Abstract:
A MEMS acceleration sensor comprising: a frame, a plurality of proofmasses; a plurality of flexures; a plurality of hinges and a plurality of gauges. The frame, proofmasses, flexures, hinges and gauges designed to measure acceleration in a direction perpendicular to the device plane while being generally resistant to motions parallel to the device plane. The measurement of the acceleration is accomplished through the piezoresistive effect of the strain in the gauges.

Description:
FIELD 
       [0001]    The present patent document relates to micro-electro-mechanical (“MEMS”) accelerometers. More particularly, the present patent document relates to accelerometers with freed gauges sensitive to accelerations perpendicular to the device plane. 
       BACKGROUND 
       [0002]    An accelerometer is a transducer that converts acceleration forces into electronic signals. Accelerometers are applied and used in a variety of devices. For example, accelerometers are often included in automobile systems for air-bag deployment and roll-over detection. Accelerometers are also used in computer devices, such as for motion-based sensing (e.g. for drop detection) and motion-based control (e.g. in gaming). 
         [0003]    A MEMS accelerometer typically includes, among other things, a proofmass and one or more sensors for sensing movement or changes in position of the proofmass that are induced by external accelerations. A MEMS accelerometer can be configured to sense acceleration along one or more axes. Typically, the proofmass is configured in a predetermined device plane, and the axes of sensitivity are referenced relative to this device plane. For example, accelerations sensed along an axis or axes parallel to the device plane are usually referred to as X- or Y-axis accelerations, and accelerations sensed along an axis perpendicular to the device plane are usually referred to as Z-axis accelerations. A single-axis accelerometer might be configured to detect only X- or Y-axis accelerations or only Z-axis accelerations. A two-axis accelerometer might be configured to detect X- and Y-axis accelerations or configured to detect X- and Z-axis accelerations. A three-axis accelerometer might be configured to detect all three of X-, Y-, and Z-axis accelerations. 
         [0004]    In the MEMS field, using a pressure- or force-sensitive element, such as a cantilever, in conjunction with a strain-sensing element for measuring acceleration, force, or pressure, is known in the art. Accelerations on the strain-sensing element along the relevant axis will put that element into tension or compression, thereby changing the element&#39;s cross-sectional area and the resistance to the flow of electrical current in proportion to the acceleration. The change in resistance is measured using techniques such as a Wheatstone bridge to determine the amount of acceleration. 
         [0005]    Prior attempts to achieve high sensitivity in acceleration sensors have been plagued by susceptibility to cross-axis, i.e. out-of-plane, accelerations. Thus, there is a need for a MEMS accelerometer that is sensitive to Z-axis accelerations, i.e. accelerations sensed along an axis perpendicular to the device plane, while being insensitive to X- and Y axis accelerations, i.e. accelerations sensed along an axis or axes parallel to the device plane. 
       SUMMARY OF THE EMBODIMENTS 
       [0006]    In view of the foregoing, an object according to one aspect of the present patent document is to provide a MEMS device for detecting accelerations along an axis perpendicular to the device plane; that is, vertical accelerations along the Z-axis. Preferably the methods and apparatuses address, or at least ameliorate, one or more of the problems described above. To this end, a MEMS acceleration sensor is provided. 
         [0007]    In one embodiment, the MEMS acceleration sensor comprises: a frame; a first proofmass located within the frame, the first proofmass separated from the frame by a gap, wherein the first proofmass includes a left side, right side, top, bottom, horizontal midline halfway between the top and the bottom and vertical midline halfway between the left side and right side; a first channel starting from the top of the first proofmass and extending down into the first proofmass towards the bottom past the horizontal midline to a first channel end, the first channel located right of the vertical midline; a second channel starting from the bottom of the first proofmass and extending up into the first proofmass towards the top past the horizontal midline to a second channel end, the second channel located left of the vertical midline; a third channel starting from the right side of the first proofmass and extending in towards the first channel along the top of the first proofmass; a fourth channel starting from the right side of the first proofmass and extending in towards the first channel along the bottom of the first proofmass; a third channel starting from the right side of the first proofmass and extending in towards the first channel along the top of the first proofmass; a fourth channel starting from the right side of the first proofmass and extending in towards the first channel along the bottom of the first proofmass; a fifth channel starting from the left side of the first proofmass and extending in towards the second channel along the top of the first proofmass; a fifth channel starting from the left side of the first proofmass and extending in towards the second channel along the top of the first proofmass; four flexures, each flexure located within one of the third, fourth, fifth and sixth channels and coupling the first proofmass to the frame; a second proofmass located within the first channel and coupled to the first proofmass via a first hinge and a first pair of gauges at the first channel end and, coupled to the frame at the top via a second hinge and a second pair of gauges; and a third proofmass located within the second channel and coupled to the first proofmass via a third hinge and a third pair of gauges at the second channel end and coupled to the frame at the bottom via a fourth hinge and a fourth pair of gauges. 
