A Survey of Test and Reliability Solutions for Magnetic Random Access Memories

Memories occupy most of the silicon area in nowadays' system-on-chips and contribute to a significant part of system power consumption. Though widely used, nonvolatile Flash memories still suffer from several drawbacks. Magnetic random access memories (MRAMs) have the potential to mitigate most of the Flash shortcomings. Moreover, it is predicted that they could be used for DRAM and SRAM replacement. However, they are prone to manufacturing defects and runtime failures as any other type of memory. This article provides an up-to-date and practical coverage of MRAM test and reliability solutions existing in the literature. After some background on existing MRAM technologies, defectiveness and reliability issues are discussed, as well as functional fault models used for MRAM. This article is dedicated to a summarized description of existing test and reliability improvement methods developed so far for various MRAM technologies. The last part of this article gives some perspectives on this hot topic.

I. Introduction

Spin electronics (Spintronics) is one of the most interesting and challenging topics in today’s nanotechnology. It has pushed scientific research and microelectronic industry to build innovative electronic devices that rely on magnetic properties. Similar to other emerging resistive memory technologies, such as resistive random access memory (RRAM) [1] and phase-change memory (PCM) [2], magnetic or magneto-RRAM (MRAM) is a form of resistive memory technology where data are stored in terms of resistive states. Moreover, MRAM uses the spin of electrons for storage instead of their charge. Comparisons of different kinds of memory technologies are shown in Table 1. As illustrated in this table, MRAM technology has demonstrated the promise of universal memory. MRAM has several characteristics that make it is useful for many applications. Nonvolatility (ability to maintain memory contents without requiring power), performance (SRAM and DRAM-like speed with low latency), endurance (durability to support memory workloads without complex management), and reliability (robustness designed for extreme conditions) are these main characteristics. Moreover, an important feature of MRAM technology is that its fabrication process is CMOS-compatible [3].TABLE 1 Comparisons of Different Memory Technologies [5]–[7]

	SRAM	DRAM	NAND	PCRAM	RRAM	STT-MRAM
Cell size ()	~ 150	~ 8	≤ 1	~ 5	~ 4	6 ~ 8
Non-Volatility
Read Time
Write Time
Endurance	> 1015	> 1015	105	~ 107	106 ~ 1012	> 1015
Byte Operation