Microwave-Irradiated Metal-Oxide Thin-Film Transistors With Recessed Gate Structure and Their Applications in Logic Circuits

The effects of a recessed gate structure on the device performance of sol-gel-based metal-oxide thin-film transistors (oxide-TFTs) consisting of aluminum oxide dielectric and indium-gallium-zinc oxide semiconducting films fabricated through effective microwave irradiation are investigated, as compared with elevated and non-patterned gate structures. Low-voltage operating oxide-TFTs with an optimized recessed gate structure exhibited improved device performance including OFF-state current of approximately $10^{-{11}}$ A and field-effect mobility of 3.4 cm2/V-s in the linear regime, compared with those with elevated (~ $10^{-{9}}$ A and 1.9 cm2/V-s) and non-patterned (~ $10^{-{10}}$ A and 2.8 cm2/V-s) gate structures. Furthermore, the charge transport mechanism responsible for improved device performance and operational stability against prolonged positive and negative gate bias stresses in the oxide-TFTs with the recessed gate structure is investigated through activation energy and velocity distribution that are determined from direct-current and time-domain non-quasi-static transient analyses, respectively. Finally, enhancement-load-type nMOS inverters operating at 5 V are developed for logic circuits, which exhibit a relatively high dc gain of 32.2 in the recessed gate structure, compared with that of 17.1 and 27.1 in the elevated and the non-patterned gate structures, respectively.