Sensitivity-Enhanced Ultrasonic Microsensors on Buckled Diaphragms through Stress Balance Control of Multilayered Structure

Sensitivity of piezoelectric ultrasonic microsensors has been improved through a novel buckling control technique of the diaphragms of which upward buckling yields higher sensitivity than downward one. The diaphragms have compressive- and tensile-stressed layers, and a fabrication process has been developed to optimize the stress balance to generate an upward buckling moment. The fabricated sensors have yielded upward-buckled diaphragms in 92% of 196 ones on a wafer and an improved sensitivity to 6.7 times on average.