Study And Fabrication Of Humidity Sensor Of Zirconia Film On Silicon Substrate

Humidity sensor is widely used in industry and people's daily life. In order to integrate with the controlling circuits, the sensor with silicon substrate and thin film is needed. For this purpose, a ZrO₂ thin film sensor on silicon substrate is studied and fabricated, including sensing electrode design, optimizing the preparation process of ZrO₂ thin film throughout the experiment, characterization of the film, fabrication of the sensor, testing the sensing performance and analyzing the mechanism of the humidity sensing.The shape of the Pt electrode is designed by ANSYS software simulation and fabricated by IC process for metal layer, such as spurting, photolithography and lift-off.The sensing film is ZrO₂/TiO₂, the TiO₂ thin film is performed as the via-layer between the metal and the ZrO₂ sensing film. The film is prepared by sol-gel method. The detail of the sol-gel method such as the raw material dose, the ageing time, the spin coating speed, the soft bake temperature and time, the sinter temperature and time is studied by experiment and TG-DSC. The character of the film is measured by the instruments of XRD, step profiler, AFM, SPS. The structure of the humidity sensor is ZrO₂/TiO₂/Pt/SiO₂/Si.The sensing performance of the sensor was measured. The result shows that the impedance of the sensor changes four orders with the relative humidity changing form 11 % to 98% which means a high sensitive. The response and recovery time of the sensor is respectively 15s and 25s. The humidity hysteresis is about 10%RH. The sensor can be used under frequency from 0.4 kHz to 10 kHz.The O 1s of XPS is used to analyze the absorbing ability of the bi-layer film. The sensing mechanism was also analyzed by equivalent circuits derived from the impedance characteristic curve.