The state-of-the-art of silicon-on-sapphire CMOS RF switches

Silicon-on-Sapphire (SOS) CMOS FETs have many properties which are desirable for RF switch applications. By being manufactured on an insulating sapphire substrate, the bulk parasitic capacitances typical of CMOS FETs are eliminated. The SOS FET has a very low Ron-Coff product, allowing for low insertion loss and high isolation in high frequency applications. Despite the low breakdown voltage intrinsic to Si, SOS FETs can be stacked in series to withstand high voltages when biased in subthreshold. This work studies the tradeoffs of SOS RF switch design and compares SOS against other technologies such as GaAs and Si-based SOI. Also presented is a high power SP6T switch with insertion loss of 0.6 dB at 2 GHz and isolation of 40 dB at 2 GHz. The presented switch has the highest linearity reported to date of any SP6T switch with a P1dB of 20 W and OIP3 of <+70 dBm.