Abstract:
Various means for improvement in signal-to-noise ratio (SNR) for a magnetic field sensor are disclosed for low power and high resolution magnetic sensing. The improvements may be done by reducing parasitic effects, increasing sense element packing density, interleaving a Z-axis layout to reduce a subtractive effect, and optimizing an alignment between a Z-axis sense element and a flux guide, etc.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority to U.S. Provisional Application No. 62/156,013, filed May 1, 2015, and U.S. Provisional Application No. 62/154,210, filed Apr. 29, 2015, the entire contents of which are herein incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present inventions relate generally to the field of magnetic field sensors and more particularly to methods of increasing signal-to-noise ratio (SNR) of magnetic field sensors. 
       BACKGROUND OF THE INVENTION 
       [0003]    Magnetic field sensors have been commonly used in various electronic devices, such as computers, laptops, media players, smart phones, etc. There are several techniques/devices that can be used for detecting a magnetic field. Tunneling Magnetoresistance (TMR) is a promising magnetic sensing technology for handset applications due to its advantages in sensitivity, power, and process cost compared with other magnetic sensors. Another closely related technology in magnetic field sensing is Giant Magnetoresistance (GMR), and many of the disclosed embodiments apply equally well to GMR based sensing technologies. 
         [0004]    A TMR element is composed of two ferromagnetic layers separated by a non-magnetic, insulating tunnel barrier. One layer has a magnetization direction that is “free” to rotate in a magnetic field. The other layer (reference layer) has a “fixed,” reference magnetization that does not rotate when in a magnetic field of moderate to low strength that is of sensing interest. If the magnetization directions of the two layers are parallel to each other, the electrical resistance of the tunnel barrier is low. Conversely, when the magnetization directions are anti-parallel, the resistance is high. A magnetic field sensor based on TMR therefore converts magnetic field into electrical signal by a change in electrical resistance due to the changing angle of the magnetization direction of the magnetic free layer relative to the reference magnetization of the fixed layer in response to the field. 
         [0005]    The performance of a magnetic sensor may be defined by its signal-to-noise ratio (SNR). Magnetic sensors with high SNR need high power for operation to achieve desired output signal quality and generally are not applicable to situations where high precision magnetic field measurement is required. 
         [0006]    Therefore, it would be desirable to have a system, device, and method to effectively increase a signal-to-noise ratio (SNR) of magnetic field sensors for lower power and high resolution magnetic sensing. 
       SUMMARY OF THE INVENTION 
       [0007]    Certain embodiments of the inventions provide for systems, devices, and methods to effectively increase a SNR of a TMR magnetic field sensor for low power, high resolution magnetic sensing. 
         [0008]    According to various embodiments of the inventions, various means for improvement in a SNR for a TMR field sensor are disclosed. The improvement may be done by reducing parasitic effects, increasing sense element packing density, interleaving a Z-axis layout to reduce a subtractive effect, and optimizing an alignment between a Z-axis sense element and a flux guide, etc. 
         [0009]    In certain embodiments, a magnetic sensor is built with a Wheatstone bridge circuit with each leg comprising an identical number of sense elements. Such a design may avoid a differential response to in-plane fields since all elements respond in the same way. Moreover, an even number of sense elements, preferably 4 sense elements, per metal magnetic tunnel (MMT) is utilized for a balanced sense current flow (e.g., equal SNR weighting for each sense element), and the sense current flows vertically through the magnetic tunnel junction (MTJ) sense elements and perpendicular to an MMT orientation, which interconnects adjacent sense elements for minimal resistive losses. 
