Simulation And Characterization Of Piezoelectric Micromachined Ultrasonic Transducers (pMUTs) Based On Pzt/Soi Membranes

Piezoelectric micromachined ultrasonic transducers for airborne and immersed applications in the frequencies from 20 kHz in liquid up to 750kHz in air have been simulated by finite element approach, fabricated and investigated. The basic element consisted of a oxidized and platinized silicon membrane coated with a 2 μm thick (100)-textured Pb(Zr,Ti)O3 (PZT) thin film deposited by sol-gel techniques. SOI wafers have been applied to obtain a good definition of the silicon part of the membrane. The unclamping of the silicon membrane at the border increases drastically the coupling factor. For unclamped structures the membranes completely covered with top electrode show the highest coupling coefficient (k2 = 5.6%). Immersed (in FluorinertTM) membranes show 7 times smaller quality factor, while the coupling factor k2 remains the same. The obtained structures were enough sensitive to detect acoustic waves in air and in liquid emitted from the same type of elements at a distance of few centimeters. Good agreemen...