Patent Publication Number: US-7220602-B2

Title: Magnetic tunnel junction sensor method

Description:
TECHNICAL FIELD 
     The present invention generally relates to sensing, and more particularly to methods for sensors employing magnetic tunnel junctions (MTJ). 
     BACKGROUND 
     Sensors are widely used in modern systems to measure or detect physical parameters such as, and not intended to be limiting, position, motion, force, acceleration, temperature, pressure and so forth. Many different types of sensors exist in the prior art for measuring these and other parameters. However, they all suffer from various limitations well known in the art, for example, excessive size and weight, inadequate sensitivity and/or dynamic range, cost, reliability and other factors. Thus, there continues to be a need for improved sensors, especially sensors that can be easily integrated with semiconductor devices and integrated circuits and manufacturing methods therefore. 
     Accordingly, it is desirable to provide an improved sensor and method, adaptable for measuring various physical parameters. In addition, it is desirable that the sensor and method be simple, rugged and reliable, and further, be compatible with semiconductor device and integrated circuit structures and fabrication methods, and preferably but not essentially adapted to be formed on the same substrate. It is further desirable that the improved sensor and method convert the physical parameter being measured into an electrical signal. Other desirable features and characteristics of the invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a simplified schematic side view and electrical circuit of a sensor employing a magnetic tunnel junction (MTJ), according to an exemplary embodiment of the invention; 
         FIG. 2  is collection of side views of the magnetic tunnel junction of  FIG. 1  illustrating different orientations of the magnetic spin axes therein; 
         FIG. 3  is collection of exploded plan views of the magnetic tunnel junction of  FIG. 1  illustrating different orientations of the magnetic spin axes therein; 
         FIG. 4  is a simplified plot of current versus voltage of a magnetic tunnel junction for two different orientations of the magnetic spin axes; 
         FIGS. 5–7  are simplified plots the resistance of a magnetic tunnel junction as a function of applied magnetic field; 
         FIG. 8  is a simplified schematic side view of a magnetic tunnel junction sensor according to another exemplary embodiment of the invention employing a moveable cantilever beam supporting a magnetic field source whose position is dependent upon the sensor input; 
         FIG. 9  is a simplified plan view of the magnetic tunnel junction sensor of  FIG. 8  wherein a current carrying flexible U-shaped cantilevered beam provides a varying magnetic field to the magnetic tunnel junction, depending upon the sensor input; 
         FIG. 10  is a simplified plan view of the magnetic tunnel junction sensor of  FIG. 8  wherein a single flexible cantilever beam supports a permanent magnet for providing a varying magnetic field to the magnetic tunnel junction, depending upon the sensor input; 
         FIG. 11  is a simplified schematic cross-sectional view through a magnetic tunnel junction sensor according to a further exemplary embodiment of the invention; 
         FIG. 12  is a simplified partially cut-away plan view of the sensor of  FIG. 11 ; 
         FIG. 13  is a simplified schematic cross-sectional view similar to that of  FIG. 11  but according to a still further exemplary embodiment of the invention; 
         FIG. 14  is a simplified schematic cross-sectional view analogous to that of  FIG. 11  but according to a yet further exemplary embodiment of the invention and employing an active magnetic field source; 
         FIG. 15  is a simplified partially cut-away plan view of the sensor of  FIG. 14  showing further details; 
         FIG. 16  is a simplified schematic cross-sectional view analogous to that of  FIG. 14  but according to a still further exemplary embodiment of the invention, adapted to measure temperature or pressure; 
         FIG. 17  is a simplified flow diagram of a method of manufacture of the invented sensor; 
         FIG. 18  is a simplified flow diagram analogous to the flow diagram of  FIG. 17  but showing further details; 
         FIG. 19  is a schematic set of cross-sectional views illustrating still further details of an embodiment of the method of  FIGS. 17–18 ; 
         FIG. 20  is a schematic set of cross-sectional views analogous to those of  FIG. 19  but according to a further exemplary embodiment of the method of the invention; 
         FIG. 21  is a schematic set of cross-sectional views analogous to those of  FIGS. 19–20  but according to a still further exemplary embodiment of the method of the invention; 
         FIG. 22  is an exploded plan view of the electrodes of a MTJ according to an embodiment of the invention where at least one of the electrodes is square; 
         FIG. 23  is an exploded plan view of the electrodes of a MTJ according to embodiments of the invention where either or both electrodes have various exemplary, non-square, shapes; 
         FIG. 24  is a plan view of the electrodes of a MTJ according to embodiments of the invention where at least one of the electrodes has various angular arrangements with respect to the other electrode; 
         FIG. 25  is a simplified plan view of multiple sensors with cantilever beams of different sizes supporting magnetic field sources in proximity to multiple MTJs; 
         FIG. 26  is a simplified electrical schematic circuit diagram wherein the multiple MTJs of  FIG. 25  are illustrated as being electrically coupled in parallel; and 
         FIG. 27  is a simplified plot of tunneling resistance R T  versus force or acceleration F for the parallel arrangement of  FIG. 26 , where R T  is the parallel combination of the tunneling resistances through the multiple tunnel junctions and F is the acceleration or force being simultaneously applied to the multiple sensors. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawings figures are not necessarily drawn to scale. For example, the dimensions of some of the elements or regions in the figures may be exaggerated relative to other elements or regions to help improve understanding of embodiments of the invention. 
     The terms “first,” “second,” “third,” “fourth” and the like in the description and the claims, if any, may be used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “comprise,” “include,” “have” and any variations thereof, are intended to cover non-exclusive inclusions, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. 
     The terms “left,” right,” “in,” “out,” “front,” “back,” “up,” “down, “top,” “bottom,” “over,” “under,” “above,” “below” and the like in the description and the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. 
       FIG. 1  is a simplified schematic side view and electrical circuit of sensor  30  employing magnetic tunnel junction (MTJ)  32  and moveable magnetic field source (MFS)  34 , according to an exemplary embodiment of the invention. Magnetic field source (MFS)  34  is free to move as indicated by arrows  44 - 1 ,  44 - 2  (collectively  44 ) and provides magnetic field  35  that moves with respect to MTJ  32 , thereby changing the intensity and/or direction of the magnetic field H at MTJ  32  depending upon the relative position of MFS  34  and MTJ  32 . MTJ  32  comprises first electrode  36 , insulating tunneling dielectric  37  and second electrode  38 . When voltage V t  is applied across MTJ  32 , current I t  flows by quantum mechanical tunneling through insulator  37  from electrode  36  to electrode  38  or vice versa depending upon the polarity of the applied voltage. 
