Multi-scale electrothermal simulation and modelling of resistive random access memory devices

In this study, 10-nm rare-earth metal-oxide (REMO) films, namely, pure HoScO x (HSO) and HoScO x doped with Nb (HSO-Nb) and Zn (HSO-Zn), were deposited to build resistive random access memory (RRAM) devices with a Pt/REMO/Pt structure using radio frequency magnetron sputtering. The results of x-ray diffraction and transmission electron microscopy showed that all as-deposited REMO films are featureless microstructures lacking long-range order. In all RRAM devices, layer structures were well adhered to each other with relatively smooth interfaces and no cracks or holes were observed. Hall measurements demonstrated n-type conduction in the as-deposited films. The addition of Nb and Zn increased carrier concentration and mobility of the HSO films and reduced electrical resistivity. The former was possibly caused by the electronic compensation of NbSc ··, thereby triggering the formation of polarons, and the latter was probably due to the increase in concentration of oxygen vacancies associated with acceptor doping. The RRAM devices revealed unipolar switching behavior characterized by a resistance ratio of more than three orders of magnitude, good endurance, and a long retention time. The switching behavior of the RRAM with amorphous HSO films was altered by the doping species. Doping with Nb and Zn decreased the forming voltage, facilitated the use of a smaller switching voltage, and increased the resistance ratio of high- and low-resistance states. The conduction mechanisms for the low resistive state and high resistive state were dominated by Ohmic conduction and trap-controlled space-charge-limited current mechanisms, respectively.

The transition from idealized memristor models to physical implementations, such as resistive random access memory (RRAM) devices, is pivotal for advancing neuromorphic circuits in hardware. However, real‐world RRAM devices face challenges due to inherent variability and fabrication tolerances, which hinder their adoption. This study presents the variability intensity model (VIM), a statistical framework designed to assess variability in RRAM devices. The VIM is employed to evaluate the resilience of a memristor‐based Hindmarsh–Rose circuit, which models neuronal behavior in biological systems. The results indicate that the circuit exhibits heightened sensitivity to variability in high‐conductance states, while demonstrating increased tolerance in low‐conductance states. This observation is consistent with RRAM characteristics, where conductance variability decreases as conductance increases. Furthermore, robust spiking dynamics are observed, though the bursting behavior remains sensitive, leading to critical parameter constraints for RRAM devices. By employing a variability model based on real‐world measurements, this work establishes a crucial foundation for the implementation of memristor‐based Hindmarsh–Rose circuits in hardware, where variability is a paramount consideration.

The morphological evolution of the conducting filament (CF) predominantly controls the electric response of the resistive random access memory (ReRAM) devices. However, the parameters—in terms of the material and the processing—which control the growth of such CF are plenty. Extending the phase field technique for ReRAM systems presented by Roy and Cha [J. Appl. Phys. 128, 205102 (2020)], we could successfully model the complete SET (to attain low resistance state) and RESET (to attain high resistance state) processes due to the application of sweeping voltage. The key parameters that influence the stability of the multi-cycle I-V response or the endurance behavior are identified. The computational findings of the presented model ReRAM system are practical in correlating the multi-parametric influence with the stability, variability, and reliability of the endurance cycle that affect the device performance and also lead to the device failure. We believe that our computational approach of connecting the morphological changes of the CF with the electrical response has the potential to further understand and optimize the performance of the ReRAM devices.

This article focuses on the relevance of the effect of ambient temperature and annealing in the context of compact modeling of metal oxide resistive random access memory (RRAM) devices. The ambient temperature affects the conduction characteristic of resistive switching memories, so it becomes an essential factor to include when adjusting the experimental data. Reported the fabricated results and memory switching parameters with the defined set (Vset) and reset (Vreset) transition voltages for the fabricated annealed HfO2-based RRAM. Additionally, to illustrate the importance of this characteristic in the form of the I-V curve, the Stanford model (SFM) for RRAM devices is enhanced by incorporating the annealing temperature as an additional parameter in the script of the Verilog-A model. Stanford and modified Stanford model (MSFM) are analyzed at the device level using cadence circuit simulator and implemented in the nonvolatile memory circuit (3 *3 memory arrays). Results confirmed that the experimental switching voltages, Vset, Vreset are 1.7 V, −0.8 V. These values are well suited along the simulated MSFM switching voltages of, Vset, Vreset (1.8 V, −0.7 V). The mean error percentage of the MSF is 18.42%.

