Abstract:
A Hall element comprises a region having a non-zero Hall constant, a first contact for supplying an operating current to the region, a third contact for conducting the operating current from the region, the first and third contacts defining a direction of the operating current within the region, a second and a fourth contact for tapping a Hall voltage, and a conductor pattern connected to the first contact or to the third contact and substantially surrounding the region laterally or being arranged above or below the region. The conductor pattern has the effect that the intrinsic field of the operating current through the Hall element is suppressed outside the Hall element such that the Hall element effects an at least reduced offset in adjacent Hall elements. In addition thereto, the arrangement of the conductor pattern has the effect that effects of the current return on the Hall voltage generated by the Hall element itself are also at least reduced. An offset reduction is possible simultaneously on an element, by way of suitable implementation, also for both operating current directions in a spinning-current operating mode.

Description:
FIELD OF THE INVENTION 
     The present invention relates to Hall elements, and in particular to Hall elements with offset compensation. 
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     Hall elements make use of the Hall effect, for example, for measuring a magnetic field. The Hall effect is understood to be the occurrence of an electric field perpendicular to the current density vector j as a result of the effect of a magnetic field. The perpendicular electric field E is calculated by the following equation: 
     
       
           E=−R ( j×B ). 
       
     
     In this equation, R is the Hall constant. For impurity semiconductors, the Hall constant is proportional to the difference between the mobility of the holes in the semiconductor and the mobility of the electrons in the semiconductor. 
     Materials having Hall constants that are sufficiently high to be used as substrate or sensor region or simply as a region for a Hall element, are for example intrinsic-conduction InSb, In(AsP), InAs or lightly p- or n-doped regions on silicon. Two contacts are used to conduct an operating current through the region. 
     In contrast thereto, the two other contacts are used for tapping the Hall voltage formed due to the Lorentz force which leads to deflection of the moving charge carriers due to a magnetic field acting on the Hall element. After a short period of time, there is created an electric field in the Hall element that is directed perpendicularly to the operating current and has such an intensity that the Lorentz force acting on the charge carriers of the operating current is compensated. 
     The Hall effect or a Hall element, in addition to measuring a magnetic field in accordance with magnitude and sign thereof, may also be utilized for multiplication of two electric quantities, i.e. the magnetic field and the control current, or for contactless signal generators. An additional possibility consists in arranging a Hall element in the vicinity of a conductor track and to measure, in non-contacting manner, the current in this conductor track by detection of the magnetic field generated by the current through said conductor track. 
     FIG. 5 illustrates a planar Hall element  100 , comprising a region  100  formed of a material having a sufficiently high Hall constant. It is to be pointed out that, in the sense of the present description, the region of the Hall element having a non-zero Hall constant may either be a Hall substrate itself, which could be applicable for larger Hall elements, while however the region may also be a portion or region of an integrated circuit which in known manner is embedded in the IC substrate, e.g. in a well, or which has been modified by specific technological steps in order to have a corresponding Hall constant. 
     The region illustrated in FIG. 5 is of cruciform shape, which affords the advantage that the Hall element shown in FIG. 5 is also suited for so-called spinning current operation, i.e. that the operating current I can be passed through region  100  via contacts K 1  and K 3 , while however in a different mode of operation, the operating current I may also be passed through the region via contacts K 2  and K 4 , with the Hall voltage, of course, being present then at contacts K 1  and K 3  such that the same can be tapped at terminals A 1  and A 3 . For the following considerations, however, and without restriction to the general nature, it will be assumed for reasons of convenience that the operating current I is applied via terminals A 1  and A 3 , i.e. is fed to and removed from the region via the contacts K 1  and K 3 , while the Hall voltage is given by a potential difference between the contacts K 2  and K 4 , i.e. can be tapped at the terminals A 2  and A 4 . 
