Abstract:
A magnetic field sensor with at least one three-dimensional spiral reset coil, as well as a method of making the same, are provided. The magnetic field sensor comprises at least one sensing unit having a magnetic easy axis and a magneto-sensitive axis perpendicular to the magnetic easy axis, and at least one three-dimensional spiral reset coil spirally surrounding a corresponding sensing unit of the at least one sensing unit. The spiral reset coil comprises a first wire portion disposed on two opposite sides of the corresponding sensing unit, and a third wire portion coupling the first and second wire portions. Compared with a conventional planer reset coil, the three-dimensional spiral reset coil provides a stronger magnetic field under same current. Therefore, a substrate area for fabricating the magnetic field sensors may be utilized more effectively.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present disclosure is a continuation-in-part (CIP) of U.S. patent application Ser. No. 15/299,283, filed on 20 Oct. 2016, and also claims the priority benefit of Chinese Patent Application No. 201510700943.X, filed on 26 Oct. 2015, as well as Chinese Patent Application No. 201510759597.2, filed on 10 Nov. 2015. Each of the two Chinese patent applications is incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a magnetic field sensor, and in particular, to a magnetic field sensor with at least one three-dimensional spiral reset coil, and a method for manufacturing the same. 
       BACKGROUND 
       [0003]    Sensors based on magneto-resistance (MR) effects have been widely used. Typically, MR-based sensors include anisotropic magneto-resistance (AMR)-based sensors, giant magneto-resistance (GMR)-based sensors, and tunneling magneto-resistance (TMR)-based sensors. 
         [0004]    In general, an electrical resistance (i.e., magneto-resistance) of a MR-based sensor changes with a change of a magnetic field, such as a change in magnitude or direction thereof. A magnetic field sensor of this kind typically has a layer of soft magnetic material of iron, cobalt, nickel, or permalloy such as cobalt-iron-boron alloy or nickel-iron alloy. A change in magnitude or direction of a magnetic field would change a magnetization direction of the soft magnetic material, thereby changing a resistance thereof. 
         [0005]    To achieve an accurate measurement of the magnetic field, the soft magnetic layer needs to be re-magnetized before the magnetic field sensor is used for the measurement. A common method for re-magnetizing the soft magnetic layer is passing a large current through a wire adjacent to a basic sensing unit of the magnetic field sensor. The large current would produce a strong magnetic field, and all magnetic domains of the basic sensing unit would be arranged to align with a magnetic easy axis. The magnetic easy axis depends on anisotropy of the basic sensing unit of the magnetic field sensor. Depending on the direction of the current in the wire, the magnetic domains may be arranged along one of the two opposite directions parallel with the magnetic easy axis. Generally, such an operation is called a function of “set” or “reset”. In addition to initializing the magnetization of the soft magnetic layer, the set-reset function may also help restoring the magnetization of the soft magnetic layer. That is, if the magnetic field sensor is disturbed momentarily by an external magnetic field which is rather strong, even after the disturbing magnetic field is removed, the magnetic domains of the soft magnetic layer may not be able to restore to their initial states. This could result in a subsequent measurement error. With the set-reset function, the magnetic domains of the soft magnetic layer can be restored. 
         [0006]      FIG. 1  shows a structural diagram of a conventional magnetic field sensor  100 . The magnetic field sensor  100  includes a first power supply terminal  131 , a second power supply terminal  132 , a first output terminal  133 , a second output terminal  134 , a first sensing unit  111 , a second sensing unit  112 , a third sensing unit  113 , a fourth sensing unit  114 , and a reset coil  120  disposed adjacent to (e.g., above or below) the sensing units  111 ,  112 ,  113  and  114 . The magnetic field sensor  100  may operate in a set-reset mode. In other words, the magnetic field sensor  100  has a set-reset function. 