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

This chapter introduces resistive random-access memory (RRAM), a futuristic memory technology that excels its counterparts in terms of reliability, nano-scale dimensions, energy per bit, and fast read/write times. Also, it is promising for use in neuromorphic computing and digital applications. However, the major challenge encountered during the progress of the technology is the presence of leakage current (sneak path current) while using it in crossbar arrays. Various techniques are employed to mitigate the sneak current problem. However, associating a selector with RRAM is an efficient method. To study the one selector-one RRAM (1S-1R) characteristics, the electrical model of the selector, as well as RRAM, is necessary; therefore, this chapter discusses the electrical modeling of selector device (1S), RRAM devices (1R), integration of selector models with the RRAM model (1S-1R), and formation of 1S-1R crossbar arrays. The selector device used to model this is Pt/Ta2O5/TaOx /TiO2/Pt, and the RRAM model adopted is Pt/Ta2O5/TaOx/Pt. Further, various parameters are analyzed, such as R off /R on ratio, nonlinearity, and off-current are improved in the 1S-1R cell compared to RRAM characteristics. Besides, it is perceived that 98% of the sneak path current is mitigated in the 1S-1R crossbar array compared to the 1R crossbar array.

Resistive Random Access Memory (ReRAM) devices have gathered significant attention recently for high-density non-volatile data storage applications. However, there are several challenges that need to be addressed to take complete benefit of this enabling technology. This paper discusses the role of intentional doping in transition metal oxide dielectrics, particularly HfO2, and its implications on the device performance. Our studies indicate that Mg doped HfO2 based ReRAM devices require lower electroforming voltage compared to undoped HfO2 based ReRAM devices. The reduction in set/reset voltages was also achieved in ReRAM devices with Mg doped HfO2. Excellent bipolar switching and endurance characteristics were achieved demonstrating doping in HfO2 as a viable route for achieving the desired ReRAM characteristics.

Resistance switching characteristics, observed in metal oxide thin films, has recently attracted a great deal of attention to develop next generation low power, low cost, high speed, rugged and nonvolatile resistive random access memory (RRAM) devices. The memory effect in these materials is realized through the switching of the resistance of their thin films between two states of high and low resistances. Amongst the known metal oxides currently being explored for the development of RRAM, ZnO has been demonstrated to be a potential candidate. ZnO is an n‐type wide bandgap semiconductor and is highly transparent in the visible spectral region. Moreover its conductivity can be tailored in a broad range from metal like to insulator like by suitable impurity doping. Therefore it is possible to develop a fully transparent RRAM entirely based on ZnO. In this paper we report growth of a novel transparent RRAM devices based on ZnO and its variants. We studied the resistive switching characteristics of these devices and associated conduction mechanisms responsible for the switching. The details of this study will be presented in the paper (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In this study, multilevel switching at low-power in Ti/TiN/Ga2O3/Ti/Pt resistive random-access memory (RRAM) devices has been systematically studied. The fabricated RRAM device exhibits an excellent non-overlapping window between set and reset voltages of ∼1.1 V with a maximum R off/R on ratio of ∼103. Moreover, to the best of our knowledge, the multi-bit storage capability of these RRAM devices with a reasonably high R off/R on ratio is experimentally demonstrated, for the first time, for lower compliance currents at 10 μA, 20 μA and 50 μA. The multi-bit resistive switching behavior of the Ga2O3 RRAM device at a low compliance current paves the way for low-power and high-density data storage applications.

