Nitride sensors can cope with high temperatures and harmful radiation
Toyohashi Tech researchers have fabricated Hall effect magnetic field sensors which can operate above 400oC.
Under extreme radiation conditions, the gallium nitride-based heterostructures operate with a two-dimensional electron gas.
Silicon and III-V compound semiconductor Hall effect magnetic field sensors are widely used in the electronics industry for monitoring rotation in equipment such as optical memory disks and for banknote authentication in vending machines.
However, the use of Hall sensors for monitoring magnetic fields in outer space and nuclear power stations is more challenging. This is due to large fluctuations in temperature and harmful radiation in these environments. To resolve these issues, the Toyohashi Tech researchers used AlGaN/GaN two-dimensional electron gas heterostructures to fabricate high sensitivity micro-Hall effect magnetic field sensors that are stable at high temperatures and high fluxes of proton irradiation.
They used micro-Hall sensors based on AlGaN/GaN. These devices were stable up to at least 400 oC, whereas sensors fabricated using GaAs and InSb degraded from about 120 oC.
Optical image of 5µm2×5µm2AlGaN / GaN Hall sensor
Temperature dependence of current-related magnetic sensitivity What's more, the electron mobility and two dimensional electron density of the AlGaN / GaN micro-Hall sensors were only slightly affected by a 1x1013cm-2 proton dose at 380 keV.
Variation of Hall voltage with magnetic field with drive current for an AlGaN/GaN Hall sensor before and after irradiation with proton fluence of 1014cm-2
The researchers are actively seeking industrial partners to exploit the robust properties of the 2DEG-AlGaN/GaN 2DEG Hall sensors for operation at high temperatures and in harsh radiation environments.
A potential application included imaging of ferromagnetic domains at the surface of permanent magnetics. Adarsh Sandhu, a lead researcher at Electronics Inspired Interdisciplinary Research Institute, based in Japan, has previously demonstrated the imaging of magnetic domains in ferromagnetic materials with an AlGaN / GaN micro-Hall sensor in a high temperature scanning Hall probe microscope (SHPM).
SHPM images of a bismuth substituted iron garnet thin films at 25–100 °C under an external perpendicular magnetic field Hextof 150 Oe
Further details of this research will be available soon in the paper, "High Temperature Hall sensors using AlGaN/GaN HEMT Structures", by S. Koide et al, Institute of Physics Journal of Physics Conference Series (http://iopscience.iop.org/1742-6596) (in press).
