For over 15 years, researchers have explored ways to develop electronics using 2D materials. While graphene has been at the center of research efforts, until recently, no methods for manufacturing graphene have been suited for commercialization.
This may no longer be the case with UK-based company Paragraf entering the scene as of 2017. Since spinning out of Cambridge University, the company has developed the world’s first process for creating graphene on a semiconductor wafer, effectively bringing graphene-based electronics out of academia and into the industry.
GHS01AT graphene Hall sensor. Image used courtesy of Paragraf
Now, the company is bringing the “world’s first commercial graphene Hall effect sensors” to market. The All About Circuits team spoke with Ellie Galanis, product owner of Paragraf’s new line of Hall effect sensors, to hear about the news firsthand.
Of all of the 2D materials, graphene has been arguably the most intensely studied for the past decade—and for good reason. “Graphene is incredible in that you have something that is just an atom-thick layer of carbon,” Galanis says. “There’s barely anything there, and yet it does incredible things.”
Because graphene is only one atom thick, it promises a day of electronics that are flexible, transparent, and immune to the effects of stray magnetic fields—crucial for developing high-resolution Hall effect sensors.
Electron mobility of graphene vs. other materials. Image used courtesy of MIT
However, the benefits of graphene go beyond its dimensionality. Graphene also has an electron mobility of 2.5×10^5 cm−2 V−1 s at room temperature, a number 200 times higher than silicon. Additionally, graphene also offers an extremely high thermal conductivity of 4000 Wm−1 K−1, which also trumps silicon. Together, these two factors make graphene an energy-efficient conductor that can operate over a very wide range of temperatures, including cryogenic temperatures.
Because any field components in the same plane as the graphene itself aren’t seen by the sensor, graphene-based GHS offer precise measurements of perpendicular field components, which in turn results in high-resolution.
Any one of those properties would make graphene very interesting in terms of how it could transform electronics,” Galanis notes. “But the fact that this one material has it all built into one is what makes it very interesting.”
Previous Obstacles to Graphene Wafers
If graphene is such a “wonder material,” why hasn’t it been commercialized for sensors and solid-state electronics? Galanis explains that at the laboratory scale, researchers typically produce graphene by growing it on a copper substrate.
However, this technique of growing graphene on a conducting base renders the material useless for electronics. Researchers must extract the graphene from the copper by coating the material in polymer and etching away the copper before placing the graphene onto a substrate of choice. The problem is, the final graphene material is then contaminated with the original copper.
The challenge of transferring graphene off a copper base renders the material useless for electronic devices. Image used courtesy of Paragraf
Additionally, this manual process can be quite tedious, making it impossible to scale graphene production.
Paragraf claims to have cracked the code of scalability by growing the graphene directly onto a semiconductor wafer, essentially absolving the need for any cumbersome transfer techniques. The company conducts all of its own research, design, and manufacturing in-house at its Cambridge facility.
New Graphene Hall Effect Sensors
Paragraf’s new graphene hall effect sensor (GHS), the GHS01AT, performs like very expensive magnetic field sensors in a much smaller, cheaper, and lower-power device. The company says it is also especially resistant to radiation, high frequency, and high voltage.
The sensor achieves a resolution <0.2 ppm, consumes power on the magnitude of picowatts, and withstands temperatures up to 250°C. Yet, this device is comparable in size and cost to a lower-end, solid-state sensor. Still, Galanis compared the magnetic sensing performance of the new GHS to fluxgate magnetometers or NMR probes.
Paragraf GHS specs. Image used courtesy of Paragraf
The GHS is built with design ease in mind. The device is a four-terminal IC, operating with an input current and a voltage readout as an output.
GHS Array Starter Kit
In addition, Paragraf is releasing a GHS Array Starter Kit, which will allow users to test batteries by collecting data from eight sensors at once. Testers can position sensors at various points on the cell and simultaneously monitor what’s going on in a cell or pack of cells.
Galanis explains that this testing tool could provide great value for developers repurposing battery cells that have been used in electric vehicles. To screen these cells for quality control, researchers currently explore battery chemistry, format, form factor, and cell age to detect hotspot formation before it becomes a problem.
GHS Array Starter Kit. Image used courtesy of Paragraf
Using an array of GHS sensors, developers can take an image and quickly assess whether there are indications of hotspot formation. If warning of these hotspots are present, developers might then build graphene Hall sensors into battery packs to provide alerts of early failure.
Graphene Hall Sensors Take on Battery R&D
Paragraf feels these new GHS show promise across several industries, including Tier 1 automotive manufacturers, aviation supply chains, medical systems manufacturers, and scientific laboratories.
The primary use case of the GHS01AT is battery R&D testing and monitoring. Graphene Hall sensors are uniquely able to measure the currents blowing in battery cells (in the μT to mT range).
“No other magnetic sensor can measure this full range to the required resolution, and that opens up really exciting opportunities for battery cell analysis,” Galanis remarks. “Our graphene Hall sensor can therefore provide a faster, more direct measurement of cell current density and internal resistance.”