Abstract:
A micro electrical-mechanical system (MEMS) is disclosed. The MEMS includes a substrate, a first pivot extending upwardly from the substrate, a first lever arm with a first longitudinal axis extending above the substrate and pivotably mounted to the first pivot for pivoting about a first pivot axis, a first capacitor layer formed on the substrate at a location beneath a first capacitor portion of the first lever arm, a second capacitor layer formed on the substrate at a location beneath a second capacitor portion of the first lever arm, wherein the first pivot supports the first lever arm at a location between the first capacitor portion and the second capacitor portion along the first longitudinal axis, and a first conductor member extending across the first longitudinal axis and spaced apart from the first pivot axis.

Description:
FIELD 
     The present invention generally relates to devices that are used to measure magnetic field intensity and direction and more particularly to inertial sensing elements modified to sense in-plane magnetic fields. 
     BACKGROUND 
     Inertial sensing and magnetic field sensing are useful in a variety of different applications. Furthermore, inclusion of inertial sensing elements using micro electrical mechanical systems (MEMS) are continually finding new applications, e.g., attachments for video games and navigation systems to determine change of direction of the attachment. MEMS offer inexpensive solutions for these applications in a small package. Therefore, many MEMS-based inertial sensing elements can be used to increase sensitivity for determining directional acceleration of a moving object. 
     In the prior art it has been shown that using a seismic mass which includes a movable electrode that is arranged opposite to a fixed electrode can form a capacitor. Movement of the moveable electrode due to inertial forces resulting from an acceleration vector can result in changes in the capacitance. The change in the capacitance can be measured and correlated to the acceleration. 
     Similarly, various sensors are known that can correlate a perpendicular magnetic field to a change in electrical characteristics that can be measured to determine the magnitude of the magnetic field. However, the solutions provided in the prior art either lack the necessary sensitivity for effectively measuring magnetic fields that are parallel to the surface of a sensor or for measuring an acceleration vector that is perpendicular to the surface of the sensor. 
     A need exists to provide a MEMS-based sensor for effectively sensing magnetic fields that are tangential to the sensor and for sensing an acceleration vector that is perpendicular to the sensor. 
     SUMMARY 
     In accordance with one embodiment, a micro-electrical-mechanical system (MEMS) is disclosed. The MEMS includes a substrate, a first pivot extending upwardly from the substrate, a first lever arm with a first longitudinal axis extending above the substrate and pivotably mounted to the first pivot for pivoting about a first pivot axis, a first capacitor layer formed on the substrate at a location beneath a first capacitor portion of the first lever arm, a second capacitor layer formed on the substrate at a location beneath a second capacitor portion of the first lever arm, wherein the first pivot supports the first lever arm at a location between the first capacitor portion and the second capacitor portion along the first longitudinal axis, and a first conductor member extending across the first longitudinal axis and spaced apart from the first pivot axis. 
     In another embodiment, a method of forming a micro electrical-mechanical system (MEMS) is disclosed. The method includes providing a substrate, forming a first pivot extending upwardly from the substrate, forming a first lever arm with a first longitudinal axis extending above the substrate to be pivotably mounted to the first pivot for pivoting about a first pivot axis, forming a first capacitor layer on the substrate at a location selected to be beneath a first capacitor portion of the first lever arm, forming a second capacitor layer on the substrate at a location selected to be beneath a second capacitor portion of the first lever arm, and selected such that the first pivot will support the first lever arm at a location between the first capacitor portion and the second capacitor portion along the first longitudinal axis, and forming a first conductor member to extend across the first longitudinal axis at a location and to be spaced apart from the first pivot axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. 
         FIG. 1  depicts a block diagram of a micro electrical mechanical system (MEMS) including a micro electromechanical sensor; 
         FIG. 2  depicts a perspective view of a MEMS sensor in accordance with one embodiment; 
         FIG. 3  depicts a side view of the MEMS sensor depicted in  FIG. 2 ; 
         FIG. 4  depicts a perspective view of a MEMS sensor in accordance with one embodiment; 
         FIGS. 5-14  depict fabrication steps for fabricating a MEMS sensor in accordance with one embodiment; 
         FIG. 15  depicts a schematic for measuring a ΔV associated with one MEMS sensor; and 
         FIGS. 16 and 17  depict arrays of MEMS sensors placed on a common substrate for measuring magnetic fields and acceleration vectors of various directions. 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
     Referring to  FIG. 1 , there is depicted a representation of a circuit generally designated  10  for an in-plane magnetic field and/or out of plane acceleration sensing sensor (MEMS sensor). The circuit  10  includes an I/O device  12 , a processing circuit  14  and a memory  16 . The I/O device  12  may include a user interface, graphical user interface, keyboards, pointing devices, remote and/or local communication links, displays, and other devices that allow externally generated information to be provided to the circuit  10 , and that allow internal information of the circuit  10  to be communicated externally. 
     The processing circuit  14  may suitably be a general purpose computer processing circuit such as a microprocessor and its associated circuitry. The processing circuit  14  is operable to carry out the operations attributed to it herein. 
     Within a memory  16  are various program instructions  18 . The program instructions  18  are executable by the processing circuit  14  and/or any other components as appropriate. 
     The circuit  10  further includes a sensor stimulus/response circuit  20  connected to the processing circuit  14 . The sensor stimulus/response circuit  20  provides a stimulus for a MEMS sensor  100  and measures the effects of the stimulus. The stimulus may be controlled by the processing circuit  14  and the measured value is communicated to the processing circuit  14 . 
