Abstract:
Disclosed herein is an inertial sensor including: a flexible part; a mass body connected to the flexible part; and a support part connected to the flexible part and supporting the mass body in a floated state to displace the mass body, wherein the flexible part has an upper piezoresistor disposed on one surface thereof and a lower piezoresistor disposed on the other surface thereof to detect a displacement of the mass body.

Description:
CROSS REFERENCE TO RELATED ED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2013-0061601, filed on May 30, 2013, entitled “Inertial Sensor And Method Of Manufacturing The Same” which is hereby incorporated by reference in its entirety into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to an inertial sensor and a method of manufacturing the same. 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, an inertial sensor has been used in various applications, for example, military such as an artificial satellite, a missile, an unmanned aircraft, or the like, vehicles such as an air bag, electronic stability control (ESC), a black box for a vehicle, or the like, hand shaking prevention of a camcorder, motion sensing of a mobile phone or a game machine, navigation, or the like. 
         [0006]    The inertial sensor has generally adopted a configuration in which a mass body is adhered to an elastic substrate, such as a membrane, and the like, which is a flexible part, in order to measure acceleration and angular velocity. Through the above-mentioned configuration, the inertial sensor may calculate the acceleration by measuring inertial force applied to the mass body and may calculate the angular velocity by measuring Coriolis force applied to the mass body. 
         [0007]    In detail, a method of measuring the acceleration using the inertial sensor will be described below. First, the acceleration may be calculated by Newton&#39;s law of motion “F=ma”, where “F” represents inertial force applied to the mass body, “m” represents a mass of the mass body, and “a” is acceleration to be measured. Among others, the acceleration a may be obtained by sensing the inertial force F applied to the mass body and dividing the sensed inertial force F by the mass m of the mass body that is a predetermined value. 
         [0008]    Meanwhile, as an example of the inertial sensor, a piezoresistive type of acceleration sensor according to the prior art includes a piezoresistor mounted on a membrane (diaphragm) to sense a displacement of the mass body. However, as the piezoresistor is provided as a single layer, there is a limitation in detecting the displacement of the mass body. 
       PRIOR ART DOCUMENT 
       [0000]    
       
