Abstract:
A micro-electromechanical system (MEMS) based current &amp; magnetic field sensor includes a MEMS-based magnetic field sensing component a structural component comprising a silicon substrate and a compliant layer comprising a material selected from the group consisting of silicon dioxide and silicon nitride, a magnetic-to-mechanical converter coupled to the structural component to provide a mechanical indication of the magnetic field, and a strain responsive component coupled to the structural component to sense the mechanical indication and to provide an indication of the current in the current carrying conductor in response thereto.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 11/129,682 entitled “MICRO-ELECTROMECHANICAL SYSTEM (MEMS) BASED CURRENT &amp; MAGNETIC FIELD SENSOR HAVING CAPACITIVE SENSE COMPONENTS”, which in turn is a continuation-in-part of U.S. patent application Ser. No. 10/863,442 entitled “MEMS BASED CURRENT SENSOR USING MAGNETIC-TO-MECHANICAL CONVERSION AND REFERENCE COMPONENTS”, both of which are hereby fully incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     The present disclosure relates generally to electrical current and magnetic field sensing devices. More particularly, the present disclosure relates to a micro-electromechanical system (MEMS) based current and magnetic field sensor.  
         [0003]     It is known that a current carrying conductor produces a magnetic field in the vicinity of the current carrying conductor. It is also known that the magnetic field produced by the current carrying conductor can induce a force with another current carrying conductor disposed in the magnetic field produced by that current carrying conductor. As such, one approach used to sense electrical current involves the use of a sensor that measures the magnetic field induced by current flowing in a current carrying conductor. Since the generated magnetic field is proportional to the current flowing in the current carrying conductor, such a sensor can use the magnitude of the magnetic field to determine the current.  
         [0004]     Current sensors that use magnetic fields to measure electrical current are well suited for high voltage applications from a safety perspective because they do not have to contact the high voltage circuitry. However, there are several disadvantages associated with existing current sensors that use magnetic fields to measure electrical current in high voltage applications. In general, existing current sensors tend to have a large form factor because they require a thick conductor that can withstand the varying levels of current flow that may be experienced. This current flow induces heating, which reduces the efficiency of the current sensors and introduces a possible error factor in sensor accuracy. Since existing current sensors are large and bulky, their physical and electrical operating characteristics have up to now prevented their use in smaller scale environments. Moreover, existing current sensors do not provide the required levels of sensitivity needed to operate in such small scale environments.  
       BRIEF DESCRIPTION  
       [0005]     In accordance with one aspect of the disclosure a micro-electromechanical system (MEMS) current and magnetic field sensor for sensing a magnetic field produced by a current carrying conductor is provided. The MEMS current and magnetic field sensor includes a structural component comprising a silicon substrate, and a compliant layer comprising a material selected from the group consisting of silicon dioxide and silicon nitride. The sensor further includes a magnetic-to-mechanical converter coupled to the structural component to provide a mechanical indication of the magnetic field, and a strain responsive component coupled to the structural component to sense the mechanical indication and to provide an indication of the current in the current carrying conductor in response thereto.  
         [0006]     In accordance with another aspect of the disclosure, a method for fabricating a MEMS magnetic field sensing component is described. The method includes providing a substrate including a compliant layer comprising a material selected from the group consisting of silicon dioxide and silicon nitride. The method further includes forming a strain responsive component on the substrate, forming a magnetic-to-mechanical converter on the substrate, and removing at least a portion of the substrate to release a spring element formed at least partly by the compliant layer.  
     
    
     DRAWINGS  
       [0007]     These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:  
         [0008]      FIG. 1  is a schematic diagram representative of a MEMS-based current and magnetic field sensing device constructed in accordance with various embodiments of the invention;  
         [0009]      FIG. 2  is a schematic diagram illustrating one embodiment of a MEMS-based magnetic field sensing component of a MEMS-based current sensor;  
         [0010]      FIG. 3  illustrates one embodiment of a MEMS magnetic field sensing component having a cantilever design;  
         [0011]      FIG. 4  illustrates an example MEMS magnetic field sensing component including a half-torsion cantilever design in accordance with one embodiment of the present invention;  
         [0012]      FIG. 5  illustrates an example MEMS magnetic field sensing component including a full-torsion cantilever design in accordance with another embodiment of the invention;  
         [0013]      FIG. 6  illustrates an example MEMS magnetic field sensing component including a half-torsion U-shaped cantilever design in accordance with another embodiment of the invention;  
         [0014]      FIG. 7  illustrates an example MEMS magnetic field sensing component including a full-torsion U-shaped cantilever design in accordance with another embodiment of the invention;  
         [0015]      FIG. 8  illustrates an example MEMS magnetic field sensing component including a shutter-shaped cantilever design in accordance with yet another embodiment of the invention;  
         [0016]      FIG. 9  illustrates an example MEMS magnetic field sensing component including a full-torsion shutter-shaped cantilever design in accordance with yet another embodiment of the invention;  
         [0017]      FIG. 10  illustrates one embodiment of a strain concentrator suitable for use with one or more spring elements described herein;  
         [0018]      FIG. 11  is a schematic sectional side view illustrating aspects of a MEMS magnetic field sensing component in accordance with one embodiment of the present invention;  
         [0019]      FIG. 12  illustrates a resistive bridge suitable for use with the MEMS magnetic field sensing component in accordance with one embodiment; and  
         [0020]      FIG. 13  is a flow diagram illustrating an example fabrication method for one embodiment of a MEMS magnetic field sensing component such as illustrated in  FIG. 11 . 
