Micro Humidity Sensor Using ALD Zirconium Oxide for Low Frequency Applications

In this paper, we report an atomic layer deposited (ALD) zirconium oxide-based micro humidity sensor. The sensor comprises of a pair of interdigital platinum electrodes on a silicon substrate and a humidity sensing film (ZrO2) coated on the electrodes. The atomic layer deposition technique is utilized to conformally coat 42 nm thick zirconium oxide on 410 nm thick electrodes to increase the surface area of the sensing film. The sensor is tested under various humidity levels. It is evident from experimental results that the impedance of the sensor decreases with increase in relative humidity. Furthermore, the sensor is highly sensitive to humidity at the low frequency of the applied signal. At 20 Hz frequency when relative humidity is varied from 0.1% to 92%, the impedance of the sensor decreased from 143.46 M to 62.04 k with a net change in impedance of about 2,312 times, which is much higher than most of the reported zirconium oxide based humidity sensors.