Improvement of device characteristics of plasma-treated indium gallium zinc oxide thin-film transistors through thermal annealing

Abstract

In this study, an Ar/O2 plasma mixture treatment with different proportions of O2 was used to reduce the oxygen vacancy density in an amorphous indium gallium zinc oxide (a-IGZO) thin film. The objective was to enhance the field-effect carrier mobility in a thin-film transistor (TFT) with the IGZO film as the channel layer. Atomic force microscopy revealed that the roughness of the IGZO film after plasma treatment was higher than that of the untreated film; however, the surface roughness of the IGZO film decreased after the proportion of O2 was increased in the plasma. The Hall measurement results showed that the resistivity of the plasma-treated IGZO film increased with a decrease in the electron concentration in the film; in addition, the carrier mobility considerably increased. The IGZO TFT fabricated from this film exhibited a high field-effect carrier mobility of 36 cm2 V−1 s−1, a subthreshold swing (SS) of 1.25 V/decade, an I OFF current of 4.58 × 10−11 A, and an I ON/I OFF current ratio of 7.55 × 105. To further improve the device performance, the plasma-treated IGZO films were subjected to thermal annealing with the annealing temperature ranging from 100 °C to 300 °C. After the annealing process, the plasma-treated IGZO TFTs demonstrated a further improvement in the device performance with a field-effect carrier mobility of 38.8 cm2 V−1 s−1, SS of 0.7 V/decade, I OFF current of 1.04 × 10−11 A, and an I ON/I OFF current ratio of 9.93 × 106. In addition, a reliability test was performed to evaluate the stability of the IGZO TFT devices, which revealed that the threshold voltage maintained a high degree of stability during the long-term tests. Therefore, the plasma-treated IGZO TFTs with subsequent postgrowth annealing could be helpful for the fabrication of next-generation flat-panel displays.