Researchers from the National University of Singapore (NUS) have developed a hybrid magnetic sensor that is more than 200 times more sensitive than most commercially available sensors. This technological breakthrough could yield opportunities for the development of smaller and cheaper sensors for applications in consumer electronics, information and communication technology, biotechnology and the automotive industry.

When an external magnetic field is applied to certain materials, a change in electrical resistance, also known as magnetoresistance, occurs as the electrons are deflected. The discovery of magnetoresistance paved the way for magnetic field sensors used in hard disk drives and other devices, revolutionizing how data is stored and read.

In the search for an ideal magnetoresistance sensor, researchers have prized the properties of high sensitivity to low and high magnetic fields, tunability and very small resistance variations due to temperature.

Principal investigator and associate professor Yang Hyunsoo of the National University of Singapore’s Department of Electrical and Computer Engineering.Principal investigator and associate professor Yang Hyunsoo of the National University of Singapore’s Department of Electrical and Computer Engineering.The hybrid sensor developed by the team led by Professor Yang Hyunsoo of the Department of Electrical and Computer Engineering at NUS, appears to meet these requirements. Made of graphene and boron nitride, the sensor comprises several layers of carrier-moving channels, each of which can be controlled by the magnetic field. The researchers characterized the new sensor by testing it at various temperatures, angles of magnetic field and with a different pairing material.

"We started by trying to understand how graphene responds under the magnetic field. We found that a bilayer structure of graphene and boron nitride displays an extremely large response with magnetic fields. This combination can be utilized for magnetic field sensing applications," says team member Dr. Kalon Gopinadhan, of the NUS Nanoscience and Nanotechnology Institute and the Center for Advanced 2D Materials at the NUS Faculty of Science.

Compared to existing sensors, which are commonly made of silicon and indium antimonide, the group's hybrid sensor displays much higher sensitivity to magnetic fields. In particular, when measured at 127 degrees Celsius (the maximum temperature at which most electronics products are operated), the researchers observed an increase in sensitivity more than eight times greater than previously reported laboratory results and over 200 times that of most commercially available sensors.

Another breakthrough in this research was the discovery that mobility of the graphene multilayers can be partially adjusted by tuning the voltage across the sensor, enabling the sensor's characteristics to be optimized. This control gives the material an advantage over commercially available sensors. In addition, the sensor showed very little temperature dependence over the range of room temperature to 127 degrees Celsius, making it an ideal sensor suitable for environments of higher temperature.

The magnetoresistance sensor industry, estimated to be worth $1.8 billion in 2014, is expected to grow to $2.9 billion by 2020. Graphene-based magnetoresistance sensors hold significant promise over existing sensors due to their stable performance over temperature variation, eliminating the necessity for expensive wafers or temperature correction circuitry. Production cost for graphene is also much lower than silicon and indium antimonide.

Potential applications for the new sensor include the automotive industry, where sensors in cars, located in devices such as flow meters, position sensors and interlocks are currently made of silicon or indium antimonide. For instance, when there is a change in temperature due to the car's air-conditioner or heat from the sun, properties of the conventional sensors in the car change as well. To counter this, a temperature correction mechanism is required, incurring additional production cost. However, with the team's new hybrid sensor, the need for expensive wafers to manufacture the sensors and additional temperature correction circuitries can be eliminated.

The research team has filed a patent for the invention and plans to scale up their studies and manufacture industry-size wafers for industrial use.

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