Forming-free Resistive Switching Behavior Research Articles

Magnetic properties and oxygen migration induced resistive switching effect in Y substituted multiferroic bismuth ferrite

Multiferroic Y-doped BiFeO3 (BY10FO) thin films were deposited on FTO coated glass substrate using sol-gel spin coating technique. Y-doping causes structural distortion without changing the structure of the parent BiFeO3 (rhombohedral: R3c). The M-H hysteresis curve reveals that the BY10FO film exhibits saturation magnetization at a low-coercive field by suppressing the spiral spin modulated structure. The bipolar resistive switching behavior has been investigated on a Ag/BY10FO/FTO hetero-structure through conventional I-V curve measurements and the device can produce an ON/OFF ratio of around 12 over 30 complete testing cycles. The space charge limited current and Schottky barrier emission conduction mechanism play a crucial role in switching the states between HRS and LRS. The impedance spectroscopy analysis at HRS and LRS confirms the significant degradation of resistance from MΩ to kΩ. The switching mechanism in the hetero-structure is due to migration and recombination of oxygen vacancies present in the film. The non-degradation of the Ag/BY10FO/FTO device after several testing cycles confirms that the switching of resistance between ON and OFF states is reproducible, reversible and controllable to be used for possible future non-volatile resistive random access memory application.

Characteristics of flexible and transparent Eu2O3 resistive switching memory at high bending condition

The characteristics of ITO/Eu2O3/ITO/PET transparent and flexible resistive switching memory are studied. The device exhibits superior characteristics such as device area-independent and forming-free resistive switching behavior with a resistance on/off ratio of 104, good retention of >104 s and high AC endurance of >107 cycles. The conduction mechanism of the high-resistance state is the Poole–Frenkel mechanism, while that of the low-resistance state is ohmic conduction. The electrical characteristics of the flexible device have shown excellent results up to 5 mm bending radius, at which a degradation in the on/off ratio of the memory window is observed, due to the change in the dielectric layer resistance. The resistive switching characteristics can be improved during bending up to the radius of 2 mm by the incorporation of an aluminum-doped zinc oxide layer in the device as the bottom electrode, proving its application in future flexible and transparent memory devices.

Switchable diode effect in oxygen vacancy-modulated SrTiO3 single crystal

SrTiO3 (STO) single crystal wafer was annealed in vacuum, and co-planar metal–insulator–metal structure of Pt/Ti/STO/Ti/Pt were formed by sputtering Pt/Ti electrodes onto the surface of STO after annealing. The forming-free resistive switching behavior with self-compliance property was observed in the sample. The sample showed switchable diode effect, which is explained by a simple model that redistribution of oxygen vacancies (OVs) under the external electric field results in the formation of n–n+ junction or n+–n junction (n donated n-type semiconductor; n+ donated heavily doped n-type semiconductor). The self-compliance property is also interpreted by the formation of n–n+/n+–n junction caused by the migration of the OVs under the electric field.

Resistive switching properties of alkaline earth oxide-based memory devices

A reduced high-resistance state (HRS) current assists in obtaining high ON/OFF ratio and is beneficial to operation flexibility. This study proposes that less difference in the atomic radius of alkaline earth oxide-based memory devices is beneficial to reduce the HRS current. Forming-free resistive-switching behavior in the alkaline earth oxide-based memory device using magnesium titanate (MTO), strontium titanate (STO), and barium titanate (BTO) thin films is fabricated by sol-gel method. The dependence of HRS current on the difference in atomic radius was predicted by the Hume–Rothery rule and confirmed experimentally. The hydrolyzed particles, surface roughness, and density of oxygen vacancy were decreased when the difference in atomic radius between the Ti element and alkaline earth metal was less. Compared with the BTO thin film, the MTO thin film has fewer particles, smoother surface, and less density of oxygen vacancy, resulting in lower HRS current. Thus, suitable element selection for the alkaline earth oxide-based memory devices can reduce the HRS current.