         [0007]    Each of the sensing units  111 - 114  has a magnetic easy axis, as well as a magneto-sensitive axis that is perpendicular to the magnetic easy axis. In  FIG. 1 , the magnetic easy axes of the sensing units  111 - 114  are in parallel, and the magneto-sensitive axes of the sensing units  111 - 114  are also in parallel. For the convenience of description, an x-axis and a y-axis perpendicular to the x-axis are defined in  FIG. 1 . Specifically, the x-axis is defined to be parallel with the magnetic easy axis of each of the sensing units  111 - 114 , and the y-axis is defined to be parallel with the magneto-sensitive axis of each of the sensing units  111 - 114 . 
         [0008]    When the magnetic field sensor  100  operates in the set-reset mode, a strong current flows through the reset coil  120  to generate a magnetic field in a plane where the sensing units  111 ,  112 ,  113  and  114  are located. The magnetic field generated by the reset coil  120  sets or resets the sensing units  111 ,  112 ,  113  and  114  such that magnetic domains of the each of sensing units  111 ,  112 ,  113  and  114  are aligned with, or return to, the magnetic easy axis of the respective sensing unit. 
         [0009]    The sensing units in  FIG. 1  constitute a Wheatstone bridge structure.  FIG. 2  shows a circuit diagram of the Wheatstone bridge structure in  FIG. 1 . The first power supply terminal  131  may be a power supply voltage terminal, and the second power supply terminal  132  may be a ground terminal. A magnetic field having a component parallel with the magneto-sensitive axes (i.e., having a y-axis component, or y-component) may change the magneto-resistance(s) of one or more of the sensing units  111 - 114 . The change of the magneto-resistance(s) may lead to a change of a voltage across the first output terminal  133  and the second output terminal  134 , and by detecting the change of the voltage a value of the magnetic field may be detected. 
         [0010]    A disadvantage of the magnetic field sensor  100  resides in a physical structure of the reset coil  120 , which is a planner reset coil as shown in  FIG. 1 . Specifically, the reset coil  120  is disposed in, or made of, a single layer of metal. Being a planner reset coil, the reset coil  120  needs to occupy a larger area in order to generate a magnetic field that is strong enough to set or reset the sensing units. 
         [0011]    Therefore, there is a need for an improved magnetic field sensor to overcome the disadvantage mentioned above and improve an area utilization of the reset coil. 
       SUMMARY 
       [0012]    This section is for the purpose of summarizing some aspects of the present disclosure and to briefly introduce some preferred embodiments. Simplifications or omissions in this section as well as in the abstract or the title of this description may be made to avoid obscuring the purpose of this section, the abstract and the title. Such simplifications or omissions are not intended to limit the scope of the present disclosure. 
         [0013]    One object of the present disclosure is to provide an improved magnetic field sensor with a three-dimensional spiral reset coil surrounding a corresponding sensor unit. With a certain current passing through, the three-dimensional spiral reset coil is able to generate a stronger magnetic field as compared to a conventional planner reset coil. 
         [0014]    Another object of the present disclosure is to provide a method for manufacturing the improved magnetic field sensor having at least one of the three-dimensional spiral reset coil. 
         [0015]    According to one aspect of the present disclosure, the present disclosure provides a magnetic field sensor. The magnetic field sensor may include at least one sensing unit having a magnetic easy axis and a magneto-sensitive axis perpendicular to the magnetic easy axis. The magnetic field sensor may also include at least one spiral reset coil, each spiral reset coil spirally surrounding a corresponding sensing unit of the at least one sensing unit. Each spiral reset coil may include a first wire portion disposed on a first side of the corresponding sensing unit. Each spiral reset coil may also include a second wire portion disposed on a second side of the corresponding sensing unit, wherein the second side opposite the first side. Each spiral reset coil may further include a third wire portion coupling the first wire portion and the second wire portion and passing through a plane where the corresponding sensing unit is located. 
