A Single-Chip Liquid Crystal Variable Capacitor Using a Microfabrication Process for Tunable RF and Microwave Applications

This article presents the implementation of a single-chip silicon-micromachined variable capacitor employing nematic liquid crystal (LC). The LC substance is confined within a slender micromachined enclosure, enabling electronic tuning of its dielectric characteristics. The compact dimensions of these chip capacitors facilitate their utilization across an extensive range of RF tunable/reconfigurable applications. This article thoroughly explains the fabrication procedure and includes comprehensive discussions on simulation as well as measurement results of the chip-based LC variable capacitors. Three chip capacitor configurations are demonstrated: 1) single port shunt capacitor; 2) two-port series capacitor with an integrated bias line; and 3) two-port series capacitor. The shunt capacitor displays an 18% variation in capacitance, while the quality factor ranges from 44 to 123. The measurements of the capacitor with the integrated bias line reveal a 21% tuning range accompanied by a quality factor ranging from 22 to 45 at 1.25 GHz. On the other hand, the two-port series capacitor exhibits a 23% change in capacitance values while demonstrating a quality factor that varies between 30 and 105 at 1.25 GHz. The chip capacitors discussed in this work are manufactured utilizing an in-house multilayer microfabrication process. An ion beam irradiation (IBI) process is developed for the treatment of the prealignment layer of highly miniature capacitors.