Development of compact phase shifters on silicon for monolithic integration of voltage controllers

摘要

A ferroelectric thin film RF phase shifter on silicon has been designed and developed with the implementation of polysilicon and BST thin film layers on small device area (8 mm~2) and fabrication processes fully compatible with current silicon IC technology. The design of a bilateral interdigital coplanar waveguide (BI-CPW) phase shifter is analyzed. This new design has shown a phase shift of 180° at 25 GHz with efficient use of a (Ba,Sr)TiO_3 thin film in the bilateral interdigital finger section. Inherent insertion loss and DC current leakage caused by conductivity of silicon substrate have been investigated. Due to the implementation of polysilicon thin film on silicon, insertion loss was controlled below 6.7 dB and signal dissipation with bias increase was not observed. It is shown that the polysilicon trap layer helped to reduce surface charge accumulation on the silicon surface.