Vanadium Oxide Thin-Film Variable Resistor-Based RF Switches

Vanadium dioxide (VO₂) is a unique phase change material (PCM) that possesses a metal-to-insulator transition property. Pristine VO₂ has a negative temperature coefficient of resistance, and it undergoes an insulator-to-metal phase change at a transition temperature of 68 °C. Such a property makes the VO₂ thin-film-based variable resistor (varistor) a good candidate in reconfigurable electronics to be integrated with different RF devices such as inductors, varactors, and antennas. Series single-pole single-throw (SPST) switches with integrated VO₂ thin films were designed, fabricated, and tested. The overall size of the device is 380 μm × 600 μm. The SPST switches were fabricated on a sapphire substrate with integrated heating coil to control VO₂ phase change. During the test, when VO₂ thin film changed from insulator at room temperature to metallic state (low-resistive phase) at 80 °C, the insertion loss of the SPST switch was <;3 dB at 10 GHz. In addition, the isolation of the SPST improved to better than 30 dB when the temperature dropped to 20 °C. These tunable characteristics of the RF switch provide evidence for VO₂ as a useful PCM for the broad range of applications in reconfigurable electronics.