Yudi Zhao

Reconfigurable Nonvolatile Logic Operations in Resistance Switching Crossbar Array for Large-Scale Circuits

Resistance switching (RS) devices have potential to offer computing and memory function. A new computer unit is built of RS array, where processing and storing of information occur on same devices. Resistance states stored in devices located in arbitrary positions of RS array can be performed various nonvolatile logic operations. Logic functions can be reconfigured by altering trigger signals.

Oxide-based RRAM: Requirements and challenges of modeling and simulation

New physical insights on the underlying physics from switching behaviors to operating mechanisms of oxide-based RRAM are presented by taking the microstructure nature of switching materials and correlated physical effects with switching process into account. Based on the new physical insights, a platform for HfOx- and TaOx-based RRAM including simulation tools and compact models is developed, which is able to reproduce the essential electrical and microscopic characteristics of RRAM and bridge the link between device and circuit systems, meeting the requirements of device-circuit-system co-design and optimization.

Self-Selection RRAM Cell With Sub-

A high-K/metal gate (HKMG)-stack (TiN/Al-dopedHfOx/SiO2/Si)-based bipolar resistive random access memory (RRAM) cell is proposed and fabricated by 28/20-nm HKMG CMOS compatible technology. Robust reliability behaviors (retention at 200°C 4 × 104 s and endurance 105 cycles) and ultralow switching current (<;0.1 μA for RESET and <;0.3 μA for SET) are both demonstrated. The sub-μA switching current and self-selection nonlinear I-V characteristics are attributed to the SiO2 interfacial layer rather than the decrease of conductive filament size and oxygen vacancy (VO) density, which can be verified by HRTEM and measured conduction behavior. Therefore, robust reliability property is also achieved. The demonstrated excellent memory characteristics of HKMG stacked RRAM cell enable constituting 1-Mb workable crosspoint array even though the feature size scales down to 10 nm according to the HSPICE simulation.

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A comprehensive physical model on the resistive switching (RS) behaviors of bilayered TaO_x-based RS access memory [resistive random access memory (RRAM)] is presented. In the model, the effects of the generation and recombination (G-R) of oxygen vacancies (V_O), phase transition (P-T) between Ta₂O₅ and TaO₂, and the interaction (I-A) between Ta₂O₅ and TaO_x layers are involved to explain the RS behaviors based on ab initio calculations. An atomistic Monte Carlo simulation method based on the model is developed to investigate the dynamic physical processes and reproduce the experimental phenomena. The impacts of G-R and P-T as well as the I-A effects on the RS behaviors of a bilayered Ta₂O₅/TaO_x structure and the device performances are identified. This paper indicates that the G-R effect dominates the RS behaviors, and self-compliance is due to the I-A effect. Based on the simulations, the optimization guidance of a bilayered TaO_x-based RRAM is presented.

Switching Current and Robust Reliability Fabricated by High-

Resistive switching behaviors of oxide-based resistive random access memory (RRAM) and the applications for the data storage and computing systems have been widely studied. In this paper, the critical issues correlated with the applications of oxide-based RRAM are addressed. The physical mechanism and models of oxide-based RRAM are first introduced. Then the optimization design methodology of devices and operation schemes is discussed. Finally, a novel architecture for unifying memory/computing system is presented.

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In this paper, resistive random access memory (RRAM)-based crossbar arrays with the cell structure of Pt/[AlOy/HfOx]m/TiN were fabricated by using atomic layer deposition (ALD) technique. The RRAM devices in the arrays show excellent performances such as good uniformity and high reliability. Based on the fabricated RRAM array, a complete set of basic logic operations including NOR and XNOR were successfully demonstrated.

/Metal Gate CMOS Compatible Technology

A high-K/metal gate (HKMG) stack (TiN/Al-doped-HfO_X/SiO₂/Si) based bipolar RRAM cell is proposed and fabricated by 28/20nm HKMG CMOS compatible technology. Robust reliability behaviors (retention @200 °C >4×10⁴ s and endurance > 10⁵) and sub-μA switching current are both demonstrated. The sub-μA switching current and self-selection nonlinear I-V characteristics are attributed to the SiO₂ interfacial layer rather than the decrease of conductive filament (CF) size and oxygen vacancy (V_O) density, which can be verified by HRTEM and measured conduction behavior. Therefore, robust reliability property is also achieved. The demonstrated excellent memory characteristics of HKMG stacked RRAM cell can constitute workable 1 Mb crosspoint array when feature size scales down to 10 nm according to the HSPICE simulation.

Modeling and Optimization of Bilayered TaO x RRAM Based on Defect Evolution and Phase Transition Effects

Oxide-based resistive random access memory (RRAM) has been widely studied as the promising candidate for the applications of next generations of data storage and computing technologies. In this paper, we will discuss the physical mechanism and optimization design of oxide-based RRAM devices, the novel RRAM-based computing/memory unifying architectures and the applications for data storage and computing technologies.

Design and Application of Oxide-Based Resistive Switching Devices for Novel Computing Architectures

NbO2-based selector with threshold switching characteristics was studied as a probable candidate to address the sneak-path problem in the resistive-switching random access memory(RRAM) arrays. In this work, we simulate the forming and switching process of the selector with consideration of the thermally driven metal-insulator transition and crystallization effects. Based on the simulator, we analyze the influence and optimization of the working conditions and device dimensions on the device characteristics.

Demonstration of Logic Operations in High-Performance RRAM Crossbar Array Fabricated by Atomic Layer Deposition Technique

Combination with the RRAM analytic model with varation and the Monte Carlo simulator based on the microcosmic processes of oxygen vacancies and oxygen ions generation, transportation and recombination, a TMO RRAM reliability simulation platform is developed to simulate and evaluate the main reliability issues of RRAM including retention, endurance, operation disturb considering the intrinsic variation.