A submicrometre silicon-on-insulator resonator for ultrasound detection

Abstract

Point-like broadband ultrasound detection can significantly increase the resolution of ultrasonography and optoacoustic (photoacoustic) imaging 1,2 , yet current ultrasound detectors cannot be miniaturised sufficiently. Piezoelectric transducers lose sensitivity quadratically with size reduction 3 , while optical micro-ring resonators 4 and Fabry-Pérot etalons 5 fail to adequately confine light at dimensions smaller than ~50 microns. Micromachining methods have been used to generate arrays of capacitive 6 and piezoelectric 7 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 world's smallest ultrasound detector with a sub-micron sensing area of 220 x 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 (>125 detectors/mm 2 ), which have the potential to revolutionise ultrasonography and optoacoustic imaging.Ultrasound detection based on optical methods has a fundamental advantage over piezoelectric detection because the detectors can be miniaturised without sacrificing sensitivity 3 . One highly miniaturisable approach for ultrasound detection is the use of optical interferometry with a shifted Bragg grating etalon embedded in a fibre waveguide 8 . In this configuration, ultrasound waves perturb an optical cavity established between two Bragg gratings, which act as optical mirrors. The ultrasound waves alter the optical path by changing the cavity's length and refractive index 9 , allowing the waves to be detected. However, such etalons are unattractive for biomedical imaging because their large sensing length (100-300 microns) 9,10 and narrow

Perspective on fast-evolving photoacoustic tomography

“…In addition to 2D ultrasound transducer arrays based on piezoelectric materials, optical ultrasound detectors, such as the Fabry–Perot interferometer, 58 , 59 micro-ring resonator, 60 and Bragg grating fiber, 61 – 63 have been actively explored for volumetric PACT. Compared with piezoelectric transducers, optical ultrasound detectors often have smaller size ( ), larger detection bandwidth and receiving angle, higher detection sensitivity per unit area, better transmittance of the PA excitation light, and simpler PA signal readout, all of which can help improve the resolution and penetration depth of volumetric PACT.…”

“…Other optical ultrasound sensors, including polymer micro-ring 60 and Bragg-grating fiber, 61 have recently been demonstrated as point-like detectors in PAT, often with sensor sizes that are orders of magnitude smaller than their piezoelectric counterparts. However, one major obstacle met by these optical sensors is the extreme difficulty in scaling up the production while maintaining consistent optical properties, such as the optical resonant wavelength, Q factor, and transmission efficiency.…”

The Recent Progress of MEMS/NEMS Resonators

“…The sensitivity per unit area of the SOI based optical resonator is 1000 times higher than that of the microring resonator and 100,000,000 times higher than that of the piezoelectric detector, and it also supports ultrawide detection bandwidth. Moreover, this ultra-miniaturization detector can perform ultrasound imaging with a resolution comparable to that of an optical microscope [ 117 ].…”

Recent Advances on Multivalued Logic Gates: A Materials Perspective

“…For example, extreme ultraviolet (EUV) photolithography using the EUV wavelength of 13.5 nm enables sub-10nm patterning. [5][6][7] New device structures for achieving high computing performance, such as gate-all-around field-effect transistors (FETs), [8][9][10][11] silicon-on-insulator (SOI) structures, [12][13][14][15][16] and fin-FET devices, [17][18][19][20] have been proposed. Although these approaches temporarily reinstate Moore's law, next-generation computing systems are moving into a new era of hyper Moore's law.…”