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 degrees 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 mu m x 600 mu m. 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 degrees 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 degrees 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.