemical transport equations and Ginzburg–Landau equations using the Chebyshev collocation algorithm. We considered a single domain structure relative to a thin film BaTiO3 single crystal orientated to the normal of the electrode plates (Ni) in a single parallel plate capacitor configuration. The capacitor was subjected to a dc bias of 0.5 V either along the polarization direction or opposite to the polarization direction at 25°C. It is shown that the polarization bound charges at the metal/ferroelectric interface play an important role in charge carrier transport and leakage current evolution in BaTiO3 capacitor.
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Effect of Ferroelectric Polarization on Ionic Transport and Resistance Degradation in BaTiO3 by Phase‐Field Approach
Journal of the American Ceramic Society, 2014Co-Authors: Ye Cao, Clive A Randall, Jie Shen, Longqing ChenAbstract:We proposed a model to study the Resistance Degradation behavior of ferroelectric oxides in the presence of ferroelectric spontaneous polarization by combining the phase-field model of ferroelectric domains and nonlinear diffusion equations for ionic/electronic transport. We took into account the nonperiodic boundary conditions for solving the electrochemical transport equations and Ginzburg–Landau equations using the Chebyshev collocation algorithm. We considered a single domain structure relative to a thin film BaTiO3 single crystal orientated to the normal of the electrode plates (Ni) in a single parallel plate capacitor configuration. The capacitor was subjected to a dc bias of 0.5 V either along the polarization direction or opposite to the polarization direction at 25°C. It is shown that the polarization bound charges at the metal/ferroelectric interface play an important role in charge carrier transport and leakage current evolution in BaTiO3 capacitor.
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Role of polaron hopping in leakage current behavior of a SrTiO3 single crystal
Journal of Applied Physics, 2013Co-Authors: Ye Cao, Clive A Randall, Jie Shen, Saswata Bhattacharya, Longqing ChenAbstract:We studied the ionic/electronic transport and Resistance Degradation behavior of dielectric oxides by solving the electrochemical transport equations. Here, we took into account the non-periodical boundary conditions for the transport equations using the Chebyshev collocation algorithm. A sandwiched Ni|SrTiO3|Ni capacitor is considered as an example under the condition of 1.0 V, 1.0 μm thickness for SrTiO3 layer, and a temperature of 150 °C. The applied voltage resulted in the migration of ionic defects (oxygen vacancies) from anode towards cathode. The simulated electric potential profile at steady state is in good agreement with the recent experimental observation. We introduced the possibility of polaron-hopping between Ti3+ and Ti4+ at the electrode interface. It is shown that both the oxygen vacancy transport and the polaron-hopping contribute to the Resistance Degradation of single crystal SrTiO3, which is consistent with the experimental observations.
Seok-hyun Yoon - One of the best experts on this subject based on the ideXlab platform.
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Resistance Degradation behavior of Zr-doped BaTiO 3 ceramics and multilayer ceramic capacitor
Journal of Materials Research, 2013Co-Authors: Seok-hyun Yoon, Jeong-ryeol Kim, Sun-ho Yoon, Chang Hoon Kim, Doo Young KimAbstract:Resistance Degradation of zirconium (Zr)-doped barium titanate (BaTiO 3 ) was investigated. A series of Ba(Ti 1− y Zr y )O 3 powders and coarse-grained ceramics ranging y from 0 to 0.1 were prepared. The increase of Zr concentration systematically increased the time to as well as electric field to Degradation. Such behaviors directly corresponded to those of ionic conduction contribution as evaluated by the Warburg impedance. The magnitude of Warburg impedance decreased with the increase of Zr concentration, which demonstrates that the Zr incorporation inhibits the ionic conduction caused by oxygen vacancies. The prototype multilayer ceramic capacitor (MLCC) samples were also prepared by applying these Ba(Ti 1− y Zr y )O 3 base powders and formulated X5R additives of commercial application. In this case, however, such distinct difference in Degradation behavior with the variation of Zr concentration did not appear. It is supposed that the influence of additives far outweighs the effect of relative difference in the ionic conduction of Ba(Ti 1− y Zr y )O 3 under the MLCC test condition where the applied electric field strength is much higher than those for the coarse-grained bulk ceramics. Resistance Degradation of MLCC under such high field might not be explained by only oxygen vacancy-related behavior alone.
