Contact Length Scaling in Dual-Gate IGZO TFTs

In this work, the contact length scaling in dual-gate (DG) InGaZnO (IGZO) thin film transistors (TFTs) was experimentally investigated. With source/drain metal of Nickel (Ni) deposited in ultra-high vacuum condition ( $\sim \,\,{8}\times {10} ^{-{8}}$ Torr), the contact resistance ( ${R}_{C}{)}$ is achieved to be as low as $340~\Omega \cdot \mu \text{m}$ at an overdrive voltage of 2.5 V with contact resistivity $\rho _{C}$ = ${1}.{72}\times {10} ^{-{7}}\,\,\Omega \cdot $ cm2. Scaling the contact length ( ${L}_{C}{)}$ from 300 nm to 20 nm is then performed for both long-channel and short-channel DG IGZO TFTs and find that, in long-channel devices, the ${L}_{C}$ can be scaled down to 20 nm without noticeable performance degradation; in short-channel devices, a shorter ${L}_{C}$ (< 30nm) would cause a pronounced performance degradation, including lower current density and worse subthreshold swing. Based on this observation, ultra-scaled high-performance DG IGZO TFTs are fabricated with a record-low contact pitch of 80 nm ( ${L}_{C}$ = 40 nm and ${L}_{\textit {CH}}$ = 40 nm), achieving an ultra-high ${I}_{\textit {ON}}$ of $68.4\,\,\mu \text{A}\cdot \mu \text{m}^{-{1}}$ (at ${V}_{G} $ = ${V}_{\textit {TH}}+1$ V and ${V}_{\textit {DS}}$ = 1 V) and a low SS of 83.4 mV $\cdot $ dec $^{-{1}}$ .