A bulk micromachined distrubuted digital phase shifter for microwave phased array applications

In this paper, a novel distributed digital MEMS( Micro-Electro- Mechanical System) microwave phase shifter, fabricated with bulk Si micromachining techniques, is presented. Utilizing distributed nonlinear transmission line technique, with single crystal silicon based multiplayer microbridge structures as loading varactors, this phase shifter delivers true time delay and wideband performance. A micromachining process flow, combining anodic bonding and single crystal silicon etching with heavy boron doping, was developed to fabricate the movable Si-based microbridges over a coplanar waveguide(CPW). An electrostatic voltage applied between the Si layer of the microbridges ( varactors) and CPW ground plane pulls down the microbridges, effecting a phase shift varying linearly with frequency. The principle, process and RF performance charaterization are described. The actuated phase shifter has achieved 90.2 degrees phase shift at 20.5 GHZ, with good reflection loss (-12dB) in the frequency range of 5 20.5GHz. The insertion loss is a little high, 3.8 7dB, however, due to the lossy substrate of Pyrex 7740 glass and thin metalization of CPW.Engineering, Electrical & ElectronicMaterials Science, MultidisciplinaryPhysics, Condensed MatterCPCI-S(ISTP)