     Referring to  FIG. 2 , a perspective view of the MEMS sensor  100  is depicted. A substrate  102  is provided. Examples of a suitable substrate material for the substrate  102  are silicon, glass, carbon, germanium, silicon carbide, and silicon germanium. The substrate  102  is electrically isolated by an isolation layer  104 . Examples of suitable isolation material for the isolation layer  104  are silicon dioxide, and silicon nitride for use with a silicon substrate. A semiconductor layer  106  is provided in a suspended manner over the isolation layer  104  by way of a pivot member  108 . An example of the material of the semiconductor layer  106  is undoped polysilicon. The pivot member  108  provides a pivoting function between the substrate/isolation layer  102 / 104  and the semiconductor layer  106  such that the semiconductor layer  106  can pivot about the pivot member  108 . The pivot member  108  is below the dotted line designated as AA, dividing the semiconductor layer  106  into two lever arms  110  and  112 . The length of each lever arm  110  and  112  runs along a longitudinal axis, e.g., the X-axis. In one embodiment each of the two lever arms  110  and  112  have the same length. However, in the embodiment shown in  FIG. 2 , the lever arm  110  has a shorter length than lever arm  112 . Two structural windows  114  and  116  are provided in each lever arm  110  and  112 , respectively, to further facilitate torsional bending of the lever arms  110  and  112 . The portions between the window  114  and the edges of the semiconductor layer  106  define a spring arm  111 . Similarly, the portions between the window  116  and the edges of the semiconductor layer  106  define a spring arm  113 . A combination of the spring arms  111  and  113  and a pivoting action of the lever arms  110  and  112 , described below, provide the torsional bending of the lever arms when the lever arms  110  and  112  are subjected to a force. The dimensions (lengths, widths, and thicknesses) of the spring arms  111  and  113  are one factor that determines the amount of torsional bending of the lever arms  110  and  112  that can occur for a given force. Specifically, longer/thinner spring arms  111  and  113  bend more, while shorter/thicker spring arms  111  and  113  bend less for the same applied force. Therefore, flexibility is provided by design of the spring arms  111 / 113  that can be used to achieve the desired sensitivity. Another factor is the lengths of the lever arms  110 / 112 . The longer the lever arms  110 / 112 , the more torsional bending when the edges of the lever arm are subject to a given force. 
     The pivot member  108  has a vertical support section  118 . The pivot member  108  is integrally formed with the bottom side of the semiconductor layer  106  and provides the pivoting function in conjunction with the spring arms  111  and  113 . The pivot member  108  can also include a top horizontal support section, not shown, under the semiconductor layer  106  to form a “T” shaped pivot member. The length of the top horizontal support section can range from covering a small portion of the bottom side of the semiconductor layer  106  to almost the entire width of the semiconductor layer  106 . The length of the top horizontal support section can affect whether the semiconductor layer  106  is allowed to twist about the pivot member  108  or only pivot about the pivot member  108 . In one embodiment, extra material can also be integrally provided to form a bottom horizontal support section, not shown, with the substrate/isolation layer  102 / 104  to form an “I” shaped pivot member. The height of the vertical support section  118  determines capacitances of a pair of capacitors. An example of the material of the pivot member  108  is undoped polysilicon. 
     Two sensing electrodes  122  and  128  are provided over the isolation layer  104  and below the semiconductor layer  106 . The sensing electrodes  122  and  128  extend in the “Y” direction substantially the entire width of the semiconductor layer  106 . The sensing electrodes  122  and  128  provide electrical connectivity, not shown, to the stimulus/response circuit  20  by, e.g., bond pads and bond wires in a manner known in the art. Two biasing electrodes  124  and  126  provide electrical connectivity to a conductor member  130 . In the embodiment depicted in  FIG. 2 , the biasing electrodes  124  and  126  are placed on opposite sides of the isolation layer  104 . However, in another embodiment both biasing electrodes  124  and  126  can be placed on the same side. In the embodiment shown in  FIG. 2 , the conductor member  130  is provided on the top surface of the semiconductor layer  106 . In other embodiments, the conductor member  130  can be embedded in the semiconductor layer  106  or be provided at the bottom surface of the semiconductor member  106 . In any of these embodiments, ends  132  and  134  of the conductor member  130  are electrically coupled to the biasing electrodes  124  and  126 , respectively. 
     The conductor  130  includes a lateral portion  142  and axial portions  144 . Lateral portion  142  of the conductor member  130  crosses the longitudinal axis, e.g., the “X” axis, at a distance  136  away from the pivot member  108 , associated with only one of the two spring arms  111  and  113  (spring arm  113 , as shown in  FIG. 2 ). The distance  136  determines the amount of pivot the spring arm would be subjected to as a result of a Lorentz force generated which has a vector that is parallel with the “Z” axis, discussed in greater detail below. 
     The sensing electrodes  122  and  128  provide capacitor layers beneath capacitor portions  204  and  202  (shown in  FIG. 3 ) of the lever arms  112  and  110  respectively. The combination of the sensing electrode  122  and the capacitor portions  204  forms a capacitor  140 , shown in phantom. Similarly, the combination of sensing electrode  128  and the capacitor portions  202  forms a capacitor  138 . The capacitance of each capacitor is defined by: 
                   C   =     ɛ   ⁢     A   d               (   1   )               
where ε is permittivity of a dielectric,
     A is the effective area defined by the areas of the sense electrode  122 / 128  and the capacitor portions  204  and  202 , i.e., where charges collect,   and d is the distance between the sense electrodes  122 / 128  and the capacitor portions  202 / 204 . In one embodiment, the dielectric is air. Since the capacitance is inversely proportional to the distance between the sense electrodes  122 / 128  and the capacitor portions  202 / 204 , bending of a capacitor portion toward the sense electrodes  122 / 128  increases the capacitance. Conversely, bending of a capacitor portion away from the sense electrodes  122 / 128  decreases the capacitance.   