         [0010]    In certain embodiments, for Z-axis magnetic sensing, a Z-axis layout is interleaved to take advantage of both sides of a flux guide. Preferably, dual flux guides are utilized for an optimal trench width while maintaining pitch and spacing constraints of a reference layer within a TMR sense element. Sense elements may also be used on both sides of a flux guide to eliminate the subtractive effect that is present when the inactive ferromagnetic side of one trench is close enough to interact with a side of an adjacent sense element column. Adjacent sense elements may be arranged to have an opposite response to an out-of-plane field, and hence, Z-axis sensor legs become interleaved with one another to allow for denser packing, a relatively higher sense element occupation area, and a relatively higher SNR without impacting sensitivity due to the aforementioned subtractive effect. 
         [0011]    In certain embodiments, built-in reset lines within the TMR sensor are routed at a 45 degree cross angle to the easy (long) axis of a magnetic sense element to lower a switching threshold by about a factor of two, as compared to a 90 degree cross angle reset line routing. Furthermore, the reset lines within the TMR sensor may be utilized in a bipolar chopping method in combination with the aforementioned means to further lower sensor output signal noise. 
         [0012]    While the present inventions are discussed below using TMR magnetic fields sensors having TMR elements, all aspects of the inventions will directly apply to devices based on giant magnetoresistance (GMR) technology as well. The inventions disclosed here also apply to any magnetic sensing technology that utilizes soft-magnetic films for sensing magnetic fields, such as, for example, anisotropic magnetoresistance (AMR), Fluxgate, and Hall sensors with a flux concentrator. For simplicity and clarity, the inventions will be described in more detail below using TMR technology as an example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Reference will be made to exemplary embodiments of the present inventions that are illustrated in the accompanying figures. Those figures are intended to be illustrative, rather than limiting. Although the present inventions are generally described in the context of those embodiments, it is not intended by so doing to limit the scope of the present inventions to the particular features of the embodiments depicted and described. 
           [0014]      FIG. 1  depicts a cross-section view of a single TMR element cell, according to various embodiments of the inventions. 
           [0015]      FIG. 2  depicts an exemplary structure overview of a TMR transducer leg, with multiple element cells, according to various embodiments of the inventions. 
           [0016]      FIG. 3  depicts an exemplary structure overview of a Z-axis TMR transducer leg, with multiple Z-axis TMR element cells, according to various embodiments of the inventions. 
           [0017]      FIG. 4  depicts a prior art cross-section structure overview of typical interconnections of X/Y-axis TMR element cells. 
           [0018]      FIG. 5  depicts an exemplary cross-section structure overview of interconnections of X/Y-axis TMR element cells, according to various embodiments of the inventions. 
           [0019]      FIG. 6  depicts a prior art cross-section structure overview of typical interconnections of Z-axis TMR element cells. 
           [0020]      FIG. 7  depicts an exemplary cross-section structure overview of interconnections of Z-axis TMR element cells according to various embodiments of the inventions. 
           [0021]      FIGS. 8A-8C  show cross-section views of Z-axis TMR sense element cells and flux guides according to various embodiments of the inventions. 
           [0022]      FIG. 9  depicts an exemplary structure overview of a TMR magnetic field sensor comprising a bridge circuit with multiple TMR transducer legs according to various embodiments of the inventions. 
           [0023]      FIGS. 10A-10B  depict exemplary diagrams of bridge circuit for measurement of X- or Y-axes of a magnetic field according to various embodiments of the inventions. 
           [0024]      FIGS. 11A-11B  depict exemplary diagrams of bridge circuits for measurement of a Z-axis magnetic field according to various embodiments of the inventions. 
           [0025]      FIG. 12  depicts an exemplary structure diagram of an array of X/Y-axis TMR element cells according to various embodiments of the inventions. 
           [0026]      FIG. 13  depicts a second exemplary structure diagram of an array of X/Y-axis TMR element cells according to various embodiments of the inventions. 
           [0027]      FIG. 14  depicts an exemplary structure diagram of an array of Z-axis TMR element cells according to various embodiments of the inventions. 
           [0028]      FIGS. 15A-15C  depict exemplary schematic diagrams of an array of Z-axis TMR element cells according to various embodiments of the inventions. 
