Abstract
We report two-step annealing, high temperature and sequent low temperature, for amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) to improve its stability and device performance. The annealing is carried out at 300 oC in N2 ambient for 1 h (1st step annealing) and then at 250 oC in vacuum for 10 h (2nd step annealing). It is found that the threshold voltage (VTH) changes from 0.4 V to -2.0 V by the 1st step annealing and to +0.6 V by 2nd step annealing. The mobility changes from 18 cm2V-1s-1 to 25 cm2V-1s-1 by 1st step and decreases to 20 cm2V-1s-1 by 2nd step annealing. The VTH shift by positive bias temperature stress (PBTS) is 3.7 V for the as-prepared TFT, and 1.7 V for the 1st step annealed TFT, and 1.3 V for the 2nd step annealed TFT. The XPS (X-ray photoelectron spectroscopy) depth analysis indicates that the reduction in O-H bonds at the top interface (SiO2/a-IGZO) by 2nd step annealing appears, which is related to the positive VTH shift and smaller VTH shift by PBTS.
Highlights
Control of O-H bonds at amorphous indium-gallium-zinc oxide (a-IGZO)/SiO2 interface by long time thermal annealing for highly stable oxide thin-film transistor (TFT)
The amorphous indium-gallium-zinc oxide (a-IGZO) is the most popular Amorphous oxide semiconductor (AOS) used for thin-film transistor (TFT) of active-matrix displays because of its advantages such as relatively high field-effect mobility (> 10 cm2V-1s-1), low threshold voltage (< 1 V), low subthreshold swing (< 0.3 Vdec-1), low-temperature process (< 200 oC) and optical transparency in visible region
A-IGZO TFTs are being used for liquid-crystal display (LCD) and organic light-emitting diode (OLED) displays.[1,2,3,4,5]
Summary
Control of O-H bonds at a-IGZO/SiO2 interface by long time thermal annealing for highly stable oxide TFT. It is found that the transfer curve shifts to negative VGS direction, which makes mobility increases after 1st step annealing, resulting in VTH shifts from 0.4 V to -2 V and μLin from 18 cm2V-1s-1 to 25 cm2V-1s-1.
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