Conductive Bridge Random Access Memory Research Articles

Atomistic study of dynamics for metallic filament growth in conductive-bridge random access memory.

The growth dynamics for metallic filaments in conductive-bridge resistive-switching random access memory (CBRAM) are studied using the kinetic Monte Carlo (KMC) method. The physical process at the atomistic level is revealed in explaining the experimental observation that filament growth can originate at either the cathode or the anode. The statistical nature of the filament growth is best shown by the random topography of dendrite-like conductive paths obtained. Critical material properties, such as charged-particle mobility in the switching layer of a solid electrolyte or a dielectric, are mapped to KMC model parameters through activation energy, etc. The accuracy of the simulator is established by the good agreement between the simulated forming time and the measured data.

The role of the local chemical environment of Ag on the resistive switching mechanism of conductive bridging random access memories.

Conductive bridging random access memories (CBRAMs) are one of the most promising emerging technologies for the next generation of non-volatile memory. However, the lack of understanding of the switching mechanism at the nanoscale level prevents successful transfer to industry. In this paper, Ag/GeSx/W CBRAM devices are analyzed using depth selective X-ray Absorption Spectroscopy before and after switching. The study of the local environment around Ag atoms in such devices reveals that Ag is in two very distinct environments with short Ag-S bonds due to Ag dissolved in the GeSx matrix, and longer Ag-Ag bonds related to an Ag metallic phase. These experiments allow the conclusion that the switching process involves the formation of metallic Ag nano-filaments initiated at the Ag electrode. All these experimental features are well supported by ab initio molecular dynamics simulations showing that Ag favorably bonds to S atoms, and permit the proposal of a model at the microscopic level that can explain the instability of the conductive state in these Ag-GeSx CBRAM devices. Finally, the principle of the nondestructive method described here can be extended to other types of resistive memory concepts.

REALIZATION OF A CONDUCTIVE BRIDGING RF SWITCH INTEGRATED ONTO PRINTED CIRCUIT BOARD

This paper presents a new approach for the realization of RF switches based on the Conductive Bridging Random Access Memory technology (CBRAM). This promising approach allows the realization of RF switches in an extremely simple manner at low cost. For the first time, an RF switch based on a MIM structure is realized with an insulator layer obtained from a commonly used resin deposited by spin coating. The paper reports a RF switch based on CBRAM and demonstrates a device integration onto plastic circuit board (PCB). The realized switch is validated by experimental measurements for a frequency range up to 1.5 GHz with an activation voltage less than 1 V.

Improved thermal stability and retention properties of Cu–Te based CBRAM by Ge alloying

Ge alloyed Cu–Te thin films showing improved thermal stability and enhanced retention properties when implemented as a cation supply layer in conductive bridge random access memory cells.

Enhanced stability of the HfO2 electrolyte and reduced working voltage of a CB-RAM by an ionic liquid

Supplying a trace volume of ionic liquid, [bmim][Tf2N], which contains 5000 ppm of H2O, on the HfO2 film in the conducting-bridge random access memory composed of Cu/HfO2/Pt allows improved efficiency of the memory properties: reduction of operating voltage and prevention of destruction of the electrolyte.

Statistical characteristics of reset switching in Cu/HfO2/Pt resistive switching memory.

A major challenge of resistive switching memory (resistive random access memory (RRAM)) for future application is how to reduce the fluctuation of the resistive switching parameters. In this letter, with a statistical methodology, we have systematically analyzed the reset statistics of the conductive bridge random access memory (CBRAM) with a Cu/HfO2/Pt structure which displays bipolar switching property. The experimental observations show that the distributions of the reset voltage (Vreset) and reset current (Ireset) are greatly influenced by the initial on-state resistance (Ron) which is closely related to the size of the conductive filament (CF) before the reset process. The reset voltage increases and the current decreases with the on-state resistance, respectively, according to the scatter plots of the experimental data. Using resistance screening method, the statistical data of the reset voltage and current are decomposed into several ranges and the distributions of them in each range are analyzed by the Weibull model. Both the Weibull slopes of the reset voltage and current are demonstrated to be independent of the on-state resistance which indicates that no CF dissolution occurs before the reset point. The scale factor of the reset voltage increases with on-state resistance while that of the reset current decreases with it. These behaviors are fully in consistency with the thermal dissolution model, which gives an insight on the physical mechanism of the reset switching. Our work has provided an inspiration on effectively reducing the variation of the switching parameters of RRAM devices.

Set statistics in conductive bridge random access memory device with Cu/HfO2/Pt structure

The switching parameter variation of resistive switching memory is one of the most important challenges in its application. In this letter, we have studied the set statistics of conductive bridge random access memory with a Cu/HfO2/Pt structure. The experimental distributions of the set parameters in several off resistance ranges are shown to nicely fit a Weibull model. The Weibull slopes of the set voltage and current increase and decrease logarithmically with off resistance, respectively. This experimental behavior is perfectly captured by a Monte Carlo simulator based on the cell-based set voltage statistics model and the Quantum Point Contact electron transport model. Our work provides indications for the improvement of the switching uniformity.

