The processing limit of silicon materials is generally considered to be a line width of 10 nanometers. Restricted by physical principles, it is impossible to produce products with stable performance and higher integration after less than 10 nanometers. However, a new type of transistor invented by British scientists will extend the life of Moore's Law. The transistor is expected to lead to a breakthrough in the development of new ultra-fast computer chips. It is worth mentioning that the main developers of the world's smallest transistor are also the ones who developed graphene in 2004. They are Professor Andre K. Geim of the Department of Physics and Astronomy at the University of Manchester in the UK and Researcher Kostya Novoselov. It was for their development of graphene that they were nominated for the 2008 Nobel Prize in Physics.
The world's smallest transistor developed by British scientists led by the above two people is only 1 atom thick and 10 atoms wide. The material used is graphene, which is composed of a single atomic layer. Graphene, as a new semiconductor material, has received widespread attention from the scientific community in recent years. British scientists used standard transistor technology, first using an electron beam to carve a channel on a single-layer graphite film. Then electrons are sealed in the remaining central part called an "island" to form a quantum dot. The structure of the gate part of the graphene transistor is more than 10 nanometers of quantum dots sandwiched by a few nanometers of insulating medium. Such quantum dots are often called "charge islands." Since the conductivity of the quantum dot changes when a voltage is applied, the quantum dot can remember the logic state of the transistor just like a standard field-effect transistor. It is also reported that the scientific research team led by Professor Andre Heim of the University of Manchester in the United Kingdom has developed a 10-nanometer-scale graphene transistor that can actually operate. Their latest research results that have not yet been announced include: Developed a smaller graphene transistor with one molecule in length and width. The graphene transistor is actually a transistor made of single atoms.
Amazing semiconductor materials
Dr. Novoselov of the University of Manchester, one of the developers of graphene, pointed out that graphene is a "gold mine" in the field of research and has been used for a long time. Over a period of time, researchers will continue to "mine" new research results.
So what is graphene? Graphene is a single-layer carbon atom film peeled off from graphite material. It is a honeycomb-shaped two-dimensional crystal composed of a single layer of hexagonal cell carbon atoms. In other words, it is a single-atom layer graphite crystal film whose lattice is a two-dimensional honeycomb structure composed of carbon atoms. The thickness of this graphite crystal film is only 0.335 nanometers. If 200,000 films are stacked together, it is only equivalent to the thickness of a hair. The material has many novel physical properties. Graphene is a zero-bandgap semiconductor material with a much higher carrier mobility than silicon, and theoretically, its electron mobility and hole mobility are equal, so its n-type field effect transistor It is symmetrical to the p-type field effect transistor. In addition, because it has zero bandgap characteristics, the mean free path and coherence length of carriers in graphene can be on the micron level even at room temperature, so it is a semiconductor material with excellent performance. In addition, graphene can also be used to manufacture composite materials, batteries/supercapacitors, hydrogen storage materials, field emission materials, and ultra-sensitive sensors. Therefore, scientific researchers are rushing to study how to prepare and characterize their physical, chemical, and mechanical properties.
One of the reasons why scientists are interested in graphene is that they were inspired by the scientific research results of carbon nanotubes. Graphene is likely to become a replacement for silicon. In fact, carbon nanotubes are graphene microsheets rolled into cylinders. Like carbon nanotubes, they have excellent electronic properties and can be used to make ultra-high-performance electronic products. Its advantage over carbon nanotubes is that the nanotubes have to be carefully screened and positioned when making complex circuits, and very good methods have not yet been developed, whereas this is much easier with graphene.
Silicon-based microcomputer processors can only perform a certain number of operations per second at room temperature, yet electrons pass through graphene with almost no resistance and generate very little heat. In addition, graphene itself is a good thermal conductor and can dissipate heat quickly. Due to its superior properties, electronics made from graphene run much faster. Relevant experts pointed out: "The speed of silicon has a limit. It can only reach this point and cannot be improved." At present, the working speed of silicon devices has reached the gigahertz range.
Computers made of graphene devices can run at terahertz speeds, which is 1,000 times faster than 1 gigahertz. If it can be further developed, its significance is self-evident.
