Geometry-Based Tunability Enhancement of Flexible Thin-Film Varactors

In this letter, flexible voltage-controlledcapacitors (varactors) based on an amorphous Indium-Gallium-Zinc- Oxide (a-IGZO) semiconductor are presented. Two different varactor designs and their influence on the capacitance tuning characteristics are investigated. The first design consists of a top electrode finger structure which yields a maximum capacitance tunability of 6.9 at 10 kHz. Second, a novel interdigitated varactor structure results in a maximum tunability of 93.7 at 100 kHz. The design and frequency-dependencies of the devices are evaluated through C-V measurements. Furthermore, we show bending stability of the devices down to a tensile radius of 6mm without altering the performance. Finally, a varactor is combined with a thin-film resistor to demonstrate a tunable RC-circuit for impedance matching and low-pass filtering applications. The device fabrication flow and material stack are compatible with standard flexible thin-film transistor fabrication which enables parallel implementation of analog or logic circuitry and varactor devices.