Abstract:
Disclosed herein is an acceleration sensor including: a mass; a flexible beam on which an electrode or a piezoresistive element is disposed and the mass is coupled; and a support part connecting to and supporting the flexible beam and having therein a stress isolating slit facing the mass, wherein the mass, the flexible beam and the support part are formed by coupling first and second substrates, wherein the first substrate has a first masking pattern formed thereon corresponding to the flexible beam, the mass and the support part and the second substrate has a second masking pattern formed thereon corresponding to the mass and the support part.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2013-0103025, filed on Aug. 29, 2013, entitled “Acceleration Sensor,” 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 acceleration sensor. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, an inertial sensor is being variously used in automobiles, airplanes, mobile communication terminals, toys and the like. It includes a 3-axis acceleration sensor and an angular velocity sensor to measure acceleration and angular velocity on x-, y-, and z-axes. Further, it is being developed to have high performance and to be small in order to detect minimal acceleration. 
         [0006]    The acceleration sensor included in the inertial sensor includes a technical feature to convert motions of a mass and a flexible beam into an electric signal. The types of acceleration sensors include a piezoresistive type in which the motion of the mass is detected from a change in resistance of a piezo element located on a flexible beam, and a capacitive type in which the motions of the mass is detected from a change in capacitance between fixed electrodes. 
         [0007]    The piezoresistive type uses an element having a resistance varying by stress. For example, the resistance increases where tensile stress is distributed and decreases where compressive stress is distributed. 
         [0008]    Further, in the piezoresistive type acceleration sensors according to the prior art, including one disclosed in Patent Document below, the area of the beam is reduced in order to increase sensitivity, so that it is vulnerable to shock, and especially reliability on a fall is lowered. 
         [0009]    Further, in order to increase sensitivity, it is preferred to locate a piezoresistive element at an end of the flexible part where stress is concentrated. However, if there is a variation in the angle of a sidewall during the etching process for forming the flexible part, the distance between the end of the flexible part and the piezo element is changed, so that sensitivity is lowered. Moreover, the thickness of the mass has to be thick in order to increase sensitivity, whereas a variation in the angle of the sidewall becomes greater as the etching depth becomes deeper. 
         [0010]    Additionally, if stress, a change in temperature, mechanical shock and vibration from outside and the like are applied to a beam-like flexible part in an acceleration sensor, rigidity is changed as tension changes, and thus sensitivity is changed. Excessive tension causes the beam to be broken. Moreover, since a stress isolating beam has a narrow width to isolate external weight, when the thickness of the stress isolating beam and that of the mass is the same, it is difficult to form a desired width due to a narrow variation in the angle of the sidewall for etching. In the worst case, the flexible part and the stress isolating beam are separated. 
       PRIOR ART DOCUMENT  
     [Patent Document] 
       [0011]    (Patent Document 1) US 2006/0156818 A 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention has been made in an effort to provide an acceleration sensor which maximally isolates external weight by way of lowering rigidity of a stress isolating beam. 
         [0013]    Further, the present invention has been made in an effort to provide an acceleration sensor capable of improving sensitivity and reducing sensitivity variations by way of configuring the acceleration sensor in multiple layers having first and second substrates to form components through first and second masking patterns, thereby forming a flexible beam having a shallow etching depth and locating a piezo element at the optimum position. 
         [0014]    According to a first preferred embodiment of the present invention, there is provided an acceleration sensor including: a mass; a flexible beam on which an electrode or a piezoresistive element is disposed and the mass is coupled; and a support part connecting to and supporting the flexible beam and having therein a stress isolating slit facing the mass, wherein the mass, the flexible beam and the support part are formed by coupling first and second substrates, wherein the first substrate has a first masking pattern formed thereon corresponding to the flexible beam, the mass and the support part and the second substrate has a second masking pattern formed thereon corresponding to the mass and the support part. 
         [0015]    The support part may include therein a stress isolating beam by the presence of the stress isolating slit, and the stress isolating beam may be formed with the first substrate. 
         [0016]    The stress isolating beam may include: a membrane part connected to the flexible beam; and a stress isolating part perpendicularly connected to the membrane part. 
         [0017]    A coupling portion of the stress isolating part coupled with the membrane part may be smaller than the membrane part in area. 
         [0018]    The stress isolating part may include: a beam part perpendicularly coupled with the membrane part; and a protruding part protruding from the beam part toward the flexible beam. 
         [0019]    The flexible beam may be formed with the first substrate. 
         [0020]    The mass may include: a first mass formed with the first substrate; and a second mass formed with the second substrate. 
         [0021]    The first masking pattern may be formed on a surface of the first mass facing the second mass, and the second masking pattern may be formed on the second mass. 
         [0022]    The first masking pattern may be larger than the second masking pattern in area. 
         [0023]    The support part may include: a first support part formed with the first substrate; and a second support part formed with the second substrate. 
         [0024]    The first masking pattern may be formed between the first support part and the second support part, and the second masking pattern may be formed on the second support part. 
         [0025]    The first masking pattern may be larger than the second masking pattern in area. 
         [0026]    The second support part may be smaller than the first support part in area. 
