Phase-change Memory Research in Which Any Point Reached Marks a New Starting Point

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Research policy taking a unique point of view with the motto, “We can do it if we try”

Junji Tominaga, PhD, National Institute of Advanced Industrial Science and Technology

The phase-change memory developed in the 1960s is based on a technology that records differences/changes that occur between crystallized and amorphous states of the same material. This technology had been overshadowed by magneto-optical (MO) technology until the 1990s. However, with the commercialization of blue lasers, the requirements for ultra-high density memory increased, which suddenly sparked greater interest in phase-change technology. Dr. Junji Tominaga, a Prime Senior Researcher at the National Institute of Advanced Industrial Science and Technology who is featured in this issue of Vision, has been researching phase-change technology since the 1990s. His research results first led to the development of phase-change CD-RW and Blu-ray compatible ultra-high density DVC-RW disk media, and then to the creation of many wonderful devices, such as the superlattice energy-saving phase-change memory, which he devised essentially on his own.
He is currently working on finding practical applications for topological insulators, which hold new possibilities for phasechange memory. We asked Dr. Tominaga about his research on phase-change memory as well as related subjects.

*This article was released in “PR Magazine No.69 published in December, 2019”


A carefree boyhood surrounded by nature’s abundance

――What was your boyhood like?
I was born in Ohira Village, Miyagi Prefecture. It is a farming village located on the Sendai Plain, and is the only “village” in Miyagi Prefecture. A Toyota Plant has been built there and the village is now financially better off than the neighboring towns. But it is still a “village.” Ohira Village is unusual in that approximately half of its area is owned by the Ministry of Defense (Japan), and a Self Defense Forces maneuver training field is located near the elementary school.
During class, we often heard the sound of cannons and the engines of fighter planes. It might be due to these experiences that I have an affinity for airplanes.
All through elementary school and up to seventh grade, I was so absorbed in the abundance of nature surrounding me that I hardly studied. In summer, we used to dam up a river and use it as a swimming pool. In autumn, you could see a lot of dragonflies flying around. The rice paddies and reservoirs were full of frogs, which we caught and played with. I often dug up potatoes in the fields, too.
When I was in fourth grade, our family moved to a neighboring town (Taiwacho). This was the town where the movie “The Magnificent Nine” (distributed by Shochiku Company Limited), which debuted in 2016, was filmed. When I was in elementary school, I enjoyed drawing. My drawings were always selected for prizes in sketching contests and I was awarded supplies such as crayons and paints, so I never had to buy them. The other hobby I had was making model planes. When I was in ninth grade, instead of studying to prepare for the high school entrance exam, I was secretly focused on studying to obtain an amateur radio operator license, without my parents’ knowledge. I did not study my school subjects much, but I was good at math and science.
I also liked history. When I entered high school, I really began to enjoy math and physics. I formed a physics club and was active in  it. Since it was not an official club, the school did not give us any money. So I used my own spending money to cover expenses for physics experiments.
One of the devices we made was a sunlight- collecting furnace called a solar furnace. We bought aluminum plates and built something resembling a parabolic antenna after making calculations that would allow us to focus the sunlight on a single point. At a subsequent presentation, we made 1 liter of water boil in 10 minutes.


Following my studies in England, I began research on phase-change technology when magneto-optical technology was the mainstream.

Dr. Tominaga (second from right) with his academic advisors at the Cranfield Institute of Technology in England.

――Is it true that you first joined a private corporation?
After getting my master’s degree, I joined TDK’s R&D Laboratory in 1985, where I started out working on hard disk research. After about two and a half years (in 1987), TDK’s foreign study program sent me to study at Cranfield Institute of Technology in England. During Japan’s rainy season, the read-write heads (flying heads) of hard disk systems often broke down due to moisture. TDK decided to send me to England to find out why this was happening.
The Cranfield Institute of Technology that existed when I was studying there cannot be found on maps. That’s because an Air Force facility was also present at the Institute. There was a 2,400-meter runway on which even passenger jets could land. I got my PhD at the Institute. I had many wonderful experiences studying in England, and it is not an overstatement to say that my career as a researcher began there. Therefore, I actively encourage the staff at my laboratory to study abroad. Learning about cultures that are different from Japan’s and forming new networks can become assets in the future. I send my staff out, telling them just to enjoy life in foreign countries.
When I was finishing my studies in England, the Japanese yen abruptly began to appreciate because of the Plaza Accord, and this caused the hard disk business in Japan to shrink significantly. TDK also withdrew from the hard disk business, except for flying heads, and asked me to work on magneto-optical discs. However, judging that it was too late for that technology, I decided to work on phase-change technology in 1990 and started with research on phase-change CD-RW.
The Magneto-optical (MO) Group had 40 researchers, but my Phase-change Research Group started with just me. The people in the MO Group used to tell me that phase-change technology would never end up producing any products. However, the golden days of MO discs came to an end within a short period. This was mainly because the market around 1994 began to demand a gigabyte class of high-density media in order to handle images.
Just around then, a major debate started over whether to use phase-change or magneto-optical technology for DVDRAM. A heated controversy was taking place between companies pushing MO and those pushing phase change. It turned out to be a decisive battle. The phasechange camp won in the end.