Chituo Technology's latest research paper sparked heated discussions among experts

SOT-MRAM (spin-orbit moment magnetic random access memory), with its nanosecond write speed and unlimited erase and write times, is a high-performance non-volatile storage technology that is expected to replace CPU cache at all levels, and is expected to solve the current problems of SRAM cost and high static power consumption. However, SOT-MRAM is extremely challenging in device manufacturing process, especially the traditional solution leads to low etching yield in principle, which seriously restricts its large-scale production and application.

From December 7 to 11, 2024, the 70th Annual Conference of IEDM, the top academic conference in the field of international microelectronics, was held in San Francisco, USA. Samsung, Kioxia, European Microelectronics Center IMEC and Zhejiang Chituo Technology, Beihang University, Units such as Zhizhen Memory have disclosed their recent technological progress in the field of MRAM. Among them, Zhejiang Chituo Technology Company released a breakthrough development - "A novel Channel-less SOT-MRAM with 115% TMR, 2 ns Switching, and High Bit Yield (>99.9%)". % TMR (tunnel magnetoresistance ratio), 2 nanosecond switching speed and high bit yield (>99.9%) trackless SOT-MRAM" is particularly eye-catching.

It is understood that Chituo Technology has proposed for the first time a trackless vertical SOT-MRAM device structure suitable for large-scale manufacturing, which can significantly reduce the complexity and difficulty of the SOT-MRAM process and improve the device yield in principle. The release of the research results has attracted the attention of many industry experts. Dr. Huai Yiming, a technical authority in the field from AVALANCHE Company with 20 years of experience in MRAM development, believes that this work has high industrialization value. Researcher Yang Meiyin from the Institute of Microelectronics, Chinese Academy of Sciences, who has been engaged in SOT-MRAM research for a long time, commented that Chituo Technology has innovatively designed a "write path-less" SOT memory device, which fundamentally eliminates the problem of the write path being etched and broken. risk. This design allows for more thorough cleaning of metal attachments on the device sidewalls during the etching process, successfully achieving a manufacturing yield of more than 99.9%. This achievement not only provides new possibilities for the large-scale production and application of SOT-MRAM, but also provides new ideas and solutions for solving etching process problems. Professor Cai Kaiming of Huazhong University of Science and Technology said that this research shows that China's next-generation MRAM devices may make significant progress, fully confirms Zhejiang Chituo Technology Company's superior manufacturing capabilities and deep technology accumulation in the field of third-generation magnetic storage, and begins to realize the Technical catch-up and surpassing of relevant international research institutions. Its breakthroughs in core technologies in the field will lay an important foundation for the development of the third-generation MRAM industry.

Interpretation of the new SOT-MRAM device without extended track layer

The structure of the vertical SOT-MRAM device without extended spin-orbit layer released by Chituo Technology is shown in the figure below.

Traditional Solution

Chituo Technology Innovation Program

The key innovation of this structure is to place the MTJ directly between the two bottom electrodes, with the two sides of the MTJ partially overlapping the bottom electrodes. When performing MTJ etching, the structure does not need to stop precisely on the surface of the track layer with a thickness of about 5 nm, but can be over-etched, thereby greatly increasing the etching window. This innovation significantly reduces the difficulty of the etching process and solves the high requirements for precise control of MTJ etching in traditional processes. This breakthrough design has increased the bit yield of SOT-MRAM devices on 12-inch wafers from the current industry level of 99.6% to over 99.9% (indirect test values have reached 99.99%). This yield level is basically The threshold required for large-scale manufacturing has been reached. At the same time, the device achieves a writing speed of 2 nanoseconds and more than 1 trillion (10 to the 12th power, the upper limit of measurement time) write/erase operations. The device has the potential for continuous shrinkage. Many of the indicators in the paper are at the international forefront, marking the company's Mb-level SOT-MRAM demonstration chip manufacturing capabilities and laying a solid technical foundation for the design and manufacturing of the next generation of high-speed, high-density, and high-reliability MRAM chips.

The future of SOT-MRAM 

SOT-MRAM may become the mainstream technology route for new storage in the future and has great development prospects.

SOT-MRAM technology has only been around ten years since its inception, but has made significant progress in device verification and material innovation. In particular, the proposal of a new trackless SOT-MRAM device structure has further promoted its move towards industrial application. In the future, with continued breakthroughs in material science, device design and manufacturing technology, SOT-MRAM is expected to gradually become commercially available. As a strong competitor of SRAM memory, SOT-MRAM can not only be used in traditional fields such as high-performance embedded storage and cache, but will also show great potential in emerging fields such as in-memory computing, neuromorphic computing, and stochastic computing.

About Zhejiang Chituo Technology Co., Ltd.

Zhejiang Chituo Technology Co., Ltd. was established in 2016 and is a leading company in the research and development, production and manufacturing of new MRAM non-volatile memory chip technology in China. Its official website shows that it has achieved mass production of multiple STT-MRAM products.

About IEDM

IEDM (International Electron Devices Meeting) is hosted by the Institute of Electrical and Electronics Engineers (IEEE). It is the most influential academic conference in the field of microelectronic devices. It enjoys a high academic status and wide influence in the international semiconductor technology community. It is one of the main windows and platforms for well-known academic institutions and companies in the international semiconductor industry to report their latest research results and technological breakthroughs.

About MRAM

Magnetic random access memory (Magnetoresistive Random Access Memory, MRAM) is a non-volatile storage technology. It uses a magnetic tunnel junction (MTJ) as a storage unit to switch between high and low resistance states by changing the direction of the magnetic moment, thereby achieving Data storage of "0" and "1". Unlike traditional charge memories (such as DRAM and Flash), MRAM does not need to rely on charges to retain data, so it has significant advantages such as fast speed, low power consumption, high rewrite times, and strong resistance to radiation and harsh environments.

In recent years, spin-transfer torque magnetic random access memory (STT-MRAM, Spin-Transfer Torque MRAM) has been commercialized. STT-MRAM uses the spin transfer torque effect to change the magnetization direction of the magnetic layer through spin polarization current to complete data writing. At present, this technology has shown broad application prospects in civilian scenarios such as intelligent Internet of Things, industrial control, and vehicle-mounted electronics.

Spin-Orbit Torque Magnetic Random Access Memory (SOT-MRAM, Spin-Orbit Torque MRAM) is an important improvement based on STT-MRAM. It uses a new writing mechanism-the Spin-Orbit Torque effect to improve the writing speed. It has been shortened from 10-50 nanoseconds to about 2 nanoseconds. The power consumption under the same working conditions has been reduced to one thousandth of the original. The number of rewrites has been increased to unlimited. However, it is currently limited by key issues such as low bit yield. Does not meet the conditions for productization.

View more at EASELINK