Development of Silicon Photonic Opto-mechanical Ultrasound Sensor with Ultra-thin Membrane: Proof-of-concept study

Abstract

The optical ultrasound sensing technique typically provides higher sensitivity and wider bandwidth, even though its application is limited due to the bulky optical system size. Silicon photonics has a great potential to fabricate large-scale optical systems on tiny silicon chips with sub-micron-sized components. In this study, we report on a silicon photonic-based new opto-mechanical ultrasonic sensor and its design scheme that allows easy fabrication while allowing to have a very thin membrane structure. Compared to previous work, which has a 2 μm-thick membrane defined by a wafer bonding technique, we have a much broader design space as the dimension and shape of the membrane are defined by lithography and etching. As a proof of concept, we implemented a sensor with only a 70 nm-thick membrane having acoustic resonance at 6.5 MHz. The sensitivity and fractional bandwidth of the device are 0.41μV/Pa and 62%, respectively. © ICA 2022.All rights reserved