Improving device characteristics of IGZO thin-film transistors by using pulsed DC magnetron sputtering deposition

Abstract

This study investigated the use of pulsed direct current (DC) magnetron sputtering for depositing indium–gallium–zinc oxide (IGZO) thin films that can serve as channel layers and fabricating high-performance thin-film transistors (TFTs). Unlike a typical radio-frequency (RF) sputtering system, a pulsed DC system can be operated using a modulated pulse frequency for increasing the deposition rate, reducing the surface roughness, and increasing plasma density for dense thin-film deposition with reduced arc-induced structural defects at a specific sputtering power. In this study, pulse frequencies ranging from 170 to 350 kHz were modulated for obtaining IGZO thin films with higher surface flatness, carrier mobility, and material quality than those of IGZO films deposited using RF sputtering. The IGZO film fabricated at a pulse frequency of 350 kHz was used as a transistor channel layer in one of the fabricated TFTs; this TFT showed an advantageous field-effect mobility of 9.78 cm2 V−1 s−1, a subthreshold swing of 0.72 V/decade, an off current of 1.57 × 10−11 A, and an on–off current ratio of 4.87 × 107. These results revealed that pulsed DC sputtering is a promising technique for fabricating TFTs with excellent device characteristics.