Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1995-01-31
1996-05-28
O'Shea, Sandra L.
Electricity: measuring and testing
Magnetic
Magnetometers
32420712, 338 32R, G01R 3302, G01B 714, H01L 4302
Patent
active
055215017
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
As is generally known, the measurement of magnetic fields of a low intensity such as, for example, the earth's magnetic field, is possible with sensors utilizing an anisotropic magnetoresistive effect. But when large temperature changes occur, considerable problems arise because of a quite significant zero drift, in spite of a sufficient magnetic field sensitivity.
One method for the eliminating zero drift for magnetoresistive sensor bridges is described in the Technical Information 901 228 of Philips Components. The magnetoresistive sensor bridge is placed in a wound coil. Short current pulses of alternating direction through the coil generate a sufficient magnetic field to set the self-magnetization of the magnetoresistive film strips in the corresponding direction. Since the sensor signal changes its polarity with the reversal of the magnetization direction, the drift of the sensor bridge is also eliminated when the magnetic-field-proportional alternating component is separated from the steady component, which contains the zero voltage of the sensor bridge. But the production of such coils is expensive. Their inductance limits the measuring frequency. Adjusting the sensor elements in the coil is an expensive step, in particular when all three magnetic field components in the space are to be measured with an arrangement.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a magnetic field sensor having minimal zero drift, which can be cost-effectively produced entirely in thin-film technique, and in which limitations in the measuring frequency are not caused by the sensor element.
The above and other objects are accomplished according to the invention, in its simplest case by the provision of a single magnetic-field-dependent resistor comprising one or a plurality of magnetoresistive film strips on a highly-conductive thin-film conductor strip disposed perpendicular to the longitudinal direction of the magnetic-field-dependent resistor in an insulated manner. The highly-conductive thin-film conductor strip, however, is provided with a meandering structure. To create a resistance under current flow, in spite of the meandering strips of alternating magnetic field direction which are disposed adjacent to each other with the resistance changing equidirectionally in all subranges under the influence of a field that is to be measured, the magnetoresistive film strips are divided into regions having Barber pole structures with an angle of inclination that is opposite to the longitudinal direction of the strip. Advantageously, the meandering of the highly-conductive thin-film conductor strip results in the fact that only a little current is needed for the reversal of the direction of magnetization. Furthermore, the stray magnetic field existing outside of the sensor chip is very low because the magnetic fields of the meandering strips that are disposed adjacent to each other largely cancel each other because of their opposing direction. Thus, the magnetic field sensors can be operated in immediate proximity to each other. For that same reason, the remagnetization conductor also has a very low inductance, so that limitations of the measuring frequency due to the inductance no longer occur.
When the magnetic field sensor is operated with a magnetoresistive resistor, the latter is fed with a constant current. The voltage at the magnetoresistive resistor is measured as an output signal. Following a current pulse of a certain direction through the highly-conductive thin-film conductor strip, the self-magnetization in the areas of the magnetoresistive resistor is set in a certain manner. In this state, the magnetic field that is to be measured causes an increase of the resistance value of the magnetoresistive resistor. This means that the output signal is greater than in the case without a magnetic field. If a current pulse of opposite direction to the previous pulse is now fed into the highly-conductive thin-film conductor strip, the directions of the self-magnetizatio
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Ueda et al.: "AC Bias Type Magnetoresistive Sensor". In: IEEE Transactions n Magnetics, vol. 26, No. 5, Sep. 5, 1990, New York, NY, pp. 1572-1574.
Technical Information 901 228 of Philips Components Dec. 28, 1990.
Dettmann Fritz
Loreit Uwe
Institut fuer Mikrostrukturtechnologie und Optoelektronik e.V.
O'Shea Sandra L.
Phillips Roger
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