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Difference between Resistance Degradation of fixed valence acceptor (Mg) and variable valence acceptor (Mn)-doped BaTiO3 ceramics
Journal of Applied Physics, 2010Co-Authors: Seok-hyun Yoon, Clive A Randall, Kang-heon HurAbstract:The difference in the Resistance Degradation behavior was investigated between fixed valence acceptor (Mg) and the variable valence acceptor (Mn)-doped BaTiO3 ceramics with an increase of each acceptor concentration. Coarse-grained specimens with uniform grain sizes and different acceptor concentrations were prepared. In the case of Mg-doped BaTiO3, the time to Degradation systematically decreased with the increase in Mg concentration. In contrast, there is a systematically increased time to Degradation with the increase in Mn concentration in Mn-doped BaTiO3. The fast Degradation by the increase in Mg concentration directly corresponded to an increase in the Warburg impedance and ionic transference number (tion) associated with an increase in oxygen vacancy concentration ([VO••]). On the other hand, no distinct Warburg impedance or ionic conduction contribution could be observed with the increase in Mn concentration. It is supposed that the increase in [VO••] is negligible in spite of the increase in acc...
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correlation between Resistance Degradation and thermally stimulated depolarization current in acceptor mg doped batio3 submicrometer fine grain ceramics
Journal of the American Ceramic Society, 2010Co-Authors: Seok-hyun Yoon, Clive A RandallAbstract:Thermally stimulated depolarization current (TSDC) of acceptor (Mg)-doped BaTiO3 ceramics was analyzed for submicrometer fine grain specimens. For a fixed condition of polarization field (EP) and polarization time (tP), the TSDC associated with an oxygen vacancyrelaxation showed two peaks with relaxation temperatures (Tm) under low polarization temperature (TP) conditions. It is inferred that the TSDC peak of the lower Tm is due to the relaxation of adistributed space charge within a grain and has a short relaxation time constant (τ0), and the higher Tm is due to the long-range relaxation across grain boundaries with a larger time constant, τ0. The onset condition for Resistance Degradation can be correlated with the breaking point of TP, at which the TSDC peak changes from in-grain relaxation to across-grain boundary relaxation. The breaking point of TP and the time to Degradation systematically decreased with the increase of acceptor concentration. Such behavior can be correlated with the decrease of TP, Tm, τ0, and little change of activation energy ofrelaxation, which is due to the increase ofconcentration.
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Resistance Degradation behavior of Ca-doped BaTiO3
Journal of Materials Research, 2010Co-Authors: Seok-hyun Yoon, Sung-hyung Kang, Sang Hoon Kwon, Kang-heon HurAbstract:Resistance Degradation of Ca-doped BaTiO 3 ceramics was investigated. A series of coarse and fine-grained (Ba 1– x Ca x )TiO 3 with only Ba site incorporation ranging x from 0 to 0.1, and Ba(Ti 1– y Ca y )O 3 ceramics with only Ti site incorporation ranging y from 0 to 0.015, were prepared with similar grain sizes. The increase of x did not cause any distinct difference in Degradation, whereas an increase in y caused a significant Resistance Degradation in both coarse and fine-grained specimens. The variation of ionic transference number ( t ion ) as evaluated by the Warburg impedance was negligible with increase in x , but significantly increased with the increase in y . These results demonstrate that the decrease of lattice parameters and lattice shrinkage by the Ba site incorporation of Ca has little influence on the Resistance Degradation, and that the oxygen vacancy concentration generated by the Ti site incorporation of acceptor Ca is a very important factor that governs Resistance Degradation.
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Influence of Grain Size on Impedance Spectra and Resistance Degradation Behavior in Acceptor (Mg)‐Doped BaTiO3 Ceramics
Journal of the American Ceramic Society, 2009Co-Authors: Seok-hyun Yoon, Clive A Randall, Kang-heon HurAbstract:The effect of acceptor concentration in (Mg)-doped BaTiO3 on the Resistance Degradation behavior was contrasted between coarse- and fine-grain samples with ∼90 and ∼0.8 μm in size, respectively. Both cases showed similar trends that the time to Degradation decreased systematically with the increase of acceptor concentration, however the absolute rates are very different for a given dopant concentration. Although the grain size and grain boundaries are important, it is also shown through an impedance analysis that the Degradation behavior depends on the grain conductivity (σg) and ionic transference number (tion) as evaluated by the Warburg impedance. Under the condition of the same nominal acceptor concentration, fine-grain samples showed much lower grain conductivity (σg) but little differences in the grain boundary conductivity (σgb) than that of coarse-grain samples. The ionic transference number (tion) was also much smaller in fine-grain samples. These results show that the actual effective acceptor concentration on being ionically compensated to enhance oxygen vacancies becomes smaller with the decrease of grain size. This fact coupled to the increase of the number of grain boundaries accounts for the improved Degradation behavior with the decrease of grain size.
