A single-sided micromachined piezoresistive SiO₂ cantilever sensor for ultra-sensitive detection of gaseous chemicals

This paper presents a novel SiO₂ microcantilever sensor for high-sensitive gaseous chemical detection. A thin single-crystalline silicon piezoresistor is integrated in the SiO₂ cantilever for low-noise and high-resoluble signal readout. The paper relates the MEMS formation, modeling and detecting experiments of the sensor. The micro-fabrication of the cantilever sensor is processed at a single side (front side) of the silicon wafer, combined with functionalization of a self-assembled monolayer (SAM) on the sensing cantilever for specific molecular capturing. The model of the piezoresistive SiO₂ cantilever sensor is given by using both analysis and simulation, resulting in good agreement with the measuremental data. With the cantilever modified by the specific SAM, the detecting performance of the sensor is experimentally obtained. Attributed to the high sensitivity and the low electric noise of the piezoresistive SiO₂ cantilever, ammonia gas of 0.1 ppm level concentration and dimethyl methylphosphonate vapor of 10 ppb concentration have been well detected. The integrated cantilevers are promising for inexpensive, highly resoluble and portable chemical/biological detection.