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

The effect of low-temperature (200 degrees 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 degrees C. The TFTs fabricated from as-deposited IZO operate in the depletion mode with on-off ratio of >10(6), sub-threshold slope (S) of similar to 1.5 V/decade, field effect mobility (mu(FE)) of 18 +/- 1.6 cm(2)/Vs, and threshold voltage (V-Th) of -3 +/- 0.7 V. Low-temperature annealing at 200 degrees 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 (mu(FE)) from 18.2 to 23.3 cm(2)/Vs but also results in a V-Th, shift of -15 +/- 1.1 V. The carrier density in the channel of the as-deposited (4.3 x 10(16) /cm(3)) and annealed at 200 degrees C (8.1 x 10(17) /cm(3)) 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. (C) 2011 Elsevier B.V. All rights reserved.