Piezoresistive pressure sensor using nanocrystalline silicon thin film on flexible substrate

A flexible pressure sensor fabricated at processing temperatures as low as 300 degrees C using piezoresistive elements of nanocrystalline silicon (nc-Si) on flexible polyimide substrate is reported. Aluminium induced crystallization (AIC) of Hot Wire Chemical Vapour deposited a-Si:H films is used to obtain the nc-Si films with almost 100 % crystalline fraction as revealed by Raman Spectroscopy, and with a measured piezoresistive gauge factor of 413. A novel processing method is adopted, wherein the photoresist itself acts as a mask for the transfer of the pattern on the polyimide diaphragm. This enables bypassing the micro machining step, which otherwise is unavoidable for patterning the sensing elements. A full Wheatstone bridge configuration of nc-Si piezoresistors is realized with acceptable linear response of the output signal for an applied pressure range up to 50 psi and the sensitivity is found to be 183.10 +/- 3.48 mV/mA/MPa. A novel pressure jig is also designed with the capability to characterize four sensors simultaneously with an arrangement to apply hydrostatic pressure of compressed air. (c) 2020 Elsevier B.V. All rights reserved.