Resistive Switching Memory Characteristics Research Articles

Effect of heat treatment on resistive switching memory characteristics of NiO nanodots of tens of nanometers shattered by AFM tips

The characteristics of resistive random access memory (RRAM) at the nanometer scale are increasingly important for RRAM cells with further miniaturization. We report the RRAM characteristics of NiO nanodots in the order of tens of nanometers. NiO nanodots of approximately 70 nm were created on a single-crystal Nb-doped SrTiO3 (Nb:STO) substrate by dip-pen nanolithography. For comparison, a NiO thin film was also deposited on the Nb:STO substrate by spin coating. To reduce the size of NiO nanodots, they were shattered by an atomic force microscope tip, obtaining nanodots of approximately 10 nm. Using a conductive atomic force microscope, we characterized the current according to the applied electric field of the NiO nanodots on the Nb:STO substrate with a capacitor configured of Pt/NiO/Nb:STO substrate. When compared with the NiO thin film, the forming voltage of the NiO nanodots decreased. In addition, the shattered NiO nanodots exhibited unipolar switching characteristics, and the forming and set/reset voltages decreased with the reduction in nanodot size. Furthermore, the NiO nanodots exhibited a substantially reduced forming and set/reset voltages after heat treatment in vacuum. We suggest that the oxygen-depleted layer formed on the surface of NiO nanodots by heat treatment plays a crucial role in the reduction of the forming and operation voltages.

Resistive switching properties of CdTe/CdSe core–shell quantum dots incorporated organic cow milk for memory application

Our study focuses on the resistive switching memory characteristics of devices containing active layers of CdTe/CdSe core–shell quantum dots (QDs) dispersed in organic cow milk. We fabricated devices containing CdTe/CdSe particles per volume of milk using a direct-dipping method, with particle concentrations of 2.4 × 10[Formula: see text] (S1), 4.8 × 10[Formula: see text](S2), and 7.2 × 10[Formula: see text](S3). This method was cost-free. Distinct memory characteristics were observed among devices featuring these concentrations. S1- and S2-based devices exhibited memory behavior with ‘S-type’ and ‘O-type’ hysteresis, respectively. The device based on S3 exhibited an initial asymmetric ‘N-type’ behavior with a large ON/OFF ratio ([Formula: see text]104). The memory attribute of the aforementioned device disappeared after the initial three cycles but was subsequently restored by modifying the scan voltage step from 10 mV to 1 mV. The observed results indicate typical symmetric ‘N-type’ behavior of the device, accompanied by threshold switching under positive voltage bias. Additionally, the switching was observed to be as low as 0.04 V. The S1- and S2-based devices were found to exhibit hopping conduction and Schottky emission in the OFF- and ON-state, respectively, while the S3-based device showed conductive bridge resistive switching as the conduction mechanism. The findings indicate that it is possible to produce biodegradable and disposable memory devices using full cream cow milk and CdTe/CdSe core–shell QDs. The device’s switching and memory functions can be manipulated by regulating the quantity of CdTe/CdSe particles present in the milk. Finally, we have demonstrated that the switching behavior of ReRAMs based on milk can be influenced by the voltage steps used during scanning.

Thickness-dependent resistive switching memory characteristics of NiO nanodisks fabricated by AAO nanotemplate

Forming and set/reset operating voltages are critical issues encountered with a decrease in resistive random-access memory (RRAM) sizes. This study investigated the thickness-dependent resistive switching properties of NiO nanodisks. The NiO RRAM nanodisks, with a diameter of 100 nm and varying thicknesses, were fabricated on Pt/Ta/SiO2/Si substrates using anodic aluminum oxide templates through the RF sputtering process. In the electroforming process, the forming voltage of the NiO nanodisk effectively reduced with a decrease in the thickness. The electric field enhancement in localized regions appeared to contribute to the reduction in the forming voltage. In addition, the set/reset operating voltage of the NiO nanodisk RRAM decreased with a decrease in the thickness. We conclude that the use of the C-AFM tip strengthened the local electric field in NiO nanodisk RRAM cells, leading to the reduction of the set/reset voltage with a decrease in the thickness.

Contrasting analog and digital resistive switching memory characteristics in solution-processed copper(i) thiocyanate and its polymer electrolyte-based memristive devices

Analog and digital resistive switching characteristics of ITO/CuSCN/Cu and ITO/Cu-SPE/Cu memristive devices.

