Abstract:
A z-axis fluxgate magnetometer is formed in a semiconductor wafer fabrication sequence, which significantly reduces the size and cost of the fluxgate magnetometer. The semiconductor wafer fabrication sequence forms a vertical magnetic core structure, a first wire structure wound around the magnetic core structure, and a second wire structure wound around the magnetic core structure.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to fluxgate magnetometers and, more particularly, to a z-axis semiconductor fluxgate magnetometer. 
     2. Description of the Related Art 
     A magnetometer is a device that measures the strength of an external magnetic field. There are a number of different approaches to measuring magnetic fields, and various different types of magnetometers have been developed based on these different approaches. One type of magnetometer based on flux variations in a magnetic core is a fluxgate magnetometer. 
       FIG. 1  shows a block diagram that illustrates an example of a prior art fluxgate magnetometer  100 . As shown in  FIG. 1 , fluxgate magnetometer  100  includes a drive coil  110 , a sense coil  112 , and a magnetic core structure  114  that lies within drive coil  110  and sense coil  112 . 
     As further shown in  FIG. 1 , fluxgate magnetometer  100  also includes a drive circuit  120  that is connected to drive coil  110 , and an sense circuit  122  that is connected to sense coil  112  and drive circuit  120 . Sense circuit  122  generates an output voltage V OUT  that is proportional to the magnitude of an external magnetic field. 
       FIGS. 2A-2E  show views that illustrate the operation of fluxgate magnetometer  100 .  FIG. 2A  shows a graph that illustrates a BH curve  200  for magnetic core structure  114 , while  FIG. 2B  shows a graph that illustrates an alternating current input to drive coil  110 ,  FIG. 2C  shows a graph that illustrates the magnetic induction field B that results from the alternating current input to drive coil  110 ,  FIG. 2D  shows a graph that illustrates an induced voltage in sense coil  112  plotted in the time domain that results from the magnetic induction field B, and  FIG. 2E  shows a graph that illustrates the induced voltage in sense coil  112  plotted in the frequency domain that results from the magnetic induction field B. 
     As shown by BH curve  200  in  FIG. 2A , when the magnitude of a magnetic field H increases, magnetic core structure  114  increases the magnitude of the magnetic induction field B until magnetic core structure  114  saturates. Once in saturation, further increases in the magnitude of the magnetic field H lead to very little increase in the magnitude of the magnetic induction field B. 
     As a result, saturation is commonly illustrated as in  FIG. 2A  as the region where increases in the magnitude of the magnetic field H lead to no additional increase in the magnitude of the magnetic induction field B. In the present example, the magnitude of the magnetic field H is increased by increasing the magnitude of the alternating current flowing through drive coil  110 . 
     As shown in  FIGS. 2A-2C , when no external magnetic field is present and an alternating current waveform  210 , which has an amplitude that is sufficient to drive magnetic core structure  114  into saturation, is input to drive coil  110  from drive circuit  120 , an alternating magnetic induction field B, as represented by waveform  212 , is generated in response. 
     In other words, when alternating current waveform  210  is input to drive coil  110 , magnetic core structure  114  is driven through cycles (magnetized, un-magnetized, inversely magnetized, un-magnetized, magnetized again, and so on) that generate an alternating magnetic induction field B as represented by waveform  212 . In the present example, the alternating current waveform  210  is triangular, while the magnetic induction field waveform  212  has flat tops and bottoms that represent the periods of saturation. 
     As shown in  FIG. 2D , the alternating magnetic induction field B induces an alternating voltage  214  in sense coil  112 . The induced alternating voltage  214  is proportional to the change in the magnetic induction field B over time (dB/dt). In addition, the induced alternating voltage  214  is processed by sense circuit  122  to generate the output voltage V OUT , which is proportional to the external magnetic field. 
     As shown in  FIG. 2E , in the frequency domain, the induced alternating voltage  214  has a fundamental frequency  1   f , but only odd harmonics, such as a third harmonic  3   f , of the fundamental frequency  1   f . As a result, when no external magnetic field is present, the induced alternating voltage  214  has no second harmonic. 
     However, when an external magnetic field is present, the external magnetic field interacts with magnetic core structure  114  and changes the alternating magnetic induction field B. In other words, magnetic core structure  114  is more easily saturated when magnetic core structure  114  is in alignment with the external magnetic field, and less easily saturated when magnetic core structure  114  is in opposition to the external magnetic field. 
     In the present example, as shown by waveform  220  in  FIG. 2C , alignment to the external magnetic field increases the duration of the positive magnetic induction field B and decreases the duration of the negative magnetic induction field B. As a result, as shown by waveform  222  in  FIG. 2B , the external magnetic field has the effect of shifting alternating current waveform  210  to the right. 
     In other words, when no external magnetic field is present, each half cycle of the waveform  210  drives magnetic core structure  114  into positive and negative saturation by substantially an equal amount. However, when exposed to an external magnetic field, as illustrated by the waveform  222 , the external magnetic field causes one half-cycle of the waveform  222  to drive magnetic core structure  114  more deeply into saturation, and one half-cycle of the waveform  222  to drive magnetic core structure  114  less deeply into saturation. 
     In addition, as shown in  FIG. 2D , the change in the alternating magnetic induction field B phase shifts the induced alternating voltage  214  to generate a phase-shifted induced alternating voltage  224 . Further, as shown in  FIG. 2E , in the frequency domain, the phase-shifted induced alternating voltage  224  that results from the external magnetic field includes even harmonics, specifically a second harmonic  2   f.    
     The magnitude of the second harmonic  2   f , in turn, is proportional to the magnitude of the external magnetic field. Thus, by filtering the phase-shifted induced alternating voltage  224  to isolate the second harmonic  2   f , and then detecting the magnitude of the second harmonic  2   f , the magnitude of the external magnetic field can be determined. 
       FIG. 3  shows a block diagram that illustrates an example of a prior art fluxgate magnetometer  300 . Fluxgate magnetometer  300  is similar to fluxgate magnetometer  100  and, as a result, utilizes the same reference numerals to designate the structures which are common to both fluxgate magnetometers. 
     As shown in  FIG. 3 , fluxgate magnetometer  300  differs from fluxgate magnetometer  100  in that fluxgate magnetometer  300  includes a feedback coil  310  that is wrapped around magnetic core structure  114  along with drive coil  110  and sense coil  112 , and a feedback circuit  312  that is connected to feedback coil  310  and sense circuit  122 . Feedback circuit  312  generates an output voltage V CAN  that has an amplitude which is proportional to the magnitude of an external magnetic field. 
     Fluxgate magnetometer  300  operates the same as fluxgate magnetometer  100 , except that feedback coil  310  and feedback circuit  312  are utilized to generate a magnetic field that opposes the external magnetic field.  FIG. 2C  shows that alignment to the external magnetic field increases the duration of the positive magnetic induction field B and decreases the duration of the negative magnetic induction field B. 
     In addition, as the strength of the external magnetic field increases, the duration of the positive magnetic induction field B increases while the duration of the negative magnetic induction field B decreases. Thus, as the strength of an external magnetic field increases, the duration of the negative induction field B decreases until the fluxgate magnetometer reaches saturation where there is substantially no negative magnetic induction field B. Once the fluxgate magnetometer saturates, further increases in the strength of the external magnetic field can not be detected by the fluxgate magnetometer. 
     To prevent a strong external magnetic field from saturating a fluxgate magnetometer, the alternating current input to feedback coil  310  is selected to generate a magnetic field that cancels out the external magnetic field, and effectively make the output voltage V OUT  appear as though no external magnetic field were present. 
     The magnitude of the alternating current input to feedback coil  310  when the output voltage V OUT  appears as though no external magnetic field was present can then be used to generate the output voltage V CAN . Since the amplitude of the output voltage V CAN  is proportional to the magnitude of the external magnetic field, the magnitude of the external magnetic field can then be determined. Thus, the advantage of fluxgate magnetometer  300  is that fluxgate magnetometer  300  can be used in very strong magnetic fields. 
