A DC-120 GHz SPDT Switch Based on 22 nm FD-SOI SLVT NFETs with Substrate Isolation Rings Towards Increased Shunt Impedance

Abstract

A DC-120 GHz SPDT switch is proposed using GlobalFoundries' 22FDX® SLVT devices with improved substrate isolation rings. For mm-wave switch applications, 22FDX® offers BFMOAT devices that include substrate isolation zones beneath them to reduce high-frequency shunt loss, though, compared to SLVT devices, this sacrifices the back-gate functionality, resulting in higher RonCoff. This paper proposes and analyses substrate isolation zones implemented in ring-shapes around SLVT-FETs to reduce parasitic shunt admittance while preserving the back-gate. The resulting effective device boasts a low RonCoff metric (thanks to an SLVT-FET core with back-gate) and simultaneously achieves high substrate impedance to the reference ground node (similar performance as BFMOAT-FETs). From such devices, a full SPDT switch was fabricated and characterized up to 130 GHz. Having less than 2.4 dB insertion loss and better than 22 dB isolation from DC to 120 GHz, it outperforms analogous SPDT modules implemented using conventional SLVT or BFMOAT FETs.