           [0029]      FIG. 16  depicts an exemplary schematic diagram of an array of Z-axis TMR element cells, with 45 degree reset current lines, according to various embodiments of the inventions. 
       
    
    
       [0030]    One skilled in the art will recognize that various implementations and embodiments of the inventions may be practiced in accordance with the specification. All of these implementations and embodiments are intended to be included within the scope of the inventions. 
         [0031]    As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. The term “exemplary” is used in the sense of “example,” rather than “ideal.” 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    In the following description, for the purpose of explanation, specific details are set forth in order to provide an understanding of the present inventions. The present inventions may, however, be practiced without some or all of these details. The embodiments of the present inventions described below may be incorporated into a number of different electrical components, circuits, devices, and systems. Structures and devices shown in block diagram are illustrative of exemplary embodiments of the present inventions and are not to be used as a pretext by which to obscure broad teachings of the present inventions. Connections between components within the figures are not intended to be limited to direct connections. Rather, connections between components may be modified, re-formatted, rerouted, or otherwise changed by intermediary components. 
         [0033]    When the specification makes reference to “one embodiment” or to “an embodiment”, it is intended to mean that a particular feature, structure, characteristic, or function described in connection with the embodiment being discussed is included in at least one contemplated embodiment of the present inventions. Thus, the appearance of the phrase, “in one embodiment,” in different places in the specification does not constitute a plurality of references to a single embodiment of the present inventions. 
         [0034]    Various embodiments of the inventions are used for systems, devices, and methods to effectively increase the SNR of a TMR magnetic field sensor and maintain desired measurement sensitivity. The TMR magnetic field sensors, and the TMR element(s) therein, may be integrated on a single component or contain discrete components. Furthermore, embodiments of the inventions are applicable to a diverse set of techniques and methods. 
         [0035]    As mentioned above, the magnetic field sensors as claimed herein may mean one or more of TMR magnetic fields sensors, GMR magnetic field sensors, AMR magnetic field sensors, Fluxgate magnetic field sensors, and/or Hall magnetic field sensors with a flux concentrator. Further, magnetoresistance sense elements as claimed herein may mean one or more of TMR elements, GMR elements, AMR elements, Fluxgate elements, and/or Hall elements with flux concentrators. 
         [0036]      FIG. 1  illustrates a cross-section view of a single TMR element cell  100 , according to various embodiments of the inventions. The TMR element cell  100  is composed of a first patterned ferromagnetic layer  112  and a second ferromagnetic layer  114  separated by a non-magnetic, insulating tunnel barrier  116  (also called a tunnel junction (TJ)). In one embodiment, the first layer  112  (also referred as sense element) has a magnetization direction  132  that is free to rotate in a magnetic field. The second layer  114  (reference layer) has a fixed reference magnetization direction  134  that does not rotate when in a magnetic field. If the magnetization directions of the two layers are parallel to each other, the electrical resistance of the tunnel barrier  116  is relatively low. Conversely, when the magnetization directions are antiparallel, the resistance is relatively higher. 
         [0037]    The TMR element cell  100  therefore converts a magnetic field into electrical signal by changing the electrical resistance due to a changing angle of the magnetization direction  132  of the magnetic free layer relative to the reference magnetization direction  134  of the fixed layer in response to the field. The ferromagnetic layers  112  and  114  may be formed from any suitable ferromagnetic material, such as Ni, Fe, Co, or their alloys. The insulating tunnel barrier  116  may be composed of insulator materials such as AlOx, MgOx, ZrOx, TiOx, HfOx, or any combinations thereof. 
         [0038]    Typically, the first ferromagnetic layer  112  is connected to a first conductive line  124  by a first contact  122 , and the second ferromagnetic layer  114  is connected to a second conductive line  128  by a second contact  126 , which may contact from above as well as below the second ferromagnetic layer  114 . The second conductive line  128  may also be referred as metal magnetic tunnel (MMT) layer. In one embodiment, the first conductive line  124  and the second conductive line  128  may connect to other TMR element cells  100  to form a TMR element cell array. 