     
    
     DETAILED DESCRIPTION  
       [0021]     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments of the present invention. However, those skilled in the art will understand that embodiments of the present invention may be practiced without these specific details, that the present invention is not limited to the depicted embodiments, and that the present invention may be practiced in a variety of alternative embodiments. In other instances, well known methods, procedures, and components have not been described in detail.  
         [0022]     Furthermore, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present invention. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, nor that they are even order dependent. Moreover, repeated usage of the phrase “in one embodiment” does not necessarily refer to the same embodiment, although it may. Lastly, the terms “comprising”, “including”, “having”, and the like, as used in the present application, are intended to be synonymous unless otherwise indicated.  
         [0023]      FIG. 1  illustrates one embodiment of a MEMS current and magnetic field sensing device described herein and hereinafter generally referred to as a “current sensor” or “MEMS current sensor”. As shown, the conductor  4  carrying a current I generates a magnetic field  20 . In accordance with one embodiment of the present disclosure, the current sensor  100  can be used to sense the current I in a current carrying conductor  4 , without having to make physical contact with the current carrying conductor. In accordance with the illustrated embodiment, the current sensor  100  operates to sense and determine the current I carried by the conductor  4  by making use of the Lorentz force resulting when the current sensor  100  is positioned in the magnetic field  20  generated by current I. In one embodiment, the current sensor  100  includes a magnetic field sensing component for sensing magnetic fields and for providing, in response thereto, an indication of the current present in the respective conductors to be measured.  
         [0024]     The advantageous size of a MEMS-based current and magnetic field sensor, such as the current sensor  100  described herein, facilitates the sensing of current in applications where space is limited. Moreover, the use of MEMS-based components in a current sensor provides a current sensor that is highly accurate, reliable, robust, and introduces little to no error to the current being sensed. Due, at least in part, to the non-contact sensing methods described herein for sensing current using a MEMS current sensor, the MEMS current sensor preferably has no impact on the magnitude and/or direction of the current being sensed. For example, given the dimensions of MEMS-based components and the sensitivity of the same, the MEMS current sensor preferably does not introduce or cause any appreciable variation or change in the current being sensed or measured. Moreover, the MEMS current sensor is advantageous for its reduced cost and significantly reduced size over existing current sensors. Further, due to micro-lithography and micro-fabrication techniques, the fabrication of the MEMS current sensor is advantaged through increased accuracy and precision.  
         [0025]      FIG. 2  is a schematic diagram illustrating one embodiment of a MEMS-based magnetic field sensing component  25  of a MEMS-based current sensor such as MEMS-based current sensor  100 . In accordance with one embodiment of the present invention, the MEMS-based magnetic field sensing component  25  senses magnetic fields such as magnetic field  20  and provides an indication of the current in a corresponding current carrying conductor, such as conductor  4 . The sensed indication of the current may include both a magnitude and a directional component of the current being sensed. In one embodiment, the sensed indication of the current may be an electrical indication of the current being sensed whereas in other embodiments, the sensed indication may be a mechanical indication.  
         [0026]     In the illustrated embodiment of  FIG. 2 , the MEMS-based magnetic field sensing component  25  includes a magneto-MEMS component  30 , a compensator  55  and an output component  70 . In one embodiment, the magneto-MEMS component  30  may sense a magnetic field and, in response thereto, convert the sensed magnetic field to a mechanical indicator of a corresponding current I. In one embodiment, the output component  70  may provide an output indicative of the current I in the conductor being measured. In one embodiment, output from the output component  70  may take the form of an electrical signal indicative and representative of the magnitude and sign of the current flowing in the conductor being measured.  
         [0027]     In accordance with the illustrated embodiment, the magneto-MEMS component may  30  include a magnetic-to-mechanical converter  35  for converting the magnetic representation of the current I to a mechanical change. In one embodiment, the magnetic-to-mechanical converter  35  may be a conductor such as a metal (e.g., gold (Au) and aluminum (Al)) or another electrically conductive material such as polysilicon. Additionally, the magneto-MEMS component  30  may include a structural component  40  for providing structural support to magneto-MEMS component  30 . The structural component  40  may represent one or more heterogeneous or homogeneous structures, devices, materials, assemblies, sub-systems, elements and so forth. For example, the structural component  40  may include a substrate and one or more spring elements such as but not limited to a deflectable membrane, diaphragm, cantilever, flexure member, torsion element or any number of other elements. In one embodiment of the present invention, the substrate may include a silicon substrate and a low stress silicon region. In one embodiment, the low stress silicon region may include a silicon containing layer having a residual stress of about 50-100 Mega pascals (MPa). In one embodiment, the low stress silicon region may include a low stress silicon nitride layer or film deposited on the silicon substrate.  
