A Bulk Micromachined Distributed Digital Microwave Phase Shifter with Butterfly Multilayer Bridges and MAM Capacitors

This paper reports a bulk Si micromachined distributed digital microwave phase shifter with butterfly-like loading microbridges. Having a multilayer structure, the bridges use heavily boron-doped single crystal silicon (SCS) as the skeleton layer, so that the excellent mechanical property of SCS can be utilized to ensure the performance and reliability of the device. The fabrication is shown to be much simpler than surface micromachining which have been widely used by MEMS phase shifters ever reported. A finite-element-method full-wave simulation, was made for the microwave performance validation of this device, the application of which in phase shifter microwave performance analysis has not been reported as far as the authors know. Since Si is used as the skeleton of the bridges, thermal mismatch between all-metal bridge and dielectric substrate is avoided, and reliability at high temperature is guaranteed. Besides, the biasing network is simple to implement and no DC blocking capacitors are needed to realize a multi-bit device. The microwave test results show that a 180deg 1-bit phase shift has been realized with return loss <10 dB and true time delay performance