Graphene-based oscillator reaches the ultrahigh-frequency band

Ars Technica : Graphene is not a natural semiconductor, but it is attractive for use in electronics because it is only one atom thick and still lets electrons move through it. Some devices have been made using graphene, but they tend to perform at low levels because of current leakage. One such device is a ring oscillator, a circuit made of an odd number of NOT gates arranged in series, where the last gate feeds into the first, and the output is the opposite of the input. The frequency of the oscillations in the output can be used to measure the effectiveness of the circuit, and previous graphene ring oscillators have operated in the MHz frequency. A new ring oscillator, created by an international team of researchers, has exceeded 1.2 GHz, which lies in the ultrahigh-frequency band used for TV broadcasting. To build the device, the team grew the graphene parts of the circuit via chemical vapor deposition and varied the size of the circuit features from 1 to 3 µm. They found that the smallest features resulted in the highest frequency. They then combined the oscillator with a frequency mixer also made from graphene. Although the device experienced fewer voltage fluctuations than similar silicon devices, it still suffered from current leakage and slower speeds, which the researchers blamed on other aspects of the setup. By fixing those things, the team expects they can make versions of the devices that operate at hundreds of GHz, which could find use in specialized applications.