Abstract:
A microelectromechanical systems (MEMS) Device manufactured on a microscopic scale using integrated circuit techniques provides a sensitive magnetic field sensor by detecting motion caused by the Lorentz force produced by a current through a MEMS conductor. The resulting MEMS may be used as a component in a variety of devices including current sensors and proximity sensors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This case claims the benefit of provisional application Serial No. 60/308,714 filed Jul. 30, 2001. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     BACKGROUND OF THE INVENTION 
     The present invention relates to sensors for detecting the presence and/or strength of a magnetic field and, in particular, to a microelectromechanical system (MEMS) device providing for such measurements. 
     A magnetic field can be detected by noting its influence on a magnetic material or a current carrying wire. The former technique is used in a compass; the latter technique describes the common D&#39;Arsonval movement used in electrical meters. 
     A Hall effect sensor may be used in applications that require a more compact and rugged sensor. Hall effect sensors detect the drift of charge carriers in a semiconductor material in the presence of a magnetic field. This drift causes a transverse polarization of that semiconductor which can be detected as a voltage. 
     Hall effect sensors are currently used in a number of applications including, switches, proximity sensors and magnetometers. 
     SUMMARY OF THE INVENTION 
     The present invention provides an alternative to the Hall effect sensor that is both rugged and small and promises improved sensitivity over, and more flexible implementation than the Hall effect sensor. In this regard, the invention provides a sensor constructed using a microelectromechanical system (MEMS) device, which may be mass-produced using integrated circuit techniques. 
     In the invention, a microscopic conductor extends between two terminals on a substrate and conducts a proof current. Deflection of the current carrying conductor under the influence of a magnetic field, caused by the Lorentz force, is measured by a detector coupled to the conductor to produce an output dependent on that deflection. The small size and mass of the flexible conductor make kilohertz or higher response speeds possible. 
     Generally, the output signal may be analog or digital depending on the selection of the detector and its processing circuitry. Optionally, the invention may include circuit elements providing the proof current on-board or the proof current may be supplied externally using a conventional current source. The flexible conductor may be a straight conductive segment for simple fabrication. 
     In one embodiment, a beam connects the flexible conductor to the detector and the beam and the flexible conductor may include a metalization layer on an insulating or semiconducting material. The metalization layer may be interrupted on the beam to provide electrical isolation between the detector and flexible conductor. 
     The detector may include a bias means producing a force resisting the Lorentz force on the flexible conductor. The bias means may be a mechanical element such as a MEMS spring or may be an electrical element such as an electrostatic, piezoelectric or thermal motor. The bias means may be either passive or active. If an electrical element is used, the invention may include a feedback circuit communicating with the bias means and responding to the output signal to vary a bias force resisting the Lorentz force on the flexible conductor. In this way, the bias means may receive feedback to provide improved linearity in the detection of magnetic fields. 
     In an alternative embodiment, the invention may include a compensation coil. A feedback circuit responding to the output signal may energize the compensation coil to oppose the crossing magnetic field. This approach provides the benefits of feedback without the need for an electrically actuable bias means, but with the need for a coil structure. 
     The invention may include a second flexible conductor and detector also producing an output signal and a combiner circuit combining the output signal from the first and second flexible conductors to reject detector signals not related to the strength of the crossing magnetic field B. The flexible conductors may be arranged to have countervailing current flows or may be oriented (in connection to their beams) in opposite directions so that the effect of environmental noise such as mechanical shock or vibration may be distinguished from the Lorentz forces. 
     The invention may further include a measurement conductor conducting a current to be measured and positioned adjacent to the flexible conductor so that the crossing magnetic field B is a magnetic field produced by the current through the measurement conductor. In this way, the present invention may be used to measure currents. A magnetic core may be used to concentrate the flux from the measurement conductor on the flexible conductor. 
     Alternatively, the invention may include a magnet providing the crossing magnetic field B and, in this way, may be employed as a proximity detector detecting distortions of the magnetic field caused by nearby ferromagnetic materials. The invention finds potential application in all applications currently served by Hall effect devices. 
