New Type Of Non-volatile Memory Research Articles

Analysis of conductive filament heat transfer in TiO2-based RRAM device

Abstract Resistive random access memory (RRAM) has developed into a new type of non-volatile memory that has attracted much attention for its high density and low power; TiO2 has been studied to make RRAM because of its high conductivity. Based on the COMSOL Multiphysics finite element method and domain decomposition method, an electrically-thermally coupled model of TiO2-based RRAM with oxygen vacancy (Vo) conduction mechanism is constructed, the formation and cutting process of RESET and SET conductive filament (CF) under different voltages is simulated. Moreover, the characteristics of the internal temperature distribution of the CF are explored. The results show that the RESET process is more sensitive to heat changes, the transverse direction thermal value of the CF is more obvious than the longitudinal direction, and the rate of change is faster. Additionally, the electric field induces the migration of the Vo in filament, which affects the enthalpy change of the device’s heat transfer and resistive properties. This is an important reference for a deeper understanding of the switching behavior of RRAM devices and the control mechanisms for thermal studies.

Improving resistive switching effect by embedding gold nanoparticles into ferroelectric thin films

The ferroelectric memristor, as a new type of nonvolatile memory, has a broad prospect in the fields of information storage, exchange, and neural computing. Nowadays, it is still a challenge to achieve ferroelectric memristor with high resistive switching effect. In this work, epitaxial Ca-doped Pb(Zr0.40Ti0.60)O3 films embedded various concentrations Au nanoparticles (NPs) (Abbreviated as Au-PCZT) were deposited on the Nb:SrTiO3 (NSTO) substrate to form Au-PCZT/NSTO heterostructures. On the one hand, adding appropriate Au NPs into the PCZT films can improve the leakage current. When Au NPs capture electrons, the current in the high resistance state will be decreased due to the coulomb blocking effect. On the other hand, the ferroelectric polarization still maintains at a good level. Eventually, the resistive switching (RS) on/off ratio can reach 106 by embedding 3 mol% Au NPs. Compared with the pure PCZT thin films, the resistance-variable switching ratio is improved by two orders of magnitude. In addition, multi-level data storage can be realized under different bias voltages. Our results provide a feasible way to achieve high-on/off-ratio ferroelectric memristors with multi-level data storage capabilities.

Enhanced memristor performance via coupling effect of oxygen vacancy and ferroelectric polarization

As a new type of nonvolatile memory, the resistive memristor has broad application prospects in information storage and neural computing based on its excellent resistive switching (RS) performance. At present, it is still a great challenge to improve both ferroelectric polarization and leakage current to achieve a high RS on/off ratio of ferroelectric memristors. Herein, epitaxial Pb(Zr0.40Ti0.60)O3 (PZT) thin films with low content Ca doping were deposited on the Nb:SrTiO3 substrate to prepare PCZT/NSTO heterostructures and their RS behaviors were studied. The research findings show that compared with pure PZT film, the ferroelectric polarization of 1-mol%-Ca-doped PZT film is slightly improved, while the leakage current is increased by three orders of magnitude. Therefore, the RS on/off ratio reaches 2.5 × 105, about three orders of magnitude higher than pure PZT films. The theoretical analysis reveals that the RS behavior of PCZT/NSTO heterostructures is controlled by the PCZT/NSTO interfacial barrier and the space charge-limited current mechanism. Our results demonstrate that the ferroelectricity and electricity of ferroelectric thin films can be improved simultaneously by doping low-content Ca ions to increase the RS performance, which provides a good reference for the development of high-performance ferroelectric memristor devices.

Bipolar Resistive Switching in Lanthanum Titanium Oxide and an Increased On/Off Ratio Using an Oxygen-Deficient ZnO Interlayer.

The present study pioneered an oxygen migration-driven metal to insulator transition Mott memory, a new type of nonvolatile memory using lanthanum titanium oxide (LTO). We first show the reset first bipolar property without an initial electroforming process in LTO. We used oxygen-deficient ZnO as an interlayer between LTO and a W electrode to clarify whether oxygen migration activates LTO as the Mott transition. ZnO oxygen deficiency provides oxygen ion migration paths as well as a reservoir, facilitating oxygen migration from LTO to the W electrode. Thus, including the ZnO interlayer improved oxygen migration between LTO and the W electrode, achieving a 10-fold increased on/off current ratio. The current research contributes to a better understanding of valence change Mott memory by exploring the LTO resistive switching mechanism and ZnO interlayer influences on the oxygen migration process.

