Ferroelectric PZT/Si structure for integrated sensor applications

Abstract
Pulsed laser ablation of ferroelectric PZT thin films on silicon cantilever beams to form composite structures for acceleration sensing applications is reported. Optimal thin film growing conditions and voltage sensitivity and linearity properties of the sensor as well as piezoelectric properties of the PZT films are presented and discussed in this paper. PZT layers have been deposited on the highly stressed part of silicon cantilever beams, by using a Nd-YAG pulsed laser. The depositions were made onto Au electrodes previously patterned on the silicon beam. The active layers were grown to a thickness of approx. 2 µm. The substrate temperature of 375°C was found to be sufficient to obtain a high crystallization and orientation of the films. Moreover the moderate heating during deposition allowed to avoid damage to the Au electrode and Si substrate. The obtained films were analyzed by EDS, XRD, SIMS and SEM. After deposition the upper electrode was patterned and the silicon beam was mounted on a holder. Few different sensor structures have been constructed. An acceleration of the support applied by a standard vibrator device produced a variation of stress in the silicon beam which was sensed by the piezoelectric thin film whose output signal was amplified by a charge amplifier and calibrated with a standard accelerometer. The frequency response and voltage sensitivity have been obtained for each configuration. Piezoelectric coefficient and free dielectric permittivity have been also obtained. These simple cantilever experiments confirmed that a piezoelectric thin film structure can be used in integrated sensors on silicon substrates.