Research results in graphene sensors with considerably more sensitivity than silicon for a wide range of applications.
Hosted by The University of Manchester in June, Graphene Week 2015 was awash with outstanding research results, many focusing on the magnetic properties of graphene. A University of Manchester team led by Dr Irina Grigorieva has shown how to create elementary magnetic moments in graphene and then switch them on and off – the first time magnetism itself has been toggled, rather than the magnetisation direction being reversed. This opens a new avenue towards electronics with very low energy consumption.
Elsewhere, Robert Roelver of Bosch reported that company researchers in Stuttgart, together with scientists at the Max-Planck Institute for Solid State Research, have created a graphene-based magnetic sensor 100 times more sensitive than an equivalent device based on silicon.
Bosch has long been involved in sensor technology, notably in the automotive sector. In 2008, the company expanded beyond its pressure, acceleration and gyroscopic motion sensors, to geomagnetic, temperature, humidity, air quality and sound pressure devices, including many for use in consumer electronics devices such as mobile phones, with over. Roelver noted that Bosch has over €1 billion in sales of microelectromechanical sensors.
Bosch has been investigating the use of graphene in pressure, magnetic, humidity, gas and sound pressure devices. The first step was to look at fabrication methods. Bosch has focussed instead on techniques such as the thermal decomposition of silicon carbide, and chemical vapour deposition onto metal surfaces, processes which are likely to be suited to mass production.
Roelver cautioned that graphene-based sensor applications will require 5-10 years before they can compete with established technologies. This is due to the current lack of large-scale wafer-based and transfer-free synthesis techniques. Various substrates have been considered, hexagonal boron nitride in the case of magnetic sensors (Bosch magnetic sensors are based on the Hall effect, in which a magnetic field induces a Lorentz force on moving electric charge carriers, leading to deflection and a measurable Hall voltage). It is high carrier mobility that makes graphene useful in such applications.
Comparing and contrasting materials, Roelver showed that the worst case graphene scenarios roughly match a silicon reference, whilst in the best case is a huge improvement over silicon, with much lower source current and power requirements for a given Hall sensitivity.
In terms of hard numbers, a direct comparison between the sensitivity of a silicon-based Hall sensor with that of the Bosch-MPI graphene device, showed that the silicon sensor has a sensitivity of 70V/A.T, whereas with the boron nitride and graphene device the figure is 7000.