Indium zinc oxide thin films deposited by sputtering at room temperature

The deposition of amorphous indium zinc oxide (IZO) thin films on glass substrates with n-type carrier concentrations between 10¹⁴ and 3 × 10²⁰ cm⁻³ by sputtering from single targets near room temperature was investigated as a function of power and process pressure. The resistivity of the films with In/Zn of ∼0.7 could be controlled between 5 × 10⁻³ and 10⁴ Ω cm by varying the power during deposition. The corresponding electron mobilities were 4-18 cm² V⁻¹ s⁻¹.The surface root-mean-square roughness was <1 nm under all conditions for film thicknesses of 200 nm. Thin film transistors with 1 μm gate length were fabricated on these IZO layers, showing enhancement mode operation with good pitch-off characteristics, threshold voltage 2.5 V and a maximum transconductance of 6 mS/mm. These films look promising for transparent thin film transistor applications.