Micro-electromechanical system (MEMS) based current and magnetic field sensor having capacitive sense components

A micro-electromechanical system (MEMS) based current & magnetic field sensor includes a MEMS-based magnetic field sensing component having a capacitive magneto-MEMS component, a compensator and an output component for sensing magnetic fields and for providing, in response thereto, an indication of the current present in a respective conductor to be measured. In one embodiment, first and second mechanical sense components are electrically conductive and operate to sense a change in a capacitance between the mechanical sense components in response to a mechanical indicator from a magnetic-to-mechanical converter.

BACKGROUND

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.

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.

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.

BRIEF DESCRIPTION

In one embodiment, there is provided a micro-electromechanical system (MEMS) current & magnetic field sensor for sensing a magnetic field produced by a conductor including a MEMS-based magnetic field sensing component having a capacitive magneto-MEMS component for sensing the magnetic field and, in response thereto, providing an indication of the current in the conductor.

In one embodiment, there is provided a MEMS current & magnetic field sensor for sensing a magnetic field produced by a current carrying conductor. The MEMS current & magnetic field sensor includes a first structural component, a second structural component coupled to the first structural component, and a magnetic-to-mechanical converter coupled to at least one of the first and second structural components for providing a mechanical indication of the magnetic field. The MEMS current & magnetic field sensor further includes a mechanical sense component for sensing the mechanical indication based at least in part upon a change in capacitance, and in response thereto, providing an indication of the current in the current carrying conductor.

In yet another embodiment, there is provided a method of fabricating a MEMS current & magnetic field sensor including providing a first substrate having a front side, a back side, and a first electrode. Forming a cavity through the back side of the first substrate to produce a membrane on the front side. Providing a second substrate having a second electrode and aligning the first and second substrates such that as the membrane is deflected into the cavity, a capacitance defined between the first and second electrodes changes.

DETAILED DESCRIPTION

FIG. 1illustrates one embodiment of a MEMS current and magnetic field sensing device described herein and hereinafter generally referred to as “current sensor100”. As shown, conductor4carrying a current I generates a magnetic field20. In accordance with one embodiment of the present disclosure, current sensor100can be used to sense the current I in a current carrying conductor4, without having to make physical contact with the current carrying conductor. In accordance with the illustrated embodiment, the MEMS-based current sensor100operates to sense and determine the current I carried by the conductor4by making use of the Lorentz force resulting when current sensor100is positioned in the magnetic field20generated by current I. In one embodiment, the current sensor100includes a magnetic field sensing component having a capacitive magneto-MEMS component for sensing magnetic fields and for providing, in response thereto, an indication of the current present in the respective conductors to be measured.

The advantageous size of a MEMS-based current and magnetic field sensor, such as current sensor100described herein, facilitates the sensing of current in applications where space is limited. Moreover, the use of MEMS-based components 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 MEMS current sensor100, the MEMS current sensor100preferably 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 sensor100preferably does not introduce or cause any appreciable variation or change in the current being sensed or measured. Moreover, the MEMS current sensor100is 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 sensor100is advantaged through increased accuracy and precision.

FIG. 2is a schematic diagram illustrating one embodiment of a MEMS-based magnetic field sensing component25of MEMS-based current sensor100. The MEMS-based magnetic field sensing component25senses magnetic fields such as magnetic field20and provides an indication of the current in a corresponding current carrying conductor, such as conductor4. The sensed indication of the current may include both a magnitude and a directional component regarding the current being sensed. In one embodiment, the sensed indication of the current is an electrical indication of the current being sensed.

In the illustrated embodiment ofFIG. 2, the MEMS-based magnetic field sensing component25includes a capacitive magneto-MEMS component30, a compensator55and an output component70. The capacitive magneto-MEMS component30senses a magnetic field and, in response thereto, converts the sensed magnetic field to a mechanical indicator of a corresponding current I. The output component70provides an output indicative of the current I in the conductor being measured. In one embodiment, output from the output component70may take the form of an electrical signal indicative and representative of the magnitude and sign of the current flowing in the conductor being measured.