         (Patent Document 1) US 20030209075 A 
       
     
       SUMMARY OF THE INVENTION 
       [0010]    The present invention has been made in an effort to provide an inertial sensor which can have improved sensing sensitivity and efficiency by detecting displacements from an upper piezoresistor and a lower piezoresistor each formed on upper and lower portions of a flexible part and calculating an inertial force by summing detection signals depending on the displacements and can be implemented in a small and light type, and a method of manufacturing the same. 
         [0011]    According to a preferred embodiment of the present invention, there is provided an inertial sensor, including: a flexible part; a mass body connected to the flexible part; and a support part connected to the flexible part and supporting the mass body in a floated state to displace the mass body, wherein the flexible part has an upper piezoresistor disposed on one surface thereof and a lower piezoresistor disposed on the other surface thereof to detect a displacement of the mass body. 
         [0012]    The flexible part may include an upper piezoresistance wiring electrically connected to the upper piezoresistor and a lower piezoresistance wiring electrically connected to the lower piezoresistor. 
         [0013]    The flexible part may include membrane layers formed on the lower piezoresistor and the lower piezoresistance wiring. 
         [0014]    The flexible part may include a metal wiring electrically connected to the upper piezoresistance wiring and the lower piezoresistance wiring, the metal wiring being exposed to an outside of the flexible part. 
         [0015]    The flexible part may be provided with a metal via hole through which the metal wirings are connected to the upper piezoresistance wiring and the lower piezoresistance wiring. 
         [0016]    The flexible part may include a passivation layer covering the upper piezoresistor and the upper piezoresistance wiring. 
         [0017]    The upper piezoresistor and the lower piezoresistor may be adjacently disposed to the mass body. 
         [0018]    The upper piezoresistor and the lower piezoresistor may be each disposed two by two at both sides based on the mass body to be symmetrical with each other. 
         [0019]    The upper and lower piezoresistance wirings may be adjacently disposed to the support part. 
         [0020]    The upper piezoresistor and the lower piezoresistor may be each adjacent to the support part and may be disposed two by two to be symmetrical with each other. 
         [0021]    According to another preferred embodiment of the present invention, there is provided a method of manufacturing an inertial sensor, including: (A) forming a lower piezoresistance wiring on a base substrate; (B) forming a lower piezoresistor to contact the lower piezoresistance wiring; (C) forming a membrane layer on the lower piezoresistor and the lower piezoresistance wiring; and (D) forming the upper piezoresistor and the piezoresistance wiring on the membrane layer to contact an upper piezoresistor and an upper piezoresistance wiring. 
         [0022]    In the (A), a silicon oxide layer may be disposed on the base substrate and the lower piezoresistance wiring may be disposed on the silicon oxide layer. 
         [0023]    In the (A), the lower piezoresistance wiring may be formed two by two at both sides based on a central portion of the base substrate. 
         [0024]    In the (B), the lower piezoresistor may be disposed two by two at both sides based on a central portion of the base substrate to form a first lower piezoresistor, a second lower piezoresistor, a third lower piezoresistor, and a fourth lower piezoresistor. 
         [0025]    In the (D), the upper piezoresistor may be disposed two by two at both sides based on a central portion of the base substrate to form a first upper piezoresistor, a second upper piezoresistor, a third upper piezoresistor, and a fourth upper piezoresistor. 
         [0026]    The method of manufacturing an inertial sensor may further include: after the (D), (E) forming a passivation layer on the upper piezoresistor and the upper piezoresistance wiring. 
         [0027]    The method of manufacturing an inertial sensor may further include: after the (E), (F) forming a via hole through which a metal wiring insertion path is formed in the membrane layer and the passivation layer to connect the metal wiring to the lower piezoresistance wiring and the upper piezoresistance wiring, respectively. 
         [0028]    The method of manufacturing an inertial sensor may further include: after the (F), (G) filling a metal in the via hole. 
         [0029]    The method of manufacturing an inertial sensor may further include: after the (G), (H) deposing a metal wiring to contact the metal filled in the via hole and forming a pattern. 
         [0030]    The method of manufacturing an inertial sensor may further include: after the (H), (I) forming a mass body and a support part by selectively etching the base substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0032]      FIG. 1  is a cross-sectional view schematically illustrating an inertial sensor according to a preferred embodiment of the present invention; 
           [0033]      FIG. 2  is a diagram illustrating a wheatstone bridge structure according to a first preferred embodiment for one-axis direction signal detection, in the inertial sensor illustrated in  FIG. 1 ; 
           [0034]      FIG. 3  is a diagram illustrating a wheatstone bridge structure according to a first preferred embodiment for the other-axis direction signal detection, in the inertial sensor illustrated in  FIG. 1 ; 
           [0035]      FIG. 4  is a diagram illustrating a wheatstone bridge structure according to a second preferred embodiment for one-axis direction signal detection, in the inertial sensor illustrated in  FIG. 1 ; 
