Unipolar Resistive Switching Memory Research Articles

Unipolar resistive switching in porous perovskite-like Bi3.15Nd0.85Ti3O12 thin films

In this study, the unipolar resistive switching (RS) effect is exhibited in porous perovskite-like Bi3.15Nd0.85Ti3O12 (BNT) thin films fabricated on Pt/Ti/SiO2/Si substrates through chemical solution deposition technique employed PEG template. The unipolar RS characteristics can be adjusted by the size and density of the pores in the porous perovskite-like Bi3.15Nd0.85Ti3O12 thin films. The size and density of the pores are controlled by the processing parameters of the annealing temperature or the dwell time or the both during the preparation of the porous perovskite-like Bi3.15Nd0.85Ti3O12 thin films. The porous BNT thin films annealed at 720 °C for 10 min show large current ratio of low/high resistance state of four orders and low operating voltage of 5 V for SET and 1.5 V for RESET. Moreover, the LRS/HRS can be reversed repeatedly without large decay. After the retention test of 104 s for low/high resistance state, the devices still show as large current ratio of low/high resistance state as about four orders. The present study should have guide to develop a unipolar RS memory using the perovskite oxides.

Thermal assisted reset modelling in nickel oxide based unipolar resistive switching memory

This paper utilizes an analytical and a filament dissolution model to calculate the local temperature increase in conducting filaments (CFs) of pulsed laser ablated unipolar NiO resistive switching memory devices. Electrical current voltage characteristics indicate unipolar switching. The formation of NiO phases is confirmed from the X-ray diffraction study. Transmission electron microscopy confirms the polycrystalline nature of NiO films having a thickness of ∼20 nm. Electrothermal simulations based on the filament dissolution model are performed using COMSOL Multiphysics® to model the CF rupture during the reset transition in the samples owing to the Joule heating effect. Obtained temperature profiles from the simulations are compared with the analytical model. Both the models corroborate with each other, allowing us to closely approximate the maximum temperature across the CF (Tcrit). This is the point corresponding to which the voltage applied across the cell (Vreset) drives the device into the reset state. The effect of annealing temperature on the maximum temperature, reset voltage, and CF diameter of the device is also discussed. The CF diameter and area of the filament are precisely estimated from the simulation.

Flexible Nonvolatile Polymer Memory Array on Plastic Substrate via Initiated Chemical Vapor Deposition.

Resistive random access memory based on polymer thin films has been developed as a promising flexible nonvolatile memory for flexible electronic systems. Memory plays an important role in all modern electronic systems for data storage, processing, and communication; thus, the development of flexible memory is essential for the realization of flexible electronics. However, the existing solution-processed, polymer-based RRAMs have exhibited serious drawbacks in terms of the uniformity, electrical stability, and long-term stability of the polymer thin films. Here, we present poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3)-based RRAM arrays fabricated via the solvent-free technique called initiated chemical vapor deposition (iCVD) process for flexible memory application. Because of the outstanding chemical stability of pV3D3 films, the pV3D3-RRAM arrays can be fabricated by a conventional photolithography process. The pV3D3-RRAM on flexible substrates showed unipolar resistive switching memory with an on/off ratio of over 10(7), stable retention time for 10(5) s, excellent cycling endurance over 10(5) cycles, and robust immunity to mechanical stress. In addition, pV3D3-RRAMs showed good uniformity in terms of device-to-device distribution. The pV3D3-RRAM will pave the way for development of next-generation flexible nonvolatile memory devices.

Fully Si compatible SiN resistive switching memory with large self-rectification ratio

In this letter, we report unique unipolar resistive switching memory behaviors in the Ni/Si3N4/p-Si structure by controlling the impurity concentration of Si bottom electrode. It is found that we can decrease the reset current drastically by reducing dopant concentration by reducing dopant concentration, which helps low-power operation in the high density resistive switching memory array. Also, the samples with high impurity concentration exhibited ohmic conduction in the low-resistance state (LRS) while those with low dopant concentration below 1018 cm−3 showed a remarkable self-rectifying behavior. The nonlinear metal-insulator-semiconductor (MIS) diode characteristics in the samples with low doping concentration (∼1018 cm−3) are explained by the formation of Schottky barrier at the metal and semiconductor interface. As a result, we demonstrate high rectification ratio (>105) between forward and reverse currents along with the robust nonvolatile properties including endurance cycles and retention from the devices with large self-rectification ratio. The high self-rectifying characteristics of Si3N4-based RRAM cell would be one of the most virtuous merits in the high-density crossbar array.