         [0039]    In one embodiment, the TMR element cell  100  comprises a built-in current line  410  located, disposed, or deposited adjacent to the second ferromagnetic layer  114  to carry a reset current. The current line  410  of one TMR element cell  100  may be coupled to current lines of multiple other TMR element cells. In another embodiment, the TMR element cell  100  also comprises a second built-in current line  420  located, disposed, or deposited adjacent to the first ferromagnetic layer  112 . The first ferromagnetic layer  112  is patterned into a shape that has a long axis and a short axis. In a zero magnetic field, the magnetization direction of the first ferromagnetic layer  112  lies along the long axis of the element  100 , and can be directed in either of the two directions along this axis. By applying a reset current signal to the current line  410  and/or the current line  420 , an induced magnetic field is generated in an ambient area surrounding the respective current line  410 / 420 . Since the first layer  112  has a magnetization direction  132  that is free to rotate and switch, the magnetization direction  132  will switch to be along the direction projected on its axis by the induced magnetic field. As an exemplary illustration in  FIG. 1 , when the current in the current line  410  has a direction pointing outward (relative to the page) and the current in the current line  420  has a direction pointing inward (relative to the page), the magnetization direction  132  points leftward, which is has a component that is negatively aligned to the reference magnetization direction  134 , and will switch the magnetization direction  132  of the free layer to the left; when the current in the current line  410  has a direction pointing inward and/or the current in the current line  420  has a direction pointing outward, the magnetization direction  132  points rightward, which has a component that is positively aligned to the reference magnetization direction  134 , and will switch the magnetization direction  132  of the free layer to the right. 
         [0040]    In one embodiment, the TMR element cell  100  comprises at least one built-in flux guide (not shown in  FIG. 1  for figure clarity) for Z-axis magnetic field sensing. The flux guide  118  is shown in  FIGS. 3, 6, and 7 , and will be described below. 
         [0041]      FIG. 2  depicts an exemplary structure overview of a TMR transducer leg  210 , with multiple element cells  100 , according to various embodiments of the inventions. The TMR transducer leg  210  comprises an array of multiple active sense element cells  100   a - 100   d , preferably arranged in a matrix layout. In one embodiment, each TMR transducer leg  210  comprises an array of 24×24 sense element cells  100 , which is approximately 100×100 um 2  in size overall. The current flow in current lines  410   a  and  410   b  of each sense element cell  100  may or may not be the same direction. It is understood that the structure shown in  FIG. 2  is only for a general illustration purpose. Various sense element coupling patterns within the array may be implemented other than the pattern disclosed in  FIG. 2 . In one embodiment, a sense element cell (e.g., cells  100   a ,  100   c ) may have the opposite current direction relative to a current line of a neighbor sense element cell (e.g., cells  100   b  and  100   d ). For the highest signal-to-noise ratio in a given chip area (the densest packing of sense element cells), multiple TMR element cells  100  may share a common reference layer (such as, for example, a common second ferromagnetic layer  114 ). In one embodiment, four sense element cells may share the common reference layer for a balanced sense current flow, where each TMR element cell has equal SNR weighting. Such a configuration is shown in the circled region labeled One MMT″ in  FIG. 12 . 
