An enhanced MEMS-based polyimide capacitive-type relative-humidity sensor with halloysite nanotube as a modifier

Polymers have been widely used in the fabrication of humidity sensing materials, although, issues including sensitivity and hysteresis still exist, limiting its potential. Herein, we aim to enhance the humidity sensing performances of a polyimide (PI) capacitive-type relative-humidity sensor via a simple and efficient approach. Specifically, modified halloysite nanotubes (HNTs) were doped in the polyimide sensing layer to optimize the humidity sensing capabilities of the MEMS (Micro-electromechanical Systems)-based sensor. The configurational and morphological characteristic of the sensing membrane with different content of the nanofiller were char-acterized. The humidity sensing capabilities of the enhanced sensors were investigated under the relative hu-midity (RH) range of 10-90%. Owing to the rational structure design of the sensing layer, the modified sensor exhibited enhanced sensitivity, low humidity hysteresis and good linearity. The highest sensitivity of the device with the best overall performance reached 0.87 pF/%RH, which is 1.81 times that of the pure PI based humidity sensor. Meanwhile, the sensor maintained moderate humidity hysteresis (2.18%) as well as good linearity (R2 = 0.9813) within the humidity boundary from 10 to 90% RH. The aforementioned advantages of the PI-HNTs-NH2 based humidity sensor demonstrate its promising application in humidity measurement. As a low-cost and effective additive, HNTs own great application potential in the preparation of polymer sensing devices. This work provides valuable guidance for fabricating humidity sensors with outstanding sensing performances.