Electronic components have finally come into practical use with carbon nanotubes that have been discovered for more than 20 years and microcarbon materials such as graphene that have been discovered for 10 years. In addition to recent diamond semiconductors with significantly improved performance, "carbon electronics" will dramatically change the form of electronic components and electronic circuits.
"My dream is to replace silicon (Si) with carbon (C), to achieve full carbonization of all electronic circuits made of carbon", "the bronze (Cu) era 3000 years ago, and the iron (Fe) era in the first half of the 20th century. This is followed by the Silicon Age, and the future will be the Carbon Age."
A carbon material researcher said this about the meaning and goals of the research. In particular, the full carbonization of electronic circuits can be said to be the consensus of carbon materials researchers. Today, this dream is moving towards achieving progress. If full carbonization becomes a reality, electronic products will be lighter and stronger than they are now, and flexible products can achieve ultra-high performance, and the price will be greatly reduced.
Hon Hai Development, Huawei adoptedThe trend of carbonization seems to move from the periphery of the electronic product to the center. A carbon fiber reinforced resin-based composite material (CFRP) is often used for a casing material such as a personal computer. Its biggest advantage is that it is light and strong.
In the interior of electronic products, although the use of carbon as a conductive material has not progressed, in the middle of 2013, it has finally begun to be put into practical use in touch panels and solar cells. The touch panel is equipped with a smartphone that was launched by China Huawei Technologies Co., Ltd. in May 2013.
The developer of the touch panel is CNH, a group company of Taiwan Hon Hai Precision Industry in mainland China. A tubular carbon material, carbon nanotubes (CNT), is used for a high degree of transparency and electrical conductivity.
Remarks:
Carbon nanotubes are tubular carbon materials. A film (graphene) in which carbon atoms are connected in a honeycomb shape is further formed into a tubular shape. The diameter of the tube is as fine as 0.4 nm to 50 nm. According to the difference (chirality) of the method of winding a film into a tube, it is classified into a metal type and a semiconductor type. The band gap of the semiconductor type varies depending on the diameter. Carbon nanotubes were discovered in 1991 by Professor Yukio Iida, a professor at the Graduate School of Science and Engineering at the University of Minnesota and a special researcher at NEC.
In the case of solar cells, a conventional football-like carbon material called fullerene* has been used as an n-type semiconductor. After long-term research and development, Mitsubishi Chemical began mass production in 2013 and began sampling.
Fullerene is a general term for spherical or ellipsoidal materials formed by the interconnection of carbon atoms constituting a five-membered or six-membered ring. A material consisting of 60 carbon atoms in total is called C60. The connection between the five-ring and six-ring of the C60 is the same as that of football. The material was discovered in 1985 and three discoverers received the 1996 Nobel Prize in Chemistry.
A powerful candidate for the post-silicon eraNot only that, but materials and components that have been developed and are only waiting to be listed have emerged one after another. Capacitors, memories, various high-performance sensors and other components have also been developed using thin film carbon materials such as CNTs and graphene*. The performance is very high, and if the mass production cost of the material is reduced, there are many development cases that can be put into practical use immediately.
Remarks:
Graphene = six carbon atoms forming a six-membered ring which is then joined to form a honeycomb film. It is also the basic unit that constitutes graphite. The basic unit was recognized in 1962, but it was separated from graphite in the form of impurities-free in 2004. It is realized by mechanical peeling method of tape transfer. The separation was achieved, and two people who identified a large number of special physical properties won the 2010 Nobel Prize in Physics.
The practical use of diamond semiconductors is also under consideration by researchers. It is intended to use only vacuum tubes. For example, high-voltage control components for power system control and TV towers.
Next, the technology that can be called the core of full carbonization, high-performance ICs and microprocessors that use carbon materials to exceed the silicon limit is also seen. At present, CNT transistors have been integrated, the original microprocessor has been prototyped, and the work has been confirmed.
IBM says it is possible to achieve transistor integration comparable to current high-performance microprocessors using CNT transistors and existing semiconductor fabrication processes. We are promoting development with the goal of achieving practical use in the first half of the 1920s.
High material potentialCarbon materials are receiving attention, and there are two main reasons for the goal of full carbonization. (1) The basic characteristics of carbon materials are much higher than other materials, (2) carbon is a common element, and the procurement cost is low.
Regarding (1), it is much higher than other materials in terms of electrical properties, thermal conductivity, and mechanical properties. In terms of electrical properties, the carrier mobility of single-layer CNTs and graphene is theoretically 100,000 to 200,000 cm 2 /Vs at room temperature, and the measured value is also 30,000 cm 2 /Vs, which is 20 to 100 times that of silicon. Resistance to high currents is also as high as 1000 times that of copper (Cu).
Thermal conductivity is also very high compared to other materials. For example, the thermal conductivity of CNTs and graphene is 20 to 30 times that of silicon, which is about 10 times that of copper (Cu) and silver (Ag), and is about twice as high as that of diamonds with the highest thermal conductivity.
In terms of mechanical properties, the breaking strength is about 20 times higher than that of steel, and the hardness is also equivalent to or higher than that of diamond. The specific surface area is 1300 to 2600 m 2 /g, which is the lightest among the materials of the same surface.
Potential for light-receiving componentsThe optical properties of CNTs and graphene are also high. Both are direct transition type, that is, materials that are very easy to emit light, and silicon is the opposite, which is a material that is difficult to emit light. Graphene also has the characteristic that the electromagnetic wave absorption rate is not affected by the frequency.
Moreover, graphene has many properties not found in other carbon materials. For example, it has extremely high barrier properties, does not pass through erbium atoms; has magnetic properties due to different shapes, etc. 2).
Note 2) In addition to the geometric phase Berry phase, the effective mass of electrons on graphene is zero like photons.
Regarding (2) carbon as a common material, it is expected to significantly reduce costs compared with silicon-based electronic components. This is because the cost of carbon materials is inherently low and the manufacturing equipment can be greatly simplified. To be extreme, even a pencil can be a manufacturing device. Writing with a pencil is like painting a graphene. There are actually examples of making batteries and sensors with pencils.
It takes time to develop manufacturing technologyAlthough these materials have very high potential, they have not been used in the electronics field so far. The discovery of CNT has been more than 20 years, and graphene has been found for 10 years. Diamond has a long history, but it has always been in an "unknown state."
The reason is that there is no material synthesis technology and electronic component manufacturing technology that can exert such high potential. In particular, in the case of a synthetic material, there is a problem that the purity is low and the crystal defects are large, and mass production is extremely difficult. The refining costs for obtaining high quality CNTs and graphene are very high, and the final price will reach several hundred thousand to several million yen per gram.
There are also many problems in the use of carbon for electronic components. The synthesized single-layer CNT has a diameter of 0.4 nm to several tens of nm, and the graphene has a thickness of only about 0.3 nm per atom, which is difficult to handle. Moreover, there are also deep problems in the use of transistors, such as a single-layer CNT generally in a state in which a metal type and a semiconductor type are mixed, graphene cannot be directly used as a semiconductor, and the like.
The application of carbon materials has suddenly grown explosively in recent years because of the great progress made in this material synthesis technology and the technology of electronic component manufacturing technology. Although the research and development of carbon materials is still in the process of research and development, the high potential of carbon materials has begun to emerge.
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