Towards Wafer-Level Integration of Photonic Ultrasound Sensors in a SOI Platform

Abstract:
Photoacoustic imaging leverages laser-induced ultrasound for tissue visualization but is limited by the bandwidth and sensitivity of conventional piezoelectric detectors. Silicon photonic sensors offer a promising alternative by enabling optical ultrasound detection with higher sensitivity and broader bandwidth through refractive index modulation. In this work, we evaluate a sensor concept for photonic ultrasound detection that combines a backside release of silicon waveguides with a PDMS cladding for ultrasound interaction. This approach enables a fully backend-of-line (BEOL) compatible design, offering a scalable and application-oriented packaging solution by spatially separating the sensing interface from the optical input and output. Finite element simulations are performed to assess the waveguide sensitivity for both TE and TM modes and to estimate the overall device sensitivity and detection limit (iLOD) of a microring resonator. Initial wafer-level measurements investigate the impact of the backside release process on the quality factor (Q-factor). While a reduction in Q-factor is observed, simulated and measured values suggest that sensitivity and iLOD remain within suitable ranges for photoacoustic imaging.