Intrinsic SiOx-based unipolar resistive switching memory. II. Thermal effects on charge transport and characterization of multilevel programing

Multilevel programing and charge transport characteristics of intrinsic SiOx-based resistive switching memory are investigated using TaN/SiOx/n++Si (MIS) and TiW/SiOx/TiW (MIM) device structures. Current transport characteristics of high- and low-resistance states (HRS and LRS) are studied in both device structures during multilevel operation. Analysis of device thermal response demonstrates that the effective electron energy barrier is strongly dependent on the resistance of the programed state, with estimates of 0.1 eV in the LRS and 0.6 eV in the HRS. Linear data fitting and conductance analyses indicate Poole-Frenkel emission or hopping conductance in the low-voltage region, whereas Fowler-Nordheim (F-N) or trap-assisted tunneling (TAT) is indicated at moderate voltage. Characterizations using hopping transport lead to hopping distance estimates of ∼1 nm in the LRS for both device structures. Relative permittivity values (εr) were extracted using the Poole-Frenkel formulism and estimates of local filament temperature, where εr values were ∼80 in the LRS and ∼4 in the HRS, suggesting a strongly polarized medium in the LRS. The onset of F-N tunneling or TAT corresponds to an observed “overshoot” in the I-V response with an estimated threshold of 1.6 ± 0.2 V, in good agreement with reported electro-luminescence results for LRS devices. Resistive switching is discussed in terms of electrochemical reactions between common SiO2 defects, and specific defect energy levels are assigned to the dominant transitions in the I-V response. The overshoot response in the LRS is consistent with TAT through either the Eγ' oxygen vacancy or the hydrogen bridge defect, both of which are reported to have an effective bandgap of 1.7 eV. The SET threshold at ∼2.5 V is modeled as hydrogen release from the (Si-H)2 defect to generate the hydrogen bridge, and the RESET transition is modeled as an electrochemical reaction that re-forms (SiH)2. The results provide further insights into charge transport and help identify potential switching mechanisms in SiOx-based unipolar resistive switching memory.

Intrinsic SiOx-based unipolar resistive switching memory. I. Oxide stoichiometry effects on reversible switching and program window optimization

The physical mechanisms of unipolar resistive switching (RS) in SiOx-based resistive memory are investigated using TaN/SiOx/n++Si and TiW/SiOx/TiW device structures. RS is independent of SiOx thickness and device area, confirming that RS occurs in a localized region along a filamentary pathway. Results from experiments varying electrode type, series resistance, and the oxygen content of SiOxNy materials show the potential to optimize switching performance and control device programming window. Device materials with stoichiometry near that of SiO2 are found to have better operating stability as compared to extrinsic, N-doped SiOxNy materials. The results provide further insight into the physical mechanisms of unipolar operation and lead to a localized switching model based on electrochemical transitions involving common SiOx defects. High-temperature data retention measurements for over 104 s in high- and low-resistance states demonstrate the potential for use of intrinsic SiOx RS devices in future nonvolatile memory applications.

The enhancement of unipolar resistive switching behavior via an amorphous TiOx layer formation in Dy2O3-based forming-free RRAM

We present effects of an amorphous TiOx layer formation on the behavior of a unipolar resistive switching memory device, which consists of Pt/Ti embedding layer (Ti-EL)/Dy2O3/Pt structure. The better properties have been obtained from the Pt/Ti-EL/Dy2O3/Pt system, including lower switching voltage, higher switching uniformity, and better endurance, besides, a reversed set/reset process is observed, in comparison with Pt/Dy2O3/Pt device. It is considered that the spontaneous formation of an amorphous TiOx layer and Ti–Pt–O nano-crystal clusters from Ti layer between Pt top electrode and Dy2O3 film is the main factor for the improvement of unipolar resistive switching behavior.

Unipolar Resistive Switching Memory Characteristics Using IrOx/Al2O3/SiO2/p-Si MIS Structure

Unipolar resistive switching memory characteristics using high-κ Al2O3 film in an IrOx/Al2O3/SiO2/p-Si metal-insulator-semiconductor (MIS) structure have been investigated. The devices show hysteresis memory window of ~0.9 V with a sweeping gate voltage of +/- 6 V, which proves charge trapping phenomena of the Al2O3 film. A sufficiently large resistance ratio of ~1e3 at a self limited current compliance of 100 uA is obtained, due to the defective Al2O3 film. A large resistance ratio of >1e3 after 10 years of data retention is obtained for future nanoscale nonvolatile memory application.

