In this study, a NiO-based resistive memristor was manufactured using a solution combustion method. In this device, both analog and digital bipolar resistive switching were observed. They are dependent on the stressed bias voltage. Prior to the electroforming, the analog bipolar resistive switching was realized through the change of the Schottky barrier at p-type NiO/Ag junction by the local migration of the oxygen ion in the interface. On the basis of the analog resistive switching, several synaptic functions were demonstrated, such as nonlinear transmission characteristics, spike-rate-dependent plasticity, long-term/short-term memory, and "learning-experience" behavior. In addition, once the electroforming operation was carried out using a high applied voltage, the resistive switching was changed from analog to digital. The formation and rupture of the oxygen vacancy filaments is dominant. This novel memristor with the multifunction of analog and digital resistive switching is expected to decrease the manufacturing complexity of the electrocircuits containing analog/digital memristors.

Cu2O film based single sandwich structure with complementary resistive switching characteristics is demonstrated. Unlike the conventional complementary resistive switching devices, the Pt/Cu2O/fluorine doped tin oxide sandwich structure is fabricated without anti-serially bipolar resistive switching cells or interfacial layer. In addition, the forming-step is unnecessary to turn on the device, which makes the complementary resistive switching process easy to control. With high resistance ratio, stable retention and reproducible switching properties, this complementary resistive switching device can be used in three dimensional stacked crossbar memory arrays. The switching mechanism is also discussed by developing a conductive path model.

In this study, a nickel oxide (NiO)-based resistive random-access memory (RRAM) was demonstrated with multistate data storage. The NiO thin film was fabricated by solution procession combined with UV irradiation at a low temperature of 200 °C. The device exhibited a high on/off resistance ratio (>10 5 ), as well as good endurance and excellent retention characteristics. It is important that multistate data storage was obtained by adjusting the RESET stop voltage, which resulted in a multilevel cell (MLC) to increase storage density. Unintentionally doped carbon (C) was distributed in the NiO thin film with periodic fluctuation. C-related filaments formation and multistate rupture were suggested as the resistive switching mechanism.

In this work, a solution processed Al-In-O/InOx bilayer resistive switching random access memory (RRAM) is demonstrated at temperature as low as 180 °C. The memory cell exhibits remarkable forming free resistive switching characteristics with stable data retention and low set/reset voltages. More importantly, this solution processed bilayer shows stable memory properties under different bending angles on a flexible substrate. The resistive switching mechanism was systematically investigated. Compared to single layer devices, an Al-In-O mixing layer is induced by the solution process in the bilayer RRAM. The first principle calculation confirms that in the Al-In-O mixing layer, the formation energy of oxygen vacancies is significantly reduced compared with the AlOx layer. As a result, the formation of the oxygen vacancy based conductive filament is realized without the electroforming process. The RRAM fabricated by the printable solution process at low temperature shows great application potential in next generation wearable electronics.

In this work, an all‐inorganic memristor based on In ion‐diffused Al2O3 (IAO) is realized by low temperature solution method. Compared to single layer devices, the electrical properties of IAO‐based memristor are highly improved. In this device, both of synaptic and digital switching can be observed by controlling the applied voltage. At a low applied voltage, the memristor exhibits synaptic switching behavior including gradual switching, learning process, forgetting process, and relearning process. If a higher voltage is applied, the switching behavior is changed to digital bipolar switching which could be also archived in bending condition. The switching mechanism is dominated by oxygen vacancies modulation on concentration and formation energy. This novel device can be expected to open a new road for hybrid and printable circuits including synaptic and digital flexible memristors.