Jack C. Lee - One of the best experts on this subject based on the ideXlab platform.
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The niobium doping effects on Resistance Degradation of strontium titanate thin film capacitors
Applied Physics Letters, 1999Co-Authors: Jian Hung Lee, Razak Mohammedali, Jeong H. Han, Venkatasubramani Balu, Sundararaman Gopalan, Chun Hui Wong, Jack C. LeeAbstract:The rate of Resistance Degradation of thin (
Jie Shen - One of the best experts on this subject based on the ideXlab platform.
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effect of ferroelectric polarization on ionic transport and Resistance Degradation in batio3 by phase field approach
Journal of the American Ceramic Society, 2014Co-Authors: Jie Shen, Clive A Randall, Longqing ChenAbstract:We proposed a model to study the Resistance Degradation behavior of ferroelectric oxides in the presence of ferroelectric spontaneous polarization by combining the phase-field model of ferroelectric domains and nonlinear diffusion equations for ionic/electronic transport. We took into account the nonperiodic boundary conditions for solving the electrochemical transport equations and Ginzburg–Landau equations using the Chebyshev collocation algorithm. We considered a single domain structure relative to a thin film BaTiO3 single crystal orientated to the normal of the electrode plates (Ni) in a single parallel plate capacitor configuration. The capacitor was subjected to a dc bias of 0.5 V either along the polarization direction or opposite to the polarization direction at 25°C. It is shown that the polarization bound charges at the metal/ferroelectric interface play an important role in charge carrier transport and leakage current evolution in BaTiO3 capacitor.
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Effect of Ferroelectric Polarization on Ionic Transport and Resistance Degradation in BaTiO3 by Phase‐Field Approach
Journal of the American Ceramic Society, 2014Co-Authors: Ye Cao, Clive A Randall, Jie Shen, Longqing ChenAbstract:We proposed a model to study the Resistance Degradation behavior of ferroelectric oxides in the presence of ferroelectric spontaneous polarization by combining the phase-field model of ferroelectric domains and nonlinear diffusion equations for ionic/electronic transport. We took into account the nonperiodic boundary conditions for solving the electrochemical transport equations and Ginzburg–Landau equations using the Chebyshev collocation algorithm. We considered a single domain structure relative to a thin film BaTiO3 single crystal orientated to the normal of the electrode plates (Ni) in a single parallel plate capacitor configuration. The capacitor was subjected to a dc bias of 0.5 V either along the polarization direction or opposite to the polarization direction at 25°C. It is shown that the polarization bound charges at the metal/ferroelectric interface play an important role in charge carrier transport and leakage current evolution in BaTiO3 capacitor.
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Role of polaron hopping in leakage current behavior of a SrTiO3 single crystal
Journal of Applied Physics, 2013Co-Authors: Ye Cao, Clive A Randall, Jie Shen, Saswata Bhattacharya, Longqing ChenAbstract:We studied the ionic/electronic transport and Resistance Degradation behavior of dielectric oxides by solving the electrochemical transport equations. Here, we took into account the non-periodical boundary conditions for the transport equations using the Chebyshev collocation algorithm. A sandwiched Ni|SrTiO3|Ni capacitor is considered as an example under the condition of 1.0 V, 1.0 μm thickness for SrTiO3 layer, and a temperature of 150 °C. The applied voltage resulted in the migration of ionic defects (oxygen vacancies) from anode towards cathode. The simulated electric potential profile at steady state is in good agreement with the recent experimental observation. We introduced the possibility of polaron-hopping between Ti3+ and Ti4+ at the electrode interface. It is shown that both the oxygen vacancy transport and the polaron-hopping contribute to the Resistance Degradation of single crystal SrTiO3, which is consistent with the experimental observations.