     In addition to a region  100  with a non-zero Hall constant and the contacts K 1 , K 2 , K 3  and K 4  for contacting the region  100 , a Hall element of course needs also leads  110 ,  120 ,  130  and  140  for electrically connecting the corresponding contacts K 1  to K 4  to the corresponding terminals A 1  to A 4 . In case of the known Hall element shown in FIG. 5, the leads  110  to  140  are designed in accordance with the practical circumstances. Practical circumstances consist in particular in that there is, for example, the requirement that all terminals A 1  to A 4  should be arranged closely together in order to be passed, for example, to a central switching unit for spinning current operation. In that case, it is necessary, as shown in FIG. 5, to pass at least one lead, namely lead  130 , around the Hall region  100 . In other words, lead  130  comprises a first section  130   a  corresponding to the direction of the current I, a second section  130   b  perpendicular thereto, as well as a section  130   c  directed parallel to current I, but having the current flowing therethrough in the direction opposite to the operating current I. 
     As has already been pointed out, Hall elements serve for measuring an external magnetic field acting on the Hall region. For carrying out such a magnetic field measurement, however, an operating current must be sent through the region so that a Lorentz force can act at all on moving charge carriers. Of course, this operating current I, like any current, also has a magnetic field which also leads to local Hall voltages in the region. However, as the effects of this local intrinsic field are symmetric with respect to the central axis of the current in the element proper, there is no Hall voltage created on the outside of the element, i.e. at the contacts K 2  and K 4 , that could be tapped via the terminals A 2  and A 4 . This local intrinsic field of the operating current I in the Hall region, however, acts in its full magnitude on neighboring Hall elements if arrays of Hall elements are used, as is the case in spinning current operation with mechanical pre-compensation. The intrinsic magnetic field of a Hall element in an array of Hall elements, due to its magnetic field generated and penetrating the neighboring element, leads to a measurement signal there that makes itself felt as an offset. The magnetic field generated by the operating current thus is superimposed on the external magnetic field to be measured in the first place. Thus, there is always an offset problem caused by the magnetic intrinsic field of the active sensor region when there are several sensors provided in the immediate vicinity, since the intrinsic fields of the sensors have the effect of an external magnetic field on the respective other sensors. 
     An additional problem in the known arrangement shown in FIG. 5 arises due to the terminal leads  110  to  140  which any Hall element needs to have. For connecting the terminals A 1  to A 4  of the Hall element to a driving control, it is as a rule necessary, as already pointed out hereinbefore, to pass at least one of the current-carrying leads, in the example of FIG. 5 lead  130 , around the region  100 . In the typical example of the prior art, as shown in FIG. 5, the unfavorable lead from terminal A 3  to contact K 3  consists of the differently aligned partial lengths  130   a  to  130   c.    
     Leads  130   a  to  130   c  deliver the following magnetic fields. The magnetic field generated by the operating current flowing through element  130   a  still is symmetric with the current flow in the active part of the Hall region and therefore generates in region  100  no Hall voltage that is externally measurable. However, this does no longer apply to the two partial lengths  130   b  and  130   c . The magnetic field generated in these conductors acts on the region in its full magnitude and is measured by said region as well, i.e. itself produces a Hall voltage between the terminals A 2  and A 4 . Due to the fact that this additional field is always present when the element is in operation, it appears to the outside like a fixed offset which the element has. Only by changing the operating current is it possible to distinguish this share from a real offset, in that a normal offset changes linearly with the operating current, whereas the offset caused by the operating current due to interference fields changes in square fashion with the operating current. 
     The document DE 1 019 745 A discloses a magnetic-field dependent resistor assembly and in particular a Hall generator in which a resistor body is of parallelepiped shape having on two opposite narrow sides contacts for supplying an operating current and for removing an operating current, respectively. Each electrode has connected thereto a lead wire extending laterally around the resistor body. In the middle of two other sides of the parallelepiped shape, there are arranged the tapping locations for the Hall voltage, which have lead wires connected thereto. The lead wires are twisted with each other. 
