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:
Renesas Electronics announced that it has developed two new technologies that reduce the energy and voltage application time for the write operation of STT-MRAM chips.
On a 20-Mbit test chip with embedded MRAM memory cell array in a 16 nm FinFET logic process, a 72% reduction in write energy and a 50% reduction in the voltage application time were confirmed.
Researchers from Tohoku University managed to fabricate the world's smallest STT-MRAM MTJ, at 2 nm. In addition, the researchers demonstrated fast switching (3.5 ns) in sub-five-nm STT-MRAM MTJs.
The new MTJ were developed using a new multilayered ferromagnetic structure that can engineer characteristic relaxation time, which governs the magnetization dynamics in the ns regime.
Hprobe announced a new magnetic test head for MRAM Wafer Sort. The new module, the H3DM-XL, is at the heart of the latest addition to Hprobe’s IBEX line, the IBEX-WS.
The IBEX-WS test equipment integrates 3D magnetic field capabilities, while increasing field area and uniformity for wafer probing large MRAM arrays. It also features a unique patented robotized 3D Field Calibration Unit (FCU) for high-speed field mapping and monitoring.
pMTJ STT-MRAM developer Avalanche Technology announced that it has signed an agreement with LinearASICs Inc. to develop companion chiplets to offer a complete portfolio of Space Grade products with SPI and DDR interfaces, based on Avalanche's 1Gb Space Grade MRAM.
Avalanche's 2nd-Gen P-SRAM evaluation kit
LinearASICs will provide standalone serial interface chiplets such as Octal SPI (OSPI), as well as standard memory interface chiplets such as DDR. These chiplets will be available as standalone devices or integrated modules through Avalanche.
Everspin Technologies announced its financial results for Q2 2021. Revenues were $11.85 million, up 15% over Q1 2021 (and similar to Q2 2020), as STT-MRAM revenues jumped 56%. Net profit was $0.25 million, up from a loss of $0.46 million in Q1 2021 (and $1.29 million in Q2 2020).
At the end of Q2 2021, Everspin had $14.2 million in cash and equivalents, down from $15.5 million from the end of Q1 2021. Cash flow from operations was negative at $0.56 million. Looking into the next quarter, Everspin expects revenues to be in the range of $11.7 million to $12.8 million.
Orthogonal Spin Transfer MRAM (OST-MRAM) technology developer Spin Memory is shutting down. The company's main investor and founding company, Allied Minds, said in a statement that the main reasons challenges in securing new customers and COVID-19 which "significantly delayed the required testing of its development chip with ARM".
This is a sad ending to Spin Memory, which began its way as Spin Transfer Technologies - a spin-off from NYU that was established together with Allied Minds.
pMTJ STT-MRAM developer Avalanche Technology announced that NexAIoT has adopted the company's 8Mbit MRAM (P-SRAM) products in its new fanless NISE & NIFE series industrial computers.
NexAIoT says that Avalanche's P-SRAM non-volatile memory provides the performance and reliability needed for its computers. The P-SRAM helps prevent data loss during power failures.
pMTJ STT-MRAM developer Avalanche Technology announced its third-generation 1Gb space-grade parallel asynchronous x32-interface high-reliability P-SRAM (Persistent SRAM) memory devices. The company says that these new devices enable customers to design unified memory architecture systems for high reliability aerospace applications, in extremely small form factors.
Avalanche's 2nd-Gen P-SRAM evaluation kit
The new Parallel x32 Space Grade series is offered in 512Mb, 1Gb, 2Gb and 4Gb density options and has asynchronous SRAM compatible 45ns/45ns read/write timings. Data is always non-volatile with >10^14 write cycles endurance and 10-year retention at 125°C. All four density options are available in a small footprint 142-Ball FBGA (17mm x 11mm) package.
pMTJ STT-MRAM developer Avalanche Technology announced that it is now shipping new space-grade parallel asynchronous x16-interface high-reliability P-SRAM (Persistent SRAM) memory devices, based on its latest STT-MRAM technology.
Avalanche says that its STT-MRAM devices are smaller and more efficienct compared to Toggle MRAM based products, currently adopted in aerospace applications. The Parallel x16 Space Grade series is offered in 16Mb, 32Mb and 64Mb density options and has asynchronous SRAM compatible 45ns/45ns read/write timings. All three density options currently in production and available within industry standard lead times.
Integral Solutions International (ISI) announced its first shipment of a commercial SOT-MRAM tester system. This new equipment was developed by integrating a commercial pulser with ISI’s proprietary bias-tee and measurement electronics.
ISI says that the new tester system generates pulses as narrow as 300pS, suitable for R&D applications which require extremely narrow pulse widths. In parallel, ISI is also developing its proprietary Gen-4 Pulser System, which will provide high-throughput and cost-effective measurement solutions with the flexibility of testing either STT-MRAM or SOT-MRAM devices. The Gen-4 system is expected to be released in the fall of 2021.