Evaluation of Hybrid Memory Technologies Using SOT-MRAM for On-Chip Cache Hierarchy

Abstract

Magnetic Random Access Memory (MRAM) is a very promising emerging memory technology because of its various advantages such as non-volatility, high density and scalability. In particular, Spin Orbit Torque (SOT) MRAM is gaining interest as it comes along with all the benefits of its predecessor Spin Transfer Torque (STT) MRAM, but is supposed to eliminate some of its shortcomings. Especially the split of read and write paths in SOT-MRAM promises faster access times and lower energy consumption compared to STT-MRAM. In this work, we provide a very detailed analysis of SOT-MRAM at both circuit-and architecture-level. We present a detailed evaluation of performance and energy related parameters and compare the novel SOT-MRAM with several other memory technologies. Our architecture-level analysis shows that a hybridcombination of SRAM for the L1-Data-cache, SOT-MRAM for the L1-Instruction-cache and L2-cache can reduce the energy consumption by 60 % while the performance increases by 1 % compared to an SRAM-only configuration. Moreover, the retention failure probability of SOT-MRAM is 27x smaller than the probability of radiation-induced Soft Errors in SRAM, for a 65 nm technology node. All of these advantages together make SOT-MRAM a viable choice for microprocessor caches.Index Terms-spin orbit torque, non-volatile memory, cache, hybrid, magnetic memory, reliability, failure rate 0278-0070 (c)

Spin-Polarized Current in Noncollinear Antiferromagnets

“…The SHE on the other hand is responsible (though other effects can contribute) for the spin-orbit torque (SOT) [7,8] in multilayer heterostructures, which can be used for efficient and fast switching of FM layers. The SOT is now also being explored for use in MRAMs [9,10].While spintronics has traditionally focused on FM and non-magnetic materials, in the past few years also antiferromagnetic (AFM) materials have attracted a considerable interest. AFMs offer some unique advantages compared to FMs, but are much less explored (see reviews [11][12][13]).…”

“…The SHE on the other hand is responsible (though other effects can contribute) for the spin-orbit torque (SOT) [7,8] in multilayer heterostructures, which can be used for efficient and fast switching of FM layers. The SOT is now also being explored for use in MRAMs [9,10].…”

A Survey of Soft-Error Mitigation Techniques for Non-Volatile Memories

“…5. A recently-proposed magnetic RAM, named SOT-RAM (spin orbit torque RAM), does not suffer from RDE [36], and hence, this can be used as an alternative of STT-RAM.…”

“…Due to this, adjacent states show overlap [30], and hence, an incorrect value may be read, leading to read errors. Similarly, the stochastic bit-flip due to random thermal fluctuation can lead to retention failure in STT-RAM [27,36]. Furthermore, a decision failure occurs when the datum stored is incorrectly sensed on a read operation.…”

Exploring MRAM Technologies for Energy Efficient Systems-On-Chip

“…This is due to a smaller load capacitance for STT-MRAM as it is denser than SRAM. Hence, when the cache capacity increases, SRAM read latency increases much more than that of STT-MRAM [33]. Concerning the difference in cache area between the two technologies, a SRAM bit cell consists of six CMOS transistors whereas a STT-MRAM bit cell consists of one CMOS transistor and a MTJ.…”