Thermally Controlled Vanadium Dioxide Thin Film Microwave Devices

Vanadium dioxide (VO2) thin films have unique insulator to metal transition above the critical temperature of 68 degrees C. In this study, VO2 thin films were deposited on a sapphire substrate for thermally controllable RF/microwave devices such as switches, limiters and resonators. The selectively deposited VO2 thin film based devices showed similar to 2 k Omega at room temperature and less than 2 Omega at 70 degrees C. These thermally controlled varistors were utilized in shunt as well as series configurations for microwave switching and in resonant structures. Switching devices designed using a VO2 shunt varistor showed good isolation (>20 dB) and low insertion loss (<1 dB) up to 20 GHz. This paper presents two types of shunt varistor devices designed and fabricated on sapphire substrates.