About carbon: electrical properties
Carbon is an element that can have very interesting electrical properties . It is cheap, we find it in mines, and it is used in many things around us, from the lead in a pencil in the form of graphite, to diamonds (carbon with an ordered crystalline structure), to steel (iron + carbon), electrodes in batteries, etc.
Graphite, for example, only conducts current in one direction of its structure, but not in the other, which can also be interesting for certain electrical applications. In fact, depending on the direction in which the current is applied, it can generate enormous resistance and cause very high temperatures. Other forms of carbon, such as diamond, are not conductive at all, which is curious…
The fact that graphite does not conduct electricity in all directions is due to an anisotropic property , meaning that electrons flow through it only in one direction. To understand this, it is important to keep in mind that carbon atoms are arranged in hexagonal layers. Electrical conductivity is much higher parallel to these layers than perpendicular to them:
Parallel to the layers : Free electrons can easily move between carbon atoms within the same layer, due to the strong covalent bond between them. This allows electricity to flow easily in this direction.Perpendicular to the layers : the bond between the graphite layers is weaker, which makes it difficult for free electrons to move between them. This makes the electrical conductivity much lower in this direction, even acting as a dielectric and heating up.
On the other hand, the different forms of carbon also have interesting thermal properties , such as high thermal conductivity, which allows for better heat transfer. However, this will also depend on the way the atoms are arranged, as is the case with electrical properties.
In short, by playing with carbon atoms , very diverse properties can be achieved, something that when applied to chips, such as processors, can be of great help.
Graphene is another possible form of carbon. It can be obtained from graphite, i.e. from the material in a pencil lead… However, while graphite is made up of sheets of atoms, graphene is a two-dimensional material. This means that it is made up of carbon atoms arranged in a hexagonal network in a layer one atom thick.
This thin film has exceptional properties that make it a promising candidate to revolutionize semiconductor chip technology . However, this has been talked about for a long time, just as memristors were presented as the great revolution, and they did not revolutionize anything. With graphene, it is true that for the moment we will have to wait, among other things, because the mass production of graphene is still under development.
Producing graphene is not easy. There are methods as rudimentary as top-down, in which an adhesive tape is used that is stuck and peeled off the graphite to obtain a thin layer of carbon in the form of graphene. A very crude method. A solvent can also be used that is intercalated between the graphite layers and then reduced to obtain the graphene, or it can even be done using a silicon carbide substrate, through epitaxial growth. Other methods called bottom-up involve chemical vapor deposition (CVD) to create graphene in a reactor using caseous precursors such as methane or ethylene, and depositing the carbon on a substrate. Organic precursor molecules, such as cyclohexane or benzene, can also be used to synthesize graphene on a surface…
Notwithstanding the problems associated with this technology, graphene could help future processors in several ways :
Faster, more efficient transistors : Graphene can conduct electricity up to 100 times faster than silicon, which would allow for faster, more efficient transistors in chips. This would translate into electronic devices with higher clock speeds, greater processing capacity and lower energy consumption.Flexible and transparent electronics: It is a flexible and transparent material, which opens up the possibility of creating flexible or rollable electronic devices.Size reduction : This could also be used to increase density, which would allow for smaller, more powerful electronic devices.Chip cooling : Graphene has high thermal conductivity, making it an ideal material for heat dissipation in electronic chips. This could help reduce overheating.
Today, large research centres such as IMEC, universities around the world, etc., are researching graphene for applications in the semiconductor industry. We have seen some examples or experiments such as that of IBM in 2018, which created a functional graphene chip with a 90nm node and capable of reaching 100 Ghz. Samsung, in 2020, also applied the technology to RAM, creating faster and more efficient cells, achieving speeds 10 times higher than a current DDR5. Another example is MIT, which achieved graphene transistors with 100 times lower consumption.
Carbon nanotubes (CNT or Carbon NanoTube) are , as their name suggests, cylindrical structures made up of carbon atoms arranged in a hexagonal network similar to graphene. In other words, it is basically a rolled sheet of graphene.
Producing carbon nanotubes efficiently and cheaply is a problem, as is the case with graphene. There are several methods for doing so, such as:
By arc : with an electric arc discharge between two graphite electrodes under an inert atmosphere. Something that cannot be applied to the semiconductor industry and that produces impurities in the nanotube. Laser ablation : A high-power laser pulse vaporizes a carbon material such as a carbon polymer or graphite, and the vaporized atoms rearrange to form CNTs.
These are still complex methods that are difficult to implement… But, regardless of this, if transistors are made with carbon nanotubes , variable electrical conductivity properties can be achieved, and with applications in which current transistors would be made faster, more efficient and smaller. They could also be used as fast interconnections, or for applications in heat dissipation.
In short, these transistors, in which the drain and source are connected by a nanotube, can reach switching speeds up to 100 times higher than current ones, with energy efficiencies up to 10 times higher, and sizes up to 10 times smaller , in addition to allowing the creation of flexible substrates…