     U.S. Pat. No. 3,293,586 discloses a Hall plate element comprising a semiconducting material displaying the Hall effect and applied on a layer of mechanically protective, insulating material. Contacts for supplying an operating current are formed by depositing a conductive material in electric contact with the semiconducting material. Furthermore, contacts for tapping the Hall voltage at the semiconducting material are provided by establishing ohmic contact with the semiconducting material. The ohmic contacts have conductive strips connected thereto that extend beyond the semiconducting material, so that contact wires may be soldered thereto. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide a Hall element of reduced offset. 
     In accordance with a first object of the present invention, this object is achieved by a Hall element comprising a region having a non-zero Hall constant; a first contact for supplying an operating current to the region; a third contact for conducting the operating current away from the region, the first and third contacts defining a direction of the operating current within the region; a second and a fourth contact for tapping a Hall voltage; and a conductor pattern connected to the first contact or to the third contact and substantially surrounding the region laterally , the conductor pattern comprising two partial conductors that are connected to the first or the third contact, that are connected to each other and extend, on respective opposite sides of the region, around the region in the direction of the contact to which they are connected, such that an operating current across the contact to which the two partial conductors are connected, can be divided into two operating current shares across the two partial conductors. 
     In accordance with a second object of the present invention, this object is achieved by a Hall element comprising a region having a non-zero Hall constant; a first contact and a third contact for supplying an operating current to the region and for conducting the operating current away from the region or, optionally, for tapping a Hall voltage; a second and a fourth contact for tapping a Hall voltage or, optionally, for supplying an operating current to the region and conducting the same away from the region; wherein two conductive areas are provided which are both arranged above the region or below the region or are arranged with respect to the region such that one conductive area is arranged above the region and the other conductive area is arranged below the region, wherein the first conductive area is connected to the region in electrically conductive manner in order to form the first contact, with the first conductive area in a contact region of the first contact being moreover electrically isolated from a remainder of the first conductive area; wherein the second conductive area is connected to the region in electrically conductive manner in order to form the third contact, with the first conductive area being not present in a contact region of the third contact, so that the first contact is electrically isolated from the third contact except for the region; wherein the first conductive area is connected to the region in order to form the second contact, with the second conductive area being not present in a contact region of the second contact; and wherein the second conductive area is connected to the region in order to form the fourth contact, with the second conductive area, in a contact region of the fourth contact, being moreover electrically isolated from a remainder of the second conductive area. 
     The present invention is based on the finding that one has to depart from the opinion valid so far, namely to design the leads merely in accordance with the practical circumstances, but without taking into consideration the operation of the Hall element and the effects thereof on the environment, respectively, in order to provide an offset-reduced Hall element having on the one hand a reduced offset due to its own operating current and having on the other hand also lesser effects on adjacent Hall elements. Although there are presumably methods known in technology for calibrating such offset errors out, it is generally better at all times to not allow such errors to be generated at all, whereby more reliable and less complex and thus less expensive elements may be implemented. 
     Contrary to the prior art, in which the operating current leads are designed simply in accordance with the external practical circumstances, a Hall element according to the invention has a conductor structure or pattern that is connected to the first or third contact and substantially surrounds the region laterally or is arranged above or below the region. Such a conductor pattern has the effect that the magnetic fields of the current through the Hall element and of a current in the conductor pattern for returning the operating current cancel each other out at least in part in a region outside of the Hall element, i.e. where other Hall elements may be placed, while the magnetic field of the current in the leads at the same time acts on the region as well as symmetrically as possible, so that the magnetic field generated by the current in the conductor pattern, itself does not lead to a Hall voltage in the element. Thus, according to the invention, the intrinsic magnetic field of a Hall element is shielded at least in part from other Hall elements by simple measures, and the additional effect achieved is that the magnetic field of the leads acts at least somewhat symmetrically on the Hall element itself, so that the operating current does not result in a Hall voltage at the element itself. 
