Patent Publication Number: US-8113054-B2

Title: Capacitive accelerometer

Description:
TECHNICAL FIELD 
     This application claims the benefit of Korean Patent Application No. 10-2006-0122551, filed on Dec. 5, 2006 and Korean Patent Application No. 10-2007-0043804, filed on May 4, 2007, in the Korean Intellectual Property Office, the disclosure of which are incorporated herein in their entirety by reference. 
     The present invention relates to a capacitive accelerometer, and more particularly, to a capacitive accelerometer which has high sensitivity, can be simply manufactured by maintaining a narrow distance between a reference electrode and a sensing electrode, and can make it unnecessary to individually correct each manufactured accelerometer by removing or drastically reducing a functional variance due to a process error. This work was supported by the IT R&amp;D program of MIC/IITA. [2006-S-054-01, Development of CMOS based MEMS processed multi-functional sensor for ubiquitous environment] 
     BACKGROUND ART 
     Ultra-small accelerometers have drawn much research interest due to their low cost, high performance, and the miniaturization trend of a variety of electronic devices used in automobiles, military systems, robot systems, and safety diagnostic systems. Among the ultra-small accelerometers, capacitive accelerometers measure the acceleration generated due to an external force by measuring a change in capacitance due to the acceleration, between a reference electrode and a sensing electrode. 
     Capacitance C is defined by Equation 1, and increases as a distance d between the electrodes decreases. 
     
       
         
           
             
               
                 
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     Also, since a change in the capacitance C when the distance d between the electrodes is small is higher than that when the distance d between the electrodes is large, the smaller the distance d is, the more sensitive the accelerometers are. Accordingly, when ultra-small capacitive accelerometers are manufactured, it is very important to precisely reduce a distance between electrodes. 
       FIG. 1  is a plan view of a conventional ultra-small capacitive accelerometer manufactured by bulk micromachining. 
     Referring to  FIG. 1 , a substrate  64  is selectively etched to form sensing mass bodies  130  and  140  including sensing electrodes  110  and  120  and support springs  132  and  142 , support parts  136 ,  138 ,  146 , and  148  fixing the support springs  132  and  142  to the substrate  64  and acting as pads for applying signals, reference electrodes  80  and  90  spaced apart by a predetermined distance from the sensing electrodes  110  and  120 , and pads  88  and  98  applying signals to the reference electrodes  80  and  90 . 
     When acceleration is generated by an external force, the sensing mass bodies  130  and  140  are moved by an inertial force, and thus the distance between the sensing electrodes  110  and  120  and the reference electrodes  80  and  90  is changed. As a result, the capacitance between the sensing electrodes  110  and  120  and the reference electrodes  80  and  90  is changed and the acceleration can be measured according to the changed capacitance. 
     However, the conventional ultra-small capacitive accelerometer has a problem in that as an aspect ratio of the electrodes increases, a minimum distance between the electrodes is limited by a manufacturing process. Also, the distance between the sensing electrodes  110  and  120  and the reference electrodes  80  and  90  may be different for each manufactured accelerometer due to a process error, such as overetching, and thus each accelerometer must be individually corrected. 
       FIG. 2A  is a perspective view of a conventional highly sensitive capacitive accelerometer manufactured by both bulk micromachining and surface micromachining.  FIG. 2B  is a cross-sectional view taken along a line perpendicular to the length direction of sensing electrodes  41  of the conventional highly sensitive capacitive accelerometer of  FIG. 2A . 
     Referring to  FIGS. 2A and 2B , sensing mass bodies  42  are formed by bulk micromachining, and support springs  51  and sensing electrodes  41  are formed by surface micromachining. A distance between the sensing electrodes  41  and the sensing mass bodies  42  is determined by the thickness of a deposited sacrificial layer, not shown, which surrounds the sensing electrodes  41  and is removed in  FIG. 2B . The distance between the sensing electrodes  41  and the sensing mass bodies  42  can be narrowed. Also, since an entire substrate  40  is etched, sensitivity can be increased by sufficiently increasing the mass of the sensing mass bodies  42 . 
     However, a method of manufacturing the conventional highly sensitive capacitive accelerometer is very complex and expensive, and has a high risk of causing a difference in sensitivity between different accelerometers due to a process error because it is difficult to precisely and uniformly control the thickness of the sacrificial layer. 
