Humidity Sensors Based on Photolithographically Patterned PVA Films Deposited on SAW Resonators

Relative humidity (RH) sensors are fabricated based on anti-corrosive gold electrodes surface acoustic wave (SAW) resonators, which are covered with photolithographically patterned polyvinyl- alcohol (PVA) films in micrometer resolution. The patterned films enable RH sensors conveniences of measurement and integration with clean contact pads, and facilitate the sensor design with various patterns for different applications requirements. Two RH sensors with almost the same PVA film thickness but different patterns are investigated. The sensor with the PVA film patterned only on the reflectors of the SAW resonator has larger RH operation range, higher maximum reflection, and narrower relative bandwidth. In comparison, the sensor shows higher sensitivity when the PVA film is only open at interdigital transducer pads.