     Electrodes  36 ,  38  are desirably magnetic materials, for example, and not intended to be limiting, NiFe, CoFe, and the like, or more generally, materials whose electronic spin axes can be collectively aligned. Examples of suitable electrode materials and arrangements are the materials and structures commonly used for electrodes of magnetoresistive random access memory (MRAM) devices, which are well known in the art and contain, among other things, ferromagnetic materials. It is desirable that electrodes  36 ,  38  have different coercive force, that is, electrode  36  should have a high coercive force so that its spin axes orientation can be pinned so as to be substantially unaffected by movement of MFS  34 , and electrode  38  should have a comparatively low coercive force so that its spin axes orientation are altered by movement of MFS  34 . It is desirable that the coercive force of electrode  36  be about two orders of magnitude larger than that of electrode  38 , but bigger and smaller ratios are also useful. The coercive force of the electrodes can be adjusted by varying their composition according to means well known in the art. Exemplary spin axes alignments are indicated in  FIG. 1  wherein vectors  40  (hereafter spin axes  40 ) of electrode  36  indicate that the electron spin axes in electrode  36  are aligned perpendicular to and facing into the plane of the drawings of  FIG. 1 , and vector  42  (hereafter spin axes  42 ) of electrode  38  indicates that the electron spin axes in electrode  38  are aligned parallel to the plane of the drawing and facing to the right in  FIG. 1 , that is, orthogonal to spin axes  40 . It is known in the art that the spin axis orientation can be pinned in one direction or another by appropriate heat treatment in the presence of a magnetic field and by other means. The spin axes in lower electrode  36 , that is, in the electrode furthest from magnetic field source  34  are desirably pinned. The spin axes may be pinned in any convenient direction depending, for example, on the magnetic field direction of source  34 . Spin axes  42  in upper (closest to MFS  34 ) electrode  38  are free, that is, not pinned and change orientation with respect to pinned spin axes  40  in electrode  36  in response to magnetic field  35  provided by MFS  34 . Magnetic field source conductor  34 A is conveniently provided proximate MTJ  32  but on the side opposite MFS  34  and oriented so as to be at right angles to MFS  34  in terms of its magnetic field. Current I f  is conveniently provided in MFS conductor  34 A in order to assist in flipping spin axes  42  to other directions than may be possible with MFS  34  alone, or to restore spin axes  42  to a previous state after being flipped by proximity to MFS  34 . 
       FIG. 2  is collection of side views of magnetic tunnel junction (MTJ)  32  of  FIG. 1 , that is, of MTJs  32 - 1  . . . .  32 - 5 , illustrating different relative orientations of magnetic spin axes  40 ,  42  in electrodes  36 ,  38 . In MTJ  32 - 1 , free spin axes  42 - 1  and pinned spin axes  40 - 1  are parallel, lying in the plane of the drawing of  FIG. 2  and both facing to the right. In MTJ  32 - 2  free spin axes  42 - 2  and pinned spin axes  40 - 2  are parallel and lying in the plane of the drawing but facing in opposite (anti-parallel) directions, axes  42 - 2  facing left and axes  40 - 2  facing right. In MTJ  32 - 3 , the spin axes are orthogonal, free spin axes  42 - 3  in electrode  38  lying in the plane of the drawings and facing right and pinned spin axes  40 - 3  of electrode  36  facing perpendicular to and into the plane of the drawing. In MTJ  32 - 4 , the spin axes are anti-parallel, spin axes  42 - 4  facing into the plane of the drawing and spin axes  40 - 4  facing out of the plane of the drawing. In MTJ  32 - 5 , spin axes  42 - 5  and  40 - 5  are parallel, perpendicular to and facing into the plane of the drawing. The examples of  FIG. 2  are not meant to be exhaustive, but to merely illustrate that various relative spin axes orientations are possible. Other relative orientations are also possible. 
       FIG. 3  is collection of exploded plan views  32 - 6 ,  32 - 7 ,  32 - 8  of magnetic tunnel junction  32  of  FIG. 1  illustrating different orientations of the magnetic spin axes therein, as seen perpendicular to the view of  FIG. 2 . While in  FIGS. 1–2 , electrode  38  lies above electrode  36  separated therefrom by tunneling dielectric  37 , in  FIG. 3  electrodes  36 ,  38  are displaced from such alignment so that the azimuthal orientation of the spin axes lying in the plane of electrodes  36 ,  38  may be more easily seen. For example, in MTJ  32 - 6  of  FIG. 3  spin axes  42 - 6 , and  40 - 6  have the same orientation as spin axes  42 - 1  and  40 - 1  of MTJ  32 - 1  of  FIG. 2 , and in MTJ  32 - 7  of  FIG. 3 , spin axes  42 - 7  and  40 - 7  have the same orientation as spin axes  42 - 3  and  40 - 3  of MTJ  32 - 3  of  FIG. 2 . However, MTJ  32 - 8  of  FIG. 3  illustrates another possibility, that is, spin axes  42 - 8  have an azimuthal orientation that is neither parallel to nor orthogonal to spin axes  40 - 8 , but lies at an intermediate azimuthal angle relative to spin axes  40 - 8 . In the foregoing, it is presumed that electrodes  36 ,  38  are sufficiently thin that spin axes  40 ,  42  always lie in the planes of electrodes  36 ,  38 , but may be oriented at different relative azimuthal angles in the planes of electrodes  36 ,  38 . 
     The relative orientation of the spin axes in electrode  36  and  38  affects the electrical properties of MTJ  32 . This is because, the spin orientation affects the density of electron states near the Fermi level where most tunneling occurs and therefore affects the tunneling probability for the same applied electric field or applied voltage at constant barrier thickness.  FIG. 4  shows representative current versus voltage plot  50  of magnetic tunnel junction  32  for two different orientations of the magnetic spin axes  40 ,  42 . Trace  51  corresponds to the case where spin axes  40 ,  42  are parallel and trace  52  corresponds to the case where spin axes  40 ,  42  are anti-parallel. For a given voltage V t =V t (1) across MTJ  32 , MTJ  32  has conductance C t (1) when the I t  vs V t  characteristic correspond to trace  51  and different conductance C t (2) when I t  vs V t  characteristic corresponds to trace  52 . Stated another way, when MTJ  32  is in the state characterized by trace  51 , then for V t =V t (1), I t =I t (1) and when MTJ  32  is in the state characterized by trace  52 , for the same voltage V t =V t (1), then I t =I t (2)&lt;I t (1). This difference in conductance C t  or resistance R t  or current I t  at constant voltage may be used to detect changes in the relative orientation of spin axes  40 ,  42  in electrodes  36 ,  38 . Because the spin axes orientation in electrode  38  depends upon the applied magnetic field H (e.g., see  FIG. 1 ), the change in conductance or resistance or the change in current at constant voltage may be used to detect changes in H or changes in any physical parameter that can cause a variation in H. As illustrated in  FIG. 1 , changes in location or orientation of MFS  34  with respect to MTJ  32  (e.g., as illustrate by arrows  44 - 1  and  44 - 2 ) causes H at MTJ  32  to vary and therefore can cause the electrical properties of MTJ  32  to vary in a predictable way. As indicated on  FIG. 4 , the tunneling resistance R t  for the two cases may be calculated from the relations R t (2)=V t (1)/I t (2) and R t (1)=V t (1)/I t (1). 