     Accordingly, there is a high demand for an accelerometer that can be simply manufactured at low cost and has a low risk of causing a difference in sensitivity between devices. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The present invention provides a capacitive accelerometer that has high sensitivity, can be simply manufactured, and can make it unnecessary to individually correct each manufactured accelerometer. 
     Technical Solution 
     According to an aspect of the present invention, there is provided a capacitive accelerometer comprising: a substrate; a sensing mass body disposed above and spaced apart from the substrate, and comprising a mass main body, a support spring, and a sensing electrode; a support part coupling the sensing mass body to the substrate; a reference electrode disposed adjacent to the sensing electrode and movable farther away from or closer to the sensing electrode; a driving unit moving the reference electrode; and a stopper limiting the motion of the reference electrode. 
     An allowable clearance of the stopper may be less than a distance between the sensing electrode and the reference electrode when the driving unit is not driven. 
     When the driving unit is driven to move the reference electrode by a maximum distance toward the sensing electrode, a distance between the reference electrode and the sensing electrode may range from 0.2 to 0.7 mm. 
     Each of the sensing electrode and the reference electrode may have a comb shape, and teeth of the sensing electrode and teeth of the reference electrode may alternate with each other. 
     A distance A between the reference electrode and the sensing electrode when the driving unit is not driven may be equal to a sum of a distance B between the reference electrode and the sensing electrode when the driving unit is driven and an allowable clearance C of the stopper. 
     The driving unit may move the reference electrode by an electrostatic force. The driving unit may comprise a first finger, the capacitive accelerometer further comprising a reference electrode body comprising a plurality of reference electrodes, a connecting part connecting the plurality of reference electrodes, and a second finger spaced apart from and engaging with the first finger, wherein an allowable clearance of the stopper is less than a distance between the first finger and the second finger when the driving unit is not driven. 
     The stopper may be connected to the reference electrode by a spring. 
     According to another aspect of the present invention, there is provided a capacitive accelerometer comprising: a substrate; a reference electrode fixed to the substrate; a sensing mass body disposed above and spaced apart from the substrate, comprising a sensing electrode disposed adjacent to the reference electrode, a support spring, and a mass main body, and movable farther away from or closer to the reference electrode; a driving unit capable of moving the sensing mass body; and a stopper capable of limiting the motion of the sensing mass body caused by the driving unit. 
     An allowable clearance of the stopper may be less than a distance between the sensing electrode and the reference electrode when the driving unit is not driven. 
     When the driving unit is driven to move the sensing electrode by a maximum distance toward the reference electrode, a distance between the sensing electrode and the reference electrode may range from 0.2 to 0.7 mm. 
     Each of the sensing electrode and the reference electrode may have a comb shape, and teeth of the sensing electrode and teeth of the reference electrode may alternate with each other. 
     A distance a between the reference electrode and the sensing electrode when the driving unit is not driven may be equal to a sum of a distance b between the reference electrode and the sensing electrode when the driving unit is driven and an allowable clearance c of the stopper. 
     The driving unit may move the sensing mass body by an electrostatic force. The driving unit may comprise a first finger, wherein the sensing mass body further comprises a second finger extending from the support spring and spaced apart from and engaging with the first finger, wherein an allowable clearance of the stopper is less than a distance between the first finger and the second finger when the driving unit is not driven. 
     According to another aspect of the present invention, there is provided a capacitive accelerometer comprising: a substrate; a reference electrode disposed above and spaced apart from the substrate; a sensing electrode disposed above and spaced apart from the substrate; a driving unit capable of adjusting relative positions of the reference electrode and the sensing electrode; and a stopper capable of limiting the motion of the driving unit. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a plan view of a conventional accelerometer; 
         FIG. 2A  is a perspective view of another conventional accelerometer; 
         FIG. 2B  is a cross-sectional view of the conventional accelerometer of  FIG. 2A ; 
         FIG. 3  is a plan view of an accelerometer according to an embodiment of the present invention; 
         FIG. 4  is a cross-sectional view taken along line IV-IV′ of  FIG. 3 ; 
         FIG. 5  is a plan view illustrating a relationship between a distance between a first finger and a second finger and an allowable clearance of a stopper; 
         FIG. 6  is a conceptual view illustrating a relationship between a distance between a sensing electrode and a reference electrode and an allowable clearance of a stopper; 
         FIGS. 7A through 7C  are side cross-sectional views for explaining a method of manufacturing a part of an accelerometer according to an embodiment of the present invention; 
         FIG. 8  is a plan view of an accelerometer according to another embodiment of the present invention; and 
         FIG. 9  is a plan view of an accelerometer according to still another embodiment of the present invention. 
