Together with the Industrial Technology Research Institute (ITRI), National Taiwan University (NTU) and National Tsinghua University (NTHU), the Taiwan Semiconductor Research Institute (TSRI) has announced a breakthrough in the research of Spin-orbit torque Magnetoresistive RAM (SOT-MRAM) device.
MRAM has high potential in automotive and aerospace applications
Using electron spin for information storage, MRAM technology is expected to go mainstream, especially given its ability to resist high radiation and operate under high temperature – characteristics that make it suitable for automotive, industrial, aerospace and military applications.
Back in 2006, US manufacturer Freescale Semiconductor became the first to commercialize MRAM chips, using toggle memory switching. Despite the relative ease of development, the first-generation technology is difficult to scale up. Currently, toggle MRAM chips are only limited to 32 Mb.
Instead of using magnetic field to change the electron spin, Spin-transfer Torque MRAM (STT-MRAM) uses a spin-polarized current to do the job, representing a significant improvement in terms of efficiency and cost. With its scalability, STT-MRAM is generally considered a serious contender to DRAM and SRAM. Currently, companies like Samsung, IBM and Everspin (A spinoff from Freescale) are all developing STT-MRAM chips. In 2016, Everspin shipped its first 256Mb STT-MRAM chips, and recently it has released the world’s first 1GB STT-MRAM chips based on 28nm process.
Even though it is mostly confined to laboratories, Spin-orbit-torque MRAM (SOT-MRAM) is perceived to be a potential challenger to STT-MRAM technology with a further improvement in architecture. In 2018, Belgium’s IMEC became the first to have succeeded in manufacturing SOT-MRAM devices on 300mm wafers on CMOS-compatible processes.
One step closer to SOT-MRAM commercialization
The latest result from Taiwan Semiconductor Research Institute represented laid another milestone on the road to SOT-MRAM’s commercialization. Using perpendicular magnetic anisotropy (PMA) to produce MRAM chips, the institute became the second in the world, after Intel, to have achieved so. According to TSRI, it had to redesign the structure and material involved in the technology, including the fabrication of more than 30 layers of film, each of which measured 0.4 nm.
Back in 2019, project participant NTHU already demonstrated and patented a technique to manipulate the exchange bias in SOT-MRAM by adding a platinum layer under the ferromagnetic and antiferromagnetic layers. The NTHU team claimed that it was the first in the world to use spin current for exchange manipulation, and published its findings in the journal Nature Materials. Another project participant, ITRI, has also accumulated years of research on SOT-MRAM, and has built a platform based on 200mm wafers to trial the technology. ITRI was reportedly transferring its relevant know-how to Taiwanese chipmakers.
Despite the success, TSRI indicated that many obstacles were yet to be overcome to bring SOT-MRAM into commercialization, a process entailing circuit redesign as well as deeper engagement with manufacturing equipment and raw material suppliers. The US firm Applied Materials, for example, provided the physical vapour deposition system used in TSRI’s research.
An expert from National Taiwan University estimated that it would take another ten years to see the commercialization of SOT-MRAM, as it not only depended on superior technologies, but also production cost.