       FIGS. 5–7  are simplified plots  60 ,  62 ,  64  of tunneling resistance R t  of MTJ  32  as a function of applied magnetic field H. Plot  60  of  FIG. 5  illustrates the case where electrode  38  switches like a single magnetic domain, that is, its spin axis  42  remains substantially unchanged until a critical field H c  or −H c  is reached, whereupon it substantially snaps or flips to a new orientation. For example, if MTJ  32  is in the state characterized by R t =R t (1) at V t =V t (1), it remains in this state until H=H c  and then flips to the state characterized by R t =R t (2). It remains in this state until H=−H c  when it flips back. This type of hysteresis behavior is very useful when it is desired that sensor  20  has a binary output in response to changes in acceleration, force, temperature, position, pressure or whatever other physical parameter causes H to change, for example, by causing MFS  34  to move with respect to MTJ  32 . Magnetic field −H c  needed to flip back can be conveniently provided by current lead  34 A shown in  FIG. 1 . 
     Plot  62  of  FIG. 6  illustrates the case where electrode  38  exhibits what amounts to multiple magnetic domains, that can individually flip at slightly different magnetic fields H c ′≦H≦H c ″. Assuming for purposes of explanation that MTJ  32  is in the state characterized by R t =R t (1), then as H is increased, R t  remains unchanged until H=H c ′, whereupon R t  begins to gradually increase at constant voltage until H=H c ″ whereupon R t  locks at R t =R t (2). Hysteresis loop  62  has a slanted parallelepiped shape.  FIG. 7  shows the situation when the material and orientation of electrode  38  are such (e.g., at right angles to each other) that the magnetization can rotate continuously in response to an increase or decrease in H. Then the hysteresis loop essentially collapses into a nearly straight line as shown by R t  vs H plot  64  with its two extremities at R t =R t (1) and R t =R t (2). This situation occurs when spin axes  42  can rotate continuously relative to spin axes  40 , as shown for example in MTJ  32 - 8  of  FIG. 3 . Current line  34 A shown in  FIG. 1  is conveniently used in connection with the arrangements depicted by plots  60 ,  62  to provide magnetic field −H c  so that spin axes  42  may be reset, that is, flipped back to its initial orientation before it was perturbed by magnetic field  35 . 
       FIG. 8  is simplified schematic side view of magnetic tunnel junction sensor  70  according to exemplary embodiments of the invention employing deflectable cantilever beam  84  with magnetic field source  86 , whose position depends upon the input to sensor  70 . MTJ sensor (MTJS)  70  comprises substrate  72 , conveniently a semiconductor substrate on which MTJ device  32  and cantilever beam  84  with magnetic field source  86  are formed. Substrate  72  desirably has portion  74  wherein electronic circuitry  73  for measuring the change in electrical properties of MTJ  32  is provided, but this is not essential. When an active magnetic field source is employed (e.g., see  FIG. 9 ), circuitry  73  may also include the current drivers for magnetic field source (MFS) portion  86 , but this is not essential. Conductor  76  conveniently makes electrical contact to MTJ electrode  36  and conductor  78  makes electrical contact to MTJ electrode  38 . Conductors  76 ,  78  are conveniently of Ta/TaN but this is not intended to be limiting, and any reasonably conductive material may be used. An insulating layer (not shown) may be provided between conductor  76  and portion  74 . Although not shown to avoid unduly cluttering  FIGS. 8–10 , current line  34 A of  FIG. 1  may also be provided beneath MTJ  32 , that is, between conductor  76  and region  74  of substrate  72 , but this is not essential. Dielectric region  75  is provided to support electrode  78 . Tunneling dielectric  37  is conveniently of aluminum oxide, although other highly insulating materials that can be fabricated in very thin, substantially uniform, pin-hole free layers may also be used, such as MgO. Dielectric planarization layer  77  is provided above conductors  76 ,  78 . Region  82  of cantilever beam  84  is supported by region  92  of layer  77 . Portions  85  and  86  of cantilevered beam  84  are free, that is, they may move as indicated by arrows  88 . Magnetic field source (MFS) portion  86  of beam  84  lies above MTJ  32 . Recess or opening  80  is provided in layer  77  to allow portion  85  and MFS portion  86  of cantilever beam  84  to deflect, for example, toward and away from MTJ  32 , as indicated by arrows  88 . As explained in connection with  FIGS. 9 and 10 , MFS  86  may be active, that is, current carrying (e.g., see  FIGS. 8–9 ) or may be passive, that is, include permanent magnet  87  (e.g., see  FIGS. 8 ,  10 ). Whatever physical parameter is desired to be measured by sensor  70 , such physical parameter is coupled to cantilevered beam  84  so as to cause it to deflect as shown by arrows  88  in response to changes in such physical parameter. 
       FIG. 9  is simplified plan view  90 - 1  of magnetic tunnel junction sensor  70 - 1  corresponding to an exemplary embodiment of sensor  70  of  FIG. 8 , wherein cantilevered beam  84  has a U-shape, as may be seen in  FIG. 9 . Current carrying deflectable cantilevered beam  84 - 1  has MFS portion  86 - 1  that provides the varying magnetic field to magnetic tunnel junction (MTJ)  32 . MTJ  32  is seen in plan view  90 - 1  with electrode  38  nearest to the viewer. U-shaped cantilever beam  84 - 1  has end regions  82 - 1  anchored on region  92 - 1  of layer  77  and portions  85 - 1  and  86 - 1  extending over recessed area or opening  80 - 1  in layer  77 . MFS portion  86 - 1  forms the bottom of the “U” and overlies MTJ  32 . Current  96  flows through U-shaped cantilever beam  84 - 1  including MFS portion  86 - 1  and produces a magnetic field in the vicinity of MTJ  32 , analogous to magnetic field  35  of sensor  20  of  FIG. 1 . Such an arrangement is referred to as having an active magnetic field source (MFS), that is, the magnetic field is generated by a current rather than a permanent magnet. While cantilever beam  84 - 1  is illustrated as having straight, constant width, leg portions of the “U” shape, such straight constant width leg portions are merely for convenience of illustration and not intended to be limiting and persons of skill in the art will understand based on the description herein that any U-shape may be employed that is suitable for accommodating the desired current and providing the desired deflection characteristics in the direction of arrows  88 . 
