Graphene sensor plays it cool

Written by: Andrew Wade | Published:

A UK-developed graphene Hall effect sensor has been put through its paces at extreme low temperatures and magnetic field strengths.

Developed by Cambridge outfit Paragraf, the GHS09CC sensor device underwent a rigorous testing regime carried out by Oxford Instruments, whereby it was exposed to a 14T magnetic field and subjected to temperatures below 100mK, closely approaching absolute zero. These temperatures were achieved using Oxford Instruments’ newly released Proteox dilution refrigerator. According to Paragraf, mK-rated graphene sensors will pave the way for more advanced scientific instruments and electronic devices.

“Though there are huge opportunities to carry out fundamental research at these temperature levels, Hall Effect sensors have not been able to offer mK operation until now,” said Ellie Galanis, product owner at Paragraf.

“The tests conducted by Oxford Instruments underline the quality of the graphene substrates we can fabricate for cutting-edge electronic systems, as well as our innate ability to tailor them as customer requirements dictate. There is no other cryogenic temperature Hall Effect sensor that is rated to these operational parameters, showing that we can really differentiate ourselves here.”

According to Paragraf, previous Hall sensor research has had to rely on off the shelf cryo-rated Hall sensors - rated only to 1.5K at the lowest - or expensive custom Nuclear Magnetic Resonance (NMR) probes. These generate a considerable amount of heat, leading to a detrimental influence on the ability to maintain a mK environment. In contrast, the new Paragraf sensor generates six orders of magnitude less heat, increasing performance.

“High-resolution field measurement at ultralow temperatures and high magnetic fields has always been a challenge” said Benjamin Bryant, senior development engineer at Oxford Instruments.

“Conventional Hall sensors can suffer carrier freeze-out at mK temperatures, and even if they could still function their heat dissipation is much too high. Graphene sensors give us and our customers the opportunity, for the first time, to monitor high magnetic fields in-situ in ultra-low temperature experiments.”

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