Effect of Back-Channel Surface on Reliability of Solution-Processed In0.51Ga0.15Zn0.34O 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 (ΔVth) 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 ΔVth for stress time was rarely changed with variations below 0.3 mV/s. The thickness of the fabricated IGZO layer (In0.51Ga0.15Zn0.34O) was approximately 10 nm. The Debye length (LD) was larger than IGZO thickness (tIGZO) 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 ΔVth based on the two-dimensional technology computer-aided design (TCAD) simulation. Furthermore, we investigated the degradation phenomenon with the ΔVth equation regarding the adsorbates, and the result confirmed that the adsorption process could cause the linear ΔVth. We experimentally confirmed the effect of back-channel surface by comparing the ΔVth between different atmospheric conditions and LD. Consequently, the reaction at the back-channel surface should be considered to develop the metal-oxide semiconductor devices.

Glucose Sensing Using Functionalized Amorphous In-Ga-Zn-O Field-Effect Transistors.

Recent advances in glucose sensing have focused on the integration of sensors into contact lenses to allow noninvasive continuous glucose monitoring. Current technologies focus primarily on enzyme-based electrochemical sensing which requires multiple nontransparent electrodes to be integrated. Herein, we leverage amorphous indium gallium zinc oxide (IGZO) field-effect transistors (FETs), which have found use in a wide range of display applications and can be made fully transparent. Bottom-gated IGZO-FETs can have significant changes in electrical characteristics when the back-channel is exposed to different environments. We have functionalized the back-channel of IGZO-FETs with aminosilane groups that are cross-linked to glucose oxidase and have demonstrated that these devices have high sensitivity to changes in glucose concentrations. Glucose sensing occurs through the decrease in pH during glucose oxidation, which modulates the positive charge of the aminosilane groups attached to the IGZO surface. The change in charge affects the number of acceptor-like surface states which can deplete electron density in the n-type IGZO semiconductor. Increasing glucose concentrations leads to an increase in acceptor states and a decrease in drain-source conductance due to a positive shift in the turn-on voltage. The functionalized IGZO-FET devices are effective in minimizing detection of interfering compounds including acetaminophen and ascorbic acid. These studies suggest that IGZO FETs can be effective for monitoring glucose concentrations in a variety of environments, including those where fully transparent sensing elements may be of interest.