       FIG. 10  is simplified plan view  90 - 2  of magnetic tunnel junction sensor  70 - 2  corresponding to a further exemplary embodiment of sensor  70  of  FIG. 8 , wherein cantilevered beam  84 - 2  having MFS portion  86 - 2  with permanent magnet  87  thereon provides the varying magnetic field to magnetic tunnel junction  32 , in response to changes in the input to sensor  70 - 2 . Such an arrangement is referred to as having a passive magnetic field source, that is, the magnetic field is generated by a permanent magnet rather than a current carrying wire or coil. MTJ  32  is seen in plan view  90 - 2  with electrode  38  nearest to the viewer. Cantilever beam  84 - 2  is conveniently a single beam with end region  82 - 2  anchored on region  92 - 2  of layer  77  and portions  85 - 2  and  86 - 2  extending over recess or opening  80 - 2  in layer  77 . Permanent magnet  87  is provided, attached by any convenient means to MFS portion  86 - 2  over MTJ  32 . Magnet  87  is conveniently but not essentially mounted on the underside of beam  84 - 2  below portion  86 - 2 , but could also be mounted above or elsewhere on portion  86 - 2 . Magnet  87  produces a magnetic field in the vicinity of MTJ  32 , analogous to magnetic field  35  of sensor  20  of  FIG. 1 . While cantilever beam  84 - 2  is illustrated in  FIG. 10  as having tapering width  93  between anchor region  82 - 2  and MFS portion  86 - 2 , this is merely for convenience of illustration, and persons of skill in the art will understand that any shape may be used so as to provide the desired deflection characteristics for cantilevered beam  84 - 2  in the direction of arrows  88 . 
       FIGS. 11–16  illustrate how MTJ  32  may be employed to provide sensors able to detect a variety of physical parameters.  FIGS. 11–16  are intended as non-limiting examples, and persons of skill in the art will understand based on the description herein that many other implementations are possible following the basic principals that these and other examples herein teach. For convenience of description, the sensors of  FIGS. 11–16  are illustrated as being in discrete, free-standing form rather than part of an integrated circuit that includes the sensing and/or driving circuitry, but that is not precluded.  FIGS. 11–16  and the associated discussion are intended merely to facilitate explanation and are not intended to be limiting. Persons of skill in the art will understand based on the description herein that the principals taught in these various examples may be employed in discrete or integrated form. 
       FIG. 11  is a simplified schematic cross-sectional view through magnetic tunnel junction sensor  100  according to a further exemplary embodiment of the invention.  FIG. 12  is a simplified partially cut-away plan view of sensor  100  of  FIG. 11 . In order to make them easily visible in  FIG. 12  and not intended to be limiting, MTJ  32  is assumed to be substantially square in plan view and magnetic field source  104  is assumed to be circular in plan view, but this is merely for convenience of description. Sensor  100  comprises MTJ  32  with leads or conductors  76 ,  78  mounted in body  101 . Referring again to  FIG. 11 , diaphragm  102  with magnetic field source  104  analogous to source  87  of  FIGS. 8 and 10 , and source  34  of  FIG. 1  is located above MTJ  32 , wherein MFS  104  is analogous to source  87  of  FIGS. 8 and 10 , and source  34  of  FIG. 1 . Diaphragm  102  with magnetic field source  104  moves as shown by arrows  106  in response to various external stimuli. This has the effect of altering the magnetic field H at MTJ  32 , thereby causing its electrical properties to change, as has been explained in connection with  FIGS. 1–7 . Thus, sensor  100  can detect changes in any physical parameter or function that can alter the relative position of magnetic field source (MFS)  104  and MTJ  32 . Non-limiting examples of such physical phenomena are motion, acceleration, force, pressure, temperature, and so forth. 
       FIG. 13  is a simplified schematic cross-sectional view of sensor  111  similar to that of sensor  100  of  FIG. 11  but according to a still further exemplary embodiment of the invention. Sensor  111  differs from sensor  100  by inclusion of attachment lug  105  with attachment hole  107 , to facilitate coupling diaphragm  102  with MFS  104  to a remote input, for example, and not intended to be limiting, an object whose position or acceleration is to be monitored or detected, or for coupling to a device whose size or separation changes with temperature, pressure, or other physical parameter. 
       FIG. 14  is a simplified schematic cross-sectional view of sensor  112  generally like that of  FIG. 11  but according to a yet further exemplary embodiment of the invention employing active magnetic field source cantilever beam  108  analogous to magnetic field source cantilever beam  84 ,  86  of  FIGS. 8–9  and source  34  of  FIG. 1 .  FIG. 15  is a simplified partially cut-away plan view of sensor  112  of  FIG. 14  showing further details. Mounted between diaphragm  102  and MTJ  32  is cantilevered beam  108  analogous to cantilevered beam  84  of  FIGS. 8–9 , and with end  110  analogous to magnetic field source  86 , located above MTJ  32 . Boss or coupling means  109  is conveniently provided on the lower side of diaphragm  102 , that is, the side facing toward cantilevered beam  108 , to facilitate coupling motion  106  of diaphragm  102  to cantilevered beam  108 . A first end of cantilevered beam  108  is anchored in body  101  in region  101 - 1  and distal end  110  is free to move in a vertical direction in  FIG. 14  toward or away from MTJ  32 . As can be more readily seen in  FIG. 15 , cantilevered beam  108  is desirably U-shaped with distal end  110  forming the “bottom” of the “U” located above MTJ  32 , analogous to MFS  86  of  FIGS. 8–9 . Cantilevered beam  108  is adapted to carry current  114  analogous to current  96  of  FIG. 9  that produces magnetic field H in the vicinity of MTJ  32  analogous to field  35  of  FIG. 1 . Changes in the position of diaphragm  102  coupled to cantilevered beam  108  via boss or coupling means  109 , changes the magnetic field H at MTJ  32 , thereby changing its electrical properties as has been explained in connection with  FIGS. 1–7 . Thus, the arrangement of  FIGS. 14–15  can serve as a sensor for any of the physical parameters already mentioned with the further advantage that by varying driving current  114 , the ambient magnetic field H at MTJ  32  may be adjusted so that sensor  112  operates in a most favorable range depending upon whether binary output (e.g., see  FIG. 5 ) or analog output (e.g., see  FIG. 7 ) or a combination thereof (e.g., see  FIG. 6 ) is desired. This is a significant advantage. 
       FIG. 16  is a simplified schematic cross-sectional view of sensor  116  analogous to sensor  112  of  FIG. 14 , but according to a still further exemplary embodiment of the invention. Sensor  116  is particularly adapted to measure pressure and/or temperature. Sensor  116  differs from sensor  114  by inclusion of housing  118  with interior chamber  120  above diaphragm  102 . When it is desired that sensor  116  function primarily as a pressure sensor, optional I/O port  119  is provided in housing  118  and coupled to the chamber or line or region whose pressure is to be determined. An increase in pressure in chamber  120  causes diaphragm  102  and distal end  110  of cantilevered beam  108  to move toward MTJ  32 , thereby increasing the magnetic field H at MTJ  32 . When the pressure in chamber  120  drops, the reverse occurs and the magnetic field H at MTJ  32  decreases. The corresponding change in electrical properties in response to the changes in magnetic field H provides an electrical output reflecting the pressure changes. As has been previously explained, this output maybe binary, analog or a mixture of the two. 
