Successful high-voltage vacuum power switch uses a diamond semiconductor

A high-voltage vacuum power switch for smart power grids has been developed by a group of Japanese researchers. In the future, this technology may contribute to a new energy strategy through offshore wind energy, efficient power transmission and more.

As part of problem-solving-oriented basic research sponsored by the Japan Science and Technology Agency (JST), a group consisting of researchers at the National Institute of Advanced Industrial Science and Technology (AIST) and the National Institute for Materials Science (NIMS) succeeded in fabricating a vacuum-based high withstand-voltage power switch and demonstrating its operation. This result was achieved by utilising the features of a diamond semiconductor.

In order to introduce renewable energy in power grids and realise the ‘smart grid’ concept, compact power conversion devices (devices that combine multiple power switches) that make it possible to convert and control voltage, current and frequency are necessary. However, for the power switches developed to date using silicon and similar materials, an extremely large-scale power conversion device had been necessary to withstand high voltages, and this had a been a problem for practical application. Because the withstand voltage (dielectric voltage) of a vacuum is superior to that of semiconductors, which are solids, the development of an innovative vacuum-based power switch that offers an ultra-high withstand voltage, high efficiency and compact size has been expected.

In order to use a vacuum in a switch, an electron emission device that passes a current through a vacuum when the switch is ‘on’ is necessary. This research group clarified the fact that electrons can be freely emissioned into vacuum when a diamond surface is covered with hydrogen atoms. Therefore, the group developed a vacuum power switch in which a diamond semiconductor is used as the electron emission source. In verification of switch operation, the group confirmed that the device functions as a power switch at a voltage of 10 kV. Based on these experimental results, if a vacuum power switch that can withstand voltages as large as 100 kV can be fabricated, high-power conversion devices with a size 10% that of conventional devices are theoretically possible.

In the future, the use of this technology is expected to contribute to realising a new energy strategy in Japan through introduction of offshore wind energy in the seas surrounding Japan, efficient power transmission across the Japanese archipelago, and similar efforts.