PZT thin films integration for the realisation of a high sensitivity pressure microsensor based on a vibrating membrane

Pb(Zr,Ti)O-3 (PZT) thin films are widely used both to make actuator and sensor. In this paper, a vibrating pressure sensor based on a (PZT thin film)/Si membrane is presented. This sensor is based on a 3 mm. x 3 mm, 15.5 mum thick silicon membrane actuated by a Pt/Ti/PZT/Pt/Ti/SiO2 multilayer. All depositions have been performed by magnetron RF-sputtering. After a RTA (700 degreesC, 30 s in air), a PZT perovskyte phase [1 1 1] oriented has been obtained as observed by XRD. In order to improve this preferential orientation for PZT, the bottom Pt electrode has been annealed by RTA (400 degreesC, 30 s in argon). The electrodes have been patterned by lift-off. The silicon membranes have been realised by anisotropic chemical etching in KOH. A finite element analysis has been developed to optimise the top electrode and to determine the fundamental resonant frequency of our device. The mechanical behaviour of the sensor under pressure has been analysed by means of a laser vibrometer. The fundamental resonant frequency without additional pressure was 18.6 kHz. A frequency shift has been observed for an applied pressure from 15 mbar up to 140 mbar with a good linearity and a high sensitivity of 115 Hz mbar(-1). The normalised sensitivity observed is 6800 ppm mbar(-1). (C) 2002 Elsevier Science B.V. All rights reserved.