         [0028]     In one embodiment, the structural component  40  may be responsive to the mechanical change provided by the magnetic-to-mechanical converter  35  and the structural component  40  may provide a mechanical indicator representative of the current I. In one embodiment, the mechanical indicator may be a force or stress induced on one or more elements of the structural component  40 . The induced force or stress may in turn cause a movement such as a deflection or displacement in a spring element of the structural component  40 . In one embodiment, the structural component  40  may be configured to register a bending or a concurrent bending and twisting action experienced by the structural component  40  responsive to the mechanical indication from the magnetic-to-mechanical converter  35 .  
         [0029]     In yet another embodiment, the mechanical indicator may include modification of a mechanical property of the structural component  40 , such as, for example, a spring constant and the mass thereof. Moreover, the mechanical indicator provided by the structural component  40  may convey the vector space value of the mechanical indicator, including one or more of an associated amplitude, direction, speed, and any other characteristic thereof that can be used to convey the vector space value of the mechanical indicator. In one embodiment, the magneto-MEMS component  30  further includes a strain responsive component  45  which functions as a mechanical sense component for sensing the mechanical indicator provided by the structural component  40 . In one embodiment, the strain responsive component  45  may convert the mechanical indicator or change imparted to the structural component  40  into a strain. In one embodiment, the strain responsive component  45  may include a piezo-resistive element, which exhibits a change in resistive properties responsive to the mechanical indicator. In turn, the change in resistance may be converted to interface signal (e.g., by the output component  70 ) representative of the sensed current I. For example, the amount of stress placed on the piezo resistor may be proportional to the amount of deflection experienced by one or more corresponding spring elements and the magnitude of the current flowing in the magnetic-to-mechanical converter  35 .  
         [0030]     In one embodiment, the strain-to-electrical converter  75  converts the sensed mechanical indicator to a form that may be interpreted and/or further processed by the output stage  80 . Output stage  80  may interface with a memory, an indicator (e.g., a display screen), and/or another device or apparatus (e.g., a digital signal processor or computer-based analyzer) for additional processing of the signal(s) or indicators received from the strain-to-electrical converter  75 .  
         [0031]     The strain-to-electrical converter  75  may be designed based on the nature of the strain responsive component. In one embodiment, the strain-to-electrical converter  75  may be based on a piezo resistive element, however in other embodiments the strain-to-electrical converter  75  may be based on, for example, a metal strain element, a piezoelectric element, a tunneling element, a capacitive element, or an optical element. In one embodiment, the strain-to-electrical converter  75  may include a resistive Wheatstone bridge or a capacitive bridge. In certain embodiments, the functions of the strain responsive component  45  and the strain-to-electrical converter  75  may be performed by a single device or material.  
         [0032]     Additionally, compensator  55  may be used to compensate for effects due to e.g., aging of the sensor, temperature, environmental factors, etc. The compensator  55  may include an excitation source  60  (such as a current source) and a controller  65 . The excitation source  60  may provide excitation quanta (i.e., an amount of excitation energy) for use by the MEMS magnetic field sensing component  25 . The controller  65  may control, for example, a switching and an application of the excitation quanta of the excitation source  60  and the reference signal of the reference component  50 . In one embodiment, reference component  50  may provide a reference indicator for the mechanical indication to the structural component  40 . The controller  65  may be, for example, a switch, an analog processor, a digital signal processor, a digital computing device or an analog-computing device. In the present example, the controller controls at least an on, off, and a value of a bias current supplied to the magnetic-to-mechanical converter  35 . In another embodiment, the controller may select between differing values of the excitation quanta and a plurality of reference components  50 . Such reference components may be included for enhancing a function of the MEMS current sensor. For example, a switch may be included for activating, processing, and controlling logic functions associated with the MEMS current sensor.  
         [0033]     In the illustrated embodiment, a magnetic-to-mechanical converter  35  is coupled to the structural component  40  such that when the magneto-MEMS component  30  is placed in the vicinity of an external current carrying conductor, and a small bias current is flowed in the magnetic-to-mechanical converter  35 , the magnetic field generated by the external conductor will exert a force (e.g., Lorentz force) on the magnetic-to-mechanical converter  35 . The bias current used may be in the range of micro-amps (μA) or milliamps (mA) however a typical bias current might be 1-10 mA. Moreover, a DC or AC bias current may be used without modification to the magneto-MEMS component  30 . Moreover, by driving an AC bias current at frequency that coincides with the resonant frequency of the device, it is possible to further increase sensitivity of the device.  
