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

Control of Crystallographic Texture and Surface Morphology of Pt/TiO₂ Templates for Enhanced PZT Thin Film Texture

Optimized processing conditions for Pt/TiO₂/SiO₂/Si templating electrodes were investigated. These electrodes are used to obtain [111] textured thin film lead zirconate titanate (Pb[ZrₓTi₁₋ₓ]O₃ 0≤x≤1) (PZT). Titanium deposited by dc magnetron sputtering yields [0001] texture on a thermally oxidized Si wafer. It was found that by optimizing deposition time, pressure, power, and the chamber preconditioning, the Ti texture could be maximized while maintaining low surface roughness. When oxidized, titanium yields [100] oriented rutile. This seed layer has as low as a 4.6% lattice mismatch with [111] Pt, thus it is possible to achieve strongly oriented [111] Pt. The quality of the orientation and surface roughness of the TiO₂ and the Ti directly affect the achievable Pt texture and surface morphology. A transition between optimal crystallographic texture and the smoothest templating surface occurs at approximately 30 nm of original Ti thickness (45 nm TiO₂). This corresponds to 0.5 nm (2 nm for TiO₂) RMS roughness as determined by atomic force microscopy and a FWHM of the rocking curve 0002 (200) peak of 5.5° (3.1° for TiO₂). A Pb[Zr₀.₅₂Ti₀.₄₈]O₃ layer was deposited and shown to template from the textured Pt electrode, with a maximum [111] Lotgering factor of 87% and a minimum 111 FWHM of 2.4° at approximately 30 nm of original Ti.©2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works. This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by IEEE-Institute of Electrical and Electronics Engineers and can be found at: http://www.ieee-uffc.org/publications/tr/ and at: http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=58Keywords: Piezoelectric, Thin Films, Crystallographic Orientatio

Piezoelectric Micromachined Ultrasound Transducer (PMUT) Arrays for Integrated Sensing, Actuation and Imaging

Many applications of ultrasound for sensing, actuation and imaging require miniaturized and low power transducers and transducer arrays integrated with electronic systems. Piezoelectric micromachined ultrasound transducers (PMUTs), diaphragm-like thin film flexural transducers typically formed on silicon substrates, are a potential solution for integrated transducer arrays. This paper presents an overview of the current development status of PMUTs and a discussion of their suitability for miniaturized and integrated devices. The thin film piezoelectric materials required to functionalize these devices are discussed, followed by the microfabrication techniques used to create PMUT elements and the constraints the fabrication imposes on device design. Approaches for electrical interconnection and integration with on-chip electronics are discussed. Electrical and acoustic measurements from fabricated PMUT arrays with up to 320 diaphragm elements are presented. The PMUTs are shown to be broadband devices with an operating frequency which is tunable by tailoring the lateral dimensions of the flexural membrane or the thicknesses of the constituent layers. Finally, the outlook for future development of PMUT technology and the potential applications made feasible by integrated PMUT devices are discussed