Metal Oxide-based (ZnO and IZO) Thin Film Transistors and Circuits

This work emphasizes room temperature deposition and fabrication of staggered bottom-gate ZnO and IZO TFTs. We synthesized these oxide thin films by RF sputtering in an Ar/Oxygen ambience with no intentional heating of the substrates. Bottom gate staggered structure ZnO TFTs were fabricated (Ti/Au/Ti gate and Au/Ti source/drain) and characterized. ZnO TFTs retained well-behaved transfer characteristics down to a channel length of 4 μm with field effect mobility of 5 cm2/V.s, on/off current ratio exceeding 106 and threshold voltage around -5V. The IZO TFTs, with ITO as gate metal layer and highly conducting amorphous IZO forming the source/drain material had reasonably high field effect mobility of 20 cm2/V.s and on/off current ratio exceeding 106, which are well suited for active matrix display applications. Finally, to demonstrate the viability of oxide-based device integration, simple circuits such as inverters and pseudo-logic circuits are designed, fabricated and tested.