In addition to making computers run faster, graphene devices can also be used in communications and imaging technologies that require high-speed operation. Relevant experts believe that graphene is likely to be first used in high-frequency fields, such as terahertz wave imaging. One of its uses is to detect hidden weapons. However, speed is not the only advantage of graphene. Silicon cannot be broken into pieces smaller than 10 nanometers or it will lose its attractive electronic properties. Compared with silicon, when graphene is divided into a nanometer piece, its basic physical properties do not change, and its electronic properties may also display abnormally.
Research results are being released one after another
Experiments by a research team led by Michael S. Fuhrer, professor of physics at the University of Maryland Center for Nanotechnology and Advanced Materials, show that the electron mobility of graphene does not change with temperature. And change. They measured the electron mobility of graphene between 50 Kelvin and 500 Kelvin and found that regardless of the temperature change, the electron mobility was approximately 150,000 cm2/Vs. The electron mobility of silicon is 1400 cm2/Vs. The transmission speed of electrons in graphene is 100 times faster than that of silicon, so the future semiconductor material is graphene rather than silicon. This will enable the development of higher-speed computer chips and biochemical sensors. They also measured the thermal vibration effect of electron conduction in graphene for the first time. The experimental results showed that the thermal vibration effect of electron conduction in graphene is very small.
The calculation results of researchers Ming Pingbing and collaborators Liu Fang and Li Ju of the Institute of Mathematics and Systems Science of the Chinese Academy of Sciences show that the ideal strength of graphene is predicted to be 110GPa~121GPa. This means that graphene is currently the strongest material known to mankind.
The research team of James Hone and Jeffrey Kysar of Columbia University announced in Science magazine in July 2008 that graphene is the strongest material known in the world. They found that the maximum pressure the graphene sample particles could withstand per 100 nanometers before they began to fragment was about 2.9 micronewtons. This result is equivalent to applying a pressure of 55 Newtons to break a meter of graphene.
If graphene could be made with a thickness equivalent to that of a plastic packaging bag (about 100 nanometers thick), it would take about 20,000 Newtons of pressure to tear it apart. This means graphene is harder than diamond.
It was announced in the "Science" magazine on September 26, 2008 that Cai Weiwei, a doctoral student from the Institute of Physics, Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter Physics, Solid State Quantum Information Laboratory, went to the University of Texas at Austin in the United States. During the campus period, under the guidance of Professor Rodney Ruoff and Researcher Chen Dongmin, high-quality 13C isotope synthetic graphite was prepared, and 13C-graphite was further dissociated into 13C-graphene and its derivative 13C-graphene oxide. Analysis of the material revealed the long-debated chemical structure of graphene oxide.
Low-noise graphene transistor
In March 2008, scientists at IBM Watson Research Center became the first in the world to make a low-noise graphene transistor.
As the size of ordinary nanodevices decreases, the noise called 1/f will become more and more obvious, worsening the signal-to-noise ratio of the device. This phenomenon is "Hooge's law" and is produced by graphene, carbon nanotubes and silicon materials. Therefore, how to reduce 1/f noise has become one of the key issues in realizing nanocomponents. IBM successfully produced a transistor by overlapping two layers of graphene. Due to the strong electron bonding generated between the two layers of graphene, the 1/f noise is controlled. The discovery by IBM Chinese researcher Ming-Yu Lin proves that two-layer graphene is expected to be used in a variety of fields.
In May 2008, Dehill, a professor at the Georgia Institute of Technology in the United States, collaborated with the MIT Lincoln Laboratory to generate hundreds of graphene transistor arrays on a single chip.
At the end of June 2008, Professor Suemitsu Maki from the Institute of Electrical and Communications Technology of Tohoku University in Japan generated a single-layer graphite film, namely graphene, on a silicon substrate. It can achieve high-speed operation of the device without shrinking it, and can be used for example to produce 1012 Hz-level high-frequency devices and super microprocessors per second.
A single-layer graphite film is difficult to make and is a honeycomb graphite structure with a thickness of only one carbon atom. Professor Suemitsu's team controlled the crystallization direction of silicon carbide during formation and the crystallization direction of silicon substrate cutting, and obtained a two-layer graphite film with an area of ??100×150 square microns, with a lattice distortion rate of only 1.7%. Other scientific research teams have used traditional methods with a lattice distortion rate of 20%, which makes them unable to produce devices that can be used in practical applications. Professor Suemitsu's method is to heat the silicon carbide substrate to more than 1,000 degrees under vacuum conditions to remove the silicon and the remaining carbon to form a single-layer graphite film through self-organization.