         [0042]      FIG. 3  depicts an exemplary structure overview of a Z-axis TMR transducer leg  310 , with multiple element cells  311 , according to various embodiments of the inventions. Each Z-axis TMR transducer leg  310  comprises an array of multiple active Z-axis TMR element cells  311   a - 311   d , preferably arranged in a matrix layout. In one embodiment, each Z-axis TMR transducer leg  310  comprises an array of 60×40 Z-axis sense elements cells  311 , which is approximately 150×200 um 2  in size overall. The Z-axis TMR element cells  311  have similar structure as the TMR element cell  100  shown in  FIG. 1 , except that a Z-axis TMR element cell  311  also comprises at least one flux guide  118 . While flux guides  118  are located, disposed, or deposited on the right side and underneath a first ferromagnetic layer  312  of the Z-axis sense elements cells  311  (equivalent to the first ferromagnetic layer  112  shown in  FIGS. 1 and 2 ) as illustrated in  FIG. 3 , it is understood that flux guides  118  may be located, disposed, or deposited on the left side and/or above the first ferromagnetic layer  312  of the Z-axis sense elements cells  311 . The Z-axis sensitivity may be doubled by locating, disposing, or depositing flux guides  118  on opposing sides and planes of the sense element cell  311 ; i.e., right side, underneath and left side, above. The current flow in current lines  410  of each Z-axis TMR element cell  311  may or may not be the same direction. In one embodiment, a Z-axis sense element cell  311   a ,  311   c  may have the opposite current direction relative to the current line of a neighbor Z-axis sense element  311   b ,  311   d.    
         [0043]      FIG. 4  depicts a prior art cross-section structure overview of typical interconnections of X/Y-axis TMR element cells. Each second ferromagnetic layer  114  (MMT) couples to only one first ferromagnetic layer  112 . The TJ  116  is not shown explicitly in  FIGS. 4-7 . Therefore, a separate via  142  on the second ferromagnetic layer  114  (MMT) has to be used for electrical connection between TMR sense element cells. 
         [0044]      FIG. 5  depicts an exemplary cross-section structure overview of interconnections of X/Y-axis TMR element cells according to various embodiments of the inventions. Compared to  FIG. 4 , a second ferromagnetic layer  114  (MMT) and an upper conductor layer  124  couple to multiple first ferromagnetic layers  112 , and are used directly as a connection conductor for series coupling between TMR sense elements without additional vias or interconnection length. By doing so, the electrical coupling path is lowered significantly, as are the parasitic effects from the coupling path. In a preferred embodiment, each second ferromagnetic layer  114  (MMT) couples to four first ferromagnetic layers  112 . In one embodiment, all sense element cells are arranged in a single row or column on the MMT (see, e.g.,  FIG. 12 ). Moreover, a sense current flows vertically through the MTJ sense element cells and perpendicular to an MMT orientation, which interconnects adjacent sense element cells for minimal resistive losses. 
         [0045]      FIG. 6  depicts a prior art cross-section structure overview of typical interconnections of Z-axis TMR element cells. Similar to  FIG. 4 , each second ferromagnetic layer  114  (MMT) couples to only one first ferromagnetic layer  112 . Therefore, a separate via  142  on the second ferromagnetic layer  114  (MMT) has to be used for electrical connection connections between sense element cells. 
         [0046]      FIG. 7  depicts an exemplary cross-section structure overview of interconnections of Z-axis TMR element cells according to various embodiments of the inventions. Compared to  FIG. 6 , the second ferromagnetic layer  114  (MMT) couples to multiple first ferromagnetic layers  112 , and is used directly as a connection conductor for series coupling between sense element cells. By doing so, the electrical coupling path is lowered significantly, as are the parasitic effects from the coupling path. In a preferred embodiment, each second ferromagnetic layer  114  (MMT) couples to two first ferromagnetic layers  112 . Such an arrangement would be beneficial for a balanced sense current flow because each sense element cell has equal SNR weighting. 
         [0047]      FIGS. 8A-8C  show a comparison between cross-section views of typical Z-axis TMR element cells and Z-axis TMR element cells according to various embodiments of the inventions. The cross-section views extend to multiple TMR element cells. For clarity, some components such as the second ferromagnetic layers  114 , the insulating tunnel barriers  116 , etc., are not shown in  FIGS. 8A-8C . The flux guides  118  are high aspect ratio vertical bars made from a high permeability magnetic material with ends terminating in close proximity to opposed edges of the TMR sense elements (i.e., the first ferromagnetic layers  112 ). A flux guide  118  captures magnetic flux from an applied field oriented in the Z-axis direction, and bends the field lines to have a horizontal component near the ends of the flux guide  118 . The first ferromagnetic layer  112  responds only to in-plane magnetic fields, and therefore, does not respond to a Z-axis magnetic field directly. The flux guide  118  bends the Z-axis magnetic field into a horizontal direction such that the first ferromagnetic layer  112  may respond accordingly. 