Effects of Gibbs free energy of interfacial metal oxide on resistive switching characteristics of solution-processed HfOx films

Effects of bottom electrodes (BEs) of Al, Mo, and Pt on resistive switching characteristics of sol-gel HfOx films were investigated in this work. To avoid influences of plasma or thermal energy on HfOx RS characteristic, the top electrodes were formed by pressing indium balls onto the HfOx surface rather than by using a sputter or an evaporator. When using Mo as the BE, the as-deposited HfOx film can give a forming-free resistive switching behavior with low set/reset voltages of 0.28V / − 0.54V. In contrast, non-switching characteristics of the HfOx films were observed when using Al and Pt as the BEs. The HfOx conduction current was found to be highly dependent on the BE. However, when an annealing process at 350°C in an oxygen ambient was performed to the HfOx films on different BEs, the resistive switching behavior of the HfOx/Mo was absent while it can be found in the HfOx/Al sample. Differences in I-V characteristics of the HfOx films on different BEs were explained by considering Gibbs free energies of interfacial oxide layers. X-ray photoelectron spectroscopy (XPS) depth profile was used to examine the interfacial oxide layer. The resistive switching mechanism was also studied.

Forming-free electrochemical metallization resistive memory devices based on nanoporous TiOxNy thin film

We demonstrate a forming-free electrochemical metallization resistive memory device (Ag/TiOxNy/Pt) based on the nanoporous titanium oxynitride (TiOxNy) thin film. Due to the nanoporous structure of TiOxNy, Ag atoms can migrate into the film during the Ag electrode evaporation process, resulting in a pre-formed Ag conductive filament inside the switching layer. This is responsible for the forming-free resistive switching behavior. Subsequently, resistive switching with attractive performance is achieved after a reset process, including good endurance, low operation voltages, and fast switching speed. The forming-free and reliable switching characteristics suggest that nanoporous TiOxNy thin film is one of the promising material candidates for future nonvolatile memory applications.

Resistive switching behaviors of Cu/TaOx/TiN device with combined oxygen vacancy/copper conductive filaments

Forming-free and self-compliant bipolar resistive switching is observed in Cu/TaOx/TiN conductive bridge random access memory. Generally, Pt has been investigated as an inert electrode. However, Pt is not desirable material in current semiconductor industry for mass production. In this study, all electrodes are adapted to complementary metal-oxide-semiconductor compatible materials. The self-compliant resistive switching is achieved via usage of TiN bottom electrode. Also, dissolved Cu ions in TaOx lead to forming-free resistive switching behavior. The resistive switching mechanism is formation and rupture of combined oxygen vacancy/metallic copper conductive filament. We propose that Cu/TaOx/TiN is a promising candidate for a conductive bridge random access memory structure.

Unipolar resistive switching behavior in Dy2O3 films for nonvolatile memory applications

In this article, we report the forming-free resistive switching behavior of a Ru/Dy2O3/TaN memory device incorporating a Dy2O3 thin film fabricated entirely through processing at room temperature. We used X-ray diffraction, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy to investigate the structural and chemical features of the Dy2O3 film. The dominant conduction mechanisms in the low- and high-resistance states were ohmic behavior and Poole–Frenkel emission, respectively. The Ru/Dy2O3/TaN memory device exhibited a high resistance ratio and provided nondestructive readout and reliable data retention. This memory device has a great potential for application in nonvolatile resistive switching memory.

Comment on “Forming-free resistive switching behavior in Nd2O3, Dy2O3, and Er2O3 films fabricated in full room temperature” [Appl. Phys. Lett. 99, 113509 (2011)

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Forming-free resistive switching behavior in Nd2O3, Dy2O3, and Er2O3 films fabricated in full room temperature

In this study, we reported the forming-free resistive switching behavior in the Ru/RE2O3/TaN (RE = Nd, Dy, and Er) memory devices using thin Nd2O3, Dy2O3, and Er2O3 films fabricated with full room temperature process. The dominant conduction mechanisms of the Ru/RE2O3/TaN devices in the low-resistance state and high-resistance state are Ohmic behavior. The Ru/Dy2O3/TaN memory device exhibited high resistance ratio, nondestructive readout, reliable data retention, and good endurance. Ru/Dy2O3/TaN memory device has a great potential for the application in nonvolatile resistive switching memory.