       FIG. 4  shows a block diagram that illustrates an example of a prior art fluxgate magnetometer  400 . As shown in  FIG. 4 , fluxgate magnetometer  400  includes a drive coil  410 , a sense coil  412 , and a pair of magnetic core structures  414  and  416  that lie within drive coil  410  and sense coil  412 . Drive coil  410  and sense coil  412  are wrapped around the magnetic core structures  414  and  416  in a differential coil arrangement. 
     As further shown in  FIG. 4 , fluxgate magnetometer  400  also includes a drive circuit  420  that is connected to drive coil  410 , and a sense circuit  422  that is connected to sense coil  412 . Sense circuit  422  generates an output voltage V DIF  that has an amplitude which is proportional to the magnitude of an external magnetic field. 
     In operation, drive coil  410  is wrapped around the magnetic core structures  414  and  416  so as to generate equal and opposing alternating magnetic induction fields when drive circuit  420  outputs an alternating current to drive coil  410 . Thus, when no external magnetic field is present, no voltage is induced in sense coil  412  because no alternating magnetic induction field is present. 
       FIG. 5  shows a graph that further illustrates the operation of fluxgate magnetometer  400 . As shown in  FIG. 5 , although no current is induced in sense coil  412  when no external magnetic field is present, the presence of an external magnetic field induces an alternating voltage in sense coil  412 . 
     Sense circuit  422  detects the induced alternating voltage in sense coil  412  and generates in response the output voltage V DIF , which has an amplitude that is proportional to the magnitude of the external magnetic field. Thus, by detecting the amplitude of the output voltage V DIF , the magnitude of the external magnetic field can be determined. 
     One of the advantages of fluxgate magnetometer  400  over fluxgate magnetometer  100  is that fluxgate magnetometer  400  requires less support circuitry than fluxgate magnetometer  100 . For example, drive circuit  120  commonly generates a second harmonic clock signal which drive circuit  420  need not generate. The second harmonic clock signal, which has a frequency that is equal to the second harmonic of the fundamental frequency of the clock signal used to input current to drive coil, is typically required by sense circuit  122 . 
       FIG. 6  shows a block diagram that illustrates an example of a prior art fluxgate magnetometer  600 . Fluxgate magnetometer  600  is similar to fluxgate magnetometer  100  and, as a result, utilizes the same reference numerals to designate the structures which are common to both fluxgate magnetometers. 
     As shown in  FIG. 6 , fluxgate magnetometer  600  differs from fluxgate magnetometer  100  in that fluxgate magnetometer  600  utilizes a magnetic core structure  610  in lieu of magnetic core structure  114 . Magnetic core structure  610  differs from magnetic core structure  114  in that magnetic core structure  610  has flared ends. Fluxgate magnetometer  600  operates the same as fluxgate magnetometer  100  except that the flared ends of magnetic core structure  610  capture additional flux and channel the additional flux into the body of magnetic core structure  610 , thereby functioning as a flux concentrator. 
       FIG. 7  shows a block diagram that illustrates an example of a prior art fluxgate magnetometer  700 . Fluxgate magnetometer  700  is similar to fluxgate magnetometer  100  and, as a result, utilizes the same reference numerals to designate the structures which are common to both fluxgate magnetometers. 
     As shown in  FIG. 7 , fluxgate magnetometer  700  differs from fluxgate magnetometer  100  in that fluxgate magnetometer  700  utilizes a magnetic core structure  710  in lieu of magnetic core structure  114 . Magnetic core structure  710  differs from magnetic core structure  114  in that magnetic core structure  710  has a narrow center section. In addition, fluxgate magnetometer  700  differs from fluxgate magnetometer  100  in that sense coil  112  of fluxgate magnetometer  700  is only wrapped around the narrow center section of magnetic core structure  710 . 
     Fluxgate magnetometer  700  operates the same as fluxgate magnetometer  100  except that the narrow section of magnetic core structure  710  saturates faster than the remaining sections of magnetic core structure  710 . As a result, less current is required to saturate the section of magnetic core structure  710  that is wrapped by sense coil  112 . 
     Although the fluxgate magnetometers  100 ,  300 ,  400 ,  600 , and  700  each measures the strength of an external magnetic field, the fluxgate magnetometers  100 ,  300 ,  400 ,  600 , and  700  tend to be bulky and expensive to manufacture. In addition, the fluxgate magnetometers  100 ,  300 ,  400 ,  600 , and  700  provide only a one dimensional (1D) measure of a magnetic field. 
     Two dimensional (2D) measurements of the magnetic field taken along an x-axis and a y-axis can be provided, for example, by using two fluxgate magnetometers with two magnetic core structures that have been arranged so that the two magnetic core structures lie perpendicular to each other. 
     Three dimensional (3D) measurements of the magnetic field can be provided by adding a z-axis fluxgate magnetometer to a 2D fluxgate magnetometer, where the z-axis fluxgate magnetometer has a magnetic core structure that lies perpendicular to both the x-axis and y-axis magnetic core structures. 
     3D magnetometers tend to use a co-packaged solution, such as Honeywell&#39;s HMC6343, where the magnetometer in a first package is attached to a 2D magnetometer in a second package. However, in addition to being bulky, it is difficult to attach the two packages together so that the magnetic core structures for the three axes are mutually perpendicular. Thus, there is a need for a smaller, easier to fabricate, and less expensive fluxgate magnetometer which can measure a magnetic field in the z direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of a prior art fluxgate magnetometer  100 . 
         FIGS. 2A-2E  are views illustrating the operation of fluxgate magnetometer  100 .  FIG. 2A  is a graph illustrates a BH curve  200  for magnetic core structure  114 .  FIG. 2B  is a graph illustrating an alternating current input to drive coil  110 .  FIG. 2C  is a graph illustrating the magnetic induction field B that results from the alternating current input to drive coil  110 .  FIG. 2D  is a graph illustrating an induced voltage in sense coil  112  plotted in the time domain that results from the magnetic induction field B.  FIG. 2E  is a graph illustrating an induced voltage in sense coil  112  plotted in the frequency domain that results from the magnetic induction field B. 
         FIG. 3  is a block diagram illustrating an example of a prior art fluxgate magnetometer  300 . 
         FIG. 4  is a block diagram illustrating an example of a prior art fluxgate magnetometer  400 . 
         FIG. 5  is a graph further illustrating the operation of fluxgate magnetometer  400 . 
         FIG. 6  is a block diagram illustrating an example of a prior art fluxgate magnetometer  600 . 
         FIG. 7  is a block diagram illustrating an example of a prior art fluxgate magnetometer  700 . 
         FIGS. 8A-8F  are views illustrating an example of a z-axis semiconductor fluxgate magnetometer  800  in accordance with the present invention.  FIG. 8A  is a perspective view.  FIG. 8B  is a plan view of a fourth metal layer,  FIG. 8C  is a plan view of a third metal layer,  FIG. 8D  is a plan view of a second metal layer, and  FIG. 8E  is a plan view of a first metal layer.  FIG. 8F  is a cross-sectional view that shows a coil section of magnetometer  800  taken along line  8 F- 8 F of  FIGS. 8B-8E , and a die section of magnetometer  800 . 
         FIGS. 9A-9C  through  42 A- 42 C are a series of views illustrating an example of a method of forming a z-axis semiconductor fluxgate magnetometer in accordance with the present invention.  FIGS. 9A-42A  are a series of plan views, while  FIGS. 9B-42B  are a series of cross-sectional views taken along lines  9 B- 42 B, respectively, in  FIGS. 9A-42A , and  FIGS. 9C-42C  are a series of cross-sectional views taken along lines  9 C- 42 C, respectively, in  FIGS. 9A-42A . 
