Wireless flexi-sensor using narrow band quasi colloidal 3D tin telluride (SnTe) for respiratory, environment, and proximity sensing

Abstract

We developed a wireless and flexible humidity sensor based on three-dimensional (3D) narrow band quasi colloidal (NBQC) tin telluride (SnTe) material. Pristine SnTe granules were exfoliated into a homogeneous quasi colloidal (HQC) solution through mechanical liquid phase exfoliation (MLPE). Resulting HQC solution had a higher surface area with randomly shaped 3D NBQC SnTe particles that increased its humidity sensing ability by rendering more active sites and irregular pathways for interaction with water molecules. Fabrication of SnTe humidity sensor included highly conductive (2.5 μΩ/cm) and precise plasma sputtered gold (Au) inter-digital electrodes (IDEs) using a shadow mask on the flexible substrate followed by coating the thin film of 3D HQC SnTe. The SnTe humidity sensor showed variance in both capacitance and impedance with changing relative humidity (%RH). Impedance response of SnTe humidity sensor was more sensitive compared to its capacitance. We adjusted the operating frequency of our humidity sensor (1, 10, and 100 kHz) to maximize sensitivity, enhance accuracy, and reduce interference. The developed humidity sensor exhibited efficient performance, including a wide operating range (5–92 %RH), high sensitivity (85.6 kΩ/%RH), consistent stability (>48 days), and a fast response/recovery time (1.7/3.2 s). The narrow band gap of SnTe enabled strong interaction with water molecules, leading to a highly sensitive impedance response to %RH. To improve its mobility, portability, and measurability, the SnTe humidity sensor was made wireless for easy integration into a variety of devices. Our 3D NBQC SnTe humidity sensor showed its potential applications in environment monitoring, health monitoring, and proximity sensing.