Sensors converting magnetic or magnetically coded information to an electric signal play an ever-greater role in today's technology. They find application in all fields of technology in which the magnetic field may serve as an information carrier, i.e. in vehicle technology, mechanical engineering/robotics, medical technology, non-destructive materials testing, and in micro-system technology. With the aid of such sensors, a multiplicity of different mechanical parameters are sensed, such as position, velocity, angular position, rotational speed, acceleration, etc., but current flow, wear, or corrosion may also be measured.
For the sensing and evaluation of magnetic or magnetically coded information, magnetoresistive devices or sensor elements are increasingly employed in technology. Magnetoresistive devices, which may be arranged as single elements or also in form of a plurality of connected single elements, increasingly find application today in numerous applications for contactless position and/or movement detection of a giver object with reference to a sensor arrangement, particularly in automobile technology, such as for ABS systems, traction control systems, etc. For this purpose, rotation angle sensors on the basis of magnetoresistive elements or structures, which will generally be referred to as xMR structures in the following, are frequently used. In the following description, the term “xMR structure” shall include all known magnetoresistive structures, such as AMR (anisotropic magnetoresistance) structures, GMR (giant magnetoresistance) structures, CMR (colossal magnetoresistance) structures, TMR (tunnel magnetoresistance) structures, or EMR (extraordinary magnetoresistance) structures. In technical applications of GMR sensor arrangements, so-called spin valve structures are preferably used today, as illustrated in FIGS. 5a-c, for example.
In the following, it will now at first be briefly gone into GMR structures in general. GMR structures are almost always operated in a so-called CIP (current-in-plane) configuration, i.e. the applied current flows in parallel to the sheet structure. In the GMR structures, there are some basic types that have gained acceptance in practice. In practice, e.g. when employed in automobile technology, above all large temperature windows, for example from −40° C. to +150° C., and small field strengths of few kA/m are necessary for optimum and safe operation. The most important GMR structures for the practical employment are illustrated in FIGS. 5a-c. 
The GMR structure illustrated in FIG. 5a shows the case of a coupled GMR system 500, in which magnetic layers 502, 506, e.g. of cobalt (Co), are separated by a non-magnetic layer 504, e.g. of copper (Cu). The thickness of the non-magnetic layer 504 is chosen so that antiferromagnetic coupling of the soft-magnetic layers 502, 506 develops without a magnetic field applied. This is meant to be illustrated by the depicted arrows. An external field then forces the parallel orientation of the magnetization of the soft-magnetic layers 502, 506, whereby the resistance of the GMR structure decreases.
The GMR structure illustrated in FIG. 5b shows a spin valve system 501, in which the non-magnetic layer 504 is chosen so thick that no more coupling of the soft-magnetic layers 502, 506 develops. The lower magnetic layer 506 is strongly coupled to an antiferromagnetic layer 508, so that it is magnetically hard (comparable with a permanent magnet). The upper magnetic layer 502 is soft magnetic and serves as measuring layer. It may be remagnetized by already a small external magnetic field M, whereby the resistance R changes.
In the following, it is now gone into the spin valve arrangement 501 illustrated in FIG. 5b in greater detail. Such a spin valve structure 501 consists of a soft-magnetic layer 502, which is separated, by a non-magnetic layer 504, from a second soft-magnetic layer 506, the magnetization direction of which is, however, pinned by the coupling with an antiferromagnetic layer 508 by means of the so-called “exchange bias interaction”. The principle functioning of a spin valve structure may be illustrated by means of the magnetization and R(H) curve in FIG. 5b. The magnetization direction of the magnetic layer 506 is pinned in negative direction. If the external magnetic field M is increased from negative to positive values, the “free”, soft-magnetic layer 502 switches near the zero crossing (H=0), and the resistance R rises sharply. The resistance R then remains high until the external magnetic field M is great enough to overcome the exchange coupling between the soft-magnetic layer 506 and the antiferromagnetic layer 508 and to switch also the magnetic layer 506.
The GMR structure illustrated in FIG. 5c differs from the GMR structure illustrated in FIG. 5b in that here the lower antiferromagnetic layer 508 is replaced by a combination of a natural antiferromagnet 510 and a synthetic antiferromagnet (SAF) 506, 507, 509 on top, consisting of the magnetic layer 506, a ferromagnetic layer 507, and a non-magnetic layer 509 in between. In this manner, the magnetization direction of the magnetic layer 506 is pinned. The upper, soft-magnetic layer 502 in turn serves as measuring layer, the magnetization direction of which may easily be rotated by an external magnetic field M. The advantage of the use of the combination of natural and synthetic antiferromagnets as compared to the construction according to FIG. 5b is the greater field and temperature stability.
In the following, it is now gone into so-called TMR structures in general. For TMR structures, the application spectrum is very similar to that of GMR structures. FIG. 6 shows a typical TMR structure. The tunnel magnetoresistance TMR is obtained in tunnel contacts, in which two ferromagnetic electrodes 602, 606 are decoupled by a thin, insulating tunnel barrier 604. Electrons can tunnel through this thin barrier 604 between the two electrodes 602, 606. The tunnel magnetoresistance is based on the tunnel current being dependent on the relative orientation of the magnetization direction in the ferromagnetic electrodes.
The magnetoresistive structures (GMR/TMR) previously described thus have an electrical characteristic dependent on an applied magnetic field, i.e. the resistivity of an xMR structure of a magnetoresistive device is influenced by an influencing external magnetic field.
