A fast response and CMOS compatible micro gas flow sensor with thermal feedback

This letter presents a CMOS compatible micro flow sensor (MFS) that operates in a thermal feedback (TF) mode. The proposed MFS contains four parallel polysilicon resistors on the micro bridges. The gas flow induced temperature difference between two outlying thermistors is minimized and balanced through the negative thermal feedback, while the power distribution on two inlying microheaters is automatically adjusted. Accordingly, the measured voltage difference between two inlying microheaters is used as the sensor output signal. For the N2 gas flow, the proposed MFS works in TF mode achieve a prominent sensitivity of 1.74V/(m/s) and a bidirectional detection range of -6 ∼ 6 m/s, which shows an almost 2X enhanced flow range as compared to the counterpart works in a constant voltage mode. Moreover, the rise time of MFS under a suddenly generated gas flow is experimentally determined as 3.1 ms (error ±0.13 ms). The measured rise time is 43% faster than that of the micro flow sensor without thermal feedback, which proves the successful development of a fast response MFS.