     The pivoting action of the semiconductor layer  106  about the pivot member  108  is such that if a force is acting on one of the lever arms  110 / 112 , causing that lever arm to deflect downward toward the respective sense electrode, then the other lever arm moves in an opposite direction, i.e., away from its respective sense electrode. Such a relationship in deflections of the lever arms  110 / 112  is similar to a teeter-tooter mechanism. For example, if a downward force is acting on the lever arm  112  causing the lever arm  112  to deflect downward toward the sense electrode  122 , the lever arm  110  deflects upward away from the sense electrode  128 , or vice versa. An imbalanced force is needed, e.g., a summation of force applied on one of the lever arms to cause the teeter-tooter mechanism. Thus, for inertial/acceleration sensing where both the lever arms experience the same force density, geometrical design parameters, e.g., length of lever arms  110 / 112 , can be used to generate the imbalanced force needed to cause the teeter-tooter mechanism. For example, one lever arm, e.g.,  112 , is longer than the other lever arm, e.g.,  110 . By implementing different lengths for the two lever arms  110 / 112 , different motions can be generated. 
     Variations in deflections between the two lever arms  110  and  112  can be translated into variation in capacitances of the capacitors  138  and  140 . These variations can then be sensed using electrical circuitry as will be discussed in greater detail, below. 
     Referring to  FIG. 3 , a side view of the MEMS sensor  100  is provided. The capacitor portions  202  and  204  are depicted as part of lever arms  110  and  112 . As discussed above, the sensing electrodes  122  and  128  provide capacitor layers  208  and  206  beneath the capacitor portions  202  and  204  of the lever arms  110  and  112 , respectively. The combination of the capacitor layer  206  and capacitor portion  202  forms the capacitor  138 . Similarly, the capacitor layer  208  and the capacitor portion  204  forms the capacitor  140 . 
     As depicted in  FIG. 3 , the ends  132  and  134  of the conductor member  130  are electrically connected to the biasing electrodes  124  and  126  by way of vias  210  and  212 . The biasing electrodes  124  and  126  include horizontal sections and vertical sections. The vertical sections are connected to the vias  210  and  212 . In the embodiment where the conductor member  130  is on the bottom side of the semiconductor layer  106 , the vias  210  and  212  can be avoided. 
     In operation, electric current is applied to the conductor member  130  by way of the biasing electrodes  124  and  126  through the vias  210  and  212 . When the MEMS sensor  100  is placed in a magnetic field with magnetic field vectors tangential to the surface of the semiconductor layer  106 , a vertical force due to the Lorentz force law is generated. The Lorentz force law states that when a charge carrying particle is in the presence of a magnetic field, the Lorentz force applied to the particle is expressed as
 