Resistance random access memory (RRAM) based on resistive switching in metal oxides has attracted considerable attention as a promising candidate for next-generation nonvolatile memory due to its high operating speed, superior scalability, and low power consumption. However, some operating parameters of RRAM cannot meet the practical requirement, which impedes its commercialization. A lot of experimental results show that doping is an effective method of improving the performance of RRAM, while the study on the physical mechanism of doping is rare. It is generally believed that the formation and rupture of conducting filaments, caused by the migration of oxygen vacancies under electric field play a major role in resistive switching of metal oxide materials. In this work, the first principle calculation based on density functional theory is performed to study the effects of transition metal element X (X=Mn, Fe, Co, and Ni) doping on the migration barriers and formation energy of oxygen vacancy in ZnO. The calculation results show that the migration barriers of both the monovalent and divalent oxygen vacancy are reduced significantly by Ni doping. This result indicates that the movement of oxygen vacancies in Ni doped ZnO is easier than in undoped ZnO RRAM device, thus Ni doping is beneficial to the formation and rupture of oxygen vacancy conducting filaments. Furthermore, the calculation results show that the formation energy of the oxygen vacancy in ZnO system can be reduced by X doping, especially by Ni doping. The formation energy of the oxygen vacancy decreases from 0.854 for undoped ZnO to 0.307 eV for Ni doped ZnO. Based on the above calculated results, Ni doped and undoped ZnO RRAM device are prepared by using pulsed laser deposition method under an oxygen pressure of 2 Pa. The Ni doped ZnO RRAM device shows the optimized forming process, low operating voltage (0.24 V and 0.34 V for Set and Reset voltage), and long retention time (>104 s). Set and Reset voltage in Ni doped ZnO device decrease by 80% and 38% respectively compared with those in undoped ZnO device. It is known that the density of oxygen vacancies in the device is dependent on the oxygen pressure during preparation. The Ni doped ZnO RRAM device under a higher oxygen pressure (5 Pa) is also prepared. The Ni doped ZnO RRAM device prepared under 5 Pa oxygen pressure shows a little higher Set and Reset voltage than the device prepared under 2 Pa oxygen pressure, while the operating voltages are still lower than those of undoped ZnO RRAM. Thus, the doping effect in the ZnO system is affected by the density of oxygen vacancies in the device. Our work provides a guidance for optimizing the performance of the metal oxide based RRAM device through element doping.

Resistive random access memory (ReRAM) is a novel form of non-volatile memory expected to replace FLASH memory in the near future. As a further step toward use of ReRAM in computer architectures, we have developed a CMOS/ReRAM hybrid process, integrating ReRAM into a CMOS process flow. In this study, we investigate yield, reliability, endurance, threshold voltages (forming, set and reset voltages) of ReRAM devices implemented in the back end of the line (BEOL). The focus of this study is on single ReRAM devices operated with an external transistor (1T1R configuration). Yield and endurance of these 1T1R configured devices show a strong dependence on device position on the wafer, the device size, and the current compliance used during the initial forming and subsequent set sweeps. Elevated temperatures resulted in a shift of the optimum operation conditions and could be used to improve device performance. Variance in performance of the ReRAM devices was directly correlated with manufacturing issues and material properties to gain maximum information for future improvements

Resistive random access memory (ReRAM) devices are considered to be one of the most promising candidates for the next generation of nonvolatile memory devices because of their superior properties such as low power consumption, simple structure, high integration density, and fast operation speed. In this study, we used zinc oxide (ZnO) thin films to fabricate ReRAM devices comprising Au/ZnO/Al and Al/Au/ZnO/Al structures. We observed that the operating stability of the device containing the Al/Au/ZnO/Al structure improved. The devices displayed effective and stable operational characteristics. The operational voltage of the ZnO ReRAM devices was less than 3 V, and the reset operational voltage was less than −1.5 V.

The power consumption (PC), window margin (WM), thermal stability (TS), and reliability [i.e., endurance (EN) and retention-time (RT)] of aluminum nitride (AlN) resistive random access memory (RRAM) devices with different film orientations [i.e., amorphous, (100)- and (002)-oriented] are investigated. It is shown that the charge carrier transport mechanism of the three devices is dominated by Ohmic behavior under low electric fields and the trap-controlled space charge limited current (TC-SCLC) model under high electric fields. Among the three devices, the (002)-oriented AlN sample provides the best overall PC, WM, TS, EN, and RT performance due to its ${c}$ -axis orientation, which is favorable for the formation and rupture of the vertically arranged conductive filaments (CFs) in the AlN film.

Reducing the process variation is a significant concern for resistive random access memory (RRAM). Due to its ultra-high integration density, RRAM arrays are prone to lithographic variation during the lithography process, introducing electrical variation among different RRAM devices. In this work, an optical physical verification methodology for the RRAM array is developed, and the effects of different layout parameters on important electrical characteristics are systematically investigated. The results indicate that the RRAM devices can be categorized into three clusters according to their locations and lithography environments. The read resistance is more sensitive to the locations in the array (~30%) than SET/RESET voltage (<10%). The increase in the RRAM device length and the application of the optical proximity correction technique can help to reduce the variation to less than 10%, whereas it reduces RRAM read resistance by 4×, resulting in a higher power and area consumption. As such, we provide design guidelines to minimize the electrical variation of RRAM arrays due to the lithography process.

The resistive random access memory (RRAM) device has been widely studied due to its excellent memory characteristics and great application potential in different fields. In this paper, resistive switching materials, switching mechanism, and memory characteristics of RRAM are discussed. Recent research progress of RRAM in high-density storage and nonvolatile logic application are addressed. Technological trends are also discussed.