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The effects of atomic layer deposition (ALD) conditions for the HfO2 gate insulators (GI) on the device characteristics of the InGaZnO (IGZO) thin film transistors (TFTs) were investigated when the ALD temperature and Hf precursor purge time were varied to 200, 225, and 250 °C, and 15 and 30 s, respectively. The HfO2 thin films showed low leakage current density of 10−8 A cm−2, high dielectric constant of over 20, and smooth surface roughness at all ALD conditions. The IGZO TFTs using the HfO2 GIs showed good device characteristics such as a saturation mobility as high as 11 cm2 V−1 s−1, a subthreshold swing as low as 0.10 V/dec, and all the devices could be operated at a gate voltage as low as  ±3 V. While there were no marked differences in transfer characteristics and PBS stabilities among the fabricated devices, the NBIS instabilities could be improved by increasing the ALD temperature for the formation of HfO2 GIs by reducing the oxygen vacancies within the IGZO channel.

In this work, we proposed new type of synapse device with thin-film transistor (TFT) configuration using an In–Ga–Zn–O (IGZO) as active channel and a poly(4-vinylphenol)–sodium β-alumina (PVP–SBA) as gate insulator for emulating brain-like functions.

We propose the design concept for dramatically reducing the power consumption of integrated circuit using TFTs, which is named as Read-out Modulation (RoM). In the RoM scheme, the read-out voltages applied to the charge-trap memory TFTs are intentionally modulated to replace the clocks of shift registers to minimize the clocking power consumption. The test circuit is fabricated and the proposed RoM is successfully verified with the frequency characteristics.

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