     The foregoing features may not apply to all embodiments of the inventions and are not intended to define the scope of the invention, for which purpose claims are provided. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment also does not define the scope of the invention and reference must be made therefore to the claims for this purpose. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective, schematic representation of one embodiment of the magnetic sensor of the present invention showing orientation of the magnetic flux, the proof current and the resulting Lorentz force on a flexible conductor whose deflection is measured by a capacitive sensor; 
     FIG. 2 is a block diagram of the embodiment of FIG. 1 using a flexible conductor coupled directly to a sensor; 
     FIG. 3 is a figure similar to that of FIG. 2 showing the addition of a feedback circuit and a compensation coil to provide improved linearity to the device of FIG. 1; 
     FIG. 4 is a figure similar to that of FIG. 2 showing the addition of an electronically controllable bias device such as may be used for feedback without the need for an external compensation coil; 
     FIG. 5 is a block diagram similar to FIG. 2 showing the use of two separate systems whose outputs are combined by a combiner circuit to distinguish between the Lorentz forces and external mechanical shock or vibration; 
     FIG. 6 is a top plan view of the embodiment of FIG. 4 using one flexible conductor for responding to Lorentz forces, an electrostatic motor as the bias device, and a capacitive sensor element; 
     FIG. 7 is a perspective fragmentary view of FIG. 11 showing an insulating segment connecting the flexible conductor to the beam leading to the bias device as is produced by a break in the metalization layer; 
     FIG. 8 is a perspective view of a simplified representation of a current sensor implemented with the invention in which magnetic fields induced about a measuring conductor are measured; 
     FIG. 9 is a simplified representation of a switch implemented with the invention in which a movable magnetic is detected; 
     FIGS. 10 a  and  10   b  are simplified representations of a proximity detector as implemented using the present invention to detect distortion of a magnetic field by the presence of nearby ferromagnetic material; 
     FIG. 11 is a top plan view of the embodiment of FIG. 2 using one flexible conductor for responding to Lorentz forces and a capacitive sensor element; 
     FIG. 12 is a simplified perspective view of an insulating section of the beam of FIG. 6 showing the use of laminated conductive and nonconductive layers and the removal of the conductive layer to create the insulating sections between sensing and biasing portions of the device; and 
     FIG. 13 is a perspective fragmentary view of FIG. 11 showing an insulating layer separating the flexible conductor from a conductive beam in one portion of the beam and a metalization layer in direct contact with the beam in a second portion of the beam forming the detection device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Non-Feedback System 
     Referring now to FIGS. 1 and 2, a microelectromechanical system (MEMS) magnetic field sensor  10  of the present invention provides a first terminal  22   c  and a second terminal  22   d  formed on a substrate such as of an integrated circuit but electrically insulated therefrom so that an electrical voltage may be established across the terminals  22   c  and  22   d . In this regard, the substrate may be an insulator or have an insulating top layer so that conductive layers or wire bonding attached to these terminals are all mutually isolated. The substrate may provide for the support and fabrication of other integrated circuitry. 
     Terminals  22   c  and  22   d  are connected by a flexible conductor  46 , typically also formed on the substrate material, but separated from the substrate by undercutting so as to provide an unsupported span between terminals  22   d  and  22   c  free to flex generally along a longitudinal axis parallel to the plane of the integrated circuit substrate to form a bow  12  indicated by a dotted line. The flexible conductor  46  is positionable within a crossing magnetic field B generally perpendicular to the substrate plane so that a proof current i p  passing from terminal  22   d  to  22   c  moves it to the bow  12  in response to Lorentz force F. The flexible conductor thus provides a Lorentz motor actuator device  36   a.    
     A beam  20  is attached to the center of the flexible conductor  46  and may include an insulating section  15  separating a first beam section  32   a  from a continuation beam section  32   b . The beam section  32   b  may optionally be attached to a bias device  36   b  providing an additional restoring force tending to restore the flexible conductor  46  from the bow  12  to a straight configuration that compliments the naturally occurring restoring force of the flexible conductor itself. The bias device  36   b , if used, may be either a physical or electrical device as will be described below. In addition, bias device  36   b , if used, may be either passive or active. 
