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.