High Field-Effect Mobility Two-Channel InGaZnO Thin-Film Transistors for Low-Voltage Operation

In this study, two-channel thin-film transistors (TC TFTs) using sputtered-deposited amorphous indium-gallium-zinc oxide (a-IGZO) as a channel layer and atomic-layer-deposition Al 2 O 3 as gate insulator (GI) are proposed for wearable and portable device application. Symmetric-TC (S-TC) TFT structure consisted of conventional bottom gate (BG) TFT stacked on top of top gate (TG) TFT. Asymmetric-TC (A-TC) TFT contained BG TFT with tandem structure on the TG TFT. It was shown that the TC TFTs exhibited excellent performance such as high field-effect mobility ( \mu _{\text {FE}} ) and ON/ OFF current ratio ( I_{\scriptstyle{\text{ON/OFF}}} ) at low voltages (< 2 V). For instance, the S-TC TFTs gave \mu _{\text {FE}} of 19.67 cm 2 /Vs and I_{\scriptstyle{\text{ON/OFF}}} of 5.48\times 10^{{8}} . Furthermore, the A-TC TFTs with tandem structure yielded \mu _{\text {FE}} of 30.15 cm 2 /Vs, a small threshold voltage of −1.25, a low subthreshold swing of 89 mV/decade, and a high I_{\scriptstyle{\text{ON/OFF}}} of 1.70\times 10^{{9}} . It was found that the TC TFTs demonstrated better electrical performance than the sum of individual TG and BG TFTs. Under bias stress tests, the TC TFTs experience less {V}_{\text {th}} shift ( \Delta {V}_{\text {th}} ) than the TG and BG TFTs.