     In a first embodiment of the present invention, the conductor pattern is in the form of a sheet-like metallization above the region so that, analogous with two adjacent flat conductors with different directions of current flow in the interior thereof, i.e. between the region and the metallization plane, an in theory twice as large magnetic field is present tangentially to the surface of the region, whereas the fields perpendicular to the surface as well as all fields outside of the arrangement of region and metallization area are substantially zero or greatly reduced. 
     Due to the fact that the Hall region can only detect fields extending perpendicularly to the surface, this leads to a considerable reduction of the electric field in the element caused by the intrinsic field. 
     This metallization area may be arranged either above or below the region, and may have a geometric shape corresponding to that of the region, which provides for high offset freedom, or a shape not corresponding to the geometric shape of the region which, though resulting in reduced offset freedom, already leads to distinct improvements as compared to the prior art. 
     In accordance with an additional embodiment of the present invention, the conductor pattern for return comprises a first section and a second section which branch in the vicinity of the third contact and are passed around the region preferably symmetrically so as to substantially surround the region. Here too, a shift of the magnetic field in the surroundings of the Hall region takes place so that the magnetic field in the surroundings of the Hall region becomes symmetric to the same and thus does not lead to a Hall voltage. Outside of the return, i.e. in areas where other Hall elements may be placed, there is in contrast thereto just a greatly reduced magnetic field present. This embodiment can be realized more easily in terms of circuit technology since there are no different metallization planes necessary. However, as compared to a second metallization plane as conductor pattern, it has the disadvantage that the offset freedom is not quite as complete. 
     It may thus be summarized that the conductor pattern according to the invention, due to the fact that it substantially surrounds the region laterally or is arranged above or below the region, at the same time reduces both the interfering influence of the return line on the region as well as the intrinsic field acting on other Hall elements that are arranged in the vicinity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention will be described in detail hereinafter with reference to the drawings in which 
     FIG. 1A shows a Hall element according to a first embodiment of the present invention; 
     FIG. 1B shows a Hall element according to a second embodiment of the present invention; 
     FIG. 2 shows a cross-sectional view of a Hall element shown in FIG. 1A or FIG. 1B; 
     FIG. 3 shows a Hall element according to a further embodiment of the present invention; 
     FIG. 4 shows a Hall element according to an additional embodiment of the present invention; and 
     FIG. 5 shows a known Hall element. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1A shows a Hall element according to a first preferred embodiment of the present invention. The Hall element comprises, just as the Hall element shown in FIG. 5, a region  100  having a non-zero Hall constant, four contacts K 1 , K 2 , K 3  and K 4  as well as four terminals A 1  to A 4  each connected to their respective contacts, as shown in FIG.  1 A. In contrast to the known Hall element shown in FIG. 5, the Hall element shown in FIG. 1A comprises as conductor structure or pattern a metallization  10 , which in the embodiment illustrated in FIG. 1A is arranged above region  100 . However, it is to be pointed out that the metallization  10  could also be arranged below the region, yielding the same effect. 
     The leads from terminals A 2  and A 4  to contacts K 2  and K 4 , in static operation, may be chosen in the usual manner as they are unproblematic with respect to magnetic fields as they are almost no currents flowing therein if the Hall voltage is measured in non-contacting manner. 
     However, in the event of a mode of operation corresponding to “spinning current”, the contacts K 2  and K 4  must be designed in accordance with the contacts K 1  and K 3  as well. This means a further metallization plane above the Hall region which, for example, returns the contact K 4  to the location of the contact K 2  in accordance with the contact K 3  above the region. 
     In the embodiment of the present invention shown in FIG. 1A, the geometric shape of the conductor pattern  10  is substantially equal to the geometric shape of the region  100 , except for the fact that the contacts K 1 , K 2  and K 4  are not covered, such that the leads from terminals A 1 , A 2  and A 4  can be terminated here without a problem. However, if a suitable technology is employed, the conductor pattern may also extend completely over the region  100  or be larger than the region, however, with the best compensation results being achieved when the conductor pattern  10  also is symmetric with respect to the axis of symmetry of the region. 