     When it is desired that sensor  116  functions as a temperature sensor, optional I/O port  119  is omitted or sealed, thereby trapping a known quantity of gas within chamber  120 . As the temperature of the gas within chamber  120  goes up or down in response to changes in the temperature of housing  118 , the pressure of the gas within chamber  120  responds accordingly, diaphragm  102  moves toward or away from MTJ  32  and the electrical properties of MTJ  32  change in the same manner as already described for the case of a pressure sensor. By adjusting the initial gas pressure at the reference temperature and, optionally drive current  114 , the reference temperature output from MTJ  32  maybe set to a desired value. Likewise, the dynamic range of sensor  116  may be varied by selecting the spring constants of cantilever beam  108  and diaphragm  102 . By proper design of diaphragm  102  and/or cantilever beam  108 , the response of sensor  116  may be made linear or non-linear depending upon the desired application. Persons of skill in the art understand how to make cantilever springs or diaphragms with linear or non-linear responses. These are further advantages of the invention. While pressure and temperature sensor  116  of  FIG. 16  has been illustrated using a U-shaped, active magnetic field source, this is not intended to be limiting and a passive magnetic field source and single arm cantilevered beam may also be used. It may be desirable to provide temperature stabilization for MTJ  32  so that temperature variations in the properties of MTJ  32  itself are not significant compared to the changes induced by motion of MFS  104  or  110 . 
       FIG. 17  is a simplified flow diagram of method of manufacture  122  of the invented sensor. Method  122  begins with START  123  and initial FORM MTJ step  124  wherein a magnetic tunnel junction (MTJ), for example, analogous to MTJ  32  of FIGS.  1  and  8 – 18  is prepared, with or without conductor  34 A of  FIG. 1 . Persons of skill in the art will understand that the geometry and arrangement of MTJ  32  is merely exemplary and not intended to be limiting. Other MTJ configurations may also be used. In subsequent step  125 , a moveable magnetic field source (MFS), as for example MFS  34 ,  86 ,  87 ,  104 ,  110  illustrated in FIGS.  1  and  8 – 16 , is moveably coupled to MTJ  32 , such that the magnetic field at MTJ  32  is modified by motion of the corresponding MFSs. Any type of magnetic field source may be used. In the case of sensors of the configuration illustrated in  FIGS. 11–16 , diaphragm  102  containing MFS  104 ,  110  is attached above MTJ  32 . Method  122  is then generally complete at END  126 . 
       FIG. 18  is a simplified flow diagram of method  122 ′ analogous to method  122  of  FIG. 17  but showing further details. START  123 ′ and FORM MTJ step  124  are the same as in method  122 . In  FIG. 18 , step  125  is subdivided into ADD PLANARIZING SPACER OVER MTJ step  127 , followed by FORM MFS ON PLANARIZING SPACER step  128 , and then step  129  wherein a portion of the planarizing spacer provided in step  128  is removed to form cavity or opening  80  so that the MFS (e.g., MFS  34 ,  86 ,  87 ,  104 ,  110 ) can move relative to the MTJ (e.g., MTJ  32 ) in response to a changing physical parameter desired to be sensed or measured, whereby the movement varies the magnetic field at the MTJ (e.g., MTJ  32 ). Method  122 ′ is suited to the situation where sensor  30 ,  70  is being fabricated using integrated circuit technology, but is not limited thereto. Method  122 ′ then proceeds to END  126 ′. 
       FIG. 19  is a simplified schematic set of cross-sectional views (hereafter method  130 ) illustrating by means of steps  132 - 148  still further details of an embodiment of the method of  FIGS. 17–18 . Method  130  can be subdivided into steps  132 - 138  corresponding to step  124  of  FIGS. 17–18  and steps  140 - 148  (collectively  125 - 1 ) analogous to steps  125  of  FIGS. 17–18 . Method  130  is conveniently described for the case wherein MTJ sensor  32  is being fabricated as part of an integrated circuit, but persons of skill in the art will understand how to go about fabricating the sensor as a free-standing element. In initial step  132 , substrate  150  is provided, preferably a semiconductor substrate (e.g., Si, GaAs, etc.) suitable for preparation of an integrated circuit. In step  134 , transistors and/or other elements are formed using well known semiconductor integrated circuit processing techniques to provide in and/or on substrate  150 , measuring and/or driving circuitry  152  for the MTJ sensor and current lead  34 A if desired. Persons of skill in the art will understand how to do this. This is not essential for the invention. In step  136 , dielectric layer  154  of, for example silicon oxide and/or silicon nitride or other insulating material is grown or deposited and first conductor  76  of, for example aluminum, copper, tantalum, tantalum nitride, titanium, titanium nitride or the like is deposited or formed thereon and patterned to, optionally, make contact in region  157  with the appropriate elements of circuit  152 . First electrode  36  of, for example iridium manganese, platinum manganese, cobalt iron, cobalt iron boron, ruthenium, and the like, and combinations of thereof, is deposited on and in electrical contact with conductor  76  and patterned to form first electrode  36  of MTJ  32  (see  FIG. 8 ). The combination of materials chosen should have a relatively high coercive force. It is desirable but not essential that the various semiconductor, dielectric and conductor regions or layers provided up to now, as well as substrate  150 , be sufficiently refractory so as to withstand annealing temperatures (e.g., 200 to 350 degrees C.) that can be used to pin spin axes  40  in electrode  36  in a predetermined orientation. However, other means for pinning spin axes  40  may also be used. In step  138 , tunneling dielectric  37  of, for example aluminum oxide or magnesium oxide is grown or deposited on electrode  36  and conductive electrode  38  of, for example, nickel iron, cobalt iron, cobalt iron boron, ruthenium, and/or the like and potentially capped with a conductive material such as tantalum, tantalum nitride, titanium, titanium nitride, and the like is grown or deposited on tunneling dielectric  37 . The combination of materials used in electrode  38  should have a lower coercive force than the materials making up electrode  36 . Electrode  36 , dielectric  37  and electrode  38  form MTJ  32  illustrated in  FIGS. 1 and 8 . Conductors  76 ,  78  are conveniently provided to make contact to electrodes  36 ,  38  respectively. While conductors  76 ,  78  are shown as contacting the appropriate elements of circuit  152  at locations  157 ,  169  this is not essential and they may be coupled to the drive electronics in any convenient manner. 
     First planarization layer  166  of, for example silicon dioxide, silicon nitride, phosphorous doped silicon dioxide, and the like is deposited or grown or otherwise formed over the existing structure so that the upper surface of electrode  38  is exposed. Alternatively, first planarization layer  166  may be deposited and then selectively removed, for example by a chemical mechanical polishing (CMP) process or by a sequence of photolithography and etch, from all or part of the upper surface of electrode  38 . Conductor  78  of, for example aluminum, copper, tantalum, tantalum nitride, titanium, titanium nitride, and the like or even combinations of these types of materials is then deposited, grown or otherwise formed thereon to make electrical contact with electrode  38  and optionally with the appropriate elements of circuit  152  at location  169 . Sinker  163  extending from conductor  78  to location  169  may be formed at the same time and as a part of conductor  78  or may be formed separately, before or after formation of conductor  78 . Either arrangement is useful. However, sinker  163  (and sinker  153  of step  136 ) is not essential and conductor  78  (and conductor  76 ) may be routed elsewhere rather than to buried circuit  152 . In step  140 , second planarization layer  170  of, for example silicon dioxide, silicon nitride, phosphorous doped silicon dioxide, and the like, with upper surface  171  is deposited, grown or otherwise formed over first planarization layer  166  and conductor  78 . Thickness  173  of second planarization layer  170  will determine in part the ambient separation of cantilevered beam  84  and MTJ  32 . Thickness  173  is usefully in the range 0.1 to 1.0 microns, conveniently in the range 0.1 to 0.5 microns and preferably in the range 0.2 to 0.4 microns. If permanent magnet  87  is to be mounted on the lower face of cantilever beam  84  facing MTJ  32 , then its thickness needs to be taken into account. 
