Nonvolatile Bipolar Resistive Switching Research Articles

Impact of Light on Coexistence of Memresistance, Meminductance, and Memcapacitance (MEMRIC) in Nanostructured Copper Oxide (CuO) based Random Access Memory Devices.

We demonstrated the coexistence of memresistance, memcapacitance, and meminductance non-volatile bipolar analog resistive switching in Cu (top electrode)/CuO (active layer)/ SS (bottom electrode) memory devices with and without the presence of the light. The onset of memcapacitance and meminductance is noticed from the pinched-shaped characteristics in the first and third quadrants. The variation in the scan rate also impacts the coexistence characteristics by shifting the intercept point for low resistance (LRS) and high resistance (HRS) states in positive and negative biasing voltages. The durability and retention are measured over a period of 150 cycles and 1500 s with and without light illumination. The Weibull slope for set/reset state with and without light are 106.80/114.23 and 70.21/102.25, respectively, suggesting that stability of the device increases with light illumination. Interestingly, the memcapacitance disappears after 600 cycle and after 60 . The double logarithmic I-V characteristics suggest the trap assisted conduction (higher slope > 2) in the higher external electric field, and Ohmic behaviour in the lower applied field region. Thus, the present study provides a way for low power electronics and photoresistors together with memresistance, memcapacitance, and meminductance, simultaneously, i.e., MEMRIC in a single device.

Light-induced multilevel resistive switching in cesium-doped lead-free halide double perovskite memory device

A series of (CH3NH3)2-xCsxAgBiBr6 films (x=0, 0.1, 0.2, 0.3, 0.4) were fabricated on ITO/glass substrates through the sol-gel method. 15 % Cs doping (x=0.3) was the optimal condition for enhancing the film quality and achieving nonvolatile bipolar resistive switching (BRS) performance in the devices. The on/off ratio in the (CH3NH3)1.7Cs0.3AgBiBr6 (Cs-MAABB-3)-based RS device reached 7.7×104, high and low resistance states were maintained for over 104 s. Under different light intensities with a wavelength of 430 nm, six distinct resistance states were recorded at −0.3 V in the Au/Cs-MAABB-3/ITO/glass device. These multilevel states remained after 5000 s and 650 cycles, indicating the excellent retention and endurance of multilevel RS memory in the Au/Cs-MAABB-3/ITO/glass device. The RS behavior in this device followed the trap-controlled space charge-limited current and conductive filament models. Cs-doping increased the concentration of intrinsic vacancies appropriately, leading to a more prominent RS effect. With varying intensities of illumination, the change of Schottky-like barrier at the Au/Cs-MAABB-3 interface, modulated by the photo-induced carriers, affected the multilevel resistance states in the device. The excellent multilevel RS performance was observed for the first time in the Cs-MAABB-3-based device. It presents broad possibilities for improving high-density memory in lead-free halide double perovskite-based devices.

Nonvolatile bipolar resistive switching characteristics of aluminum oxide grown by thermal oxidation processes

This study proposes a bipolar resistive random-access memory (RRAM), which is fabricated using an aluminum oxide (AlO x ) resistive switching (RS) layer. The RRAM shows a large memory window of 106 at a low read voltage of 0.5 V. In addition, high switching speed, long retention time, and superior read-disturb immunity are observed. AlO x layers are prepared by a thermal oxidation growth process. Aluminum metal films deposited on n+-Si wafers are oxidized at O2/(O2 + N2) flow rate ratios of 50%–100%. Al/AlO x /n+-Si device shows no RS behavior when the AlO x is grown in a pure O2 environment. As the O2/(O2 + N2) flow rate ratio decreases to 50%, Al/AlO x :N/n+-Si device reveals stable bipolar RS characteristics. A filamentary mode based on oxygen interstitial and Al vacancy is proposed to explain the difference in electrical characteristics of AlO x devices prepared at different O2 flow rates.

The Effect of Nitrogen Annealing on the Resistive Switching Characteristics of the W/TiO2/FTO Memory Device

In this paper, the effect of nitrogen annealing on the resistive switching characteristics of the rutile TiO2 nanowire-based W/TiO2/FTO memory device is analyzed. The W/TiO2/FTO memory device exhibits a nonvolatile bipolar resistive switching behavior with a high resistance ratio (RHRS/RLRS) of about two orders of magnitude. The conduction behaviors of the W/TiO2/FTO memory device are attributed to the Ohmic conduction mechanism and the Schottky emission in the low resistance state and the high resistance state, respectively. Furthermore, the RHRS/RLRS of the W/TiO2/FTO memory device is obviously increased from about two orders of magnitude to three orders of magnitude after the rapid nitrogen annealing treatment. In addition, the change in the W/TiO2 Schottky barrier depletion layer thickness and barrier height modified by the oxygen vacancies at the W/TiO2 interface is suggested to be responsible for the resistive switching characteristics of the W/TiO2/FTO memory device. This work demonstrates the potential applications of the rutile TiO2 nanowire-based W/TiO2/FTO memory device for high-density data storage in nonvolatile memory devices.

