Influences of Nitrogen Doping on the Electrical Characteristics of Indium-Zinc-Oxide Thin Film Transistors

Thin film transistors (TFTs) with nitrogen doped amorphous indium-zinc-oxide (a-IZO:N) as the channel layer were prepared by rf magnetron sputtering with an argon, oxygen, and nitrogen gas mixture at room temperature. XRD measurements confirm the amorphous structure of a-IZO:N thin film and AFM verifies its uniformity. Transmittance curves show that nitrogen doping in a-IZO films can narrow the optical band gap and suppress oxygen vacancies, which is also proved by XPS. When the nitrogen flow rate is 4 SCCM, a-IZO TFTs possess optimized the characteristics, with saturation mobility 24.67 cm
²
V
^-1
s
^-1
, subthreshold swing 0.41 V/decade, on/off ratio 1.7 × 10
⁹
, and threshold voltage -14.46 V. Threshold voltages shift from -22.76 to -9.59 V as the nitrogen flow rate raises from 0 to 6.5 SCCM. The positive gate bias stability and negative bias illumination stability of a-IZO:N TFT are also improved with the nitrogen flow rate of 4 and 2.5 SCCM, respectively.