         [0016]    According to one aspect of the present disclosure, the present disclosure provides a method for manufacturing a magnetic field sensor. The method may involve depositing a first conductive layer on a substrate. The method may also involve patterning the first conductive layer to form a second wire portion. The method may also involve depositing a first dielectric layer on the patterned first conductive layer. The method may also involve forming a plurality of sensing units on the first dielectric layer. The method may also involve depositing a second dielectric layer on the sensing units and an exposed portion of the first dielectric layer. The method may also involve etching the second dielectric layer and the first dielectric layer to form a plurality of through-holes. The method may also involve filling the through-holes to form the third wire portion in the through-holes and depositing a second conductive layer on the second dielectric layer. The method may also involve patterning the second conductive layer to form a first wire portion. Moreover, the first wire portion, the second wire portion and the third wire portion are coupled to form a plurality of spiral reset coils each spirally surrounding corresponding a corresponding sensing unit of the plurality of sensing units. 
         [0017]    One of the features, benefits and advantages in the present disclosure is to provide techniques for providing a three-dimensional spiral reset coil spirally surrounding a corresponding sensing unit. Compared to a conventional planner reset coil, the three-dimensional spiral reset coil can generate a stronger magnetic field using a same current. Thus, an area utilization of the magnetic field sensor may be enhanced by employing one or more three-dimensional spiral reset coils that utilize the area more effectively. 
         [0018]    Other objects, features, and advantages of the present disclosure will become apparent upon examining the following detailed description of an embodiment thereof, taken in conjunction with the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following description, appended claims, and accompanying drawings. 
           [0020]      FIG. 1  is a structure diagram of a conventional magnetic field sensor. 
           [0021]      FIG. 2  is a circuit diagram of a Wheatstone bridge of the magnetic field sensor shown in  FIG. 1 . 
           [0022]      FIG. 3 a    is a structure diagram of a magnetic field sensor according to a first embodiment of the present disclosure. 
           [0023]      FIG. 3 b    is a cross-sectional schematic view along a sectional line a-a in  FIG. 3   a.    
           [0024]      FIG. 3 c    is a cross-sectional schematic view along a sectional line b-b in  FIG. 3   a.    
           [0025]      FIG. 4  is a structure diagram of a magnetic field sensor according to a second embodiment of the present disclosure. 
           [0026]      FIG. 5  is a flowchart of a process for manufacturing a magnetic field sensor according to one embodiment of the present disclosure. 
           [0027]      FIGS. 6 a -6 f    are step-by-step diagrams showing the magnetic field sensor during the manufacturing process of  FIG. 5 . 
           [0028]      FIG. 7  is a structure diagram of a magnetic field sensor according to a third embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    The detailed description of the present disclosure is presented largely in terms of procedures, steps, logic blocks, processing, or other symbolic representations that directly or indirectly resemble the operations of devices or systems contemplated in the present disclosure. These descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. 
         [0030]    Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the order of blocks in process flowcharts or diagrams or the use of sequence numbers representing one or more embodiments of the present disclosure do not inherently indicate any particular order nor imply any limitations in the present disclosure. 
         [0031]      FIG. 3 a    is a structure diagram of a magnetic field sensor  200  according to a first embodiment of the present disclosure.  FIG. 3 b    is a cross-sectional schematic view of the magnetic field sensor  200  along a sectional line a-a in  FIG. 3 a   . Likewise,  FIG. 3 c    is a cross-sectional schematic view of the magnetic field sensor  200  along a sectional line b-b in  FIG. 3 a   . As shown in  FIGS. 3 a -3 c   , the magnetic field sensor  200  includes a sensing unit  210  and a three-dimensional spiral reset coil  220 . 
         [0032]    The sensing unit  210  has a magnetic easy axis, as well as a magneto-sensitive axis that is perpendicular to the magnetic easy axis. For the convenience of description, an x-axis and a y-axis perpendicular to the x-axis are defined in  FIG. 3 a   . Specifically, the x-axis is defined to be parallel with the magnetic easy axis of the sensing unit  210 , and the y-axis is defined to be parallel with the magneto-sensitive axis of the sensing unit  210 . The sensing unit  210  may be an AMR-based sensing unit, a GMR-based sensing unit, or a TMR-based sensing unit. 
