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    The National Commendation for Invention honors the achievements of Japan's leading researchers and scientists. The award program consists of two divisions. Division 1 awards recognize inventions that have already made significant contributions. Division 2 awards recognize inventions expected to make significant future contributions.

    Sony researchers Minoru Ishida, Katsuhisa Aratani, Akira Kouchiyama and Tomohito Tsushima recently won the 21st Century Invention Prize (the highest Division 2 award) for their development of core technology for a memory storage device based on resistance switching in transition metal oxides. The following interview with Ishida and Aratani traces the development of this technology.

    Developing a Large-capacity Memory Device with the Potential to be Number One in a Decade

    Aratani recalls receiving a directive from a senior R&D executive in 2002 which stated "We want you to develop a large-capacity memory device. We don't care how you do it, but the device must have the potential to become number one in a decade."

    Aratani: Until then, I'd been involved in the development of Blu-ray Disc manufacturing technology. However, with the majority of work behind us, I'd begun to feel that there was a need for a recording medium other than optical discs. I believe that senior management was also aware of this need, given that Sony uses memory in most of its products, and that this is what led them to direct me to develop such a device. I asked him to assign Sony's best semiconductor memory R&D engineer.

    The engineer chosen was Minoru Ishida. At the time, Ishida was involved in semiconductor design and had experience supervising the development of memory devices. This new role brought him back to hands-on work in memory development, together with Akira Kouchiyama, who had also been working with Aratani on the development of Blu-ray disc manufacturing technology. Tomohito Tsushima, who had been studying memory devices since his university days, was also drafted, creating a four-member team. The group was now ready to start development.


    Ishida: Even back in 2002, people were already aware of flash memory as well as a next-generation memory contender known as phase-change memory, and it was apparent that, going forward, both would continue to evolve. Instead of relying on existing technologies, however, Sony wanted to study the weaknesses of these devices and find a completely different method that could surpass them in terms of performance and density. When approaching something like creating a memory device which must be viable in a decade, you naturally feel compelled to create something really amazing. So, even ideas that seemed impractical were put on the table for discussion.

    Leveraging Changes in Materials Caused by Oxidation/Reduction

    While there were already several types of memory technologies on the market, including flash memory, these four researchers targeted resistive memory technology. With resistive memory, data is written through repetitions of switching between low resistance (0) and high resistance (1) between the electrodes in the recording elements (0,1,0,1,0,1...). The faster this repetition occurs, the faster data can be stored.



    Aratani: The question is what to use to cause resistance. In the extreme sense, you can change resistance with just about kind of insulating materials such as paper or glass. However, we wanted something that could be used repeatedly without the risk of deterioration, and that would work reliably even on an atomic scale. We tried various methods and substances in our quest for this material. Eventually we opted for oxidized redox active material.

    The memory element works by applying voltage to electrodes sandwiching a layer of oxidized redox active material to cause oxidation/reduction, thereby changing the resistance. This is basically the same as the principle by which iron becomes resistant to electricity as a result of rusting (oxidation).



    The team also invented a way to confine the oxidation/reduction reaction to a limited region by creating microscopic openings in electrodes that have first been covered across their entire surface with a layer of oxidized material. This reduces the area in which the oxidation/reduction reaction occurs, thereby reducing power requirements and enhancing both processing speed and performance durability.



    Ishida: With flash memory, sophisticated technology is used to store highly-mobile electrons inside the elements. The memory device developed by Sony stores oxides, which are chemically stable and immobile, inside the elements. Because of its simple structure, this system is ideal for achieving highly-compact structures and expanding capacity. Furthermore, since the oxidation/reduction reaction occurs on a limited area of the electrode surface, the reaction is rapid, making the system suitable for high-speed operations.

    Overcoming Conventional Memory Limitations to Realize Unlimited Potential

    This new memory device has been confirmed to operate 5 to 100 times faster than flash memory, and retrieve data 10,000 times faster than a hard drive while consuming less than 10% as much power. Leveraging these performance advantages should make it possible to promote the further evolution of cloud services, which have until now been limited due to the use of conventional hard drives. There is also likely to be an expanding range of potential uses for this technology in the information processing industry, including the high-speed retrieval of massive image and video files.

    Sony has applied for patents for these basic technologies. Since this patent application was disclosed in 2005, various companies have started to develop related memory products and mass production is expected to be possible within a few years. The generic term for resistive memory is "resistive random access memory" (ReRAM), but this term is now applied specifically to resistive memory based on resistance shifts in transition metal oxides.

    The prize was given in recognition of the significance of these contributions, to establishing a next-generation memory technology which will enrich the society of the 21st century. The two who developed this,after being given the mission of devising a memory technology for the coming decade, intend to pass on this same mission to today's young generation of engineers.

    Aratani: I hope that today's young generation will not focus solely on their immediate tasks at hand, but will instead develop an ability to propose new projects with a view to create the future.

    Ishida: I agree. People should at least try, even if they aren't sure how things will turn out. I think that this approach leads to the creation of new things, and that Sony has an environment that welcomes this.




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