         [0008]    In preferred embodiments of the MEMS acceleration sensor, the combination of the hinges and flexures are designed to allow the first proofmass to translate relative to the frame in a direction perpendicular to a device plane and restrict motion parallel to the device plane. In a preferred embodiment, hairsprings may be used for the flexures. In yet another embodiment a coiled spring may be used. In yet other embodiments, other types of flexures may be used. 
         [0009]    In a preferred embodiment, the hinges that connect the first proofmass to the frame are primarily responsible for controlling the motion perpendicular to the device plane. Although the flexures may contribute to controlling the motion of the first proofmass, in a preferred embodiment, the primary purpose of the flexures is to provide an electrical path from the frame to the first proofmass. Accordingly, in a preferred embodiment, the spring constant of the flexures is smaller than the spring constant of the hinges. In an even more preferred embodiment, the spring constant of the flexures is at least 50%, 80% or even 95% smaller than the spring constant of hinges. 
         [0010]    In some embodiments of the MEMS acceleration sensor, rather than having a single pair of gauges at a particular location, multiple pairs of gauges may be used. However, using a single pair or more than two pairs in any one location is acceptable in other embodiments. In yet other embodiments, some gauge locations may use a single pair of gauges while other gauge locations use multiple pairs of gauges. 
         [0011]    In preferred embodiments, the gauges are made of a piezoresistive material and the movement of the first proofmass relative to the frame causes a piezoresistive effect in at least one of the gauges. 
         [0012]    Generally, the proofmasses may be of any shape. However, in preferred embodiments, the second proofmass and third proofmass are rectangular cuboids. In yet other embodiments, the first proofmass is also a rectangular cuboid. In yet other embodiments, other shapes may be used. 
         [0013]    In preferred embodiments, the frame is a stationary rim and used as a mounting location for the MEMS acceleration sensor. In yet other embodiments, mounting locations may be appended to the frame. 
         [0014]    The MEMS acceleration sensor can have any size and shape. As just one example of the size and shape, the frame of the MEMS acceleration sensor has a length of approximately 6 millimeters, a width of approximately 3 millimeters, and a thickness of approximately 1 millimeter. 
         [0015]    In preferred embodiments, the hinges couple the second and third proofmasses to the frame and the main proofmass. In a preferred embodiment, the hinges are located above a centerline of a thickness of the first proofmass. The centerline of thickness is hallway through the thickness of the proofmass in a direction perpendicular to the device plane. 
         [0016]    In another aspect of the embodiments disclosed herein, a MEMS acceleration sensor is disclosed that comprises: a frame; a first proofmass located within the frame comprising a large center block flanked on a right side by a rectangular right side block and flanked on a left side by a rectangular left side block wherein, the right side block is separated from the center block by a first slit that cuts in from a top of the first proofmass such that the right side block is coupled to the center block by a first bridge at a bottom of the first proofmass and wherein the left side block is separated from the center block by a second slit that cuts in from the bottom of the first proofmass such that the left side block is coupled to the center block by a second bridge at the top of the first proofmass; a second proofmass located in the first slit, the second proofmass coupled to the frame by a first hinge along the top of the first proofmass and coupled to the first bridge by a second hinge; a third proofmass located in the second slit, the third proofmass coupled to the frame by a third hinge along the bottom of the first proofmass and coupled to the second bridge by a third hinge; a first pair of gauges located above the first hinge and spanning between the second proofmass and the frame; a second pair of gauges located above the second hinge and spanning between the second proofmass and the first proofmass; a third pair of gauges located above the third hinge and spanning between the third proofmass and the frame; a fourth pair of gauges located above the fourth hinge and spanning between the third proofmass and the first proofmass; and, a plurality of flexures that couple the first proofmass to the frame. 