         [0033]    In one embodiment, the sensing unit  210  may include a longitudinal magneto-resistive bar extending along the magnetic easy axis. The sensing unit  210  may also include a plurality of electrically conductive stripes that are parallel with each other. Each conductive stripe may be disposed on the magneto-resistive bar and form a predetermined angle with the magneto-resistive bar. The magneto-resistive bar may be made of a soft magnetic material such as iron, cobalt, nickel, cobalt-iron-boron alloy or nickel-iron alloy. A layer where the magneto-resistive bar is located is called a soft magnetic layer or a magneto-resistive layer. The conductive stripes may be made of an electrically conductive material such as titanium (Ti), copper (Cu), and the like. 
         [0034]    With reference to  FIG. 3 a   ,  FIG. 3 b    and  FIG. 3 c   , the spiral reset coil  220  spirally surrounds the corresponding sensing unit  210 . The spiral reset coil  220  includes a first wire portion  221  disposed above the corresponding sensing unit  210 , a second wire portion  222  disposed below the corresponding sensing unit  210 , and a third wire portion  223  coupling the first wire portion  221  and the second wire portion  222  and passing through a plane where the corresponding sensing unit  210  is located. The first wire portion  221  is formed by patterning a conductive layer disposed above the sensing unit  210 , and the second wire portion  220  is formed by patterning a conductive layer disposed below the sensing unit  210 . Namely, the spiral reset coil  220  is formed by at least two conductive layers and is a three-dimensional spiral reset coil. 
         [0035]    The magnetic field sensor  200  further includes a first dielectric layer (not shown in  FIGS. 3 a -3 c   ) disposed between the sensing unit  210  and the second wire portion  222  of the spiral reset coil  220 . In addition, the magnetic field sensor  200  also includes a second dielectric layer (not shown in  FIGS. 3 a -3 c   ) disposed between the sensing unit  210  and the first wire portion  221  of the spiral reset coil  220 . 
         [0036]    The magnetic field sensor  200  may operate in a set-reset mode. When the magnetic field sensor  200  operates in the set-reset mode, a current may pass through the spiral reset coil  220  to produce a magnetic field in a plane where the sensing unit  210  is located. The magnetic field may be parallel with the magnetic easy axis of the sensing unit  210 , which may set or reset the corresponding sensing unit  210  such that magnetic domains of the sensing unit  210  are aligned with, or return to, the magnetic easy axis. Compared to the planner set coil of  FIG. 1 , the three-dimensional spiral reset coil  220  of  FIG. 2  may generate a stronger magnetic field with the same current. In other words, the magnetic field sensor  200  may enable a more effective area utilization of a substrate on which a plurality of magnetic field sensors  200  may be manufactured. 
         [0037]      FIG. 4  shows a diagram of a magnetic field sensor according to a second embodiment  400  of the present disclosure. As shown in  FIG. 4 , the magnetic field sensor  400  includes a first power supply terminal  431 , a second power supply terminal  432 , a first output terminal  433 , a second output terminal  434 , a first sensing unit  411 , a second sensing unit  412 , a third sensing unit  413 , a fourth sensing unit  414 , a first spiral reset coil  421 , a second spiral reset coil  422 , a third spiral reset coil  423 , and a fourth spiral reset coil  424 . In particular, the first spiral reset coil  421 , the second spiral reset coil  422 , the third spiral reset coil  423  and the fourth spiral reset coil  424  correspond to the first sensing unit  411 , the second sensing unit  412 , the third sensing unit  413  and the fourth sensing unit  414 , respectively. 
         [0038]    Furthermore, the first power supply terminal  431  is coupled to a first end of the first sensing unit  411  and a first end of the second sensing unit  412 ; the second power supply terminal  432  is coupled to a second end of the third sensing unit  413  and a second end of the fourth sensing unit  414 ; the first output terminal  433  is coupled to a second end of the first sensing unit  411  and a first end of the third sensing unit  413 ; and the second output terminal  434  is coupled to a second end of the second sensing unit  412  and a first end of the fourth sensing unit  414 . 
