Significant Performance Enhancement of Very Thin InGaZnO Thin-Film Transistors by a Self-Assembled Monolayer Treatment

The use of amorphous InGaZnO (IGZO) has become more and more popular especially in display technologies because of its high mobility, excellent large area uniformity, and low-temperature processability. However, unlike Si-based thin-film transistors (TFTs), the top channel surface of IGZO TFTs is extremely sensitive to air, resulting in a degraded device performance, particularly when a very-thin channel layer is used. To avoid such detrimental effects and improve the device performance, a top surface treatment such as encapsulation is necessary. In this work, very thin, 1 V IGZO TFTs with top surface modified by a self-assembled monolayer (SAM) were studied. The electrical performance of the presented TFTs was significantly enhanced after the SAM modification because of a much reduced desorption-adsorption effect on the IGZO surface. The importance of top surface condition on TFTs with ultrathin channel layers was discussed. TFTs with a 5 nm thick IGZO channel layer showed a carrier mobility almost tripled plus an 18% decrease of total trap density after the SAM treatment. The treated devices also showed a superb air stability with negligible change of electrical performance after being stored in ambient air for a year. Considering the high cost of indium, this approach has a high potential to significantly reduce the manufacturing cost of IGZO-based electronics.