Sub-micron silicon-on-insulator resonator for ultrasound detection

TL;DR

This paper introduces the world's smallest silicon-on-insulator ultrasound detector with sub-micron size, offering unprecedented sensitivity and bandwidth, enabling high-resolution imaging and dense detector arrays for advanced ultrasonography.

Contribution

Developed a sub-micron SOI-based ultrasound detector with significantly higher sensitivity and bandwidth than existing technologies, suitable for dense array fabrication.

Findings

Achieved a 220 x 500 nm sensing area.

Demonstrated 230 MHz bandwidth.

First imaging using an SOI ultrasound detector.

Abstract

Point-like broadband ultrasound detection can significantly increase the resolution of ultrasonography and optoacoustic (photoacoustic) imaging, yet current ultrasound detectors cannot be miniaturised sufficiently. Piezoelectric transducers lose sensitivity quadratically with size reduction, while optical micro-ring resonators and Fabry-P\'erot etalons fail to adequately confine light at dimensions smaller than $\sim$ 50 microns. Micromachining methods have been used to generate arrays of capacitive and piezoelectric transducers, but at bandwidths of only a few MHz and dimensions not smaller than 70 microns. Here we use the widely available silicon-on-insulator (SOI) platform to develop the worlds smallest ultrasound detector with a sub-micron sensing area of 220 $\times$ 500 nanometers. The SOI-based optical resonator design can provide per-area sensitivity that is $10^{4}$-fold higher than for micro-ring resonators and $10^{8}$-fold higher than for piezoelectric detectors. We also demonstrate ultra-wide bandwidth reaching 230 MHz and conduct the first imaging based on an SOI ultrasound detector. The technology showcased is suitable for manufacturing ultra-dense detector arrays ($\geq125$ $detectors\backslash mm^{2}$), which have the potential to revolutionise ultrasonography and optoacoustic imaging.