Reconfigurable Low-Voltage Hexagonal Boron Nitride Nonvolatile Switches for Millimeter-Wave Wireless Communications.

Recently, nonvolatile resistive switching memory effects have been actively studied in two-dimensional (2D) transition metal dichalcogenides and boron nitrides to advance future memory and neuromorphic computing applications. Here, we report on radiofrequency (RF) switches utilizing hexagonal boron nitride (h-BN) memristors that afford operation in the millimeter-wave (mmWave) range. Notably, silver (Ag) electrodes to h-BN offer outstanding nonvolatile bipolar resistive switching characteristics with a high ON/OFF switching ratio of 1011 and low switching voltage below 0.34 V. In addition, the switch exhibits a low insertion loss of 0.50 dB and high isolation of 23 dB across the D-band spectrum (110 to 170 GHz). Furthermore, the S21 insertion loss can be tuned through five orders of current compliance magnitude, which increases the application prospects for atomic switches. These results can enable the switch to become a key component for future reconfigurable wireless and 6G communication systems.

Inkjet-printed h-BN memristors for hardware security.

Inkjet printing electronics is a growing market that reached 7.8 billion USD in 2020 and that is expected to grow to ∼23 billion USD by 2026, driven by applications like displays, photovoltaics, lighting, and radiofrequency identification. Incorporating two-dimensional (2D) materials into this technology could further enhance the properties of the existing devices and/or circuits, as well as enable the development of new concept applications. Along these lines, here we report an easy and cheap process to synthesize inks made of multilayer hexagonal boron nitride (h-BN)-an insulating 2D layered material-by the liquid-phase exfoliation method and use them to fabricate memristors. The devices exhibit multiple stochastic phenomena that are very attractive for use as entropy sources in electronic circuits for data encryption (physical unclonable functions [PUFs], true random number generators [TRNGs]), such as: (i) a very disperse initial resistance and dielectric breakdown voltage, (ii) volatile unipolar and non-volatile bipolar resistive switching (RS) with a high cycle-to-cycle variability of the state resistances, and (iii) random telegraph noise (RTN) current fluctuations. The clue for the observation of these stochastic phenomena resides on the unpredictable nature of the device structure derived from the inkjet printing process (i.e., thickness fluctuations, random flake orientations), which allows fabricating electronic devices with different electronic properties. The easy-to-make and cheap memristors here developed are ideal to encrypt the information produced by multiple types of objects and/or products, and the versatility of the inkjet printing method, which allows effortless deposition on any substrate, makes our devices especially attractive for flexible and wearable devices within the internet-of-things.

Low power highly flexible BiFeO3-based resistive random access memory (RRAM) with the coexistence of negative differential resistance (NDR).

We demonstrated the resistive random access memory characteristics for Cu (top contact)/BFO/PMMA (active layer)/ITO (bottom electrode)/PET sheet as a flexible substrate device configuration. The device showed non-volatile bipolar resistive switching characteristics with good repeatability and the coexistence of NDR for 100 cycles or more with 0.28/3.43 mW power consumption for 1st/100th cycles. The device retains its read state for 104 s or more and switches from LRS to HRS or vice versa for 103 cycles with a pulse width of 100 ms for a write-read-erase-read pulse without affecting the memory characteristics. The Weibull distribution suggests that a set state is more stable than the reset state with shape factor β = 25.20. The device follows Ohmic behavior for the lower applied external field and Child square and Schottky emission for the higher external fields. The Joule heating, Sorets, and Fick's forces are responsible for the formation and rupturing of ionic filament. The coexistence of resistive switching and flexible strength of the device sustains the bending curvature of infinity, 0.2 cm, 1 cm, 1.7 cm, and 2.2 cm. The memory characteristics are retained under tensile conditions for 100 cycles or more. More interestingly, the power consumption for sustaining the NDR region with bending (19 μW) is much lower than without bending (0.19 mW). Thus, this study provides the possibility of integrating BFO with flexible substrates suitable for hybrid organic/inorganic memory structures.

