Patent Publication Number: US-10310026-B2

Title: Bias field generation for a magneto sensor

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/056,284, filed on Feb. 29, 2016, now U.S. Pat. No. 9,678,170; which is a continuation of U.S. application Ser. No. 14/093,567, filed on Dec. 2, 2013, now U.S. Pat. No. 9,297,669; which is a continuation of U.S. application Ser. No. 12/885,349, filed on Sep. 17, 2010, now U.S. Pat. No. 8,610,430; which is a continuation in part of U.S. application Ser. No. 12/130,571, filed on May 30, 2008, now U.S. Pat. No. 8,058,870; each of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Sensors are nowadays used in many applications for monitoring, detecting and analyzing. One type of sensors includes magnetic sensors which are capable of detecting magnetic fields or changes of magnetic fields. Magnetoresistive effects used in magnetoresistive sensors include but are not limited to GMR (Giant Magnetoresistance), AMR (Anisotropic Magnetoresistance), TMR (Magneto Tunnel Effect), CMR (Colossal Magnetoresistance). Another type of magnetic sensors is based on the Hall effect. Magnetic sensors are used for example to detect position of moving or rotating objects, the speed or rotational speed of rotating objects etc. 
     Magnetoresistive sensors are typically sensitive to the in plane x and y components of the Magnetic fields which may be herein referred to as lateral components of the magnetic fields. One component of the magnetic field which may without limitation be referred to as y-component changes the sensitivity, whereas the other component x has a linear relation to the resistance at low fields below for example 5 mT. This component is typically used as the sensing field component. 
     Typically, the magnetoresistive effect has a working range in which the sensitivity for example the change of resistance versus magnetic field change is high. Outside of the working range, unfavorable behavior of the magnetoresistive effect such as saturation limits does not allow the use of the sensor for many applications. The working range may also be referred for some magnetoresistive devices as the anisotropic range. In applications such as for example for the detection of a rotational speed of an object, a bias magnet field is applied to the magnetoresistive sensors in order to avoid saturation of the magnetoresistive sensor. Typical examples include for example a back bias magnet arrangement. In the back bias magnet arrangement, the magnetic sensor is provided between the object to be sensed and the bias magnet. 
     SUMMARY 
     According to one aspect, embodiments include a manufacturing method comprising providing a bias field generator to generate a bias magnetic field having a field component in a first direction, wherein the bias field generator comprises a body of permanent magnetic material or magnetizable material with a cavity such that the cavity is laterally bounded by material of the body at least in a second and third direction, the second direction being orthogonal to the first direction and the third direction being orthogonal to the second direction and the first direction and arranging a magneto sensor in a part of the cavity. 
     According to another aspect, a method comprises rotating an object, operating a magneto sensor to sense the rotation, wherein a bias magnetic field arrangement provides a bias field for sensing the rotation, the bias magnetic field arrangement comprising a magnetic body with an opening, the magnetic body comprising magnetic material, the opening extending in a vertical direction and in lateral directions, wherein the opening is in lateral directions bounded by magnetic material of the magnetic body, wherein inclined surfaces sections of the magnetic body are shaped by the opening, wherein each of the inclined surface sections comprise an inclination angle between the surface sections and at least one lateral direction in the range between 5° and 20°. 
     According to a further aspect, a device comprises a sensor having at least one magnetosensitive element and a magnetic body with an opening, the magnetic body comprising magnetic material, the magnetic body having inclined surface sections shaped by the opening, wherein the sensor is arranged within the opening such that the magnetosensitive element is in lateral directions bounded by the inclined surface sections. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIGS. 1 a  to 1 h    schematic cross-sectional views of embodiments; 
         FIGS. 2 a  to 2 c    schematic top views of embodiments; 
         FIGS. 3 a  and 3 b    three-dimensional views of embodiments; 
         FIG. 4 a    a schematic view of a system according to embodiments; and 
         FIG. 4 b    a simulation showing magnetic field lines according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description explains exemplary embodiments of the present invention. The description is not to be taken in a limiting sense, but is made only for the purpose of illustrating the general principles of embodiments of the invention while the scope of protection is only determined by the appended claims. 
     It is to be understood that elements or features shown in the drawings of exemplary embodiments might not be drawn to scale and may have a different size or different extension in one direction with respect to other elements. 
     Further, it is to be understood that the features described or shown in the various exemplary embodiments may be combined with each other, unless specifically noted otherwise. 
     In the various figures, identical or similar entities, modules, devices etc. may have assigned the same reference number. 