Percolation theory based model of conduction mechanism and characteristic contradiction in ZnO RRAM

Resistive random access memory (RRAM) has been intensively investigated for nearly two decades. However, RRAM has not been applied widely in the market because of the poor characteristics, such as reliability and uniformity, which could be improved by the accurate comprehension of the mechanism. In this paper, a model based on percolation theory is proposed to simulate the I-V characteristics of ZnO resistive switching memory. It demonstrates that three different conductions of space charge limited current, Poole–Frenkel effect, and thermionic emission are determined by the relationship between the oxygen vacancy concentration and the bias. Furthermore, this model well explains the effect of conductive filaments' diameter and compliance current on the I-V characteristics of ZnO resistive switching memory, which demonstrates the rationality of the percolation model.

Self-Rectifying Resistive Switching and Short-Term Memory Characteristics in Pt/HfO2/TaOx/TiN Artificial Synaptic Device.

Here, we propose a Pt/HfO2/TaOx/TiN artificial synaptic device that is an excellent candidate for artificial synapses. First, XPS analysis is conducted to provide the dielectric (HfO2/TaOx/TiN) information deposited by DC sputtering and atomic layer deposition (ALD). The self-rectifying resistive switching characteristics are achieved by the asymmetric device stack, which is an advantage of the current suppression in the crossbar array structure. The results show that the programmed data are lost over time and that the decay rate, which is verified from the retention test, can be adjusted by controlling the compliance current (CC). Based on these properties, we emulate bio-synaptic characteristics, such as short-term plasticity (STP), long-term plasticity (LTP), and paired-pulse facilitation (PPF), in the self-rectifying I–V characteristics of the Pt/HfO2/TaOx/TiN bilayer memristor device. The PPF characteristics are mimicked by replacing the bio-stimulation with the interval time of paired pulse inputs. The typical potentiation and depression are also implemented by optimizing the set and reset pulse. Finally, we demonstrate the natural depression by varying the interval time between pulse inputs.

Flexible Resistive Switching Memory Devices Based on Graphene Oxide Polymer Nanocomposite

Flexible resistive switching memory devices based on graphene oxide (GO) polymer nanocomposite were prepared on flexible substrate to research the influence of bending on resistive switching behavior. The devices showed evident response in resistive switching memory characteristics to flexible bending. The 2000 cycles flexible bending leads to the switch of resistive switching memory characteristic from write-once-read-many time memory (WORM) to static random access memory (SRAM). Both WORM and SRAM memory properties are all repeatable, and the threshold switching voltage also showed good consistency. The resistive switching mechanism is attributed to the formation of carbon-rich conductive filaments for nonvolatile WORM characteristics. The bending-induced micro-crack may be responsible for the partial broken of the electrical channels, and may lead to the volatile SRAM characteristics.

Multilevel Switching Characteristics of Si3N4-Based Nano-Wedge Resistive Switching Memory and Array Simulation for In-Memory Computing Application

In this research, nano-wedge resistive switching random-access memory (ReRAM) based on a Si3N4 switching layer and silicon bottom electrode was fabricated, and its multilevel switching characteristics were investigated. The wedge bottom electrode was formed by a tetramethyl ammonium hydroxide (TMAH) wet-etching process. The nano-wedge ReRAM was demonstrated to have different reset current levels by varying the compliance currents. To explain the effect of modulating the compliance currents, the switching characteristics of both the SET and RESET behaviors were shown. After measuring the device under four different compliance currents, it was proved to have different current levels due to an inhibited resistive state after a SET switching process. Furthermore, SPICE circuit simulation was carried out to show the effect of line resistance on current summation for the array sizes of 8 × 8 and 16 × 16. These results indicate the importance of minimizing the line resistance for successful implementation as a hardware-based neural network.

Layered (C6H5CH2NH3)2CuBr4 Perovskite for Multilevel Storage Resistive Switching Memory

AbstractAlthough there have been attempts to use non‐lead based halide perovskite materials as insulating layers for resistive switching memory, the ratio of low resistance state (LRS) to high resistance state (HRS) ( = ON/OFF ratio) and/or endurance is reported to be mostly lower than 103. Resistive switching memory characteristics of layered (BzA)2CuBr4 (BzA = C6H5CH2NH3) perovskite with high ON/OFF ratio and long endurance are reported here. The X‐ray diffraction (XRD) pattern of the deposited (BzA)2CuBr4 layer shows highly oriented (00l) planes perpendicular to a Pt substrate. An Ag/PMMA/(BzA)2CuBr4/Pt device shows bipolar switching behavior. A forming step at around +0.5 V is observed before the repeated bipolar switching at the SET voltage of +0.2 V and RESET voltage of ‐0.3 V. The ON/OFF ratio as high as =108 is monitored along with an endurance of ≈2000 cycles and retention time over 1000 s. The high ON/OFF ratio enables multilevel storage characteristics as confirmed by changing the compliance currents. Ohmic conduction at the LRS and Schottky emission at HRS are involved in electrochemical metallization process. The bipolar resistive switching property is retained after storing the device at ambient condition under relative humidity of about 50% for 2 weeks, which indicates that (BzA)2CuBr4 is stable memory material.