         [0017]    In yet another aspect of the present patent document, a MEMS acceleration sensor is provided. In a preferred embodiment, the MEMS acceleration sensor comprises: a frame; a first proofmass located within the frame; a second proofmass nested within three sides of the first proofmass; a third proofmass nested within three sides of the first proofmass; four flexures that couple the first proofmass to the frame; a hinge and a pair of gauges that couple the second proofmass to the frame; a hinge and a pair of gauges that couple the third proofmass to the frame; a hinge and a pair of gauges that couple the second proofmass to the first proofmass; and a hinge and a pair of gauges that couple the third proofmass to the first proofmass. 
         [0018]    As described more fully below, the apparatuses of the embodiments of the MEMS acceleration sensors help solve or at least ameliorate problems with prior accelerometers. Further aspects, objects, desirable features, and advantages of the apparatuses disclosed herein will be better understood from the detailed description and drawings that follow in which various embodiments are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the claimed embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1A  illustrates a top surface view of one embodiment of a MEMS acceleration sensor. 
           [0020]      FIG. 1B  illustrates an isometric view of the MEMS acceleration sensor of  FIG. 1A . 
           [0021]      FIG. 1C  illustrates a cross-sectional view A-A of the embodiment of a MEMS acceleration sensor shown in  FIG. 1A . 
           [0022]      FIG. 1D  illustrates a cross-sectional view B-B of the embodiment of a MEMS acceleration sensor shown in  FIG. 1A . 
           [0023]      FIG. 1E  illustrates a cross-sectional view C-C of the embodiment of a MEMS acceleration sensor shown in  FIG. 1A . 
           [0024]      FIG. 2  illustrates a top view of one embodiment of a MEMS acceleration sensor. 
           [0025]      FIG. 3  illustrates a top view of one embodiment of a MEMS acceleration sensor. 
           [0026]      FIG. 4  illustrates a top view of one embodiment of a MEMS acceleration sensor wherein the primary proofmass has been divided into additional sections and the slits between those additional sections each contain additional proofmasses. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0027]      FIG. 1A  illustrates a top surface view looking down on the device plane of one embodiment of a MEMS accelerometer as taught herein. MEMS acceleration sensor  100  includes the top surface  119 .  FIG. 1B  illustrates an isometric view of the MEMS acceleration sensor  100  in  FIG. 1A .  FIGS. 1C ,  1 D, and  1 E illustrate different cross-sectional views A-A, B-B, and C-C of the embodiment of the MEMS acceleration sensor  100  in  FIGS. 1A and 1B . 
         [0028]    In the embodiment of the MEMS acceleration sensor  100  shown in  FIGS. 1A-1E , the acceleration sensor  100  includes frame  110 ; proofmasses  120 ,  121 , and  122 ; flexures  131 ,  132 ,  133 , and  134 ; channels  141  and  142 ; hinges  101 ,  103 ,  105  and  107 ; and pairs of gauges  151 ,  152 ,  153 , and  154 . Proofmass  120  has a left side  10 , right side  12 , top  14 , and bottom  16 , and is located within frame  110 . 
         [0029]    The flexure  131  is located near the top  14  of proofmass  120  and couples the left side  10  of the proofmass  120  to the frame  110 . Flexure  132  is located near the bottom  16  of proofmass  120  and couples the left side  10  of the proofmass  120  to the frame  110 . In the embodiment shown in  FIG. 1A , flexures  133  and  134  are in mirrored symmetry to flexures  131  and  132  and provide the same function on the other side of the proofmass  120 . Flexures  133  and  134  are thus mirrored about the vertical midline of the proofmass  120 . To this end, flexure  133  is located near the top  14  of proofmass  120  and couples the right side  12  of the proofmass  120  to the frame  110 . Flexure  134  is located near the bottom  16  of proofmass  120  and couples the right side  12  of the proofmass  120  to the frame  110 . 
         [0030]    In the embodiment in  FIG. 1A , the proofmass  120  has a couple channels  141  and  142  cut into it. The channels  141  and  142  may be also referred to as slits. Channel  141  starts from the bottom  16  of proofmass  120  and extends up to a channel end  143 . In a preferred embodiment, channel  141  extends towards the top of proofmass  120  past the horizontal midline. Also in a preferred embodiment, channel  141  is located left of the vertical midline of the proofmass  120  such that it is on the left side of proofmass  120 . Channel  142  starts at the top  14  of the proofmass  120  and extends down to a channel end  144 . In a preferred embodiment, channel  142  extends towards the bottom of proofmass  120  past the horizontal midline. Also in a preferred embodiment, channel  142  is located right of the vertical midline of the proofmass  120  such that it is on the right side of proofmass  120 . 
