Electricity: measuring and testing – Magnetic – Displacement
Patent
1997-12-11
2000-01-04
Strecker, Gerard
Electricity: measuring and testing
Magnetic
Displacement
324252, G01B 730, G01D 516, G01R 3309
Patent
active
060113901
DESCRIPTION:
BRIEF SUMMARY
The subject matter of the present invention is a sensor chip having resistive layers being dependent on a magnetic field to be used for contactless measuring angles and positions.
The advantages of employing sensor chips, the thin-film resistances of which exhibit the anisotropic magnetoresistance effect are already set out for such measurements for example in a paper by A. Petersen and T. Rinschede "Beruhrungslose Winkelmessung mit magnetoresistiven Sensoren", in Elektronik 6/1994, pages 91-93. A disadvantage of using a single sensor bridge is the highly limited measuring range and the high temperature dependence of the output signal of the bridge, Therefore, sensor chips having two bridges for determining the sine and cosine values of the angle of the magnetic field with respect to an edge of the sensor chip are already disclosed in the Patent Specification DE 43 17 512 and in a paper by A. Petersen "Beruhrungslose Winkelmessung" in Design & Elektronik Sensortechnik, May 1995, pages 64-66. The angle is obtained therein from the ratio of the output signals of both bridges. As both sensor chips are arranged on the same chip the difference of their temperatures is merely minor, and, hence, the ratio of both output signals becomes essentially independent of the temperature. However, a disadvantage of both sensor chips is that the magnetoresistive strip conductors which form the bridge resistances have a form-anisotropy which substantially exceeds the inherent anisotropy of a layer extending to infinity. The higher the total anisotropy of the respective layer strip, the higher is also the deviation of the direction of the external magnetic field from the direction of magnetization within the interior of the layer material. The output signal of the bridge, however, always corresponds to the direction of the internal magnetization. Therefore, deviations occur being observed as corresponding errors of the angle measurement, During evaluation it is extremely complicated to correct these errors because magnetoresistive layer strips with different longitudinal directions and different lengths are used. Therefore, the deviations of each magnetoresistive layer strip are of different magnitudes. Therefore, in the disclosed arrangements, the only possibility for eliminating the errors is to employ magnets having very high field strengths. This means that magnets having considerable volumes of magnetic materials which provide high field strengths, have to be employed and that only relatively small distances between the magnet and the sensor chip are allowed. The first necessity mentioned results in high cost, the latter in narrow assembly tolerances.
A further drawback of employing long magnetic layer strips of different longitudinal directions on the chip surface is solely caused by geometry. The total chip surface cannot be used to accomodate the layer providing the magnetic field dependent resistance due to the angles of about 45.degree. between the strips. Hence, a larger chip surface is absolutely necessary which results in higher chip cost.
The influence of the anisotropy of the layers is substantially eliminated in an arrangement which utilizes the planar Hall-effect in magnetoresistive layers, disclosed in the Patent Specification EP 0 217 478 B1. The disadvantage connected therewith is, however, that only very small resistances of the elements can be implemented. This directly leads to small output voltages of the measuring elements as these voltages are proportional to the applied operating voltages. Additionally, when employing circular thin-film areas having nearly dot-like current feeding points at the circular circumference, the directions of the current lines are not parallel. Hence, a distribution of the current directions always exists with respect to the direction of the magnetization, and the maximum resistance variation of the magnetic layer achievable with parallel current lines is hardly reached. In correspondence with such a reduced resistance variation, the output signal is also reduced. A distri
REFERENCES:
patent: 4533872 (1985-08-01), Boord et al.
patent: 5602471 (1997-02-01), Muth et al.
Andra Wulf
Dettman Fritz
Loreit Uwe
Ellis Garrettson
Institut fur Mikrostrukturtechnologie und Optoelektronik E.V.
Strecker Gerard
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