           [0036]      FIG. 5  is a diagram illustrating a wheatstone bridge structure according to a second preferred embodiment for the other-axis direction signal detection, in the inertial sensor illustrated in  FIG. 1 ; 
           [0037]      FIG. 6  is flow chart schematically illustrating a method of manufacturing an inertial sensor illustrated in  FIG. 1 ; and 
           [0038]      FIGS. 7A to 7I  are process diagrams schematically illustrating the method of manufacturing an inertial sensor illustrated in  FIG. 6 ,  FIG. 7A  is a diagram illustrating a process of forming a lower piezoresistance wiring,  FIG. 7B  is a diagram illustrating a process of forming a lower piezoresistor,  FIG. 7C  is a diagram illustrating a process of forming a membrane layer,  FIG. 7D  is a diagram illustrating a process of forming an upper piezoresistor and an upper piezoresistance wiring,  FIG. 7E  is a diagram illustrating a process of forming a passivation layer,  FIG. 7F  is a diagram illustrating a process of forming a via hole,  FIG. 7G  is a diagram illustrating a process of filling a metal,  FIG. 7H  is a diagram illustrating a process of depositing a metal and forming a pattern, and  FIG. 7I  is a diagram illustrating a process of forming a mass body and a support part. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]    The objects, features and advantages of the present invention will be more clearly understood from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings. Throughout the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant descriptions thereof are omitted. Further, in the following description, the terms “first,” “second,” “one side,” “the other side” and the like are used to differentiate a certain component from other components, but the configuration of such components should not be construed to be limited by the terms. Further, in the description of the present invention, when it is determined that the detailed description of the related art would obscure the gist of the present invention, the description thereof will be omitted. 
         [0040]    Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. 
         [0041]      FIG. 1  is a cross-sectional view schematically illustrating an inertial sensor according to a preferred embodiment of the present invention. As shown, an inertial sensor  100  includes a flexible part  110 , a mass body  120 , and a support part  130 . 
         [0042]    Further, the flexible part  110  is formed in a plate shape and is configured of a flexible substrate, such as a membrane, a beam, and the like, which have elasticity to allow the mass body  120  to be displaced. 
         [0043]    Further, the mass body  120  is coupled with one surface of the flexible part  110  and is displaced by inertial force, external force, Coriolis force, driving force, and the like. 
         [0044]    Further, the support part  130  is coupled with one surface of the flexible part and supports the mass body  120  in a floated state to be able to displace the mass body  120 . 
         [0045]    In this case, the mass body  120  is disposed at a central portion of the flexible part  110 , the support part  130  is formed in a hollow shape, such that the mass body is disposed in the hollow part to be displaced, and as the support part  130  is disposed at an edge portion of the flexible part  110 , a space to allow the mass body  120  to be displaced is secured. 
         [0046]    Further, the mass body  120  may be formed in a cylindrical shape and the support part  130  may be formed in a cylindrical shape or a square pillar shape. Further, the shape of the mass body  120  and the support part  130  is not limited thereto, and therefore may be formed in any shape known in the art. 
         [0047]    Meanwhile, the flexible part  110 , the mass body  120 , and the support part  130  which are described above may be formed by selectively etching a silicon on insulator (SOI) substrate on which a micro electro mechanical systems (MEMS) process is easily performed. 
         [0048]    Therefore, a silicon oxide layer (SiO2)  115  of the SOI substrate may remain between the mass body  120  and the flexible part  110  and between the support part  130  and the flexible part  110 . However, the flexible part  110 , the mass body  120 , and the support part  130  are not necessarily formed by etching the SOI substrate, but may also be formed by etching a general silicon substrate, or the like. 
         [0049]    Hereinafter, the technical configuration, the shape, the organic coupling, and the acting effect of the flexible part of the inertial sensor according to the preferred embodiment of the present invention will be described in more detail. 
         [0050]    The flexible part  110  is configured of an upper piezoresistor  111 , a lower piezoresistor  112 , a piezoresistance wiring  113 , a metal wiring  114 , the silicon oxide layer  115 , a membrane layer  116 , and a passivation layer  117 . 
         [0051]    Further, as the laminated order, a lower portion of the flexible part  110  coupled with the mass body  120  is provided with the silicon oxide layer  115  and an upper portion of the silicon oxide layer  115  is provided with the lower piezoresistor  112  and a lower piezoresistance wiring  113   b . Further, the membrane layer  116  is disposed on the lower piezoresistor  112  and the piezoresistance wiring and the upper piezoresistor  111  and the upper piezoresistance wiring  113   a  are disposed on the membrane layer  116 . Further, the passivation layer  117  is disposed on the upper piezoresistor  111  and the upper piezoresistance wiring  113   a  and the metal wiring  114  is exposed on the passivation layer  117 . 
         [0052]    Further, the flexible part  110  is formed in a duplex type in which the upper piezoresistor  111  is disposed on one surface thereof and the lower piezoresistor  112  is disposed on the other surface thereof. Further, the sensing sensitivity and efficiency may be improved by calculating the inertial force by summing detected signals from the upper piezoresistor  111  and the lower piezoresistor  112 , respectively. 
