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 °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 ~2 kΩ at room temperature and less than 2 Ω at 70 °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.