High Performance Thin Film Transistors With Sputtered In–Al–Zn–O Channel and Different Source/Drain Electrodes

High performance thin film transistors (TFTs) based on sputtered In-Al-Zn-O (IAZO) channel layer with excellent photoelectric properties were fabricated and characterized. The IAZO films remained amorphous with low surface roughnesses both before and after annealing. The Hall mobility increased from 27.1 to 74.2 cm
²
/Vs after annealing. High average transmittances over 95% in the visible range and wide optical band gaps around 4.1 eV were obtained for both unannealed and annealed IAZO films. The energy level diagrams of IAZO films before and after annealing were derived based on the ultraviolet photoelectron spectroscopy measurements. A high field-effect mobility of 20.57 cm
²
/Vs, a high ON-OFF current (I
_on
/I
_off
) ratio of 4.02×10
⁷
, and a subthreshold swing (SS) of 0.55 V/dec were obtained for the IAZO TFT with Au electrodes. In comparison, though a lower mobility of 9.54 cm
²
/Vs was exhibited, a higher I
_on
/I
_off
ratio of 7.39 × 10
⁷
, a lower SS, and a much lower hysteresis were obtained for the TFT with Ti electrodes.