         FIGS. 43A-43F  are views illustrating an example of a z-axis semiconductor fluxgate magnetometer  4300  in accordance with an alternate embodiment of the present invention.  FIG. 43A  is a plan view of a fourth metal layer,  FIG. 43B  is a plan view of a third metal layer,  FIG. 43C  is a plan view of a second metal layer, and  FIG. 43D  is a plan view of a first metal layer.  FIG. 43E  is a cross-sectional view that shows a coil section of magnetometer  4300  taken along line  43 E- 43 E of  FIGS. 43A-43D , and a die section of magnetometer  4300 .  FIG. 43F  is a cross-sectional view that shows a coil section of magnetometer  4300  taken along line  43 F- 43 F in  FIGS. 43A-43D , and a die section of magnetometer  4300 . 
         FIGS. 44A-44E  are views illustrating an example of a z-axis semiconductor fluxgate magnetometer  4400  in accordance with an alternate embodiment of the present invention.  FIG. 44A  is a plan view of a fourth metal layer,  FIG. 44B  is a plan view of a third metal layer,  FIG. 44C  is a plan view of a second metal layer, and  FIG. 44D  is a plan view of a first metal layer.  FIG. 44E  is a cross-sectional view that shows a coil section of magnetometer  4400  taken along line  44 E- 44 E in  FIGS. 44A-44D , and a die section of magnetometer  4400 . 
         FIGS. 45A-45E  are views illustrating an example of a z-axis semiconductor fluxgate magnetometer  4500  in accordance with an alternate embodiment of the present invention.  FIG. 45A  is a plan view of a fourth metal layer,  FIG. 45B  is a plan view of a third metal layer,  FIG. 45C  is a plan view of a second metal layer, and  FIG. 45D  is a plan view of a first metal layer.  FIG. 45E  is a cross-sectional view that shows a coil section of magnetometer  4500  taken along line  45 E- 45 E in  FIGS. 45A-45D , and a die section of magnetometer  4500 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 8A-8F  show views that illustrate an example of a z-axis semiconductor fluxgate magnetometer  800  in accordance with the present invention.  FIG. 8A  shows a perspective view.  FIG. 8B  shows a plan view of a fourth metal layer,  FIG. 8C  shows a plan view of a third metal layer, FIG.  8 D shows a plan view of a second metal layer, and  FIG. 8E  shows a plan view of a first metal layer.  FIG. 8F  shows a cross-sectional view that illustrates a coil section of magnetometer  800  taken along line  8 F- 8 F of  FIGS. 8B-8E , and a die section of magnetometer  800 . As described in greater detail below, the present invention provides a semiconductor fluxgate magnetometer that measures magnetic fields in the z-direction. 
     As shown in  FIGS. 8A-8F , z-axis semiconductor fluxgate magnetometer  800  includes a semiconductor structure  810  that has a bottom surface  810 B, a top surface  810 T, and a cavity  814  that extends from the top surface  810 T down into semiconductor structure  810 . Cavity  814 , in turn, has a side wall surface  814 S and a bottom surface  814 B that lies above and vertically spaced apart from the bottom surface  810 B of semiconductor structure  810 . In addition, bottom surface  814 B can be either conductive or non-conductive. 
     As further shown in  FIGS. 8A-8F , z-axis semiconductor fluxgate magnetometer  800  includes a die  816  that lies in cavity  814 , and an adhesive  818  that attaches die  816  to the bottom surface  814 B of cavity  814 . Die  816  has a side wall surface  816 S, a bottom surface  816 B that touches adhesive  818 , and a number of conductive pads  816 P that provide external electrical connection points for die  816 . 
     In addition, die  816  includes the drive and sense circuits. In the present example, the drive circuit is conventionally implemented, and includes all of the electrical components that are required to output an alternating current to a drive coil, and a clock signal to the sense circuit that is equal to the second harmonic of the fundamental frequency of the alternating current that is output to the drive coil. 
     Further, the sense circuit is conventionally implemented, and includes all of the electrical components that are required to detect an alternating voltage that has been induced in a sense coil, isolate the second harmonic of the induced alternating voltage, and generate an output voltage that represents the magnitude of the second harmonic of the induced alternating voltage (which is proportional to the magnitude of an external magnetic field). 
     Adhesive  818 , in turn, can be implemented with, for example, a conductive or non-conductive epoxy or die attach film. In addition, adhesive  818 , which can be, for example, 25 μm thick, can be selected based on any isolation and thermal requirements of die  816  and whether the bottom surface  814 B of cavity  814  is conductive or non-conductive. 
     Z-axis semiconductor fluxgate magnetometer  800  also includes a non-conductive structure  820  that touches die  816  and semiconductor structure  810 . Non-conductive structure  820 , which fills up the remainder of cavity  814 , has a number of openings  820 P that expose the conductive pads  816 P on die  816 . 
     Further, z-axis semiconductor fluxgate magnetometer  800  includes a magnetic core structure  822  and number of metal-1 structures  824  that touch non-conductive structure  820 . The metal-1 structures  824  include a number of via structures  824 V that extend through non-conductive structure  820  to touch a first group of the conductive pads  816 P which represent the power/ground and input/output signal pads of die  816 , a number of via trace structures  824 T with via sections that extend through non-conductive structure  820  to touch a second group of the conductive pads  816 P which represent input/output coil pads, and a trace structure  824 C that touches a via trace structure  824 T. 
     Trace structure  824 C, in turn, has a number of loops that form a planar coil where all of the top surface of trace structure  824 C lies substantially in a plane P 1 . In addition, although trace structure  824 C is illustrated with two loops in  FIG. 8E , a larger number or a smaller number of loops can alternately be used. 
     Z-axis semiconductor fluxgate magnetometer  800  further includes a non-conductive structure  830  that touches non-conductive structure  820 , magnetic core structure  822 , the via structures  824 V, the via trace structures  824 T, and trace structure  824 C. Non-conductive structure  830  has a substantially planar top surface  830 T, and a number of openings  830 P that expose the surfaces of magnetic core structure  822 , the via structures  824 V, the via traces  824 T that are to be connected to higher metal layers, and an end of trace structure  824 C. 
     In addition, z-axis semiconductor fluxgate magnetometer  800  includes a magnetic core structure  832  and number of metal-2 structures  834  that touch non-conductive structure  830 . Magnetic core structure  832  touches and lies above magnetic core structure  822 . The metal-2 structures  834 , in turn, include a number of via structures  834 V that extend through non-conductive structure  830  to touch the via structures  824 V, and a number of via trace structures  834 T with via sections that extend through non-conductive structure  830  to touch the via traces  824 T. The metal-2 structures  834  also include a vertical member  8343  that touches the end of trace structure  824 C, and a trace structure  834 C that touches a via trace structure  834 T. 
     Trace structure  834 C, in turn, has a number of loops that form a planar coil where all of the top surface of trace structure  834 C lies substantially in a plane P 2 . In addition, although trace structure  834 C is illustrated with one and one quarter loops in  FIG. 8D , trace structure  834  can alternately be implemented with a larger number or a smaller number of loops. 
     Z-axis semiconductor fluxgate magnetometer  800  further includes a non-conductive structure  840  that touches non-conductive structure  830 , magnetic core structure  832 , the via structures  834 V, the via trace structures  834 T, and trace structure  834 C. Non-conductive structure  840  has a substantially planar top surface  840 T, and a number of openings  840 P that expose the surface of magnetic core structure  832 , the via structures  834 V, the via traces  834 T that are to be connected to higher metal layers, an end of trace structure  834 C, and vertical member  8341   
     In addition, z-axis semiconductor fluxgate magnetometer  800  includes a magnetic core structure  842  and a number of metal-3 structures  844  that touch non-conductive structure  840 . Magnetic core structure  842  touches and lies above magnetic core structure  832 . The metal-3 structures  844  include a number of via structures  844 V that extend through non-conductive structure  840  to touch the via structures  834 V, and a number of via trace structures  844 T with via sections that extend through non-conductive structure  840  to touch the via traces  834 T. Further, the metal-3 structures  844  include a vertical member  8443  that touches the end of trace structure  834 C, and a trace structure  844 C that touches vertical member  8343  and a via trace structure  844 T. 
