Abstract:
A Hall sensor on a semiconductor substrate includes a Hall plate in the semiconductor substrate, where the Hall plate includes a first zone having a first conduction type. The semiconductor substrate also include a second zone having a second conduction type. A space-charge zone in the semiconductor substrate separates the first zone and the second zone, first contacts supply a control current to the first zone, and second contacts supply a compensation current to the second zone.

Description:
TECHNICAL FIELD 
   The invention relates to a Hall sensor on a semiconductor substrate as well as to an operating method for the Hall sensor. 
   From the printed publication U.S. Pat. No. 4,929,993, Hall sensors on a silicon substrate are known in which an n-doped zone has been placed in a p-doped trough. In this arrangement the n-doped zone forms the active zone of the Hall sensor, i.e. the Hall plate. The Hall plate comprises four external connections, wherein in each instance opposite connections are provided for feeding in the control current and for reading out the Hall voltage respectively. 
   Known Hall sensors are associated with a disadvantage in that they are not particularly suited to the measuring of very small static magnetic fields because even if a magnetic field=0, due to material inhomogeneities, Hall sensors generate a Hall voltage in the form of an offset voltage. 
   In order to reduce offset voltages, from printed publication P. J. A. Munter, A low Offset spinning-current hall plate, Sensors &amp; Actuators A, A22 (1990) 743-746, the operation of Hall sensors with a special operating method is known. To this effect a control current which over time rotates on the axis of the magnetic field is applied to the Hall plate. Since during rotation of the direction of current by 90 degrees the offset voltage changes its sign, by way of adding offset voltage pairs measured with a rotation of 90 degrees the overall offset voltage can be compensated for, except for a residual offset voltage. 
   BACKGROUND 
   In a Hall plate comprising an n- or p-doped zone, embedded in a semiconductor substrate of the respective other conduction type, the size of the residual offset voltage is influenced by an effect which is described below. A space-charge zone between the Hall plate and its surroundings is created. If a control current is impressed on the Hall plate, a voltage drop results over one direction of the Hall plate, which voltage drop changes the width of the space-charge zone and consequently the width of the Hall plate, i.e. in the end the active zone in the semiconductor material in which the Hall effect takes place. 
   SUMMARY 
   It is thus the object of the present invention to state a Hall sensor which can be operated such that the residual offset voltage is reduced. 
   This object is met by a Hall sensor according to claim  1  and by a method according to claim  4  for operating said Hall sensor. Advantageous embodiments of the invention are provided in the further dependent claims. 
   A Hall sensor is stated which is arranged on a semiconductor substrate. A Hall plate is formed from a zone of one conduction type in the substrate. A zone of the other conduction type adjoins the Hall plate. The zone of the other conduction type and the Hall plate are separated from each other only by a space-charge zone. The Hall plate comprises contacts which are suited to the supply of a control current. Furthermore, the zone of the other conduction type comprises contacts for supplying a compensation voltage. 
   The Hall element provides an advantage in that by providing the option of feeding a compensation current into a region adjacent to the space-charge zone the thickness of the space-charge zone and consequently the thickness of the Hall plate can be positively influenced. Accordingly, a method for operating the Hall sensor is stated, wherein a compensation current flows parallel to the control current whose magnitude is such that the thickness of the Hall plate is essentially constant. 
   In a first embodiment of the Hall element, the Hall plate is arranged between two zones of the other conduction type. This embodiment provides the advantage of making it possible to influence the thickness of the Hall plate from both sides by means of compensation current. 
   In another embodiment, the Hall plate is arranged on the surface of the substrate. Furthermore, the zone of the other conduction type is embedded in a substrate of the same conduction type as the Hall plate. In this special design variant, too, compensation of the deformation of the Hall plate due to the voltage drop is achieved by supplying a control current. 
   Below, the invention is explained in more detail by means of exemplary embodiments and the associated figures: 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a top view of a Hall sensor of a first and a second embodiment; 
       FIG. 2  shows a cross section, along the line II-II in  FIG. 1 , of a Hall sensor for a first and second embodiment; 
       FIG. 3  shows a cross section corresponding to that of  FIG. 2 ; 
       FIG. 4  shows a diagrammatic cross section of a first embodiment of a Hall sensor; and 
       FIG. 5  shows a diagrammatic cross section of a further embodiment of a Hall sensor. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a top view of a substrate  1 . The substrate  1  can for example comprise silicon. The substrate  1  forms an outer p-doped zone  51 . In a middle region of the substrate  1 , an n-doped zone  52  is formed by doping. The zone  52  is in the shape of a cross with four contacts  321 ,  322 ,  323 ,  324  each on the outer ends of the cross. However, the zone  52  can also be in the shape of a square, rectangle or circle. In the interior of the zone  52  a p-doped zone  53  is formed as a result of p-doping. The zone  53  is similar to the zone  52 , and the outer edges of the zone  53  are parallel to corresponding outer edges of the zone  52 . On the lateral edges of zone  53 , which edges correspond to those of zone  52 , contacts  311 ,  312 ,  313 ,  314  are arranged. The contacts  311 ,  312 ,  313 ,  314 ,  321 ,  322 ,  323 ,  324  are used for feeding currents into the individual zones  51 ,  52 ,  53 , i.e. for acquiring a Hall voltage. 