     Beam section  32   b  also supports moving capacitor plates  66  extending laterally from the beam section  32   b  along the plane of the substrate and having longitudinally extending fingers in a forward and backward direction interdigitating with opposed fingers of corresponding stationary capacitor plates  68  on opposite sides of the beam  20 . Two pairs of opposed capacitor plates  66 ,  68  are thus formed, one of which moves closer together and one of which moves farther apart with motion of the beam  20 . The capacitor plates  66 ,  68  provide a detector device  36   c.    
     The detector device  36   c  may further include a capacitive sensing circuit  73  such as is described in U.S. patent application Ser. No. 09/677,037, incorporated by reference, attached to a terminal  26   c  being common with moving capacitor plates  66  and also be attached to terminal  26   a  and  26   d  communicating with the two moving capacitor plates  66 , respectively. The capacitive sensing circuitry  73  may, but need not be implemented as integrated circuitry on or supported by the same substrate  42  as the (MEMS) magnetic field sensor  10 . Measurement of the change in capacitance detects longitudinal movement of the beam  20  and forms the basis of detector output  14  indicating movement of the beam section  32   b  and hence beam  20  and hence flexible conductor  46 . 
     For a fixed proof current i p  and a restoring force from the stiffness of the flexible conductor observing Hook&#39;s law, movement of the beam section  32   b  will be proportional to the strength of the crossing magnetic field B and thus the detector output  14  will provide a measurement of the strength of the crossing magnetic field B. Control of the proof current i p  will affect the relationship between the force F and the crossing magnetic field B thus allowing change in the sensitivity of the device. The detector output  14  may be an analog output or may be digitized according to methods well known in the art. 
     Specifically, referring now to FIG. 11, the beam  20  may extend above a substrate  42  along the longitudinal axis  40  between longitudinally opposed pylons  44 ′. The beam  20  may thereby define a midline dividing transversely opposed pylons  44 , the latter attached and extending upward from a substrate  42 . The leftmost pylons  44 ′ form the terminals  22   d  and  22   c  described above while the right most pylons  44 ′ form terminals  26   c . The transversely opposed pair of pylons  44 , provide terminals  26   a  and  26   d  described above. 
     The beam  20  is supported away from the substrate  42  and held for movement along the longitudinal axis  40  by means of flexible conductors  46  and  46 ″ extending transversely on opposite sides of both ends of the beam  20  and its middle. The flexible conductors  46  and  46 ″ extend transversely away from the beam  20  to elbows  48  removed from the beam  20  on each side of the beam  20 . The elbows  48  in turn connect to expansion compensators  50 , which return to be attached to the substrate  42  at a point near the beam  20 . The support structure and operation of the elbows is described in U.S. patent application Ser. No. 09/805,410 filed Mar. 13, 2001 and hereby incorporated by reference. 
     The flexible conductors  46  and  46 ″ are connected to expansion compensators  50  which in turn provide electrical connections between each of the beam sections  32   a  and  32   b  and stationary electrical terminals. Specifically, the expansion compensators  50 , connected to either end of the leftmost flexible conductor  46 , connect to terminals  22   c  and  22   d  respectively. The expansion compensators  50  attached to rightmost flexible conductor  46 ″ connect to terminal  26   c  of beam section  32   b.    
     The portion  32   a  of the beam  20 , such as forms part of the Lorentz motor actuator device  36   a , is isolated by insulating section  15  from the beam portion  32   b  and thus a voltage imposed across terminals  22   c  and  22   d  provides a current through the flexible conductor  46 . 