     Trace structure  844 C, in turn, has a number of loops that form a planar coil where all of the top surface of trace structure  844 C lies substantially in a plane P 3 . In addition, although trace structure  844 C is illustrated with one and one quarter loops in  FIG. 8C , trace structure  844 C can alternately be implemented with a larger number or a smaller number of loops. 
     Z-axis semiconductor fluxgate magnetometer  800  further includes a non-conductive structure  850  that touches non-conductive structure  840 , magnetic core structure  842 , the via structures  844 V, the via trace structures  844 T, and trace structure  844 C. Non-conductive structure  850  has a substantially planar top surface  850 T, and a number of openings  850 P that expose the surfaces of the magnetic core structure  842 , the via structures  844 V, the via trace structures  844 T that are to be connected to higher metal layers, and vertical member  8441   
     Z-axis semiconductor fluxgate magnetometer  800  additionally includes a magnetic core structure  852  and number of metal-4 structures  854  that touch non-conductive structure  850 . Magnetic core structure  852  touches and lies over magnetic core structure  842 . The metal-4 structures  854 , in turn, include a number of via structures  854 V that extend through non-conductive structure  850  to touch the via structures  844 V, a number of via trace structures  854 T with via sections that extend through non-conductive structure  850  to touch the via traces  844 T, and a trace structure  854 C that touches vertical member  8443  and a via trace structure  854 T. 
     In addition, z-axis semiconductor fluxgate magnetometer  800  includes a non-conductive structure  860  that touches non-conductive structure  850 , magnetic core structure  852 , the via structures  854 V, the via trace structures  854 T, and trace structure  854 C. Non-conductive structure  860  has a substantially planar top surface  860 T, and a number of openings  860 P that expose the via structures  854 V. 
     Z-axis semiconductor fluxgate magnetometer  800  further includes a number of bond pad structures  864  that touch non-conductive structure  860  and extend through non-conductive structure  860  to touch the via structures  854 V, and a non-conductive passivation structure  870  that touches non-conductive structure  860  and the bond pad structures  864 . Passivation structure  870  has a substantially planar top surface  870 T. 
     Thus, together the non-conductive structures  820 ,  830 ,  840 ,  850 ,  860 , and  870  form a non-conductive structure  872  that has a top surface  872 T. In addition, the magnetic core structures  822 ,  832 ,  842 , and  852  together form a magnetic core pole structure  874 . 
     Further, vertical member  8343  electrically connects trace structure  824 C to trace structure  844 C to form a drive coil  880  which has vertically spaced apart horizontal loops that are wrapped around magnetic core pole structure  874 . Similarly, vertical member  8443  electrically connects trace structure  834 C to trace structure  854 C to form a sense coil  882  which has vertically spaced apart horizontal loops that are wrapped around magnetic core pole structure  874 . Further, a loop of drive coil  880  lies vertically between the horizontal loops of sense coil  882 . 
     In operation, the drive circuit of die  816  outputs an alternating current to drive coil  880 , and a clock signal to the sense circuit of die  816  that is equal to second harmonic of the fundamental frequency of the alternating current that is output to drive coil  880 . The alternating current in drive coil  880  sets up an alternating magnetic induction field that induces an alternating voltage in sense coil  882 . 
     The sense circuit detects the alternating voltage in sense coil  882 , isolates the second harmonic of the alternating voltage in sense coil  882 , identifies a magnitude of the second harmonic, and generates an output voltage with a magnitude that is proportional to the magnitude of the external magnetic field. 
       FIGS. 9A-9C  through  42 A- 42 C show a series of views that illustrate an example of a method of forming a z-axis semiconductor fluxgate magnetometer in accordance with the present invention.  FIGS. 9A-42A  show a series of plan views, while  FIGS. 9B-42B  show a series of cross-sectional views taken along lines  9 B- 42 B, respectively, in  FIGS. 9A-42A , and  FIGS. 9C-42C  show a series of cross-sectional views taken along lines  9 C- 42 C, respectively, in  FIGS. 9A-42A . 
     As shown in the  FIGS. 9A-9C , the method of forming a z-axis semiconductor fluxgate magnetometer utilizes a conventionally-formed semiconductor wafer  910 . Wafer  910 , in turn, can be implemented with a conducting material, such as silicon, or a non-conducting material such as quartz or G10-FR4 glass epoxy laminates. As further shown in  FIGS. 9A-9C , the method begins by forming a patterned photoresist layer  912  on the top surface of wafer  910 . 
     Patterned photoresist layer  912  is formed in a conventional manner, which includes depositing a layer of photoresist, projecting a light through a patterned black/clear glass plate known as a mask to form a patterned image on the layer of photoresist that softens the photoresist regions exposed by the light, and removing the softened photoresist regions. 
     As shown in  FIGS. 10A-10C , after patterned photoresist layer  912  has been formed, the exposed regions of wafer  910  are etched in a conventional manner to form a large number of cavities  914 , which each has a bottom surface  914 B, in wafer  910 . (Only one cavity  914  is shown for simplicity.) Wafer  910  can be etched using a dry etch such as reactive ion etching, or a timed wet etch. 
     After the etch, the resulting structure is rinsed, and patterned photoresist layer  912  is then removed in a conventional manner, such as with acetone. Once patterned photoresist layer  912  has been removed, the resulting structure is conventionally cleaned to remove organics, such as with a Piranha etch (e.g., using a solution of 50 H 2 SO 4 :1 H 2 O 2  @ 120° C. removes approximately 240 nm/minute). If wafer  910  is conductive, wafer  910  can optionally include a non-conductive top layer, such as an oxide layer with an overlying nitride layer, which lines cavity  914  to provide a non-conductive surface. 
     Next, as shown in  FIGS. 11A-11C , a die  916  is placed in each cavity  914  and attached to the bottom surface  914 B of the cavity  914  using an adhesive  918  such as, for example, a conductive or non-conductive epoxy or die attach film. Adhesive  918 , which can be, for example, 25 μm thick, can be selected based on any isolation and thermal requirements of die  916  and whether the bottom surface  914 B of cavity  914  is conductive or non-conductive. Die  916 , which includes the drive and sense electronics and a number of conductive pads  920 , can be placed in and attached to the bottom surface  914 B of cavity  914  using a conventional pick and place machine. 
     As shown in  FIGS. 12A-12C , after die  916  has been attached to the bottom surface  914 B of cavity  914 , a non-conductive structure  922  is formed to touch die  916  and wafer  910 . Non-conductive structure  922 , which fills up the remainder of cavity  914 , has a number of openings  922 P that expose the conductive pads  920  on die  916 . 
     In the present example, as shown in  FIGS. 13A-13C , non-conductive structure  922  is formed by depositing a layer of photoimageable epoxy or polymer  924 , such as SU-8, benzocyclobutene (BCB), or polybenzoxazole (PBO), which are substantially self planarizing. Once the photoimageable epoxy or polymer has been deposited, a number of openings  924 P are formed in photoimageable epoxy or polymer layer  924  by projecting a light through a mask to form a patterned image on layer  924  that softens the regions of layer  924  that are exposed by the light, and then removing the softened regions of layer  924 . 
