On the oxygen content in sputtering InO_x film for transparent electronics

Transparent undoped semiconductor indium oxide films were deposited by using a long-throw rf magnetron sputtering at room temperature. It was found that the variation of oxygen content in sputtering gas has a strong influence on the microstructure and electrical properties of the films. The electrical resistivity varying from 3.5 × 10⁻² to 4.7 × 10⁴ Ω-cm for oxygen contents ranging from 0 to 50 % was obtained. The optical band gap decreases as the oxygen content increases, and the average visible transmittance of the indium oxide is ~85 %. To put into practice, the as-sputtered indium oxide was employed as a channel of thin film transistors on glass substrate with a channel length, 6 μm, and a channel width, 20 μm. Its saturation mobility, threshold voltage, and on/off ratio were obtained to be 9.4 V⁻¹ s⁻¹, 1.5 V, and 2.2 × 10⁷. To approach a flexible device, a plastic substrate is employed to replace the rigid substrate, glass; and the relative parameters, saturation mobility, threshold voltage, and on/off ratio, are also measured to be 8.2 V⁻¹ s⁻¹, 1.8 V, and 1.4 × 10⁶, respectively.