Improved Performance of the Al2O3-Protected HfO2-TiO2 Base Layer with a Self-Assembled CH3NH3PbI3 Heterostructure for Extremely Low Operating Voltage and Stable Filament Formation in Nonvolatile Resistive Switching Memory.

Herein, we report intriguing observations of an extremely stable nonvolatile bipolar resistive switching (NVBRS) memory device fabricated using HfO2-TiO2 topologically protected by Al2O3 as a stacked base layer for a CH3NH3PbI3 (MAPI) electrolyte layer sandwiched between Ag and fluorine-doped tin oxide (FTO) electrodes. MAPI has been successfully synthesized by a rapid microwave-solvothermal (MW-ST) method within 10 min at 120 °C without requiring any inert gas atmosphere using low-cost precursors and solvents. Subsequently, MAPI powders are dissolved in aprotic solvents (DMF/DMSO = 8:2), and a spin-coated thin film is allowed to recrystallize upon annealing at 120 °C via a solution-based nanoscale self-assembly process. The fabricated memory device with the Ag/MAPI/Al2O3/TiO2-HfO2/FTO configuration shows an enhanced resistance ratio of 105 for >104 s at an extremely lower operating voltage (SET +0.2 V, RESET -0.2 V) when compared to that of the pristine MAPI device (±1 V, 102, 104 s). We show that the memory device also exhibits a remarkable endurance of ≥3500 cycles due to the Al2O3 robust coating on the HfO2-TiO2 layer, facilitating prompt heterojunction formation. Thus, the adopted innovative strategies to prepare structurally and optically stable (∼1.5 years) MAPI under high-humid conditions could offer enhanced performance of NVBRS memory devices for medical, security, internet of things (IoT), and artificial intelligence (AI) applications.

Coexistence of Nonvolatile WORM, Bipolar, Unipolar, and Volatile Resistive Switching Characteristics in a Dry Oxide Layer With Ag Conductive Bridges

In this study, we demonstrate multimemory functions of anAg/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> /n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -Si device, including nonvolatile (NV) write-once-read-many-times (WORM), NV bipolar, NV unipolar, and volatile resistive switching (RS) characteristics. The SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> layer is grown using a dry oxidation process. Different RS features are obtained by modulating the compliance current during device operation. The resistance switch from the OFF to ON state, corresponding to a set process, is observed in the positive voltage region, which indicates that the Ag cations are responsible for the RS process. When the Ag/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> /n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -Si memory switches to the ON state, an Ag conductive bridge (CB) in the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> layer is indeed observed under transmission electron microscopy (TEM) examination. A CB-based model is used to explain the different RS behaviors of the Ag/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> /n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -Si resistive memory.

Enhancement of resistive switching behavior of organic resistive random access memory devices through UV-Ozone treatment

We fabricated organic resistive random-access memory (RRAM) devices using a low-cost solution-process method. All the processes were performed at temperatures below 135 °C under ambient atmospheric conditions. The RRAM resistive switching layer was formed from a polymer-fullerene bulk heterojunction using poly(3-hexylthiophene-2,5-diyl) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM). The fabricated organic RRAM device exhibited typical nonvolatile bipolar resistive switching behavior with an ON/OFF ratio of ∼40, but it provided a low endurance of 27 cycles. Therefore, for enhanced stability, simple UV–Ozone (UVO) treatment was applied to the P3HT:PCBM organic bulk heterojunction layer. The organic RRAM device with UVO treatment exhibited an enhanced performance with an ON/OFF ratio of ∼400 and an endurance of 47 cycles. In addition, complementary resistive switching behavior was observed. The conduction mechanisms of the organic RRAM device were investigated by fitting the measured I–V data to numerical equations, and Schottky emission and Ohmic conduction were the main conduction mechanisms for the high-resistance and low-resistance states for the RRAM device with or without UVO treatment.

Modulation of the electrical characteristics on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)-based resistive random access memory device by the impact of top electrode materials

In this study, we fabricated polymer resistive random access memory (RRAM) devices using the conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) as an active layer and investigated the influence of various top electrode materials such as Cu, Al, and Ag on the modulation of the electrical characteristics of the RRAM. The fabricated RRAM devices with different top electrodes provided non-volatile bipolar resistive switching depending on the polarity of the applied voltage and current compliance (CC). Among these, RRAM devices with Ag top electrodes provided the best memory performance with a RON/ROFF ratio of >102, > 140 cycles endurance, and a good retention time of ∼104 s. In addition, multi-level cell switching was achieved by controlling the CC, which is desirable for neuromorphic computing applications. The analysis of the current-voltage curves revealed that the Schottky emission was dominant in the high-resistance state. The proposed switching mechanism model was based on the formation and rupture of the conducting filaments by the electrochemical metallization effect.

