Making small sense

Scientists at Southampton University's School of Electronics and Computer Science (ECS) are to develop low-power silicon sensors for biosensing and environmental monitoring applications.

The researchers claim that not only will the new sensors be the smallest on the market, they will have extreme sensitivity and very low power consumption. This will be achieved by integrating single-electron transistors (SETs) and nano-electro-mechanical systems (NEMS) onto a single device.

‘Power consumption is a big issue at the moment as, today, devices use current whether they are in the on or off state,’ said ECS's Prof Hiroshi Mizuta, who is involved with many other European research groups as part of a three-year European FP7-funded NEMSIC (Nano-Electro-Mechanical-System-Integrated-Circuits) project to build the new devices. ‘But the single-electron transistor combined with the NEM device technology will reduce power consumption whatever state the device is in.’

Prof Mizuta and his team will develop the single-electron transistor with a unique suspended silicon nanobridge that will work as an extremely sensitive molecular detector. 'This is the first time that anyone has combined these two nanotechnologies to develop a smart sensor,’ he added.

Speaking from Japan exclusively to The Engineer Online, Prof Mizuta said that, in fact, the researchers planned to develop two kinds of nanosensor devices. Both will be built on silicon-on-insulator (SOI) substrates and both will make use of a thin suspended silicon nanobridge. Only their operational characteristics will differ.

In the first nanosensor device, the suspended nanobridge will be used at the gate of a transistor. Molecules captured on the surface of the nanobridge channel will be detected electrically as they change the conductance of the gate.

In the second nanosensor device, the suspended nanobridge will be used as a moveable transistor gate. When molecules land on the nanobridge, they will change its mass and this change in mass will be detected electrically as a change in the resonant frequency of the gate.

Both the sensing devices will be fabricated using a new electron beam lithography machine, which has been installed at the University's Mountbatten building that opens this month.

The NEMSIC project is headed by Prof Adrian Ionescu of Ecole Polytechnique Fédérale de Lausanne.

Other partners include the Delft University of Technology, Stitching IMEC Nederland, Commissariat à l’Energie Atomique – Laboratoire d’Electronique de la Technologie de l’Information, SCIPROM Sarl, Interuniversity Micro-electronics Center , Honeywell Romania SRL – Sensors Laboratory Bucharest and the Université de Genève.