Flexible humidity sensors composed with electrodes of laser induced graphene and sputtered sensitive films derived from poly(ether-ether-ketone)

Abstract

Currently, there are still many challenges to fabricate flexible humidity sensors with excellent properties in large-scale production. In this paper, a new and convenient method was proposed to prepare flexible humidity sensors, which were composed with interdigital electrode (LIG-IDE) of laser-induced graphene on flexible substrates of poly(ether-ether-ketone) (PEEK) and impedance-type hygroscopic film by PEEK sputtering and polymerization. The humidity sensors displayed good humidity sensing properties with high sensitivity, fast response/recovery time (4.2/6.8 s), and a wide operating range of relative humidity (11% RH∼97% RH). In the mechanism study of PEEK sputtered and polymerized humidity sensors, we found that the impedance-humidity response can be attributed to hydrophilic functional groups formed on the polymer chains by moist aging with oxidation. The above humidity sensitive advantages extended the flexible sensor's versatility, including contactless humidity sensing and breath detection for human applications. Therefore, a high-performance flexible humidity sensor entirely based on the PEEK polymer material is reported here, which provides a novel approach for the development of flexible gas and humidity sensors.