         [0031]    The channels  141  and  142  each extend across the proofmass  120 . In a preferred embodiment, the channels extend almost entirely across the proofmass  120 . In a more preferred embodiment, the channels  141  and  142  extend at least 80% of the way across proofmass  120 . In an even more preferred embodiment, the channels  141  and  142  extend at least 90% of the way across the proofmass  120 . In yet even more preferred embodiments, the channels  141  and  142  extend at least 95% or at least 99% of the way across proofmass  120 . In yet other embodiments, the channels  141  and  142  only extend up to the horizontal centerline of proofmass  120 . 
         [0032]    In preferred embodiments, a proofmass  121  and  122  is contained within each channel  141  and  142 . As may be seen in  FIG. 1A , proofmass  121  is located within channel  141 . In a preferred embodiment, the proofmasses  121  and  122  are not touching the sides of their respective channels  141  and  142  but instead, are coupled to the proofmass  120  by a hinges  101  and  107  at their respective channel ends  143  and  144 . In addition, proofmasses  121  and  122  are coupled to the frame on their opposite sides from the channel ends by additional hinges  103  and  105  respectively. 
         [0033]    As may be seen in  FIG. 1A , in a preferred embodiment, above each hinge in the direction of the device plane is a pair of gauges. However, using more than one pair of gauges in any one location is acceptable in other embodiments. In yet other embodiments, some gauge locations may use a single pair of gauges while other gauge locations use multiple pairs of gauges. 
         [0034]    In the embodiment shown in  FIG. 1A , a pair of gauges  151 , couple the proofmass  121  to the proofmass  120  at channel end  143 . Proofmass  121  is further coupled to the frame  110  at the opposite end from hinge  101  by hinge  103  and pair of gauges  152 . Proofmass  122  is located within channel  142 , and is coupled to proofmass  120  via hinge  107  and pair of gauges  154  at channel end  144 . Proofmass  122  is further coupled to the frame  110  at the opposite end from hinge  107  via hinge  105  and pair of gauges  153 . 
         [0035]    In the preferred embodiment, proofmasses  120 ,  121 , and  122  are formed from the wafer layer of a silicon wafer. In a preferred embodiment, proofmasses  120 ,  121 , and  122  are formed by etching away the material between the proofmasses and between the proofmasses and the frame  110 , as shown in  FIG. 1A . The removal of the material forms channels  141  and  142 . In a preferred embodiment, during the etching process, hinges  101 ,  103 ,  105 , and  107  are left in the spaces between the proofmasses, and the spaces between the proofmasses and the frame  110 , as shown. As may be seen in cross sections A-A and B-B shown in  FIGS. 1C and 1D , in a preferred embodiment, the hinges are formed above a centerline of a thickness of the proofmass  120 . The centerline of the thickness of the proofmass  120  being defined by the halfway point between the top surface  119  and the bottom surface  117  of the proofmass  120 . In a preferred embodiment, the hinges  101 ,  103 ,  105 , and  107  are formed by etching both down from the top surface  119  and up from the bottom surface  117 . 
         [0036]    In a preferred embodiment, pairs of gauges  151 ,  152 ,  153 , and  154  are formed from the device layer of a silicon wafer. In an even more preferred embodiment, pairs of gauges  151 ,  152 ,  153 , and  154  are pairs of freed gauges. Free gauges are described in U.S. Pat. Nos. 4,498,229 and 4,737,473, which are herein incorporated by reference in their entirety. 
         [0037]    As may be seen in  FIG. 1A , in a preferred embodiment, the frame  110  and the proofmass  120  are connected by flexures  131 ,  132 ,  133 , and  134 . In some embodiments, during manufacture, the frame and proofmasses all start from a single contiguous piece of silicon wafer. 