     Referring now to  FIG. 1 a   , a first cross-sectional view according to embodiments is shown. The cross-sectional view is taken along a line A-A′ at a location where the sensor is arranged. The plane shown in  FIG. 1 a    is spanned by a first axis which may herein be also referred as vertical axis or vertical direction and a second axis. The second axis is with respect to the vertical direction defined by the first axis a lateral axis and may herein also be referred to as a second lateral axis or second lateral direction. The first axis may herein further on be referred to as z-axis or z direction, the second axis may herein further be referred to as y-axis or y direction. 
       FIG. 1 a    shows a device  100  having a body  102  formed of permanent magnetic material or magnetizable material such as soft magnetic material or a combination of both as will be described later in more detail. The body  102  constitutes a magnet for providing the magnetic bias field for a magneto sensor  106  such as a magnetoresistive sensor. In embodiments, the magnetic bias field along the x-axis generated at the sensor  106  may be about or above 5 mT (Milli Tesla), whereas the main bias field along the magnetization direction z may be higher than 100 mT. The body  102  shown in  FIG. 1 a    has an opening  104  in the form of a cavity which does not completely penetrate through the body  102 . The opening shapes the geometrical form of the main surface  102   a  of the body  102  to be non-planar. In  FIG. 1 a   , the main surface  102   a  is the main surface of the body  102  which is closest to the sensor  106  while the main surface  102   b  is the opposite main surface farther from the sensor  106 . 
     The cavity may in embodiments include shallow cavities such as shallow indentations. An angle of inclination of the surface sections shaped by the cavity may in one embodiment be selected from the range between 5° and 65° when taken from the x-axis. In one embodiment, the angle of inclination may be selected between 5° and 40°. In one embodiment, the angle of inclination may be selected between 5° and 20°. 
     In embodiments described below in more detail, the cavity may have a pyramid form, a conical form or a polyhedron form. As will be described later in more detail, the sensor  106  may be located completely within the body  102 , i.e. within the maximum extensions of the body  102 . Thus, in one embodiment the z-axis position of the sensor  106  may be below the maximum z-axis extension of the body  102 . 
     The sensor  106  may comprise a semiconductor chip having at least one magnetoresistive or Hall sensor element provided thereon. The sensor  106  may have an integrated circuit included. The magnetoresistive sensing element may be a GMR, MTR, CMR, AMR element or any other form of magnetoresistive sensor elements. The magnetoresistive sensor may have two sensing elements provided in a gradiometer arrangement. Furthermore, in one embodiment, a differential signal may be supplied from at least two sensing elements for sensing an object. In one embodiment, the sensor includes a plurality of magnetoresistive sensing elements arranged in a Wheatstone bridge configuration. In one embodiment, the sensor  106  may comprise at least one Hall effect sensing element. 
     As can be seen from  FIG. 1 a   , the opening  104  of the body  102  is bounded along the z-axis region  108  along both ends by surface sections  110   a  and  110   b  of the body  102 . Thus, the opening  104  is at least for the z-axis region  108  surrounded in the y-direction by the surface sections  110   a  and  110   b.    
       FIG. 1 b    shows a cross-sectional view of the same device  100  as shown in  FIG. 1 a    in a plane spanned by the z-axis and a x-axis at the sensor location. The x-axis can be considered to be a lateral axis being orthogonal to the z-axis and y-axis. As can be seen from  FIG. 1 b   , the opening  104  of the body  102  is bounded, at least for a z-axis region  108 , also in the direction of the x-axis by surface sections  110   c  and  110   d . Thus, the opening  104  is at least for the z-axis region  108  surrounded by the surface sections  110   c  and  110   d  in the x-direction. 
     In some embodiments, the opening  104  may be filled with other material such as mold material which is neither magnetic nor magnetizable. 
     It can be seen from the cross-section of  FIG. 1 a    that the lateral width of the opening  104  in the direction of the y-axis decreases when moving in the vertical direction away from the sensor  106 . Furthermore, it can be seen from the cross-section of  FIG. 1 b    that the lateral width of the opening  104  in the direction of the x-axis decreases when moving in the vertical direction away from the sensor  106 . In other words, the cross-sectional views of  FIGS. 1 a  and 1 b    show a forming of the body  102  such that the surface  102   a  of the body  102  has a tapered shape in the vertical direction away from the sensor  106 . 
     While  FIGS. 1 a  and 1 b    show the overall surface  102   a  with the surface sections  110   a ,  110   b    110   c  and  110   d  as having a non-orthogonal inclination with respect to the y-axis or x-axis, respectively, it is to be understood that the main surface  102   a  may in other embodiments have in addition one or more sections which are parallel to the x-axis. 
