Increasing the speed and efficiency of electrical devices has traditionally involved reducing device size, but it is becoming increasingly difficult to achieve further miniaturization. One alternative approach is to enhance the efficiency of devices by introducing mechanical components to work alongside electronics. Chengkuo Lee and Wenfeng Xiang from the National University of Singapore1 have now fabricated a nanometer-scale electromechanical switch for integration into electronic devices.

The miniature switch consists of two electrodes bridged by a twisting silicon beam and cantilever assembly. Similar devices with nanowire or nanotube beams have been demonstrated in the past, but while such devices offer fast switching times, they also require high voltages. Devices with larger rectangular cantilever beams, on the other hand, are too slow to keep up with modern electronic devices.

Fig. 1: The miniature electromechanical torsion switch in the ‘on’ state. An applied voltage pulls the cantilever down to the electrode, twisting the torsion spring. The entire device is only a few micrometers across.© 2010 C. Lee

The researchers have now combined the two approaches by forming a silicon ‘T’-shaped structure consisting of a 530 nm-wide torsion beam and a 9 μm-long cantilever (Fig. 1). When a voltage is applied between the cantilever and the electrode underneath, electrostatic force pulls the cantilever downwards to make contact with the electrode. When the voltage is turned off, the cantilever returns to its starting position by the spring action of the torsion beam.

Lee and Xiang found that the voltage required to bend the cantilever downward decreased as the cantilever became larger and the spring became less stiff. By optimizing the dimensions of the cantilever and torsion beam, the researchers were able to tune the switch to turn on with a relatively low ‘pull-in’ voltage of 5.5 V.

The device could be switched between two distinct ‘on’ and ‘off’ states, with conductance a thousand times higher in the ‘on’ state. This ratio could be sufficient for certain data storage applications, but to realize such uses, the device will need to be made more reliable — it was only able to switch six times before the cantilever seized. The researchers believe that the reliability could be improved either by blocking the development of a charged layer between the cantilever and substrate, which they think is the cause of cantilever sticking, or by sealing the device in a hermetic package.

The research team also plans to reduce the operating voltage even further. “We intend to pursue real working devices that can be operated at less than 1 V,” says Lee. “We may also explore the use of intriguing new materials in our switch, such as graphene.”