         [0038]    In operation, an acceleration in the Z or -Z direction of  FIG. 1A  causes proofmass  120  to move in a direction perpendicular to the device plane—in the Z or -Z direction—relative to the frame  110 . The movement of proofmass  120  perpendicular to the device frame can occur in either an upwards or a downwards direction. In such embodiments, the gauges  151 ,  152 ,  153 , and  154  are made of a piezoresistive material. Accordingly, an acceleration in the Z or -Z direction causes vertical movement of the proofmass  120  relative to the frame  110 , which in turn causes a piezoresistive effect in at least one of the gauges  151 ,  152 ,  153 , and  154 . At the same time, in preferred embodiment, the flexures resist movement parallel to the device plane. Thus, MEMS acceleration sensor  100  is sensitive to accelerations in a single axis perpendicular to the device plane that result in vertical movement of the proofmass  120  along the Z-axis, but is insensitive to accelerations in the X or Y axis, as shown in  FIG. 1A . 
         [0039]    The proofmass  120  is isolated from the frame by a gap except for a single connection by a hinge  103 ,  105  and a pair of gauges  152 ,  153  on the top and bottom of the proofmass  120 , and the four flexures  131 ,  132 ,  133  and  134 . As will be explained in more detail below, in a preferred embodiment the main purpose of the four flexures is to provide an electrical path from the frame  110  to the proofmass  120 . Although the flexures may contribute to the motion of proofmass  120 , in a preferred embodiment, they contribute very little. In a preferred embodiment, the hinges  103  and  105  that connect the proofmass  120  to the frame  110  are primarily responsible for the motion of the proofmass  120  perpendicular to the device plane and relative to the frame  110 . Accordingly, in a preferred embodiment, the spring constant of the flexures  131 ,  132 ,  133  and  134  is smaller than the spring constant of the hinges  103  and  105 . In an even more preferred embodiment, the spring constant of the flexures is at least 50%, 80% or even 95% smaller than the spring constant of hinges. 
         [0040]    In a preferred embodiment, the combinational effect of both the hinges  103  and  105  and the flexures  131 ,  132 ,  133  and  134  control the motion of the proofmass  120  in a direction perpendicular to the device plane and relative to the frame  110 . 
         [0041]    The routing of the electrical currents will now be explained. The electrical currents must traverse from the frame  110  through the gauges  151 ,  152 ,  153  and  154  over the spaces above each of the hinges  101 ,  103 ,  105  and  107  and back to the frame  110 . However, two of those pairs of gauges  151  and  154  are not connect to the frame but rather couple the proofmass  120  to the proofmasses  121  and  122  respectively. To this end, a paths must be provided to get the electrical currents from proofmass  120  back to the frame  110 . In a preferred embodiment, these paths are provided by the flexures  131 ,  132 ,  133  and  134 . As just one example of a possible electrical routing, the path may begin on the frame  110  in the top left corner by hairspring  131 . The path travels from the frame  110  over the hairspring  131  to the proofmass  120 . The path then proceeds from the proofmass  120  across the first gauge of the pair of gauges  151  onto the proofmass  121 . The path then u-turns or doubles back over the second gauge of the pair of gauges  151  back onto the proofmass  120 . The path may then proceed to the bottom left corner of proofmass  120  and back across the hairspring  132  to the frame  110 . Accordingly, a path is provided from the frame  110 , to proofmass  120 , across gauge  151  to proofmass  121  and back again. 
         [0042]    The pair of gauges  152  on the opposite side of proofmass  121  have a direction connection to the frame  110 . Accordingly, the electrical path may go directly from the frame through the first gauge in the pair of gauges  152  to proofmass  121  and back to the frame  110  over the second gauge of the pair of gauges  152 . In a preferred embodiment, the electrical path from the frame  110  to proofmass  122  across gauges  153  and  154  happens in mirrored symmetry to the paths just explained but over hairsprings  133  and  134 . 
         [0043]      FIG. 1B  shows the MEMS acceleration sensor of  FIG. 1A  under a 2 g (1 g=9.81 m/s 2 ) acceleration along the Z axis. In a preferred embodiment, the MEMS acceleration sensor is designed to be sensitive to a 2 g acceleration. However, in other embodiments, the MEMS acceleration sensor may be designed to work with any size acceleration. For example, the MEMS acceleration sensor may be designed to work with &lt;1 g, 1 g, 2 g, 5 g, 10 g or even 100 g. 
