Fabricating Capacitive Micromachined Ultrasonic Transducers with Wafer Bonding Technique

Abstract

We report the fabrication of capacitive micromachined ultrasonic transducer by wafer bonding technique. Membrane is transferred from SOI wafer to the prime wafer having silicon dioxide cavity. The thickness of cavity height depends on silicon dioxide grown on prime wafer by dry/wet oxidation. Thinning of device wafer of SOI by oxidation, controls membrane thickness. Two wafers are bonded in vacuum under optimized controlled parameters. Using this method, we can get single crystal silicon as membrane, whose mechanical and electrical parameters are well known. Silicon membrane is free from stress and density variation. Focused Ion Beam etching and laser Doppler Vibrometer were used to do structural and electrical characterization respectively. The measured resonance frequency of fabricated device i.e. 2.24 MHz is much closer to the designed value i.e. 2.35 MHz.

Keywords

• Wafer bonding
• Ultrasonic transducer
• Capacitive transducer