Amorphous structure and electrical performance of low-temperature annealed amorphous indium zinc oxide transparent thin film transistors

The effect of low-temperature (200 °C) annealing on the threshold voltage, carrier density, and interface defect density of amorphous indium zinc oxide (a-IZO) thin film transistors (TFTs) is reported. Transmission electron microscopy and x-ray diffraction analysis show that the amorphous structure is retained after 1 h at 200 °C. The TFTs fabricated from as-deposited IZO operate in the depletion mode with on–off ratio of > 106, sub-threshold slope (S) of ~ 1.5 V/decade, field effect mobility (μFE) of 18 ± 1.6 cm2/Vs, and threshold voltage (VTh) of − 3 ± 0.7 V. Low-temperature annealing at 200 °C in air improves the on-current, decreases the sub-threshold slope (1.56 vs. 1.18 V/decade), and increases the field effect mobility (μFE) from 18.2 to 23.3 cm2/Vs but also results in a VTh shift of − 15 ± 1.1 V. The carrier density in the channel of the as-deposited (4.3 × 1016 /cm3) and annealed at 200 °C (8.1 × 1017 /cm3) devices were estimated from test-TFT structures using the transmission line measurement methods to find channel resistivity at zero gate voltage and the TFT structures to estimate carrier mobility.