In the illustrated embodiment, the capacitive magneto-MEMS component30includes a magnetic-to-mechanical converter35for converting the magnetic representation of the current I to a mechanical change. In one embodiment, the magnetic-to-mechanical converter35may be a conductor such as a coil. Additionally, the illustrated capacitive magneto-MEMS component30includes a structural component40for providing structural support to capacitive magneto-MEMS component30. The structural component40may represent one or more heterogeneous or homogeneous structures, devices, materials, assemblies, sub-systems, and so forth. For example, in one embodiment, the structural component40may represent a first structural component in the form of a first substrate and a second structural component in the form of a second substrate. In one embodiment, the structural component40is responsive to the mechanical change provided by the magnetic-to-mechanical converter35and provides a mechanical indicator representative of the current I. The mechanical indicator may be representative of movement experienced by the structural component40that registers or otherwise indicates the sensing of the magnetic field. In one embodiment, the mechanical indicator may be an induced force or stress on the structural component40. In yet another embodiment, the mechanical indicator may include modification of a mechanical property of the structural component40, such as, for example, a spring constant and the mass thereof. In one embodiment, the structural component40may include one or more of a deflectable membrane, a cantilever, a diaphragm, a flexure member, a cavity, a surface micro-machined structure, a bulk micro-machined structure, a comb structure, a bridge or any number of other structural devices. Moreover, the mechanical indicator provided by the structural component40may 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 capacitive magneto-MEMS component30includes at least one mechanical sense component45for sensing the mechanical indicator provided by structural component40. In the illustrated embodiment, the capacitive magneto-MEMS component30includes a first mechanical sense component45aand a second mechanical sense component45b. The first and second mechanical sense components (45a,45b) may be electrically conductive and may be supported by respective first and second structural components such that a capacitance is produced between the two mechanical sense components. In one embodiment, the first and second mechanical sense components operate to sense a change in the capacitance between the sense components in response to the mechanical indicator from magnetic-to-mechanical converter35. In one embodiment, the mechanical indicator is sensed as a measurable force, such as a Lorentz force, exerted on at least one of the first and second mechanical sense components (45a,45b) via the magnetic to mechanical converter35. In one embodiment, the magnetic to mechanical converter35is coupled to at least one of the first and second mechanical sense components.

The sensed mechanical indicator may be converted to an interface signal representative of the sensed current I. In one embodiment, the mechanical-to-electrical converter75converts the sensed mechanical indicator for interpretation and/or further processing by the output stage80. The mechanical-to-electrical converter75may be designed based on the nature of the mechanical sense components45aand45b. In one embodiment, the mechanical-to-electrical converter75is based on a capacitive element, however in other embodiments the mechanical-to-electrical converter75may be based on, for example, a metal strain element, a piezoresistive element, a piezoelectric element, a tunneling element, or an optical element. In particular, the mechanical-to-electrical converter75may include a capacitive bridge and a resistive Wheatstone bridge. Output stage80may 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 further processing.

Additionally, compensator55may be used to compensate for effects due to e.g., aging of the sensor, temperature, environmental factors, etc. The compensator55may include an excitation source (such as a current source)60and a controller65. The excitation source60may provide excitation quanta (i.e., an amount of excitation energy) for use by the MEMS current sensor100. The controller65may control, for example, a switching and an application of the excitation quanta of the excitation source60and the reference signal of the reference component50. The controller65may 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 converter35. In another embodiment, the controller may select between differing values of the excitation quanta and a plurality of reference components50. 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.

Although the output component70, the capacitive magneto-MEMS component30and the compensator55ofFIG. 2appear as separate components, these components and their respective functional blocks can be further combined or further partitioned without departing from the spirit and scope of the disclosure.