In bridge arrangement, rotation angle sensors on the basis of the GMR effect may provide an inherent 360° uniqueness of the magnetic field to be detected and have relatively high sensitivity with reference to the magnetic field to be detected.
In order to realize 360° detection by means of a magnetoresistive structure and particularly an GMR/TMR spin valve structure of a plurality of magnetoresistive devices, to detect the rotation direction of a wheel or a shaft with reference to the sensor arrangement, for example, eight magnetoresistive devices are connected with two Wheatstone bridge arrangements (connected in parallel), wherein one of the bridge circuits has reference magnetizations aligned perpendicularly to those of the other bridge circuit. Within each bridge circuit of four magnetoresistive devices, the reference magnetizations are arranged in antiparallel manner, so that both bridge circuits provide sinusoidal signals dependent on the rotation angle of an external magnetic field, which are 90° phase shifted with respect to each other. Via an arctan computation of both output signals, i.e. the output signal of the first and second bridge circuits, the angle over a 360° range can be uniquely determined.
The reference magnetizations of the individual elements of the GMR/TMR spin valve structure may have up to four locally different directions. For adjusting the reference direction, the spin valve layer system has to be heated above the so-called “blocking temperature” (depending on magnetoresistive material system employed) up to 400° C. and cooled again in a lateral magnetic field of the desired direction. This procedure is also referred to as conditioning the magnetoresistive structure. For manufacturing a magnetoresistive sensor structure, locally heating the respective individual elements is therefore required, without also heating neighboring magnetoresistive elements above the blocking temperature during the magnetization procedure. Here, one possibility is locally illuminating with a laser with sufficient radiation energy per unit area, for example.
In FIG. 7, a principle circuit diagram of a possible connection in form of a double bridge circuit 700 with eight magnetoresistive magnetic field sensor elements is illustrated. The double bridge arrangement 700 includes a first bridge circuit arrangement 702 and a second bridge circuit arrangement 704, each out of four magnetoresistive individual elements 702a-b, 704a-b, the magnetizations of which are indicated with reference to the x-axis and y-axis illustrated in FIG. 7. The first bridge circuit 702 includes two magnetoresistive devices 702a with permanent magnetization antiparallel to the x-axis indicated and two magnetoresistive devices 702b with permanent magnetization parallel to the x-axis. The double bridge circuit arrangement 700 further includes a second bridge circuit 704, which comprises two magnetoresistive devices 704a with permanent magnetization in the y direction and two magnetoresistive devices 704b with permanent magnetization antiparallel to the y direction each. The individual magnetoresistive devices 702a, 702b, 704a, 704b are connected, as indicted in FIG. 7, wherein the first and second bridge circuits 702 and 704 are connected to each other in parallel and further connected between a supply voltage and a ground potential.
During the operation of the magnetoresistive sensor arrangement 700 of FIG. 7, the first bridge circuit 702 provides an output signal VX between the two center taps of the first bridge circuit, wherein the second bridge circuit 704 provides an output signal VY between the two center taps of the second magnetoresistive bridge circuit. The connection of the magnetoresistive devices 702a,b and 704a,b described with reference to FIG. 7 allows for the detection of an external, rotating magnetic field over an angle range of 360°. The sinusoidal output signals VX and VY of the two bridge circuits connected in parallel are obtained as a function of the rotating, external magnetic field, wherein the two output signals VX and VY are phase shifted with reference to each other by an angle of 90° each.
GMR sensor elements are constructed such that meander-shaped GMR structures form the resistance elements, which are preferably connected in a bridge circuit. Meander-shaped structures are used to provide sufficiently long, magnetoresistive resistance elements, so that sufficiently high changes in resistance can be determined.
Manufacturing processes known in the prior art for GMR/TMR sensor elements include only the construction of a GMR/TMR sensor device and its contacting. Up to now, only GMR or TMR sensor structures in form of discrete devices are known. GMR/TMR sensor devices previously known in the prior art substantially are magnetoresistive resistance structures accommodated in normal SMD (surface mounted device) packages, wherein a GMR sensor device and its pin occupancy (terminal occupancy) are shown in FIG. 8a, for example. In FIG. 8b, the accompanying functional block diagram is illustrated in principle. The sensor device illustrated in FIG. 8a is to be coupled externally with an evaluating circuit (not shown in FIGS. 8a-b).
An electronic circuit externally associated with the GMR sensor device 800 is required to calibrate the sensor output signal (out+, out−), in order to obtain high absolute accuracy of a GMR sensor arrangement on the one hand. An electronic circuit is also required to condition the sensor output signal and also to provide the sensor output signal in a correspondingly processed, digital or analog interface for further evaluation. Such an additional electronic circuit has to be made available in form of a second device on a circuit board, for example.
According to the prior art, it is indeed also possible to accommodate the electronic circuit for evaluating or rendering the GMR sensor output signal on an additional semiconductor chip to the GMR sensor element within a device package, wherein the GMR sensor element and the semiconductor chip are connected to each other by means of bond wires, for example. But this procedure is problematic in that the necessary chip areas and the connection of both chips, i.e. of the GMR sensor element and the electronic evaluation and rendering circuit, generate corresponding, additional chip costs and assembly costs due to the greater package effort owing to the additional bondings between the GMR sensor element and the semiconductor chip. This additional package effort may also lead to increased parasitic influences, which may affect the sensor properties. Moreover, it should be noted that the final sensor application is limited to the package shapes customary in the market for reception and connection of two chips, i.e. the GMR sensor element and the electronic evaluating and rendering circuit.
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