     The material desired for beam  84  is then grown or deposited or otherwise formed on surface  171  in the appropriate location so that MFS region  86 ,  110  (see  FIGS. 8–12 ) will be located over MTJ  32  and anchor region  82  (see  FIGS. 8–12 ) located on layer  170  spaced apart therefrom by the desired beam length. A wide variety of materials, either pure or alloys or composites or layered structures may be used for the material of beam  84 . Cu, Al, Au, Ti, W, poly-Si and various mixtures and alloys thereof are non-limiting examples of suitable materials but other materials can also be used. Such materials are conveniently but not essentially formed or deposited by sputtering, co-sputtering, evaporation, electroplating, electrode-less plating or chemical vapor deposition or combinations thereof may be used. Sputtering and co-sputtering, perhaps in combination with electroplating, are preferred, but other materials and processes may also be used. What is important is that beam  84  has a size and stiffness appropriate for the desired application. Persons of skill in the art will understand based on the description herein, how to design and fabricate cantilevered beams of the desired properties for their applications. Exemplary beam structures of the type illustrated in  FIG. 9  were fabricated using Cu with a beam thickness in the range of about 0.3 to 1.0 microns and U-shaped arm widths of about 100 microns and with MFS region  86  (see  FIGS. 8–10 ) of about 5 microns width. 
     In step  144 , additional masking layer  174  of, for example silicon dioxide or silicon nitride, is conveniently grown or deposited or otherwise formed over second planarization layer  170  and still supported beam  84 . Hole or opening  175  is provided therein using means well known in the art, as for example, using a sequence of photolithography and etch. What will be portion  82  of cantilevered beam  84  (see  FIGS. 8–12 ) is left covered by masking layer  174 . Hole or opening  175  otherwise extends slightly beyond the periphery of the remainder of beam  84  so that in method step  146 , portion  178  of planarization layer  170  underlying opening  175  can be removed, e.g., by for example, a wet etch process, thereby creating cavity or recess  80  in its place. It will be recognized by those skilled in the art that better control of this process is achieved if an etch stop layer (not shown) is provided both vertically along the inside walls of the cavity  80  as well as along the bottom of cavity  80  prior to its formation. Beam  84  is now free except for the portion (e.g., portion  82  of  FIG. 8 ) anchored to a portion (e.g. portion  92  of  FIG. 8 ) of planarization layer  170  (e.g., region  77  of  FIG. 8 ). In method step  148 , the remains of masking layer  174  are (desirably but not essentially) removed and, optionally, lead(s)  179  for supplying current  96  (see  FIGS. 8–9 ) are bonded or otherwise coupled to portions  82  of beam  84 . If the configuration of  FIG. 11  is used with passive MFS  87 , then lead(s)  179  are not needed. 
       FIG. 20  is a simplified schematic set of cross-sectional views  132 – 138 ,  140 ′– 148 ′ (collectively method  130 ′), analogous to steps  132 - 148  of method  130  of  FIG. 19  but according to a further exemplary embodiment of the method of the invention. Method  130 ′ can be subdivided into steps  132 - 138  corresponding to step  124  of  FIGS. 17–18  and steps  140 ′– 148 ′ (collectively  125 - 2 ) analogous to steps  125  of  FIGS. 17–18 . The same reference numerals are used in  FIGS. 19–20  to identify like regions or layers and where the regions or layers are not necessarily identical but are analogous, they are identified by using the same reference number with a prime (′) added. For example, step  140 ′ in  FIG. 20  is analogous to step  140  in  FIG. 19 , surface  171 ′ in  FIG. 20  is analogous to surface  171  in  FIG. 19 , and so forth. Because of the significant commonality between methods  130 ,  130 ′, the discussion of method  130  is incorporated herein by reference and only the significant differences explained here. Steps  132 - 138  of method  130 ′ are substantially the same as in method  130  and are not further described here. Steps  140 ′– 148 ′ differ in some respects. In step  140 ′, sacrificial region  172  of, for example phosphorous doped silicon dioxide is deposited and patterned so as to have substantially the same shape, location and thickness  173 ′ as desired for cavity  80  (see  FIG. 8 ) to be provided beneath cantilever beam  84 . It is important that region  172  and second planarizing layer  170 ′ be differentially etchable or dissolvable, that is, that region  172  be able to be dissolved away without significantly affecting second planarizing layer  170 ′ or any underlying layers or regions. Second planarizing layer  170 ′ of, for example silicon dioxide or silicon nitride is formed in step  142 ′ so as to have upper surface  171 ′ substantially level with upper surface  171 ″ of sacrificial region  172 . This may be achieved, for example, by a sequence of depositing second planarizing layer  170 ′ followed by a CMP step or other planarizing process. In step  144 ′, cantilever beam  84  is then formed in substantially the same manner and of substantially the same materials and shape and size as previously described in method  130 . In step  146 ′, sacrificial region  172  is etched away leaving behind cavity or recess  80  beneath cantilever beam  84  corresponding to cavity or recess  80  of  FIG. 8 . In step  148 ′, leads  179  are optionally attached to beam  84  as previously described in connection with step  148  of method  130 . The end result of method  130 ′ is analogous to that obtained by method  130 . Method  130 ′ is preferred. 
