Ultrawideband, Photothermally Excited mmWave Vanadium Dioxide Switches
David L. West, Ashley Goodnight, Nima Ghalichechian
Abstract
We report the first demonstration of photothermally excited vanadium dioxide (VO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {2}}$ </tex-math></inline-formula>) RF switches. The switches operate from dc to 65 GHz. VO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {2}}$ </tex-math></inline-formula> is a phase-change material with a volatile insulator-metal transition (IMT) at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$68~^{\circ }$ </tex-math></inline-formula>C, and it is a promising technology for millimeter-wave (mmWave) switching applications that require low-loss performance. However, the traditional activation of VO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {2}}$ </tex-math></inline-formula> switches using microheaters results in undesirable parasitic capacitance. We propose heating VO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {2}}$ </tex-math></inline-formula> 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/(<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\pi $ </tex-math></inline-formula>R<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{on}}$ </tex-math></inline-formula>C<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{off}}$ </tex-math></inline-formula>) is extracted as 12.4 THz. We achieve switching times in the microsecond range using a continuous-wave 786-nm semiconductor laser.