     After the openings  924 P have been formed, as shown in  FIGS. 14A-14C , a layer of nitride  926  approximately 0.6 μm thick is conventionally formed on photoimageable epoxy or polymer layer  924  to line the openings  924 P using, for example, plasma-enhanced chemical vapor deposition (PECVD). 
     Following this, a patterned photoresist layer  928  is conventionally formed on nitride layer  926 . The exposed regions of nitride layer  926  are then etched to expose the conductive pads  920  on die  916 . Patterned photoresist layer  928  is then removed in a conventional manner to complete the formation of non-conductive structure  922 . (The formation and etch of nitride layer  926 , which is used to provide a copper diffusion barrier, are optional and can be omitted.) 
     As shown in  FIGS. 15A-15C , after non-conductive structure  922  has been formed, a number of metal-1 structures  930  are formed to touch non-conductive structure  922 . The metal-1 structures  930  include a number of via structures  930 V that also touch a first group of the conductive pads  920 , a number of via trace structures  930 T that also touch a second group of the conductive pads  920 , and a trace structure  930 C with a number of loops. The metal-1 structures  930  can be formed in a number of different ways. 
     As shown in  FIGS. 16A-16C , in a first embodiment, the metal-1 structures  930  can be formed by depositing a seed layer  932  to touch non-conductive structure  922  and the conductive pads  920 . For example, seed layer  932  can be implemented with a layer of aluminum copper. Seed layer  932  can alternately be formed by depositing 300 Å of titanium, 3000 Å of copper, and 300 Å of titanium. After seed layer  932  has been formed, a plating mold  934  is formed on the top surface of seed layer  932 . 
     As shown in  FIGS. 17A-17C , following the formation of plating mold  934 , copper is electroplated in a conventional manner to form a number of copper regions  936  approximately 5 μm thick. After the electroplating, as shown in  FIGS. 18A-18C , plating mold  934  and the underlying regions of seed layer  932  are removed to form the via structures  930 V, the via trace structures  930 T, and trace structure  930 C. 
     Alternately, in a second embodiment, as shown in  FIGS. 19A-19C , the metal-1 structures  930  can be formed by first depositing a liner layer  940  on non-conductive structure  922  to line the openings  922 P. Liner layer  940  can be implemented with, for example, titanium/titanium nitride. After liner layer  940  has been formed, a metal layer  942 , such as tungsten, is conventionally deposited on liner layer  940  to fill up the openings  922 P. 
     Following this, as shown in  FIGS. 20A-20C , metal layer  942  is planarized, such as with chemical-mechanical polishing, to expose the top surface of non-conductive structure  922 , and form via plug structures  942 P in the openings  922 P that make electrical connections to the conductive pads  920  of die  916 . 
     As shown in  FIGS. 21A-21C , after the via plug structures  942 P have been formed, a metal layer  944 , such as aluminum, is sputter deposited onto non-conductive structure  922  to a depth of approximately 5 μm. Alternately, metal layer  944  can include multiple layers of metal such as, for example, a layer of titanium, a layer of titanium nitride, a layer of aluminum copper, a layer of titanium, and a layer of titanium nitride. 
     Once metal layer  944  has been formed, a patterned photoresist layer  946  approximately 1.0 μm thick is formed on the top surface of metal layer  944  in a conventional manner. Following the formation of patterned photoresist layer  946 , metal layer  944  is etched to remove the exposed regions of metal layer  944  and form the metal-1 structures  930 . 
     Metal layer  944  can be etched using a dry etch such as reactive ion etching, or a timed wet etch. For example, aluminum can be wet etched in a 10:1 hydrogen fluoride solution for the necessary period of time. After the etch, the resulting structure is rinsed, and patterned photoresist layer  946  is then removed in a conventional manner, such as with acetone. Once patterned photoresist layer  946  has been removed, the resulting structure is conventionally cleaned to remove organics, such as with a Piranha etch. 
     As shown in  FIGS. 22A-22C , after the via structures  930 V, the via trace structures  930 T, and trace structure  930 C have been formed, a magnetic core structure  950  is formed on the top surface of non-conductive structure  922 . Magnetic core structure  950 , in turn, can be formed in a number of ways. 
     In a first embodiment, as shown in  FIGS. 23A-23C , a layer of silicon nitride  952  approximately 0.6 μm thick is deposited on the top surfaces of non-conductive structure  922 , the via structures  930 V, the via trace structures  930 T, and trace structure  930 C, followed by the deposition of a seed layer  954  on the top surface of nitride layer  952 . For example, seed layer  954  can be implemented with a layer of aluminum copper. Seed layer  954  can alternately be formed by depositing 300 Å of titanium, 3000 Å of copper, and 300 Å of titanium. 
     After seed layer  954  has been formed, a magnetic material with a high permeability and a low resistance, such as an alloy of nickel and iron like permalloy, is electroplated to a thickness of, for example, 5 μm to form a magnetic material layer  956 . Following this, a patterned photoresist layer  958  is formed on magnetic material layer  956 . 
     Next, as illustrated in  FIGS. 24A-24C , the exposed regions of magnetic material layer  956  and seed layer  954  are etched and removed to form magnetic core structure  950 . In this example, nitride layer  952  is left in place, but the exposed regions of nitride layer  952  could alternately be removed. Patterned photoresist layer  958  is then removed in a conventional manner, such as with acetone. Once patterned photoresist layer  958  has been removed, the resulting structure is conventionally cleaned to remove organics. In addition, a plating mold can alternately be used to define the regions where the magnetic material is to be electroplated. 
     In a second embodiment, as shown in  FIGS. 25A-25C , a layer of silicon nitride  960  approximately 0.6 μm thick is deposited on the top surfaces of non-conductive structure  922 , the via structures  930 V, the via trace structures  930 T, and trace structure  930 C, followed by the sputter deposition of a magnetic material layer  962  onto the top surface of non-conductive structure  922 , the via structures  930 V, the via trace structures  930 T, and trace structure  930 C. Magnetic material layer  962  can be implemented with, for example, cobalt tantalum zirconium (CoTaZr) or permalloy, materials which have a high permeability and a low resistance. 
     Following this, a patterned photoresist layer  964  is formed on magnetic material layer  962 . As shown in  FIGS. 26A-26C , after patterned photoresist layer  964  has been formed, the exposed regions of magnetic material layer  962  are etched and removed to form magnetic core structure  950 . Patterned photoresist layer  964  is then removed in a conventional manner, such as with acetone. Once patterned photoresist layer  964  has been removed, the resulting structure is conventionally cleaned to remove organics. (The order of forming the metal-1 structures  930  and magnetic core structure  950  can alternately be reversed.) 
     In the present example, the magnetic material layers  956  and  962  are subjected to the presence of a strong magnetic field that so that the magnetic material layers  956  and  962  are uniaxially anisotropic. The strong magnetic field can be applied during the plating or deposition of the magnetic material. Alternately, the strong magnetic field can be applied during an anneal at elevated temperatures after the plating or deposition of the magnetic material. 
     Following the formation of magnetic core structure  950 , as shown in  FIGS. 27A-27C , a non-conductive structure  966  is formed on non-conductive structure  922 , the via structures  930 V, the via trace structures  930 T, and trace structure  930 C. Non-conductive structure  966  has a substantially planar top surface  966 T, and a number of openings  966 P that expose the via structures  930 V, the via trace structures  930 T that are to be connected to higher metal levels, the end of trace structure  930 C, and magnetic core structure  950 . Non-conductive structure  966  can be formed in a number of different ways. 
     For example, as shown in  FIGS. 28A-28C , in a first embodiment, non-conductive structure  966  can be formed by conventionally depositing a silicon nitride layer  966 N approximately 0.6 μm thick on non-conductive structure  922 , the via structures  930 V, the via trace structures  930 T, trace structure  930 C, and magnetic core structure  950 . After this, a layer of silicon dioxide  966 X is conventionally formed on the top surface of silicon nitride layer  966 N. 
