STT-MRAM (also called STT-RAM or sometimes ST-MRAM and ST-RAM) is an advanced type of MRAM devices. STT-MRAM enables higher densities, low power consumption and reduced cost compared to regular (so-called Toggle MRAM) devices. The main advantage of STT-MRAM over Toggle MRAM is the ability to scale the STT-MRAM chips to achieve higher densities at a lower cost.
STT-MRAM has the potential to become a leading storage technology as it is a high-performance memory (can challenge DRAM and SRAM) that can scale well below 10nm and challenge the low cost of flash memory.
What is STT-MRAM?
STT stands for Spin-Transfer Torque. In an STT-MRAM device, the spin of the electrons is flipped using a spin-polarized current. This effect is achieved in a magnetic tunnel junction (MTJ) or a spin-valve, and STT-MRAM devices use STT tunnel junctions (STT-MTJ). A spin-polarized current is created by passing a current though a thin magnetic layer. This current is then directed into a thinner magnetic layer which transfers the angular momentum to the thin layer which changes its spin.
What is perpendicular STT-MRAM?
A "regular" STT-MRAM structure (similar to the one you see above) uses an in-plane MTJ (iMTJ). Some STT-MRAM devices use a more optimized structure called perpendicular MTJ (pMTJ) in which the magnetic moments are perpendicular to the silicon substrate surface.
Perpendicular STT-MRAM is more scalable compared to iMTJ STT-MRAM and is also more cost competitive. Perpendicular STT-MRAM is thus a more promising technology to replace DRAM and other memory technologies
Several companies, including IBM and Samsung, Everspin, Avalanche Technologies, Spin Transfer Technologies and Crocus are developing STT-MRAM chips. In April 2016 Everspin announced that it started shipping 256Mb ST-MRAM samples to customers. The new chips demonstrate interface speeds comparable to DRAM, with DDR3 and DDR4 interfaces. Volume production is expected "soon".
In August 2016 Everspin started sampling pMTJ-based ST-MRAM chips. The first chips are also 256Mb in size, but the pMTJ versions offer improved performance, higher endurance, lower power, and better scalability compared to previous iMTJ ST-MRAM products. Everspin is now ramping out 256Mb pMTJ ST-MRAM production and is developing a scaled-down 1Gb version.
The latest STT-MRAM news:
In October 2018 Intel revealed that it is developing embedded MRAM - and that the company has successfully integrated embedded MRAM into its 22nm FinFET CMOS technology on full 300mm wafers.
Now Intel gave more details on its embedded STT-MRAM, and said that the technology is ready for high-volume manufacturing. Intel said it has used a "write-verify-write" scheme and a two-stage current sensing technique to create 7Mb perpendicular STT-MRAM arrays in its 22FFL FinFET process.
Everspin Technologies announced that it started to ship pre-production customer samples of its 28 nm 1Gb STT-MRAM chips in December 2018. Everspin already announced that it started to sample these new 1Gb STT-MRAM chips in November 2018.
In November 2017 Everspin announced it will delay its 1Gb STT-MRAM chips as its focus has shifted to its 256 Mb STT-MRAM chips. It is great, tough, to see Everspin progressing with its larger MRAM chip and we hope that mass production will begin, as planned, in the middle of 2019.
Researchers from Japan's Tohoku University developed a 128 Mb STT-MRAM device that features a write speed of 14 nm, the world's fastest STT-MRAM chip at a density over 100 Mb.
To achieve this high speed, the researchers developed MTJs that are integrated with CMOS, which also significantly reduces the power-consumption of the memory device.
Market analyst firm Yole Developpement presents its latest next-generation memory forecasts in an interesting new article. The company says that following more than 15 years of development, PCM is finally taking off in stand-alone applications due to strong support from Intel and Micron.
STT-MRAM is expected to lead the embedded memory race as many foundries are rushing to add MRAM support and expertise to their product lines. STT-MRAM is promising for enterprise storage SCM.
IMEC: STT-MRAM is suitable for 5 nm last level cache, offers significant energy gains over SRAM in large memory densities
Researchers at Belgium-based research institute Imec presented the first power-performance area comparison between SRAM and STT-MRAM last-level cache at the 5 nm node.
The analysis, based on design-technology co-optimization and silicon verified models, reveals that STT-MRAM meets the performance requirements for last-level caches in the high-performance computing domain. For larger memory densities, STT-MRAM was found to offer significant energy gains compared to SRAM.
pMTJ STT-MRAM developer Avalanche Technology announced its 2nd-generation serial non-volatile discrete MRAM memory family. The SPnvSRAM family offers 1 Mb to 32 Mb densities at extended-temperature industrial-grade specifications. Avalanche says that these devices, available in low pin count, small package options, are ideal for a broad range of industrial, automotive and consumer applications.
Avalanche's 2-Gen SPnvSRAM is offered in 108-MHz Quad Serial Peripheral Interface (QSPI) performance as a byte addressable memory thus eliminating the need for software device drivers.
SMART Modular Technologies has launched its new nvNITRO U.2 Storage Accelerator that features Everspin's STT-MRAM technology. The nvNITRO is ideally suited for synchronous logging applications such as those used for financial trading.
SMART's nvNITRO U.2 Storage Accelerator uses a standard NVMe interface that is 1.2.1 compliant and provides less than six microseconds of industry-leading low latency access with persistence so that all logging data is safe. The U.2 form factor brings with it the advantage of being hot-swappable.
Tom Coughlin posted an interesting overview of the 2018 MRAM Developer day, which is well worth a read. Besides the conference report, Coughlin also updates on its market estimates - the market for MRAM and STT-MRAM memory solutions will experience fast growth - growing from $36 million in 2017 to about $3.3 billion in 2028. This growth will be at the expense of SRAM, NOR flash and some DRAM.
The demand for MRAM memory will result in an increased demand for MRAM production equipment, of course. MRAM equipment revenues will reach $792 million by 2028, according to Coughlin Associates.
Researchers from UC Berkeley and the Huazhong University of Science and Technology developed sub 10-nm STT MTJs that shows a thermal stability factor of more than 80.
The reserachers say that the highly efficient and dense MTJ could lead to higher efficiency and density STT-MRAM devices and spin-based computers.
A couple of days ago, Everdisplay disclosed its first major design win with a "top enterprise storage vendor" for its 40nm 256Mb STT-MRAM chips. We now know that this vendor is IBM - as it introduced its latest-generation enterprise SSD FlashSystem, which indeed includes Everspin's STT-MRAM.
Using MRAM instead of DRAM memory enabled IBM to remove the relatively large supercapacitors (used to make the DRAM non-volatile) and so the company was able to reduced the size of its drives and switch to a standard 2.5-inch U.2 drive form factor. The new FlashSystem SSDs support up to 19.2TB of 64L 3D TLC NAND. IBM's system uses a 20-channel NAND interface and a four-lane PCIe 4.0 host interface that can operate in dual-port 2+2 mode.