An ultrathin atomic-layer-deposited (ALD) AlO x gate insulator (GI) was implemented for self-aligned top-gate (SATG) amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs). Although the 4.0-nm thick AlO x exhibited ideal insulating properties, the interaction between ALD AlO x and predeposited a-IGZO caused a relatively defective interface, thus giving rise to hysteresis and bias stress instabilities. As analyzed using high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and the Hall measurement, the chemical reaction between the ALD precursor and a-IGZO is revealed. This was effectively prevented by preoxidizing a-IGZO with nitrous oxide (N2O) plasma. With 4 nm-AlO x GI and low-defect interfaces, high performance and stability were simultaneously achieved on SATG a-IGZO TFTs, including a near-ideal record-low subthreshold swing of 60.8 mV/dec, a low operation voltage below 0.4 V, a moderate mobility of 13.3 cm2/V·s, a low off-current below 10–13 A, a large on/off ratio over 109, and negligible threshold-voltage shifts less than 0.04 V against various bias-temperature stresses. This work clarifies the vital interfacial reaction between top-gate high-k dielectrics and amorphous oxide semiconductors (AOSs) and further provides a feasible way to remove this obstacle to downscaling SATG AOS TFTs.

Electrical characteristics of self-aligned topgate (SATG) amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) with 4 nm-thick atomic-layer-deposited (ALD) AlOx gate insulator (GI) are investigated. It is demonstrated that the SATG a-IGZO TFTs present highperformance metrics including a near-ideal subthreshold swing (SS) of 60.9 mV/dec, a low off-state current below 10 −12 A, a positive Vth of 0.1 V, and a decent mobility of 14.1 cm 2 /V•s. In addition, the TFTs exhibit negligible Vth shifts less than 0.02 V against electrical bias stresses. Both high performance and excellent stability are thus simultaneously achieved for the ultrathin GI of amorphous oxide semiconductor (AOS) TFTs.

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