         [0039]    Each sensing unit of magnetic field sensor  400  has a magnetic easy axis and a magneto-sensitive axis perpendicular to the magnetic easy axis. Similar to magnetic field sensor  200  of  FIG. 3 a   , an x-axis and a y-axis perpendicular to the x-axis may be defined, with the magnetic easy axes of the sensing units parallel with the x-axis, and the magneto-sensitive axes of the sensing units parallel with the y-axis. The type, structure, working principle and manufacturing process of each sensing unit in  FIG. 4  may be referred to the sensor unit  210  in  FIG. 3 a   , and will not be repeated here. 
         [0040]    Similar to magnetic field sensor  200  of  FIG. 3 a   , the magnetic field sensor  400  may also operate in a set-reset mode. 
         [0041]    When the magnetic field sensor  400  operates in the set-reset mode, each of the spiral reset coils  421 ,  422 ,  423  and  424  may pass a current to produce a respective magnetic field. The respective magnetic field may set or reset the corresponding sensing unit  411 ,  412 ,  413  or  414  such that the magnetic domains of the corresponding sensing unit are aligned with, or return to, the magnetic easy axis of the corresponding sensing unit. In one preferred embodiment, the spiral reset coils  421 ,  422 ,  423 ,  424  may be connected in a head-to-tail fashion such that only two connection terminals are needed for the spiral reset coils  421 ,  422 ,  423  and  424 . 
         [0042]    According to another aspect of the present disclosure, an example process for manufacturing a magnetic field sensor, such as one shown in  FIG. 3 a    or  FIG. 4 , is provided. As shown in  FIG. 5 , the process  500  for manufacturing a magnetic field sensor may include one or more operations, actions, or functions as illustrated by one or more blocks  510 ,  520 ,  530 ,  540 ,  550 ,  560 ,  570  and  580 . In addition,  FIGS. 6 a -6 f    provide step-by-step diagrams showing the magnetic field sensor during the manufacturing process  500  of  FIG. 5 . Process  500  may begin at block  510 . 
         [0043]    At  510 , a first conductive layer  620  may be deposited on a substrate  610 , as shown in  FIG. 6 a   . Process  500  may proceed from  510  to  520 . 
         [0044]    At  520 , the first conductive layer  620  may be patterned to form a second wire portion, such as the second wire portion  222  of  FIGS. 3 a  and 3 c   . Process  500  may proceed from  520  to  530 . 
         [0045]    At  530 , a first dielectric layer  630  may be deposited on the patterned first conductive layer  620 , as shown in  FIG. 6 b   . Process  500  may proceed from  530  to  540 . 
         [0046]    At  540 , a plurality of sensing units  640  may be formed on the first dielectric layer  630 , as shown in  FIG. 6 c   . Process  500  may proceed from  540  to  550 . 
         [0047]    At  550 , a second dielectric layer  650  may be formed or otherwise deposited on the sensing units  640  and an exposed portion of the first dielectric layer  630 , as shown in  FIG. 6 d   . Process  500  may proceed from  550  to  560 . 
         [0048]    At  560 , the second dielectric layer  650  and the first dielectric layer  630  may be etched to form a plurality of through-holes, such as through-hole  660  as shown in  FIG. 6 e   . Process  500  may proceed from  560  to  570 . 
         [0049]    At  570 , a second conductive layer  670  may be deposited on the second dielectric layer  650  after the through-holes are formed, and part of the second conductive layer  670  may fill the through-holes to form a third wire portion  680 , such as the third wire portion  223  of  FIGS. 3 a -3 c   , as shown in  FIG. 6 f   . In some embodiments, a separate through-hole filling process step may be used to fill the through-holes with an electrically conductive material and form the third wire portion  680 . The second conductive layer  670  that is subsequently deposited on the second dielectric layer  650  may also reach the through-holes that have been filled in the separate through-hole filling process step, thereby electrically coupled to the first wire portion via the third wire portion. Process  500  may proceed from  570  to  580 . 
