Piezoelectric micromachined ultrasonic transducers with thick PZT sol gel films

The fabricated micro machined ultrasonic transducers (pMUT) was based on piezoelectric laminated plates operating at flexural modes. The fabricated bimorph pMUT transducers were composed of 5-layers. A 4μm thick lead zirconate titanate (PZT) thin film deposited by a sol-gel method was used. The piezoelectric layer exhibited a capacitance corresponding to a permitivity of ɛ r = 1,200. The electromechanical coupling coefficient (k 2) and quality factor (Q) were measured as k 2 = 4.4% and Q = 145 in air for a low frequency transducer (240kHz). The effect of DC bias voltage on frequency and k 2 has been studied. The 16.9MHz transducer yielded values of Q = 25 in air and k 2 = 3

Microstructural evolution of dense and porous pyroelectric Pb1−xCaxTiO3 thin films

Pb1−xCaxTiO3 thin films with x = 0−0.3 for pyroelectric applications were deposited on platinized silicon wafers by chemical solution processing. Ca-substitution for Pb in PbTiO3 results in a reduced c/a ratio of the unit cell, which, in turn, leads to better pyroelectric properties. Control of nucleation and growth during rapid thermal annealing to 650 °C allowed the formation of either highly porous or dense (111) oriented films. The inclusion of pores creates a matrix-void composite with the low permittivity desired for pyroelectric applications, resulting in a high figure of merit. The growth mechanisms for the microstructural evolution of both dense and porous films were analyzed by x-ray diffraction, transmission electron microscopy, scanning electron microscopy, and Rutherford backscattering spectrometry and allowed establishment of microstructure/property relationship

Transmission-electron-microscopy study of quasi-epitaxial tungsten-bronze (Sr2.5Ba2.5Nb10O30) thin film on perovskite (SrTiO3) single crystal

Strontium barium niobate (Sr2.5Ba2.5Nb10O30) thin films were deposited on (001) SrTiO3 single-crystalline substrates by pulsed laser deposition. The growth nature was investigated by transmission electron microscopy (TEM). Selected-area electron diffraction and high-resolution transmission electron microscopy revealed the existence of six types of grains. These grains grew on the substrate in a partially epitaxial fashion. Geometrical models were built, which were confirmed by TEM observations. Based on the TEM results and geometrical analysis, a crystallographic model was developed. The strain nature resulting from the growth columns is discussed in this repor

In-Situ Thin Film Growth of PbTiO3 By Multi Target Sputtering

The in-situ reactive sputter deposition of PbTiO3 on Pt/Ti/SiO2/Si from two metallic targets was investigated. A minimal lead oxide flux of two to three times the titanium oxide flux is needed in order to obtain stoichiometric films with the perovskite structure. For higher fluxes, the Pb/Ti ratio in the film stays at the stoichiometric value 1; the orientation changes from random to ; and the film morphology transforms from a rough to a smooth polycrystalline film. The obtained dielectric constants vary between 40 and 150, the losses between 2 and 4 % (10 kHz). The method could be extended to PbZrxTi1-xO3 for x ≤ 0.7. The orientation is lost when the Pt electrodes are replaced by RuO2 electrodes

Fabrication, characterization, and simulation of glass devices with AlN-thin-film-transducers for excitation of ultrasound resonances

We present fabrication of 570-um-thick, millimeter-sized soda-lime-silicate float glass blocks with a 1-um-thick AlN-thin-film piezoelectric transducer sandwiched between thin metallic electrodes and deposited on the top surface. The electro-mechanical properties are characterized by electrical impedance measurements in the frequency range from 0.1 to 10 MHz with a peak-to-peak voltage of 0.5 V applied to the electrodes. We measured the electrical impedance spectra of 35 devices, all of width 2 mm, but with 9 different lengths ranging from 2 to 6 mm and with 2-7 copies of each individual geometry. Each impedance spectrum exhibits many resonance peaks, of which we carefully measured the 5 most prominent ones in each spectrum. We compare the resulting 173 experimental resonance frequencies with the simulation result of a finite-element-method model that we have developed. When using material parameters from the manufacturer, we obtain an average relative deviation of the 173 simulated resonance frequencies from the experimental ones of (-4.2 +/-0.04)%. When optimizing the values of the Young's modulus and the Poisson ratio of the float glass in the simulation, this relative deviation decreased to (-0.03 +/- 0.04)%. Our results suggest a method for an accurate in-situ determination of the acoustic parameters at ultrasound frequencies of any elastic solid onto which a thin-film transducer can be attachedComment: 9 pages, 5 pdf figures, RevTe

Matériaux piézoélectriques de structure pérovskite pour la micromécanique [Piezoelectric materials with perovskite structure for micromechanics]

