The electrical properties, resistive switching behavior, and long-term potentiation/depression (LTP/LTD) in a single indium-gallium-zinc-oxide (IGZO) and bi-layer IGZO/ZnO (ZnO: zinc oxide) memristors were investigated for synapse application. The use of the oxide bi-layer memristors, in particular, improved electrical properties such as stability, memristor reliability, and an increase in synaptic weight states. The set voltage of bi-layer IGZO/ZnO memristors was 0.9 V, and the reset voltage was around − 0.7 V, resulting in a low-operating voltage for neuromorphic systems. The oxygen vacancies in the X-ray photoelectron spectroscopy analysis played a role in the modulation of the high-resistance state (HRS) (oxygen-deficient) and the low-resistance state (oxygen-rich) region. The VRESET of the bi-layer IGZO/ZnO memristors was lower than that of a single IGZO, which implied that oxygen-vacancy filaments could be easily ruptured due to the higher oxygen vacancy peak HRS layer. The nonlinearity of the LTP and LTD characteristics in a bi-layer IGZO/ZnO memristor was 6.77% and 11.49%, respectively, compared to those of 20.03% and 51.1% in a single IGZO memristor, respectively. Therefore, the extra ZnO layer in the bi-layer memristor with IGZO was potentially significant and essential to achieve a small set voltage and a reset voltage, and the switching behavior to form the conductive path.
In this study, indium-gallium-zinc-oxide (IGZO) thin films were investigated for detection of Nitrogen Dioxide (NO2) gas. IGZO films with a thickness range of 25–100 nm were deposited using IGZO (ZnO: Ga2O3:In2O3 = 1:1:1 mol.%) polycrystalline target on interdigitated Au electrode alumina substrates and annealed in different annealing atmosphere of Nitrogen (N2) and Oxygen (O2). The effects of the IGZO thickness and different annealing ambient on IGZO were investigated on sensing properties. The N2 ambient showed a superior response (S = Rgas/Rair) compared to O2 annealing by a factor of 2.3 times. In addition, the sensor response increases with film thickness up to 25 nm and decreases with an increase in thickness. The sensor showed a high response for the IGZO thin film (25 nm), which was 519 times that of the other sensors at 200 °C. The sensor recovery and response time improved, and the sensor selectivity was tested under different gases.
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