         [0053]    In more detail, based on the laminated direction, the upper piezoresistor  111  is disposed on the membrane layer  116  and the lower piezoresistor  112  is disposed beneath the membrane layer  116 . This considers the fact that when the flexible part  110  is displaced, a stress most frequently occurs on the upper and lower portions of the flexible part. 
         [0054]    Further, the upper piezoresistor  111  and the lower piezoresistor  112  have resistance changed in response to an elastic deformation of the flexible part  110 . Further, the upper piezoresistor  112  and the lower piezoresistor  112  are adjacently disposed to the mass body  120  coupled with the flexible part  110 . This considers the fact that when the mass body is displaced, a stress most frequently occurs at a portion adjacent to the mass body  120 . 
         [0055]    Further, the upper piezoresistor  112  and the lower piezoresistor  112  are adjacently disposed to the support part  130  coupled with the flexible part  110 . This considers the fact that when the mass body  120  is displaced, a stress most frequently occurs at a portion adjacent to the support part  130 . 
         [0056]    That is, the upper piezoresistor  111  is configured of a first upper piezoresistor  111   a , a second upper piezoresistor  111   b , a third upper piezoresistor  111   c , and a fourth upper piezoresistor  111   d  and the first upper piezoresistor  111   a  and the fourth upper piezoresistor  111   d  are adjacently disposed to the support part and the second upper piezoresistor  111   b  and the third upper piezoresistor  111   c  are adjacently disposed to the mass body  120 . 
         [0057]    Further, the lower piezoresistor  112  is configured of a first lower piezoresistor  112   a , a second lower piezoresistor  112   b , a third lower piezoresistor  112   c , and a fourth lower piezoresistor  112   d  and the first lower piezoresistor  112   a  and the fourth lower piezoresistor  112   d  are adjacently disposed to the support part and the second lower piezoresistor  112   b  and the third lower piezoresistor  112   c  are adjacently disposed to the mass body  120 . 
         [0058]    Further, the upper piezoresistor  111  and the lower piezoresistor  112  are applied with a stress in an opposite direction to each other when the flexible part  110  is bent and sum a signal depending on the applied stress to perform sensing. Further, the signal detection and the sensing method depending on the upper piezoresistor  111  and the lower piezoresistor  112  will be described in detail with reference to  FIGS. 2 to 5 . 
         [0059]    Next, the piezoresistance wiring  113  is configured of an upper piezoresistance wiring  113   a  electrically connected to the upper piezoresistor  111  and a lower piezoresistance wiring  113   b  electrically connected to the lower piezoresistor  112 . 
         [0060]    Further, the metal wiring  114  is electrically connected to the upper piezoresistance wiring  113   a  and the lower piezoresistance wiring  113   b , respectively and is exposed to the outside of the flexible part  110  to be connected to the external substrate, and the like, through wire bonding, and the like, to apply the detected signal from the upper piezoresistor  111  and the lower piezoresistor  112 . 
         [0061]    Further, the membrane layer  116  may be formed with a via hole to connect the metal wiring  114  to the upper piezoresistance wiring  113   a  and the lower piezoresistance wiring  113   b , respectively. 
         [0062]    Further, as described above, the silicon oxide layer  115  is disposed between the mass body  120  and the flexible part  110  and between the support part  130  and the flexible part  110  and the lower piezoresistor  112  and the lower piezoresistance wiring  113   b  may be disposed on the silicon oxide layer  115 . 
         [0063]    Further, the passivation layer  117  is to protect the upper structure of the flexible part  110 , that is, the upper piezoresistor  111  and the upper piezoresistance wiring  113   a . Further, the passivation layer  117  may be made of silicon oxide or silicon nitride. 
         [0064]    By the above configuration, the inertial sensor according to the preferred embodiment of the present invention detects displacements from the upper piezoresistor  111  and the lower piezoresistor  112  each formed on the upper and lower portions of the flexible part  110  and calculates the inertial force by summing the detection signal depending on the detected displacements, such that the inertial sensor may have the improved sensing sensitivity and efficiency and may be implemented in a small and light type. 
         [0065]    Hereinafter, the signal detection by the inertial sensor according to the preferred embodiment of the present invention will be described in detail with reference to  FIGS. 2 to 5 . 
         [0066]      FIG. 2  is a diagram illustrating a wheatstone bridge structure according to a first preferred embodiment for one-axis direction signal detection, in the inertial sensor illustrated in  FIG. 1 . In more detail,  FIG. 2A  illustrates a wheatstone bridge structure for detecting a resistance change of the upper piezoresistor with respect to an X-axis direction and  FIG. 2B  is a wheatstone bridge structure for detecting a resistance change of the lower piezoresistor with respect to an X-axis direction. 
         [0067]    As illustrated, a two-fold signal may be obtained by summing voltages applied between VX 1 − and VX 1 + and between VX 2 − and VX 2 +. Further, when 1G is applied in an X-axis direction, the resistance change of the upper piezoresistor and the lower piezoresistor is as shown in the following Table 1. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 Upper Piezoresistor 
                   