Investigation of resistive switching in copper/InGaZnO/Al2O3-based memristor

This work investigates the resistive switching mechanism in the Cu/TiW/InGaZnO/Al2O3/Pt-based memristor. By introducing the Al2O3 layer, the nanoscale diameter of the Cu filament decreased from 6.51 to 0.83 nm as the current compliance decreases from 1 mA to 50 μA. The resistive switching memory characteristics, such as a large ratio of high-resistance state (HRS)/low-resistance state (LRS) (∼107), stable switching cycle stability (>9 × 102), and multilevel operation, are observed and apparently improved compared to the counterpart of the Cu/TiW/InGaZnO/Pt memory device. These results are attributed to the control of Cu formation/dissolution by introducing the Al2O3 nanolayer at the InGaZnO/Pt interface. The findings of this study can not only improve the performance of the amorphous InGaZnO memristor but also be promising for potential applications of next-generation flat-panel displays in wearable devices.

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.

Influence of the voltage window on resistive switching memory characteristics based on g-C3N4 device

The resistance change of an insulator or semiconductor under applied current or voltage is defined as resistive switching effect, which is a significative physical performance in the exploit of new concept nonvolatile resistance random access memory (RRAM). In our work, the g-C3N4 powder was firstly fabricated by calcination method, and continuously a device with Ag/g-C3N4/FTO structure was prepared using drop-coated g-C3N4 powder to form a film onto FTO. It can be observed that the as-prepared cell exhibits an excellent resistive switching memory characteristic (HRS/LRS resistance ratio can be reached to ~ 52) and good reliability under applied voltage window of 4.0 V. Finally, it is believed that the space charge limited conduction is appropriate to understanding such the memory behavior.

Ag filament induced nonvolatile resistive switching memory behaviour in hexagonal MoSe2 nanosheets

In this work, hexagonal MoSe2 nanosheets were prepared by hydrothermal process. Next, the resistive switching memory behaviour of single MoSe2 nanosheets was further investigated. We observed that MoSe2 nanosheets based memory device show reproducible and stable bipolar resistive switching memory characteristics. Through the analysis for conductive mechanism, the formation and rupture of nanoscale Ag filament inside the MoSe2 nanosheets is suggested to explain the memory behaviour.

Effect of sputtering atmosphere on the characteristics of ZrOx resistive switching memory

A ZrOx switching layer with different oxygen content for TiN/ZrOx/Pt resistive switching (RS) memory was prepared by magnetron sputtering in different atmospheres such as N2/Ar mixture, O2/Ar mixture as well as pure Ar. The morphology, structure and RS characteristics were systemically investigated and it was found that the RS performance is highly dependent on the sputtering atmosphere. For the memory device sputtered in N2/Ar mixture, with 8.06% nitrogen content in the ZrOx switching layer, the highest uniformity with smallest distribution of Vset and high resistance states (HRS)/low resistance states (LRS) values were achieved. By analyzing the current conduction mechanisms combined with possible RS mechanisms for three devices, we deduce that for the device with a ZrOx layer sputtered in N2/Ar mixture, oxygen ions (O2−), which are decisive to the disruption/formation of the conductive filament, will gather around the tip of the filament due to the existence of doping nitrogen, and lead to the reduction of O2− migration randomness in the operation process, so that the uniformity of the N-doped ZrOx device can be improved.

Effect of Cu ions assisted conductive filament on resistive switching memory behaviors in ZnFe2O4-based devices

Resistive random access memory (RRAM) has been developing as a most promising non-volatile memory in the current memory technology. In this work, ZnFe2O4 (ZFO) nano powder were firstly prepared by co-precipitation assisted hydrothermal process. Further, the resistive switching memory devices with Ag/Cu doped ZnFe2O4 (CZFO)/Au/Si and Ag/ZFO/Au/Si structures grown on silicon (Si) substrate were prepared by radio frequency magnetron sputtering, and their memory behaviors were contrastively investigated. It is observed the Cu doping can obviously affect the bipolar resistive switching memory characteristics. Thus a model concerning the formation and rupture of Cu ions assisted conductive filament inside the CZFO layer is suggested to explain the change of memory behaviors. These works provide a foundation for exploring the memory application of multifunctional material and further regulate their nonvolatile memory behaviors.

