Unipolar Resistive Switching Behavior Research Articles

CuInS2 quantum dots-based unipolar resistive switching for non-volatile memory applications.

Recent advancements have established quantum dots (QDs) as a promising alternative to conventional bulk materials in the fabrication of nanoscale integrated electronic devices. The appeal of QDs lies in their amenability to low-temperature processes and solution-based methodologies, facilitating the construction of devices with enhanced versatility and efficiency. The ternary metal chalcogenide CuInS2 QDs are one of the foremost, eco-friendly, and highly stable materials. In this study, CuInS2 QDs are employed as a functional layer in a memristive device featuring an Al/CuInS2/ITO configuration. The CuInS2 QDs have been synthesized by a hot injection method and characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) to reveal their structural features. The Al/CuInS2/ITO device shows a unipolar resistive switching (RS) behaviour with a high on/off ratio of 105. The switching parameters have been studied for 100 cycles of SET/RESET. The SET and RESET voltages are found to be 1.66 ± 0.25 V and 0.69 ± 0.17 V. The spatial variability of switching parameters in the Al/CuInS2/ITO structure has also been studied for 9 different devices. The device also exhibits unipolar RS behaviour in the optimum temperature range of 0 °C to 50 °C. These outcomes demonstrate the impressive performance of CuInS2 QDs, indicating their potential for future energy-efficient and large-scale non-volatile memory applications.

A stable undoped low-voltage memristor cell based on Titania (TiOx)

An asymmetric memristive device fabricated with a titania (TiOx)-based switching layer deposited through atomic layer deposition with a thickness of ∼37 nm was investigated. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy coupled with energy-dispersive x-ray spectroscopy were employed for device structural characterization. A unipolar resistive switching behavior (both at positive and negative voltages) was observed through the memristor’s current–voltage characteristics. A remarkably smaller forming voltage (from the top Pt electrode to the grounded Au electrode) of 0.46 V was achieved, while it approached (positive bias from the Au electrode and holding Pt electrode as grounded) 0.25 V, which is a much smaller forming voltage than has ever been reported for titanium-based oxides without doping. The retention and endurance characterization over 2000 switching cycles were satisfactory without degradation.

Ultralow Off‐State Current and Multilevel Resistance State in Van der Waals Heterostructure Memristors

AbstractMemristors based on 2D semiconductors hold great promise due to their atomic‐level thickness and tunable optoelectronic properties. However, a significant challenge lies in suppressing the large off‐state current, which leads to additional standby power consumption. Here, a simple and versatile method is presented to address this issue by introducing a thin h‐BN interlayer between 2D semiconductors and the electrodes. The thickness of the h‐BN interlayer serves as a pivotal parameter for modulating the interfacial Schottky barrier, thereby influencing the off‐state current level. This fabricated graphene/α‐In2Se3/h‐BN/Cr‐Au memristor, forming a van der Waals heterostructure, exhibits unipolar resistive switching behavior. Remarkably, the memristor incorporating an 8 nm h‐BN interlayer showcases an ultralow off‐state current of 4.2 × 10−13 A, five orders of magnitude lower than that without the h‐BN interlayer. It also achieves a current switching on/off ratio of up to 109 and realizes 32 distinct resistance states, enabling robust multi‐bit memory capabilities. Excellent stability and durability are maintained due to the self‐encapsulation of the h‐BN interlayer. Furthermore, this method is also applicable to memristors built on HfS2, WS2, and WSe2, highlighting its broad potential for technological applications.

Variability and power enhancement of current controlled resistive switching devices

In this work, the unipolar resistive switching behaviour of Ni/HfO2/Si(n+) devices is studied. The structures are characterized using both current and voltage sweeps, with the device resistance and its cycle-to-cycle variability being analysed in each case. Experimental measurements indicate a clear improvement on resistance states stability when using current sweeps to induce both set and reset processes. Moreover, it has been found that using current to induce these transitions is more efficient than using voltage sweeps, as seen when analysing the device power consumption. The same results are obtained for devices with a Ni top electrode and a bilayer or pentalayer of HfO2/Al2O3 as dielectric. Finally, kinetic Monte Carlo and compact modelling simulation studies are performed to shed light on the experimental results.

