Unipolar resistive switching with forming-free and self-rectifying effects in Cu/HfO2/n-Si devices

Resistance switching random access memory (ReRAM) is a highly appealing contender for a versatile replacement for the NAND flash or storage class memory, bridging the performance gap between dynamic random access memory (DRAM) and hard disk (or NAND flash) in computers. [1] The recent announcement of the production of a 3D cross-point (3D X-point) memory jointly developed by Intel and Micron appears to be a great step forward in this area, although the materials and process details are yet to be uncovered (ReRAM or phase change RAM). The eye-catching features of the 3D X-point memory are the adopted crossbar architecture that uses a two-terminal device instead of a transistor as the cell selector, and the double-layer-stacked structure, which results in an extremely small cell size (2F 2 , where F is the minimum feature size). The crossbar array (CBA) is a passive array architecture that was used in the first random access memory of the magnetic core memory ≈50 years ago. Ever since the development of the metal-insulator-semiconductor field effect transistor (MISFET), the cell selection function for a matrix-type memory has been assumed by MISFET, as in DRAM, thanks to its supreme performance as a switch. With the extreme scaling down of the memory cell to F < 10 nm, however, MISFET may not be an optimum solution as a cell selector because of its inherently larger cell size (8F 2 ) compared to the diode or threshold switch (4F 2 ), in addition to the performance degradation in accordance with the downscaling. The recent development of an ultrahighdensity (256 GB) NAND flash memory based on its vertical integrated structure and three-bit operation is an excellent demonstration of the strategy with which the integration density can be further increased without shrinking the memory cell size. [2] In this regard, the evolution of ReRAM into the third dimension (i.e., layer stacking or vertical integration of memory cells) is a natural consequence of the engineering efforts for achieving ultrahigh-density memory. Some of the authors have reported the details of the various aspects of integrating the ReRAM in 3D structures, and it was found that layer stacking and vertical integration have their respective pros and cons. [3,4] A double-layer-stacked 1 diode-1 resistor (1D1R) cross-bar array (CBA) resistance switching random access memory is fabricated. The TiO 2 -based Schottky diode and the unipolar resistance switching TiO 2 comprise the cell selector and nonvolatile memory components, respectively. All the fabrication processes are performed near room temperature through physical vapor deposition processes, and the performance degradation by the thermal budget is well suppressed. As a result, a rectification ratio as high as 1.4 × 10 9 is achieved from the appropriately cycled diode, which can last up to 10 8 cycles in the integrated structure. Such highly promising performance is confirmed from both the upper and lower memory layers, which confirm the possible route for the multistacked memory structure. The two-bi...

mentioning

confidence: 88%

Double‐Layer‐Stacked One Diode‐One Resistive Switching Memory Crossbar Array with an Extremely High Rectification Ratio of 10⁹

Yoon

Kim

Yoo

et al. 2017

“…[27] For the high field region where the ξ > 8 MV cm -1 (2 nm HfO 2 , V forming ≈1.6 V), the current conduction mechanism is dominated by the Fowler-Nordheim tunneling equation, i.e., 8 [27] For the high field region where the ξ > 8 MV cm -1 (2 nm HfO 2 , V forming ≈1.6 V), the current conduction mechanism is dominated by the Fowler-Nordheim tunneling equation, i.e., 8…”

Section: Wwwadvelectronicmatdementioning

confidence: 99%

Quantized Conduction Device with 6‐Bit Storage Based on Electrically Controllable Break Junctions

