Credit: © 2007 ACS

The miniaturization of field-effect transistors (FETs) is crucial for nanoscale electronics. However, to increase the current by a factor of ten in conventional FETs, a change in the voltage of at least 60 millivolts is required — and this would generate enough heat to damage a small device. Now, Sayeef Salahuddin and Supriyo Datta at Purdue University in the USA have shown that these limitations could be overcome by exploiting the unique properties of ferroelectric materials1.

A standard FET has a layer of insulating material between the input 'gate' terminal and the main 'drain' circuit. Conventional theory implies that the change in drain current per unit of gate voltage is limited by the capacitance of the insulating layer. Therefore, Salahuddin and Datta suggest replacing the insulator with a ferroelectric layer, which can exhibit negative capacitance. This behaviour is usually unstable, but can be stabilized by placing a normal capacitor in series with the ferroelectric.

If the ferroelectric layer is the correct thickness, it acts as a step-up transformer to amplify the gate voltage. For example, calculations for barium titanate, a ferroelectric ceramic, showed that a 250-nanometre-thick layer could give a four-fold voltage gain. This means that the operating voltage could be lowered well below 60 millivolts for use in tiny devices.