Le coefficient piézoélectrique du titanate-zirconate de plomb (PZT) et d'autres composés du même type est beaucoup plus élevé que celui des autres matériaux comme le quartz et l'oxyde de zinc. Les films minces de PZT sont donc très prometteurs pour la fabrication de composants micromécaniques (actionneurs, micromoteurs, etc). Toutefois, leur mise en oeuvre est problématique, devant se faire à des températures élevées, ce qui pose des problèmes de diffusion et d'oxydation [1-3] entre le film et l'électrode inférieure, et de perte de plomb. Le problème de stabilité de l'électrode a été résolu [1], et on se concentre ici sur la fabrication des films. Deux méthodes de fabrication existent: la déposition à basse température et la cristallisation in situ [5] à température élevée. Dans le 1er cas, il s'ensuit une perte de plomb, composant volatil, qui doit être compensée par un excès lors de la déposition, d'où possibilité de porosité dans le film après recuit, alors que pour la 2ème méthode, on compense la réévaporation de Pb instantanément. Nous utiliserons cette dernière. Ce texte concerne la fabrication préliminaire in situ de titanate de plomb (PT), plus facile thermodynamiquement et cinétiquement [4] que celle du PZ

Piezoelectric aluminum nitride thin films for microelectromechanical systems

This article reports on the state-of-the-art of the development of aluminum nitride (AlN) thin-film microelectromechanical systems (MEMS) with particular emphasis on acoustic devices for radio frequency (RF) signal processing. Examples of resonant devices are reviewed to highlight the capabilities of AlN as an integrated circuit compatible material for the implementation of RF filters and oscillators. The commercial success of thin-film bulk acoustic resonators is presented to show how AlN has de facto become an industrial standard for the synthesis of high performance duplexers. The article also reports on the development of a new class of AlN acoustic resonators that are directly integrated with circuits and enable a new generation of reconfigurable narrowband filters and oscillators. Research efforts related to the deposition of doped AlN films and the scaling of sputtered AlN films into the nano realm are also provided as examples of possible future material developments that could expand the range of applicability of AlN MEM

Oxygen reduction at thin dense La0.52Sr0.48Co0.18Fe0.82O3- δ electrodes: Part II: Experimental assessment of the reaction kinetics

The mechanism and kinetics of oxygen reduction at thin dense two-dimensional $${\text{La}}_{{0.52}} {\text{Sr}}_{{0.48}} {\text{Co}}_{{0.18}} {\text{Fe}}_{{0.82}} {\text{O}}_{{3 - \delta }}$$ (LSCF) electrodes have been investigated in air between 500 and 700 °C with electrochemical impedance spectroscopy and steady-state voltammetry. Dense and geometrically well-defined LSCF films with various thicknesses ranging between 16 and 766nm have been prepared on cerium gadolinium oxide substrates by pulsed laser deposition and structured with photolithography. The current collection was ensured by a porous LSCF layer. A good agreement was found between the experimental data and the impedance of the reaction model calculated with state-space modelling for various electrode potentials and thicknesses. It was evidenced that oxygen adsorption, incorporation into the LSCF and bulk diffusion are rate-determining while charge transfer at the electrode/electrolyte interface remains at quasi-equilibrium. The 16 and 60nm thin dense LSCF electrodes appear to be more active towards oxygen reduction than thicker layers and porous films at 600 and 700°

Thin piezoelectric films for micro-electromechanical components

PbZrxT1-x O3 (PZT) films on silicon substrates can be used for various micro mechanical devices. An insitu reactive sputter deposition process at 600°C has been developed for this application. Three magnetron sources with metal targets have been applied simultaneously. Within a certain process window, the [Pb] / ([Zr]+[Ti]) ratio in the film is self stabilized at stoichiometry by desorption of the excess Pb. Films of up to 1 micron thickness have been fabricated. For the composition x = 0.4 the films exhiba a remanent polarization of 20 to 25 µC/cm2, a dielectric constant of 1100 and a piezoelectric coefficient of 40 pC/N. The classical Pt/Ti bottom electrode needed to be improved by an additional layer of TiO2 between Ti and Pt. As a second choice the metallic oxide RuO2 has been investigated, too. PZT films on prototype membrane structures are currently processed. They will be applied in prototype micromotors for the watch industry

Growth of (111)-oriented PZT on RuO2(100)/Pt(111) electrodes by in-situ sputtering

Growth of (111)-oriented Pb(Zr,Ti)O-3 has been achieved on a RuO2 film which was (100) textured. This texture could be obtained by using a (111)-textured Pt film as a template. The whole layer stack was grown on an amorphous SiO2 layer, that is a thermal oxide of a silicon wafer. A good (111)-orientation of the Pt template layer is thus the starting point of oriented growth. XRD and TEM studies have been carried out to find the orientation relationship between Pt(111), RuO2(100) and PZT(111). (C) 1999 Elsevier Science S.A. All rights reserved