     Providing the main surface  102   a  such that an opening  104  is formed allows an independent two-dimensional shaping of the magnetic field generated by the body  102  which provides the bias field for the sensor  106  with reduced or zero lateral field components in the x- and y-directions. 
     In  FIGS. 1 a  and 1 b   , the bias field for the sensor  106  is to be applied in the z-direction. Therefore, the magnetization direction of the body  102  is provided substantially in the z-direction. The working point where the sensor  106  is most sensitive is when both lateral components of the magnetic field, i.e. the x- and y-components are zero. However for small sizes of the body  102 , due to the nature of magnetic field lines only appearing in closed loops, a plane extension of the surface  102   a  as for example for a cubic form of the body  102  with the magnetization in the z-direction would produce at the location of the sensor  106  a magnetic field with significant lateral field components in the x- and y-directions. When the size of the body  102  is small such as for example when the body  102  and the sensor  106  are integrated, the magnetic field lines returning in the space outside of the body  102  effect a significant curvature of the field lines from to z-direction towards the lateral directions at the location of the sensor  106 . The lateral component of the magnetic field lines is with a cubic bias magnet of typical dimensions so strong that for example the field strength in the y component could cause the sensitivity to be decreased by a factor of 4 in case of GMR sensors. 
     The opening  104  in the body  102  addresses the avoiding of lateral field components and provides a reshaping of the field such that at the location of the sensor  106  the lateral components of the magnetic field at least in the x-direction and the y-direction are zero or reduced to almost zero. 
     Since the opening  104  is laterally bounded by permanent magnetic or magnetisable material of the body  102  at least in both the x-direction as well as the y-direction, the x-component and the y-component of the magnetic field are shaped. In particular, the x-components and y-components can be shaped independently from each other by the shape of the opening  104 . This allows independent controlling of the magnetic x- and y-components by geometric shapes of the surface to reduce or eliminate the lateral field components caused by the effect of a small body size simultaneously at least for these two lateral dimensions. Independent controlling of the magnetic x- and y-components can be obtained for example by providing in the manufacturing process respectively different inclinations for the opening  104  in the x-direction and in the y-direction. Independent controlling provides the advantage to address that the influence of the magnetic field to the characteristic of the sensor  106  is different for the x-direction and the y-direction. The independent controlling allows increasing the region of zero lateral field components thereby relieving the need for extreme accurate positioning of the sensor  106  with respect to the body  102  and further to increase the sensitivity of the sensor  106  by providing exactly the magnetic field needed for maximum operation. However it is to be noted, that in some embodiments the sensor  106  might not be operated at the maximum sensitivity, i.e. off-centered from the center where maximum sensitivity is obtained. This can in a convenient way be achieved by sliding the sensor  106  along one of the lateral x- or y-direction as will be described later on in more detail. 
     In some embodiments, the opening  104  may be bounded by the body  102  at least within the vertical region where the sensor  106  is located. Furthermore, in embodiments, the opening  104  may be laterally bounded by the body  102  also for vertical regions which extend beyond the sensor location. Furthermore, in embodiments, the opening  104  may be completely surrounded by material of the body  102 . 
     With the above described embodiments, the usage of a bias magnet of big size can therefore be avoided and it is possible to keep both the sensor  106  and the body  102  small without having degradation in the performance or sensitivity of the sensor  106 . Furthermore, the region where a zero lateral field component or a lateral field component close to zero is obtained can be increased which might relax the requirement for extreme accurate positioning of the sensor  106  for maximum sensitivity. In some embodiments, such a region may have an extension in the x-direction from about ⅛ to ½ of the maximum extension of the cavity in the x-direction. Further, this region may have simultaneously an extension in the y-direction from about ⅛ to about ½ of the maximum extension of the cavity in the y-direction. 
     Thus compared to the usage of large bias magnets, a price advantage can be achieved and the dimensions of device  100  can be kept small. In one embodiment, the body  102  has lateral dimensions in the x- and y-direction smaller than 15 mm. In one embodiment, the body  102  has lateral dimensions in the x- and y-direction smaller than 10 mm. In one embodiment, the body  102  has lateral dimensions in the x- and y-direction smaller than 7.5 mm. The dimension of the body  102  in z-direction may in some embodiments be smaller than 10 mm. The body  102  may for example have a rectangular or cubic form where the extension in each of the x-, y- and z-dimensions is not shorter than ½ of the maximum of the extensions in the x-, y- and z-dimensions of the body  102 . 