Graphene Oxide-Based Memristive Logic-in-Memory Circuit Enabling Normally-Off Computing

Memristive logic-in-memory circuits can provide energy- and cost-efficient computing, which is essential for artificial intelligence-based applications in the coming Internet-of-things era. Although memristive logic-in-memory circuits have been previously reported, the logic architecture requiring additional components and the non-uniform switching of memristor have restricted demonstrations to simple gates. Using a nanoscale graphene oxide (GO) nanosheets-based memristor, we demonstrate the feasibility of a non-volatile logic-in-memory circuit that enables normally-off in-memory computing. The memristor based on GO film with an abundance of unusual functional groups exhibited unipolar resistive switching behavior with reliable endurance and retention characteristics, making it suitable for logic-in-memory circuit application. In a state of low resistance, temperature-dependent resistance and I-V characteristics indicated the presence of a metallic Ni filament. Using memristor-aided logic (MAGIC) architecture, we performed NOT and NOR gates experimentally. Additionally, other logic gates such as AND, NAND, and OR were successfully implemented by combining NOT and NOR universal logic gates in a crossbar array. These findings will pave the way for the development of next-generation computer systems beyond the von Neumann architecture, as well as carbon-based nanoelectronics in the future.

Coexistence of Bipolar and Unipolar Resistive Switching Behavior in Amorphous Ga₂O₃ Based Resistive Random Access Memory Device

Herein, the memory device with a structure of Ag/Ga2O3/Pt has been successfully achieved, and the coexistence of bipolar resistive switching (BRS) and unipolar resistive switching (URS) behaviors are observed. The results show that the set process of bipolar and unipolar modes can be performed only when a positive voltage is applied with the same compliance current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {cc}}$ </tex-math></inline-formula> ) of 1 mA. For the reset process, the conversion process between bipolar and unipolar modes occurs by changing the polarity of sweeping voltages without <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {cc}}$ </tex-math></inline-formula> . The conduction mechanisms in two modes are conducting filaments (CFs) for the low resistance state (LRS). But for the high resistance states (HRS), it is schottky emission in BRS and space charge limited conduction mechanism in URS, respectively.

Ag/HfOx/Pt Unipolar Memristor for High-Efficiency Logic Operation.

Unipolar resistive switching (URS) behavior, known as the SET and RESET operating in a single voltage sweep direction, has shown great potential in the simplification of the peripheral circuit. The URS memristor always involves complicated interfacial engineering and structural design. In this work, a reliable URS behavior is realized using a simple Ag/HfOx/Pt memristor structure. The memristor displays a retention time of >104 s, an ON/OFF ratio of >103, and a good operation voltage. Synergy and competition between the Ag conductive filament formed by redox reaction and the migration of an oxygen vacancy are responsible for the observed URS. By comparison, a 35% power consumption is reduced during the logical operation from 0 to 1 to 0. The operation strategy is demonstrated by exhibiting the ACSII code of the capital letter denoted by eight logic states. This work provides a low-power concept for ultrahigh data storage using the URS memristor.

Unipolar resistive switching behavior in MoS2–polyvinyl alcohol-based memory device

MoS2–polymer-based memory devices have attracted significant interest owing to their mechanical flexibility, convenient solution processability, and affordability. These devices exhibit bipolar resistive switching behavior, and their switching relies on the polarity of the applied bias. This paper presents a memory device in which a MoS2–polyvinyl alcohol (PVA) hybrid film is sandwiched between Ag and Pt electrodes. The developed Ag/MoS2–PVA/Pt device manifests typical unipolar resistive switching (URS) behavior and nonvolatile rewritable memory performance with a low operating voltage, large ON/OFF ratio (105), and multilevel cell storage ability. Notably, 1T-phase MoS2 is crucial for the URS behavior, and this switching behavior can be ascribed to the charge trapping as well as the Joule-heating-induced de-trapping of the S vacancies associated with 1T MoS2. These findings can facilitate the development of new designs for high-performance, high-density data storage.