 F=q[E +( v×B )]  (2)
 
where F is the Lorentz force in Newtons,
     q is the charge of the charge carrying particle in coulombs,   v is the instantaneous velocity in m/s,   E is the electric field in v/m, and   B is the magnetic field in Tesla. The “x” is the vector cross-product between v and B. In a current-carrying conductor wire, the applying Lorentz force is expressed as:
 
 F=L ( i×B )  (2a)
 
where F is the Lorentz force in Newtons,
   L is the length of the current-carrying wire subject to the magnetic field in meters,   i is the electric current through the wire subject to the magnetic field in Amperes,   B is the magnetic field in Tesla. If the current that is passing through a conductor that is subjected to a magnetic field has a frequency near the resonance frequency of the free-standing structure, including lever arms  110  and  112 , the amount of force applied to that structure would be amplified. Conversely, frequencies away from the resonance frequency would result in minimal forces. Therefore, in order to take advantage of the Lorentz force law and selectively test for a magnetic field affecting a conductor, an AC signal with a frequency near the resonance frequency of the structure can be used.   

     The direction of the Lorentz force is based on the right hand rule, known in the art. Depending on the direction of the magnetic field, the Lorentz force can apply to different portions of the conductor member  130 . For example, if the magnetic field is parallel to the X-axis, the Lorentz force only applies to portions of the conductor member that are parallel with the Y-axis, e.g., the lateral portion  142  of the conductor member  130 . However, if the magnetic field strikes the semiconductor layer  106  at a different angle, the Lorentz force may apply to different portions of the conductor member  130 . Application of the Lorentz force to the lateral portion  142  of the conductor member causes the lever arm  112  to deflect downward toward the sense electrode  122 . The downward deflection of the spring arm  113  also causes upward deflection of the lever arm  110  away from the sense electrode  128 . 
     Application of current to the conductor element allows free charges to collect at both ends of the semiconductor layer  106 . Free charges collect at both ends due to the semiconductor nature of the semiconductor layer  106 . These charges lead to formation of the capacitor portions  202  and  204 . The capacitor portions  202  and  204  in cooperation with capacitor layers  206  and  208  form capacitors  138  and  140 . Deflection of the lever arm  112  toward the capacitor layer  208 , i.e., sensor electrode  122 , increases the capacitance of the capacitor  140 . Deflection of the lever arm  110  away from the capacitor layer  206 , i.e., the sense electrode  128 , decreases the capacitance of the capacitor  138 . A detection circuit, discussed in greater detail below, can be used to detect the changes in the capacitances. 
     While Lorentz forces can cause deflection of the lever arms  110  and  112  in opposite directions, perpendicular acceleration vectors, i.e., acceleration vectors in the “Z” direction, can generate forces to cause deflection of both lever arms  110  and  112  in the same direction. The inertial force that is generated is governed by Newton&#39;s second law of motion, i.e.
 
F=Ma  (3)
 
where M is the seismic mass of the lever arms;
     a is the acceleration vector; and   F is the force vector acting on the lever arms. The direction of the force is the same as the acceleration vector. Therefore, with existence of the teeter-tooter action, when the MEMS sensor  100  is subjected to a perpendicular acceleration vector that is downward, the lever arm  112  deflects downward and lever arm  110  deflects upward. Conversely, when the MEMS sensor  100  is subjected to a perpendicular acceleration vector that is upward, the lever arm  112  deflects upward, and the lever arm  110  deflects downward. The teeter-totter action of the lever arms  110 / 112 , just described, is substantially not present when lever arms  110  and  112  and spring arms  111  and  113  are constructed in the same fashion. For example, if the lever arms  110  and  112  have the same length and the spring arms  111  and  113  have the same thickness, then both lever arms deflect downward or upward depending on the direction of the acceleration vector. A difference in the above mentioned construction variables, can result in the teeter-totter action, described above.   