         [0044]    As shown in  FIG. 1B , when, for example, a negative acceleration is applied along the Z axis to MEMS acceleration sensor  100 , proofmass  120  moves perpendicular to the device plane relative to the frame  110 . The combined effects of the hinges  101 ,  103 ,  105  and  107  and the flexures  131 ,  132 ,  133  and  134  allow the proofmass  120  to move relative to the frame and restricting the movement to primarily the Z axis. The movement of proofmass  120  causes the ends of the proofmasses  121  and  122  connected to the proofmass  120  through hinges  101  and  107  to be displaced. At the same time, the opposite end of each of proofmasses  121  and  122  connected to the frame  110  via hinges  103  and  105 , experience almost no displacement. Accordingly, gauges  152  and  153  experience very little stress while gauges  151  and  154  are caused to stretch and come into tension. The tension of the gauges causes a change in resistance within the gauges  151  and  154  to the flow of electrical current, in proportion to the magnitude of the acceleration. In a preferred embodiment, gauges  151 ,  152 ,  153 , and  154  are made of a piezoresistive material, and vertical movement of proofmass  120  causes a measurable piezoresistive effect in at least one of the gauges  151 ,  152 ,  153 , and  154 . 
         [0045]    In a preferred embodiment, such as the one shown in  FIG. 1A , the channels  141  and  142  are rectangles and proofmasses  121  and  122  are rectangular cuboids. However, in other embodiments, channels  141  and  142  may be other shapes and/or proofmasses  121  and  122  may be of other shapes, such as cylinders, triangular prisms, trapezoidal prisms, or cubes. 
         [0046]    In one embodiment, frame  110  is a stationary rim with a length of approximately 6 millimeters, a width of approximately 3 millimeters, and a thickness of approximately 1 millimeter. Of course, embodiments of other sizes may be made without departing from the scope of the present patent document. Thus, in other embodiments, frame  110  may have a length greater or less than 6 millimeters, a width greater or less than 3 millimeters, and a thickness greater or less than 1 millimeter. Also, in other embodiments, the frame may be square such that the length and width are the same. 
         [0047]      FIG. 1C  illustrates a cross-sectional view of cross section A-A shown in  FIG. 1A . Cross section A-A cuts parallel to top  14  and bottom  16 , and across the gap between the bottom of proofmass  120  and frame  110 . As may be seen in  FIG. 1C , the channel  141  extends the full length of the wafer such that proofmass  121  is completely separate from proofmass  120  along the sides of proofmass  121 .  FIG. 1C  illustrates hinge  103  and pair of gauges  152 . Hinge  103  and pair of gauges  152  couple proofmass  121  to the frame  110 . A similar coupling occurs between proofmass  121  and proofmass  120  on the opposite end of proofmass  121 . As may also be seen in  FIG. 1C , hinge  103  is preferably located above a centerline of the thickness of proofmass  120 . 
         [0048]      FIG. 1D  illustrates a cross-sectional view of cross section B-B shown in  FIG. 1A . Cross section B-B cuts parallel to top  14  and bottom  16 , and across the channel  142  between the end of proofmass  122  and proofmass  120 . As may be seen in  FIG. 1D , the channel  142  extends the full length of the wafer along the sides of proofmass  122 . Accordingly, proofmass  122  is completely separate from proofmass  120  and frame  110  other than the connection through the hinges  105  and  107  and the pairs of gauges  153  and  154 . 
         [0049]    In a preferred embodiment, flexures  131 ,  132 ,  133 , and  134  are of a height such that they extend from the level of top surface  119  to the level of the bottom of hinges  101 ,  103 ,  105 , and  107 . As  FIG. 1D  shows, for example, flexures  132  and  134  have a height such that they extend from the top surface  119  to the bottom of hinge  107 . In other embodiments, the thickness of flexures  131 ,  132 ,  133  and  134  may be different thicknesses. 
         [0050]    In a preferred embodiment, flexures  131 ,  132   133  and  134  are hairsprings. In other embodiments, the flexures may be another type of spring such as a coil spring. Flexures  131 ,  132 ,  133  and  134  may be any type of flexure that allows translation in one axis and resists translation or ration in the other axes. 
         [0051]      FIG. 1E  illustrates a cross-sectional view C-C from  FIG. 1A . Cross section C-C cuts parallel to top  14  and bottom  16  at about a mid-point between top  14  and bottom  16 . 