     Following the formation of oxide layer  966 X, oxide layer  966 X is planarized in a conventional manner, such as with chemical-mechanical polishing, until oxide layer  966 X has a substantially planar top surface. Once oxide layer  966 X has been planarized, a hard mask  968  is formed on substantially planar top surface of oxide layer  966 X. 
     As shown in  FIGS. 29A-29C , hard mask  968  can be formed by conventionally depositing a layer of masking material  968 M, such as a layer of aluminum, or a layer of oxide with an overlying layer of nitride, followed by the conventional formation of a patterned photoresist layer  968 H. After this, the exposed regions of masking material  968 M are etched to form the openings in hard mask  968 . Patterned photoresist layer  968 H is then removed in a conventional manner to complete the formation of hard mask  968 . 
     After hard mask  968  has been formed, as shown in  FIGS. 30A-30C , the exposed regions of oxide layer  966 X and nitride layer  966 N are etched away to form the openings  966 P that exposes the via structures  930 V, the via trace structures  930 T that are to be connected to higher metal levels, an end of trace structure  930 C, and magnetic core structure  950 . After the via structures  930 V, the via trace structures  930 T that are to be connected to higher metal levels, an end of trace structure  930 C, and magnetic core structure  950  have been exposed, hard mask  968  is removed in a conventional manner to form non-conductive structure  966 . Alternately, depending on the thickness of the dielectric to be etched, a thick patterned photoresist layer can be used in lieu of hard mask  968 . 
     When the metal-1 structures  930  are formed as in the first embodiment (electroplated), nitride layer  926  and nitride layer  966 N surround the copper structures and prevent copper diffusion. Alternately, when the metal-1 structures  930  are formed as in the second embodiment (metal deposition, mask, and etch), silicon nitride layers  926  and  966 N can be omitted when a copper diffusion barrier is not required. 
     Alternately, as shown in  FIGS. 31A-31C , non-conductive structure  966  can be formed by depositing a layer of photoimageable epoxy or polymer  966 E on non-conductive structure  922 . The photoimageable epoxy or polymer layer  966 E can be implemented with, for example, SU-8, benzocyclobutene (BCB), or polybenzoxazole (PBO), which are substantially self planarizing. 
     Once photoimageable epoxy or polymer layer  966 E has been deposited, the openings  966 P are formed in photoimageable epoxy or polymer layer  966 E by projecting a light through a mask to form a patterned image on layer  966 E that softens the regions of layer  966 E that are exposed by the light, and then removing the softened regions of layer  966 E. 
     As shown in  FIGS. 32A-32C , after non-conductive structure  966  has been formed, a number of metal-2 structures  970  are formed to touch non-conductive structure  966 . The metal-2 structures  970  include a number of via structures  970 V that touch the via structures  930 V, a number of via trace structures  970 T, a vertical member  970 M that touches the end of trace structure  930 C, and a trace structure  970 C with a number of loops. The metal-2 structures can be formed in the same way that the metal-1 structures  930  are formed. 
     Following the formation of the metal-2 structures  970 , as shown in  FIGS. 33A-33C , a magnetic core structure  972  is formed on the top surface of non-conductive structure  966  to touch magnetic core structure  950 . Magnetic core structure  972  can be formed in the same way that magnetic core structure  950  is formed. 
     Next, as shown in  FIGS. 34A-34C , a non-conductive structure  974  is formed on non-conductive structure  966 , the via structures  970 V, the via trace structures  970 T, vertical member  970 M, trace structure  970 C, and magnetic core structure  972 . Non-conductive structure  974  has a substantially planar top surface  974 T, and a number of openings  974 P that expose the via structures  970 V, the via trace structures  970 T that are to be connected to higher metal levels, an end of trace structure  930 C, and magnetic core structure  972 . Non-conductive structure  974  can be formed in the same way that non-conductive structure  966  is formed. 
     As shown in  FIGS. 35A-35C , after non-conductive structure  974  has been formed, a number of metal-3 structures  976  are formed to touch non-conductive structure  974 . The metal-3 structures  976  include a number of via structures  976 V that touch the via structures  970 V, a number of via trace structures  976 T, a vertical member  976 M that touches the end of trace structure  970 C, and a trace structure  976 C with a number of loops and an end that touches vertical member  970 M. The metal-3 structures  976  can be formed in the same way that the metal-1 structures  930  are formed. 
     Following the formation of the metal-3 structures  976 , as shown in  FIGS. 36A-36C , a magnetic core structure  980  is formed on the top surface of non-conductive structure  974  to touch magnetic core structure  972 . Magnetic core structure  980  can be formed in the same way that the magnetic core structure  950  is formed. 
     Next, as shown in  FIGS. 37A-37C , a non-conductive structure  982  is formed on non-conductive structure  974 , the via structures  976 V, the via trace structures  976 T, vertical member  976 M, trace structure  976 C, and magnetic core structure  980 . Non-conductive structure  982  has a substantially planar top surface  982 T, and a number of openings  982 P that expose the via structures  976 V, the via trace structures  976 T that are to be connected to higher metal levels, an end of trace structure  976 C, and magnetic core structure  980 . Non-conductive structure  982  can be formed in the same way that non-conductive structure  966  is formed. 
     As shown in  FIGS. 38A-38C , after non-conductive structure  982  has been formed, a number of metal-4 structures  984  are formed to touch non-conductive structure  982 . The metal-4 structures  984  include a number of via structures  984 V that touch the via structures  976 V, a via trace structure  984 T, and a trace structure  984 C with a number of loops and an end that touches vertical member  976 M. The metal-4 structures  984  can be formed in the same way that the metal-1 structures  930  are formed. 
     Following the formation of the metal-4 structures  984 , as shown in  FIGS. 39A-39C , a magnetic core structure  986  is formed on the top surface of non-conductive structure  982  to touch magnetic core structure  980 . Magnetic core structure  986  can be formed in the same way that the magnetic core structure  950  is formed. 
     Next, as shown in  FIGS. 40A-40C , a non-conductive structure  988  is formed on non-conductive structure  982 , the via structures  984 V, the via trace structures  984 T, trace structure  984 C, and magnetic core structure  986 . Non-conductive structure  988  has a substantially planar top surface  988 T, and a number of openings  988 P that expose the via structures  988 V. Non-conductive structure  988  can be formed in the same way that non-conductive structure  966  is formed. 
     As shown in  FIGS. 41A-41C , after non-conductive structure  988  has been formed, a number of bond pad structures  990  are formed to touch the via structures  984 V and non-conductive structure  988 . The bond pad structures  990  can be formed by depositing a layer of metal, such as aluminum, and then masking and etching the layer of metal to leave the bond pad structures  990 . 
     Following the formation of the bond pad structures  990 , as shown in  FIGS. 42A-42C , a passivation structure  992  is formed to touch non-conductive structure  988  and the bond pad structures  990 , and complete the formation of a z-axis semiconductor fluxgate magnetometer  994 . Passivation structure  992  has a substantially planar top surface  992 T, and a number of openings  992 P that expose the bond pad structures  990 . Passivation structure  992  can be implemented with, for example, a layer of oxide and an overlying layer of nitride. 
       FIGS. 43A-43F  show views that illustrate an example of a z-axis semiconductor fluxgate magnetometer  4300  in accordance with an alternate embodiment of the present invention.  FIG. 43A  shows a plan view of a fourth metal layer,  FIG. 43B  shows a plan view of a third metal layer,  FIG. 43C  shows a plan view of a second metal layer, and  FIG. 43D  shows a plan view of a first metal layer.  FIG. 43E  shows a cross-sectional view that shows a coil section of magnetometer  4300  taken along line  43 E- 43 E of  FIGS. 43A-43D , and a die section of magnetometer  4300 .  FIG. 43F  shows a cross-sectional view that shows a coil section of magnetometer  4300  taken along line  43 F- 43 F of  FIGS. 43A-43D , and a die section of magnetometer  4300 . Semiconductor fluxgate magnetometer  4300  is similar to semiconductor fluxgate magnetometer  800  and, as a result, utilizes the same reference numerals to designate the structures which are common to both magnetometers. 
