Effect of Back-Channel Surface on Reliability of Solution-Processed InGaZnO Thin-Film Transistors with Thin Active Layer.

We have investigated the degradation mechanism of solution-processed indium-gallium-zinc-oxide (IGZO) thin-film transistors. The threshold voltage shift (Δ) followed a linear function under negative gate bias stress (NBS), while it showed a stretched-exponential behavior under positive gate bias stress. The slope of Δ for stress time was rarely changed with variations below 0.3 mV/s. The thickness of the fabricated IGZO layer (InGaZnO) was approximately 10 nm. The Debye length () was larger than IGZO thickness () due to the fully depleted active layer under NBS. Therefore, the degradation phenomenon under NBS was related to the adsorption at back-channel surface. The back-channel surface could be affected by the gate bias under NBS, and the molecules adsorbed at the IGZO layer were positively charged and induced extra electrons by NBS. We verified that the number of positively charged adsorbates had a proportional relationship with the Δ based on the two-dimensional technology computer-aided design (TCAD) simulation. Furthermore, we investigated the degradation phenomenon with the Δ equation regarding the adsorbates, and the result confirmed that the adsorption process could cause the linear Δ. We experimentally confirmed the effect of back-channel surface by comparing the Δ between different atmospheric conditions and . Consequently, the reaction at the back-channel surface should be considered to develop the metal-oxide semiconductor devices.