Direct observation of resistive switching memories behavior from nc-Si embedded in SiO2 at room temperature

Unipolar resistive switching memory behavior is directly observed in nanocrystalline Si (nc-Si) film under atmosphere. It is found that the switching is independent of the electrode materials. No resistive switching behavior can be found in reference device without nc-Si. The nc-Si align in a pathway is observed in the HRTEM of the device after voltage was applied. Meanwhile, the same switching behavior as measured under atmosphere is also observed in vacuum. Based on the analysis of the nc-Si film structure and I–V characteristic, we further discuss the mechanism of the switching behavior.

Unipolar resistive switching in Au/Cr/Mg0.84Zn0.16O2−δ /p+-Si

Unipolar resistive switching memory cells were fabricated using a Mg0.84Zn0.16O2−δ thin film, sandwiched between p+-Si (100) substrate and Cr/Au top electrodes. Electrical measurements showed a large memory window and memory window margin of 107 and 104, respectively. Furthermore, a wide switching voltage distribution gap of 3.6 V between the switching-ON and -OFF processes was obtained for different sweeping cycles. Gas bubbles at four different stages were observed on the top electrodes after electrical stimulus, indicating that conducting filaments consisting of oxygen vacancies are responsible for the resistive switching characteristics. Conductive atomic force microscopy results show that the highly conductive areas are along the edge of the gas bubble or the edge of the device. This phenomenon suggests the potential of scaling down the device area to lower than 32 nm.

Low-voltage driving solution-processed nickel oxide based unipolar resistive switching memory with Ni nanoparticles

Resistive random access memory (RRAM) combines the advantages of nonvolatile flash memory and volatile dynamic random access memory, avoiding their drawbacks. For the practical use of RRAM, achieving low-voltage driving is strongly desired. Here we report the effect of Ni nanoparticles on solution-processed NiO based RRAM which can realize a one diode one resistor operation by unipolar resistive switching mode and low-voltage driving for future demands. The Ni nanoparticles not only contributed to high oxygen mobility, but also affected effective insulator thickness reduction, and stoichiometric variation in NiO thin films. Furthermore, the Ni nanoparticle embedded device demonstrated good reliability. These findings can enhance the applicability of RRAM as a next generation memory device.

Evolution of RESET current and filament morphology in low-power HfO2 unipolar resistive switching memory

Reduction in RESET current is crucial for future high-density resistive-switching memory. We have reported a unipolar-switching Ni/HfO2/Si structure with low RESET current of 50 μA and RESET power of 30 μW. In addition, a unique cycling evolution of RESET current across more than two orders of magnitude allows us to probe into the evolvement of filament morphology at nanoscale, using a simple yet quantitative model. Filament morphology was found to depend strongly on the charge-dissipation current proportional to the powers of SET voltage. Moreover, the formation of inactive semiconductive filaments plays an important role in the reduction in RESET current.

Reset–Set Instability in Unipolar Resistive-Switching Memory

Unipolar resistive-switching memory attracts a strong interest as high-density nonvolatile memory for future technology nodes. The high-to-low-resistance change is achieved by the set operation, whereas the reverse transition is obtained by the reset process. Due to the similarities in the set and reset pulses, instabilities may arise, e.g., set may occur after reset within a reset pulse. This reset-set instability (RSI) can result in long program-verify loops to achieve a desired cell state. This letter discusses RSI, showing that the crossover of set and reset times as a function of voltage allows for stable set/reset processes at relatively high and low voltages, respectively.

Self-Accelerated Thermal Dissolution Model for Reset Programming in Unipolar Resistive-Switching Memory (RRAM) Devices

This paper addresses the numerical modeling of reset programming in NiO-based resistive-switching memory. In our model, we simulate electrical conduction and heating in the conductive filament (CF), which controls the resistance of the low resistive (or set) state, accounting for CF thermal-activated dissolution. Employing CF electrical and thermal parameters, which were previously characterized on our NiO-based samples, our calculations are shown to match experimental reset and retention characteristics. Simulations show that reset transition is self-accelerated as a consequence of a positive feedback between the thermal dissolution of the CF and local Joule heating in the CF bottleneck, which can account for the abrupt resistance transition in experimental data. Finally, the model is used to investigate the reduction of the reset current, which is needed for device application.