Abstract: An analytical drain current model is presented for amorphous In–Ga–Zn–oxide thin-film transistors in the above-threshold regime, assuming an exponential trap states density within the bandgap. Using a charge sheet approximation, the trapped and free charge expressions are calculated, then the surface potential based drain current expression is developed. Moreover, threshold voltage based drain current expressions are presented using the Taylor expansion to the surface potential based drain current expression. The calculated results of the surface potential based and threshold voltage based drain current expressions are compared with experimental data and good agreements are achieved.

Key words: amorphous In–Ga–Zn–oxide (a-IGZO), thin-film transistors (TFTs), surface potential, threshold voltage, trap states