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.

No abstract

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.

The interfacial structure for HfO2 dielectrics on Si (100) substrate was investigated using x-ray photoelectron spectroscopy. The Hf 4f binding energy changes with the depth, which confirms the presence of Hf–O–Si state. Together with the analysis of O 1s and Si 2p spectra, it is believed that the interfacial structure includes both SiOx and Hf silicates. The electrical measurement is also consistent with the above conclusions. According to the theoretical and experimental results, a cursory model of the interfacial structure was established: The main body is SiOx species, on the top of SiOx is HfSixOy species, and Hf silicides are embedded in the Hf silicates.