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:
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.
Everspin announces its first major design win with a top enterprise storage vendor for its 256Mb STT-MRAM chips
In its PR, Everdisplay discloses its first major design win with a "top enterprise storage vendor" for its 40nm 256Mb STT-MRAM chips. Everspin says that MRAM enabled the vendor to achieves new levels of performance, storage capacity and reliability.
Researchers from the University of Lorraine in France have discovered that multilayers films made of cobalt (Co) and nickel (Ni) hold great promise for STT-MRAM applications.
It was already shown before that Co/Ni multilayers have very good properties for spintronics applications, but up until now it wasn't clear if the films have a sufficiently large intrinsic spin polarization, which is necessary to create and maintain spin-polarized currents in spintronic devices. It was now shown that the films have a spin polarization of about 90% - which is similar to the best spintronic materials.
Veeco says that it in the past quarter it has received Ion Beam Etch Solution orders from STT-MRAM developers. Veeco's systems are used for magnetic memory development, and the company is collaborating with a leading semiconductor capital equipment manufacturer in this market.
The company "continues to be encouraged by our customers interest" in the STT-MRAM market.
In 2015, the EU launched the GREAT project, with an aim to co-integrate multiple functions like sensors, RF receivers and logic/memory together within CMOS by adapting STT-MTJs to a single baseline technology in the same system on chip. GREAT stands for heteroGeneous integRated magnetic tEchnology using multifonctionnal stAndardized sTack.
After the delivery of a first demonstrator in 2017, the project partners now announced the second hybrid CMOS/MSS-MRAM 180nm Tape Out at Israel-based Tower Jazz. The project partners designed four ICs to validate Analog IP blocks and an ultra-low power MCU comprising a hardware security block.
SMART Modular Technologies announces that it has began shipping its new 1Gb nvNITRO Accelerator Card that features MRAM technology. These new nvNITRO cards use Everspin's STT-MRAM chips. SMART says that nvNITRO is ideally suited for the most demanding transaction logging applications and is designed with plug-and-play capability requiring no changes to system hardware, memory reference, bios or file systems.
SMART further says that the new cards enable a system application to write or log large amounts of data at the full performance of incoming data and provides extremely low and highly consistent read latencies of under 10µs. Because of the non-volatility of the MRAM chips, these cards do not need any power source such as super capacitors or batteries.
Spin Transfer Technologies (STT) announced that its unique Precessional Spin Current (PSC) structure can increase the spin-torque efficiency of any MRAM device by 40-70 percent, which means dramatically higher data retention while consuming less power.
Following advanced testing, the company says that these higher spin-torque efficiencies translate to retention times lengthening by a factor of over 10,000 while reducing write current.