As computer microcircuits get smaller, faster and more complicated, they also get hotter. And because this scaling process has been going on for decades, the dissipation of excess heat is one of the biggest challenges facing modern electronics. By manipulating only a single elementary charge, single-electron transistors offer the potential of much lower power consumption. However, their development has so far been largely restricted to devices that are not compatible with standard fabrication techniques and which only work well at low temperature. Jung B. Choi and co-workers at Chungbuk National University in Korea, in collaboration with colleagues at Hokkaido University in Japan and the University of Cambridge in the UK, have now demonstrated a silicon single-electron transistor produced using standard fabrication techniques and which operates at room temperature.1

Fig. 1: Five single-electron transistors integrated onto a single chip. The silicon Coulomb islands are located under the gate structure where it intersects the source–drain contact lines.

The researchers’ new transistor is based around a small sphere of silicon, known as a ‘Coulomb island’, only a few nanometers across. It is connected by silicon nanowires to source and drain electrodes, and is wrapped by a vertical (or ‘fin’) silicon gate (Fig. 1). The island is so small that any electrons injected onto it from the electrodes are strongly repelled from other electrons on the island due to their close proximity. This means that adding charge to the island requires a relatively large amount of energy, resulting in a series of pronounced peaks and valleys in the current through the device as the electrode voltages are varied.

Although room-temperature single-electron transistors have been demonstrated previously, the device developed by Choi and his co-workers has better charge stability and a comparatively large ratio between minimum and maximum current. This pronounced single-electron behavior results from the small size of the island, as well as the intimate contact between the island and the vertical gate. The team exploited these characteristics to demonstrate a novel logic circuit that allows for multiple bits to be addressed at once.

The performance and manufacturability of the device moves single-electron transistors closer to industrial feasibility. Besides reducing the power consumption of computing devices, this technology could find use in a variety of other applications, says Choi. “We are studying the application of the single-electron transistor to biological sensors, artificial intelligence and quantum computing.”