SENSORS, TEST & MEASUREMENT | GRAPHENE
depth. These false signals, together
with the non-linear response to
the eld strength, increase the
measurement uncertainty and thus
limit the application of Hall sensors.
Separating the true signals from the
systematic errors is a complex and
time-consuming process.
The Hall effect sensor from
Paragraf solves these problems
because the active sensing
component is made of atomically
thin graphene, which is therefore
two-dimensional, and hence truly
only senses magnetic elds along
one direction; giving a negligible
planar Hall effect. This enables the
true perpendicular magnetic eld
value to be obtained, allowing for
higher precision mapping of the local
magnetic eld.
“Using Hall effect sensors without
planar effect would open the door to a
new mapping technique by mounting
a stack of sensors on a rotating shaft.
The compelling advantage would
be measurements of the harmonic
content in accelerator magnets almost
point-like along the magnet axis”,
commented Stephan Russenschuck,
head of the magnetic measurement
section at CERN.
One of the other key properties
of Paragraf’s Hall effect sensor
is its wide temperature range
from +80°C down to cryogenic
temperatures of 1.5 Kelvin. For CERN,
this means that elds inside the
superconducting magnets could be
measured with high accuracy, using
sensors operating in liquid helium
temperature ranges (below -269 °C, 4
Kelvin, -452 °F) where the calibration
of sensors is less than trivial.
Based near Cambridge, Paragraf
was a spin-out from the Department
of Materials Science at Cambridge
University. At its custom R&D facility,
it produces the highest-quality
large-area graphene, and develops
step-change graphene-based
technologies utilising its expertise
in thin lm materials production;
solid state structure and device
processing; and novel material
product application
CERN’s Magnetic Measurement
section is looking to perform more indepth
tests on the Hall effect sensors,
with the eventual aim of using them
to build a novel mapping system for
magnetic elds.
Paragraf has perfected a
proprietary process for depositing
single-atom thick, two-dimensional
materials, including graphene,
directly onto silicon, silicon-carbide,
sapphire, gallium-nitride and
other semiconductor-compatible
substrates. The contaminationfree
technology is scalable, and
compatible with existing electronic
device manufacturing processes.
Serving the sensor, energy
harvesting and semiconductor
markets, Paragraf has developed
its own Hall-Effect Sensors for
measuring magnetic elds in
demanding environments. It is now
partnering with electronic device
makers to enable them to take
advantage of the unique properties of
graphene.
Paragraf graphene is directly
compatible with existing electronic
device processing and production
lines, enabling readily scalable
graphene electronic device
production. Equally, Paragraf’s ability
to highly functionalise graphene
offers the potential for new energy
harvesting ideas. These include using
other environmental interactions
and forces to create novel energy
generation approaches.
The process enables graphene
to be produced directly onto
semiconductor-compatible
substrates such as silicon,
silicon-carbide, sapphire and
gallium-nitride. It does not
require catalytic formation of the
graphene so eliminating metallic
contamination and allows synthesis
of large areas of the material (up to
8” diameter to date).
Graphene’s high transparency
(only one atomic layer thick),
outstanding exibility, mechanical
strength and exceptional conductivity
make it particularly suitable for
use in electronic device surface
applications, such as interactive
human interfaces (touchscreens);
exible mobile devices; surface
contact for SSDs; and ITO
replacement.
Full coverage with either pristine,
functionalised or multi-layer
graphene produces a surface with
all the properties required for nal
product application. This combination
of bene ts eliminates several
processing requirements – increasing
productivity while reducing cost.
Paragraf and CERN will also
be releasing a joint white paper
communicating the work to date in
more detail and showcasing the lack
of planar Hall effect in Paragraf’s
sensors, as well as detailing its high
performance across a range of
magnetic elds.
Paragraf’s graphene Hall effect
sensors are available to lead partners
in small volumes. !
22 WWW.EUREKAMAGAZINE.CO.UK | JULY 2020
/WWW.EUREKAMAGAZINE.CO.UK