Electrical Degradation in Dielectric and Piezoelectric Oxides: Review of Defect Chemistry and Associated Characterization Techniques

The properties of dielectric and piezoelectric oxides are determined by their processing history, crystal structure, chemical composition, microstructure, dopants (or defect) distribution, and defect kinetics. These materials are essential in a diverse range of applications including aerospace, medical, military, transportation, power engineering, and communication, where they are used as ceramic discs, thick and thin films, multilayer devices, etc. Significant advances in understanding the materials, processing, properties, and reliability of these materials have led to their widespread use in consumer electronics, military, and aerospace applications. This review delves into electrical degradation in dielectrics and piezoelectrics, focusing on defect chemistry and key characterization techniques. It also provides a detailed discussion of various spectroscopic, microscopic, and electronic characterization techniques essential for analyzing defects and degradation mechanisms

Strain-modulated piezoelectric and electrostrictive nonlinearity in ferroelectric thin films without active ferroelastic domain walls

In contrast to usual assumptions, it is shown that even when ferroelastic domain walls are inactive or absent, the motion of ferroelectrically active interfaces in ferroelectric materials contributes, at subcoercive electric fields, not only to the polarization but also to the strain. Specifically, in polycrystalline samples, strain coupling between adjacent grains, or mediated through the substrate in thin films, influences both the dielectric and piezoelectric response. The model developed explains the unexpected observation of piezoelectric nonlinearity in films even in cases in which the domain variants' projections are equivalent along the direction of the external driving field. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3665410

Piezoelectric amplifiers with integrated actuation and sensing capabilities

We report in this work on unprecedented levels of parametric amplification in microelectromechanical systems (MEMS) resonators with integrated piezoelectric actuation and sensing capabilities operated in air. The method presented here relies on accurate analytical modeling taking into account the geometrical nonlinearities inherent to the bridge-like configuration of the resonators used. The model provides, for the first time, precise analytical formula of the quality factor (Q) enhancement depending on the resonant mode examined. Experimental validations were conducted for resonant modes exhibiting, respectively, hard and soft-spring effects when driven in the nonlinear regime; Q amplification by a factor up to 14 has been obtained in air

OPTIMIZED DESIGN, FABRICATION AND CHARACTERIZATION OF PZT UNIMORPH MICROACTUATORS FOR DEFORMABLE MIRRORS

ABSTRACT This paper describes an optimization of PZT unimorph membrane microactuators in view of their application to deformable mirrors (DMs). PZT unimorph actuators of various electrode designs, silicon membrane thickness, and membrane sizes were fabricated and characterized. A mathematical model was developed to further assist the optimization of membrane thickness and electrode sizes, and excellent agreement with experiment was obtained. For a 2.5rnm diameter actuator with 2#m thick PZT and 15#m thick silicon membrane, the measured vertical stroke was 5.4#m at 50V. The measured resonant frequency of the unimorph actuator was 47kHz, far exceeding the bandwidth requirement of most DMs (-lkHz)

The interplay between ferroelectricity and electrochemical reactivity on the surface of binary ferroelectric Alx_xB1−x_{1-x}N

Polarization dynamics and domain structure evolution in ferroelectric Al$_{0.93}$B$_{0.07}$N are studied using piezoresponse force microscopy and spectroscopies in ambient and controlled atmosphere environments. The application of negative unipolar, and bipolar first-order reverse curve (FORC) waveforms leads to a protrusion-like feature on the Al$_{0.93}$B$_{0.07}$N surface and reduction of electromechanical response due to electrochemical reactivity. A surface change is also observed on the application of fast alternating current bias. At the same time, the application of positive biases does not lead to surface changes. Comparatively in a controlled glove box atmosphere, stable polarization patterns can be observed, with minuscule changes in surface morphology. This surface morphology change is not isolated to applying biases to free surface, a similar topographical change is also observed at the electrode edges when cycling a capacitor in ambient environment. The study suggests that surface electrochemical reactivity may have a significant impact on the functionality of this material in the ambient environment. However, even in the controlled atmosphere, the participation of the surface ions in polarization switching phenomena and ionic compensation is possible.Comment: 16 pages; 5 figure

Nanocrystalline Ferroelectric BiFeO3 Thin Films by Low-Temperature Atomic Layer Deposition

© 2015 American Chemical Society. In this work, ferroelectricity is identified in nanocrystalline BiFeO3 (BFO) thin films prepared by low-temperature atomic layer deposition. A combination of X-ray diffraction, reflection high energy electron diffraction, and scanning transmission electron microscopy analysis indicates that the as-deposited films (250 °C) consist of BFO nanocrystals embedded in an amorphous matrix. Postannealing at 650 °C for 60 min converts the sample to a crystalline film on a SrTiO3 substrate. Piezoelectric force microscopy demonstrates the existence of ferroelectricity in both as-deposited and postannealed films. The ferroelectric behavior in the as-deposited stage is attributed to the presence of nanocrystals. Finally, a band gap of 2.7 eV was measured by spectroscopic ellipsometry. This study opens broad possibilities toward ferroelectric oxides on 3D substrates and also for the development of new ferroelectric perovskites prepared at low temperature.This research was supported by MAT2011-28874-C02-01, MAT2014-511778-C2-1-R, SGR753 and Consolider. M.C. and J.G. acknowledge RyC contracts, 2013-12448 and 2012-11709, respectively. I.F. acknowledges the Beatriu de Pinós postdoctoral scholarship (2011 BP-A 00220) from AGAURGeneralitat de Catalunya. Financial support from the ERC Starting investigator grant STEMOX 239739 and Consolider IMAGINE is acknowledged (M.V.).Peer Reviewe