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 insertion loss (IL) and >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.