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Enhanced negative capacitance in La-doped Pb(Zr$_{0.4}$Ti$_{0.6}$)O$_3$ ferroelectric capacitor from tuning of bias voltage pulse

Ganga S. Kumar, Sudipta Goswami, Subhashree Chatterjee, Dilruba Hasina, Miral Verma, Devajyoti Mukherjee, Chandan Kumar Ghosh, Dipten Bhattacharya

TL;DR

The study addresses how bias voltage pulse amplitude and timescale control transient negative capacitance ($C_{NC}$) in multidomain La-doped PLZT ferroelectric capacitors. Using combined experiments on (001) and (111) PLZT/LMSO/STO heterostructures and phase-field simulations based on the time-dependent Ginzburg–Landau framework, it demonstrates that $C_{NC}$ peaks when domain-wall length during switching is maximized, at a characteristic amplitude $V_f$ and timescale $t_m$ (e.g., 0.5 ms for (111) and 1 ms for (001)). The mean switching time from a Lorentz-distributed nucleation process matches the maxima, and the $P$–$V$ loop’s radius of curvature at the coercive voltage $V_C$ tracks the negative capacitance magnitude, tying switching kinetics to NC behavior. The work shows how domain-switching pathways, defect-mediated nucleation, and pulse profiling co-determine $C_{NC}$ and suggests routes to engineer NC-based devices and sensors by controlling domain-wall density during switching.

Abstract

We report a remarkable bias voltage dependent specific negative capacitance in multidomain La-doped Pb(Zr$_{0.4}$Ti$_{0.6}$)O$_3$ (PLZT) ferroelectric capacitors. The specific negative capacitance maximizes at a specific bias voltage because of emergence of maximum domain-wall density during ``switching" of the domains. Domain configuration changes from such an ``optimum" state if higher or lower bias voltage is applied at a much faster or slower rate. Phase-field simulation using time-dependent Ginzburg-Landau equation corroborates the experimental results and shows dependence of the domain-wall length during switching on the bias voltage amplitude and its maximization at a specific bias voltage amplitude. Interestingly, the radius of curvature of the resulting polarization ($P$) versus voltage ($V$) hysteresis loop at the coercive voltage ($V_C$), as well, turns out to be depending on the bias voltage. All these results indicate a close correlation among the bias voltage pulse profile (amplitude and time scale), domain-wall length during switching, shape of the resulting ferroelectric hysteresis loop, and the transient negative capacitance. It may have important ramifications both in the context of physics behind negative capacitance in a multidomain ferroelectric capacitor and devices being developed by exploiting its advantages.

Enhanced negative capacitance in La-doped Pb(Zr$_{0.4}$Ti$_{0.6}$)O$_3$ ferroelectric capacitor from tuning of bias voltage pulse

TL;DR

The study addresses how bias voltage pulse amplitude and timescale control transient negative capacitance () in multidomain La-doped PLZT ferroelectric capacitors. Using combined experiments on (001) and (111) PLZT/LMSO/STO heterostructures and phase-field simulations based on the time-dependent Ginzburg–Landau framework, it demonstrates that peaks when domain-wall length during switching is maximized, at a characteristic amplitude and timescale (e.g., 0.5 ms for (111) and 1 ms for (001)). The mean switching time from a Lorentz-distributed nucleation process matches the maxima, and the – loop’s radius of curvature at the coercive voltage tracks the negative capacitance magnitude, tying switching kinetics to NC behavior. The work shows how domain-switching pathways, defect-mediated nucleation, and pulse profiling co-determine and suggests routes to engineer NC-based devices and sensors by controlling domain-wall density during switching.

Abstract

We report a remarkable bias voltage dependent specific negative capacitance in multidomain La-doped Pb(ZrTi)O (PLZT) ferroelectric capacitors. The specific negative capacitance maximizes at a specific bias voltage because of emergence of maximum domain-wall density during ``switching" of the domains. Domain configuration changes from such an ``optimum" state if higher or lower bias voltage is applied at a much faster or slower rate. Phase-field simulation using time-dependent Ginzburg-Landau equation corroborates the experimental results and shows dependence of the domain-wall length during switching on the bias voltage amplitude and its maximization at a specific bias voltage amplitude. Interestingly, the radius of curvature of the resulting polarization () versus voltage () hysteresis loop at the coercive voltage (), as well, turns out to be depending on the bias voltage. All these results indicate a close correlation among the bias voltage pulse profile (amplitude and time scale), domain-wall length during switching, shape of the resulting ferroelectric hysteresis loop, and the transient negative capacitance. It may have important ramifications both in the context of physics behind negative capacitance in a multidomain ferroelectric capacitor and devices being developed by exploiting its advantages.

Paper Structure

This paper contains 5 sections, 5 equations, 13 figures.

Table of Contents

  1. Introduction
  2. Experimental Details
  3. Computational Details
  4. Results and Discussion
  5. Conclusion

Figures (13)

  • Figure 1: XRD $\theta-2\theta$ patterns of (a) PLZT/LSMO/STO (111) and (b) PLZT/LSMO/STO (001) thin film heterostructures. Insets show the detector scan of asymmetric and symmetric planes for the PLZT/LSMO/STO (111) and PLZT/LSMO/STO (001) film. Reciprocal space mapping about (c) STO (111) symmetric plane of PLZT/LSMO/STO (111) and about (d) STO (113) asymmetric plane of PLZT/LSMO/STO (001) thin film heterostructures, respectively.
  • Figure 2: (a), (c) The polarization ($P$) versus bias voltage ($V$) ferroelectric hysteresis loops recorded by using standard triangular bipolar voltage pulse of different time scale for, respectively (111) and (001) films; (b), (d) corresponding variation of the $V_C$ with time scale of the bias voltage pulse.
  • Figure 3: The coercive voltage $V_C$ versus frequency $f$ plots for (a) (111) and (b) (001) films; the data follow $V_C \propto f^{\$alpha}$ power law dependence; $\alpha$ changes at a specific frequency.
  • Figure 4: (a) The height, PFM amplitude, and PFM phase images of (a) (111) and (b) (001) PLZT film. The upper panel PFM images are collected under zero bias tip voltage, whereas the lower panel images are collected under $\pm$4 V tip bias. Box-in-box pattern in the lower panel images are created by two steps electric poling with -4 V and +4 V tip bias. Scale bar is 1 $\mu$m.
  • Figure 5: The PFM switching-spectroscopy (PF-SS) on an arbitrary point of both the films. (a)-(b) Local ferroelectric butterfly-shaped amplitude loops and (c)-(d) local hysteresis phase loops as a function of the applied voltage for (111) and (001) films, respectively.
  • ...and 8 more figures