Calder, L. (2010). Behavioral Modeling of Zinc-Oxide, Thin-Film, Field-Effect Transistors and the Design of Pixel Driver, Analog Amplifier, and Low-Noise RF Amplifier Circuits. Unc Charlotte Electronic Theses And Dissertations.
Zinc-oxide (ZnO) is of great interest due to transparent properties, high breakdown voltages, and low cost. Behavioral modeling is presented in this dissertation to model ZnO thin-film field-effect transistor (FET) drain current versus gate-source overdrive voltage. Initial findings show that in "strong inversion," saturation, the drain current equation reveals a quartic-law dependency on gate-source overdrive voltage instead of square-law dependency seen in complementary metal-oxide semiconductor (CMOS) with no mobility reduction effects. This is postulated to result from the ZnO mobility showing a square-law increase with gate-source overdrive voltage. A "strong inversion," saturation model having ±1.6% deviation from measured data is created in verilog-A to simulate and design circuits. Circuits include a fabricated and measured pixel driver circuit sinking 28 μA of current while only having a gate area of 20 μm2. This ZnO thin-film FET pixel driver is believed to have the highest current density reported at the time of this writing. Also, the first known ZnO thin-film FET analog amplifier is analytically designed for a gain of 3 V/V at 10 kHz while drawing only 8 μA of supply current. Finally, the first known ZnO thin-film FET low-noise RF amplifier is designed, utilizing scattering parameters measured at the Air Force Research Laboratory on a device with minimum channel length of 1.25 μm. This amplifier has a small-signal gain of 12.6 dB at 13.56 MHz, and a current drain of 268.4 mA at a drain voltage of 13 V.