     The beam segment  32   b  may have transversely outwardly extending, moving capacitor plates  66  overlapping with corresponding transversely inwardly extending stationary capacitor plates  68  attached to the pylons  44 ′ supporting terminals  26   a  and  26   d . The capacitor plates serve as a sensing means in which variation in the capacitance between the moving capacitor plates  66  and stationary capacitor plates  68  serves to indicate the position of the beam  20 . Each of the moving capacitor plates  66  and their corresponding stationary capacitor plates  68  may have mutually engaging fingers (as opposed to being simple parallel plate capacitors) so as to provide for a more uniform capacitance variation over a greater range of longitudinal travel of the beam  20 . In this regard, the order of the stationary and moving capacitor plates  66  and  68  is reversed on opposite sides of the beam  20 . Thus, the moving capacitor plates  66  are to the right of the stationary capacitor plates  68  on a first side of the beam (the upper side as depicted in FIG. 11) whereas the reverse order occurs on the lower side of the beam  20 . Accordingly as the beam  20  moves to the right, the capacitance formed by the upper moving capacitor plates  66  and stationary capacitor plates  68  decreases while the capacitance formed by the lower plates increases. The point where the value of the upper capacitance crosses the value of the lower capacitance precisely defines a null point and is preferably set midway in the travel of the beam  20 . The moving capacitor plates  66  are connected to beam portion  32   b  and thus connected to terminals  26   c . The stationary capacitor plates  68  are connected to terminals  26   a  and  26   d  respectively. Capacitor plates  66  and  68  are cantilevered over the substrate  42  by the same under etching used to free the beam  20  from the substrate  42 . 
     Techniques for comparing capacitance well known in the art may be used to evaluate the position of the beam  20 . One circuit for providing extremely accurate measurements of these capacitances is described in co-pending application Ser. No. 09/677,037 filed Sep. 29, 2000 and hereby incorporated by reference. 
     Generally, the operating structure of the MEMS magnetic field sensor  10  is constructed to be symmetric about an axis through the middle of the beam  20  along the longitudinal axis  40  such as to better compensate the thermal expansions. In addition, the operating area of the plates of the capacitors, plates  66  and  68  on both sides of the beam  20  for the sense device  36   c  are made equal so as to be balanced. For similar reasons, beam  20  is attached to the center of the flexible conductor  46 . 
     The embodiment depicted in FIGS. 1,  2 , and  11  is suitable for providing a binary output such as may be suitable for a switch or the like or an analog output. However, the later analog output may be affected by nonlinearities in the Lorentz Force motor  36   a  or detector device  36   c  or other source, particularly for larger displacements. These nonlinearities may be reduced by implementing a feedback system. 
     Feedback System 
     Referring now to FIG. 3, in a feedback system, the detector output  14  is provided to a comparison circuit  16 , which provides a output signal  18 . The output signal  18  may serve as a new output and is also provided through feedback block  99  to a compensation coil  21  arranged to produce a countervailing magnetic flux B c  oriented to nullify the crossing magnetic field B at the flexible conductor  46 . The feedback operates to return the flexible conductor  46  to its relaxed state thus eliminating the nonlinear effects incident to bowing of the flexible conductor  46  and gross movements of the beam  20 . 
     Referring now to FIG. 4, the need for a compensation coil  21  may be eliminated by the addition of an electrically controlled bias device  36   b  interposed between the Lorentz motor actuator device  36   a  and the detector device  36   c . Specifically, Lorentz motor actuator device  36   a  may connect via beam segment  32   a  through insulating section  15  to beam segment  32   c  connected to the bias device  36   b . Beam section  32   c  may then connect through insulating section  17  to beam segment  32   b , which connects to the detector device  36   c  as has been described. The bias device  36   b  may be an electrostatic motor as will be described below, although other bias devices may also be used. 
     Specifically, referring now to FIG. 6, the beam  20  may extend above a substrate  42  along the longitudinal axis  40  between longitudinally opposed pylons  44 ′. The beam  20  may thereby define a midline dividing transversely opposed pylons  44 ′, the latter attached and extending upward from a substrate  42 . The leftmost pylons  44 ′ form the terminals  22   d  and  22   c  described above while the right most pylons  44 ′ form terminals  26   c . One transversely opposed pair of pylons  44 , positioned to the right side of the beam  20 , provide terminals  26   a  and  26   d  described above while a second transversely opposed pair of pylons  44  roughly centered on the beam  20  provide terminals  38   c  and  38   d  being part of the electrically controlled bias device  36   b.    