Non-volatile and volatile switching behaviors determined by first reset in Ag/TaOx/TiN device for neuromorphic system

We fabricate the Ag/TaOx/TiN device and confirm the structure of the element with transmission electron microscopy (TEM) and energy dispersive spectroscopy line scan (EDS). The device shows non-volatile bipolar resistive switching as well as volatile threshold switching. In order to identify the threshold switching, the first reset voltage is needed to activate the device and check how much the current level decreases by the reset voltage. The current gradually increases and drops at a relatively high compliance current (CC) with positive and negative values, respectively. To demonstrate the temporal learning in the volatile switching with short-term memory effect, the states of [1111], [1001], and [1000] 4-bits are controlled by applying different pulse streams, which outputs the letter "P" in the reservoir computing system. At the lowest CC, the abrupt threshold switching is obtained, and the relaxation time in transient measurement is investigated depending on the voltage amplitude.

Nonvolatile resistive switching memory based on monosaccharide fructose film

In this paper, we report resistive random access memory (RRAM) based on a monosaccharide—fructose for nonvolatile memory in biocompatible and “green” electronics. Fructose thin film acts as the resistive switching layer with Al and Ag top electrodes for comparison. Both devices demonstrated highly reproducible nonvolatile bipolar resistive switching behaviors with a large on/off ratio of ∼106 for the Al electrode and ∼105 for the Ag electrode. The forming voltage, set voltage, and memory window are also larger for the Al electrode than the Ag electrode, but the reset voltages are comparable. Dominant conduction mechanisms of fructose films were proposed. At a high resistance state, both electrodes reveal space charge limited conduction, while at a low resistance state, the governing mechanism is Ohm's law, and in addition, the Ag electrode also shows trap-fill limited conduction when approaching the reset voltage. This observation has yet to be reported in RRAM based on natural bio-organic materials.

Electronic phase separation induced non-volatile bi-polar resistive switching in spatially confined manganite microbridges

Correlated manganite films exhibit functional transport properties due to the co-existence of the competing electronic phase domains which are energetically similar. Here, we investigate very large bi-polar resistive switching (RS) in spatially confined La0.3Pr0.4Ca0.3MnO3 films. In this system, non-volatile bi-polar RS (up to ∼2× 106%) takes place via electric field induced expansion/shrinkage of metallic phase domains, which are separated by an insulating phase domain. These effects are observed without the need of a pre-forming process. We suggest the modification of a memristor model for phase separated systems to explain the observed non-volatile bi-polar I–V characteristics. Investigations of the endurance of the RS over many switching cycles (more than 2.7 × 104 switching) show that it does not decay and full switching occurs with a high success rate. Furthermore, the ability to carry out switching between a number of distinct resistance levels is demonstrated.

Nonvolatile resistive switching characteristics based on Ni–Al LDHs and its electronic synapse application

Future artificial intelligence circuits will require expandable electronic synapses with extremely high bit density and computing speed. In this regard, the nanostructure of two-dimensional materials achieves the goal and provides device scalability in both horizontal and vertical dimensions. In this work, we report the nonvolatile bipolar resistive switching characteristics of Ni–Al layer double hydroxide (LDH)-adsorbed thiadiazole memristors. The Ni–Al LDH-adsorbed thiadiazole memristors implement a progressive reduction process and can be used to simulate the “learning” and “forgetting” functions of biological synapses. At the same positive and negative voltage pulse width, multiple resistance stages can be observed for continuous pulse number. In addition, the application of pulse train operation scheme is an effective method to control the simulated synaptic devices during the reset process, which helps understand the nature of the evolution of conductive nanofilaments.

Programmable electronic synapse and nonvolatile resistive switches using MoS2 quantum dots

Brain-inspired computation that mimics the coordinated functioning of neural networks through multitudes of synaptic connections is deemed to be the future of computation to overcome the classical von Neumann bottleneck. The future artificial intelligence circuits require scalable electronic synapse (e-synapses) with very high bit densities and operational speeds. In this respect, nanostructures of two-dimensional materials serve the purpose and offer the scalability of the devices in lateral and vertical dimensions. In this work, we report the nonvolatile bipolar resistive switching and neuromorphic behavior of molybdenum disulfide (MoS2) quantum dots (QD) synthesized using liquid-phase exfoliation method. The ReRAM devices exhibit good resistive switching with an On–Off ratio of 104, with excellent endurance and data retention at a smaller read voltage as compared to the existing MoS2 based memory devices. Besides, we have demonstrated the e-synapse based on MoS2 QD. Similar to our biological synapse, Paired Pulse Facilitation / Depression of short-term memory has been observed in these MoS2 QD based e-synapse devices. This work suggests that MoS2 QD has potential applications in ultra-high-density storage as well as artificial intelligence circuitry in a cost-effective way.

