Flexible Lumped Microwave Passive Components and Filters on Cellulose Nanofibril Substrates

Cellulose nanofibril (CNF) substrates that are inexpensive, biodegradable, and quickly incinerable, are potential substrates for disposable RF applications. In this paper, high-performance flexible microwave lumped elements and filters fabricated on flexible CNF substrates are reported. A spiral inductor with a resonance frequency of 29.8 GHz and quality (Q) factor of 8.5 and a metal-insulator-metal (MIM) capacitor with a resonance frequency of 45 GHz and Q factor of 85.2 were achieved in a 200 μm thick CNF substrate. Meanwhile, the inductor and capacitor exhibit outstanding mechanical bendability, that is negligible performance changes were observed when they were bent to a radius as small as 15 mm. Based on the spiral inductor and MIM capacitor, a 5-GHz band-stop filter and a 4 GHz band-pass filter with excellent mechanical bendability were further demonstrated on the CNF substrate. These results indicate the potential of using CNF as substrates for broader microwave applications.