Conductive filament nanostructures and their magnetization reversal in NiO resistive switching memory cells

We demonstrate that conductive filament (CF) nanostructures in NiO thin film resistive switching memory (RRAM) cells present unique magnetic properties. The CF nanostructures of nanodots and nanorods formed using a conductive atomic force microscopy tip were fabricated through the forming process of CFs for the NiO RRAM cells. In the current–voltage curve, unipolar resistive switching behavior was observed. The ferromagnetic domain and magnetization switching of CF nanostructures were characterized using magnetic force microscopy. In principle, nanoscale-sized magnetic nanostructures possess superparamagnetism due to their thermal fluctuations. In this study, however, CF nanorods with a length of 30 nm exhibited ferromagnetism because the exchange bias effect occurred at the interface between the antiferromagnetic NiO and the CF nanorod. Therefore, the ferromagnetism of the CF nanostructures is the origin of the magnetization switching and can be favorable in magnetic storage device applications by overcoming the superparamagnetic limits with the exchange bias effect.

Ferromagnetic properties of conducting filament nanodots formed on epitaxial BiFeO3 thin film

We investigate the ferromagnetic properties of the conducting filament (CF) nanodots formed on epitaxial BiFeO3 (BFO) thin film, which exhibit resistive switching behavior. 50-nm thick epitaxial BFO thin film was grown on Nb-doped SrTiO3 single crystal substrates through pulsed laser deposition. The ferroelectric microcapacitor fabricated using the epitaxial BFO thin film shows excellent ferroelectric properties with a remanent polarization of approximately 32 μC/cm2 and unipolar resistive switching behavior. CF nanodots with a diameter of approximately 16 nm are formed in the local region of the BFO thin film through conductive atomic force microscopy. Generally, ferromagnetic materials exhibit superparamagnetism, on a scale of tens of nanometers, as a result of the thermal energy of the magnetic moments. In this study, magnetic force microscopy demonstrates that the CF nanodot possesses ferromagnetism. It is suggested that exchange coupling between the CF nanodot and surrounding BFO causes the ferromagnetism of the nanodot. Our study provides new insight on the design of multistate memory cells with resistive switching and magnetic spin ordering, for application in high-density information storage media.

Enhanced performance and reduction in operating voltage of TiO2 thin film based resistive switching memory under optical stimulus

Resistive switching memory devices are emerging class of non-volatile-memories and have shown outstanding device performance originates from the migration of oxygen vacancies. Research efforts are made to enhance the resistive switching behavior of devices using electrical and thermal stimuli, for example. Here we report optically modulated resistive switching behavior in Pt/TiO2/Al structure at low operating voltages. Highly stable unipolar resistive switching behavior with long retention of the resistance states (in the order of 104 min) and stable endurance (for > 300 cycles) is reported. Interestingly, the operating voltages of structure were observed to shift towards lower voltage side under optical illumination, which indicates that photo generated charge carriers play an important role. The present finding demonstrates the possible utilization of photo-responsive materials in manufacturing non-volatile memory device for future high-performance information storage and computing applications.

Electric field control of magnetization reversal in conducting filament nanostructures in NiO resistive random access memory

Abstract Magnetic nanostructures are attracting attention for use in magnetic storage applications because of the magnetization reversal that occurs when information is read and written. Here, we reveal that conducting filament (CF) nanostructures undergo magnetization switching on NiO thin film. We fabricated epitaxial NiO thin films deposited on a single-crystal Cu substrate through the pulsed laser deposition method. The resistive random access memory characteristics indicated that the current-voltage properties of the Au/NiO/Cu capacitor showed unipolar resistive switching behavior. Using conducting atomic force microscopy (CAFM), various CF nanostructures, i.e., nanodots, nanorods, and nanorings, were formed on the NiO thin film. We studied the reversal in the direction of the magnetization induced by the electric field in the CF nanorods and nanorings on the NiO thin film by using the tip of the CAFM. The CF nanostructures on the NiO thin film have ferromagnetic properties. The coercive field of the nanorings is larger than that of the nanorods, based on Ampere’s law. Our results showed that the magnetic field induced by applying voltage to the tip of the CAFM enables magnetization switching in the nanorods and nanorings.

