Silicon-Micromachined Liquid Crystal Variable Capacitors for Tunable RF Devices

This paper presents the design and fabrication of a silicon-micromachined variable capacitor based on nematic liquid crystal (LC). The LC material is encapsulated in a thin micromachined housing, and its dielectric properties are controlled electronically. The chip capacitor can be used in a wide range of RF reconfigurable applications that require analog tuning. Measurement and simulation results are presented for the chip LC variable capacitor. It exhibits a measured quality factor ranging from 44-123 at 1 GHz. Biasing voltage ranging from 0 V to 40 V results in a measured capacitance change of 18% for the fabricated micromachined capacitor. The devices are fabricated using an in-house multi-layer microfabrication process. An ion beam irradiation system is employed for the treatment of the pre-alignment layer. To our knowledge, this is the first time a chip LC-based variable capacitor has been demonstrated.