         [0034]     While discussed primarily in the context of using the Lorentz force between the first and second sense components, the magnetic-to-mechanical converter  35  can be modified to use mutual inductance, a moving loop and a magnetic field generated by an external current carrying conductor. Additionally, other characteristic relationships may be used to derive a mechanical indicator of the mechanical indicator corresponding to the current being sensed.  
         [0035]     Due to batch manufacturing techniques of micro-machining and the associated cost efficiencies, the MEMS magnetic field sensing component and associated MEMS-based current sensor as described herein can be manufactured in large batches using for example, photolithography and etching. As noted above, the MEMS device of  FIG. 2  is but one example of a current sensor contemplated in accordance with the present disclosure. Other embodiments of a MEMS-based current sensor of the present invention may include the use of multiple MEMS devices in the current sensor for the purpose of, for example, magnetic field shaping, magnetic field sensing, current value indicating, and other purposes. Moreover, the description of the components illustrated in  FIG. 2  is intended to be illustrative of one embodiment of a MEMS magnetic field sensing component  25 . To that end, although the output component  70 , the magneto-MEMS component  30  and the compensator  55  of  FIG. 2  appear as separate components, these components and their respective functions may be further combined or further partitioned without departing from the spirit and scope of the disclosure.  
         [0036]      FIG. 3  illustrates one embodiment of a MEMS magnetic field sensing component having a cantilever design. As illustrated in  FIG. 3 , MEMS magnetic field sensing component  200  includes a structural component  40  and a magnetic-to-mechanical converter in the form of a conductor  37 . The structural component  40  includes a substrate portion  103  and a spring element in the form of a cantilever plate  105 . The cantilever plate  105  has been released from the bulk of the substrate  103  along three edges and is supported by a single edge as shown. Accordingly, the cantilever plate  105  may tend to deflect about strain line  125  at the unsupported end in an upward or downward direction perpendicular to the plane of the substrate. In other embodiments, a spring element such as a membrane may be used in place of a cantilever design. Since a membrane would likely be attached to the substrate  103  on four sides, four corresponding strain lines would likely develop.  
         [0037]     In one embodiment, the conductor  37  may be coupled to the structural component  40  to receive a small bias current (I BIAS ) as shown. The conductor  37  may be anchored to the structural component  40  by supports  110  and may be routed in various patterns across and around the cantilever plate embodiment where the magnetic-to-mechanical converter is a conductor (such as the conductor  37  of  FIG. 3 ), the magnetic field sensitivity of the current sensor can be increased depending upon the routing pattern chosen for the conductor. For example, in  FIG. 3  although the conductor  37  is illustrated as a single trace routed along the periphery of the cantilever plate  105 , the conductor  37  may instead include multiple traces routed across the cantilever plate  105  or may be formed into a coil. In one embodiment, nested or coiled conductor traces may be arranged such that the bias current I BIAS  is caused to flow in the same direction across the cantilever plate  105  acting additively to effectively enhance the response of the cantilever plate  105  due to the Lorentz force  120 .  
         [0038]     Based at least in part upon the illustrated configuration, when the MEMS magnetic field sensing component  200  is placed in a magnetic field B, the cantilever plate  105  acting as a spring element is deflected at the end unsupported by the substrate  103  by an amount that is proportional to the magnetic field and by extension, the current being sensed. This is due to the mechanical indication in the form of a Lorentz force  120  generated by the conductor  37  in response to the interaction of the bias current I BIAS  and the magnetic field. In the illustrated embodiment, the cantilever plate  105  may be deflected down into the cavity  115  (formed through e.g., the controlled etching of the bulk substrate  103  as described in further detail below) above which the cantilever plate  105  has been suspended. As the cantilever plate  105  deflects, it experiences a bending force and a resulting strain in the cantilever plate  105  where it joins the substrate  103  as generally indicated by strain line  125 .  
         [0039]     In accordance with one embodiment of the present invention, MEMS magnetic field sensing component  200  is further equipped with strain responsive components  45   a  and  45   b  coupled to the structural component  40  so as to sense the strain generated due to the bending of the cantilever plate  105 . In one embodiment, the strain responsive components  45   a  and  45   b  may represent piezo-resistive elements that are positioned at a location that is coincident with the largest strain experienced by the structural component. For example, in the illustrated embodiment the strain responsive components  45   a  and  45   b  are positioned partially on the substrate  103  and partially on the cantilever plate  105  across the strain line  125 . In the illustrated embodiment, the strain responsive components  45   a  and  45   b  are arranged in a serpentine fashion where multiple ‘legs’ or sections of the strain responsive components cross the strain line  125 . However, in other embodiments the strain responsive components  45   a  and  45   b  may take on other geometric configurations without departing from the spirit and scope of the invention. As will be described in further detail below, one or more strain concentrators may be employed to focus the resulting strain to a more localized area thereby enhancing the sensitivity of the magnetic field sensing component.  
