Speeding Up the Write Operation for Multi-Level Cell Phase Change Memory with Programmable Ramp-Down Current Pulses.

Chenchen Xie,Zhitang Song,Xi Li,Houpeng Chen,Qian Wang,Kun Ren,Yang Li,Yuanguang Liu

doi:10.3390/mi10070461

Abstract

Multi-level cell (MLC) phase change memory (PCM) can not only effectively multiply the memory capacity while maintaining the cell area, but also has infinite potential in the application of the artificial neural network. The write and verify scheme is usually adopted to reduce the impact of device-to-device variability at the expense of a greater operation time and more power consumption. This paper proposes a novel write operation for multi-level cell phase change memory: Programmable ramp-down current pulses are utilized to program the RESET initialized memory cells to the expected resistance levels. In addition, a fully differential read circuit with an optional reference current source is employed to complete the readout operation. Eventually, a 2-bit/cell phase change memory chip is presented with a more efficient write operation of a single current pulse and a read access time of 65 ns. Some experiments are implemented to demonstrate the resistance distribution and the drift.

Highlights

Data is the most competitive resource in the twenty-first century and its heat has never been cut down
The large resistance contrast between amorphous and crystalline states in the memory cell means that Phase change memory (PCM) has more potential in multi-level cell (MLC) storage, which is a crucial feature for reducing the cost-per-bit and increasing the memory capacity
The MLC PCM can be used in artificial neural networks as synapses, which provides a promising solution for energy-efficient artificial neural networks (ANNs) [3,4]

Summary

Introduction

Data is the most competitive resource in the twenty-first century and its heat has never been cut down. The large resistance contrast between amorphous and crystalline states (typically three or four orders of magnitude) in the memory cell means that PCM has more potential in multi-level cell (MLC) storage, which is a crucial feature for reducing the cost-per-bit and increasing the memory capacity. A PCM memory chip that demonstrates an MLC operation at 2-bit/cell is presented.

Basic Characteristics of Phase Change Memory

Chip Architecture

BLOCKs

Program Scheme and Circuit

Experimental Results

Conclusions