     FIG. 1B shows a conductor pattern of reduced surface area, which is in the form of a strip  10 ′ only and results in not as complete offset compensation as in case of the conductor pattern  10  of FIG. 1A, but which already provides for considerable improvements as compared to the prior art. The best offset reduction results are achieved again if the conductor pattern  10 ′ is arranged symmetrically with respect to the axis of symmetry of region  100 ; if region  100 , as in case of FIGS. 1A and 1B illustrating a cruciform region, has two axes of symmetry, the conductor pattern should be symmetric with respect to the axis of symmetry along which the operating current I flows through region  100 . 
     FIG. 2 shows a longitudinal sectional view of the Hall element illustrated in FIGS. 1A and 1B, respectively. It is assumed that the operating current is introduced into the region  100  via terminal A 1  and the lead from terminal A 1  to contact K 1  and flows along the arrow marked I to the contact K 3  and there flows a short distance upwardly and then reverses its direction and flows back to terminal A 3  in a direction opposite to the operating current I in region  100 . 
     As regards the current path outside of the region, it is to be pointed out that it is sensible here too, for reducing the effects on neighboring Hall elements, that the lead-in and lead-out of the operating current continue in two different planes on top of each other. This is possible in case of many manufacturing technologies by two metallization planes ME 1  and ME 2 , as outlined in FIG.  2 . As an alternative, the leads may also extend immediately adjacent each other or even in intertwined fashion in order to obtain the effect that the magnetic fields of the two conductors are greatly reduced, except in the region between the conductors. As regards the space between region  100  and the metallization structure  10 , there may be used any dielectric  12 , which typically will be predetermined by the technology used. 
     It is to be pointed out that, due to the anti-parallel current conduction in region  100  on the one hand and in the conductor pattern  10  on the other hand, the effect occurs that a relatively strong magnetic field appears in dielectric  12 , whereas a greatly reduced magnetic field is present in the area outside the conductor pattern, i.e. above conductor pattern  10  and below region  100 , respectively, since the two magnetic fields cancel each other out there. The very strong magnetic field present in dielectric  12 , however, due to the direction provided (tangentially with respect to the surface), does not have the effect of a Hall voltage, so that there is thus no Hall voltage appearing between contacts K 2  and K 4 . It is to be pointed out that properties of complete symmetry of the conductor pattern  10  are indeed desirable, but possibly cannot be realized at all times. The compensation effect, however, does not decrease suddenly, but slowly so that certain asymmetries due to external conditions may be acceptable since there is still a considerable part of magnetic field cancellation taking place in the outer region. 
     It is obvious that the conductor pattern  10  may also be provided underneath the region  100  and that the effects achievable thereby are substantially the same as if the return current were passed above the region, i.e. if the conductor pattern  10  is provided above region  100 . 
     In the following, reference will be made to FIG. 3 illustrating a Hall element according to the invention comprising two metallization planes, with the return line shown for contacts K 1  and K 3  in FIGS. 1A,  1 B and  2  being realized in analogous manner for the contacts K 2  and K 4  on the other metallization plane as well. Such an element then has terminal portions  30  and  32  on two sides only, and both terminal portions may be used either as lead-in and lead-out of the operating current (terminal portion  30  for terminals A 1  and A 3 ) or as Hall voltage tap (terminal portion  32  for terminals A 2  and A 4 ). In FIG. 3, the region  100  is of square configuration. Furthermore, there are a first metallization plane, shown in FIG. 3 in hatched form from the upper left to the lower right, as well as a second metallization plane, shown in FIG. 3 in hatched form from the lower left to the upper right. The two contacts K 1  and K 2  establish a connection between Hall region  100  and the first metallization plane, i.e. the metallization plane hatched from the upper left to the lower right, whereas the contacts K 3  and K 4  establish a connection between region  100  and the second metallization plane, i.e. the metallization plane hatched from the lower left to the upper right. The diamond-shaped hatching in the essential part of FIG.  3  and in terminal portions  30  and  32  is to point out schematically that both metallization planes, i.e. the first metallization plane and the second metallization plane, are provided on top of each other here, while being isolated from each other, of course. 