     
    
    
     BEST MODE 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the same reference numeral denotes the same element. Further, various elements and regions shown in the drawings are schematically illustrated and thus the present invention is not limited to thicknesses or distances shown in the drawings. 
     The present invention provides a capacitive accelerometer comprising: a substrate; a sensing mass body disposed above and spaced apart from the substrate, and including a mass main body, a support spring, and a sensing electrode; a support part coupling the sensing mass body to the substrate; a reference electrode disposed adjacent to the sensing electrode and movable farther away from or closer to the sensing electrode; a driving unit moving the reference electrode; and a stopper limiting the motion of the reference electrode. 
       FIG. 3  is a plan view of an accelerometer according to an embodiment of the present invention. 
     Referring to  FIG. 3 , a sensing mass body  210  is disposed above and spaced apart from a substrate  200 . The sensing mass body  210  may include a mass main body  212 , a support spring  214 , and a sensing electrode  216 . 
     The mass main body  212  may have an area great enough to have a sufficient mass. However, the present invention is not limited thereto, and for example, the mass main body  212  may have a beam shape. The sensing electrode  216  may be disposed on a side surface of the mass main body  212 . At least one sensing electrode  216  may be used. The sensing electrode  216  may have a comb shape as shown in  FIG. 3 . 
     The support spring  214  is attached to an end of the mass main body  212 . The support spring  212  may be coupled to the substrate  200  by a support part  220 , such that the sensing mass body  210  is coupled to the substrate  200 . The support spring  214  may have a zigzag shape as shown in  FIG. 3 , and may generate an elastic force with respect to a motion perpendicular to the repeated zigzag shape. 
     When acceleration is generated by an external force, the mass main body  212  is displaced from its initial position due to an inertial force, and thus the support spring  214  is deformed. The support spring  214  accumulates a restoring force corresponding to the deformation, and when the acceleration is stopped and the inertial force is removed, the mass main body  212  returns to its original position due to the restoring force of the support spring  214 . 
     The reference electrode  232  may be disposed adjacent to the sensing mass body  210 . Optionally, when a plurality of reference electrodes  232  is used, the reference electrodes  232  may be connected to one another by a connecting part  234 . 
     The reference electrode  232  is disposed adjacent to the sensing electrode  216  of the sensing mass body  210 , and is movable farther away from or closer to the sensing electrode  216 . The reference electrode  232  may have a comb shape like the sensing electrode  216 . In particular, both the sensing electrode  216  and the reference electrode  232  may have comb shapes, and teeth of the sensing electrode  216  and teeth of the reference electrode  232  may alternate with each other. 
     The stopper  236  limits the motion of the reference electrode  232 . In order to explain in detail how the stopper  236  limits the motion of the reference electrode  232 , a driving unit  240  and the stopper  236  are shown in  FIG. 5 . 
       FIG. 5  is a plan view illustrating a relationship between a distance between a first finger  242  and a second finger  235  and an allowable clearance of the stopper  236 . 
     Referring to  FIG. 5 , the driving unit  240  has the first finger  242  having a comb shape, and the connecting part  234  having the second finger  235  formed on an end thereof, wherein the first finger  242  and the second finger  235  engage with each other. The reference electrode  232  and the connecting unit  234  may constitute a reference electrode body  230 . Optionally, the connecting part  234  may be connected to the stopper  236  by a spring  237 . The stopper  236  may be fixedly coupled to the substrate (rot shown). 
     When a potential opposite to that of the first finger  242  and the second finger  235  of the driving unit  240  is applied, the second finger  235  and the connecting part  234  are moved to the right side of  FIG. 5  due to an electrostatic attractive force. 
