[paper] JART VCM v1 Verilog-A Compact

JART VCM v1 Verilog-A Compact

Model User Guide

Christopher Bengel, David Kaihua Zhang, Rainer Waser, Stephan Menzel

Electronic Materials Research Laboratory; RWTH Aachen University
Forschungszentrum Jülich

Abstract: The JART VCM v1a model was developed to simulate the switching characteristics of ReRAM devices based on the valence change mechanism. In this model, the ionic defect concentration (oxygen vacancies) in the disc region close to the active electrode (AE) defines the resistance state. The concentration changes due to the drift of the ionic defects. Furthermore, these oxygen vacancies act as mobile donors and modulate the Schottky barrier at the AE/oxide interface. In this model, Joule heating is considered, which significantly accelerates the switching process at high current levels. Since the JART VCM v1b model represents an improvement of the JART VCM v1a model, this user guide will have its focus on the JART VCM v1b model. Here, the equivalent circuit diagram (ECD) as well as some equations have been modified to explain the switching dynamics more accurately  Based on the JART VCM v1b model, a variability model was developed, which includes both device-to-device and cycle-to-cycle variability. In terms of the device-to-device variability, the VCM cells are initiated with statistical distributed parameters: filament lengths, filament radii and maximum and minimum values for the oxygen vacancy concentration in the disc. The cycle-to-cycle variability is achieved by changing the four quantities during SET and RESET. The latest extension of the JART VCM v1b also includes RTN, which is based on statistical jumps of oxygen vacancies into and out of the disc region.

Fig: Equivalent circuit diagram of the JART VCM v1b model (a) 

along with the electrical model in Verilog-A (b).

The Verilog-A code of this model can be downloaded here (Verilog-A file).
The User Guide for this model version can be downloaded here (User Guide PDF).

[paper] Memory Technology – A Primer for Material Scientists.

Schenk, Tony, Milan Pesic, Stefan Slesazeck, Uwe Schroeder, and Thomas Mikolajick

Memory Technology–A Primer for Material Scientists

Reports on Progress in Physics (2020)

Abstract - From our own experience in the group, we know that there is quite a gap to bridge between scientists focused on basic material research and their counterparts in a close-to-application community focused on identifying and solving final technological and engineering challenges. In this review, we try to provide an easy-to-grasp introduction to the field of memory technology for materials scientists. As an understanding of the big picture is vital, we first provide an overview about the development and architecture of memories as part of a computer and point out some basic limitations that all memories are subject to. As any new technology has to compete with mature existing solutions on the market, today's mainstream memories are explained and the need for future solutions is highlighted. The most prominent contenders in the field of emerging memories are introduced and major challenges on their way to commercialization are elucidated. Based on these discussions, we derive some predictions for the memory market to conclude the paper.

TABLE OF CONTENTS

1. INTRODUCTION
2. OVERVIEW AND BASIC LIMITATIONS
3. COMMERCIALLY AVAILABLE MAINSTREAM MEMORIES

3.1. Static and Dynamic Random Access Memory (SRAM/DRAM)
3.2. Flash Memory and Solid-State Drive (SSD)
3.3. Magnetic Hard Disk Drives (HDD) and Magnetic Tapes
3.4. Outlook: Market Trends and Drivers

4. EMERGING MEMORIES

4.1. Resistance-based Read-out: Memory Concepts and Basic Considerations
4.2. Anion migration or valence change memory (VCM)
4.3. Cation migration or electrochemical metallization memory (ECM)
4.4. Phase change memory (PCM)
4.5. Magnetoresistive memory (MRM)
4.6. Ferroelectric Memory (FEM)
4.7. Miscellaneous

5. SUMMARY AND CONCLUSION

FIG: Evolution of the mainstream solutions for the respective memories classes. The introduction of Flash memory partially bridged a technology gap around the year 2009. Today, two types of so-called storage-class memories – a memory-type SCM (SCM 1) and a storage-type SCM (SCM 2) – were proposed to overcome the memory gap. NAND flash already fulfills the role of a mainstream SCM 2. For SCM 1, 3D XPoint could be a promising candidate, but is not a dominant mainstream memory. In future, we will likely see different types of SCMs and NV-RAM with different specifications as required by the respective application – because in the end, the overall system cost decides about the choice of the memory.