FIG. 3illustrates one embodiment of a capacitive magneto-MEMS component. InFIG. 3, capacitive magneto-MEMS component30includes structural component40shown as a first structural component40aand a second structural component40bpositioned substantially opposite the first structural component40a. In one embodiment, the first structural component40aincludes a first mechanical sense component45aand the second structural component40bincludes a second mechanical sense component45b. The first and second mechanical sense components45aand45bmay each represent an electrically conductive region or material (herein referred to as an “electrode”) contained by or coupled to the first or second structural components40aor40b, respectively. In one embodiment, the first and second structural components40aand40brespectively represent first and second substrates. For example, the first and second mechanical sense components may each represent a layer, region or trace of conductive material, such as a metal, disposed on or formed within a substrate such as Silicon. In one embodiment, the first structural component40arepresents a substrate having a cavity28defined therein such that a membrane is formed at least partly above the cavity. In one embodiment, the membrane is formed from released silicon nitride disposed on the substrate.

In accordance with one embodiment, during operation of the capacitive magneto-MEMS component30, a voltage differential is applied across the first and second structural components (40aand40b) causing a capacitance to develop between the first and second mechanical sense components45aand45b(thereby causing the sense components to effectively act as plates of a capacitor). Since the capacitance between the first and second sense components45aand45b(e.g. plates) is a function of the distance D separating the sense components, a change in distance D will affect a corresponding change in the capacitance. In the illustrated embodiment, a magnetic-to-mechanical converter35is coupled to the first structural component40asuch that when the capacitive magneto-MEMS component30is placed in the vicinity of an external current carrying conductor, and a small bias current is flowed in the magnetic-to-mechanical converter35, the magnetic field generated by the external conductor will exert a force (e.g., Lorentz force) on the magnetic-to-mechanical converter35. The bias current used may be in the range of uA or 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 capacitive magneto-MEMS component30. 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. As shown in the bottom half ofFIG. 3, the Lorentz force will cause the first structural component40a(e.g. first substrate) to deflect a distance D′ thereby decreasing the distance D, and in turn increasing the capacitance, between the first and second sense components45aand45b. In an alternative embodiment, the magnetic-to-mechanical converter35may itself act as a sense component depending upon the structure of the capacitive magneto-MEMS component30.

While discussed primarily in the context of using the Lorentz force between the first and second sense components, the magnetic-to-mechanical converter35can 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.

Due to batch manufacturing techniques of micro-machining and the associated cost efficiencies, the MEMS-based current sensor100as described herein can be manufactured in large batches using for example, photolithography and etching. As noted above, the MEMS device ofFIG. 2is but one example of a current sensor contemplated in accordance with the present disclosure. Other embodiments of the MEMS-based current sensor100may 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.

Using micro-machining and micro-lithography manufacturing processes, the first and second structural components (40a,40b), the first and second mechanical sense components (45a,45b) and magnetic-to-mechanical converter35may be constructed in separate layers of conductive metal and insulating material to provide a single MEMS-based current sensor that uses the force between current carrying conductors to sense an unknown current flowing in an external one of the conductors. In various embodiments the magnetic-to-mechanical converter35may be a conductor formed from a single metal or two or more metals. In the event the magnetic-to-mechanical converter35is formed from two or more metals, each such metal may be separated wholly or partly by an insulating layer or a dielectric layer. For example,FIGS. 4-15illustrate aspects of a capacitive magneto-MEMS component employing a magnetic-to-mechanical converter formed from two metal layers according to one embodiment. In comparison,FIGS. 16-22illustrate aspects of a capacitive magneto-MEMS component employing a magnetic-to-mechanical converter formed from a single metal layer structure according to another embodiment. Depending upon various design considerations, it may be preferable to use a capacitive magneto-MEMS component having a single metal conductor over one with multiple metal conductors, or vice-versa. For example, the overall fabrication of the capacitive magneto-MEMS component and resultant MEMS current sensor can be simplified through the use of a single metal conductor. On the other hand, multiple metal conductors may be useful to facilitate signal routing from the structural component40(e.g., membrane) in situations where the magnetic-to-mechanical converter or coil is located on the structural component. Additionally, multiple metal layers may be useful in balancing the effects of differing temperature coefficients of expansion, which may otherwise initiate an unnecessary stress upon the system.