         [0048]      FIG. 8A  depicts a cross-section view of TMR sense element cells and flux guides for two adjacent typical Z-axis TMR element cells. Each TMR sense element cell only comprises one flux guide  118 , which is placed asymmetrically between two neighbor sense element cells (i.e., the first ferromagnetic layers  112 ). Because of the asymmetry, a subtractive effect arises between the flux guide  118  and the farther sense element cell (this interaction is depicted with the (-) symbol in  FIG. 8A . While smaller in magnitude due to the distance from the flux guide edge, the Z-axis field conversion from the farther sense element cell (in-plane component) is opposite to and subtracts from the in-plane component of the Z-axis field conversion for the neighbor sense element cell. 
         [0049]      FIGS. 8B and 8C  show cross-section views of TMR sense element cells and flux guides for two different types of Z-axis TMR element cells according to various embodiments of the inventions. In  FIG. 8B , dual flux guide trenches  118   a  and  118   b  instead of a single wide flux guide  118   c  ( FIG. 8C ) are utilized. The dual flux guide trenches  118   a  and  118   b  are located, disposed, or deposited symmetrically between neighbor sense element cells (i.e., first ferromagnetic layers  112 ). Furthermore, the dual flux guide trenches  118   a  and  118   b  (with the gap between the dual flux guide trenches) cover the whole space between the neighbor sense element cells widthwise. Such an arrangement decouples requirements on sense element pitch, MMT spacing, and trench width, allowing for optimal use of all. In  FIG. 8C , a wide trench flux guide  118   c  is located, disposed, or deposited symmetrically between the neighbor sense element cells (i.e., first ferromagnetic layers  112 ), and covers the whole space between the neighbor sense element cells widthwise. Although the dual flux guide trenches  118   a  and  118   b  and wide trench flux guide  118   c  are shown below the first ferromagnetic layers  112  in  FIGS. 8B and 8C , the dual flux guide trenches  118   a  and  118   b  and wide trench flux guide  118   c  may also be located, disposed, or deposited above the first ferromagnetic layers  112 . In one embodiment, the flux guides shown in  FIGS. 8A-8C  are fabricated with a thin ferromagnetic material layer  119  coated on both sides of the trench to respond to a Z-axis magnetic field. 
         [0050]      FIG. 9  shows a schematic diagram of a TMR magnetic field sensor  200  according to various embodiments of the inventions. The magnetic field sensor  200  comprises a first bridge circuit  220  powered by a voltage source  300  connected via a voltage source connection  300   a , and a second circuit  400  powered by an optional reset field source  500 , which may be a current source connected via a reset field source connection  500   a . The first bridge circuit  220  comprises a plurality of TMR transducer legs  210  (or a plurality of Z-axis TMR transducer legs  310 ). The bridge circuit  220  may be a half bridge circuit, a full bridge circuit, or any combinations thereof. In one embodiment, the bridge circuit  220  is a Wheatstone bridge circuit having two circuit branches with a bridge output signal  260  between the two branches at some intermediate point along the branches. The TMR transducer leg  210  (or the Z-axis TMR transducer leg  310 ) electrically functions as a resistor with its resistance value variable in response to internal and external magnetic fields. The current line  410  of each TMR element cell  100  (or Z-axis TMR element cell  311 ) routes together with various routing patterns to form the second circuit  400 . 
