Characterization of zeolite-trench-embedded microcantilevers with CMOS strain gauge for integrated gas sensor applications

Custom-synthesized zeolite is coated and fixed into microcantilevers with microtrenches of 1 to 5 µm width. Zeolite is a porous material that absorbs chemical substances; thus, it is expected to work as a sensitive chemical-sensing head. The total mass increases with gas absorption, and the cantilever resonance frequency decreases accordingly. In this paper, a thick zeolite cantilever sensor array system for high sensitivity and selectivity is proposed. The system is composed of an array of microcantilevers with silicon deep trenches. The cantilevers are integrated with CMOS-made polysilicon strain gauges for frequency response electrical measurement. The post-process fabrication of such an integrated array out of a foundry-made CMOS chip is successful. On the cantilevers, three types of custom zeolite (FAU-X, LTL, and MFI) are integrated by dip and heating methods. The preliminary measurement has shown a clear shift of resonance frequency by the chemical absorbance of ethanol gas.