     As shown in  FIG. 5 , a distance d between the first finger  242  and the second finger  235  before the potential is applied is greater than an allowable clearance c of the stopper  236 . The allowable clearance c refers to a maximum distance by which the sensing mass body  210  can be moved when the driving unit  240  is driven. Accordingly, although the second finger  235  and the connecting part  234  are moved to the right side of  FIG. 5  when the potential is applied, the motion of the connecting part  234  is limited by the stopper  236  before the first finger  242  contacts the second finger  235 . 
     Since the connecting part  234  is moved by driving the driving unit  240 , a distance between the reference electrode  232  and the sensing electrode  216  coupled to the connecting part  234  can be reduced. The distance between the reference electrode  232  and the sensing electrode  216  reduced by the driving of the driving unit  242  may range from 0.2 to 0.7 mm. If the distance between the reference electrode  232  and the sensing electrode  216  is less than 0.2 mm, a van der Waals force is increased disadvantageously. 
     The allowable clearance c of the stopper  236  is less than the distance between the sensing electrode  216  and the reference electrode  232  before the potential is applied. Otherwise, the sensing electrode  216  and the reference electrode  232  may contact each other. 
     Meantime, if the application of the potential is stopped, the reference electrode body  230  can return to its original position due to the restoring force of the spring  237 . 
     Although the stopper  236  is connected to the connecting part  234  by the spring  237  in  FIGS. 3 through 5 , the present invention is not limited thereto, and the stopper  236  may not be connected to the connecting part  234  and the spring  237 . 
     The driving unit  240  is not limited to  FIG. 5 , and may have any structure as long as the driving unit  240  can move the reference electrode  232  and/or the reference electrode body  230 . 
     The advantages of the accelerometer constructed as described above will now be explained. 
     The accelerometer constructed as described above can maintain a narrow distance between the reference electrode  232  and the sensing electrode  216  and can be simply manufactured without a difference in capacitance between manufactured accelerometers. Since there is no difference in capacitance, a separate correcting process is unnecessary and the accelerometer can be simply manufactured at low costs and with high yield. 
       FIG. 6  is a conceptual view illustrating a relationship between the sensing electrode  216 , the reference electrode  232 , the connecting part  234 , and the stopper  236 . Referring to  FIG. 6 , when an allowable clearance of the stopper  236  is c and a distance between the sensing electrode  216  and the reference electrode  232  when the driving unit  240  is not driven is a, a distance between the reference electrode  232  and the sensing electrode  216  when the driving unit  240  moves the reference electrode  232  toward the sensing electrode  216  is (a−c). 
     Accordingly, since the distance (a−c) between the sensing electrode  216  and the reference electrode  232  is determined by the distance a between the sensing electrode  216  and the reference electrode  232  when the driving unit  240  is not driven and the allowable clearance c of the stopper  236 , when a distance between the sensing electrode  216  and the reference electrode  232  needs to be reduced, a difference between the distance a and the allowable clearance c is reduced, thereby avoiding a burden for a process margin. 
     Conventional accelerometers have a difference in capacitance between them because they are etched to different degrees. The accelerometer according to the present invention can solve the problem. If it is assumed that the accelerometer is designed to have the distance a and the allowable clearance c as shown in  FIG. 6  but each part is over-etched by e/2, the allowable clearance c of  FIG. 6  becomes (c+e) and the distance d between the reference electrode  232  and the sensing electrode  216  becomes (a+e). Since the distance between the reference electrode  232  and the sensing electrode  216  when the driving unit  240  is driven is (a−c) obtained by subtracting the allowable clearance (c+e) from the distance (a+e), a distance between the reference electrode  232  and the sensing electrode  216  when the driving unit  240  is driven is (a−c) irrespective of the existence of over-etching. 
     Accordingly, the accelerometer of  FIG. 3  can have an extremely fine structure without being limited by a process margin, and there is no functional variance between manufactured accelerometers. 
       FIG. 4  is a cross-sectional view taken along line IV-IV′ of  FIG. 3 . Referring to  FIG. 4 , since the reference electrode  232 , the sensing electrode  216 , the second finger  235  formed on the end of the connecting part  234 , and the spring  237  are spaced apart from the substrate  200 , and thus the reference electrode  232 , the sensing electrode  216 , the second finger  235 , and the spring  237  can be moved. The stopper  236  and the first finger  242  of the driving unit  240  may be fixed to the substrate  200 . 
