Effective Mobility Enhancement by Using Nanometer Dot Doping in Amorphous IGZO Thin‐Film Transistors

IO N With a high mobility ( > 10 cm 2 V − 1 s − 1 ) and a low threshold voltage ( < 5 V) in low-temperature processes, transparent oxide semiconductor thin-fi lm transistors (TOS TFTs) have drawn considerable attention due to their applications on fl exible displays, level shifters, drivers, and pixel-driving circuits for activematrix organic light-emitting-diode (AMOLED) displays. [ 1 − 3 ] In addition to display applications, amorphous indium gallium zinc oxide (a-IGZO) TFTs are also promising for the development of radio-frequency identifi cation (RFID) tags, smart cards, and other types of fl exible electronics. When TOS TFTs are developed for a low-power high-frequency circuit, high electron mobility and a low parasitic capacitance are required. Most TFTs fabricated with ZnO, SnO 2 , In 2 O 3 , IGZO, or other semiconducting oxide thin fi lms exhibit electron mobilities smaller than 35 cm 2 V − 1 s − 1 . [ 4–6 ] Recent reports on transparent oxide nanowire transistors (NWTs) have demonstrated high electron mobilities approximately 70 to 4000 cm 2 V − 1 s − 1 . [ 7–9 ] The quasi1D structure of NWTs may reduce low-angle carrier scattering to produce high electron mobility. [ 9 ] However, the fabrication process of NWTs has poor reproducibility and is still not practical for real-world applications. Because TOS transistors are transparent, developing TOS circuits on windows is appealing. Particularly, for modern buildings or trains with series of windows, TOS RFID circuits on windows can deliver various types of signals through a low-power transmission system. In this type of application, the dimension of the transparent transistor can be large because an integrated circuit on a small chip is not necessary. A low-cost production method for delivering a highperformance TOS transistor is a critical challenge. Here, a nanostructure to improve the effective mobility in a-IGZO TFTs is proposed. A large channel dimension of 1000 μ m, defi ned by a shadow mask, is utilized. The nanostructure is developed using a low-cost, lithography-free process to produce abundant nanometer-scale dot-like doping in a-IGZO channel. The new method, called nanodot doping (NDD) increases the effective electron mobility to a level 19 times higher than that of the control and the intrinsic electron mobility is also 10 times higher than that of the control. This study demo nstrates a process utilizing self-organized polystyrene spheres with a diameter of 200 nm to fabricate a porous gate structure. Ar plasma treatment through the porous gate performs dot-like doping on a-IGZO channel region. A top-gate