Precise extension-mode resonant sensor with uniform and repeatable sensitivity for detection of ppm-level ammonia

Abstract

This paper presents a micromechanical resonant gas sensor, which is operated in extensional bulk mode, for high-accuracy sensing of ultra-low concentration chemical vapors. The designed and fabricated gravimetric resonant microsensor has exhibited both high Q-factor of 11157 in air and high mass sensitivity of 10.16 Hz pg−1. Much more importantly, both theoretical analysis and sensing experiment have verified that such an extensional resonance mode is technically advantageous in sensing accuracy (e.g., output signal linearity in terms of gas concentration and reproducibility of sensitivity), which can be attributed to the uniform vibration amplitude at each point of the gas-adsorbing area. Loaded with –COOH functionalized mesoporous-silica nanopaticles as sensing material, which features an ultra-large surface area, the chemical sensing micro-resonator experimentally performs precise detection performance to ppm-level ammonia vapor. The limit of detection is as low as 1 ppm and the response time of the sensor is as short as 10 s.