NUS Researchers set New Benchmarks for Magnetic Field Sensors

It is not often that one piece of research achieves multiple ground-breaking firsts and garners invaluable scientific insights as well. A team of NUS researchers comprising Dr. Kalon Gopinadhan, Dr. Shin Youngjun, Prof. Antonio H. Castro Neto, Prof. T. Venky Venkatesan, and Prof. Yang Hyunsoo, from the Centre for Advanced Two-Dimensional Materials, the Department of Electrical and Computer Engineering, and NUS Nanoscience and Nanotechnology Institute, has done exactly that with their latest invention in sensor technology.

Prof. Yang and his colleagues, together with Prof. Andre Geim from the University of Manchester, have developed a new type of sensor that leaves those in the market, and laboratories, literally, in the dust. They have also carried out a definitive study of graphene-based MR sensors that hints at their immense promise in developing into the next generation of extremely sensitive sensors.

Their invention utilizes a characteristic property of many materials, i.e. magnetoresistance (MR), in which electrical resistance is changed by an external magnetic field. This very exciting piece of research, spearheaded by Prof. Yang, has just been published (in Sep 2015) in the prestigious journal, Nature Communications, highlighting graphene’s crucial role in making the accomplishment possible.

The significant benchmarks attained by the sensor include extremely high sensitivity to low and high magnetic fields, tunable MR effects that expands its potential scope of applications, very small resistance variations due to temperature, and the ability to act as thermal switches due to heat-related MR effects. In particular, the 2000% MR measured at 400 K (the practical sensor temperature) is a gain of more than 8 times on previously reported laboratory results and easily over 200 times that of most Hall sensors in the market.

When compared to existing silicon-based Hall sensors, the team’s graphene- boron nitride (BN) MR sensor has a much higher sensitivity due to its higher mobility. It is also cheaper to produce since raw material costs for graphene are very low. An added bonus is its very small change in resistance with temperature unlike other sensors in the market.

Another breakthrough came with the finding that the mobility of the graphene multilayers can be partially adjusted by tuning the voltage across the sensor. This is a huge advantage in terms of possible applications over other sensors in the market. The discovery of heat-related MR effects of nearly 90,000% also suggests that graphene-based thermal switches are additional applications to add to an already long list.

This invention is broadly flexible in that other 2D materials such as transition metal heterostructures or other graphene derivatives may work as well including varying the substrates that have been used with graphene in other research.

The MR sensor developed in this research is perfectly poised to pose a serious challenge in a market estimated at USD1.8 billion in 2014 and expected to grow to USD2.9 billion by the year 2020. With sterling credentials matched by its capacity to fill the performance gaps of existing sensors, the potential of this novel device for making an impact is probably very substantial, to say the least.

Some closing words from Prof. Yang sum up this research as: “… an opportunity to understand magnetic and transport properties of few-layer graphene at practical device temperatures of 300–400 K, which has not been reported previously. As we have demonstrated that the field sensitivity and magnetoresistance can be engineered in graphene/boron-nitride heterostructures, our results indicate a promising avenue for magnetic field sensing applications.”