Piezoelectric Ultrasonic Microsensors on Buckled Diaphragms Using Sol-Gel Derived PZT Films

Abstract

Piezoelectric ultrasonic microsensors with a PZT (lead-zirconate-titanate) capacitor on a buckled diaphragm were fabricated and deposition condition of the sol-gel derived PZT films was investigated from the viewpoint of high mechano-electrical conversion efficiency. The buckling of the diaphragm affects the conversion efficiency in the geometrical aspect and is influenced by the residual stress of the diaphragm. The films were deposited through various thermal treatment in the sol-gel process; four pyrolysis temperatures and two first-crystallized gel film thickness, and were evaluated in their stress and ferroelectric property. The thickness of the gel film affected the crystallographic orientation, (100) or (111), of the film, and dominated the film stress and remanent polarization, e.g., the stress and polarization of the (100)-oriented films were smaller than those of the (lll)-oriented films, meaning the (100) orientation is better in the stress but worse in the remanent polarization than (111) orientation. The pyrolysis temperature was then precisely controlled and finally orientation-distributed samples were fabricated and evaluated. The samples with mixed orientation of (100) and (111) in around 50% showed intermediate stress and remanent polarization, and their sensitivity was enhanced by 1.4-4 times to those with (100) or (111) single oriented films.