Resistive properties of CuInS<sub>2</sub> quantum dots regulated by niobium-doped lead zirconate titanate ferroelectric films

As a new type of non-volatile memory, quantum dot resistive random access memory (RRAM) has attracted much attention for its easy preparation, fast responding time, high storage density, and smaller device size. CuInS<sub>2</sub> quantum dot (CuInS<sub>2</sub> QD) is a kind of excellent resistive functional material with abundant electron capture sites, high optical absorption coefficient, and high carrier mobility. In this work, CuInS<sub>2</sub> QDs/Nb:Pb (Zr<sub>0.52</sub>Ti<sub>0.48</sub>)O<sub>3</sub> (PNZT) films are prepared by spin-coating CuInS<sub>2</sub> QDs on PNZT films. The results show that the resistive properties of CuInS<sub>2</sub> QDs RRAMs can be effectively improved by introducing PNZT films and can be controlled by changing the polarization direction. The CuInS<sub>2</sub> QDs/PNZT film in the negative polarization state promotes the interfacial electrons to enter into the PNZT film, which will reduce the height of the interfacial barrier and the thickness of the interfacial depletion region. And it will reduce the resistance of the composite film at the low resistance state (LRS). Compared with the switching voltage and resistive switching ratio of the pure CuInS<sub>2</sub> QDs film (10<sup>3</sup>), the switching voltage of the device decreases to –4.1/3.4 V and the resistive switching ratio increases to 10<sup>6</sup>. Furthermore, it maintains good stability in the 10<sup>3</sup> cycle durability test. In contrast, the CuInS<sub>2</sub> QDs/PNZT film interface has a larger barrier height and depletion-layer thickness when the PNZT is in the positive polarization state, which increases the resistance of the composite film in the LRS state. As a result, the switching voltage of the device increases to –6.4/5.7 V with a resistive switching ratio of 10<sup>4</sup>. The resistive properties of the CuInS<sub>2</sub> QDs/PNZT film can be tuned by changing the polarization direction, as the polarization direction of the PNZT changes the interfacial energy band structure and affects the conduction mechanism. This work reveals the feasibility of using ferroelectric thin films to improve the resistive properties of quantum dots RRAMs and thus providing an approach to further developing RRAMs.

A monolithic artificial iconic memory based on highly stable perovskite-metal multilayers

Artificial iconic memories, also called photomemories, are new types of nonvolatile memory that can simultaneously detect and store light information in a monolithic device. Several approaches have been proposed to construct artificial iconic memories, such as three-terminal field effect transistors, which can achieve an effective control of the gate voltage and external light terminals. The drawbacks in constructing these memories involve complicated fabrication processes, and the resulting performance of, for example, perovskite transistor-type photomemories is limited by the low carrier mobilities and poor ambient stabilities, whereas architectures based on floating gate modulations entail strict interface engineering and poor device reliability. In this paper, we propose a novel monolithic artificial iconic memory with a multilayer architecture of indium tin oxide/perovskite/gold/perovskite/silver, which combines the memory and photodetector functionalities of perovskites in an integrated device. The bottom perovskite layer plays the role of a photodetector, modulating the voltage bias on the top perovskite layer that serves as a resistive switching memory. This multilayer perovskite device can store photo-sensing data in its resistive states, with a memory retention of 5 × 103 s and ambient stability longer than sixty days. As a prototype demonstration, a 7 × 7 artificial iconic memory array is constructed to detect and store data on light intensity distribution, enabling a nonvolatile imaging functionality. Our work provides a new platform for designing perovskite-based architectures with simultaneous light detection and data storage capabilities.

Nonvolatile Memory (NVM) Operation of Tunnel Field-Effect Transistor (TFET) Using Ferroelectric HfO₂ Sidewall.

In this paper, we propose a new type of nonvolatile memory (NVM) device based on a tunnel field-effect transistor (TFETs) with Ferroelectric HfO₂ sidewall. By simply utilizing the ferroelectricity of orthorhombic HfO₂ and conventional sidewall spacer technique, TFET can operate as a NVM device. The polarized charges in the ferroelectric HfO₂ spacer induced by program/erase pulse modulate the tunneling barrier between the source and channel; thus, change the threshold voltage (Vt) of TFET. The proposed NVM TFET has lower subthreshold swing (SS) and higher on/off ratio than conventional NVM TFETs while maintaining equivalent program/erase efficiency. Further-more, we also investigate the optimal HfO₂ sidewall formation conditions to achieve higher NVM performances.