         [0051]      FIGS. 10A and 10B  depict exemplary diagrams of bridge circuits for measurement of X- or Y-axes of a magnetic field, with the current lines energized, according to various embodiments of the inventions. When a reset current is applied to the current line  410  of  FIG. 1 , for example, a magnetic field pulse with a magnetization direction  132  is generated on the first ferromagnetic layer  112 . Depending on the polarity of the applied current pulse, the generated magnetic field switches the free layer direction  132  to have a component that is positively or negatively aligned to the reference magnetization direction  134  of the second ferromagnetic layer.  FIG. 10A  shows a generally positively aligned magnetization direction  132  in the first ferromagnetic layer  112 , and  FIG. 10B  shows a generally negatively aligned magnetization direction  132  in the first ferromagnetic layer  112 . 
         [0052]      FIGS. 11A and 11B  depict exemplary diagrams of bridge circuits for measurement of a Z-axis of a magnetic field, with current lines energized, according to various embodiments of the inventions.  FIGS. 11A and 11B  show two exemplary Z-axis bridge configurations, with different sense element magnetizations. It is understood that the flux guides  118  shown in  FIGS. 11A and 11B  are only for a general illustration purpose. It is referred to as a collection of the flux guides within each Z-axis TMR transducer leg  310 . Each Z-axis TMR transducer lea  310   a ,  310   b ,  310   c , and  310   d  may also have different magnetizations other than the pattern shown in  FIGS. 11A and 11B . 
         [0053]      FIG. 12  depicts an exemplary structure diagram of an array of X/Y-axis TMR element cells according to various embodiments of the inventions. The reset line  410  has a 45 degree cross angle to the first ferromagnetic layers  112 . Such a reset line routing will have a relatively lower switching threshold and only need half of a reset current to switch the magnetization directions of the first ferromagnetic layers  112  as compared to a 90 degree reset line routing. In one embodiment, four sense element cells may share a common reference layer (MMT) for balanced sense current flow, whereby each TMR element cell has equal SNR weighting. The element cells are electrically connected via a horizontal link (e.g., the first conductive line  124  shown in  FIGS. 5 and 7 ). Each horizontal link  124  couples a pair within a row of elements to a pair in the adjacent row. 
         [0054]      FIG. 13  shows a second exemplary structure diagram of an array of X/Y-axis TMR element cells according to various embodiments of the inventions. The reset line  410  has a 90 degree cross angle to the first ferromagnetic layers  112 . The 90 degree reset line routing pattern needs a relatively higher reset current threshold to switch a magnetization direction of the first ferromagnetic layers  112  compared to the 45 degree reset line routing pattern, but in some configurations, the 90 degree reset line routing pattern is more robust. The 90 degree reset line routing pattern may be used for applications with a relatively higher power budget for the TMR sensor. 
         [0055]      FIG. 14  shows an exemplary structure diagram of an array of Z-axis TMR element cells according to various embodiments of the inventions. Dual flux guides trenches  118   a  and  118   b  are used for optimal trench width while maintaining TJ pitch and spacing constraints. In one embodiment, a single wide flux guide  118   c  (not shown) may also be used instead of the configuration of dual flux guide trenches  118   a  and  118   b . Similar to  FIG. 8B , the Z-axis TMR element cells on each row are electrically connected via a horizontal link  124  through a sense element (i.e., first ferromagnetic layer  112 ) to a second ferromagnetic layer  114  (MMT), which may be connected in a desired pattern to construct the final TMR sensor. In one embodiment, a row  1030  of Z-axis TMR element cells have an opposite response to an out-of-plane field (Z-axis field) as compared to a neighboring row  1040  of Z-axis TMR element cells. For example, the TMR element cells of row  1030  may have an increasing resistance response, but the TMR element cells of row  1040  may have a decreasing resistance response. Therefore, the TMR element cells of the same row may be bundled together and act as a bridge leg ( 310 ) or a part of a bridge leg for the bridge circuit  220  (shown in  FIG. 9 ). 