     The beam  20  is supported away from the substrate  42  and held for movement along the longitudinal axis  40  by means of flexible conductors  46  and  46 ″ extending transversely on opposite sides of both ends of the beam  20  and its middle. The flexible conductors  46  and  46 ″ extend transversely away from the beam  20  to elbows  48  removed from the beam  20  on each side of the beam  20 . The elbows  48  in turn connect to expansion compensators  50 , which return to be attached to the substrate  42  at a point near the beam  20 . The support structure and operation of the elbows is described in U.S. patent application Ser. No. 09/805,410 referred to above. 
     The flexible conductors  46 ,  46 ′ and  46 ″ are connected to expansion compensators  50  which in turn provide electrical connections between each of the beam sections  32   a ,  32   b  and  32   c  and stationary electrical terminals. Specifically, the expansion compensators  50  connected to either end of the leftmost flexible conductor  46  connect to terminals  22   c  and  22   d  respectively. The expansion compensators  50  connected to the middle flexible conductor  46 ′ provide an electrical connection between beam section  32   c  and terminal  38   a . The expansion compensators  50  attached to rightmost flexible conductor  46 ″ connect to terminal  26   c  to beam section  32   b.    
     The portion  32   a  of the beam  20 , such as forms part of the Lorentz motor actuator device  36   a , is isolated by insulating section  15  from the beam portion  32   c  and thus a voltage imposed across terminals  22   c  and  22   d  provides a current through the flexible conductor  46 . 
     The beam segment  32   c  may have transversely outwardly extending, moving capacitor plates  66  overlapping with corresponding transversely inwardly extending stationary capacitor plates  68  attached to the pylons  44  supporting terminals  38   c  and  38   d . Stationary capacitor plates  68  are leftward of moving capacitor plates  66  on both sides of the beam  20 . Each of the moving capacitor plates  66  and their corresponding stationary capacitor plates  68  may have mutually engaging fingers (as opposed to being simple parallel plate capacitors) so as to provide for a more uniform electrostatic force over a greater range of longitudinal travel of the beam  20 . An electrostatic motor is thus formed using the attraction between the stationary capacitor plates  68  charged via terminals  38   c  and  38   d  and moving capacitor plate  66  charged via terminal  38   a  to urge the beam  20  leftward. It will be understood from this description that if rightward movement of beam  20  is desired then the left/right order of  68 / 66  plates can be reversed Capacitor plates  66  and  68  are cantilevered over the substrate  42  by the same under etching used to free the beam  20  from the substrate  42 . 
     Referring still to FIG. 6, portion  32   b  of the beam  20 , isolated from beam portion  32   c  by insulating section  17  also supports moving capacitor plates  66  and stationary capacitor plates  68 . However as mentioned above, in this case, the capacitor plates do not serve the purpose of making an electrostatic motor but instead serve as a sensing means in which variation in the capacitance between the moving capacitor plates  66  and stationary capacitor plates  68  serves to indicate the position of the beam  20 . In this regard, the order of the stationary and moving capacitor plates  66  and  68  is reversed on opposite sides of the beam  20 . Thus, the moving capacitor plates  66  are to the right of the stationary capacitor plates  68  on a first side of the beam (the upper side as depicted in FIG. 6) whereas the reverse order occurs on the lower side of the beam  20 . Accordingly as the beam  20  moves to the right, the capacitance formed by the upper moving capacitor plates  66  and stationary capacitor plates  68  decreases while the capacitance formed by the lower plates increases. The point where the value of the upper capacitance crosses the value of the lower capacitance precisely defines a null point and is preferably set midway in the travel of the beam  20 . The moving capacitor plates  66  are connected to beam portion  32   b  and thus connected to terminals  26   c . The stationary capacitor plates  68  are connected to terminals  26   a  and  26   d  respectively. 
     Techniques for comparing capacitance well known in the art may be used to evaluate the position of the beam  20 . One circuit for providing extremely accurate measurements of these capacitances is described in co-pending application Ser. No. 09/677,037 filed Sep. 29, 2000 and hereby incorporated by reference. 