     Applying an electric current to the conductor member  130  facilitates in measuring capacitances generated by the capacitor portions  202  and  204  on the lever arms  110  and  112  forming capacitors  138  and  140 . Deflection of the capacitor portion  202  and  204  toward the capacitor layers  206  and  208  increases capacitance of the capacitors  138  and  140 . In the embodiment where one lever arm, e.g. the lever arm  112 , is longer the capacitance of the respective capacitor, e.g., the capacitor  140 , increases while the other capacitor, e.g., the capacitor  138 , decreases. The difference in the change in capacitances can be used to determine the magnitude of the acceleration. 
     Passing an alternating current (AC) type signal through the conductor member  130 , causes capacitive coupling of the AC signal through the capacitors  138  and  140 . The interaction of the AC signal with a magnetic field that is parallel to the semiconductor layer  106 , in particular the X-axis depicted in  FIG. 2 , can cause a deflection of the lever arm  112  according to the Lorentz law. If the frequency of the AC signal is near the resonance frequency the free-standing structure of the MEMS sensor  100 , the deflection of the lever arms  110  and  112  can be maximized. By measuring the voltage at sense electrodes  128  and  122  and passing these voltages through a differential amplifier a ΔV quantity can be produced that relates to a magnetic field ΔB acting on the conductor member  130  and an acceleration vector Δa acting on both lever arms  110  and  112 . The ΔV quantity is expressed as:
 
Δ V=S   A   Δa+S   M   ΔB   (4)
 
where ΔV is the change in the output voltage measured in volts (V);
     Δa is the change in acceleration measured in m/s 2 ;   ΔB is the change in the magnetic field acting on the conductor member  130  and measure in Tesla (T);   S A  is the sensitivity to acceleration measured in V/(m/s 2 );   and S M  is the sensitivity to magnetic field measured in (V/T).   

     According to one embodiment, a pair of identical MEMS sensors  100   1  and  100   2  can be placed in the same inertial/magnetic environment with the ΔV 1  and ΔV 2  for the two sensors measured simultaneously. A first AC signal with a frequency near the resonance frequency of the free-standing structures of the MEMS sensors  100   1  and  100   2  spring arms  111  and  113  is applied to the biasing electrodes  124  and  126  of the first MEMS sensor  100   1  and a second electric current is applied to the biasing electrodes  124  and  126  of the second MEMS sensor  100   2 . The first and second electric currents are opposite in direction, i.e., 180° phase shifted signals. ΔV values for each MEMS sensor  100   1  and  100   2  are measured. The ΔV measurement represents the differential voltage readout for the sense electrodes  128  and  122  with respect to the AC ground. Therefore, ΔV 1  is the ΔV for the first MEMS sensor  100   1  and ΔV 2  is the ΔV for the second MEMS sensor  100   2 . In this embodiment, ΔB and Δa are provided by the following proportionalities:
 
ΔBα(ΔV 1 −ΔV 2 )/2  (5a)
 
Δaα(ΔV 1 +ΔV 2 )/2  (5b)
 
     When the electric currents in MEMS sensors  100   1  and  100   2  are in opposite directions, the output voltage signals contributed by the magnetic field (S M ΔB) have opposite signs. On the other hand, the output voltage signals contributed by the acceleration vector (S A Δa) are identical with no alternation. Therefore, ΔB can be calculated by the proportionality  5   a  by taking differential terms from the measured signals. Conversely, Δa can be calculated by the proportionality  5   b  taking common terms from the measured signals. By using this measurement scheme, the magnetic field and acceleration vector applied to the MEMS sensor pair can be uncoupled and retrieved simultaneously. 
     In another embodiment, two identical MEMS sensors  100   1  and  100   2  can be placed in the same inertial/magnetic environment with the ΔV 1  and ΔV 2  for the two sensors measured simultaneously. A first AC signal with a frequency away from the resonance frequency of lever arms  110  and  112  is applied to the first MEMS sensor  100   1  and a second AC signal with a frequency near or at the resonance frequency of the free-standing structure of the second MEMS sensor  100   2 . The frequency of the first AC signal does not result in any appreciable deflection of the lever arms  110  and  112  by way of the Lorentz force. ΔV 1  and ΔV 2  are measured for both MEMS sensors  100   1  and  100   2 . ΔV 1  is the ΔV for the first MEMS sensor  100   1  and ΔV 2  is the ΔV for the second MEMS sensor  100   2 . In this embodiment, ΔB and Δa are provided by the following proportionalities:
 
ΔBα(ΔV 2 −ΔV 1 )  (6a)
 
ΔaαΔV 1   (6b)
 