Highly stable, solution-processed quaternary oxide thin film-based resistive switching random access memory devices via global and local stoichiometric manipulation strategy

Optimization and performance enhancement of a low-cost, solution-processed InGaZnO (IGZO) resistance random access memory (ReRAM) device using the manipulation of global and local oxygen vacancy (Vo) stoichiometry in metal oxide thin films was demonstrated. Control of the overall Ga composition within the IGZO thin film reduced the excessive formation of oxygen vacancies allowing for a reproducible resistance switching mechanism. Furthermore, sophisticated local control of stoichiometric Vo is achieved using a 5 nm Ni layer at the IGZO interface to serve as an oxygen capturing layer through the formation of NiOx, consequently facilitating the formation of conductive filaments (CFs) and preventing abrupt degradation of device performance. Additionally, reducing the cell dimension of the IGZO-based ReRAMs using a cross-bar electrode structure appeared to drastically improve their performances parameters, including operating voltage and resistance distribution due to the suppression of excessive CFs formation. The optimized ReRAM devices exhibited stable unipolar resistive switching behavior with an endurance of >200 cycles, a retention time of 104 s at 85 °C and an on/off ratio greater than about 102. Therefore, our findings address the demand for low-cost memory devices with high stability and endurance for next-generation data storage technology.

Effects of Resistance States on the Magnetoresistance in Ni/Al2O3/Ni by Resistive Switching

Formation and rupture of conductive filaments is one of the main mechanisms for unipolar resistive switching (URS), which can be manifested by the observation of magnetoresistance (MR) effect if ferromagnetic metallic filaments are formed. In this work, ferromagnetic metallic Ni is used as top and bottom electrodes on Al2O3 film, and stable URS behavior is observed after a forming process. By inserting a series resistor in the circuit during the set process, the resistance value at low resistance state (LRS) increases with increasing resistance of the series resistor. The URS behavior can be attributed to the formation and rupture of metallic Ni filaments penetrating through the thin Al2O3 layer, which has been confirmed by the observation of tunneling magnetoresistance. However, the MR value decreases continuously with increasing resistance in LRS, which is due to that the diameter of Ni conductive filaments becomes smaller. Thus, the nonmagnetic scattering at the surfaces of filaments increases, leading to the decrease of MR.

Realization of resistive and magnetization switching in sol-gel derived yttrium iron garnet thin films

In this work, large-area ferrite thin films of ferromagnetic yttrium iron garnet (Y3Fe5O12, YIG) were synthesized on Pt/Ti/SiO2/Si (Pt) substrates by a sol-gel method to investigate the resistive and magnetization switching properties. The synthesized YIG thin films acquire a single garnet structure. The Pt/YIG/Pt stack illustrates unipolar resistive switching behavior with excellent switching uniformity, large memory window (102), stable cycle-to-cycle endurance, and good data storage retention (104 s). The ~46% saturation magnetization variation could be realized via the conversion between high and low resistance states by manipulating the electric field. Schottky emission is governed in the high-field region for the high resistance state. Temperature dependence of resistance and magnetization variation confirms that oxygen vacancies conductive filament model and valence state change (Fe2+ and Fe3+) are responsible for the resistive and magnetization switching mechanisms. These results indicate that YIG ferrite based stack is suitable to design the electro-magnetic coupling multifunctional nonvolatile memory devices.

