The present invention relates to a sensor element and a gradiometer assemblage for measuring magnetic field gradients, as well as a method for measuring magnetic field gradients using a sensor element or a gradiometer assemblage.
Magnetic sensors are widely used in motor vehicles, for example as rotation speed sensors on the wheel, as rotation speed or travel transducers for the motor control system, or as steering angle sensors for vehicle dynamics control systems. Magnetic sensors are also used in current sensor technology, for example for electrical battery management of motor vehicles. The problem occurring in this context is that the currents which occur are very different, so that the sensors must detect magnetic field gradients over at least five orders of magnitude; and that no technology has hitherto been available that can cover this measurement range with one sensor element. A cost-intensive assemblage of multiple sensors covering different measurement ranges has therefore hitherto been necessary.
Magnetoresistive sensor elements based on giant magnetoresistive (GMR) technology and anisotropic magnetoresistance (AMR) technology, which operate on the principle either of coupled multiple-ply layered systems or spin-valve layered systems, and gradiometer assemblages constructed therewith, are fundamentally known from the existing art. Reference may be made in that context, for example, to German Patent Application No. 101 28 135.8, in which magnetoresistive layered assemblages and gradiometers having such layered assemblages based on GMR or AMR technology are explained in detail. An overview of magnetoresistive sensor elements is also described by U. Dibbern in “Sensors—A Comprehensive Survey.” edited by W. Göpel et al., Vol. 5, Magnetic Sensors, VCH-Verlag, Weinheim, 1989, pp. 342-380.
An object of the present invention is to make available a sensor element and a gradiometer assemblage with which magnetic field gradients can be detected over the widest possible measurement range using a single sensor element. An object is to measure magnetic field gradients, using a sensor element or gradiometer assemblage of this kind, over at least five orders of magnitude at typical magnetic field strengths of between 1/T and 30 mT, in particular from 1/T to 10 mT.
An example sensor element and example gradiometer assemblage according to the present invention have, as compared to the existing devices, the advantage that magnetic field gradients can be detected therewith over a very wide measurement range. It is additionally advantageous that with a plurality of magnetoresistive layered assemblages, each being patterned at least locally, in particular (if possible) completely, in strip-shaped fashion, a differing width of the strips of these magnetoresistive layered assemblages can be established in controlled fashion in such a way that in terms of the measurement range of the overall sensor element obtained, or the overall gradiometer assemblage obtained, a total measurement range of the multiple layered assemblages is obtained, for the magnetic field gradients to be measured, that exceeds the individual measurement range of one individual layered assemblage.
In addition, it may be advantageous (compared to the existing art) that the example sensor element and the example gradiometer assemblage according to the present invention can be of very compact configuration and can be integrated onto a common sensor chip while requiring a very small installation space. This results, in particular, in a very low outlay for packaging of the sensor element or the gradiometer assemblage, and in greatly reduced production and assembly costs.
Lastly, it may be advantageous in the context of the example sensor element and the example gradiometer assemblage according to the present invention that, especially in the case of magnetoresistive layered systems based on the GMR effect and operating on the spin-valve principle, the slope of the characteristic curve of the magnetoresistive layered assemblage, i.e., the change in electrical resistance in the intermediate layer as a function of the change in an externally applied magnetic field, and thus also the working range or individual measurement range and the sensitivity of the magnetoresistive layered assemblage, can be adjusted very easily by way of the strip width (in plan view) with which the layered assemblage is patterned or configured.
It is sufficient in principle if the layered assemblage is embodied at least locally in strip form, in plan view; preferably, however, it is embodied at least largely or entirely in strip form, this also being understood as meanders that are embodied at least in part in strip form.
It is thus now possible to apply, on a common substrate or a common sensor chip, several interconnected magnetoresistive layered assemblages that have different feature widths or strip widths and thus different sensitivities and working ranges, thus yielding an enlarged overall measurement range.
It may be particularly advantageous if the strips have a width in the range from 0.5 μm to 200 μm, in particular from 1 μm to 100 μm.
It moreover may be particularly advantageous if the sensor element has two or three magnetoresistive layered assemblages, a first magnetoresistive layered assemblage being patterned in strip form with a first strip width that lies in the range between 0.5 μm and 2 μm; if a second magnetoresistive layered assemblage is patterned in strip form with a second strip width that lies in the range between 8 μm and 15 μm; and if a third magnetoresistive layered assemblage is patterned in strip form with a third strip width that lies in the range between 3 μm and 7 μm. Magnetic field gradients can be measured particularly well in this fashion over at least five orders of magnitude, at typical fields of about 5 mTesla.
It may be furthermore advantageous if, in the case of the sensor element according to the present invention and in the case of the gradiometer assemblage according to the present invention, there is also simultaneously provided, on the substrate having the magnetoresistive layered assemblages, an electrical evaluation unit interconnected thereto. The latter can, however, also be positioned outside the common substrate, although this requires the provision of signal outputs and interfaces, and a larger configuration.
Lastly, a particularly simple and advantageous gradiometer assemblage is obtained if two or three full gradiometer bridges are provided on the common substrate, each of these full gradiometer bridges having, in particular, four magnetoresistive layered assemblages interconnected in the manner of a Wheatstone bridge, the strip widths within these magnetoresistive layered assemblages interconnected into a Wheatstone bridge preferably being identical, and the strip widths being different in each case between the magnetoresistive layered assemblages associated with the various Wheatstone bridge circuits.
The present invention will be explained in more detail with reference to the drawings and the description below.
The present invention proceeds initially from a magnetoresistive layered assemblage 5, depicted in
Specifically,
As shown in
Further details of the configuration of magnetoresistive layered assemblage 5 and its interconnection to yield a Wheatstone bridge and a gradiometer 30 are explained in German Patent Application No. 101 28 135.8, so there is no need for further discussion of those details here.
The individual gradiometers 30, 31, 32 are identical in principle, and are each configured in accordance with
For example, strip width b according to
The strip widths are selected so that the individual measurement ranges of the individual gradiometers 30, 31, 32 combine to yield a greater overall measurement range for gradiometer assemblage 40.
Assemblage 40 is based, in particular, on the recognition that with narrow strip widths of, e.g., 1.5 μm, the change in electrical resistance as a function of a changing magnetic field has less of a slope than with a greater strip width of, for example 10 μm.
In addition, the change in resistance as a function of the magnetic field change increases (within certain limits) with strip width, so that it is advantageous to position on common substrate 10 several gradiometers 30, 31, 32 that have quite dissimilar strip widths, and that therefore cover different measurement ranges.
For optimum adaptation of gradiometer assemblage 40 to the desired measurement range for a magnetic field gradient, it is thus sufficient to record the resistance change as a function of magnetic field change for various magnetoresistive layered assemblages 5 according to
Depending on the individual case, it may be sufficient to position only two gradiometers on substrate 10, but it may also be necessary, in contrast to what is shown in
All in all, it is an insight of the present invention that the characteristic curve slope in magnetoresistive layered systems, based on the GMR effect and operating in particular according to the spin-valve principle, can be modified, and can be adjusted in controlled fashion, as a function of the feature width of the strip-shaped features.
Number | Date | Country | Kind |
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102 13 941.5-33 | Mar 2002 | DE | national |