         [0052]    The frame  110  in the embodiment shown in  FIGS. 1A ,  1 B,  1 C,  1 D, and  1 E, is in the shape of a rectangular cuboid. However, other shapes may be used. For example, the frame  110  may be a cube, circle, rhombus, or be any other shape having any number of sides. In a preferred embodiment, however, the frame  110  is a rectangular cuboid. 
         [0053]    In the embodiment shown in  FIGS. 1A ,  1 B,  1 C,  1 D, and  1 E, proofmass  120  is located at equal distances from the frame  110  on the left side, right side, top, and bottom. The proofmass  120  is offset from the frame  110  or separated from the frame  110  by gap  102 . In a preferred embodiment, gap  102  is formed by etching in a similar manner to channels  141  and  144 . However, in other embodiments, proofmass  120  may not be equally spaced from the frame  110  on the left side, right side, top, and bottom. For example, proofmass  120  may be a shorter distance from the frame  110  at the top than it is from the bottom. In such cases, proofmass  120  may be located off-center. 
         [0054]      FIG. 2  illustrates a view of the top surface  119  of another embodiment of a MEMS acceleration sensor  200 . The embodiment shown in  FIG. 2  is similar to the embodiment shown in  FIG. 1  except that the embodiment has been rotated in the view 90 degrees counter-clockwise. However, in order to clarify the embodiments disclosed herein, the description of the embodiment shown in  FIG. 2  will incorporate alternative language for some of the elements compared to the description of the embodiment shown in  FIG. 1 . 
         [0055]    The instant embodiment of MEMS acceleration sensor  200  shown in  FIG. 2  includes frame  210 ; proofmass  220 ; rectangular cuboid proofmasses  221  and  222 ; flexures  231 ,  232 ,  233 , and  234 ; hinges  201 ,  203 ,  205 , and  207 ; pairs of gauges  251 ,  252 ,  253 , and  254 ; and channels  241  and  242 . Proofmass  220  is located within the frame  210  and includes a top horizontal piece  223 , center rectangular piece  224 , bottom horizontal piece  225 , bridge piece  226  that connects top horizontal piece  223  to center rectangular piece  224 , and bridge piece  227  that connects center rectangular piece  224  to bottom horizontal piece  225 . Proofmass  220  has a left side  214 , right side  216 , top  212 , and bottom  210 . Flexure  231  is located near the left side  214  and couples the top horizontal piece  223  to the frame  210 , and flexure  232  is located near the right side  216  and couples the top horizontal piece  223  to the frame  210 . Similarly, flexure  233  is located near the left side  214  and couples the bottom horizontal piece  225  to the frame  210 , and flexure  234  is located near the right side  216  and couples the bottom horizontal piece  225  to the frame  210 . 
         [0056]    Proofmass  220  includes a channel  242  between the top horizontal piece  223  and center rectangular piece  224 . Channel  242  extends from the frame  210  to the bridge piece  226 . Proofmass  220  also includes a channel  241  between the center rectangular piece  224  and bottom horizontal piece  225 . Channel  241  extends from the frame  210  to the bridge piece  227 . 
         [0057]    Rectangular cuboid proofmass  222  is located within channel  242 , coupled to the bridge piece  226  of proofmass  220  by hinge  207  and pair of gauges  254 , and coupled to the frame  210 , at an opposite end of proofmass  222 , by hinge  205  and pair of gauges  253 . Rectangular cuboid proofmass  221  is located within channel  241 , coupled to the bridge piece  227  of proofmass  220  by hinge  201  and pair of gauges  251 , and coupled to the frame  210 , at an opposite end of proofmass  221 , by hinge  203  and pair of gauges  252 . 
         [0058]    In operation, acceleration sensor  200  operates in a similar fashion to acceleration sensor  100  shown in  FIGS. 1A-1E . In addition, acceleration sensor  200  has cross sections similar to those shown in  FIGS. 1C-1E . 
         [0059]      FIG. 3  illustrates a view of the top surface  119  of the same embodiment of a MEMS acceleration sensor as shown in  FIG. 2  except that it has been rotated back to the same orientation as the embodiment shown in  FIG. 1 , i.e. a 90-degree clockwise rotation. However, for clarity of the description, the embodiment shown in  FIG. 3  will be described with some elements varying from the descriptions used in  FIGS. 1 and 2 . 
