Electrode-Adaptive Thin-Film Integrated Logic Circuits

Amorphous oxide-based thin-film logic circuits have been fabricated using only an n-type amorphous silicon-zinc-tin-oxide (a-SZTO) channel layer with different source/drain electrodes. Enhancement-mode thin-film transistors (TFTs) were fabricated with oxide electrodes. Depletion-mode TFTs were fabricated with metal electrode. Work functions were measured by Kelvin probe microscopy. The barrier heights (Phi(B)) between the a-SZTO channel layer and the electrode were measured to be 1.831, 2.341, and 2.339 eV for the Ti/Al electrode, Indium-silicon-oxide (ISO) electrode, and indium-tin-oxide (ITO) electrode, respectively. The physical mechanism on the variation of sheet and contact resistances was investigated using a transmission line method, and the change in the resistances is closely related to Phi(B). Inverters were fabricated, with different V-TH values adopted simply by using different contact characteristics between various electrodes and the semiconductor channel. High values of voltage gains in inverters were obtained: 12.33 (ISO) and 11.75 (ITO) at V-DD = 5 V. It was also confirmed that more complicated n-type-based NAND and NOR thin-film circuits, implemented with different electrodes, functioned as conventional logic circuits. This simple fabrication method of thin-film logic circuits opens the possibility of implementing next-generation stacked integrated circuit technology.