Poling Effect to Piezoelectric Diaphragm-Type Ultrasonic Microsensors and Sensitivity Enhancement through Buckling Profile Control

This paper describes that poling to piezoelectric sensors, which is considered to enhance their sensitivity, has a side effect to decline the sensitivity of piezoelectric diaphragm-type ultrasonic microsensors, and also demonstrates how to cancel the side effect. The poling to the piezoelectric/ferroelectric films improves their piezoelectric property but also causes converse-piezoelectric stress on the sensor diaphragms. The sensors on upward-buckled diaphragms, which yield higher sensitivity than downward ones, decline their sensitivity because the buckling profile is modified through the converse-piezoelectric stress by the poling. An extra electrode on the diaphragm has been utilized to generate an additional converse-piezoelectric stress so that the extra stress cancels the profile modification. Moreover, a diaphragm which accidentally buckled downward in fabrication process has been re-buckled upward by the extra stress.