       FIG. 21  is a schematic set of cross-sectional views  132 – 138 ,  140 ′,  202 – 206  analogous to those of  FIGS. 19–20  but according to still further exemplary embodiment  200  of the method of the invention. Method  200  can be subdivided into steps  132 - 138  corresponding to step  124  of  FIGS. 17–18  and steps  140 ′,  202 – 206  (collectively  125 - 3 ) analogous to steps  125  of  FIGS. 17–18 . The same reference numerals are used in  FIGS. 19–21  to identify like regions or layers and where the regions or layers are not necessarily identical but are analogous, they same convention is followed as used in connection with method  130 ′ of identifying them by using the same reference number with a prime (′) added. Steps  132 - 138  of method  200  are substantially the same as in methods  130 ,  130 ′ and are not further described here. Steps  140 ′ and  202 – 206  differ in some respects. In step  140 ′, sacrificial region  172  is formed and patterned in the same manner as already described in method  130 ′, so as to have substantially the same shape, location and thickness  173 ′ as desired for cavity  80  (see  FIG. 8 ) to be provided beneath cantilever beam  84 ′. It is important that region  172  and first planarizing layer  166  be differentially etchable or dissolvable, that is, that region  172  be able to be dissolved away without significantly affecting first planarizing layer  166  or electrode  78 . In step  202 , cantilever beam  84 ′ is then formed in substantially the same manner and of substantially the same materials, as previously described in methods  130 ,  130 ′. In step  202 , beam  84 ′ is conveniently anchored on planarization layer  166 , but this is not essential and a structure employing a second planarization layer similar to what is employed in method  130 ′ could also be used. In step  204 , sacrificial region  172  is dissolved or etched away leaving behind cavity or recess  80 ′ beneath cantilever beam  84 ′. In step  206 , leads  179  are optionally attached to beam  84  as previously described in connection with step  148  of method  130 . The end result of method  200  is analogous to that obtained by method  130 ′. 
       FIG. 22  shows exploded plan view  300  of electrodes  36 ,  38  of MTJ  32  according to an embodiment of the invention where at least one of the electrodes is square. Electrodes  36 ,  38  are laterally displaced in  FIG. 23  so that their relative shape and size may be more easily seen. When assembled to form MTJ  32 , they lie one above the other, that is, electrode  38  above electrode  36 . Electrode  38  is closest to MFS  34 ,  86 . Electrodes  36 - 1 ,  38 - 1  are shown as being substantially square, that is having X and Y dimensions Y 36-1 =X 36-1 =Y 38-1 =X 38-1 . For convenience of explanation, this is the representation that has been used up to now for the most part, but that is not essential. Electrodes  36 - 2 ,  38 - 2  are different with electrode  36 - 2  being rectangular with Y 36-2 &gt;X 36-2  and Y 38-2 =X 38-2 . Again, this is intended merely to be illustrative of various possible shapes of the electrodes and not to be exhaustive or limiting. 
       FIG. 23  shows plan view  310  of electrodes  36 ,  38  of a MTJ according to embodiments of the invention where either or both electrodes have various exemplary, non-square, shapes. For example, in  310 - 1 , either or both of electrodes  36 ,  38  are rectangular and elongated with dimension X significantly greater then Y, in  310 - 2 , either or both of electrodes  36 ,  38  are elongated with X&gt;&gt;Y and with triangular ends, and in  310 - 3 , either or both of electrodes  36 ,  38  are elongated with X&gt;&gt;Y and with rounded ends. When electrodes are placed one above the other to form MTJ  32 , their longer dimensions may make various angles with respect to each other, as is illustrated schematically in  FIG. 24 . It is useful under certain circumstances to use electrode shapes that are significantly asymmetric since the plan view asymmetry in thin electrodes affects the ease or difficulty with which the electron spin axes may be rotated. For example, while it is known in the art to pin the electron spin axes in the first electrode by heat treatment in the presence of a magnetic field, another approach is to make the electrode shape highly asymmetric, e.g., long and narrow in plan view, since it is very difficult to rotate the electron spin axes away from the long direction of such an asymmetric shape. However, either arrangement for pinning the spin axes may be used. 
       FIG. 24  shows plan view  320  of the electrodes of a MTJ according to embodiments of the invention where at least one of the electrodes  36 ,  38  has various angular arrangements with respect to the other electrode. For convenience of illustration first electrode  36 - 4  is shown as a single continuous electrode, with various segmented second electrodes  38 - 4 - 1  . . .  38 - 4 - 4  crossing it at different angles. But this is not intended to be limiting and electrode  36 - 4  can be composed of separate segments, each underlying a single one of second electrodes  38 - 4 - 1 . . . .  38 - 4 - 4 . Second electrode  38 - 4 - 1  is oriented with its long dimension at angle (α3) to electrode  36 - 4 , e.g., substantially orthogonal to the long dimension of first electrode  36 - 4 . Second electrode  38 - 4 - 2  is oriented with its long dimension substantially parallel (or anti-parallel) with the long dimension of first electrode  36 - 4 . Second electrode  38 - 4 - 3  is oriented with its long dimension at angle (α1) and second electrode  38 - 4 - 4  is oriented with its long dimension at angle (α2) with respect to the long dimension of first electrode  36 - 4  where 0≦α≦90 degrees. Thus, a wide variety of different relative angular orientations may be used for the first and second electrodes  36 ,  38 . 
       FIG. 25  shows simplified plan view  330  of multiple cantilever beams  332 ,  334 ,  336  of different lengths  333 ,  335 ,  337  used to support magnetic field sources  86 A,  86 B,  86 C located in proximity to multiple MTJs  32 A,  32 B,  32 C. By using cantilevered beams of the same cross-section but different lengths (or different cross-sections and similar lengths or of other size and shape variations) the force or acceleration needed to deflect the different beams can be made different. Thus, each beam can be made to respond over a different range of force or acceleration or pressure or temperature or other physical parameter. By combining them in a single sensor, the overall dynamic range of the sensor can be expanded at will. In the example of  FIG. 25 , the only differences among sensors  332 ,  334 ,  336  are beam lengths  333 ,  335 ,  337 . Such multiple sensors may be manufactured by the same process on the same substrate substantially simultaneously, the different geometry of the individual sensors being provided by mask variations rather than process variations. This is a significant advantage of the present invention. 
