Thick sol-gel PZT film integrated in SOI-Based, micromachined ultrasonic transducers

Piezoelectric micro machined ultrasonic transducers (pMUT) are piezoelectric laminated plates operating at flexural modes. The pMUT's fabricated in this work contained a 4 mu m thick lead zirconate titanate (PZT) thin film deposited by a sol-gel technique, and exhibiting a permittivity of s(r)=1200, and an effective transverse piezoelectric coefficient e(31,f) of 12 C/m(2). A further optimization of the sol-gel process yielded larger grain diameters and consequently improved properties: s(r)=1600, e(31,f) of 16 C/m(2). A design and micromachining concpet for easy scating in frequency has been developed. The electromechanical coupling coefficient (0) and the quality factor (Q) of rectangular clamped elements (with former PZT process) were measured as k(2)=4.4% and Q=145 in air for a low frequency transducer (@240 kHz). The 16.9 MHz transducer yielded values of Q=25 and k(2)=3% in air. The effect of DC bias voltage on frequency and k(2) has been studied.