Optically Detected, Framed Silicon Cantilever for High Precision Acoustic Sensing

Optically readable silicon cantilevers have been designed, fabricated and applied to photoacoustic spectroscopy. The working principle is based on detecting the acoustic wave induced displacement of the cantilever with laser interferometry. The rectangular, 9.5 mum thick components were fabricated using two-sided anisotropic etching of silicon-on insulator (SOI) wafers. The flexible cantilever is surrounded by narrow gaps from three sides and it moves very sensitively relative to the thick frame. The cantilever sensor has been applied to detect weak pressure variations in trace gas analysis and it has been shown to improve the sensitivity of photoacoustic measurements by many orders of magnitude.