An ultrathin, 5 nm, Al2O3 film grown by atomic-layer deposition was used as a gate dielectric for amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). The Al2O3 layer showed a low surface roughness of 0.15 nm, a low leakage current, and a high breakdown voltage of 6 V. In particular, a very high gate capacitance of 720 nF/cm2 was achieved, making it possible for the a-IGZO TFTs to not only operate at a low voltage of 1 V but also exhibit desirable properties including a low threshold voltage of 0.3 V, a small subthreshold swing of 100 mV/decade, and a high on/off current ratio of 1.2 × 107. Furthermore, even under an ultralow operation voltage of 0.6 V, well-behaved transistor characteristics were still observed with an on/off ratio as high as 3 × 106. The electron transport through the Al2O3 layer has also been analyzed, indicating the Fowler–Nordheim tunneling mechanism.

Amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) enabled by an ultrathin, 5 nm, HfO2 film grown by atomic-layer deposition were fabricated. An ultra-low operation voltage of 1 V was achieved by a very high gate capacitance of 1300 nF/cm2. The HfO2 layer showed excellent surface morphology with a low root-mean-square roughness of 0.20 nm and reliable dielectric properties, such as low leakage current and high breakdown electric field. As such, the a-IGZO TFTs exhibit desirable properties such as low power devices, including a small subthreshold swing of 75 mV/decade, a low threshold voltage of 0.3 V, and a high on/off current ratio of 8 × 106. Furthermore, even under an ultralow operation voltage of 0.5 V, the on/off ratio was also up to 1 × 106. The electron transport through the HfO2 layer has also been analyzed, indicating the Poole-Frenkel emission and Fowler-Nordheim tunneling mechanisms in different voltage ranges.

A synaptic memristor based on IGZO and oxygen-deficient HfO2 films has been demonstrated. The memristor exhibits a fatigue response to a monotonic stimulus of voltage pulses, which is analogous to the habituation behavior of biological memory. The occurrence of habituation is nearly simultaneous with the transition from short-term memory to long-term memory. The movement and redistribution of oxygen species with the assistance of polarization in HfO2 layer are responsible for the above results. The observation of habituation behavior proves the potential prospect of memristor on the mimic of biological neuron.

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Oxide semiconductors are desirable for large-area and/or flexible electronics. Here, we report highly optimised complementary inverters based on n-type indium gallium zinc oxide and p-type tin monoxide thin-film transistors. Oxide-based inverters with a record voltage gain of 142 have been achieved. The switching point voltage has also been tuned to reach the ideal value, namely half value of the supply voltage. A narrow transition width of 1.04 V (13% of the supply voltage) is achieved which offers a strong anti-jamming ability to avoid logic errors. Rail-to-rail output voltage swing has been achieved. The inverters still maintain high performance at a low supply voltage of 6 V. A very large number of inverters have been fabricated and showed excellent uniformity in a working area of 1 cm × 1 cm. The switching point voltage and transition width show very small standard deviations of only 0.55% (0.022 V) and 2.3% (0.024 V), respectively, demonstrating promises for large-scale circuit integration.