Single-electron transistor will enable extremely low power computing
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Single-electron transistors consume much less electric energy than today’s Field Effect Transistors FETs that are the technological foundation of the CMOS technology. The problem with these power-saving devices is that they refuse to operate at normal room temperature; instead they require very low temperatures. Plus, the manufacturing process for Single-electron transistors is not compatible with anything in today’s semiconductor industry. The research project Ions4Set, coordinated by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) aims at changing this situation.
In the SET, a single electron can switch the transistor on or off. The constituting element of such a transistor is a quantum dot that consists of several hundred of silicon atoms, embedded in an isolating layer. This layer in turn is placed between two conducting layers. To enable the SET to work at room temperature, it is necessary that the quantum dot is smaller than 5 nanometres. And the distance between quantum dot and conducting layers must not exceed two to three nanometres; otherwise the electrons cannot pass the transistor. With existing technology it is hitherto not possible to meet these two conditions.
The Icons4Set scientists have a new approach. “Our transistor has the shape of a nano column. In addition, we discovered a mechanism that ensures that in a way the quantum dots create themselves”, explains Karl-Heinz Heinig, the initiator of the project. “We create slim silicon columns with a size of about 20 nanometres. Embedded is a 6 nm strong disk made of silicon dioxide as isolator. If we bombard the nano column with fast, electrically charged particles, silicon atoms are inserted into the isolator. If consequently the structure is heated, the atoms automatically form a single quantum dot located in the centre of the isolator disk. To make this technique repeatable and achieve comparable results in an industrial environment, leading research institutions as well as several large players in the semiconductor industry have joined the research project. These are Globalfoundries, X-Fab and STMicroelectronics.
While French microelectronics research institute CEA-Leti is focusing on manufacturing the nano columns at high precision, the Spanish microelectronics centre CISC in Barcelona will devise a demonstrator that will act as proof-of-concept of the four-year research project. Since the SETs have not enough energy to interact with standard electronic circuits, it also will be necessary to integrate a number of FET-based drivers that enable the SET array to communicate with the outside world.
During the time this article was written, the first meeting of all partners involved in the project took place at the Helmholtz-Zentrum Dresden-Rossendorf. Besides the HZDR, CEA-Leti and CISC, the Fraunhofer Institute for Integrated Systems IISB as well as the Institute of Microelectronics and Microsystems of the Italian CNR and the University of Helsinki (Finland) are part or the team. “We are very optimistic that we will be successful in the end,” said Heinig. The research team was able to build on the findings of earlier projects, and the HZDR has the necessary equipment and experience.
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