High Performance, Low Temperature Aqueous Route Calcium-Doped Indium Zine Oxide Thin Film Transistors

The high-performance Calcium-doped Indium Zine oxide thin film transistors (CIZO TFTs) were fabricated using an aqueous route with low temperature annealing. The effects of different atomic percentages of Ca on electrical performance of TFTs were examined. The experimental results shows that the turn-on-voltage (V_on) shifts in a positive direction and the off-current (I_off) decreases as the Ca content is increased, which attributes to the incorporation of Ca with low standard electrode potential (-2.87 V) and high optical band gap (7.03 eV), when oxidized. The electrical characteristics of CIZO TFTs with an atomic ratio of In:Ca:Zn=6.8:0.2:2.2 are optimized as follows: saturation mobility (μ_sat) of 2.14 cm²/V•s, threshold voltage (V_th) of 3.00 V, on/off current ratio (I_on/I_off) of 7.7•10⁶, subthreshold swing (S.S.) of 0.41 V/decade. In addition, the effects of pre-annealing in N₂O-plasma environment (PA-N₂O-PE) were also investigated. The electrical characteristics are improved, and the optimized electrical characteristics of CIZO TFTs are observed with an atomic ratio of In:Ca:Zn=6.8:0.3:2.2.