     While  FIGS. 1 a  and 1 b    show the body  102  being completely formed of permanent magnetic material such as hard magnetic material,  FIGS. 1 c  and 1 d    show a further embodiment wherein the body  102  is composed of a part  202   a  formed of magnetizable material and a part  202   b  formed of permanent magnetic material. Part  202   a  has a plate form with a smaller vertical extension than part  202   b . However, other embodiments may have other forms and shapes of parts  202   a  and  202   b . The magnetizable material of part  202   a  may be soft magnetic material such as iron, steel, steel alloy etc. The magnetic material provides the magnetization for the magnetizable material such that the part  202   a  is capable of generating the bias magnetic field for the sensor  106 . It can be seen that in the embodiments of  FIGS. 1 c  and 1 d   , the opening  104  is formed only in the part  202   a . However, in other embodiments the opening  104  may partially be formed also in the part  202   b . Furthermore, it is to be noted that in other embodiments, multiple parts of magnetisable material and multiple parts of magnetic material may be included to form a composite body  102 . 
     In the embodiments of  FIGS. 1 a  to 1 d   , the sensor  106  is arranged with respect to the vertical direction (z-axis) such that the sensor  106  is within the body  102 . In other words, the sensor  106  is laterally bounded at least in the x- and y-direction by the body  102 . 
       FIG. 1 e    shows an embodiment, wherein the sensor  106  is placed in the x-direction atop of plane surface portions  112   a  and  112   b . The plane surface portions  112   a  and  112   b  are provided at the lateral border of the body  102 . 
       FIG. 1 f    shows a further embodiment wherein the body  102  comprises in the x-direction two opposing protrusions  114   a  and  114   b . The protrusions  114   a  and  114   b  which are located at the respective lateral ends provide a rim or “border ears” for the body  102  allowing a more effective shaping of the x-component of the magnetic field and providing increased linearity to the magnetic field. The protrusions being placed at the border or border area results in having a maximum extension of the body  102  at the border or a local region near the border. The protrusions  114   a  and  114   b  may also form a lateral fixation or support for holding and keeping the sensor device  106  in place in the lateral direction. Protrusions  114   a  and  114   b  may also be provided for keeping the position of the sensor  106  in the y-direction. However, in one embodiment, the protrusions  114   a  and  114   b  may only be provided such that the sensor  106  can be slide along the y-direction at least from one side into the body  102 . 
       FIG. 1 g    shows a further embodiment in which the protrusions  114   a  and  114   b  have a crane-like form with overhanging surfaces. The crane-like form of the protrusions  114   a  and  114   b  in  FIG. 1 g    allows obtaining an even more increased linearity of the magnetic field and therefore a more effective shaping of the magnetic field. In addition to providing a more effective shaping with higher linearity of the magnetic field, the synergetic effect of a positional fixation in the x-direction as well as a positional fixation in the vertical direction is obtained. The positional fixations may be advantageously used for example during a molding step in which the sensor  106  and the magnet are together over molded with mold material to obtain a protection for the sensor  106  and the body  102 . 
       FIG. 1 h    shows an embodiment wherein the opening  104  penetrates in the vertical direction throughout the whole body  102  to form a hole in the body  102 . The sensor  106  is placed in the embodiment according to  FIG. 1 h    completely within the body  102 .  FIG. 1 h    shows the opening  104  to have an inclined surface with respect to the vertical direction such that the width in x-direction increases towards the sensor  106 . However, other embodiments may provide other inclinations or no inclination with respect to the vertical direction. 
     Having now described cross-sectional views of embodiments,  FIGS. 2 a  to 2 c    show exemplary top views which may apply to each of the embodiments described with respect to  FIGS. 1 a    to  1   h.    
       FIG. 2 a    shows a top-view of the body  102  wherein the opening  104  has a pyramid shape or a shape of half of an octahedron. A three-dimensional view of the pyramid-shape when provided in an embodiment described with respect to  FIG. 1 e    is shown in  FIG. 3 a   . Furthermore, a three-dimensional view of the pyramid shape when applied to an embodiment having a protrusion at a lateral border as described with respect to  FIG. 1 g    is shown in  FIG. 3   b.    
     While  FIG. 2 a    shows the pyramid shape in top-view to have a quadratic form, it may be noted that also a rectangle form with extensions in x and y-direction being different may be provided in embodiments. 
       FIG. 2 b    shows a top-view of the body  102  wherein the opening  104  has the shape of one half of a polyhedron with  16  surfaces. In embodiments, the opening  104  may have the form of regular polyhedrons or parts of regular polyhedrons. 
       FIG. 2 c    shows a top-view of the body  102  according to a further embodiment where the opening  104  has a circular form with decreasing radius when moved along the vertical line.  FIG. 2 c    shows the opening  104  in the form of a cone. In a further embodiment, the opening  104  may have the form of a truncated cone. 
