Author: Kwok, Kin-pong
Title: Preparation and characterization of sol-gel derived niobium-doped lead zirconate titanate films for membrane-actuator applications
Degree: M.Phil.
Year: 2004
Subject: Hong Kong Polytechnic University -- Dissertations
Ferroelectric thin films
Lead -- Electrometallurgy
Electronic ceramics
Piezoelectric ceramics
Department: Department of Applied Physics
Pages: 1 v. (various pagings) : ill. ; 30 cm
Language: English
Abstract: In recent years, lead zirconate titanate (PZT) thin films have been widely studied for use in actuator and sensor applications. In this work, sol-gel derived Nb-doped PZT films have been prepared at a low sintering temperature, and the effects of the Nb dopant on the piezoelectric properties of the PZT films have been studied. The Nb-doped PZT film has been fabricated into micromachined membranes and their performance has been evaluated. Sol-gel derived Nb-doped PZT films were deposited on Pt/Ti/SiO2/Si/Si3N4 substrates with a lead titanate seeding layer by the multiple-spin-coating technique. The doping level of Nb ranged from 0 % to 2 %; and the film thickness was about 800 nm. Because of the seeding layer, the PZT films could crystallize well and completely into the perovskite phase at a low sintering temperature of 550C for 2 hours. The films were dense and crack-free, and had good dielectric and piezoelectric properties. Effective longitudinal and transverse piezoelectric coefficients (d33 and e3l.f) of the films have been measured using a single beam laser interferometer and a newly established method based on the direct piezoelectric effect, respectively; and the effects of Nb dopant on d33 and e3l.f of the PZT films have been studied. Our results reveal that the Nb dopant has effects on the PZT films similar to the experimentally-known effects on bulk ceramics, i.e. enhancing both the longitudinal and transverse piezoelectric properties; and the optimum doping level of Nb is about 1%. However, because of the substrate clamping effect, the observed enhancement in the d33 was much smaller than that in e31,f. At 1% Nb-doping level, the observed d33 and e31,f values of the film are increased, by about 9% and 30%, to 74 pm/V and 12.8 C/m2, respectively. The 1% Nb-doped PZT film has been fabricated into 3-mm and 4-mm square micromachined membranes, and their performance have been evaluated. The observed fundamental resonance frequencies for the membranes are 111.5 kHz and 65 kHz, respectively. At resonance, the vibrating displacements at the centre of the membranes have the maximum values of 200 nm/V and 900 nm/V, respectively. At off-resonance frequencies, the displacements are about 6.8 nm/V and 10.5 nm/V, respectively, and can be increased reversibly by about 40-50% under a dc bias field of 16 MV/m. These results indicate that the silicon-based membranes are suitable for micro-actuator applications.
Rights: All rights reserved
Access: open access

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