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Ultra-low-power graphene transistors achieve clock speeds up to 100 GHz

Ultra-low-power graphene transistors achieve clock speeds up to 100 GHz

2019-05-06

For years, scientists and engineers have been trying to find a good way to "use smaller, more efficient, two-dimensional graphene materials." Now, scientists have designed a graphene transistor that is ultra-low power and is expected to eventually raise the processor clock rate to an alarming 100 GHz. Traditional transistors allow electrons to be excited by an energy source, skip energy barriers and switch to another state. Although this method works very well, it is difficult to significantly improve in energy efficiency.

The cross-section of the graphene bilayer's electric field depends on its DoS.

In contrast, the tunneling transistor, which uses the quantum tunneling effect to skip the energy barrier (instantaneous movement), consumes less energy than the standard transistor. The problem is that the current on the other side of Tongda is too small, so it is still far away from the actual application.

But now, the scientists of the Moscow Institute of Physics and Technology (MIPT) have found a way to increase the tunneling current, which is the two-dimensional structural material that is standing by the industry—graphene.

The figure above shows a layout of a graphene bilayer (TFET/tunnel field effect transistor).

Although it is just a sheet of carbon atoms, it has some unusual electronic properties. In this case, the scientists built a model of a graphene bilayer and found that its electronic energy range was somewhat strange.

The shape of the double-layered graphene band is much like a "Mexican hat" rather than the "parabolic shape" used by most semiconductor production. The significance of this is that the electron density on the edge of the "hat" seems to be approaching infinity (also known as van Ho singularity).

The front-gate dielectric layer is 2 nm of zirconium dioxide, the latter is 10 nm of silicon dioxide, and the source/row and control grid are separated by 5 nm and 10 nm, respectively.

Just by applying a small voltage to the transistor gate, a large amount of electrons can penetrate the tunnel at once (the current changes drastically and breaks through the energy barrier). The result is the same as a standard transistor, except that the required voltage is much smaller.

Dmitry Svintsov, one of the authors of the paper, said: "This means that these transistors have less energy requirements when switching states, and the chip's power consumption, heat generation, and associated cooling requirements are also reduced, even if the clock frequency is significantly increased. No additional heat dissipation."

Most of the "effective mass values" are in InAs.

Double-layered graphene transistors can also skip complex “chemical doping” steps (which must be done to produce traditional transistors to extend the energy band of semiconductors), but can achieve the same results as conventional transistors through “electron doping”. (Including side effects).

The researchers specifically explained the "Mexico brim", saying that there were many important events in this process, but it was difficult to measure before. However, by using a better substrate (base material for creating double-layered graphene samples), Vanhof's singularity can be experimentally verified for the first time.

The electron density was maintained at a fixed 4×10^13 cm^-2 with a nominal energy gap of 0.3 eV.

Ultimately, the transistor can reach operating voltages as low as 150mV (compared to 500mV for conventional silicon transistors), and double-layer graphene is expected to be an effective way to significantly improve computer performance.

Svintsov said: "The power is low, and the temperature of electronic components is also low, which means that we can make the chip run at a very high frequency - not GHz-level improvement, but dozens of times."

The experimental data obtained at the temperature of 80K are the corresponding feature points in the strip chart.

The team's research papers have been published in the recently published Scientific Report journal. Interested users can poke here for more detailed (PDF) documents.

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