A 25–50GHz Phase Change Material (PCM) 5-Bit True Time Delay Phase Shifter in a Production SiGe BiCMOS Process

This paper presents the implementation and measurement results of a wideband (DC–67 GHz) phase change material (PCM) switch and a miniature 5-bit true time delay (TTD) phase shifter. A series-shunt single pole double throw (SPDT) switch is implemented based on the 4-terminal PCM switch integrated in the back-end-of-line (BEOL) of Tower Semiconductor SBC18H3 0.18 µm SiGe BiCMOS process. The PCM Switch core has a nominal RON of 3Ω and a COFF of 4 fF leading to a FoM of 12 fs. This core performance leads to a wideband SPDT IL of 0.9 dB at 30 GHz and to 45 dB of isolation. Using the SPDT switch, a 5-bit 0–124 ps TTD unit with a transmission line based implementation is presented. It exhibits an RMS group delay error of less than 2 ps from 25–50 GHz and less than 3 ps from 6–55 GHz.