Digital Resistive Switching Research Articles

Analog and Digital Bipolar Resistive Switching in Solution-Combustion-Processed NiO Memristor.

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.

Analog and digital Reset processes observed in Pt/CuO/Pt memristive devices

The digital resistive switching with abrupt state change is suitable for the applications of information storage and logical operation, while the analog resistive switching with gradual state change is required in the neuromorphic computing system. This paper reports the Set voltage polarity dependent analog and digital Reset processes coexisted in Pt/CuO/Pt memristive devices. After a negative Set process, the device exhibited a digital Reset process when applying negative bias. In contrast, an analog Reset process could be achieved, following a positive Set process. These digital and analog Reset processes can convert to each other by controlling the Set bias polarity. It is proposed that the Joule-heating effect induced filament rupture is responsible for the digital Reset process, while the analog Reset process can be attributed to the filament rupture dominated by the ion migration under the external electric field.

Coexistence of analog and digital resistive switching in BiFeO3-based memristive devices

The resistive switching behavior of polycrystalline BiFeO3 films was investigated, and the coexistence of analog and digital resistive switching behaviors in a single Pt/BiFeO3/Pt device was discovered. Without electroforming, the Pt/BiFeO3/Pt device showed analog switching characteristics with a resistance ratio greater than 10; however, after electroforming, the device exhibited digital bipolar resistive switching features. It is suggested that the charge trapping/detrapping is crucial in the analog resistive switching, while the conductive filament can account for the digital switching. Additionally, a physical model is proposed to disclose the diffusion kinetics of oxygen vacancies in the memristive behaviors of the device. This work opens up a way in designing multi-functional memristive devices, which could be an ideal solution for the neuromorphic computation, non-volatile information storage and logic operation.

Modulating memristive performance of hexagonal WO3 nanowire by water-oxidized hydrogen ion implantation

In a two-terminal Au/hexagonal WO3 nanowire/Au device, ions drifting or carriers self-trapping under external electrical field will modulate the Schottky barriers between the nanowire and electrodes, and then result in memristive effect. When there are water molecules adsorbed on the surface of WO3 nanowire, hydrogen ions will generate near the positively-charged electrode and transport in the condensed water film, which will enhance the memristive performance characterized by analogic resistive switching remarkably. When the bias voltage is swept repeatedly under high relative humidity level, hydrogen ions will accumulate on the surface and then implant into the lattice of the WO3 nanowire, which leads to a transition from semiconducting WO3 nanowire to metallic HxWO3 nanowire. This insulator-metal transition can be realized more easily after enough electron-hole pairs being excited by laser illumination. The concentration of hydrogen ions in HxWO3 nanowire will decrease when the device is exposed to oxygen atmosphere or the bias voltage is swept in atmosphere with low relative humidity. By modulating the concentration of hydrogen ions, conductive hydrogen tungsten bronze filament might form or rupture near electrodes when the polarity of applied voltage changes, which will endow the device with memristive performance characterized by digital resistive switching.

Electrode-induced digital-to-analog resistive switching in TaOx-based RRAM devices

In RRAM devices, electrodes play a significant role during the switching process. In this paper, different top electrodes are used for TaOy/Ta2O5−x/AlOσ triple-oxide-layer devices. Top electrode-induced digital resistive switching to analog resistive switching was observed. For Pt top electrode (TE) devices, abrupt digital resistive switching behavior was observed, while Al TE devices showed gradual analog resistive switching behavior. Devices with various AlOσ thicknesses and sizes were fabricated and characterized to evaluate the reliability of the analog resistive switching. The physical mechanisms responsible for this electrode-induced resistive switching behavior were discussed.

Voltage-dependent resistive switching characteristics in mixed layer consisting of γ-Fe2O3 and Pt-Fe2O3 core-shell nanoparticles

A mixed layer of γ-Fe2O3 and Pt-Fe2O3 core-shell nanoparticles between Ti and Pt electrodes exhibited both analog and digital bipolar resistive switching depending on applied voltage. The resistance sequentially reduced with repeated −1.5 V sweeps and pulses for 100 ms and increased as repeating +1.5 V. After forming at +3 V, digital bipolar switching was achieved with SET transition from high to low resistance at +1 to 2 V and reverse RESET transition at −1 V. Pulse operation at ±2 V led to identical bipolar switching, associated with facilitated interconnection of filament segments between Pt cores in nanoparticle layer.

(Invited) Understanding the Role of Dopants in Transition Metal Oxide Dielectrics for Digital and Analog Resistive Switching

Resistive Random Access Memory (ReRAM) devices have gathered significant attention recently for high-density non-volatile data storage applications. However, there are several challenges that need to be addressed to take complete benefit of this enabling technology. This paper discusses the role of intentional doping in transition metal oxide dielectrics, particularly HfO2, and its implications on the device performance. Our studies indicate that Mg doped HfO2 based ReRAM devices require lower electroforming voltage compared to undoped HfO2 based ReRAM devices. The reduction in set/reset voltages was also achieved in ReRAM devices with Mg doped HfO2. Excellent bipolar switching and endurance characteristics were achieved demonstrating doping in HfO2 as a viable route for achieving the desired ReRAM characteristics.

(Invited) Understanding the Role of Dopants in Transition Metal Oxide Dielectrics for Digital and Analog Resistive Switching

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Digital versus analog resistive switching depending on the thickness of nickel oxide nanoparticle assembly

The thickness-dependent digital versus analog resistive switching of nickel oxide (NiOx) nanoparticle assemblies was investigated in a Ti/NiOx/Pt structure. The NiOx nanoparticles were chemically synthesized with ∼5 nm diameter. The Ti/NiOx/Pt structure with assembly thickness of ∼60 nm exhibited the digital-type bipolar resistive switching. However, the assembly with a thickness of ∼90 nm presented analog resistive switching with gradually decreasing resistance when sweeping −V while increasing resistance after applying +V. Repeating −V pulses decreased the resistance sequentially, but the high resistance was restored sequentially by repeating +V pulses, which is analogous to the potentiation and depression of adaptive synaptic motion.