     The substrate  200 , and the reference electrode  232 , the sensing electrode  216 , the second finger  235 , and the spring  237  disposed above and spaced apart from the substrate  200  may be manufactured using a conventional method. For example, referring to  FIG. 7A , an oxide layer  320  is formed on a substrate  310 , and then an auxiliary substrate  330  is formed on the oxide layer  320 . Referring to  FIG. 7B , a pattern  334  is formed on the auxiliary substrate  330  using photolithography. 
     Referring to  FIG. 7C , a part of the oxide layer  320  is removed by wet etching. The part of the oxide layer  320  removed by the wet etching may be disposed below the pattern  334 , so that the pattern  334  can be spaced apart from the substrate  310  by a distance corresponding to the part of the oxide layer  320  removed by the wet etching. In this way, a part  332  fixed to the substrate  310  and the pattern  334  spaced apart from the substrate  310  can be manufactured. 
       FIG. 8  is a plan view of a capacitive accelerometer according to another embodiment of the present invention. 
     Referring to  FIG. 8 , a driving unit  340  and a reference electrode body  330  are almost identical to the driving unit  240  and the reference electrode body  230  of  FIG. 3 . However, a mass main body  312  has a beam shape, unlike the mass main body  212  having a plate shape of  FIG. 3 , and a support spring  314  has a beam shape, unlike the support spring  214  having a zigzag shape of  FIG. 3 . 
     In operation, like in  FIG. 3 , the driving unit  340  is driven, and an electrostatic force is generated between a first finger  342  and a second finger  335  to move the reference electrode body  330 . The reference electrode body  330  is moved by the electrostatic force, and the motion of the reference electrode body  330  is limited by a stopper  336 . 
     Due to the motion of the reference electrode body  330 , a reference electrode  332  and a sensing electrode  316  get closer to each other. If the accelerometer is accelerated in this state, the accelerometer becomes more sensitive. 
     Once the accelerometer is accelerated, a sensing mass body  310  exerts an inertial force, and thus a distance between the reference electrode  332  and the sensing electrode  316  is changed to change capacitance. Accordingly, the accelerometer of  FIG. 8  measures the acceleration using the changed capacitance. A support spring  314  is deformed by the inertial force generated by the sensing electrode  316  and the mass main body  312  and accumulates a restoring force. Then, when the accelerometer stops, the sensing mass body  310  returns to its original position due to the restoring force of the support spring  314 . 
     After the operation of the accelerometer is stopped, the operation of the driving unit  340  is also stopped. If the driving unit  340  stops the operation, since a force applied between the first finger  342  and the second finger  335  is removed, the reference electrode body  330  returns to its original position due to a restoring force of a spring  337 . 
       FIG. 9  is a plan view of a capacitive accelerometer according to another embodiment of the present invention. In  FIG. 9 , the capacitive accelerometer includes: a substrate  400 ; a reference electrode  432  fixedly disposed over the substrate  400 ; a sensing mass body  410  disposed above to be spaced apart from the substrate  400 , including a sensing electrode  416  disposed adjacent to the reference electrode  432 , a support spring  414 , and a mass main body  412 , and movable farther away from or closer to the reference electrode  432 ; a driving unit  440  moving the sensing mass body  410 ; and a stopper  436  limiting the motion of the sensing mass body  410  caused by the driving unit  440 . 
     Referring to  FIG. 9 , the reference electrode  432  may be fixed to the substrate  400 . In particular, when a plurality of reference electrodes  432  are used, the reference electrodes  432  may be connected to one another by a connecting part  434 . Optionally, the reference electrode  432  and the connecting part  434  may be fixed to the substrate  400 . Optionally, the reference electrode  432  may be fixedly disposed above and spaced apart from the substrate  400 . Optionally, at least one reference electrode  432  may be used, and the reference electrode  432  may have a comb shape as shown in  FIG. 9 . 
     The sensing mass body  410  of  FIG. 9  may be spaced apart from the substrate  400 . The sensing mass body  410  includes the sensing electrode  416 , the support spring  414 , and the mass main body  412 . 