Temperature-Dependent Non-linear Resistive Switching Characteristics and Mechanism Using a New W/WO3/WOx/W Structure.

Post-metal annealing temperature-dependent forming-free resistive switching memory characteristics, Fowler-Nordheim (F-N) tunneling at low resistance state, and after reset using a new W/WO3/WOx/W structure have been investigated for the first time. Transmission electron microscope image shows a polycrystalline WO3/WOx layer in a device with a size of 150 × 150 nm2. The composition of WO3/WOx is confirmed by X-ray photo-electron spectroscopy. Non-linear bipolar resistive switching characteristics have been simulated using space-charge limited current (SCLC) conduction at low voltage, F-N tunneling at higher voltage regions, and hopping conduction during reset, which is well fitted with experimental current-voltage characteristics. The barrier height at the WOx/W interface for the devices annealed at 500 °C is lower than those of the as-deposited and annealed at 400 °C (0.63 vs. 1.03 eV). An oxygen-vacant conducting filament with a diameter of ~34 nm is formed/ruptured into the WO3/WOx bilayer owing to oxygen ion migration under external bias as well as barrier height changes for high-resistance to low-resistance states. In addition, the switching mechanism including the easy method has been explored through the current-voltage simulation. The devices annealed at 500 °C have a lower operation voltage, lower barrier height, and higher non-linearity factor, which are beneficial for selector-less crossbar memory arrays.

Photo-electron double regulated resistive switching memory behaviors of Ag/CuWO4/FTO device

In this work, the CuWO4 film based resistive switching memory capacitors were fabricated with hydrothermal and spin-coating approaches. The device exhibits excellent photo-electron double controlled resistive switching memory characteristics with OFF/ON resistance ratio of ~103. It is believed that the interface of CuWO4 and FTO is responsible for such a switching behavior and it can be described by the Schottky-like barriers model. This study is useful for exploring the multifunctional materials and their applications in photo-electron double controlled nonvolatile memory devices.

Resistive switching memory characteristics of single MoSe2 nanorods

Resistive switching memory effect in metal–oxide–metal structures is a fascinating phenomenon toward next generation universal nonvolatile memories. Herein, the MoSe2 nanorods were prepared by hydrothermal method. Further, a resistive switching memory device of single MoSe2 nanorods is demonstrated. The device presents stable resistive switching memory behaviors with on–off ratio (memory window) of ∼50 at room temperature. Moreover, the origin of switching behavior in these devices on the basis of formation and annihilation of conducting filaments is addressed. This study is useful for exploring the multifunctional materials and their applications in nonvolatile memory devices.

Observation of Resistive Switching Memory by Reducing Device Size in a New Cr/CrO x /TiO x /TiN Structure.

The resistive switching memory characteristics of 100 randomly measured devices were observed by reducing device size in a Cr/CrOx/TiOx/TiN structure for the first time. Transmission electron microscope image confirmed a via-hole size of 0.4 µm. A 3-nm-thick amorphous TiOx with 4-nm-thick polycrystalline CrOx layer was observed. A small 0.4-µm device shows reversible resistive switching at a current compliance of 300 µA as compared to other larger size devices (1–8 µm) owing to reduction of leakage current through the TiOx layer. Good device-to-device uniformity with a yield of >85 % has been clarified by weibull distribution owing to higher slope/shape factor. The switching mechanism is based on oxygen vacancy migration from the CrOx layer and filament formation/rupture in the TiOx layer. Long read pulse endurance of >105 cycles, good data retention of 6 h, and a program/erase speed of 1 µs pulse width have been obtained.

Preparation and light-controlled resistive switching memory behavior of CuCr2O4

In this work, CuCr2O4 nanoparticles were successfully prepared by an improved hydrothermal process, and a resistive switching memory behavior with Ag/CuCr2O4/fluorine-doped tin oxide structure is demonstrated. Specially, the resistive switching memory characteristics can be controlled by white-light illumination. The device can maintain superior stability over 100 cycles with an OFF/ON-state resistance ratio of about 103 at room temperature. This study is useful for exploring the promising light-controlled resistive switching memory device in the development of resistive switching random-access memory. We demonstrate a resistive switching device based on Ag/CuCr2O4/FTO structure, and the device shows light-controlled resistive switching memory characteristics.