A novel microscale multilayer PZT MEMS cantilever for resonant photoacoustic gas sensing

This paper reports a novel photoacoustic spectroscopy (PAS) gas sensor based on micro-electro-mechanical systems (MEMS) that achieves resonance matching between a multilayer PZT piezoelectric microcantilever and an H-type acoustic resonator. The device integrates the PZT thin film and exhibits a measured mechanical resonance at 5003.3 Hz with a 3-dB bandwidth of 33.74 Hz. To the best of our knowledge, the proposed device represents one of the most miniaturized thin-film piezoelectric cantilevers reported for PAS gas sensing, with active dimensions of only 1039 μm × 250 μm × 6.43 μm. An H-type photoacoustic cell is designed to align its resonance with the cantilever. Using C₂H₂ as a sample gas, the measured results show a linear responsivity of 2.41 μV/ppm over the concentration range of 229.8-5000 ppm, with an excellent linearity of 0.999. Allan deviation analysis of the pure nitrogen background indicates a minimum detection limit (MDL) of 477 ppb at an integration time of 265 s, corresponding to a conventional NNEA of 14.39 × 10^-8 cm^-1·W·Hz^-1/2. A novel metric identified as flexural-compliance-adjusted NNEA (FCA-NNEA) is further introduced to indicate the extent to which the achieved detection performance benefits from the flexural compliance of the cantilever. The proposed device achieves an FCA-NNEA of 0.859 cm^-1·W·Hz^-1/2·mm, indicating competitive performance without relying on an extremely compliant cantilever. Together with its microscale dimensions, these results demonstrate a promising route toward compact MEMS PAS sensing.