FIG. 4shows a schematic sectional side elevational view of aspects of capacitive magneto-MEMS component30according to one embodiment. In the illustrated embodiment, capacitive magneto-MEMS component30includes a substrate10having an upper surface11and a lower surface13. Formed through a portion of the lower surface13of the substrate10is a cavity28having walls31extending to the upper surface11. Disposed on the upper surface of the substrate10and at least partially above the cavity28is a membrane32. A conductor18for carrying current is further disposed at least partially over the membrane32. InFIG. 4the conductor18is shown in the form of contact pads. The conductor18may comprise a variety of electrically conductive materials including but not limited to Ti, W, AU, Al, Pt, Pd, Cu, Cr, doped polysilicon, doped silicon, SiC, GaN and so forth. In one embodiment, the membrane32comprises silicon nitride, however, the membrane may instead comprise polymers, polysilicon, Si, oxide, oxinitride, silicon dioxide and so forth. A dielectric material21is disposed over the membrane32and the conductor18. The dielectric material21may comprise e.g., a polyimide or silicon dioxide. In one embodiment, the dielectric material has a thickness that ranges from about 1000 Å to about 1 um. In one embodiment, a second conductor is disposed on the dielectric material21. InFIG. 4, the second conductor is represented by layers24and29. Layer24may be a conductive layer such as a metal comprising Ti/W/Au, however, other electrically conductive materials such as Al, Pt, Pd, Cu, Cr, doped polysilicon, doped silicon, SiC, GaN may be used. In one embodiment, layer24has a thickness that ranges from about 1000 Å to about 1 um. Layer29is disposed on layer24and provides a connection to one of the contact pads that comprises the first conductor18. In one embodiment, layer29may be Au, however, other electrically conductive materials such as Al, Pt, Pd, Cu, Cr, doped polysilicon, doped silicon, SiC, GaN may be used.

FIGS. 5-15illustrate one embodiment of a fabrication method for a capacitive magneto-MEMS component employing a magnetic-to-mechanical converter formed from two metal layers e.g., as shown inFIG. 4. The specific processing conditions and dimensions 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. As shown inFIG. 5, the fabrication method begins with provision of a substrate10. In the illustrated embodiment, the substrate10is a silicon substrate, however other materials having similar properties may be used. Next, silicon nitride coatings12are applied to the front side and backside of the substrate10. The thickness of the silicon nitride coatings12may typically range from about 1 nm to about 10 um, however, other thickness ranges can be used. In one embodiment, the silicon nitride is of the low stress amorphous type (e.g., 50-300 Mpa), but use of materials such as crystalline silicon nitride, silicon, silicon dioxide, polymers . . . etc., in place of silicon nitride is also possible. In one embodiment, the silicon nitride coatings12are deposited on the substrate10using a low pressure chemical vapor deposition technique.

FIG. 6shows a photoresist material14coated on one of the silicon nitride coatings12at the backside of the substrate10. The photoresist material14is exposed to a pattern using a photolithographic technique at a later time. As shown inFIG. 7, a conductive layer16is deposited on the silicon nitride coating12on the front side of the substrate10. In one embodiment, the conductive layer16may include Ti/W/Au. However, other electrically conductive materials may be used for the conductive layer16such as e.g., Al, Pt, Pd, Cu, Cr, doped polysilicon, doped silicon, silicon dioxide, SiC, GaN and so forth. In one embodiment, the metallic coating16is deposited on the front side silicon nitride coating12using a sputtering technique and may have a thickness that ranges from about 1 nm to about 10 um.

FIG. 8shows photoresist material19deposited on the metallic coating16. As shown inFIG. 8, the photoresist material19takes the form of two contact pads or islands. In this embodiment, the photoresist material19has a thickness that ranges from about 10 nm to about 10 um. As shown inFIG. 9, the photoresist material19is patterned, exposed and developed using a photolithography technique. In addition,FIG. 9shows that the conductive layer16has been etched away so that the newly formed contact pads18reside on the front side silicon nitride coating12. Generally, a chemical etching or dry etching is suitable for etching the conductive layer16.

