Low-Voltage IGZO TFTs Using Solution-Deposited OTS-Modified Ta2O5 Dielectric

Abstract

Low-voltage, high-performance thin film transistors (TFTs) that use amorphous metal oxide (MO) semiconductors as the active layer have been getting tremendous attention due to their essential role in future portable electronic devices and systems. However, reducing the operating voltage of these devices to or below 1 V is a very challenging task because it is very difficult to obtain low threshold voltage ( ${V}_{\text {TH}}$ ) and small subthreshold swing (SS) MO TFTs. In this article, indium gallium zinc oxide (IGZO) TFTs that use solution-deposited Ta2O5 operating at 1 V are demonstrated. To enhance the dielectric properties of the fabricated ultrathin ( ${d} \sim {22}$ nm $\pm ~2$ nm) tantalum pentoxide films, ${n}$ -octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) was used. The morphology and electrical properties of both pristine and OTS-treated Ta2O5 films have been studied. The optimized Ta2O5/OTS IGZO TFTs operate at 1 V with saturation field-effect mobility larger than 2.3 cm2/ $\text{V}\cdot \text{s}$ , threshold voltage of around 400 mV, SSs below 90 mV/dec, and current ON- OFF ratios well above $10^{{5}}$ . The performance of the presented TFTs is high enough for many commercial applications such as disposable sensors or throwaway, low-end electronics significantly reducing the cost of their production.