We report dual ion beam sputtering fabrication of an Al/ZnO/Al memristor displaying forming-free bipolar resistive switching characteristics with memristive behavior without necessitating any post-processing steps. A nearly amorphous ZnO thin film and an appropriate concentration of oxygen vacancies play a significant role in imparting forming-free, stable, and reliable behavior to memory cells. Besides, sufficient non-lattice oxygen ions in the film play a crucial role in the resistive switching process. The AlOx interface layer is observed to strongly affect the switching mechanism in the memory device by altering the barrier at the Al/ZnO interface. The device shows stable switching behavior for >250 cycles with good retention and stable set/reset voltages.

Single synaptic device with inherent learning and memory functions is demonstrated based on a forming-free amorphous YO (yttria) memristor fabricated by dual ion beam sputtering system. Synaptic functions such as nonlinear transmission characteristics, long-term plasticity, short-term plasticity and 'learning behavior (LB)' are achieved using a single synaptic device based on cost-effective metal-insulator-semiconductor (MIS) structure. An 'LB' function is demonstrated, for the first time in the literature, for a yttria based memristor, which bears a resemblance to certain memory functions of biological systems. The realization of key synaptic functions in a cost-effective MIS structure would promote much cheaper synapse for artificial neural network.

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In this report, we study factors that dominate the mode transformation of resistive switching (RS) in yttria based memristive devices. It is found that amorphous yttria films are more suitable for RS whereas highly crystalline films are counterproductive for RS. The transformation from unipolar to bipolar resistive switching mode is demonstrated in our devices via moving from a system of single Schottky barrier diode (SBD) to double SBD. The conduction mechanism behind these transformation mechanisms is found to be predominantly interfacial. We also report a forming-free Al/Y2O3/Al based memristor fabricated by the dual ion beam sputtering without any post-processing steps for the first time. It shows stable switching behavior for  >29 000 cycles with good retention (105 s) characteristics.

The development of a new type of hybrid material comprising naphthalene-based π-conjugated amine (NBA) and zinc oxide (ZnO) nanohybrid, grown in situ on polydimethylsiloxane (PDMS) flexible substrate, is explored. The morphology of the nanohybrids is controlled by optimizing growth time of the hydrothermal reaction. The CO 2 sensor utilizing NBA−ZnO nanohybrids shows outstanding sensing performance with a maximum response of ∼9% to 500 ppm of CO 2 at room temperature and a comparatively fast response/recovery time (∼3/6 min). The sensor has excellent mechanical flexibility with consistent sensing performance under bending/relaxing process. Hydrophobic nature of the NBA provides less humidity effect on the sensing performance of the NBA−ZnO nanohybrids, which make it suitable for room-temperature application. Also, the presence of layer-by-layer assembly in the NBA−ZnO nanohybrids provides a superior path for carrier transport, which reduces the response and recovery time. All these results indicate that NBA−ZnO nanohybrid is a promising material for room temperature CO 2 sensing application.

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