         [0040]     In accordance with one embodiment of the present invention, the strain responsive components  45   a  and  45   b  may be coupled in a resistive bridge arrangement along with balancing resistors  145   a  and  145   b . For example,  FIG. 12  illustrates a resistive bridge suitable for use with the MEMS magnetic field sensing component in accordance with one embodiment. In particular, with reference to  FIG. 12 , the bridge  73  includes strain responsive components  45   a  and  45   b  coupled between balancing resistors  145   a  and  145   b  as shown. As a bias current (e.g., I BIAS ) is applied to conductor  37  and the corresponding MEMS field sensing component is positioned within a magnetic field, one or more characteristics of strain responsive components  45   a  and  45   b  may change. For example, piezo resistive strain responsive components might experience a change in resistivity which can be detected at the S+ and S-locations.  
         [0041]      FIG. 4  illustrates an example MEMS magnetic field sensing component including a half-torsion cantilever design in accordance with one embodiment of the present invention. As illustrated in  FIG. 4 , MEMS magnetic field sensing component  300  includes a structural component  40  further including a substrate  203  and a cavity  115  defined therein. Cavity  115  may be formed in a number of ways including by etching through the backside of the substrate  203 . A dry etching process such as deep reactive ion etching or a wet etching process such as a KOH etching may be used. In one embodiment, an anisotropic etching process may be used such that the walls that define the cavity  115  within the substrate  203  are formed at fixed and/or substantially reproducible angles.  
         [0042]     The MEMS magnetic field sensing component  300  further includes a cantilever plate  205  that is positioned above the cavity  115  as shown. The cantilever plate  205  is similar in form to the cantilever plate  105  of  FIG. 3 , however cantilever plate  205  includes the addition of torsion elements  230 . In the illustrated embodiment, the cantilever plate  205  is coupled to the structural component  40  at the supports  110  by way of the torsion elements  230 . More specifically, in contrast to the cantilever plate  105  of  FIG. 3 , the cantilever plate  205  is additionally released from the substrate  203  along the back edge  207  of the plate. Accordingly, as the MEMS magnetic field sensing component  300  is exposed to a magnetic field and a small bias current (I BIAS ) is applied to the conductor  37 , the cantilever plate  205  may be deflected downward into the cavity  115  (or alternatively upward away from the cavity  115 ) about the torsion elements  230 .  
         [0043]     As the cantilever plate  205  is deflected, a bending as well as a twisting force or torsion occurs in the torsion elements  230  e.g., along the strain line  125 . In accordance with the illustrated embodiment of the invention, strain responsive components  45  in the form of piezo-resistive elements may be coupled to the torsion elements  230  to sense such bending and twisting. In one embodiment, the piezo-resistive elements may be positioned such that their location coincides with those portions of torsion elements  230  that experience the largest torsional stress. The stress is then transferred to the piezo-resistive elements causing the piezo-resistive elements to exhibit a change in their resistive characteristics. This ‘sensed’ stress may then be converted into an electrical signal (e.g., by strain-to-electrical converter  75 ), which is in turn provided to the output stage  80 . In one embodiment, the strain-to-electrical converter function may be performed at least in part by the piezo-resistive element(s) used to sense the mechanical change or stress experienced by the structural component  40 .  
         [0044]      FIG. 5  illustrates an example MEMS magnetic field sensing component including a full-torsion cantilever design in accordance with another embodiment of the invention. As with MEMS magnetic field sensing component  300  of  FIG. 4 , the illustrated MEMS magnetic field sensing component  350  includes both a structural component  40  further including a substrate  203  and a cavity  115  defined therein. Although the MEMS magnetic field sensing component  350  includes a cantilever plate  209 , the cantilever plate  209  is coupled to the substrate  203  at a location between a first end  209   a  and a second end  209   b  thereby defining a first plate portion  211   a  and a second plate portion  211   b . Accordingly, both of the first and second ends ( 209   a ,  209   b ) of the cantilever plate  209  can pivot around the torsion elements  230 . This can be contrasted with the cantilever plate  105  of  FIG. 3  and cantilever plate  205  of  FIG. 4  which only pivot at a single end.  
         [0045]     In operation, as MEMS magnetic field sensing component  350  is exposed to a magnetic field and a small bias current (I BIAS ) is applied to the conductor  37 , the cantilever plate  209  may be deflected due to the resulting Lorentz force. More specifically, depending e.g., upon the routing of the conductor  37  and the corresponding direction of the bias current (I BIAS ), a first end  209   a  of the cantilever plate  209  may be deflected into the cavity  115  (e.g., into the page) due to the resulting Lorentz force  39   a , while at the same time the second and opposite end  209   b  of the cantilever plate  209  is deflected away from the cavity  115  (e.g., out of the page) due to an opposing Lorentz force  39   b . This deflection about the torsion elements  230  thus generates a bending and a twisting on the cantilever plate  209  in an area generally indicated by strain line  125 . Moreover, because the Lorentz forces acting on cantilever plate  209  act in a complimentary manner where one enhances the other, the resulting sensitivity of the MEMS magnetic field sensing component  350  can be increased above that of MEMS magnetic field sensing component  200  or  300 .  
