Fast AZO Powder Resistive MEMS Sensor for Humidity Sensing

This letter investigates the humidity detection capabilities of aluminum-doped zinc oxide (AZO) powder. The transduction technique was resistive. The humidity sensor contained two microelectrodes fabricated on a glass slide, for resistance measurements. The humidity sensitive material was a combination of AZO seed film and AZO powder, deposited on the sensing electrodes. Different relative humidity (RH) levels from 20% to 85% and back to 20% were tested. The resistance was decreasing with increasing the humidity levels, due to the electron conduction through the sensing AZO powder. The charge transfer between AZO powder and water molecules seems to enhance the conductivity of AZO in the presence of moisture. The water molecules were adsorbed onto the sensing materials and acted as electron donors. In this research, the slope of the resistance measurements was chosen as a function of the humidity level detected. The sensor's response rate of ΔR (Ω/s) increased with increasing RH percentage. The research validates that AZO powder is an effective sensing material for humidity sensors. This humidity sensor demonstrated ability to detect humidity at low levels, such as 20%, with short detection time of 30 s.