Buckling behavior of piezoelectric diaphragms for highly sensitive structures of ultrasonic microsensors controlled through intrinsic stress of PZT films

Buckling behavior of silicon-micro machined diaphragm structures was investigated for highly sensitive structures of piezoelectric ultrasonic microsensors from the viewpoint of intrinsic stress of sol-gel derived lead-zirconate-titanate (PZT) films. Since upward buckled diaphragm structures yield higher sensitivity than flat or downward ones, intrinsic PZT stress should be controlled adequately to realize the upward buckling. Calcination temperature in the sol-gel PZT deposition process was varied to control the stress, from 300°C to 400°C for various thickness up to full-thickness of 1 μm, and diaphragm structures with the PZT films were fabricated and their buckling deflections were evaluated. The full-thick PZT films calcined at 300°C or 350°C show rather large tensile stress and the diaphragms with the films showed all flat or even spontaneously broke. The PZT films calcined at 400°C had an adequate stress and the diaphragms with the full-thick PZT showed all upward buckling with large enough buckling deflection for the high sensitivity structures.