         [0046]      FIG. 6  illustrates an example MEMS magnetic field sensing component including a half-torsion U-shaped cantilever design in accordance with another embodiment of the invention. As illustrated, MEMS magnetic field sensing component  400  includes a structural component  40  further including a substrate  203  and a cavity  115  defined therein. The MEMS magnetic field sensing component  400  further includes a cantilever plate  305  that is positioned above the cavity  115  as shown. The cantilever plate  305  is similar in form to the cantilever plate  205  of  FIG. 4 , except with cantilever plate  305  a substantial portion of the cantilever plate material (e.g., as indicated by section  306 ) is missing causing the cantilever plate  305  to be U-shaped as shown. In order to fabricate the cantilever plate  305 , an otherwise whole cantilever plate first may be fabricated from which an amount of material approximating section  306  may be removed. Alternatively, a U-shaped cantilever plate such as that shown may be specifically fabricated absent section  306 . Of course although not described herein other fabrication techniques may be possible.  
         [0047]     As compared to a rectangular-shaped cantilever plate such as that shown in  FIG. 3  and  FIG. 4 , the U-shaped cantilever plate  305  of  FIG. 6  may provide additional sensitivity due at least in part to the U-shaped cantilever plate  305  being less stiff than corresponding rectangular cantilever plates. Additionally, due at least in part to its relatively small profile, U-shaped cantilever plate  305  also may be less susceptible to interfering measurands which can adversely effect the accuracy of the current sensor. Conversely, fabrication of the U-shaped cantilever plate  305  may be more challenging than that of the rectangular-shaped cantilever plate such as cantilever plate  105  or cantilever plate  205 .  
         [0048]      FIG. 7  illustrates an example MEMS magnetic field sensing component including a full-torsion U-shaped cantilever design in accordance with another embodiment of the invention. MEMS magnetic field sensing component  450  includes aspects of both MEMS magnetic field sensing component  350  and MEMS magnetic field sensing component  400 . That is to say, MEMS magnetic field sensing component  450  includes a U-shaped cantilever plate  309  that is coupled to the substrate  203  at a location between a first end  310   a  and a second end  310   b  so as to define a first plate portion  311   a  and a second plate portion  311   b . Accordingly, both of the first and second ends ( 310   a ,  310   b ) of the cantilever plate  309  can pivot around the torsion elements  330  centered at a location generally indicated by strain line  125 .  
         [0049]     In accordance with one embodiment, the cantilever plate  309  may provide even further sensitivity over the previously described cantilever plates. More specifically, cantilever plate  309  shares the increased magnetic field sensitivity and decreased interference susceptibility of the U-shaped cantilever plate  305 . Additionally, due to the full-torsion configuration, cantilever plate  309  may tend to be even more sensitive to magnetic field variations.  
         [0050]      FIG. 8  illustrates an example MEMS magnetic field sensing component including a shutter-shaped cantilever design in accordance with yet another embodiment of the invention. MEMS magnetic field sensing component  500  includes a structural component  40 , which further includes a substrate  303 , and a cavity  215  defined within the substrate  303  so as to form the illustrated cantilever based spring element. In accordance with one embodiment, the illustrated spring element includes a cantilever plate  409 , a torsion element  430  and a hinge element  417 . As illustrated, the torsion element  430  may be positioned above the cavity  215  and connected to the substrate  303  on either side of the cavity  215 . Additionally, the hinge element  417  may act to connect the torsion element  430  to the cantilever plate  409 .  
         [0051]     In operation, as MEMS magnetic field sensing component  500  is exposed to a magnetic field, and a small bias current (not shown) is applied to a conductor (not shown) coupled to the cantilever plate  409  for example, the cantilever plate  409  may be deflected into the cavity  215  due to the resulting Lorentz force. As a result, a bending induced strain may develop at least around the area of the hinge element  417  and a twisting induced strain or torsion may develop at least around the area of the torsion element  430 . In one embodiment, both a bending induced strain and twisting induced strain may occur at either or both locations corresponding to the hinge element  417  and the torsion element  430 . In accordance with one embodiment, one or more strain responsive components such as piezo-resistive elements may be adhered to the spring element to sense one or more of the bending and twisting generated strains.  
