Two years after it was launched, the European Commission’s $1-billion investment in graphene research, The Graphene Flagship, is holding a conference in Manchester, UK, called Graphene Week 2015.
While there’s been a lot of graphene news coming out of the conference, it appears that one advance has everyone a bit stunned. Researchers at Bosch and the Max-Planck Institute for Solid State Research, both in Germany, have developed a magnetic sensor that is reportedly 100 times as sensitive than the silicon variety.
This blog has covered research using graphene in biosensors, chemical sensors and pressure sensors, but we haven’t seen a lot of news about graphene in magnetic sensors. What we have noticed, however, is a lot of research effort devoted to making graphene magnetic. It started two years ago with research out of Spain. That work led to a recent advance in the magnetization of graphene by the U.S. Naval Research Laboratory that could lead to a million-fold increase in storage capacity over today’s hard drives.
Instead of enabling improved hard drives, the work out Bosch labs aims to see what effect two-dimensional materials like graphene could have on magnetic sensors of the kind used in the automotive sector.
The first thing the researchers realized was that top-down approaches for producing graphene, such as chemical vapor deposition (CVD) or exfoliation of graphite, commonly referred to as the “Scotch Tape” Method, would not meet their needs. These techniques were just not going to be scalable enough for a company like Bosch, which is doing this research with an eye towards production in five to 10 years.
For the substrate material, the researchers employed hexagonal boron nitride, a semiconductor with such a wide band gap that it essentially serves as an insulator. The researchers said they chose it for cost considerations as well as its performance.
The graphene sensors are based on the Hall effect, in which a magnetic field focused on a conductor causes a Lorentz force that deflects charge carriers in a current and leads to a measurable voltage. The key performance parameters for a Hall effect sensor are sensitivity, which is based on the number of charge carriers, and power consumption, which depends on charge carrier mobility. One of graphene’s most attractive properties is its extremely high charge carrier mobility, so it would seem to be a fit for this application.
The researchers claim that in the worst case scenario, the graphene-based sensor performs about as well as sensors using silicon as the conductor. But in the best case, the source current for the graphene sensor can be much lower than that needed by the silicon sensor, and the sensitivity of the graphene sensor is two orders of magnitude greater than that of its silicon-based counterpart.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.