Water and air friendly alkali metals synthesis of the h-BN-C QDTs and the utilization in the non-volatile resistive switching memory devices

A novel and facile hydrothermal route was designed to produce h-BN-C quantum dots (h-BN-C QDTs) using h-BN powder as a precursor and Potassium Sodium Tartare as an intercalant. The resulting yellow solution possessed mono or few-layers of quantum dots with an average size of ~2.5 nm. Due to the incorporation of functional groups (carbon, oxygen) on the surface of h-BN, an enhancement of photo luminescent magnitude and a blue shift were observed in photoluminescence spectra from h-BN-C QDTs solution. Further, h-BN-C QDTs exhibits a bright blue fluorescence under the irradiation by a 365 nm UV light. Next, h-BN QDTs was utilized as the dielectric active layer by using simple drop casting method between the electrodes and fabricated the nonvolatile resistive switching devices. The fabricated devices exhibited the nonvolatile bipolar resistive switching characteristics with 103 ON/OFF ratio and turned ON and OFF threshold voltages of −1.9 V and +1.4 V, respectively. Further, the switching mechanisms of h-BN-C QDTs were found to be space charged trapping. It provides a route toward tailoring the optical and electrical properties of the h-BN materials and can be utilized in the future potential applications.

Reversible transition between bipolar resistive switching and threshold switching in 2D layered III–VI semiconductor GaSe

Recently, two-dimensional (2D) layered materials have emerged as promising candidates for resistive switching (RS) devices. However, challenges in controllable conversion of RS types in such 2D materials still remain. Here, we report the experimental realization of reversible transition between non-volatile bipolar resistive switching (BRS) and volatile threshold switching (TS) in 2D layered III–VI semiconductor gallium selenide (GaSe) nanosheets through appropriately setting the compliance current (Icc). Under a relatively high Icc value of 1 mA, the device shows non-volatile BRS performance with a high ON/OFF ratio of nearly 104, a long retention time of 12 000 s, and a high endurance of 1200 switching cycles. Furthermore, under a relatively low Icc (lower than 10 μA), the volatile TS behaviors can be observed. For the former, the large Icc can generate stable conductive filaments (CFs) of Ga vacancy. Thus, the breakage of the stable CFs needs a high reverse voltage to re-align the Ga vacancy. For the latter, the low Icc generated unstable CFs can be broken by the current induced Joule heat. This study establishes the feasibility of integrating different RS types in 2D layered semiconductor nanosheets and understanding the underlying physical mechanism of different RS types in the 2D platform.

Physically transient memristor based on the permeation of water at the interface of electrode and substrate

Transient memristor is highly desirable for secure memory system and secure neuromorphic computing. Here, a transient memristor with the MgO thin film as resistive dielectric material and the Ni as electrode material is reported. The memristor shows reversible and nonvolatile bipolar resistive switching performance, narrow distribution of low resistance state (LRS) and high resistance state (HRS), uniform switching voltages and stable retention at room temperature. It is indicated that the resistive switching mechanism of the memristor is conductive filament in LRS and space charge limiting current in HRS. In addition, the memristor can be failed after immersed in deionized water for 5 min due to the film damage resulting from large frizzle and the dissolution of Ni and MgO film. The prepared memristor has potential for secure memory system application.

Oxygen-assisted synthesis of hBN films for resistive random access memories

In this letter, we report an oxygen-assisted chemical vapor deposition method to synthesize uniform large-area high-quality multilayer hexagonal boron nitride (hBN) films (denoted by O-hBN). Nonvolatile bipolar resistive switching (RS) of resistive random access memories (RRAMs) based on O-hBN films is presented. These RRAMs exhibit enhanced RS performance with lower cycle-to-cycle variability, lower set voltage, and higher current on/off ratio. The enhancement is benefited from the clean and smooth surface of O-hBN films and the reduction of grain boundaries which serve as an energetically favored path for ion migration. This scalable approach to synthesize hBN films could facilitate practical applications of hBN-based RRAMs.