               
             
          
           
               
                   
                 111a 
                 111b 
                 111c 
                 111d 
               
               
                   
                   
               
             
          
           
               
                   
                 Resistance 
                 − 
                 + 
                 − 
                 + 
               
               
                   
                 Change 
               
               
                   
                   
               
             
          
           
               
                   
                 Lower Piezoresistor 
                   
               
             
          
           
               
                   
                 112a 
                 112b 
                 112c 
                 112d 
               
               
                   
                   
               
             
          
           
               
                   
                 Resistance 
                 + 
                 − 
                 + 
                 − 
               
               
                   
                 Change 
               
               
                   
                   
               
             
          
         
       
     
         [0068]      FIG. 3  is a diagram illustrating a wheatstone bridge structure according to a first preferred embodiment for the other-axis direction signal detection, in the inertial sensor illustrated in  FIG. 1 . In more detail,  FIG. 3A  illustrates a wheatstone bridge structure for detecting a resistance change of the upper piezoresistor with respect to a Z-axis direction and  FIG. 3B  is a wheatstone bridge structure for detecting a resistance change of the lower piezoresistor with respect to a Z-axis direction. 
         [0069]    As illustrated, a two-fold signal may be obtained by summing voltages applied between VZ 1 − and VZ 1 + and between VZ 2 − and VZ 2 +. Further, when 1G is applied in a Z-axis direction, the resistance change of the upper piezoresistor and the lower piezoresistor is as shown in the following Table 1. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
             
               
                   
                 Upper Piezoresistor 
                   
               
             
          
           
               
                   
                 111a 
                 111b 
                 111c 
                 111d 
                   
               
               
                   
                   
               
             
          
           
               
                   
                 Resistance 
                 + 
                 − 
                 − 
                 + 
               
               
                   
                 Change 
               
               
                   
                   
               
             
          
           
               
                   
                 Lower Piezoresistor 
                   
               
             
          
           
               
                   
                 112a 
                 112b 
                 112c 
                 112d 
               
               
                   
                   
               
             
          
           
               
                   
                 Resistance 
                 − 
                 + 
                 + 
                 − 
               
               
                   
                 Change 
               
               
                   
                   
               
             
          
         
       
     
         [0070]      FIG. 4  is a diagram illustrating a wheatstone bridge structure according to a second preferred embodiment for one-axis direction signal detection, in the inertial sensor illustrated in  FIG. 1 . As illustrated, the two-fold signal may be obtained by summing the voltages of the upper piezoresistor and the lower piezoresistor applied between VX− and VX+. Further, when 1 G is applied in an X-axis direction, the resistance change of the upper piezoresistor and the lower piezoresistor is as shown in the following Table 3. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
             
             
               
                   
                 Upper Piezoresistor 
                   
               
             
          
           
               
                   
                 111a 
                 111b 
                 111c 
                 111d 
               
               
                   
                   
               
             
          
           
               
                   
                 Resistance 
                 − 
                 + 
                 − 
                 + 
               
               
                   
                 Change 
               
               
                   
