Loss Compensated PCM GeTe-Based Latching Wideband 3-bit Switched True-Time-Delay Phase Shifters for mmWave Phased Arrays

This article reports the first implementation of 3-bit millimeter-wave switched true-time-delay (TTD) phase shifters based on phase-change material (PCM) germanium telluride (GeTe). Two TTD phase shifters are presented. The first phase shifter is designed using four monolithically integrated PCM single-pole triple-throw (SP3T) switches to route the signal through delay lines. The insertion loss variation between various states is minimized by integrating two fixed PCM GeTe elements maintained in the crystalline state, along with the optimized width of the delay lines. The PCM switching cells are latching type, thus, consume no static dc power. The SP3T switches are connected back-to-back in two stages to provide a 3-bit phase shift with 20° precision. The second phase shifter is designed using two back-to-back connected PCM single-pole eight-throw (SP8T) switches. Both phase shifters are designed to operate over an 8 GHz wide frequency band with a center frequency of 30 GHz. The devices are fabricated in-house using an eight-layer microfabrication process. The proposed devices are highly miniaturized with an overall device area of 0.42mm
²
and 1.4mm
²
for the first and second phase shifter, respectively. The first phase shifter exhibit a measured average loss of 4.3 dB with a variation of ±0.3 dB and a return loss better than 20 dB, while the second phase shifter demonstrates low average measured loss of 3.8 dB with only ±0.2 dB loss variation and returns loss better than 17 dB at 30 GHz. Both phase shifters provide 180° linear phase shift with lower than 18 ps delay in the worst case.