     Generally, the operating structure of the MEMS magnetic field sensor  10  is constructed to be symmetric about an axis through the middle of the beam  20  along the longitudinal axis  40  such as to better compensate the thermal expansions. In addition, the operating area of the plates of the capacitors, plates  66  and  68  on both sides of the beam  20  for the bias device  36   b  are made equal so as to be balanced. For similar reasons, beam  20  is attached to the center of the flexible conductor  46 . 
     Referring again to FIG. 4, the detector output  14  of the detector device  36   c  and capacitive sensing circuit  73  may again be received by a comparison circuit  16  to produce output signal  18 . This output signal  18  is then passed through feedback block  99  and connected to terminals  38   c  and  38   d  and  38   a  so that rightward movement of the beam  20  produces a greater attraction between stationary plates  68  and moving capacitor plates  66  creating an opposite leftward force on the beam. This feedback provides a linearizing of the response of the MEMS magnetic field sensor  10  according to principles well known in the art. 
     The electrically controllable bias device  36   b  may also be used to create a spring-like effect (although one not observing Hooke&#39;s law) by imposing a constant voltage across terminals  38   c  and  38   d  and terminal  38   a . Thus it can be used to compliment the naturally occurring restoring spring force of the flexible conductor itself of the configuration of FIGS. 1,  2 , and  11 . 
     In yet another embodiment, the feedback current may be directed directly to a Lorentz motor to counteract or control the proof current i p  going therethrough so long as a residual biasing field B b  (not shown) is provided. B b  is oriented to augment the incident magnetic field to be measured. 
     Referring for example, to FIG. 11, a simple feedback system can be implemented in this way by controlling the proofing current i p  as a function of displacement of the beam  20  detected by the detector device  36   c . The capacitive sensing circuit  73  is used to provide a feedback signal holding the beam at it&#39;s neutral position against some mechanical biasing force. For example, with a 20 mA proof current and a residual magnetic field B b  the feedback is some predetermined value holding the beam  20  at the neutral position. As a magnetic field is applied the beam  20  displaces from neutral causing a negative feedback. This negative feedback subtracts from the proof current ip so as to bring the beam  20  back to neutral. The open loop gain in the system establishes the neutral beam error position and the feedback is a measure of the impinging field. No extra beam or coil is needed to affect the feedback. Generally (B+B b )·i p =Output. 
     Referring now to FIG. 7, flexible conductor  46  may be constructed using integrated circuit techniques in three layers, a lower semiconductor layer  60  such as silicon topped by an insulator  62 , for example, silicon dioxide, in turn, topped by metalization layer  64  such as aluminum. 
     The same structure may be carried onto beam section  32   b  of FIG.  11  and the insulating section  15  between beam sections  32   a  and  32   b  may be created by etching away the metalization layer  64  alone. A similar approach may be used for the insulating section  17  between beam portions  32   c  and  32   b  of FIG.  9 . 
     Referring now to FIG. 11, in an alternative embodiment, the insulating section  15  between the detector device  36   c  and the Lorentz motor  36   a  uses a different technique which incurs direct metal to silicon contact within  36   c  to take advantage of the total height of the silicone structure in creating opposed capacitor plates. Accordingly, referring to FIG. 13, the structure is much the same as described above as depicted in FIG. 7, with the exception that the insulating layer  62  is removed from the regions of beam section  32   b  and detector device  36   c  prior to the deposition of the metalization layer  64 . As a result, the metal is deposited directly onto layer  60  in these regions. 
     Referring again to FIGS. 6 and 12, in an alternative embodiment, the insulating section  17  between the detector device  36   c  and the biasing device  36   b  uses a different technique which incurs direct metal to silicon contact to take advantage of the total height of the silicon structure in creating opposed capacitor plates but at insulating sections  17  the beam  20  expands to create T-bars  56  flanking insulating section  17 . Insulating material  58  attached to these T-bars  56  create the insulating section  17 . Generally the beam  20  may be fabricated using well-known integrated circuit processing techniques to produce a structure suspended above the substrate  42  and composed of a laminated upper conductive layer  60  (for example, polysilicon or crystalline silicon) optionally with an upper aluminum layer  64  (not shown) and a lower insulating layer  62  such as silicon dioxide or silicon nitride. The insulating section  17  is created simply by etching away the upper layer in the region of the insulating section  17  according to techniques well-known in the art using selective etching techniques. 
