P3.1 - Silicon Diode Temperature Sensor Weakly Sensitive to Magnetic Field

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
P3 - Temperature / Humidity
V. Borblik, Y. Shwarts, M. Shwarts - Institute of Semiconductor Physics, Kyiv (Ukraine), I. Rudney - International Laboratory of High Magnetic Fields and Low Temperatures, Wroclaw (Poland)
720 - 724


At low temperatures, usual diode temperature sensors on the base of silicon are strongly subjected to influence of magnetic fields. The reason is a freezing-out of free current carriers in the diode base that results in hopping conduction via impurities which depends strongly on magnetic field. But if the diode base is doped up to metallic conductivity the freezing-out of free carriers at low temperatures does not occur and the diode resistance is determined completely by resistance of the p-n junction. The current-voltage characteristics of such the diodes measured by us previously in absence of the magnetic field demonstrate predominance at low temperatures of the tunnel current (via certain localized states). Its temperature dependence is well described by the Mott’s law that points to hopping nature of the current flow through the p-n junction region of such the diodes.
Having in view to understand the nature of this hopping conductivity now we have investigated the influence of magnetic field (up to 9.4 T) on resistance of such the diodes at cryogenic temperatures.
We have measured a voltage drop across the diode under passing through it a forward constant current of various magnitudes - 1, 10 and 100 μA (it is just the regime of temperature measuring). At low fields, a negative component is observed in the magnetoresistance of the diode which changes its sign from negative to positive with growth of the field.
After change of magnetoresistance sign its dependence on the magnetic field is quadratic at first but then it comes close to linear one. The negative component decreases with growth of the feeding current.
In connection with passing of the magnetoresistance through zero its value is proved to be extremely low as a whole. In order to assess sensor aspect of the investigated effect we have calculated relative measurement error if temperature of 4.2 K is measured by means of the investigated diode. Up to the magnetic fields of 5 T, this relative error does not exceed of 5%. For comparison, analogous value for silicon diode temperature sensor produced by Lake Shore Cryotronics, Inc. (USA) quoted in the firm catalog reaches (in the most favorable orientation) of 20 %.