     FIG. 2  shows a cross section of  FIG. 1  along the line II-II. In particular the depth structures of the zones  51 ,  52 ,  53  are shown. The zone  51  is a p-doped zone which is formed by the substrate  1 . The n-doped zone  52  is embedded in substrate  1  by n-doping. The p-doped zone  53  is embedded in zone  52  by p-doping. 
   According to  FIG. 3 , in the locations without a space-charge zone, the conducting zones  31 ,  32 ,  33 , which comprise the doped zones  51 ,  52 ,  53  according to  FIG. 2 , remain. In each instance, a space-charge zone  41 ,  42  is formed between two zones  51 ,  52 ;  52 ,  53  of opposite doping. In  FIG. 3  the space-charge zones  41 ,  42  are shown by non-hatched areas. In those positions where the compensation of p-conducting and n-conducting charge carriers is stopped, electrically conducting zones  31 ,  32 ,  33  remain. These are in particular the p-conducting zone  31  which corresponds to the p-doped zone  51 , and the p-conducting zone  33  in the middle of  FIG. 3 , which zone corresponds to the p-doped zone  53 . Each of the p-conducting zones is marked by hatched areas of the same type. Corresponding to the n-doped zone  52 , the n-conducting zone  32  forms, which is marked by hatching that extends in the direction opposite to that of the p-conducting zones  31 ,  33 . 
     FIG. 4  shows a Hall sensor according to  FIG. 3 , wherein the n-conducting zone  32  is used as a Hall plate  2 . Correspondingly, a control current IS is fed into zone  32  by way of the contacts  322 ,  324 , wherein only one direction of the control current is discussed in this document. The control current IS causes a voltage drop along the zone  32 , which voltage drop results in a corresponding variation in the thickness d 2  of the space-charge zone  42 . The current direction shown in  FIG. 4  causes the space-charge zone to be thicker towards the right end than towards the left end. Correspondingly, the form of zone  32  is influenced. This influencing of the zone  32  can now be compensated for in that a compensation current IK flows in the p-conducting zone  33 . The compensation current IK is fed into zone  33 , which is p-conducting, by way of the contacts  312 ,  314 . The compensation current IK extends parallel to the control current IS. The compensation current IK in turn influences the thickness of the space-charge zone  41  between the zone  33  and the Hall plate  2 . The compensation current IK causes the space-charge zone  41  to be thicker towards the left end than towards the right end. In other words, the thickness gradient of the space-charge zones  41 ,  42  is the exact opposite. As a result, with a suitable selection of the current IK, this allows the thickness D of the zone  32 , i.e. the thickness D of the Hall plate  2 , to be kept essentially constant along its entire length so that the residual offset voltage can be reduced in a particularly advantageous way. 
     FIG. 4  diagrammatically shows the direction of the magnetic field B to be measured. 
     FIG. 5  shows a Hall sensor according to  FIG. 4 , except that it is not zone  32  that is used as a Hall plate  2 , but instead zone  33  which is p-doped. Correspondingly, a control current IS is fed into zone  33  by way of contacts  312 ,  314 . A compensation current IK is now applied by way of the contacts  322 ,  324  to the n-conducting zone  32 , which is situated below zone  33 . As already shown in  FIG. 4 , the compensation current IK extends parallel to the control current IS. The voltage between zone  32  and zone  33  is almost identical at any location, which is why the thickness d 1  of the space-charge zone  41  is almost constant. The thickness d 1  is proportional to the root of the voltage between zone  32  and zone  33 . 
   As a result of the above, the thickness of zone  33 , represented by the Hall plate  2 , is also essentially constant along its length so that here too a positive influence on the offset voltage results.  FIG. 5  also shows the influence of the compensation current IK on the thickness d 2  of the space-charge zone  42  between zone  32  and zone  31  along the length of said space-charge zone. However, the variation in thickness d 2  of the space-charge zone  42  does not have any significant influence on the Hall plate  2 . 
   The doping used in the examples described can for example be between 1×10 14  cm −3  and 1×10 18  cm −3 ; typically it is 5×10 16  cm −3 . The currents used can for example be between 0.1 and 10 mA; typically they are 1 mA. 
   The following invention is not limited to Hall sensors in silicon substrates, but instead it can be applied to all suitable semiconductor materials.