     When the pair of MEMS sensors  100   1  and  100   2  is exposed to a magnetic field, the lever arms  110  and  112  of the pair of MEMS sensors  100   1  and  100   2  behave differently. While the first AC signal applied to the first MEMS sensor  100   1  causes no deflection for the free-standing structure exposed to a magnetic field, exposure to a perpendicular acceleration vector causes the free-standing structure to deflect. Therefore, an exposure to an acceleration vector Δa can be calculated by the proportionality  6   b . Conversely, the output voltage signal of the second MEMS sensor  100   2  is subject to both magnetic field and acceleration vector because of the frequency selection of the AC current input. Therefore, using the output voltage signal from the MEMS sensor  100   1  as reference, ΔB can be calculated by the proportionality  6   a.    
     In accordance with another embodiment, one MEMS sensor  100  can be placed in an inertial/magnetic environment with the ΔV 1  and ΔV 2  for the sensor measured at different instances, i.e., at times t=t 1  and t=t 2 . At the first instance, a first AC signal with a frequency away from the resonance frequency of the lever arms  110  and  112  is applied to the MEMS sensor  100 . At the second instance a second AC signal with a frequency near or at the resonance frequency of the free-standing structure of the MEMS  100  is applied to the MEMS sensor  100 . The frequency of the first AC signal does not result in any appreciable deflection of the lever arms by way of the Lorentz force. ΔV 1  and ΔV 2  are measured for both instances. Therefore, ΔV 1  is the ΔV for the MEMS sensor  100  at the first instance and ΔV 2  is the ΔV for the MEMS sensor  100  at the second instance. In this embodiment, ΔB and Δa are provided by the following proportionalities:
 
ΔBα(ΔV 2 −ΔV 1 )  (7a)
 
ΔaαΔV 1   (7b)
 
     When the MEMS sensor  100  is exposed to a magnetic field, the lever arms  110  and  112  of the MEMS sensors  100  behave differently at the two instances described above. While the first AC signal applied at the first instance causes no deflection for the free-standing structure exposed to a magnetic field, exposure of the lever arms  110  and  112  to a perpendicular acceleration vector causes the free-standing structure to deflect, e.g., downward. Therefore, Δa can be calculated by the proportionality  7   b . Conversely, the output voltage signal of the MEMS sensor  100  is subject to both magnetic field and acceleration vector because of the frequency selection of the AC current input. Depending on whether the MEMS sensor  100  is exposed to an acceleration vector, the lever arm  110  could deflect upward. Therefore, using the output voltage signal from the MEMS sensor  100  as a reference, ΔB can be calculated by the proportionality  7   a.    
     In accordance with another embodiment, one MEMS sensor  100  can be placed in an inertial/magnetic environment with the ΔV 1  and ΔV 2  for the sensor measured at different instances, i.e., at times t=t 1  and t=t 2 . At the first instance, a first AC signal with a frequency near or at the resonance frequency of the free-standing structure of the MEMS sensor  100  is applied to the MEMS sensor  100 . At the second instance a second AC signal with a frequency near or at the resonance frequency of the free-standing structure of the MEMS sensor  100  is applied to the MEMS sensor  100 . The first and second electric currents are opposite in direction, i.e., 180° phase shifted signals. ΔV for the MEMS sensor  100  is measured for each instance. ΔV 1  is the ΔV for the MEMS sensor  100  at the first instance and ΔV 2  is the ΔV for the MEMS sensor  100  at the second instance. In this embodiment, ΔB and Δa are provided by the following proportionalities:
 
ΔBα(ΔV 2 −ΔV 1 )/2  (8a)
 
Δaα(ΔV 2 +ΔV 1 )/2  (8b)
 