InFIG. 10, a dielectric material21is deposited on the contact pads18and the silicon nitride coating12on the front side of the substrate10. The dielectric material21may be silicon oxide or a polyimide coating such as ULTEM 10B, however, other dielectric materials may be used. The dielectric material can be deposited using chemical vapor deposition or by other deposition techniques such as spin or spray. As explained below, another metallic layer will be deposited on the dielectric material21, and if the dielectric is too thin, then the metallic layer and the dielectric material may short. Thus, the dielectric material should have a thickness sufficient to prevent such shorts. In one embodiment, the dielectric thickness ranges from about 100 nm to about 10 um. A thickness in this range results in a material having a relatively small porosity that inhibits induced diffusion of metal through the silicon oxide material.

The deposition of the dielectric material21prevents access to the contact pads18which will be used to make electrical contact and to maintain current. In order to make contact, an opening is made in the dielectric material21and a via22is created to provide access to the contact pads18as shown inFIG. 11. If the dielectric material21is a polyimide coating such as ULTEM 10B then the via22may be created by using a laser to ablate the material until access is made to the contact pads18. Alternatively, if the dielectric material is not a polymer, then etching (wet or dry) may be used. For example, if the dielectric material21is silicon oxide, then it is possible to use photolithography and etching to make contact with the contact pad18.

After accessing the contact pad18, another metal layer is deposited on the dielectric material21and in the via22.FIG. 12shows a conductive layer24deposited on the dielectric material21and in the via22. This conductive layer is patterned to create leads that will provide a bias current to the contact pads18. In one embodiment, the conductive layer24may include Ti/W/Au, however, other electrically conductive materials such as Al, Pt, Pd, Cu, Cr, doped polysilicon, doped silicon, SiC, GaN may be used. In one embodiment, the conductive layer24may be deposited on the silicon nitride coating12on the front side of substrate10using a sputtering or evaporation technique and may have a thickness that ranges from about 1 nm to about 10 um.

The metalization of conductive layer24is further refined by additional photolithography techniques. In particular,FIG. 13shows a photoresist material26deposited on the conductive layer24. The photoresist material26generally has a thickness that ranges from about 10 nm to about 10 um. The photoresist material26may be patterned, exposed and developed using optical lithography, however, the use of other photolithographic techniques are possible. After lithography and development of the photoresist material26, a portion of the conductive layer24not covered by the photoresist is etched away using e.g., using a wet etch to define a second conductor or coil of the capacitive magneto-MEMS component30.FIG. 14shows that portion of the conductive layer24etched away.

In one embodiment, the membrane32is formed after the processing steps ofFIGS. 5-14have been completed. As was alluded to above, formation of the membrane32involves the creation of the cavity28in the backside of the substrate10.FIG. 15shows the beginning of the formation of the cavity through the backside of the silicon nitride coating12and the photoresist material14. In one embodiment, the cavity28is formed by etching through the backside of the silicon nitride coating12and the photoresist material14. 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 walls31of the substrate10are formed at fixed and/or reproducible angles measured with respect to a plane containing the substrate. For example, because anisotropic etch solutions such as KOH etch preferentially in one crystallographic plane over another, the walls31may be formed at an angle determined by the etch rate in the respective crystallographic planes.

As alluded to above, in certain circumstances it might be preferable to simplify the fabrication process of capacitive magneto-MEMS component30such that a single metal layer is utilized. By doing so, it is ostensibly possible to reduce the number of processing steps, reduce the membrane thickness, improve the dynamics characteristics of the resulting current sensor while at the same time reducing manufacturing costs.