     The mass main body  412  may have an area great enough to have a sufficient mass. However, the present invention is not limited thereto. For example, the mass main body  412  my have a beam shape. The sensing electrode  416  may be disposed on a side surface of the mass main body  412 . At least one sensing electrode  416  may be used, and may have a comb shape as shown in  FIG. 9 . Optionally, each of the sensing electrode  416  and the reference electrode  432  may have a comb shape, and teeth of the sensing electrode  416  and teeth of the reference electrode  432  may alternate with each other. 
     The support spring  414  is attached to an end of the mass main body  412 . The support spring  414  may have a zigzag shape like the support spring  214  of  FIG. 3 , and may generate an elastic force with respect to a motion perpendicular to the repeated zigzag shape. 
     The driving unit  440  may further include a first finger  442 . As described above, the sensing mass body  410  may be spaced apart from the substrate  400 , and may further include an extending part  438  extending from the support spring  414  and a second finger  435  extending from the extending part  438 . By applying a potential between the first finger  442  and the second finger  435 , the sensing mass body  410  can be moved. 
     The motion of the sensing mass body  410  is limited by the stopper  436 . The stopper  436  may be fixed to the substrate  400 , or may be connected to the extending part  438  by a spring  437 . 
     The operation principle of the capacitive accelerometer of  FIG. 9  will now be explained. 
     First, the sensing mass body  410  is moved by applying a potential between the first finger  442  and the second finger  435  until the motion of the sensing mass body  410  is limited by the stopper  436 . The motion may be induced by an electrostatic force between the first finger  442  and the second finger  435 . A distance between the sensing electrode  416  and the reference electrode  432  is reduced due to the motion of the sensing mass body  410 . At this time, the support spring  414  is not deformed, and accordingly does not exert a restoring force. However, the spring  437  connecting the stopper  436  and the extending part  438  is deformed to exert a restoring force. A position of the sensing mass body  410  at this time is referred to as ‘a ready position’. 
     Next, when acceleration is generated by an external force applied to the accelerometer of  FIG. 9 , the sensing mass body  410  is moved due to an inertial force, and the distance between the sensing electrode  416  and the reference electrode  432  is changed to change capacitance formed by the sensing electrode  416  and the reference electrode  432 . The acceleration can be measured using the changed capacitance. A restoring force of the support spring  414  is generated by the motion of the sensing mass body  410 . 
     When the acceleration stops and the velocity of the accelerometer is constant, the sensing mass body  410  returns to the ready position due to the restoring force of the support spring  414 . Next, when the potential applied to the first finger  442  and the second finger  435  is removed, the sensing mass body  410  returns to its initial position. 
     A distance between the sensing electrode  416  and the reference electrode  432  when the driving unit  440  is not driven may be greater than an allowable clearance of the stopper  436 . The allowable clearance refers to a maximum distance by which the sensing mass body  410  can be moved when the driving unit  440  is driven. In detail, a distance a between the sensing electrode  416  and the reference electrode  432  when the driving unit  440  is not driven is equal to a sum of a distance b between the sensing electrode  416  and the reference electrode  432  when the driving unit  440  is driven and an allowable clearance c. 
     Also, a distance between the first finger  442  and the second finger  435  when the driving unit  440  is not driven may be greater than an allowable clearance of the stopper  436 . If the distance between the first finger  442  and the second finger  435  when the driving unit  440  is not driven is not greater than the allowable clearance of the stopper  436 , the first finger  442  and the second finger  435  may contact each other. 
     The distance between the reference electrode  432  and the sensing electrode  416  reduced by the driving of the driving unit  440  may range from 0.2 to 0.7 mm. If the distance between the reference electrode  432  and the sensing electrode  416  reduced by the driving of the driving unit  440  is less than 0.2 mm, a van der Waals force is increased disadvantageously. 
     The accelerometers described with reference to the attached drawings according to the embodiments of the present invention are capacitive accelerometers each including: a substrate; a reference electrode disposed above and spaced apart from the substrate; a sensing electrode disposed above and spaced apart from the substrate; a driving unit adjusting relative positions of the reference electrode and the sensing electrode; and a stopper limiting the motion of the driving unit. 
     As described above, the capacitive accelerator according to the present invention has high sensitivity, can be simply manufactured by maintaining a narrow distance between the reference electrode and the sensing electrode, and can make it unnecessary to individually correct each manufactured accelerometer by removing or drastically reducing a functional difference due to a process error. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.