     Each of the upper conductive layers  60  and lower insulating layers  62  are perforated by vertically extending channels  65  such as assists in conducting etchant beneath the layers  60  and  62  to remove a sacrificial layer that normally attaches layers  60  and  62  to the substrate  42  below according to techniques well known in the art. 
     The technique used to make insulating section  17  may also be used for insulating section  15  in FIGS. 6 and 11. 
     Referring now to FIG. 5, the Lorentz motor actuator device  36   a  and detector device  36   c  of MEMS magnetic field sensor  10  may be teamed with a MEMS magnetic field sensor  10 ′ having a Lorentz motor actuator device  36   a ′ and detector device  36   c ′ each receiving the same proof current i p , but arranged so that the Lorentz force on the second MEMS magnetic field sensor  10 ′ is in the opposite direction from the Lorentz force on the first MEMS magnetic field sensor  10  for a given crossing magnetic field B. This may be accomplished in a number of ways: as shown by making device  10 ′ a mirror image of device  10  (and reversing the sense of the proof current i p  as shown), or by using the same orientations of beams  20  and  20 ′ and opposite currents and reversed biasing devices. The two detector output signals  14  and  14 ′ are then combined by combiner  63 , which serves to double the Lorentz force signal components of the outputs  14  and  14 ′ and to nullify common mode mechanical shock and vibration components. Other variations of this approach described in U.S. application Ser. No. 09/805,410 referred to above. 
     Referring now to FIG. 8, the MEMS magnetic field sensor  10  may be placed adjacent to a current measuring conductor  70  conducting a test current i to produce a flux field orbiting the conductor  70  according to the right hand rule. A flux-concentrating core  72  may be placed coaxially around the conductor  70  to channel the flux through a gap  74  in the core  72  in which the MEMS magnetic field sensor  10  is placed. The flux in the gap, which originates from the conductor  70 , then becomes the crossing magnetic field B. In this way, the current measuring capabilities of the present invention may be harnessed to provide for current measurement in the conductor  70 . From this description, it will be understood that other core and conductor configurations may be used including those in which the conductor  70  is wrapped in coils or the like, possibly around the core  72  and where the compensation coil  21  of FIG. 3 is wrapped around the core  72 . 
     Referring now to FIG. 9, a switch  80  may be constructed in which the MEMS magnetic field sensor  10  is placed in proximity to a permanent magnet  82  mounted to a movable operator  84  biased toward or away from the MEMS magnetic field sensor  10  with springs  86  so that movement of the operator  84  causes movement of the magnet  82  changing the magnetic field imposed on the MEMS magnetic field sensor  10 . In this case, the bias device  36   b  may be given with a constant predetermined bias amount so that a predetermined flux of crossing magnetic field B is required to cause a switching that may be sensed by the detector device  36   c  or a threshold may be established with a comparator  16  such as shown in FIG. 3 or  4 , with or without feedback  18 . If feedback  18  is used it may be positive feedback so as to establish hysteresis according to methods understood in the art. Once the switch position changes the positive feedback would cause the beam  20  to remain in position, until some large offsetting field or another electrostatic motor caused it to go back to starting position. 
     Referring now to FIG. 10, the MEMS magnetic field sensor  10  may be used in conjunction with a magnet structure  88  providing a crossing magnetic field B for the MEMS magnetic field sensor  10 . Motions of a nearby ferromagnetic object  90  causing distortion of the crossing magnetic field B may be thus detected by the MEMS magnetic field sensor  10  to produce a proximity switch. 
     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but that modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments also be included as come within the scope of the following claims. For example, the biasing device may be a thermal, piezoelectric or other electrically controllable MEMS element and the detector device may be other forms of detectors such as optical detectors, resistive detectors, piezoelectric detectors, inductive detectors and the like.