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A high-bred transistor made of graphene

High switching speed with gentle production method

Christian ⋅ memory to silicon can be said much good. Not for nothing is the preferred material of the semiconductor industry. To be desired, however, the low mobility of its electrons. It is the reason that silicon transistors are not very fast. Where high working frequencies are in demand - such as the reinforcement of high-frequency signals in wireless communication - is one reason to semiconductors such as gallium arsenide or indium phosphide, which are distinguished by a high mobility of electrons. The competitors of the silicon itself, however, sits a competitor in the neck. Researchers at the University of California at Los Angeles (UCLA) have presented a transistor made of graphene, the inferior to the fastest transistors in anything.

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graph is a form of carbon, which consists of a single atomic layer of graphite. Six years ago it was the first time, researchers succeeded in graphene flakes with a tape from a graphite block to withdraw and transfer them to a support. In examining the flakes turned out soon, which has excellent properties graph. Wakes you high mobility of its charge carriers hope to be able to build ultra-fast transistors.

In fact in 2007 the first graphene transistor was presented. This was followed in rapid succession. At the end of 2008, already the first transistor, which was operating in the gigahertz range. Earlier this year, cracked Phaedon Avouris and his colleagues at the IBM Watson Research Center in New York the 100-GHz mark.

The graph of transistor Xiangfeng Duan and his colleagues at the UCLA breaks the record now. The cutoff frequency - this is the frequency of the signals, the transistor can reinforce just yet - is 300 gigahertz. He is as fast as comparable transistors made of gallium arsenide and indium phosphide. If one considers that the first graphene transistor was produced just three years ago, was this a remarkable result, Frank Schwierz place from the Technical University of Ilmenau. Transistors made of gallium arsenide and indium phosphide were needed for the same development for nearly three decades.

The key to success is the special production method, the researchers at UCLA have chosen. The lithographic process by which the semiconductor industry typically fabricated transistors, can in principle be transferred to graphs. Because graphene is as thin but there are often defects that may destroy the excellent qualities of the material in part.

The researchers came up with something so different. They placed first nano-wires with a conductive core and an insulating jacket and her medal winner this on the graphene layer. Then was a thin layer of platinum deposited on the graph. By just 140 nanometers thick nanowire the continuous platinum layer has been lost. Thus, two separate areas, which formed two of the electrodes of the transistor. The nanowire itself was the third electrode can be controlled by the current flow in the underlying graphene layer. The researchers were able to convince them that the mobility of charge carriers in graphene affected by this kind of production actually no.

Schwierz sees the work of California researchers a big step forward. However, he is under no Cause for euphoria. The new manufacturing process is optimal while for each transistor. He fears, however, that it is less likely to produce a large number of transistors. Avouris shares these doubts. In his eyes there is no alternative to the established lithographic methods of the semiconductor industry when they wanted to manufacture integrated circuits in graphs.

¹ Nature, online publication from 1 September 2010.


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