         [0052]      FIG. 9  illustrates an example MEMS magnetic field sensing component including a full-torsion shutter-shaped cantilever design in accordance with yet another embodiment of the invention. MEMS magnetic field sensing component  550  includes a structural component  40 , which further includes a substrate  303 , and a cavity  315  defined within the substrate  303  so as to form the illustrated full-torsion cantilever based spring element. In accordance with the illustrated embodiment, the spring element includes a first cantilever plate  409   a , and a second cantilever plate  409   b  coupled to a torsion element  430  by hinge elements  417   a  and  417   b  respectively. More specifically, the first cantilever plate  409   a  is coupled to the torsion element  430  by a first hinge element  417   a  and the second cantilever plate  409   a  is coupled to the torsion element  430  by a second hinge element  417   b . As illustrated, the torsion element  430  may be positioned above the cavity  315  and coupled to or integral with the substrate  303  on either side of the cavity  315 . Additionally, strain responsive components  45  may be positioned at various locations on and around the spring element to register both a bending induced strain (e.g., around the area of the hinge elements  417   a ,  417   b ) and a twisting induced strain or torsion around (e.g., around the area of the torsion element  430 ).  
         [0053]      FIG. 10  illustrates one embodiment of a strain concentrator suitable for use with one or more spring elements described herein. The strain concentrator  235  may be a geometric or material based modification made to one or more torsion elements  230  to focus or otherwise redirect the strain resulting from displacement of a spring element such as a cantilever. In the illustrated embodiment of  FIG. 10  for example, the strain concentrator  235  is represented by a narrowing of the torsion element  230 . Such narrowing acts to focus strain developed in torsion element  230  to an area localized or more concentrated around the strain responsive component  45 . Alternatively, torsion element  230  could be modified through physical or modification of its material properties.  
         [0054]      FIG. 11  is a schematic sectional side view illustrating aspects of a MEMS magnetic field sensing component in accordance with one embodiment. In the illustrated embodiment, magneto-MEMS component  30  is shown including a substrate  10  having an upper side  11  and a lower side  13 . In one embodiment, the substrate may be a silicon substrate. In one embodiment, the substrate may be a silicon wafer having a thickness of about 300 μm. Formed through a portion of the lower side  13  of the substrate  10  is a cavity  28  having walls  31  extending to the upper side  11 . A spring element such as, but not limited to a cantilever or membrane is formed on the upper side of the substrate  10  and at least partially above the cavity  28 . For the purposes of the following description, the spring element  32  is illustrated and described as being a cantilever (e.g., cantilever  32 ). This however, is for convenience and is not intended to limit the disclosure in any way.  
         [0055]     In one embodiment, the substrate  10  may be coated on both the upper side  11  and the lower side  13  with a compliant layer  12 . In one embodiment, the compliant layer  12  may be low stress silicon, silicon nitride, or a silicon dioxide layer. In other embodiments the compliant layer  12  may include materials such as crystalline silicon nitride and/or polymers. As used herein and unless otherwise qualified, the term “low stress silicon” is intended to refer to silicon and silicon compositions having a residual stress of less than about 100 MPa.  
         [0056]     In one embodiment, the thickness of the compliant layer  12  may be about 5000 Angstroms but may range from about 1000 Angstroms to about 10,000 Angstroms. In a further embodiment, the compliant layer  12  may include a first relatively thin layer of stoichiometrically balanced silicon nitride of formula Si 3 N 4  (hereinafter referred to as “stoichiometric silicon nitride”), and a second layer of relatively low stress non-stoichiometrically balanced silicon nitride (hereinafter referred to as “low stress silicon nitride”). In one embodiment, the stoichiometric silicon nitride may be of formula Si 3 N 4  and may have a thickness of about 300 to about 500 Angstroms. In contrast, the low stress silicon nitride may be represented by formula Si x N y , where the ratio x:y is representative of the properties of the material, and where this ratio of x to y is relatively close to unity. In particular, and in some embodiments, x may be taken as x=1 without any loss of generality, and y may range from about 0.75 to about 1 (e.g., 0.75, 0.8, 0.9, 1). In one embodiment, the low stress silicon nitride layer may have a thickness on the order of about ten times that of the stoichiometric silicon nitride and may have a residual stress of less than about 100 mega pascals.  
         [0057]     Due at least in part to the use of the low stress silicon nitride, it is possible to decrease the thickness and thereby increase the responsiveness of the spring element (e.g. cantilever  32 ) over conventional techniques. In one embodiment, the stoichiometric silicon nitride may be deposited between the substrate  10  and the low stress silicon nitride layer (shown together as compliant layer  12 ). Accordingly, the stoichiometric silicon nitride may act to decrease potential delamination between the low stress silicon nitride and the substrate  10  that may result as a side effect of an annealing process.  
         [0058]     A magnetic-to-mechanical converter in the form of a conductor  18  for carrying current is further arranged at least partially over the cantilever  32  and the cavity  28 . The conductor  18  may comprise a variety of electrically conductive materials including but not limited to Titanium, Tungsten, Gold, Aluminum, Platinum, Palladium, Copper, Chromium, doped polysilicon, doped silicon, SiC, GaN and so forth. In one embodiment, the cantilever  32  comprises silicon nitride, however, the cantilever may instead comprise polymers, polysilicon, silicon, oxide, oxinitride, silicon dioxide and so forth.  
