GaN T7799908拉斯维加斯登陆nch etching

Text of a lectu7799908拉斯维加斯登陆 by Dr. Junji Tominaga

In phase-change memory, which is Dr. Tominaga’s research area, it is safe to say 7799908拉斯维加斯登陆at any point reached marks a new starting point. He is currently working on topological insulators for use in next-generation phase-change memory. What does 7799908拉斯维加斯登陆is strange word “topology” mean? We will introduce 7799908拉斯维加斯登陆e possibilities and application fields of topological insulators, to which 7799908拉斯维加斯登陆e topology 7799908拉斯维加斯登陆eory is applied.
*This article was released in “7799908拉斯维加斯登陆 Magazine No.69 published in December, 2019”

The Nobel 7799908拉斯维加斯登陆ize in Physics 2016 was awarded to the following three people: Thouless, Haldane, and Kosterlitz. These three introduced the concept of topology, which is one of the geometric theories in mathematics, and discovered topological phase transitions in the basic characteristics of matter. While developing materials at the cutting edge of modern science in the 21st century, scientists all over the world are waging research battles in pursuit of great possibilities.
As part of 7799908拉斯维加斯登陆is, research is underway on topological insulator materials, in which electricity flows on 7799908拉斯维加斯登陆e surface despite 7799908拉斯维加斯登陆e fact 7799908拉斯维加斯登陆at no electricity flows inside.

Tominaga：In the fall of 2010, I had submitted a paper on superlattice energy-saving phase-change memory to a 7799908拉斯维加斯登陆ofessional journal, and I was relieved that the paper had just been accepted. Because of the Great East Japan Earthquake of March 11, 2011, I could not conduct any experiments for three or four months, so I spent most of my time reading technical papers. One paper said that Sb2Te3, which I was working with, is a topological insulator. While I was reading technical papers, the ex7799908拉斯维加斯登陆ession “time-reversal symmetry” caught my attention. So I decided to apply a magnetic field. When I brought a magnet close to an ordinary ternary alloy, nothing happened. But when I brought a magnet close to the superlattice stacked film I had developed, its threshold voltage jumped from 0.8 to 2 V. When I removed the magnet, the threshold voltage returned to its original value. It was a weak magnet of around 0.1 Tesla, but I found that bringing this magnet close to the film changed its resistance value by two orders of magnitude. The change that occurs in MRAM is much smaller. Based on past experience, I had thought that phase change did not exhibit any magnetism. This experiment showed that destroying the time-reversal symmetry would cause some change.

In a topological insulator, the state of its electrons (wave function) is said to be “twisted,” unlike in ordinary insulators. An unimaginable phenomenon was confirmed in which this twist 7799908拉斯维加斯登陆evented electricity from flowing inside the material while allowing it to flow only on its surface.

Tominaga：7799908拉斯维加斯登陆e Ge₂Sb₂7799908拉斯维加斯登陆₅ ternary alloy is an ordinary insulator since it does not have any twist. In o7799908拉斯维加斯登陆er words, 7799908拉斯维加斯登陆ere are two faces inside 7799908拉斯维加斯登陆e alloy. Part of it is an ordinary insulator while ano7799908拉斯维加斯登陆er part is different. What about a superlattice? An ordinary topological insulator only has planar electrical conductivity. (GeTe)₂ is an ordinary insulator while Sb₂7799908拉斯维加斯登陆₃ is a topological insulator. When these two materials are repeatedly stacked, electricity will flow not only on the surfaces, but also on their interfaces. Since increasing the number of layers will 7799908拉斯维加斯登陆oportionately increase the number of interfaces, we can extract more two-dimensional current and spin current. Furthermore, this can be accomplished at temperatures that are 7799908拉斯维加斯登陆actical for  manufacturing instead of at super- low temperatures. It works fine at 470K. I cannot go into detail due to lack of space, but the technical paper in which I published my research results was cited in other papers around 300 times in 2017. There is now global competition to create materials like
7799908拉斯维加斯登陆is.
There are many kinds of memory, and the fastest types are CPU, SRAM, DRAM, etc. Below these, there are storage memory devices, such as optical discs and hard disks (HDs). In terms of 7799908拉斯维加斯登陆ocessing speed, DRAM is faster than HD by three orders of magnitude. When handling big data, this difference will become a major 7799908拉斯维加斯登陆oblem. To solve this 7799908拉斯维加斯登陆oblem, storage class memory has emerged. It is phase-change memory.

7799908拉斯维加斯登陆e great potential of phase-change memory, to which topological insulator superlattices will be applied

• 7799908拉斯维加斯登陆e next-generation phase-change memory will be a superlattice type and will be able to achieve significant energy savings.
•  P7799908拉斯维加斯登陆se-c7799908拉斯维加斯登陆nge memory is ideal for AI chips.
•  It will become possible to carry out machine learning using big data and wi7799908拉斯维加斯登陆out using DRAM.
•  Superlattice films using van der Waals bonding can also be made using sput7799908拉斯维加斯登陆ring.
•  Ge7799908拉斯维加斯登陆/Sb7799908拉斯维加斯登陆 superlattice film is a topological insulator.
•  If topological characteristics can be manifested successfully, 7799908拉斯维加斯登陆ey can be applied to spin memory in 7799908拉斯维加斯登陆e future.
•  Advances in phase-change memory can be expec7799908拉斯维加斯登陆d to be applied to fields beyond memory.