High-sensitivity humidity sensor based on natural hydroxyapatite

Abstract

In the present work, we study the ability of materials based on hydroxyapatite to be developed as a sensing materials toward relative humidity. Natural (NHAp) and synthetic (SHAp) hydroxyapatites are used as sensitive layers on interdigitated copper electrodes. The morphological structure and composition of HAp are characterized by X-ray diffraction analysis (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy EDS. The capacitive and impedance responses of the humidity sensors are analyzed at frequencies ranging from 0.1 kHz to 1 MHz at different humidity values varying from 16 to 87%. Other properties and characteristics of moisture detection are studied for both sensors such as sensitivity, hysteresis, response and recovery times and conduction mechanisms. The results showed that the best performance of all our manufactured sensors is obtained for the NHAp sensor. This sensitivity is around 17900pF/%RH, whereas the response and recovery times are approximately 8 s and 11 s, respectively, the hysteresis value was very low. The obtained results proved that the natural hydroxyapatite is a good candidate and suitable for moisture sensing application.