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 (~ 8×10 ^-8 Torr), the contact resistance ( R_C ) is achieved to be as low as 340 Ω·μm at an overdrive voltage of 2.5 V with contact resistivity ρ _C = 1.72×10 ^-7 Ω·cm ² . 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_CH = 40 nm), achieving an ultra-high I_ON of 68.4 μA·μm ^-1 (at V_G = V_TH +1 V and V_DS = 1 V) and a low SS of 83.4 mV·dec ^-1 .