Banerjee

Hwang

2019

electron charge and h is the Planck constant. [6] Electronic switches with atomicsized functional building blocks are the main driving force of modern nanotechnology. The design of atomic dimensional memory devices is limited by the lithographic bottleneck. Nevertheless, the origin of atomic contact in nanoscale architectures is being investigated. [7] The conductive bridge RAM device with quantized conductance (QC) effect proposed by Terebe et al., [8] was based on the fabrication of a gap-type Pt/ nano-gap/Ag 2 S/Ag structure. A small operating voltage of ±600 mV can switch the device between the "OFF" and "ON" states. When a device changes its resistance from high to low, it is usually known as "set"; the reverse change is known as "reset". The QC effect is suitable to realize multiple levels in devices and has been studied in both electrochemical metallization type [9][10][11][12][13][14] and valance change memory type [15,16] gap-less RRAM. In most cases, switching is the after-effect of a stress dependent virginity breakdown, which can consolidate the CF for switching operations. Because the behavior of the CF of conductive bridge RAM is considered to be an example of atomic-switching, further discussion is mainly focused on conductive bridge RAM type devices. Higher initial stress injects more cations into the switching oxide layer that results in poor control over the reset process, resulting in abrupt state transition, and atomic conductance instability. [9][10][11][12][13][14] In another approach, single-atom memory has been proposed for mechanically controllable break junctions (MCBJs), [17] which are a kind of electronic device formed by two knife-edged metal wires placed with a nanometer sized gap, as shown in Figure 1a. MCBJs are well known as atomic or single molecular junction, and have even been investigated to in the context of control of quantum interferences in graphene. [18,19] In an MCBJ, when the two wires are curved, broadening the gap, the contact is broken, and the reverse order experiences an atomic-contact at the break junction. Break junctions are a possible approach to the fabrication of atomic switches. However, in reality, for an electronic device, such design is burdensome due to exorbitant lithographic processes. It is possible to prepare a break junction by electrically controlling the ion migration process in conductive bridge RAM devices, as the switching mechanism is driven by the formation of metallic wire like CF. Although the concept of QC in conductive bridge RAM has been investigated for over a decade, precise and reliable atomic-level control Atomic-level control of conductance in a Cu/Ti/HfO 2 /TiN-based electrically controllable break junction (ECBJ) is demonstrated. The ECBJ is designed through sophisticated stack engineering and refined electrical operation. Control over bias-induced ion migration is the key to forming the ECBJ. Precise atomic-level control is accomplished with an optimized high temperature forming (OHTF) scheme. OHTF-controlled single-atomic switch...

“…[24] It was also worth mentioning the abnormal phenomenon that the reset voltage was much large than that of set voltage, which was different from the existing unipolar performance. [39] The V set and V reset domain were further evaluated by the statistical distribution on individual ON and OFF state and fitted with Gaussian distribution (Figure 2c). The value of V set is 2.7 V ± 0.3 V and -2.7 V ± 0.3 V, corresponding to positive and negative branches, respectively, suggesting the equal reproducibility of both polarity bias.…”

Section: Introductionmentioning

confidence: 99%

Ultrathin Anion Conductors Based Memristor

Xiong

Tian

et al. 2021

realization of diffusive memristor hinges on the ion dynamics inside channel and electrode materials, depicting resistive switching characteristics, especially for metal migrations in electrochemical metallization memory (ECM). [17] The intrinsic structure and property of channel dielectrics would be changed by active electrode material due to inevitable doping in electroforming process. However, the vertical thickness of channel materials may also restrain the switching response and ions transport efficiency, considering the ions coupling effect and fabricating strategy. Feasible attempts are reported to explore synergistic nonmetal ion dynamic and channel thickness in monolayer and bilayer transition metal dichalcogenides (TMDCs) memristors by means of depleted grain boundary [18,19] and migration of vacancies, [20] which inspire exploration on intrinsic conduction mechanism for 2D materials in lower spatiotemporal region even sub-nanoscale. Layered double hydroxides (LDHs) can be presented by gen-•mH 2 O (M represents metal cations, and A represents anions) are unique specie of the 2D materials with positively charged layers and exchangeable anions in subatomic interlayer space, also exhibiting unique electronic features and memory effect. [21,22] Attributing to abundant hydroxyl groups covalently bonded within 2D brucite layer, LDHs are considered to be candidates for hydroxyl ion conductors with high conductivity, as the confinement of electrons in 2D ultrathin region facilitates their compelling electronic properties, leading to ideal state for manufacturing electronic devices. [23][24][25] The memory effect is revealed by the ability of reconstitution, which allows LDHs to recover from ex-LDH oxides, demonstrating the robust stability with respect to thermal change. [26,27] Thanks to its large specific surface area and rich element composition, 2D fabrication process could be achieved from lamellar LDHs to exfoliated nanosheets. [28,29] Moreover, arising from phase engineering, [30] doping engineering, [31] stress engineering confinement effects, [32] the ion transport efficiency, and memory behavior within the LDH plane are further improved, indicating its great potential for constructing relative nonvolatile devices.Herein, we report the MgAl LDH based memristor with abnormal resistive switching behavior for the first time based on the formation of conductive channels (CCs) in interlayer space. Pristine MgAl LDH were successfully synthesized and furthermore exfoliated into few layered flakes. To simply explore the