         [0059]      FIG. 13  is a flow diagram illustrating an example fabrication method for one embodiment of a MEMS magnetic field sensing component such as illustrated in  FIG. 11 . The specific processing conditions and dimensions described herein serve to illustrate one specific fabrication method but can be varied depending upon the materials used and the desired application and geometry of the MEMS current and magnetic field sensor.  
         [0060]     The fabrication method may begin at block  600  with provision of a substrate  10  including a compliant layer. In one embodiment, the compliant layer may be low stress silicon layer comprised of silicon, silicon nitride, or silicon dioxide. In one embodiment, the residual stress of a low stress silicon layer is less than 100 MPa. In one embodiment, the substrate  10  may be a silicon substrate, however other materials having similar properties may be used. In an alternative embodiment, the fabrication method may begin with the provision of a substrate  10 , which is in turn then coated with a low stress silicon layer. In either case, and in accordance with one embodiment of the present invention, the low stress silicon layer may be silicon nitride or silicon dioxide. However, as previously described, the low stress silicon layer may include a first relatively thin layer of stoichiometrically balanced silicon nitride and a second layer of relatively low stress non-stoichiometrically balanced silicon nitride.  
         [0061]     At block  605 , a strain responsive component is formed on the substrate. In one embodiment, this may involve a blanket coating (e.g., a coating having a substantially consistent depth or thickness) of amorphous polysilicon. The polysilicon may then be doped (e.g. through ion implantation) to form strain responsive components in the form of P-type piezo resistive elements. In one embodiment, the polysilicon may be lightly doped with Boron at a dose of 2.5E+15 atoms/(cm)2. The substrate may then be coated with a photolithographic etch resist compound in a pattern corresponding to locations where the piezo resistive elements (and optionally where conductors and/or contact pads) are to be located. Once the substrate is exposed and the etch-resist is developed the exposed areas of the polysilicon may be etched away. Next, the substrate may be annealed for between about 30 and 60 minutes at a temperature between about 800° C. and 1050° C.  
         [0062]     At block  610 , one or more magnetic-to mechanical converters in the form e.g. of a conductor may be formed. The conductors (in addition to contact pads) may be formed through additional doping of the polysilicon or through the coating of metal on the substrate. In one embodiment, areas of the polysilicon that are to be made into conductors or contact pads may be more heavily doped with Boron at a dose of 1.0E+16 atoms/(cm)2. In an alternative embodiment, a coating of an electrically conductive metal such as gold may be deposited on the substrate. The metal may be coated through e.g., sputter or evaporative techniques known to those possessing ordinary skill in the art of photolithography. In one embodiment, an adhesion layer may be deposited on the substrate before the metal deposition process. The adhesion layer may be used such that the metal better adheres to the underlying material whether it be polysilicon or nitride. In one embodiment, the adhesion layer is formed of elemental chromium, however in other embodiments, compounds such as Ti—W may be used. Once the adhesion layer and the metal have been deposited, a coating of etch resist may be applied and the substrate may be masked, exposed and developed to form the conductors and pads. Thereafter, the metal and adhesion layers may be removed through e.g., an etch process.  
         [0063]     At block  615 , a portion of the substrate is removed to release the spring element. In one embodiment, an additional layer of silicon nitride may first be deposited (e.g. to a depth of about 1 um) over the upper side of the substrate using for example, a low pressure chemical vapor deposition. Certain areas of the silicon nitride overcoat may then be exposed through e.g. the process of reactive ion etching. This allows contact pads to be exposed for the purpose of external connection and allows the cantilever plate to be released from the remainder of the compliant. In the event the spring element is a membrane, the compliant layer would not be released from the remainder of the compliant layer. In one embodiment, an anisotropic etch process (e.g., a KOH etch process) may further be performed through the bottom side  13  of the silicon substrate  10  to form the cavity  28 , the angled walls  31  and finally cantilever plate  32 .  
         [0064]     As disclosed herein, the need to physically contact a first current carrying conductor  4  to sense the current I is obviated. It is also noted that due to the small dimensions of micro-machined MEMS devices, the MEMS-based current sensor  100  is itself a dimensionally small device. Accordingly, the change in the magnetic field being sensed by the MEMS-based current sensor  100  at various points on the sensor is very small. The MEMS-based current sensor  100  is therefore accurate since there is no need to compensate for variances across the measuring sensor itself.  
         [0065]     Due at least in part to the use of MEMS technology, the magnetic forces required to operate the MEMS devices are relatively small. The current sensor hereof thus tends to generate relatively little heat. This is advantageous in that there is little heat generated by the current sensors herein that may introduce an error in the sensing of the current I.  
         [0066]     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.