Redefining Hall-Effect sensors with graphene: Page 2 of 5

false measurement signals being produced that emanate from the in-plane magnetic field component, rather than the perpendicular one; referred to as the ‘planar Hall Effect’. Such false signals interfere with the real signals and give the impression that there are additional magnetic poles present - which is of course not actually the case. Referred to as ‘pseudo-multipoles’, these will mean that measurement accuracy is impacted upon. Though the real signals and the false signals can be separated from one another using additional circuitry, this will add significantly to system complexity and power consumption, limit the operational temperature range and push up cost. Other downsides associated with conventional Hall-Effect sensors include a fairly limited dynamic field range and measurement bandwidth, plus a low measurement resolution (which is fundamentally limited by thermal drift and a high thermal noise floor).   

As graphene is a two-dimensional (2D) material, consisting of just an atom-thick monolayer of carbon, it is not susceptible to the in-plane field component and it displays a very low thermal noise floor. Hence using it in magnetic field measurement enables significantly more accurate results to be derived. It is also worth noting that the thermal stability of graphene mitigates thermal drift. Although certain organisations have demonstrated graphene-based Hall-Effect sensors, they are still a long way off offering support of a fully scalable production process.

Graphene Production

It must be acknowledged that the current most common methods for fabricating graphene are not very well aligned with high-volume commercial-grade electronics production requirements. There are basically two main options. The first method is exfoliating graphite. This can deliver good quality graphene, but it is typically over a very small area, cannot be customised to fit with specific end use requirements and can be multi-layered and non-homogeneous. These attributes seriously limit its effectiveness in a microelectronics context.

The other method is to synthesise graphene on some form of metal