Integration of Liquid Crystal With Silicon-Micromachining Technology for the Realization of Chip-Scale Millimeter-Wave Phase Shifters

This article introduces chip-scale reflective-type phase shifters (RTPSs) realized by monolithically integrating liquid crystal (LC) with silicon micromachining technology. The RTPS is formed by integrating a highly miniature Quadrature hybrid with two LC-based tunable reflective loads. The LC material is confined within a micromachined silicon trench, with its dielectric properties controlled by an applied bias voltage. Two RTPSs at 28 and 62 GHz are experimentally demonstrated. The phase shifter operating at 28 GHz exhibits a phase shift of 115° as the bias voltage varies from 0 to 25 V. Its insertion loss and return loss over the frequency range of 26 to 30 GHz are 5.95 and 15 dB, respectively, resulting in a figure of merit (FOM) of 19.16°/dB. The phase shifter operating at 62 GHz achieves a phase shift of 118° with the same bias voltage range. This device demonstrates an insertion loss of 7 dB and a return loss of 13.7 dB, yielding an FOM of 16.43°/dB. Notably, the phase shift tuning for these devices is analog and continuous, with no dc power consumption. Additionally, each phase shifter incorporates a single tuning element, simplifying their operation and integration. The device fabrication is conducted in-house using a multilayer microfabrication process, resulting in the first silicon-based, chip-level LC integrated phase shifters.