     When the electric currents in MEMS sensor  100  are in opposite directions at different instances t 1  and t 2 , the output voltage signals contributed by the magnetic field (S M ΔB) have opposite signs. On the other hand, the output voltage signals contributed by the acceleration vector (S A Δa) are identical with no alternation. Therefore, ΔB can be calculated by the proportionality  8   a  by taking differential terms from the measured signals. Conversely, Δa can be calculated by the proportionality  8   b  taking common terms from the measured signals. By using this measurement scheme, the magnetic field and acceleration vector applied to the MEMS sensor pair can be uncoupled and retrieved simultaneously. 
     Referring to  FIG. 4 , a perspective view for an embodiment for a MEMS sensor  250  is depicted. In this embodiment, the conductor member  130  has ends  132  and  134  that extend outward over tabs  262  and  264 . The bond pads  256  and  258  provide electrical connectivity between the stimulus/response circuit  20  and the conductor member  130 , by way of bondwires  252  and  254  to pads (not shown) located on ends  132  and  134 . In this embodiment, the biasing electrodes  124  and  126  and vias  210  and  212  can be eliminated. 
     Referring to  FIGS. 5-14 , steps involved in one embodiment for fabricating a MEMS sensor  100  are depicted. The steps depicted in these figures can be performed by integrated circuit fabrication processes that are known in the art.  FIG. 5  depicts the substrate  102  and the isolation layer  104 . The substrate  102  can be the starting point for a wafer which will include many MEMS sensors  100 . Individual MEMS sensors  100  can later be diced and singulated from the wafer. As discussed above, examples of a suitable substrate material for the substrate  102  are silicon, glass, carbon, germanium, silicon carbide, and silicon germanium. 
     The isolation layer  104  is deposited onto the substrate  102  in order to electrically isolate the substrate  102  from other structures. Examples of suitable isolation material for the isolation layer  104  are silicon oxides, and silicon nitrides for the silicon substrate. Examples of methods of deposition are thermal growth (for silicon oxides), chemical vapor deposition, and physical vapor deposition. The isolation layer  104  is formed over the entire span of substrate  102  and may be on backside as well during the formation process. 
     Referring to  FIG. 6 , a deposition process is depicted for forming sense electrodes  122  and  128 . A layer of a material  302  for forming the sense electrodes  122  and  128  is deposited on top of the isolation layer  104 . Examples of methods of deposition are chemical vapor deposition and physical vapor deposition. This layer can alternatively be grown by an epitaxial growing process. Examples of material of the layer  302  are doped polysilicon, gold, silver, copper, titanium, platinum, tungsten, aluminum, iridium, ruthenium, and titanium nitride. The layer  302  is formed over the entire span of the isolation layer  104 . Two strips of mask layers  304  are placed over the layer  302  for forming the sense electrodes  122  and  128 . These layers can be produced by a photolithographic process known in the art. Once the mask layer  304  is formed, the layer  302  is etched away leaving the strips of layer  302  with the mask layer  304  on top. The mask layer  304  prevents etchants to etch away the strips under the mask layer  304 . The mask layer  304  is then removed by a planarization process or a chemical removal process to leave two strips of the layer  302  which constitute sense electrodes  122  and  128 . 
     Referring to  FIG. 7 , a sacrificial layer  306  is deposited/grown and patterned over the sense electrodes  122 / 128  as the foundation for forming the remainder of the MEMS sensor  100 . A volume  307  of the sacrificial layer  306  corresponding to the position of the pivot member  108  is removed by a masking and chemical removal process. Referring to  FIG. 8 , a top view of the isolation layer  104 , the sense electrodes  122 / 128 , and the volume  307  is provided. Also depicted in  FIG. 8  is the sacrificial layer  306 . Referring to  FIG. 9 , formation of the pivot member  108  and the semiconductor layer  106  is depicted. A layer  310  is deposited/grown over the layer  306  and through the volume  307 . Example of material of the layer  310  is polysilicon. It will be appreciated that the layer  310  constitutes the semiconductor layer  106  after the following processes. In addition, the pivot member  108  is now integrally formed with the isolation layer  104 . The sacrificial layer  306  may be sufficiently thick to (1) induce a sufficiently large signal for mechanical-electrical transduction, (2) provide well-suited step coverage over the sacrificial layer  306 , and (3) provide ease of release after stripping the sacrificial layer  306  to avoid issues such as stiction on ground, known in the art. 
     Referring to  FIG. 10 , a conductor layer  312  is deposited and patterned on the semiconductor layer  106  to form the conductor member  130  with the desired shapes as depicted in  FIGS. 2 and 4 . Examples of methods of deposition are chemical vapor deposition and physical vapor deposition. Examples of material of the layer  312  are gold, silver, copper, titanium, platinum, tungsten, aluminum, iridium, ruthenium, and titanium nitride and the likes. For pattern transfer, a photolithographic process known in the art is used to realize an etch mask to facilitate structuring of the conductor layer  312  with standard wet etching or lift-off process. 
