Be-Doped ZnO Thin-Film Transistors and Circuits Fabricated by Spray Pyrolysis in Air

We report the fabrication of zinc oxide (ZnO) thin-film transistors (TFTs) and simple integrated circuits by spray pyrolysis, and examine the role of beryllium (Be) as the chemical dopant. Doping is achieved through addition of Be-acetylacetonate into the parent Zn-acetate precursor solution followed by film deposition through spray pyrolysis. The microstructural properties of as-grown Be-ZnO films with different dopant concentrations are investigated using a combination of atomic force microscopy and x-ray diffraction techniques, which show the formation of polycrystalline films. Introduction of Be is found to impact the degree of crystallinity of ZnO films where a dramatic decrease in the average grain size is observed with increasing Be concentration. To assess the effects of Be-doping on the electrical properties of ZnO films we have fabricated Be-ZnO based TFTs using different doping concentrations. The average electron mobility calculated from these transistors is on the order of ~ 2 cm²·V^-1·s^-1 with the threshold voltage (VTH) exhibiting a strong dependence on Be concentration. The ability to control VTH through the introduction of Be has been exploited for the fabrication of unipolar inverters with symmetric trip-voltages and good noise margins.