Ultrawideband, Photothermally Excited mmWave Vanadium Dioxide Switches

We report the first demonstration of photothermally excited vanadium dioxide (VO $_{\mathbf {2}}$ ) RF switches. The switches operate from dc to 65 GHz. VO $_{\mathbf {2}}$ is a phase-change material with a volatile insulator-metal transition (IMT) at $68~^{\circ }$ C, and it is a promising technology for millimeter-wave (mmWave) switching applications that require low-loss performance. However, the traditional activation of VO $_{\mathbf {2}}$ switches using microheaters results in undesirable parasitic capacitance. We propose heating VO $_{\mathbf {2}}$ with a laser, which decouples the excitation method from electromagnetic (EM) design. The coplanar waveguide (CPW) switches exhibit low-loss, ultrawideband performance, with <0.43-dB>17.7-dB return loss in the on state and >17.2-dB isolation in the off state from 10 MHz to 65 GHz. The figure of merit defined as 1/( $2\pi $ R $_{\text{on}}$ C $_{\text{off}}$ ) is extracted as 12.4 THz. We achieve switching times in the microsecond range using a continuous-wave 786-nm semiconductor laser.