Forming-free bipolar and unipolar resistive switching behaviors with low operating voltage in Ag/Ti/CeO2/Pt devices

Resistive switching devices are promising candidates to replace today’s nonvolatile memory device, and find applications in neuromorphic computing. In this study, bipolar resistive switching (BRS) and unipolar resistive switching (URS) behaviors at room temperature were shown for Ag/Ti/CeO2/Pt devices. Without forming step, the device exhibited low set voltage (about 0.3 V) and reset voltage (about −0.3 V to −0.6 V) in BRS behavior, which is beneficial for nonvolatile memory application. The I-V characteristics were analyzed, and it was concluded that the switching mechanism in BRS is dominated by the electrochemical metallization mechanism (ECM), while in URS, conduction is dominated by thermochemical mechanism (TCM).

Facile preparation of molybdenum disulfide quantum dots using a femtosecond laser

Molybdenum disulfide (MoS2) is rapidly emerging in a wide range of applications owing to its superior optical, electrical, and catalytic properties. In particular, aside from the current great interest in monolayer MoS2, MoS2 quantum dots (QDs) have received much attention in the electronics and optoelectronics fields owing to their inherent electrical and optical properties arising from the quantum confinement effect. Thus, various methods for producing MoS2 QDs, such as exfoliation, substrate growth, and colloidal synthesis, have been attempted. In this study, the method for manufacturing MoS2 QD with a size of 10 nm which is simpler than the conventional method was devised. On the basis of characterization of the prepared MoS2 QD samples, resistive switching devices was fabricated. These devices demonstrated stable unipolar resistive switching behavior without an electroforming process. This study provides a new approach for the mass production of MoS2 QD and one of their potential applications.

Unipolar resistive switching behavior in Al2O3/HfO2 multilayer dielectric stacks: fabrication, characterization and simulation

In this work, the impact of different HfO2/Al2O3-based multilayer dielectric stack (DS) configurations on the electrical characteristics and on the resistive switching (RS) performance of Ni/Insulator/Silicon devices has been systematically investigated. Significant differences are observed in the electrical characteristics of the fabricated bilayer, trilayer and pentalayer stacks compared to a single HfO2 layer of the same physical thickness. The RS analysis has shown similar low resistance state currents and set voltages for all the DS combinations whereas currents at the high resistance state and reset voltages depend on the DS. The shift of the reset voltage to lower values for HfO2 and Al2O3/HfO2/Al2O3 cases is explained by the results from thermal simulations that reveal that these differences could be associated to the different temperature distributions at the narrowest part of the conductive filament immediately before the thermally triggered reset process occurs.

All-room-temperature processed high flexibility resistive switching memory by ultraviolet-radioactive induction

Alumina-based materials are widely used in semiconductor industry due to the high reliability. However, they are usually employed as high-k gate dielectric rather than memory layer, and high temperature annealing process is also required to maintain the electrical characteristics. These factors enormously limit their further applications in new semiconductor devices such as new type non-volatile memory and flexible electronic devices. In this work, a one-step ultraviolet irradiation method was applied to rapidly achieve AlO–OH thin film at room temperature for flexible resistive memory. This flexible memory device shows satisfied electrical characteristics such as typical unipolar resistive switching behaviors, stable retention, good electrical reliability and mechanical endurance both in flat and bent states. Anion vacancies in AlO–OH layer were contributed to the formation of conductive filament. This technical route with low cost and efficient fabrication process paves a feasible way for developing flexible non-volatile memory and wearable electronics.

Any-polar resistive switching behavior in LATP films

We demonstrate the coexistence and conversion of the unipolar and bipolar resistive switching behavior in Pt/Li1+xAlxTi2−x(PO4)3 (LATP)/Pt structures fabricated by sputtering. The dielectric constant (k) of the LATP film equals 12.0. After the electroforming, the Pt/LATP/Pt resistive switching device exhibits either unipolar switching mode (URS) or bipolar switching mode (BRS). The switching mode can be freely converted between URS and BRS with the same compliance current. This will provide a foundation for a switching mode called any-polar switching mode. The switching mechanism is believed to be related to the formation and rupture of conductive filaments and the excellent oxygen storage capacitance of the LATP film.