     The operating current is supplied to contact K 1  via the first metallization plane and from there is supplied into region  100 , where the operating current then flows to contact K 3  and from there reaches the second metallization plane via contact K 3 , in order to flow back across the second metallization plane to terminal portion  30  where terminal A 3  is now constituted by the upper metallization plane. It can be seen from FIG. 3 that the first metallization around contact region K 1  is isolated from the first metallization plane arranged over the remaining area of region  100 , and that also in the region of contact K 3  the first metallization plane is not provided, so that there is no short-circuiting caused between first metallization plane and second metallization plane. 
     Terminal A 2  is connected via the second metallization plane to contact K 4  and via the contact K 4  to region  100 . The Hall element is connected furthermore to the first metallization plane via contact K 2 , so that the Hall voltage may be tapped via terminals A 4  and A 2  for the first and second metallization planes. It can be seen from FIG. 3, that in the region of contact K 4 , the second metallization plane is isolated from the sheet-like second metallization plane above. region  100 , and that furthermore the first and second metallization planes are electrically isolated from each other at contact K 4  in contact region  32  just as in contact region  30 , so as to avoid short-circuiting there. It can be seen in addition that contact K 2  is not connected to the first metallization plane, i.e. that the second metallization plane does not extend as far as the region of contact K 2 , so as to exclude short-circuiting here as well. 
     The embodiment illustrated in FIG. 3 has the advantage that there still are only two terminal portions present and that the operating current supply can take place not only via terminals A 1  and A 3 , but just as well via terminals A 2  and A 4 , which is advantageous when spinning current operation is desired. 
     FIG. 4 illustrates an additional embodiment of the present invention in which the conductor pattern for returning the current is not arranged above or below region  100 , but is designed so as to substantially surround the region. This is achieved by dividing the conductor pattern in the vicinity of contact K 3  into two conductor portions  10   a  and  10   b  such that approximately half of the operating current I flows back in both conductor portions  10   a  and  10   b . Thus, there are formed two partial terminals A 3   a  and A 3   b  for the conductor pattern. These two terminals, shown separately in FIG. 4, may readily be shorted again, i.e. connected to each other, by the external wiring. Though the embodiment illustrated in FIG. 4 is not as efficient as the first embodiment, having a metallization area above or below, respectively, as regards its reducing effect on the magnetic fields located outside of the Hall element, the embodiment shown in FIG. 4 has the advantage that there are no two different metallization areas necessary. Thus, this option can also be used if just one plane can be utilized. For reducing as much as possible the effects of the operating current return through the conductor pattern  10   a ,  10   b  on the Hall voltage to be tapped at terminals A 2  and A 4 , conductors  10   a  and  10   b  should possibly be of equal length so that the operating current is separated in like parts, since the ohmic resistance of the conductors  10   a  and  10   b  will then be the same. In addition thereto, the two elements  10   a  and  10   b  should be returned possibly symmetrically on both sides of region  100 , however, with the exact return path being not of decisive significance. The effects of the operating current return on the Hall voltage at terminals A 2  and A 4  is best when the current is split into exactly equal halves in conductors  10   a  and  10   b  and when the conductors are as symmetric as possible with respect to the axis of symmetry of the region along which the operating current I flows. Deviations from symmetry, however, do not suddenly result in loss of compensation, but merely in a slowly increasing offset which, depending on the application, should still be tolerable, but which is already reduced considerably as compared to the case shown in FIG. 5, in which the return path does not extend around region  100 .