Electrical biasing scheme for Liquid-Crystal-based tunable Substrate Integrated Waveguide structures

In this paper, an electrical biasing structure is proposed for a tunable Substrate Integrated Waveguide (SIW) device with Liquid Crystal (LC) as the tuning component. The biasing circuits or electrodes are made of chromium and gold layers. Silicon nitride layer, which has a thickness of 1 μm, is employed to isolate the electrodes against ground. Since voltage as high as ±200V may be applied, high breakdown voltages are required. As a proof of concept, a simple LC-SIW phase shifter based on a tunable delay line is manufactured and sealed with the fabricated biasing structure. Simulation results exhibit a Figure of Merit (FoM) of 89°/dB at 20GHz. The fabricated phase shifter give FoM of 32°/dB with switching time of 5s.