Oxide-PMOS Inverter Using p-SnO Thin-Film Transistors With Back-Channel SnO/a-GaOₓ p-n Heterojunction Structure

The absence of enhancement-mode (E-mode) p-channel oxide thin-film transistor (TFT) limited p-channel oxide-TFT applications. To overcome this challenge, a low-temperature back-channel pn-heterojunction structure utilizing n-type amorphous-GaOx was developed for the E-mode p-channel SnO-TFTs. This approach minimized process-induced damage to p-channel SnO, offering stable E-mode operation without compromising device performance. The E-mode SnO-TFT demonstrated a threshold voltage of –4.7 V, a hole field-effect mobility of 2.6 cm2/(Vs), demonstrating device performance compatible with the depletion mode (D-mode) device. The device experimental and simulation analysis for the pn-diode confirmed that the present SnO/a-GaOx pn-junction created a longer hole carrier depletion width of ~17 nm than the thickness of the SnO channel (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t}~\sim 10$ </tex-math></inline-formula> nm) at thermal equilibrium, implying that the excess hole in the SnO channel was fully depleted from the back-channel. The zero-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {GS}}$ </tex-math></inline-formula>-load p-channel metal-oxide-semiconductor (PMOS) inverters composed of the D-mode and E-mode SnO TFTs were successfully fabricated. The inverters exhibited full-swing operation, high gain of ~200, and noise immunity of ~60%, demonstrating a promising approach for advancing p-channel oxide-TFT technology.