Enhanced Contact Property and Thermal Stability by Suppressing Oxygen Diffusion through Subnm Ultrathin Barrier for...

We studied the effects of the interface oxide layer between amorphous indium-gallium-zinc oxide (IGZO) and metallic electrodes on contact resistance (R_C). The reduction of R_C has become imperative as IGZO devices are scaled down to achieve higher on current. Previous studies have reported the formation of low-resistance ohmic contacts, wherein oxygen vacancies generated by reactions between IGZO and metal supply free electrons. Nonetheless, such reactions inevitably lead to the formation of a high-resistivity interface oxide and the creation of defect states. In this study, we employed alkyl-phosphonic acid self-assembled monolayers (SAMs) with precisely controlled nanometer-scale thickness to minimize R_C in IGZO transistors. The optimized SAM effectively suppressed interface oxide formation between IGZO and the metal, reducing the thickness from 11 to 4.1 nm. Additionally, the SAM passivated dangling bonds on the IGZO surface, thereby facilitating electron transport with diminished trapping and detrapping phenomena. Consequently, despite the insulating properties of the SAM, the R_C was markedly decreased by 77%, and the shortening of the effective channel length was reduced by 37% following thermal stress at 150 °C.