     Referring to  FIG. 11 , the semiconductor layer  106  is structured to form the lever arms  110 / 112  and the spring arms  111 / 113 . Structuring of the semiconductor layer  106  incorporates standard wet or dry etching process with use of etch mask produced by a photolithographic process known in the art. During wet or dry etching, part of the layer  310  not covered by the etch mask are etched away. The etch mask also covers the conductor member  130  which is placed on top of lever/spring arm  111 / 113 , thus protects the conductor member  130  through the etching process of the semiconductor layer  310 . Referring to  FIGS. 12 and 13 , top views of the semiconductor layer  106 , pivot member  108 , the sense electrodes  122 / 128 , and the conductor member  130 , with pattern according to  FIGS. 2 and 4 , are depicted. The alternative design depicted in  FIG. 13  which corresponds to  FIG. 4  can be realized by transferring different patterns of the etch masks that are used for structuring the semiconductor layer  310 . Referring to  FIG. 13 , tabs  262  and  264 , seen in the embodiment depicted in  FIG. 4 , can be formed simultaneously with the lever arms  110 / 112  and the spring arms  111 / 113  when structuring the semiconductor layer  310  using standard wet or dry etching process. 
     Referring to  FIG. 14 , the complete MEMS sensor  100  is depicted after removing all the etch masks by a planarization process or a chemical removal process. Furthermore, the sacrificial layer  306  is removed by a chemical etching process. In order to efficiently remove the sacrificial layer  306 , the layer  310  may be perforated to allow the removal chemicals to reach the layer  306  in the vertical direction. Also, the open sides further assist the removal chemicals to reach the sacrificial layer  306  for effective removal of this layer. Undercuts (not shown) may occur under, e.g., the sense electrodes  122 / 128 , in the final or the initial removal process of the sacrificial layer  306 . However, providing the proper width and thickness ratios, the undercuts do not result in adverse performance issues of the MEMS sensor  100 . 
     Referring to  FIG. 15 , an example of a simplified circuit diagram  400  is provided that can be used for measuring the ΔV and hence the change in capacitance associated with a MEMS sensor  100  which is subjected to an electrical signal. An AC component of a source  402  which is part of a carrier wave is coupled to the capacitors  404  and  406  through loads  408  and  410 , respectively. Each capacitor is coupled to the AC ground. The high sides of each capacitor  404  and  406  are connected to AC amplifiers  412  and  414 . The output of each AC amplifier is coupled to a differential amplifier  416 . The source  402  is passed through a high pass filter  418  to remove its DC component. The remaining AC component is fed to a carrier detection circuit  420  to construct the carrier signal of the AC component of the source  402 . The carrier signal is used to demodulate the output of the differential amplifier  416  by the demodulation block  422 . The output of the demodulation block is then fed to a low pass filter  424  to generate the output ΔV. 
     Referring to  FIGS. 16 and 17 , top views of matrices  500  and  550  of various MEMS sensors are depicted. The matrix  500  includes a pair of MEMS sensors  502  and  504  for measuring a magnetic field component tangential to a first longitudinal axis (X-axis), a pair of MEMS sensors  506  and  508  for measuring a magnetic field component tangential to a second longitudinal axis (Y-axis), and a sensor  510 , known in the art, for measuring a magnetic field component tangential to the Z-axis (coming out of the page). The first and the second longitudinal axes are perpendicular to each other. The configuration depicted in  FIG. 16  is suitable for measurement schemes, discussed above, that involve two MEMS sensors measuring ΔV simultaneously. Additional examples of the sensor  510  are Hall sensors, magento-resistance sensors, and other sensors known in the art. 
     The matrix  550  includes one MEMS sensor  552  for measuring a magnetic field component tangential to the first longitudinal axis (X-axis), one MEMS sensor  554  for measuring a magnetic field component tangential to the second longitudinal axis (Y-axis), and a sensor  556 , known in the art, for measuring a magnetic field component tangential to the Z-axis (coming out of the page). Additional examples of the sensor  510  are Hall sensors, magento-resistance sensors, and other sensors known in the art. The configuration depicted in  FIG. 17  is suitable for measurement schemes, discussed above, that involve one MEMS sensors measuring ΔV at two instances. The MEMS sensors depicted in  FIGS. 16 and 17  are also capable of measuring acceleration vectors components that are tangential with the Z-axis (coming out of the page). Although not shown in  FIGS. 16 and 17 , known accelerometer sensors for measuring acceleration components tangential with X-axis and Y-axis can also be included on the matrices  500  and  550  for measuring the respective acceleration components. 
     In operation a magnetic field may not line up exactly with the X-axis or the Y-axis. However, the magnetic field components tangential to these axes are sensed by the respective MEMS sensors. By measuring the X-axis, the Y-axis, and the Z-axis components of the magnetic field and the acceleration vector the exact direction and magnitude of the magnetic field and the acceleration vector can be calculated based on known vector analysis. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.