Fabrication of Thick, Sol Gel Pzt Films: Applications to Macroscopic Piezoelectric Devices
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ABSTRACT Lead zirconate titanate (PZT) films of up to 60 uim in thickness have been fabricated on a wide variety of substrates using a new sol gel process. The dielectric properties (C = 900), ferroelectric (Ee = 16 kV/cm and Pr = 35 uC/cm 2) and piezoelectric properties are comparable to bulk values. The characteristic Curie point of these films is at 420 *C. Piezoelectric actuators have been developed by depositing thick PZT films on both planar and coaxial substrates. Stainless steel cantilevers and optical fibres coated with a PZT film exhibit flexure mode resonant vibrations observable with the naked eye. A low frequency in-line fibre optic modulator has been developed using a PZT coated optical fibre. The high frequency resonance of a 60 ym film on a aluminum substrate has been observed.
INTRODUCTION In recent years, there has been an increased interest in ferroelectric PZT films for piezoelectric device applications. To date, most of the development has centred around silicon microniachined structures. Combining micromachined silicon with ferroelectric films has produced novel microdevices that include membrane sensors 1, accelerometers 2 and micromotors3 . Generally, these devices are based on geometries ranging from um2 to 100 pm 2 and film thicknesses of < 1 pm. However, the application of devices based on piezoelectric films is not limited to the realm of microdevices. Many potential applications exist which require film thicknesses of 1 to 30 um and geometries of Mm2 to cm 2. Some examples of these macroscopic devices include ultrasonic high frequency transducers which are required for detailed imaging of the eye 4 ; fibre optic modulators , where a PZT film coated on the fibre is 6 used to modulate light and for self controlled vibrational damping systems6. The film thicknesses and device geometries required for these devices are difficult to achieve using conventional sol gel methods. Recently, a new sol gel technique has been developed for fabricating thick PZT films on a wide variety of substrates. With this new process, it is now possible to fabricate sol gel films of up to 60 um in thickness on a wide range of substrates. In this paper, the dielectric, ferroelectric, and piezoelectric properties of these thick PZT films are presented and the development of actuators based on these thick coatings is described. EXPERIMENTAL The (52/48) PZT films are fabricated using a new sol gel technique developed at Queen's university. The films were fired at 400 'C between each layer and a final anneal of 650 'C for 30 minutes was used to crystallize the material. An SEM cross section of a 13 Jm film on 103 Mat. Res. Soc. Symp. Proc. Vol. 360 01995 Materials Research Society
Pt coated silicon is given in figure 1. Capacitors for studying the dielectric and ferroelectric properties were made by coating a 18 jm film on a Pt-Ti-Si0 2 -Si substrate and evaporating a top aluminum electrode. The dielectric data was measured using an HP impedance bridge. The ferroelectric hysteresis loop of the film was observed usi
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