     As shown in  FIGS. 43A-43F , z-axis semiconductor fluxgate magnetometer  4300  differs from semiconductor fluxgate magnetometer  800  in that semiconductor fluxgate magnetometer  4300  includes a number of fluxgate magnetometers  4310  that are arranged in rows and columns, and a number of fluxgate magnetometers  4312  that are arranged in rows and columns so that the fluxgate magnetometers  4310  and  4312  alternate. (Only one row of fluxgate magnetometers  4310  and  4312  is shown in  FIGS. 43A-43D  for simplicity). 
     As further shown in  FIGS. 43A-43F , a fluxgate magnetometer  4310  has a magnetic core structure  4314 , and a metal-1 trace structure  4316  that touch the top surface of non-conductive structure  820 . Metal-1 trace structure  4316  has a number of loops wound around and spaced apart from magnetic core structure  4314 , a top surface that lies substantially in plane P 1 , and a segment that touches an adjacent fluxgate magnetometer  4312 . Each fluxgate magnetometer  4312 , in turn, is identical to fluxgate magnetometer  800 . 
     As additionally shown in  FIGS. 43A-43F , a fluxgate magnetometer  4310  also has a magnetic core structure  4318 , and a number of metal-2 structures  4320  that touch the top surface of non-conductive structure  830 . Magnetic core structure  4318  touches and lies over magnetic core structure  4314 . The metal-2 structures  4320 , in turn, include a vertical member  4320 J that touches an end of metal-1 trace structure  4316 , and a trace structure  4320 C that has a number of loops wound around and spaced apart from magnetic core structure  4318 . Metal-2 trace structure  4320  has a top surface that lies substantially in plane P 2 , and a segment that touches an adjacent fluxgate magnetometer  4312 . 
     A fluxgate magnetometer  4310  further has a magnetic core structure  4321 , and a number of metal-3 structures  4322  that touch the top surface of non-conductive structure  840 . Magnetic core structure  4321  touches and lies over magnetic core structure  4318 . The metal-3 structures  4322  include a vertical member  4322 J that touches an end of trace structure  4320 C, and a metal-3 trace structure  4322 C that has a number of loops wound around and spaced apart from magnetic core structure  4321 . Metal-3 trace structure  4322 C has an end that touches vertical member  4320 J, a top surface that lies substantially in the plane P 3 , and a segment that touches an adjacent fluxgate magnetometer  4312 . 
     In addition, a fluxgate magnetometer  4310  has a magnetic core structure  4323 , and a metal-4 trace structure  4324  that touch the top surface  850 T of non-conductive structure  850 . Magnetic core structure  4323  touches and lies over magnetic core structure  4321 . Metal-4 trace structure  4324  has a number of loops wound around and spaced apart from magnetic core structure  4323 , and an end that touches vertical member  4322 J. Metal-4 trace structure  4324  has a top surface that lies substantially in plane P 4 , and a segment that touches an adjacent fluxgate magnetometer  4312 . 
     As a result, as shown in  FIGS. 43A-43F , z-axis semiconductor fluxgate magnetometer  4300  has non-conductive structure  872 , which is formed from the non-conductive structures  820 ,  830 ,  840 ,  850 ,  860 , and  870 . In addition, the top surface  872 T of non-conductive structure  872  is substantially planar. 
     Z-axis semiconductor fluxgate magnetometer  4300  also has a magnetic core pole structure  4330  formed from the magnetic core structures  4314 ,  4318 ,  4321 , and  4323 . Thus, z-axis semiconductor fluxgate magnetometer  4300  has a number of magnetic core pole structures  4331  formed from the magnetic core pole structures  874  and  4330 . As shown, each magnetic core pole structure  4331  has a height H, which is the longest dimension, positioned to lie substantially perpendicular to the substantially planar top surface  872 T of non-conductive structure  872 . 
     In addition, z-axis semiconductor fluxgate magnetometer  4300  has a first wire structure  4332  formed from trace structure  824 C, vertical member  8343 , trace structure  844 C, trace structure  4322 C, vertical member  4320 J, and trace structure  4316 . In the present example, first wire structure  4332  is wound around four magnetic core pole structures  4331  to form a drive coil  4334 . 
     Thus, first wire structure  4332  has a lower segment (e.g., trace structure  824 C or trace structure  4316  wound around a magnetic core pole structure (e.g., magnetic core pole structure  874  or magnetic core pole structure  4331 ), an upper segment (e.g., trace structure  844 C or trace structure  4322 C) wound around the magnetic core pole structure, and a vertical segment (e.g., vertical member  8343  or  4320 J) that connect the lower segment to the upper segment. 
     In addition, z-axis semiconductor fluxgate magnetometer  4300  has a second wire structure  4336  formed from trace structure  834 C, vertical member  8443 , trace structure  854 C, trace structure  4324 , vertical member  4322 J, and trace structure  4320 C. In the present example, second wire structure  4336  is wound around four magnetic core pole structures  4331  to form a sense coil  4340 . 
     Thus, second wire structure  4336  has a lower segment (e.g., trace structure  834 C or trace structure  4320 C wound around a magnetic core pole structure (e.g., magnetic core pole structure  874  or magnetic core pole structure  4331 ), an upper segment (e.g., trace structure  854 C or trace structure  4324 ) wound around the magnetic core pole structure, and a vertical segment (e.g., vertical member  8443  or  4322 J) that connect the lower segment to the upper segment. As shown in  FIGS. 43A-43F , plane P 3  lies vertically between the plane P 2  and plane P 4 , and plane P 2  lies vertically between the plane P 1  and plane P 3 . 
     In operation, the drive circuit of die  816  outputs an alternating current I 1  to drive coil  4334 , and a clock signal to the sense circuit of die  816  that is equal to second harmonic of the fundamental frequency of the alternating current that is output to drive coil  4334 . The alternating current I 1  in drive coil  4334  sets up an alternating magnetic induction field that induces an alternating current I 2  and an alternating voltage in sense coil  4340 . 
     The sense circuit of die  816  detects the alternating voltage in sense coil  4340 , isolates the second harmonic of the alternating voltage in sense coil  4340 , identifies a magnitude of the second harmonic, and generates an output voltage with a magnitude that is proportional to the magnitude of the external magnetic field. 
     Z-axis semiconductor fluxgate magnetometer  4300  is formed in the same manner that semiconductor fluxgate magnetometer  800  is formed, except that the method is modified to form and connect together the additional structures. For example, trace structure  4316  is formed at the same time that trace structure  824 C is formed. 
     One of the advantages of z-axis semiconductor fluxgate magnetometer  4300  is that z-axis semiconductor fluxgate magnetometer  4300  provides substantially increased sensitivity due to the increased number of individual fluxgate magnetometers  4310  and  4312  that utilized. In an array form, the sensitivity of the individual fluxgate magnetometers  4310  and  4312  is added together. 
       FIGS. 44A-44E  show views that illustrate an example of a z-axis semiconductor fluxgate magnetometer  4400  in accordance with an alternate embodiment of the present invention.  FIG. 44A  shows a plan view of a fourth metal layer,  FIG. 44B  shows a plan view of a third metal layer,  FIG. 44C  shows a plan view of a second metal layer, and  FIG. 44D  shows a plan view of a first metal layer.  FIG. 44E  shows a cross-sectional view that shows a coil section of magnetometer  4400  taken along line  44 E- 44 E of  FIGS. 44A-44D , and a die section of magnetometer  4300 . Semiconductor fluxgate magnetometer  4400  is similar to semiconductor fluxgate magnetometer  4300  and, as a result, utilizes the same reference numerals to designate the structures which are common to both magnetometers. 