Assessment of read disturb immunity in conducting bridge memory devices – A thermodynamic perspective

Conducting bridge random access memory (CBRAM) devices operate on the basis of repeated nucleation and rupture of the metallic filament during the SET and RESET transitions. One of the critical reliability metrics for any non-volatile memory (NVM) technology is read disturb immunity, which refers to the ability of the device to keep the filament stable and unperturbed during the reading phase. While read disturb has been analyzed in detail for OxRAM which works based on the principle of oxygen vacancy generation and oxygen ion drift/diffusion, the susceptibility of CBRAM to read disturb events has not been analyzed in-depth. We make use of electrical test data, first order thermal model and fundamental thermodynamics to assess the stability of the CBRAM filament in both the high resistance state (HRS) as well as low resistance state (LRS). Our analysis reveals that the HRS retention is very good, while LRS retention can be quite poor for the Nickel-based CBRAM stack.

Effects of Ti Buffer Layer on Retention and Electrical Characteristics of Cu-Based Conductive-Bridge Random Access Memory (CBRAM)

We propose an ultrathin Ti buffer layer in the Cu/Al2O3 interface to overcome the high temperature retention failure and switching non-uniformity of conductive-bridge random access memory (CBRAM) device. The sacrificial effect of Ti resulted significant improvement in retention by minimizing Cu oxidization. A novel mechanism for this improvement on the basis of the difference in the electrode potentials of the Cu and Ti layers was also proposed. The Ti atoms help in retaining the copper filament with higher electrode potential by donating electrons to it. Moreover, device with a Ti buffer layer exhibits better uniformity that can be explained by the controlled diffusion of Cu ions through the buffer layer.

Impact of Sb doping on power consumption and retention reliability of GeS2 based conductive bridge random access memory

In this paper we present the impact of Sb doping of the GeS2 electrolyte in W/GeS2/Ag based conductive bridge random access memory (CBRAM) on the memory performance. In particular, the CBRAM resistance window, RON and ROFF values versus programming current, power consumption and reliability are analyzed in depth.We demonstrated that the Sb concentration governs the optimal operating conditions. In particular, high Sb doping allows low programming current operation (suitable for low power applications), while low Sb content improves the ROFF/RON ratio (needed in particular for nonvolatile field-programmable gate array applications).Finally, we observed that the high temperature retention could be improved by increasing the Sb doping. This result was interpreted by means of ab initio calculations, indicating that Sb reduces the dissolution rate of the Ag-based conductive filament in the electrolyte.

Nonvolatile CBRAM-Crossbar-Based 3-D-Integrated Hybrid Memory for Data Retention

This paper explores the design of 3-D-integrated hybrid memory by conductive-bridge random-access-memory (CBRAM). Considering internal states, height, and radius of the conductive bridge of one CBRAM device, an accurate CBRAM device model is developed for CBRAM-crossbar-based nonvolatile memory design with efficient estimation of area, access time, and power. Based on this design platform, one 3-D-integrated hybrid memory is designed by stacking one tier of CBRAMcrossbar with tiers of static random access memory (SRAM) and dynamic random access memory (DRAM), where the tier of CBRAM-crossbar is deployed for data retention during power gating of SRAM/DRAM tiers. One corresponding block-level data retention is developed to only write back dirty data from SRAM/DRAM to CBRAM-crossbar. When compared with phase-change random-access-memory-based system-level data retention, our design achieves 11× faster data-migration speed and 10× less data-migration power. When compared with ferroelectric random-access-memory-based bit-level data retention, our design also achieves 17× smaller area and 56× smaller power under the same data-migration speed.

Conductive-bridging random-access memory cell fabricated with a top Ag electrode, a polyethylene oxide layer, and a bottom Pt electrode

We developed a conductive-bridging random-access memory cell with a sandwiched structure of an Ag top electrode, an electrolyte (polyethylene oxide: PEO), and a Pt bottom electrode on a 250-nm hole pattern. The cell demonstrated the bipolar switching behavior of resistive randomaccess memory. The nonvolatile characteristics of the cell strongly depended on the wt% (PEO thickness): i.e., maximum memory characteristics, such as a retention-time of > 1 × 105 s with a memory margin of 1 × 104 and program/erase cycles of > 103 with a memory margin of 1.3 × 104, which are very close to thereof a commercial memory cell, were observed at a specific wt% of PEO (0.4 wt%)

A new laterally conductive bridge random access memory by fully CMOS logic compatible process

This paper proposes a novel laterally conductive bridge random access memory (L-CBRAM) module using a fully CMOS logic compatible process. A contact buffer layer between the poly-Si and contact plug enables the lateral Ti-based atomic layer to provide on/off resistance ratio via bipolar operations. The proposed device reached more than 100 pulse cycles with an on/off ratio over 10 and very stable data retention under high temperature operations. These results make this Ti-based L-CBRAM cell a promising solution for advanced embedded multi-time programmable (MTP) memory applications.

