Metal-organic Thin-film Encapsula- Tion for Gravimetric Gas Microsensors

Here we demonstrate a novel metal-organic thin-film encapsulation technique for resonant gas microsensors to efficiently filter out airborne particles which can negatively affect device performance. The gravimetric sensors are ZnO-on-silicon extensional mode resonators coated with a gas-sensitive material. Mass change caused by chemical reaction and/or physical adsorption can be detected through measured resonant frequency shifts. The gas sensors are encapsulated in microcavities made from multiple layers of Novolac-based positive-tone photoresist. Particle filtering is achieved by minimizing clearance in the lateral access holes and electrostatic attraction from the organic polymer gas channels.