       FIG. 26  is a simplified electrical schematic circuit diagram  340  wherein the multiple MTJs  32 A,  32 B,  32 C of  FIG. 25  are illustrated as being electrically coupled in parallel by leads  342 ,  344  leading respectively to terminals  343 ,  345 .  FIG. 27  is a simplified plot of R T  versus F for the parallel arrangement of MTJ&#39;s  32 A,  32 B,  32 C, where RT is the parallel combination of the resistances R t  of the individual MTJs  32 A,  32 B,  32 C and F is the acceleration or force being simultaneously applied to cantilevered beams  84 A,  84 B,  84 C of multiple sensors  332 ,  334 ,  336 . For convenience of explanation it is assumed that MTJs  32 A,  32 B,  32 C have substantially identical R t  vs H characteristics, but that cantilevered beams  84 A,  84 B,  84 C have different stiffness so that for sensor  336 , H=H c  occurs at F=1, for sensor  334 H=H c  occurs at F=2 and for sensor  332 H=H c  occurs at F=3 units. In other words, at F=1, beam  84 C is fully deflected (against its stop or with region  86 - 3  touching MTJ  32 C), at F=2, beam  84 B is fully deflected (against its stop or with region  86 - 2  against MTJ  32 B) and at F=3, beam  84 A is fully deflected (against its stop or with region  86 A touching MTJ  32 A) and that the limit position in each case produces H c  at the associated MTJ. Then for individual R t  vs H characteristics analogous to that shown in  FIG. 5 , this three beam arrangement gives the R T  vs F response shown schematically in  FIG. 27  for plots  352 ,  354 ,  356 . Trace  358  of plot  352  corresponds to the situation where a force (or acceleration) of F=1 has been applied to sensors  330  and the most easily deflected sensor (e.g., sensor  336 ) provides H c  to MTJ  32 C. Trace  360  of plot  354  corresponds to the situation where a force (or acceleration) of F=2 has been applied to sensors  330  and the next most easily deflected sensor (e.g., sensor  334 ) provides H c  to MTJ  32 B. Trace  362  of plot  356  corresponds to the situation where a force (or acceleration) of F=3 has been applied to sensors  330  and the least easily deflected sensor (e.g., sensor  332 ) provides H c  to MTJ  32 A. In this example, assuming that all of the MTJs are initially in their low resistance state, the total resistance R T  measured in circuit  340  increases in a step-wise fashion as the force or acceleration to which sensors  330  are exposed increases. A current lead (not shown here) analogous to conductor  34 A of  FIG. 1  is conveniently included with each sensor to provide −H c  to flip the spin axes in electrode  38  back to its initial state as F is removed. Thus, by using multiple sensors having different spring constants and deflection ranges, a wider overall dynamic range can be achieved, either quantized as illustrated in  FIG. 27  or analog by using MTJs whose response resembles that of  FIG. 6  or  7 . While the parallel coupled electrical arrangement illustrated in  FIG. 26  is useful, a series arrangement can also be used. Either arrangement works. Being able to easily build sensors having different responses on the same substrate using the same manufacturing process, with only mask differences to change the geometry of individual sensors, is a significant advantage of the present invention. While the use of multiple sensors to extend the dynamic range has been described in terms of cantilevered beam sensors, this is merely for purposes of illustration and not intended to be limiting. Persons of skill in the art will understand based on the description herein that diaphragm type sensors such as are illustrated in  FIGS. 11–16  and other physical arrangements combining multiple MTJs and multiple MFSs whose relative positions change in response to the sensor input can also be used. 
     A first exemplary method is provided for forming a sensor, comprising, forming a magnetic tunnel junction (MTJ), depositing a spacer over the MTJ, providing a magnetic field source (MFS) on the spacer, the MFS having a portion at least partly located above the MTJ, and removing a part of the spacer between the MFS and the MTJ so that the portion of the MFS located above the MTJ can move relative to the MTJ in response to the input to the sensor. A further exemplary method is provided wherein the first forming step comprises, depositing a first electrode configured so that the electron spin axes thereof can be pinned, providing a tunneling dielectric on the first electrode, and depositing on the tunneling dielectric a second electrode configured so that the electron spin axes thereof can be free. A still further exemplary method is provided wherein the step of depositing the first electrode comprises, depositing a material for the first electrode having a high coercive force relative to the second electrode, and the step of depositing the second electrode comprises, depositing a material for the second electrode having a low coercive force relative to the first electrode. A yet further exemplary method is provided further comprising prior to the step of providing the MFS, heat treating the first electrode in the presence of a magnetic field to pin the electron spin axes thereof in a predetermined orientation. In a still yet further exemplary embodiment, the step of providing the MFS comprises, depositing a beam on the spacer having a first end adapted to include the MFS located above the second electrode and deflectionally responsive to the input, and having a second end located on a distal portion of the spacer not above the second electrode. In a yet still further exemplary embodiment, the step of providing the MFS comprises, depositing a conductor, adapted to carry electrical current through a portion thereof located above the MTJ. 
     A second exemplary method comprises, providing a supporting substrate, depositing a first electrode on the substrate, wherein the first electrode comprises magnetic material of a first coercive force, forming a tunneling dielectric on the first electrode, depositing a second electrode in contact with the tunneling dielectric, wherein the second electrode comprises magnetic material of a second coercive force smaller than the first coercive force, suspending a cantilevered beam with a first end above the second electrode that is adapted to move relative to the second electrode and that incorporates a magnetic field source (MFS), and coupling a second distal end of the cantilevered beam to the substrate. In a further exemplary embodiment, the mounting step comprises, forming a MFS having a current carrying conductor. In a still further exemplary embodiment, the step of suspending the cantilevered beam comprises, depositing a sacrificial spacer on the substrate and above the second electrode, forming the beam at least partly lying on the sacrificial spacer, and removing a portion of the sacrificial spacer underlying the MFS. In a still yet further exemplary embodiment, the step of suspending the beam comprises, forming the beam in U-shape with a closed end of the U-shape incorporating the MFS, and the step of coupling the beam comprises, coupling the open, distal ends of the U-shape to the substrate. In a yet still further exemplary embodiment, the providing step comprises, providing a semiconductor substrate containing electronic devices coupled to the MTJ to provide, when active, electrical current to the MTJ and measure the voltage drop across the MTJ. 
     A third exemplary embodiment of the method of the invention comprises, fabricating a magnetic tunnel junction (MTJ) having a first ferromagnetic containing electrode and a second ferromagnetic containing electrode separated by a dielectric adapted to provide tunneling conduction therebetween, and mounting a magnetic field source (MFS) moveably suspended in proximity to the second ferromagnetic containing electrode so that variation of a distance between the MTJ and the MFS in response to an input to the sensor causes the magnetic field at the MTJ provided by the MFS source to vary, thereby altering the electrical properties of the MTJ. In a further embodiment of the method of the invention, the mounting step comprises, forming a MFS having a current carrying conductor. In a still further embodiment, the mounting step comprises, depositing a MFS comprising a U-shaped conductor adapted to carry a current to provide the magnetic field at the MTJ. In a yet further embodiment, the mounting step comprises, installing a permanent magnet as the magnetic field source. In an additional embodiment, the mounting step comprises, suspending the MFS on a cantilevered beam. In a yet additional embodiment, the fabricating step comprises, forming the MTJ on a support, and the mounting step comprises, coupling the MFS to a first end of a cantilevered beam spaced apart from the MTJ, and anchoring a second, distal end of the cantilevered beam to the support. In a yet still additional embodiment, the method comprises pinning electron spin axes of the first electrode in a predetermined orientation while leaving spin axes of the second electrode free. In a yet still additional embodiment, the method further comprising prior to the fabricating step, providing an electrical conductor in proximity to the MTJ and oriented to carry current in a direction substantially at right angles to a current flowing in a part of the U-shaped conductor above the MTJ. In a further additional embodiment, the fabricating step comprises, fabricating the MTJ with elongated first and second electrodes, and orienting a longer dimension of the second electrode substantially perpendicular to a longer dimension of the first electrode. In an additional further embodiment, the method further comprising, substantially simultaneously fabricating multiple tunnel junctions (MTJs) on a common substrate, substantially simultaneously mounting multiple magnetic field sources (MFSs) so that each MFS is moveably suspended in proximity to one of the MTJs, wherein such multiple MFSs receive the sensor input in common but have different moveable responses thereto, and electrically coupling at least some of the MTJs in series or in parallel or a combination thereof to provide a combined output. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.