High Sensitivity 2.8 MHz Air-Coupled Ultrasound Sensor with a Record-Small 30 μm Diameter Based on a Silicon Photonic MEMS Platform

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Abstract
High-resolution non-contact non-destructive evaluation (NDE) utilizing MHz-range ultrasound in air-coupled environments faces two significant challenges: severe signal attenuation and reduced sensitivity due to transducer miniaturization. Optical ultrasound sensors have emerged as promising candidates to overcome these limitations; however, widespread adoption remains challenging. Conventional discrete optical sensors are limited by complex fabrication and rigid form factors. Furthermore, the efforts to implement these on photonic integrated circuits (PICs)—while addressing scalability—are typically constrained by limited sensitivity. To address these requirements, we report a chip-scale optomechanical ultrasound receiver implemented, for the first time, on a silicon photonics MEMS platform. This platform facilitates CMOS-compatible scalability and design freedom to independently optimize mechanical components and optical sensitivity. Consequently, the receiver demonstrates a compact active acoustic sensing area of 4×10 −4 mm 2 . Despite this size reduction, in the noise-equivalent pressure (NEP)–active-area comparison, the proposed receiver’s measured and estimated NEP values are positioned within a range comparable to or lower than those for previously reported air-coupled optical and CMUT sensors, when interpreted relative to the ideal area-scaling trend. Designed for a 2.8 MHz mechanical resonance, the receiver was benchmarked against a commercial 1 MHz air-coupled PZT transducer to provide a practical, controlled experimental baseline. In this controlled experimental comparison, the receiver showed a more than 25,000-fold higher received response per unit active acoustic area than the PZT baseline, serving as a complementary metric for unit-area received response and structural scaling potential. These findings suggest that the silicon photonic MEMS platform can provide a route toward compact, dense-array-compatible optical ultrasound receivers for localized air-coupled sensing.
Funding Information
  • National Research Foundation of Korea (RS-2025-25420118)
  • National Research Foundation of Korea (RS-2024-00352718)
  • National Research Foundation of Korea (RS-2024-00439236)
  • National Research Foundation of Korea (RS-2024-00334727)
  • National Research Foundation of Korea (RS-2021-NR060086)
  • DGIST R&D Program of the Ministry of Science and Information and Communications Technology (25-DRJoint-02)
  • Samsung Future Technology Foundation (SRFC-IT2102-02)
  • Korea SMEs and Startups Agency (RS-2023-00222912)
  • Korea Basic Science Institute (RS-2024-00403243)
  • Institute of InformationCommunications Technology PlanningEvaluation-Information Technology Research Center (RS-2023-00259676)
  • Institute of InformationCommunications Technology PlanningEvaluation-Information Technology Research Center (RS-2025-02219093)

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