Microporous copper chromite thick film based novel and ultrasensitive capacitive humidity sensor

Abstract

In this paper we report to have developed a microporous Copper Chromite (CuCr2O4) thick film based capacitive humidity sensor that exhibits excellent response in the range of 1%–98% RH at room temperature. CuCr2O4 spinel nanopowder was synthesized by a facile sol-gel technique. The as prepared CuCr2O4 nanopowder was screen printed to develop a thick film and it was sandwiched between two parallel electrodes of silver and copper to develop a parallel plate capacitive sensor. The CuCr2O4 nanoparticles and the thick film were well characterized by XRD, XPS, FTIR spectroscopy, Raman Spectroscopy, FESEM, TEM, EDX, and contact angle measurement. Various electrical parameters of the sensor, viz. Capacitance (Cp), Dissipation (D), Conductance (Gp), Susceptance (Bp), and admittance (Y) were measured at different frequencies ranging from 100 Hz to 1 MHz. It was observed that the optimum operating frequency is 1 kHz. At this frequency the sensor exhibited very high sensitivity, especially in the low %RH range of 1%–40% (∼640 pF change in capacitance), low dissipation loss (<2 for all %RH range), and fast response (∼3.6 s) and recovery times (128 s). Further, the sensor exhibits long-term stability (at least 6 months). The sensor may find commercial applications in food packaging, tea industry, hospitals, power plants etc.