Fabrication and characterization of a novel bulk Si micromachined distributed microwave phase shifter

In order to implement X and K band micromachined phase shifter based on single crystal silicon material and thus featuring good micro-mechanical properties, a novel digital phase shifter is proposed, designed and successfully realized with bulk Si micromachining method by the authors. Utilizing the mechanism of nonlinear transmission line, it delivers true time delay through distributed archietecture. Instead of varactors in tradition devices, butterfly-like micromachined multiplayer bridges of single crystal Si-based laminate composite structure (Si/SiO2/Cr/Au/SiN) are used as the loading varactors. The microstructure can provide excellent mechanical performance over those with pure metal (alloy) microbridges because of the Si skeleton with good mechanical properties and the avoidance of the metal creep and thermal incompatability between the microbridges and dielectric substrate. The fabrication flow is introduced, which is a combination of Si etching and anodic bonding. The quasi-static actuation test was performed and showed a threshold voltage of 45similar to60V. The microwave test was made-on an Agilent Vector Network Analyzer combined with a Cascade microwave probing system. It can be seen from the result that the phase shift varies linearly with frequency and rise up to 82.4degrees @20.5GHz. Tapered adaptation sections at both ends of the device provide good impedance transformation and secure a good reflection performance in a wide frequency range (5similar to20.5GHz).