         [0050]    At  580 , the second conductive layer  670  may be patterned to form a first wire portion, such as the first wire portion  221  of  FIGS. 3 a    and  3   b.    
         [0051]    As such, the first wire portion, the second wire portion and the third wire portion of process  500  may be coupled to form a plurality of spiral reset coils which spirally surround corresponding sensing units, such as sensing units  640  of  FIG. 6 . 
         [0052]    In a preferred embodiment, the first wire portion of a spiral reset coil may be formed by a plurality of conductive layers. Similarly, the second wire portion of the spiral reset coil may also be formed by a plurality of conductive layers. Consequently, the spiral reset coil may constitute more turns within a same area, and thus an even stronger set-reset magnetic field may be resulted. In other words, by forming the first and second wire portions using a plurality of conductive layers, a strong spiral reset coil may be achieved in a limited area. 
         [0053]      FIG. 7  is a structure diagram of a magnetic field sensor  700  according to a third embodiment of the present disclosure. The magnetic field sensor  700  shown in  FIG. 7  is similar to the magnetic field sensor  200  of  FIG. 3 a   . For example, the magnetic field sensor  700  also includes a sensing unit  710  and a spiral reset coil  720 , which also spirally surrounds the sensing unit  710 . Furthermore, the spiral reset coil also includes a first wire portion  721  disposed above the sensing unit  710 , a second wire portion  722  disposed below the sensing unit  710 , and a third wire portion coupling the first wire portion  721  and the second wire portion  722  and passing through a plane where the sensing unit  710  is located. 
         [0054]    The difference between the magnetic field sensor  700  of  FIG. 7  and the magnetic field sensor  200  of  FIG. 3 a    lies in that, the first wire portion  721  and the second wire portion  722  of the spiral reset coil  720  in  FIG. 7  is at a predetermined angle a with respect to the magneto-sensitive axis of the sensing unit  710 . The predetermined angle a may be greater than 0 degrees and less than 45 degrees. Preferably, the predetermined angle a may be greater than 4 degrees and less than 15 degrees. Consequently, when a current passes through the spiral reset coil  720 , the magnetic field generated by the spiral reset coil  720  may have an x-axis component (i.e., a component parallel with the magnetic easy axis of sensing unit  710 ) and a y-axis component (i.e., a component parallel with the magneto-sensitive axis of sensing unit  710 ). It is to be noted that, if the predetermined angle a is 0 degrees, the magnetic field sensor  700  will be identical to the magnetic field sensor  200  shown in  FIG. 3   a.    
         [0055]    The magnetic field sensor  700  may operate in a set-reset mode and a self-test mode. When the magnetic field sensor  700  operates in the set-reset mode, a first current may flow through the spiral reset coil  720 , and the x-axis component (or “x-component” in short) of a first magnetic field generated by the spiral reset coil  720  may set or reset the sensing unit  710 . When the magnetic field sensor  700  operates in the self-test mode, a second current may flow through the spiral reset coil  720  and generate a second magnetic field. The second magnetic field may have a known or predetermined value, particularly a known value of its y-axis component (or “y-component” in short). A measurement reading of the magnetic field sensor  720  may then be compared with the known y-component to calibrate sensitivity, error and/or other parameters of the magnetic field sensor  700 , thereby resulting in a self-test of the magnetic field sensor  700 . In some embodiments, the second current may be less than the first current. 
         [0056]    Accordingly, the magnetic field sensor  700  may realize a set-reset function as well as a self-test function by one spiral reset coil  720 . 
         [0057]    The present disclosure has been described in sufficient details with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the present disclosure as claimed. Accordingly, the scope of the present disclosure is defined by the appended claims rather than the foregoing description of embodiments.