Giant Electroresistance in Edge Metal-Insulator-Metal Tunnel Junctions Induced by Ferroelectric Fringe Fields

An enormous amount of research activities has been devoted to developing new types of non-volatile memory devices as the potential replacements of current flash memory devices. Theoretical device modeling was performed to demonstrate that a huge change of tunnel resistance in an Edge Metal-Insulator-Metal (EMIM) junction of metal crossbar structure can be induced by the modulation of electric fringe field, associated with the polarization reversal of an underlying ferroelectric layer. It is demonstrated that single three-terminal EMIM/Ferroelectric structure could form an active memory cell without any additional selection devices. This new structure can open up a way of fabricating all-thin-film-based, high-density, high-speed, and low-power non-volatile memory devices that are stackable to realize 3D memory architecture.

RRAM Defect Modeling and Failure Analysis Based on March Test and a Novel Squeeze-Search Scheme

The Resistive Random Access Memory (RRAM) is a new type of non-volatile memory based on the resistive memory device. Researchers are currently moving from resistive device development to memory circuit design and implementation, hoping to fabricate memory chips that can be deployed in the market in the near future. However, so far the low manufacturing yield is still a major issue. In this paper, we propose defect and fault models specific to RRAM, i.e., the Over-Forming (OF) defect and the Read-One-Disturb (R1D) fault. We then propose a March algorithm to cover these defects and faults in addition to the conventional RAM faults, which is called March C*. We also develop a novel squeeze-search scheme to identify the OF defect, which leads to the Stuck-At Fault (SAF). The proposed test algorithm is applied to a first-cut 4-Mb HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based RRAM test chip. Results show that OF defects and R1D faults do exist in the RRAM chip. We also identify specific failure patterns from the test results, which are shown to be induced by multiple short defects between bit-lines. By identifying the defects and faults, designers and process engineers can improve the RRAM yield in a more cost-effective way.

Electric Pulse Induced Resistive Switching in the Narrow Gap Mott Insulator GaMo&lt;sub&gt;4&lt;/sub&gt;S&lt;sub&gt;8&lt;/sub&gt;

We report here on resistive switching measurements on GaMo4S8 a lacunar spinel compound with tetrahedral Mo4 clusters filled with 11 electrons. Alike other clustered lacunar spinel compounds with 7 or 8 electrons per cluster, this narrow gap Mott Insulator exhibits both a volatile and a non-volatile unipolar resistive switching. We found that the volatile resistive switching appears above a threshold electric field in the 7 kV/cm range. For electric field much larger than this threshold, the resistive switching becomes non-volatile. Successive electric pulses allow switching back and forth between high and low resistance states. All these results demonstrate that the narrow gap Mott insulator compound GaMo4S8 could be a relevant candidate for a new type of non-volatile memory based on an electric field induced breakdown of the Mott insulating state.

Current-induced magnetic domain wall motion below intrinsic threshold triggered by Walker breakdown

Controlling the position of a magnetic domain wall with electric current may allow for new types of non-volatile memory and logic devices. To be practical, however, the threshold current density necessary for domain wall motion must be reduced below present values. Intrinsic pinning due to magnetic anisotropy, as recently observed in perpendicularly magnetized Co/Ni nanowires, has been shown to give rise to an intrinsic current threshold J(th)(0). Here, we show that domain wall motion can be induced at current densities 40% below J(th)(0) when an external magnetic field of the order of the domain wall pinning field is applied. We observe that the velocity of the domain wall motion is the vector sum of current- and field-induced velocities, and that the domain wall can be driven against the direction of a magnetic field as large as 2,000Oe, even at currents below J(th)(0). We show that this counterintuitive phenomenon is triggered by Walker breakdown, and that the additive velocities provide a unique way of simultaneously determining the spin polarization of current and the Gilbert damping constant.

Evidence of charging effect in silicon nano-crystals using a feedback chargemethod with metal oxide–semiconductor capacitors

In some new types of non-volatile memory, where silicon nano-crystals(nc-Si) are implemented as a floating gate at a tunnel distance from thechannel, the evidence of charging effect in these nc-Si is observed andstudied experimentally. We present quasi-static capacitance–voltage (C–V) and current–voltage(I–V)measurements of MOS capacitors containing nc-Si based on a feedback chargemethod. Doing so we can measure simultaneously and separate the capacitancefrom leakage and excess currents. Depending on the presence or not of nc-Si in acapacitor, we observe the presence of a maximum of four peaks in the current, ofwhich only one depends on the voltage scan rate. This behaviour is explained interms of nc-Si dynamic charge and discharge and offset charge influence as well.