                   
               
             
          
           
               
                   
                 Lower Piezoresistor 
                   
               
             
          
           
               
                   
                 112a 
                 112b 
                 112c 
                 112d 
               
               
                   
                   
               
             
          
           
               
                   
                 Resistance 
                 + 
                 − 
                 + 
                 − 
               
               
                   
                 Change 
               
               
                   
                   
               
             
          
         
       
     
         [0071]      FIG. 5  is a diagram illustrating a wheatstone bridge structure according to a second preferred embodiment for the other-axis direction signal detection, in the inertial sensor illustrated in  FIG. 1 . As illustrated, the two-fold signal may be obtained by summing the voltages of the upper piezoresistor and the lower piezoresistor applied between VZ− and VZ+. Further, when 1 G is applied in a Z-axis direction, the resistance change of the upper piezoresistor and the lower piezoresistor is as shown in the following Table 3. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
             
             
               
                   
                 Upper Piezoresistor 
                   
               
             
          
           
               
                   
                 111a 
                 111b 
                 111c 
                 111d 
               
               
                   
                   
               
             
          
           
               
                   
                 Resistance 
                 + 
                 − 
                 − 
                 + 
               
               
                   
                 Change 
               
               
                   
                   
               
             
          
           
               
                   
                 Lower Piezoresistor 
                   
               
             
          
           
               
                   
                 112a 
                 112b 
                 112c 
                 112d 
               
               
                   
                   
               
             
          
           
               
                   
                 Resistance 
                 − 
                 + 
                 + 
                 − 
               
               
                   
                 Change 
               
               
                   
                   
               
             
          
         
       