Influence of carbon content on the copper-telluride phase formation and on the resistive switching behavior of carbon alloyed Cu-Te conductive bridge random access memory cells

In this paper, we investigate the influence of the carbon content on the Cu-Te phase formation and on the resistive switching behavior in carbon alloyed Cu0.6Te0.4 based conductive bridge random access memory (CBRAM) cells. Carbon alloying of copper-tellurium inhibits the crystallization, while attractive switching behavior is preserved when using the material as Cu-supply layer in CBRAM cells. The phase formation is first investigated in a combinatorial way. With increasing carbon content, an enlargement of the temperature window in which the material stays amorphous was observed. Moreover, if crystalline phases are formed, subsequent phase transformations are inhibited. The electrical switching behavior of memory cells with different carbon contents is then investigated by implementing them in 580 μm diameter dot TiN/Cu0.6Te0.4-C/Al2O3/Si memory cells. Reliable switching behavior is observed for carbon contents up to 40 at. %, with a resistive window of more than 2 orders of magnitude, whereas for 50 at. % carbon, a higher current in the off state and only a small resistive window are present after repeated cycling. This degradation can be ascribed to the higher thermal and lower drift contribution to the reset operation due to a lower Cu affinity towards the supply layer, leading cycle-after-cycle to an increasing amount of Cu in the switching layer, which contributes to the current. The thermal diffusion of Cu into Al2O3 under annealing also gives an indication of the Cu affinity of the source layer. Time of flight secondary ion mass spectroscopy was used to investigate this migration depth in Al2O3 before and after annealing, showing a higher Cu, Te, and C migration for high carbon contents.

Total Ionizing Dose Retention Capability of Conductive Bridging Random Access Memory

Resistance switching memory devices based on cation transport through an electrolyte and redox reactions at the electrodes have been implemented in a commercial memory technology known as conductive bridging random access memory (CBRAM). In this letter, the number of bit errors and variations in the supply current of CBRAM circuits exposed to ionizing radiation is investigated and compared with common memory technologies. The results indicate that even after exposure to high levels of ionizing radiation, CBRAM devices show no degradation in memory retention, which suggests that the technology has high reliability capability when compared with existing nonvolatile memory solutions.

Physical model of dynamic Joule heating effect for reset process in conductive-bridge random access memory

Dynamic Joule heating effect of reset process in conductive-bridge random access memory (CBRAM) was investigated theoretically. By introducing the geometry effect of conductive filament (CF), the temperature and electric field distributions in the transient state in both one-dimen-sional and three-dimensional cases were discussed in detail. We found that the CF's geometry plays an important role in the transient Joule heating process, and the transient thermal effect turns increasingly significant with increasing applied voltage in reset procedure. The proposed position where CF ruptures is between the location of temperature peak and narrow end of the CF rather than the point of temperature peak in the cone-shaped CF system. It is more interesting that the rupture of CF possibly occurs in transient process, before steady-state is established.

A Thermally Stable and High-Performance 90-nm ${\rm Al}_{2}{\rm O}_{3}\backslash{\rm Cu}$-Based 1T1R CBRAM Cell

In this paper, we optimize the stack of a 90-nm CMOS-friendly <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm W}\backslash{\rm Al}_{2}{\rm O}_{3}\backslash{\rm Cu}$</tex></formula> conductive-bridging random access memory cell integrated in the one-transistor/one-resistor configuration. We show that the excellent Cu buffering properties of a TiW layer inserted at the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Al}_{2}{\rm O}_{3}\backslash{\rm Cu}$</tex></formula> interface make it possible, on one hand, to ensure cell integrity after back-end-of-line processing at 400 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> and, on the other, to obtain excellent memory performances. After optimization of the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Al}_{2}{\rm O}_{3}$</tex></formula> layer thickness, the cell exhibits highly controlled set and reset operations, a large memory window, fast pulse programming (10 ns) at low voltage <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({&lt;}{\rm 3}~{\rm V})$</tex></formula> , and low-current (10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\rm A}$</tex></formula> ), and multilevel operation. Finally, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$10^{6}$</tex></formula> cycles of write endurance lifetime with up to a three-decade memory window is demonstrated, and state stability is assessed up to 125 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> .

Conductive Bridging Random Access Memory Cell Fabricated With Top Ag Electrode, Polyethylene Oxide Layer, and Bottom Pt Electrode

not Available.

Flexible Conductive-Bridging Random-Access Memory Cell Fabricated With Stacked Polymer Electrolyte and Conductive Polymer

not Available.

Investigation of Thomson Effect in Cu/TaOx/Pt Resistive Switching Memory

Conductive bridge random access memory (CBRAM) shows strong potential for replacing flash memory on the sub-20 nm technology nodes. The switching mechanism is primarily attributed to the electrochemical formation and rupture of conductive filaments. In Cu/TaOx/Pt devices, high electric current in the RESET process can cause significant local heating. Thomson heating effect has to be considered due to conical or cylindrical filament geometries giving cause for strong temperature gradients. The thermoelectric effect is evaluated for the Cu and oxygen vacancy nanofilaments in bipolar and unipolar switching modes. The Thomson coefficient for oxygen vacancy filament is extracted from the difference of SET voltages between two switching modes.