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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.

STT-MRAM structure diagram

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

STT-MRAM chips

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".

Everspin EMD3D256 256Mb ST-MRAM photo

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.

Latest STT-MRAM news

Spin Transfer Technologies starts sampling 80nm OST-MRAM chips

Jan 26, 2017

Spin Transfer TechnologiesSpin Transfer Technologies announced that it started to deliver fully functional ST-MRAM samples to customers in North America and Asia.

The sample devices are based on the company's Orthogonal Spin Transfer Magneto-Resistive Random Access Memory technology (OST-MRAM), and use 80nm perpendicular magnetic tunnel junctions (MTJs)., the latest generation of MRAM technology.

Toshiba and Hynix prototype a 4 Gb STT-MRAM

Dec 20, 2016

Toshiba and SK Hynix co-developed a 4-Gbit STT-MRAM chip, and presented a prototype at IEDM 2016.

Toshiba Hynix 4Gb STT-MRAM mTJ array photo

The prototype chip is made from eight 512-Mbit banks, and the cell area is equivalent to that of DRAM - at 9F2, which Hynix says is much smaller than conventional STT-MRAMs (50F2).

Samsung demonstrates a 8Mb embedded pMTJ STT-MRAM device

Dec 12, 2016

Samsung demonstrated an LCD display that uses a tCON chip that uses embedded 28nm pMTJ STT-MRAM memory, instead of the normally used SRAM. The MRAM device had a density of 8Mb and a 1T-1MTJ cell architecture. The cell size is 0.0364 um2.

Samsung LCD tCON Demo (IEDM-2017)

A tCON chip is a timing controller chip that processes the video signal input and processes it to generate control signal to the source & gate driver of the LCD display. The memory is used a a frame memory which stores previous frame data. Samsung prepared a test chip that contains both SRAM and MRAM memory devices to show that there is no difference between the two. SRAM replacement is a popular MRAM application.

IMEC researchers demonstrate the world's smallest pMTJ at 8nm

Dec 07, 2016

Researchers at IMEC developed a 8nm perpendicular magnetic tunnel junction (pMTJ) with 100% tunnel magnetoresistance (TMR) and a magnetic coercive field up to 1,500 Oe in strength. The researchers also demonstrated integrated 1Mbit STT-MRAM 1T1MTJ arrays with pitches down to 100 nm.

IMEC says that this is the world's smallest pMTJ - which paves the way for high density stand-alone MRAM applications. The pMTJ was developed on 300mm silicon wafers in a production process that is compatible with the thermal budget of standard CMOS back-end-of-line technology.

The EU-funded GREAT project presents its first hybrid CMOS-MRAM 180nm tape out

Nov 20, 2016

GREAT Project logoIn 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.

The project partners now announced the first hybrid CMOS/MSS-MRAM Tape Out with Israel-based Tower Jazz. This hybrid integrated circuit uses the 180nm CMOS process from Tower and an academic MRAM post-process that will be done by CEA Spintec within their facilities.

Interview with Bo Hansen, CEO at Capres A/S

Oct 26, 2016

Bo Hansen, Capres CEOCapres A/S was established in 1999 in Denmark to develop a unique probe technology designed for in-line production monitoring in the semiconductor industry. The company, in collaboration with IBM, developed a resistivity measurement technique to characterize MTJ stacks.

Bo Svarrer Hansen, the company's CEO since 2002, was kind enough to answers a few questions we had, and share with us his views on the MRAM market and the company's measurement systems for MRAM and STT-MRAM device developers.

Q: Can you update us on Capres' current offers to the MRAM industry?

Capres customers are using our CIPTech® tools for R&D on small samples as well as volume production on 300 mm wafers. Depending on the configuration the tools measure with an in- plane or an out- of- plane magnetic field on blanket as well as patterned wafers.

Avalanche to commence volume pMTJ STT-MRAM production in early 2017

Oct 21, 2016

STT-MRAM developer Avalanche Technology logo Avalanche Technology announced that volume production of its pMTJ STT-MRAM chips on 300 mm wafers will begin in early 2017. Avalanche started to sample 32Mb and 64Mb STT-MRAM chips in 2015

Avalanche has entered into a manufacturing agreement with Sony Semiconductor Manufacturing Corporation (SSMC) for this volume production. Avalanche targets several markets, including Storage, Automotive, IoT and embedded applications. Avalanche will offer discrete MRAM chips from 4Mb to 64Mb in size.

Spin Transfer Technologies fabricated 20nm OST-MRAM MTJs, preparing to deliver samples

Sep 27, 2016

Spin Transfer TechnologiesSpin Transfer Technologies (STT) announced that it fabricated 20nm perpendicular MRAM magnetic tunnel junctions (MTJs) based on the company's Orthogonal Spin Transfer MRAM (OST-MRAM).

STT is now preparting to deliver OST-MRAM samples to select customer, following requests from "certain major semiconductor and systems companies". The company is processing more than 40 wafer lots at its R&D fab in Fremont, California.

Samsung Foundry to start offering STT-MRAM by 2019

Sep 23, 2016

Samsung logoBack in July 2016 (yes, we missed that one, but better late than never), Samsung Foundry's business development chief Kelvin Low said that the company is set to offer STT-MRAM on its 28nm FDSOI manufacturing process by the end of 2018.

To be more precise, the STT-MRAM in 2018 will be on a not-finalized process (what Samsung calls Risk Production Phase) - and real volume production will only begin in 2019. Samsung will be pushing its eFlash 28nm production before STT-MRAM will be available - but the company expects MRAM to be a favorite in the long term.

Everspin to demonstrate the world's fastest SSD based on its ST-MRAM

Sep 11, 2016

Everspin announces that it is going to demonstrate the world's fastest solid-state drive (SSD) using its latest perpendicular ST-MRAM technology. The drive achieves continuous write operations of 1.5 Million IOPS, using Everspin's Everspin’s 256Mb DDR3 chips (manufactured by global foundries).

Everspin pMTJ EMD3D256MB photo

Everspin started sampling its new pMTJ ST-MRAM chips last month. The p-MTJ ST-MRAM offers improved performance, higher endurance, lower power, and better scalability compared to previous MRAM and ST-MRAM products. Everspin is developing on a scaled-down 1Gb version.