         [0060]    The instant embodiment of MEMS acceleration sensor  300  shown in  FIG. 3  includes a frame  310 ; a first proofmass  320  located within the frame  310  comprising a center block  324  flanked on a right side by a rectangular right side block  325  and flanked on a left side by a rectangular left side block  323  wherein, the right side block  325  is separated from the center block  324  by a first slit  342  that cuts in from a top  14  of the first proofmass  320  such that the right side block  325  is coupled to the center block  324  by a first bridge  327  at a bottom  16  of the first proofmass  320  and wherein the left side block  323  is separated from the center block  324  by a second slit  341  that cuts in from the bottom  16  of the first proofmass  320  such that the left side block  323  is coupled to the center block  324  by a second bridge  326  at the top  14  of the first proofmass  320 ; 
         [0061]    The embodiment in  FIG. 3  further comprises a second proofmass  322  located in the first slit  342 . In the embodiment shown, the second proofmass  322  is coupled to the frame  310  by a first hinge  305  along the top  14  of the first proofmass  320  and coupled to the first bridge  327  by a second hinge  307 . The embodiment in  FIG. 3  further comprises a third proofmass  321  located in the second slit  341 . In the embodiment shown, the third proofmass  321  is coupled to the frame  310  by a third hinge  303  along the bottom  16  of the first proofmass  320  and coupled to the second bridge  326  by a third hinge  301 . 
         [0062]    In the embodiment shown in  FIG. 3 , a first gauge  353 , or as shown a first pair of gauges, is located above the first hinge  305  and spans between the second proofmass  322  and the frame  310 . Similarly, a second gauge  354 , or second pair of gauges, is located above the second hinge  307  and spans between the second proofmass  322  and the first proofmass  320 . A third gauge  352  or third pair of gauges, is located above the third hinge  303  and spans between the third proofmass  321  and the frame  310 . Similarly, a fourth gauge  351 , or pair of gauges, is located above the fourth hinge  301  and spans between the third proofmass and the first proofmass  320 . In addition, the acceleration sensor  300  must have a plurality of flexures to allow the translation perpendicular to the device plane. The embodiment shown in  FIG. 3  comprises a plurality of flexures  331 ,  332 ,  333 ,  334  that couple the first proofmass  320  to the frame  310 . 
         [0063]    In a preferred embodiment, proofmass  320  is divided into three vertical blocks  323 ,  324  and  325  connected by narrow bridges  326  and  327 . In other embodiments, proofmass  320  may have other shapes and forms. Although the embodiment shown in  FIG. 3  shows three vertical blocks  323 ,  324 , and  325 , two bridge  326  and  327 , four hinges  301 ,  303 ,  305 , and  307 , and four pairs of gauges  351 ,  352 ,  353 , and  354 , in other embodiments additional vertical blocks, bridges, hinges, or gauges may be used. 
         [0064]      FIG. 4  illustrates an embodiment of MEMS acceleration sensor  400  that includes five vertical blocks  421 ,  422 ,  423 ,  424 , and  425 ; four bridges  431 ,  432 ,  433 ,  434 ; eight hinges  401 ,  403 ,  405 ,  407 ,  409 ,  411 ,  413  and  415 , and eight pairs of gauges  441 ,  442 ,  443 ,  444 ,  445 ,  446 ,  447 , and  448 . In a preferred embodiment including more additional gauges, gauges positioned the same distance from the center of the proofmass  420  may be averaged or used to produce a differential output to increase sensitivity and/or accuracy. 
         [0065]    Although the embodiments shown in  FIGS. 1A  through  FIG. 3  are shown with four pairs of gauges each, other embodiments may use fewer gauges. For example, a half bridge may be created using only two pairs of gauges. Moreover, additional parallel gauges may be used for redundancy. In addition, other electrical configurations may be used. Similarly, although the embodiment illustrated in  FIG. 4  uses eight pairs of gauges, the same embodiment may be used with only four pairs of gauges or two pairs of gauges or any number of gauges depending on the application. 
         [0066]    Thus, the present patent document provides a high temperature navigational MEMS acceleration sensor that is sensitive to vertical accelerations. 
         [0067]    Although the embodiments have been described with reference to preferred configurations and specific examples, it will readily be appreciated by those skilled in the art that many modifications and adaptations of the high-output MEMS accelerometer described herein are possible without departure from the spirit and scope of the embodiments as claimed hereinafter. Thus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the embodiments as claimed below.