         [0056]      FIGS. 15A-15C  depict exemplary schematic diagrams of an array of Z-axis TMR element cells according to various embodiments of the inventions.  FIG. 15A  shows a Wheatstone bridge circuit  1100  with each bridge leg  1110 ,  1120 ,  1130 , and  1140  representing a row (or multiple rows) of Z-axis TMR element cells. The Wheatstone bridge circuit  1100  is coupled between a voltage source Vdd and a ground GND with diagonal bridge legs having a same response to an out-of-plane field (Z-axis field). The voltage difference between the middle points m1 and m2 is the output of the Wheatstone bridge circuit  1100 . The Wheatstone bridge circuit  1100  may be constructed of different TMR element cell interleaving patterns.  FIG. 15B  shows a parallel interleaving pattern, and  FIG. 15C  shows a parallel interleaving pattern of longer serpentine paths for optimal total transducer resistance. 
         [0057]    In  FIG. 15B , each bridge leg corresponds to a row or parallel grouping of rows of TMR element cells disclosed in  FIGS. 11A and 11B . The first leg  1110  and third leg  1130  form one path between the voltage source Vdd and ground GND. The second leg  1120  and fourth leg  1140  form another path between the voltage source Vdd and ground GND. Each bridge leg corresponds to a row of TMR element cells. The first leg  1110  and third leg  1130  have opposite responses to an out-of-plane field (Z-axis field). The second leg  1120  and fourth leg  1140  have opposite responses to an out-of-plane field (Z-axis field). Moreover, the first leg  1110  and second leg  1120  have opposite responses to an out-of-plane field (Z-axis field). The interleaving pattern is designed to ensure a maximum output between the between the middle points m1 and m2, and a dense spatial fill without subtractive effects from adjacent sense element cells and flux guides outlined previously. In one embodiment, a TMR magnetic field sensor may comprise multiple such interleaving patterns coupled in parallel between the voltage source and ground. 
         [0058]    In  FIG. 15C , each bridge leg corresponds to multiple rows of TMR element cells in series connection and the number of rows included within each bridge leg is the same. Moreover, the TMR element cells within each bridge leg have the same response to a Z-axis magnetic field. Similar to  FIG. 15B , the four bridge legs  1110 - 1140  establish the Wheatstone bridge circuit  1100  to ensure a maximum output between the between the middle points m1 and m2. Although each bridge leg consists of three rows of TMR element cells, as shown in  FIG. 15C , it is understood that the bridge leg may consist of any desired odd number rows of TMR element cells. In a preferred embodiment, the bridge leg may comprise rows of TMR element cells for a bridge circuit output resistance in the order of 10 kΩ in order to balance power consumption and Johnson noise. 
         [0059]      FIG. 16  depicts an exemplary schematic diagram of an array of Z-axis TMR element cells with 45 degree reset current lines according to various embodiments of the inventions. The reset line  410  has a 45 degree cross angle to the first ferromagnetic layers  112 . A 90 degree reset line routing pattern needs a relatively higher reset current threshold to switch a magnetization direction of the first ferromagnetic layers  112  compared to the 45 degree reset line routing pattern. However, the 90 degree reset line routing pattern is more robust for some configurations. The 90 degree reset line routing pattern may be used for applications with a relatively higher power budget for the TMR sensor. 
         [0060]    One skilled in the art will recognize that various implementations may be realized within the described architecture, all of which fall within the scope of the inventions. For example, various reset current line routing and/or energizing methods may be implemented in the TMR magnetic field sensors. For example, a bipolar reset current may be applied to the reset current line to lower 1/f noise of the magnetic sensor. The bipolar reset current may be applied in addition to the reset current line routing patterns disclosed in the aforementioned embodiments. Moreover, the reset current line routing patterns may not be limited to the aforementioned illustrated embodiments. 
         [0061]    The foregoing description of the inventions has been described for purposes of clarity and understanding. It is not intended to limit the inventions to the precise form disclosed. Various modifications may be possible within the scope and equivalence of the application.