Researchers succeed in creating a processor using carbon nanotubes instead of silicon
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In recent years, many researchers have attempted to develop higher performance transistors using carbon nanotubes instead of conventional silicon transistors . A research team at the Massachusetts Institute of Technology (MIT) reported that it has successfully solved the problems associated with transistors using carbon nanotubes and displayed ' Hello World '.
Modern microprocessor built from complementary carbon nanotube transistors | Nature
https://www.nature.com/articles/s41586-019-1493-8
MIT engineers build advanced microprocessor out of carbon nanotubes | MIT News
http://news.mit.edu/2019/carbon-nanotubes-microprocessor-0828
A Carbon Nanotube Microprocessor Mature Enough To Say Hello IEEE Spectrum-IEEE Spectrum
https://spectrum.ieee.org/nanoclast/semiconductors/processors/modern-microprocessor-built-using-carbon-nanotubes
Electronic circuits that are the basis of
Carbon nanotubes have high electrical conductivity, and carbon nanotube field effect transistors (CNFETs) are said to be 10 times more energy efficient than silicon transistors. However, there were many problems with transistors using carbon nanotubes, and it was difficult to build a microprocessor that could withstand practical use.
According to the research team, there are three major issues in building transistors with carbon nanotubes. The first point is that if carbon nanotubes are placed on the wafer , the amount will not be uniform and an excessively deposited part will be created, and the second is that carbon nanotubes are divided into two types: semiconductor type and metal type The third is that it is difficult to create P-type and N-type semiconductors for transistors. The MIT research team has devised several solutions to overcome these challenges.
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When making a carbon nanotube transistor, the carbon nanotubes are placed in a solution and then spread out in order to place the carbon nanotubes on a silicon wafer. At this time, although most of the carbon nanotubes are uniform on the wafer, sometimes it becomes a bundle of more than 1000, which prevents the production of large-scale transistors.
Therefore, the research team focused on the fact that the strength of the carbon nanotubes in contact with the wafer by van der Waals force is stronger than the bond between individual carbon nanotubes. It seems that by pre-treating with a chemical that promotes adhesion between the carbon nanotubes and the wafer, only the locations where the carbon nanotubes are excessively solidified were washed away.
In addition, when manufacturing carbon nanotubes, a small amount of metallic carbon nanotubes are produced as a mixture, mixed with most semiconducting carbon nanotubes. Carbon nanotubes used in transistors must have semiconductor characteristics. However, if metal-type carbon nanotubes are mixed in, the performance of the transistors will drop or the operation will stop. To deal with the problem, it is necessary to increase the purity of semiconducting carbon nanotubes to about 99.999999%, but the purity at the time of article creation is about 99.99%.
Therefore, the research team created a solution that would allow the presence of metallic carbon nanotubes, rather than increasing the purity of semiconducting carbon nanotubes. Purity is important because of the noise in the processor logic . Therefore, the research team conducted a simulation to identify logic circuits that are susceptible to noise caused by metal-type carbon nanotubes, and solved the contamination problem of metal-type carbon nanotubes by building a processor with a combination that avoids them.
The research team also developed a technology to build P-type and N-type semiconductors by attaching an oxidized metal on the carbon nanotube layer. In this way, the research team created a transistor using the same carbon nanotubes as before, and succeeded in building a 16-bit microprocessor named “ RV16X-NANO ”.
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The microprocessor developed by the research team uses more than 14,000 carbon nanotube transistors and can execute the RISC-V instruction set. In fact, the research team has reorganized a program to display the classic “Hello World” and “Hello, World! I am RV16XNano, made from CNTs” (Hello, World! I was made from RV16X-Nano, CNT. ) 'Was displayed.
“This is the most advanced chip made by emerging nanotechnology that is promising for high performance and energy efficient computers.” “Silicon has its limits. Carbon nanotubes are the most promising to break the limits of silicon. One of the methods, ”said Emanuel Landsman, a research team.
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