Effect of polyimide layers on the permittivity tuning range of liquid crystals

Liquid crystals have potential applications in the design of tunable microwave devices. Polyimide films are commonly incorporated in designs to achieve reproducible molecule alignment in the unbiased state. In this investigation two separate resonator elements are designed and investigated: One is fabricated with polyimide layers and one without. Experimental results obtained with a patch resonator illustrate that about half of the maximum tuning range is achieved without polyimide layers. Since substrates able to sustain a temperature range of 180-300°C are required for the polyimide film curing process, avoiding polyimide enables using even lower heat resistant substrates for various tunable microwave applications and can lead to faster fabrication processes.