     
         [0072]    Hereinafter, a method of manufacturing an inertial sensor according to the preferred embodiment of the present invention will be described in more detail with reference to  FIGS. 6 and 7 . 
         [0073]      FIG. 6  is flow chart schematically illustrating a method of manufacturing an inertial sensor illustrated in  FIG. 1 . As illustrated, a method of manufacturing an inertial sensor (S 100 ) includes forming a lower piezoresistance wiring (S 110 ), forming a lower piezoresistor (S 120 ), forming a membrane layer (S 130 ), forming an upper piezoresistor and an upper piezoresistance wiring (S 140 ), forming a passivation layer (S 150 ), forming a via hole (S 160 ), filling a metal (S 170 ), depositing a metal and forming a pattern (S 180 ), and forming a mass body and a support part (S 190 ). 
         [0074]      FIG. 7A  illustrate the forming of the lower piezoresistor wiring. In more detail, the lower piezoresistance wiring  113   b  is formed on an SOI substrate or a base substrate on which the mass body and the support part are disposed. Further, the silicon oxide layer  115  may be disposed on the base substrate and the lower piezoresistance wiring  113   b  may be disposed on one surface of the silicon oxide layer  115 . 
         [0075]    In this case, the SOI may be implemented as an N type SOL Further, the lower piezoresistor is disposed two by two at both sides of the piezoresistance wiring based on the mass body to be formed by a post-process and the lower piezoresistance wirings  113   b  are each disposed two by two to be each connected to the lower piezoresistors, respectively. 
         [0076]      FIG. 7B  illustrates the forming of the lower piezoresistor. In more detail, the lower piezoresistor  112  is disposed to contact the lower piezoresistance wiring  113   b . Further, since the lower piezoresistance wiring  113   b  is disposed two by two at both sides based on the central portion of the base substrate or the SOI, the lower piezoresistors are each disposed two by two at both sides based on the central portion of the flexible part to be each connected to thereto, such that the lower piezoresistor is configured of the first lower piezoresistor  112   a , the second lower piezoresistor  112   b , the third lower piezoresistor  112   c , and the fourth lower piezoresistor  112   d.    
         [0077]      FIG. 7C  illustrates the forming of the membrane layer. In more detail, the membrane layer  116  is disposed on the lower piezoresistor  112  and the lower piezoresistance wiring  113   b . As the preferred embodiment, the membrane layer  116  may be formed by depositing polysilicon and the polysilicon may be implemented as an N type polysilicon. 
         [0078]      FIG. 7D  illustrates the forming of the upper piezoresistor and the upper piezoresistance wiring. In more detail, the upper piezoresistor  111  and the upper piezoresistance wiring  113   a  are disposed on the membrane layer  116 . 
         [0079]    Further, the upper piezoresistor  111  and the upper piezoresistance wiring  113   a  are formed to contact each other. Further, the upper piezoresistor  111  is formed to face the lower piezoresistor  112 . That is, the upper piezoresistors  111  are each disposed two by two at both sides based on the central portion of the flexible part and is configured of the first upper piezoresistor  111   a , the second upper piezoresistor  111   b , the third upper piezoresistor  111   c , and the fourth upper piezoresistor  111   d.    
         [0080]    Further, the upper piezoresistance wiring  113   a  is formed to be connected to the first upper piezoresistor  111   a , the second upper piezoresistor  111   b , the third upper piezoresistor  111   c , and the fourth upper piezoresistor  111   d , respectively. 
         [0081]    Further, the upper piezoresistance wiring  113   a  may be formed to face the lower piezoresistance wiring  113   b  connected to the lower piezoresistor  112 . 
         [0082]      FIG. 7E  illustrates the forming of the passivation layer. As illustrated, the passivation layer  117  is disposed on the upper piezoresistor  111  and the upper piezoresistance wiring  113   a . Further, the passivation layer  117  is formed to cover all of the upper piezoresistor  111  and the upper piezoresistance wiring  113   a  and the membrane layer  116  having the upper piezoresistor  111  and the upper piezoresistance wiring  113   a  formed thereon. Further, the passivation layer  117  may be made of silicon oxide or silicon nitride. 
         [0083]      FIG. 7F  illustrates the forming of the via hole. As illustrated, the via hole  116   a  is to form a metal wiring insertion path through which the lower piezoresistance wiring  113   b  and the upper piezoresistance wiring  113   a  are each connected to the metal wiring  114 . 
         [0084]    To this end, the via holes  116   a  and  117   a  are formed in the passivation layer  117  and the membrane layer  116 . In this case, the via holes  116   a  and  117   a  are formed to connect the lower piezoresistance wiring  113   b  and the upper piezoresistance wiring  113   a  from the outside. 
         [0085]      FIG. 7G  illustrates the filling of the metal. As illustrated, a metal  114   a  is filled in the via holes  116   a  and  117   a , respectively, illustrated in  FIG. 6F . In this case, the filled metal  114   a  is injected to contact the lower piezoresistance wiring  113   a  or the upper piezoresistance wiring  113   a.    
         [0086]      FIG. 7H  illustrates the depositing of the metal and the forming of the pattern. As illustrated, the metal wiring  114  is deposited to contact the metal  114   a  filled in the via hole and forms the pattern. 
         [0087]      FIG. 7I  illustrates the forming of the mass body and the support part. As illustrated, the mass body  120  and the support part  130  are formed by selectively etching the base substrate, such as the SOI substrate, and the like. Further, the mass body  120  is adjacently disposed to the lower piezoresistor  112  and the support part  130  is adjacently disposed to the lower piezoresistor  112 . 
         [0088]    By the above configuration, the inertial sensor according to the preferred embodiment of the present invention includes the upper and lower piezoresistors to be implemented as a small and light type and improve the sensitivity. 
         [0089]    According to the preferred embodiments of the present invention, it is possible to obtain the inertial sensor which can have the improved sensing sensitivity and the efficiency by detecting the displacements from the upper piezoresistor and the lower piezoresistor each formed on the upper and lower portions of the flexible part and calculating the inertial force by summing the detection signals depending on the displacements and can be implemented in a small and light type, and the method of manufacturing the same. 
         [0090]    Although the embodiments of the present invention have been disclosed for illustrative purposes, it will be appreciated that the present invention is not limited thereto, and those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention. 
         [0091]    Accordingly, any and all modifications, variations or equivalent arrangements should be considered to be within the scope of the invention, and the detailed scope of the invention will be disclosed by the accompanying claims.