FIGS. 16 and 17each illustrate a schematic view of aspects of a capacitive magneto-MEMS component according to an alternative embodiment. InFIG. 16, a cross-sectional view illustrated, whereas inFIG. 17a top view is shown. In the illustrated embodiment ofFIGS. 16 and 17, the capacitive magneto-MEMS component30includes a substrate10having an upper surface11and a lower surface13. Formed through a portion of the lower surface13of the substrate10is a cavity28having walls31extending to a portion of the upper surface11. Disposed on the upper surface of the substrate10above the cavity28is a membrane32. As with the illustrated aspects of capacitive magneto-MEMS component30ofFIG. 4, the illustrated aspects of capacitive magneto-MEMS component30ofFIGS. 16 and 17include a magnetic-to-mechanical converter35in the form of a conductor. However, in contrast toFIG. 4, the magneto-MEMS component30ofFIGS. 16 and 17includes a conductor18formed from a single metal layer.

FIGS. 18-23illustrate one embodiment of a fabrication process for fabricating at least a portion of a capacitive magneto-MEMS component as shown e.g., inFIGS. 16 and 17. The specific processing conditions and dimensions 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. As shown inFIG. 18, the fabrication method begins with provision of a substrate10. In the illustrated embodiment, the substrate10is a silicon substrate, however other materials having similar properties may be used. Next, silicon nitride coatings12are applied to the front side and backside of the substrate10. The thickness of the silicon nitride coatings12may typically range from about 1 nm to about 10 um, however, other thickness ranges can be used. In one embodiment, the silicon nitride is of the low stress amorphous type, but use of a crystalline silicon nitride is also possible. In one embodiment, the silicon nitride coatings12are deposited on the substrate10using a low pressure chemical vapor deposition technique.

FIG. 19shows a photolithography process for defining one or more metallic conductors upon the silicon nitride coating12(e.g., to act as a magnetic-to-mechanical converter or coil). The photoresist material19is patterned, exposed and developed. As shown, photoresist material19is patterned on the silicon nitride coating12such that the open areas define the future placement of the conductors. In this embodiment, the photoresist material19may have a thickness that ranges from about 10 nm to about 10 um.

FIG. 20illustrates deposition of a conductive layer16on top of the photoresist material19and uncovered areas of the silicon nitride coating12. In one embodiment, conductive layer16may be deposited through physical or chemical vapor deposition techniques such as Molecular Beam Epitaxy or Metal-Organic Chemical Vapor Deposition. In one embodiment, conductive layer16may be formed a variety of electrically conductive materials including but not limited to Ti, W, AU, Al, Pt, Pd, Cu, Cr, and AU.

FIG. 21illustrates newly formed conductors18resulting from the dissolution and removal of the photoresist19and the corresponding conductive layer16that was deposited on the photoresist. InFIG. 22, a non-photosensitive resist23is applied to protect the conductors18on the frontside of the device and a photoresist material27is applied to the backside of the device. The photoresist material27is then exposed and developed via photolithography to define the location in the substrate10where the cavity28will be created through e.g., an anisotropic etch process.

As was described above with respect toFIG. 2, capacitive magneto-MEMS component30may include a first mechanical sense component45aand a second mechanical sense component45b. In one embodiment, the first mechanical sense component45ais associated with a first substrate, whereas the second mechanical sense component45bis associated with a second substrate. The first and second substrates may together be referred to as the structural component40, and separately as a first structural component40aand a second structural component40b. As has been previously described, the first mechanical sense component45aand the second mechanical sense component45bmay be used to sense a mechanical indicator of a current as manifested by a change in capacitance between the respective sense components.

FIG. 24illustrates a further embodiment of capacitive magneto-MEMS component30. In the illustrated embodiment, the first mechanical sense component45ais aligned adjacent to the second mechanical sense component45bsuch that the distance D defined therebetween measures less than 1 um for example. In one embodiment, the distance D defined between the two mechanical sense components measures approximately 100 nm. As such, small deflections (e.g., on the order of nanometers) of the membrane32may be detected by the mechanical sense components. In one embodiment, the cavity28into which the membrane32deflects may comprise a vacuum so as to increase the sensitivity of the mechanical sense components and thereby decrease the amount of deflection of the membrane32necessary in order to be detectable. However, if the vacuum is too high, the membrane32could be caused to artificially deflect into the cavity28independently of any possible mechanical indicators. In one embodiment, one or more vent holes48may be formed through the second structural component40bto the cavity28to prevent squeeze film damping of the membrane32.

