Enhancing the Thermal Stability of the IGZO Transistors by Suppressing the Oxygen Diffusion into Metal Using Self-Assembled Monolayer for Nanoscale Devices

Amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) are extensively applied in large-area displays, machine learning, and memory devices. Recently, it was reported that the increased electron density caused by the oxygen vacancy reduces the contact resistance between a-IGZO and source/drain (S/D) metal.[1] However, a large amount of oxygen vacancies in the S/D region diffuses into the channel region by thermal stress, which causes performance degradation, such as V_th negative shift and loss of switching characteristics, especially in the nanoscale transistor.<br/>To suppress the excessive generation of oxygen vacancies, We introduced the ultra-thin barrier layer (&lt; 1nm), which prevents oxygen diffusion. A self-assembled monolayer (SAM) with various alkyl-chain lengths (C2, C4, C6, C8, C10) was used as a diffusion barrier. We extracted the effective channel length of the IGZO TFT by the transfer line method (TLM) pattern. The device with a thick barrier showed a negligible change of the channel length at 250 degrees thermal stress for 2 hours, indicating that the diffusion of oxygen vacancies was suppressed. Transmission electron microscopy (TEM) images showed reduced interfacial oxide after SAM insertion. Despite inserting a diffusion barrier with excellent insulating properties, the contact resistance was decreased by 72 % compared to the bare device due to the thinned interfacial oxide. As a result, we achieved high thermal stability by inserting a diffusion barrier and, additionally, low contact resistance due to the thinned interfacial oxide, which contributes to the realization of nanoscale devices without any side effects in the channel region.