     As shown in  FIGS. 44A-44E , z-axis semiconductor fluxgate magnetometer  4400  differs from semiconductor fluxgate magnetometer  4300  in that semiconductor fluxgate magnetometer  4400  utilizes a magnetic core structure  4404  in lieu of magnetic core structure  4314 , and a magnetic core structure  4406  in lieu of magnetic core structure  822 . The magnetic core structures  4404  and  4406  differ from the magnetic core structures  4314  and  822  in that the magnetic core structures  4404  and  4406  extend through non-conductive structure  820 . 
     As a result, fluxgate magnetometer  4400  has a number of magnetic core pole structures  4408  formed from the magnetic core structures  4404 ,  4318 ,  4321 , and  4323 , and the magnetic core structures  4406 ,  832 ,  842 , and  852 . In addition, the magnetic core structures  4404  and  4406  can be formed in the same manner as the magnetic core structures  832 ,  842 , and  852 . 
     Z-axis semiconductor fluxgate magnetometer  4400  also differs in that z-axis semiconductor fluxgate magnetometer  4400  includes a lower magnetic core structure  4410  that touches the magnetic core pole structures  4408  and lies below and spaced apart from the metal-1 trace structures  824 C and  4316 . In addition, lower magnetic core structure  4410  has a substantially planar top surface that touches non-conductive structure  820 . 
     Z-axis semiconductor fluxgate magnetometer  4400  also differs from semiconductor fluxgate magnetometer  4300  in that semiconductor fluxgate magnetometer  4400  includes an upper magnetic core structure  4412  that touches the magnetic core pole structures  4408  and lies above and spaced apart from the metal-4 trace structures  854 C and  4324 . Further, upper magnetic core structure  4412  has a substantially planar top surface that touches non-conductive passivation structure  870 . 
     In addition, z-axis semiconductor fluxgate magnetometer  4400  differs from semiconductor fluxgate magnetometer  4300  in that semiconductor fluxgate magnetometer  4400  includes a vertical magnetic core structure  4414  that lies horizontally between adjacent pairs of magnetic core pole structures  4331  and touches lower magnetic structure  4410  and upper magnetic core structure  4412 . 
     Vertical magnetic core structure  4414  has a magnetic core structure  4420  that is formed at the same time as magnetic core structures  4404  and  4406 , a magnetic core structure  4422  that is formed at the same time as magnetic core structures  832  and  4318 , a magnetic core structure  4424  that is formed at the same time as magnetic core structures  842  and  4321 , and a magnetic core structure  4426  that is formed at the same time as magnetic core structures  852  and  4323 , 
     Z-axis semiconductor fluxgate magnetometer  4400  operates in the same manner as semiconductor fluxgate magnetometer  4300 , except that lower magnetic core structure  4410 , upper magnetic core structure  4412 , and vertical magnetic core structure  4414  allow the flux to pass completely through a magnetic core material, thereby further increasing the sensitivity. 
     Z-axis semiconductor fluxgate magnetometer  4400  is formed in the same manner as z-axis semiconductor fluxgate magnetometer  4300 , except that lower magnetic core structure  4410  is formed on semiconductor structure  810  before non-conductive structure  820  is formed, and upper magnetic core structure  4412  is formed on non-conductive structure  860  before non-conductive passivation structure  870  is formed. In addition, lower magnetic core structure  4410  and upper magnetic core structure  4412  can be formed in the same manner as magnetic core structure  822  (e.g., electroplate, mask and etch; deposition, mask and etch, or mold and electroplate). Further, magnetic core structures  4420 ,  4422 ,  4424 , and  4426  are formed as indicated. 
       FIGS. 45A-45E  show views that illustrate an example of a z-axis semiconductor fluxgate magnetometer  4500  in accordance with an alternate embodiment of the present invention.  FIG. 45A  shows a plan view of a fourth metal layer,  FIG. 45B  shows a plan view of a third metal layer,  FIG. 45C  shows a plan view of a second metal layer, and  FIG. 45D  shows a plan view of a first metal layer.  FIG. 45E  shows a cross-sectional view that shows a coil section of magnetometer  4500  taken along line  45 E- 45 E of  FIGS. 45A-45D , and a die section of magnetometer  4500 . Semiconductor fluxgate magnetometer  4500  is similar to semiconductor fluxgate magnetometer  4300  and, as a result, utilizes the same reference numerals to designate the structures which are common to both magnetometers. 
     As shown in  FIGS. 45A-45E , z-axis semiconductor fluxgate magnetometer  4500  differs from semiconductor fluxgate magnetometer  4300  in that semiconductor fluxgate magnetometer  4500  utilizes a die  4510  in lieu of die  816 . Die  4510  has a side wall surface  4510 S, a bottom surface  4510 B that touches adhesive  818 , and a number of conductive pads  4510 P that provide external electrical connection points for die  4510 . Die  4510  differs from die  816  in that die  4510  utilizes simplified drive and sense circuits to support a differential coil arrangement in lieu of the drive and sense circuits utilized in die  816 . 
     As additionally shown in  FIGS. 45A-45C , z-axis semiconductor fluxgate magnetometer  4500  also differs from z-axis semiconductor fluxgate magnetometer  4300  in that z-axis semiconductor fluxgate magnetometer  4500  utilizes a first wire structure  4512  in lieu of first wire structure  4332 . 
     First wire structure  4512 , which forms a drive coil  4514 , is identical to first wire structure  4332  except that first wire structure  4512  has loops that are wound around magnetic core pole structures in a first direction (e.g., clockwise) and loops that are wound around magnetic core pole structures in a second direction (e.g., counter clockwise). Second wire structure  4336 , in turn, has loops that are all wound around the magnetic core pole structures in the first direction (e.g., clockwise). 
     First wire structure  4512  has an identical number of loops in the first direction and the second direction, with a number of connecting segments  4512 S which are laid out to minimize any contribution to the magnetic field.  FIGS. 45A-45D  illustrate a single example of the layout of first wire structure  4512 . 
     First wire structure  4512  can alternately be laid out in other ways where the number of loops in the clockwise and counter clock wise direction are equal, and the effects of the connecting segments  4512 S are minimized. For example, having an array of magnetic core pole structures, first wire structure  4512  can be laid out such that all the magnetic core pole structures in a first row, a first block, or a first pattern of magnetic core pole structures are wrapped in the first direction, and all the magnetic core pole structures in a second row, a second equivalent block, or a second equivalent pattern of magnetic core pole structures are wrapped in the second direction. 
     In operation, the drive circuit of die  4510  outputs an alternating current to drive coil  4514 , which generates equal and opposing alternating magnetic induction fields. Thus, when no external magnetic field is present, no voltage is induced in sense coil  4340  because no alternating magnetic induction field is present. 
     When an external magnetic field is present, the presence of the external magnetic field induces an alternating voltage in sense coil  4340 . The sense circuit in die  4510  detects the alternating voltage in sense coil  4340  and generates in response a sensed output voltage, which has an amplitude that is proportional to the magnitude of the external magnetic field. 
     The sense circuit in die  4510  does not detect or utilize the second harmonic of the fundamental frequency of the alternating current that is output to drive coil  4514 . Z-axis semiconductor fluxgate magnetometer  4500  is formed in the same manner that z-axis semiconductor fluxgate magnetometer  4300  is formed. 
     It should be understood that the above descriptions are examples of the present invention, and that various alternatives of the invention described herein may be employed in practicing the invention. For example, the magnetic core structures  4404 ,  4406 ,  4408 ,  4410 ,  4412 , and  4414  can also be used with magnetometer  4500 . Thus, it is intended that the following claims define the scope of the invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.