Although it may often be desirable to have the two mechanical sense components separated by a very small (e.g., less than 1 um) distance, in practice it may be difficult to achieve such a small separation. In one embodiment, a first and second substrate (including respective first and second mechanical sense components45aand45b) may be aligned with each other such that a preferred separation distance ‘D’ is achieved.FIG. 25illustrates one embodiment of a method for aligning such a first and second substrate. As shown, the bottom substrate (e.g., indicated as a first structural component40b) includes a raised portion46having a width W2. Such a raised portion may be obtained, for example, by performing a deep reactive ion etching process on the substrate. Additionally, the membrane32of the second structural component40ahas a width W1and is formed at least partially over the cavity28defined between the angled walls31of the top substrate. In one embodiment, the angled walls31are obtained through an anisotropic etch process. Since the angle θ (Theta) of angled walls31can be determined with respect to the plain containing the first and second substrates (e.g., due to the known etch rate of the anisotropic etch solution used), width components WC1and WC2can also be determined using standard geometric relationships. As such, the width W2of raised portion46necessary to achieve a preferred separation distance ‘D’ between two substrates may be determined by the following equation: W2=W1+WC1+WC2. In one embodiment, the distance D is at least an order of magnitude less than the width W.

InFIG. 25, the bottom structural component40bis bonded to the backside of the top structural component40aat location47to form a capacitive readout mechanism for the capacitive magneto-MEMS component30. In other embodiments, the various structural components may be bonded together in other configurations to form different capacitive readout mechanisms. For example,FIG. 26illustrates an alternate embodiment of a capacitive readout mechanism for magneto-MEMS component30. InFIG. 26, the second structural component40band second mechanical sense component45bare disposed at the topside of the first structural component40a. Accordingly, as a Lorentz force for example, acts upon one or more conductor(s)18, the membrane32will be deflected into the cavity28. Such deflection can then be detected as a change in capacitance between the mechanical sense component45band either the conductor18acting as a mechanical sense component in the case of a single metal layer configuration (as shown) or another mechanical sense component45ain a multiple metal layer configuration (not shown). In the illustrated embodiment, the via22may be provided to access the otherwise inaccessible mechanical sense component, whether it is the conductor18acting as a sense component or mechanical sense component45a.

FIG. 27illustrates yet another embodiment of a capacitive readout mechanism for magneto-MEMS component30. Once again, the structural component40ais similar in form to its analogue ofFIG. 24. However inFIG. 27, the top structural component40ahas been inverted. That is, the cavity28has been etched or otherwise created through the topside of the top structural component40a. Moreover, an electrode designed to operate as a mechanical sense component45bis formed on the bottom structural component40b. Additionally, one or more spacers49are formed on the bottom structural component40bto separate the top structural component40afrom the bottom structural component40b. In one embodiment, the spacers may be created from the same material as the substrate10of the bottom structural component40b. In one embodiment, at least one of the mechanical sense component45band the spacers49are created through e.g., sputtering of Au on the substrate10of the bottom structural component40b. Accordingly, as a Lorentz force for example, acts upon one or more conductor(s)18, the membrane32will be deflected upward into the cavity28. Such deflection can then be detected as a change in capacitance between the mechanical sense components45aand45b. In the illustrated embodiment, the via is provided to access the otherwise inaccessible mechanical sense component45a. In one embodiment, a first wafer containing the first structural component40aand associated materials is aligned with and bonded to a second wafer containing the second first structural component40band associated materials before the wafers are diced.

Conclusion

As disclosed herein, the need to physically contact a first current carrying conductor4to 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 sensor100is itself a dimensionally small device. Accordingly, the change in the magnetic field being sensed by the MEMS-based current sensor100at various points on the sensor is very small. The MEMS-based current sensor100is therefore accurate since there is no need to compensate for variances across the measuring sensor itself.

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.