Preparation of flexible resistive humidity sensors with different electrode gaps by screen printing and their humidity-sensing properties

Abstract

A novel, flexible resistive-type humidity sensor was fabricated through silk-screen printing of a humiditysensitive copolymer of [2-(methacryloyloxy)ethyl] dimethyl benzyl ammonium chloride and methyl methacrylate on a glass epoxy (GE) substrate. The basic structure of the sensor consisted of a 4-fingered interdigital electrode with various gaps (310, 360, 410, and 460 μm). Gold electrodes GE substrate were prepared by first printing silver nanopaste (thickness 6–7 μm), followed by consecutive electroless plating of Cu (5 μm), Ni (2 μm), and then Au (80 nm). The activation energy for ion conduction and the copolymer/substrate interface were used to explain the differences of humidity-sensing characteristics of sensors fabricated on a GE substrate. Electrode construction had a significant influence on the humidity-sensing characteristics of polymeric relative humidity sensors. Details regarding humidity sensor characteristics, including sensitivity, linearity, temperature dependence, hysteresis, and response time depending on electrode construction were compared. The flexible humidity sensor showed acceptable linearity between logarithmic impedance and relative humidity in the range of 20–95%RH, low hysteresis (within 1.5%RH), good response (75 s) and recovery time (95 s), and long-term stability (225 days at least), measured at 1 V, 1 kHz, and 25 °C. Open image in new window