Pulsed laser ablation deposition was used to synthesize polycrystalline SrBi₂Ta₂O₉ layered ferroelectric thin films on platinized silicon substrates. Top electrodes were produced by dc magnetron sputter deposition to fabricate capacitors for electrical tests. The polarization electric field hysteresis loops showed saturation in the 2–4 V range with a coercive field of 25 kV/cm. The capacitors showed practically no polarization fatigue up to 10¹¹ switching cycles. The resistivity of the SrBi₂Ta₂O₉ for a coercive field of 100 kV/cm was approximately 2×10¹¹ Ω cm. Retention and imprint characteristics of these capacitors showed no degradation as a function of cumulative waiting times.

Epitaxial Bi 4 Ti 3 O 12 (BTO) thin films were deposited on MgO(001) substrates using Pt layers as top and bottom electrodes. In spite of the apparently symmetric capacitorstructure, polarization–voltage measurements revealed strong imprint failures and current–voltage measurements showed rectifying behaviors. Imprint pulse tests with a 5 V dc bias and post-annealing treatments suggested that the asymmetric behaviors should be due to interfacial states induced by thermal processes. To probe the interfacial states, capacitance–voltage (C–V) measurements were performed. By fitting the C–V data with a model which describes the Pt/BTO/Pt structure as a series circuit composed of three capacitors, built-in voltages at the top and the bottom interfaces could be determined. Difference in the built-in voltages could explain the imprint failures and the rectifying behaviors. The interfacial states in the BTO capacitors were controlled by varying electrode materials.

The damage of ${\mathrm{Pb(Zr}}_{\mathrm{0.53}}{\mathrm{Ti}}_{\mathrm{0.47}}{\mathrm{)O}}_{\mathrm{3}}$ thin film due to dry etching process was characterized in terms of the microstructure and electrical properties. The damaged layer seems to be amorphous and the thickness of the damaged layer is about 10 nm. The existence of such a layer in ${\mathrm{Pt/Pb(Zr}}_{\mathrm{0.53}}{\mathrm{Ti}}_{\mathrm{0.47}}{\mathrm{)O}}_{\mathrm{3}}\mathrm{/Pt}$ ferroelectric capacitor tends to increase the coercive voltage and the leakage current. The damaged layer was not fully reverted to perovskite phase by the thermal annealing. With the wet cleaning treatment, however, the damaged layer was successfully removed thereby revealing significantly improved electrical properties.

A piezoelectric nanogenerator (PNG) that is based on c-axis GaN nanowires is fabricated on flexible substrate. In this regard, c-axis GaN nanowires were grown on GaN substrate using the vapor-liquid-solid (VLS) technique by metal organic chemical vapor deposition. Further, Polydimethylsiloxane (PDMS) was coated on nanowire-arrays then PDMS matrix embedded with GaN nanowire-arrays was transferred on Si-rubber substrate. The piezoelectric performance of nanowire-based flexible PNG was measured, while the device was actuated using a cyclic stretching-releasing agitation mechanism that was driven by a linear motor. The piezoelectric output was measured as a function of actuation frequency ranging from 1 Hz to 10 Hz and a linear tendency was observed for piezoelectric output current, while the output voltages remained constant. A maximum of piezoelectric open circuit voltages and short circuit current were measured 15.4 V and 85.6 nA, respectively. In order to evaluate the feasibility of our flexible PNG for real application, a long term stability test was performed for 20,000 cycles and the device performance was degraded by less than 18%. The underlying reason for the high piezoelectric output was attributed to the reduced free carriers inside nanowires due to surface Fermi-level pinning and insulating metal-dielectric-semiconductor interface, respectively; the former reduced the free carrier screening radially while latter reduced longitudinally. The flexibility and the high aspect ratio of GaN nanowire were the responsible factors for higher stability. Such higher piezoelectric output and the novel design make our device more promising for the diverse range of real applications.

The retention characteristics of ${\mathrm{Ir/IrO}}_2/\mathrm{Pb}({\mathrm{Zr}}_{\text{0.4}}{\mathrm{Ti}}_{\text{0.6}}){\mathrm{O}}_3(\mathrm{PZT}\mathrm{)/}{\mathrm{Pt/IrO}}_2$ capacitors were investigated by measuring the switching and nonswitching polarizations, the switching current profiles, and the $\mathrm{P–V}$ hysteresis loops. The retention losses of ${\mathrm{Ir/IrO}}_2/{\mathrm{PZT/Pt/IrO}}_2$ capacitors were compared with those of the Pt/PZT/Pt capacitors, and a significant improvement of an opposite-state retention was observed. It was found that the growth and the relaxation behaviors of the internal field are quite similar for both capacitors, but that the polarization backswitching becomes significantly smaller for the PZT capacitors with the ${\mathrm{IrO}}_2$ top electrodes. The difference in polarization backswitching might originate from the nature of the ferroelectric/electrode interfaces, possibly suppressing the nucleation of opposite domains at the interfaces.