     Each of the top view forms shown and described with respect to  FIGS. 2 a  to 2 c    may be have one of the cross-sectional views shown and described with respect to  FIGS. 1 a  to 1 h   . For example, the protrusions shown in  FIGS. 1 f  and 1 g    may be provided for the pyramid shape as shown and described with respect to  FIG. 2 a   , for the polyhedron shape as shown and described with respect to  FIG. 2 b    or for the cone shape as shown and described with respect to  FIG. 2   c.    
     Each of the embodiments shown in  FIGS. 2 a  to 2 c    has in the x-y plane a symmetric structure with a defined center of symmetry. For such structures, the region of zero or substantially zero magnetic x- and y-components includes the center of symmetry. However, other embodiments may have a non-symmetric structure when viewed from the top. 
     In one embodiment, the body  102  forming the bias magnet for the sensor  106  can be manufactured by molding hard magnetic and/or soft magnetic material. The molding of the body  102  with its geometrical shape can be done with mold tools directly on top of the sensor  106  as an additional packaging step. In some embodiments, the body  102  and the sensor  106  may be integrated. In some embodiments, the body  102  and the sensor  106  may be integrated within a common package which may be formed by molding over the body  102  and the sensor  106 . In some embodiments, the body  102  can be assembled on the sensor  106  with the usage of adhesive glues or only with mechanical clamping mechanism. In some embodiments, the body  102  can be assembled with the sensor  106  and fixed with a mold material that is molded around the whole system for example in a thermoplast injection mold process. 
     An embodiment showing an exemplary operation of the sensor  106  biased by the body  102  will now be described with respect to  FIG. 4   a.    
       FIG. 4 a    shows a system  400  having the sensor  106  arranged near a rotary element  402  for detecting a rotation of the element  402 . The system  400  is provided in a back bias manner with the sensor  106  arranged between the body  102  generating the bias magnet field and the rotary element  402 . While the body  102  shown in  FIG. 4 a    corresponds to the arrangement shown in  FIG. 1 g   , it is apparent that each of the described embodiments can also be implemented. 
     The sensor  106  may be provided centered in the region with zero x- and y-field components for obtaining maximum sensitivity. In other embodiments, the sensor  106  may be off-centered or outside the region with zero x- and y-field components in order to reduce the sensitivity. This may for example be achieved by having the sensor  106  moved away from the region with zero x- and y-component along the guide or support formed by protrusions  114   a  and  114   b.    
     As can be seen from  FIG. 4 a   , the rotary element  402  is capable to rotate such that the axis of the rotation is directed in the y-direction. The rotary element  402  has a plurality of magnets  404  with alternating magnetization provided at a surface of the rotary element  402 . When the rotary element  402  rotates, the magnetic field generated by the magnets  404  is applied to the sensor  106 . The sensor  106  has the sensing direction along the x-direction. The sensor  106  experiences a change of the direction of the x-component of the magnetic field which is detected by the sensor  106  having its sensing direction in the x-direction. The bias magnetic field generated by the body  102  provides the sensor  106  at a working point to avoid saturation and/or other adverse effects. 
       FIG. 4 b    shows an exemplary simulation of the magnetic field generated by an arrangement similar to  FIG. 1 g    with a moving element  408  comprising magnetic permeable material. It can be seen that the body  102  generates within a region  406  substantially zero x- and y-field components within the body  102 . It can be seen that the region  406  extends lateral over more than half of the size of the opening  104 . As described above, the sensing elements of the sensor  106  may provided to be within the region  406  to obtain maximum sensitivity or outside of the region  406  to obtain a reduced sensitivity by purpose. 
     In the above description, embodiments have been shown and described herein enabling those skilled in the art in sufficient detail to practice the teachings disclosed herein. Other embodiments may be utilized and derived there from, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. 
     This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled. 
     Such embodiments of the inventive subject matter may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description. 
     It is further to be noted that embodiments described in combination with specific entities may in addition to an implementation in these entity also include one or more implementations in one or more sub-entities or sub-divisions of said described entity. 
     The accompanying drawings that form a part hereof show by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. 
     In the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, where each claim may stand on its own as a separate embodiment. While each claim may stand on its own as a separate embodiment, it is to be noted that—although a dependent claim may refer in the claims to a specific combination with one or more other claims—other embodiments may also include a combination of the dependent claim with the subject matter of each other dependent claim. Such combinations are proposed herein unless it is stated that a specific combination is not intended. 
     It is further to be noted that methods disclosed in the specification or in the claims may be implemented by a device having means for performing each of the respective steps of these methods.