         [0027]    The first masking pattern may face the second substrate. 
         [0028]    The acceleration sensor may further include a lower cover coupled with one surface of the support part, and the second masking pattern may face the lower cover. 
         [0029]    According to a second preferred embodiment of the present invention, there is provided an acceleration sensor including: a mass; a flexible beam on which an electrode or a piezoresistive element is disposed and the mass is coupled; and a support part connecting to and supporting the flexible beam and having therein a stress isolating slit facing the mass, wherein the mass, the flexible beam and the support part are formed by coupling first and second substrates, wherein the first substrate has a first masking pattern formed thereon corresponding to the flexible beam, the mass and the support part. 
         [0030]    The support part may include therein a stress isolating beam by the presence of the stress isolating slit, and the stress isolating beam may be formed with the first substrate. 
         [0031]    The flexible beam may be formed with the first substrate. 
         [0032]    The mass may include: a first mass formed with the first substrate; and a second mass formed with the second substrate. 
         [0033]    The first masking pattern may be formed between the first mass and the second mass, and the first mass is larger than the second mass in area. 
         [0034]    The support part may include: a first support part formed with the first substrate; and a second support part formed with the second substrate, wherein the first masking pattern is formed between the first support part and the second support part, wherein the first support part is larger than the second support part in area. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    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: 
           [0036]      FIG. 1  is a plan view schematically showing an acceleration sensor according to a preferred embodiment of the present invention; 
           [0037]      FIG. 2  is a simplified cross-sectional view of the acceleration sensor taken along line A-A in  FIG. 1 ; 
           [0038]      FIG. 3  is a simplified cross-sectional view of the acceleration sensor taken along line B-B in  FIG. 1 ; 
           [0039]      FIG. 4A  is an enlarged view of a stress isolating beam which is shown as portion C in  FIG. 1 ; 
           [0040]      FIG. 4B  is an enlarged view of a stress isolating beam which is shown as portion D in  FIG. 2 ; 
           [0041]      FIG. 5A  is a simplified enlarged plan view of a stress isolating beam according to another preferred embodiment; 
           [0042]      FIG. 5B  is a simplified enlarged cross-sectional view of the stress isolating beam according to the another preferred embodiment; 
           [0043]      FIG. 6A  is a simplified enlarged plan view of a stress isolating beam according to yet another preferred embodiment; 
           [0044]      FIG. 6B  is a simplified enlarged cross-sectional view of the stress isolating beam according to the yet another preferred embodiment; 
           [0045]      FIG. 6C  is a simplified enlarged perspective view of the stress isolating beam according to the yet another preferred embodiment; and 
           [0046]      FIG. 7  is a simplified cross-sectional view of an acceleration sensor according to another preferred embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]    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. 
         [0048]    Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. 
         [0049]      FIG. 1  is a plan view schematically showing an acceleration sensor according to a preferred embodiment of the present invention,  FIG. 2  is a schematic cross-sectional view of the acceleration sensor taken along line A-A in  FIG. 1 , and  FIG. 3  is a schematic cross-sectional view of the acceleration sensor taken along line B-B in  FIG. 1 . 
         [0050]    As shown, an acceleration sensor  100  includes a flexible beam  110 , a mass  120  and a support part  130 . 
         [0051]    Specifically, the acceleration sensor  100  is formed by coupling a first substrate  100   a  with a second substrate  100   b  and performing etching in a predetermined pattern. 
         [0052]    To this end, the first substrate  100   a  has a first masking pattern  101   a  corresponding to the flexible beam  110 , the mass  120  and the support part  130  formed thereon, and the second substrate  100   b  has a second masking pattern  101   b  corresponding to the mass  120  and the support part  130  formed thereon. 
         [0053]    In addition, the support part  130  has a stress isolating slit  131  formed therein, and the stress isolating beam  132  is formed by the presence of the stress isolating slit  131 . 
         [0054]    Further, the components of the acceleration sensor  100  may be formed with the first substrate  100   a  only or with the first substrate  100   a  and the second substrate  100   b.    
         [0055]    That is, the flexible beam  110  is formed with the first substrate  100   a,  and the mass  120  includes the first mass  120   a  formed with the first substrate  100   a  and the second mass  120   b  formed with the second substrate  100   b.    
         [0056]    In addition, the first masking pattern  101   a  is formed on one surface of the first mass  120   a  facing the second mass  120   b,  and the second masking pattern  101   b  is formed on the second mass  120   b.    
         [0057]    Then, the first masking pattern  101   a  has a larger area than the second masking pattern  101   b,  and thus the first mass has a larger area than the second mass. 
         [0058]    This is resulted from the etching order, in which etching is done using the second masking pattern  101   b  first and then using the first masking pattern  101   a.    
         [0059]    Further, the support part  130  includes a first support part  130   a  formed with the first substrate  100   a  and a second support part  130   b  formed with the second substrate  100   b.    
         [0060]    In addition to  FIGS. 2 and 3 , as shown in  FIGS. 4A and 4B , the stress isolating slit  131  is formed in the first support part  130   a  and the stress isolating beam  132  is formed by the presence of the stress isolating slit  131 . That is, the stress isolating beam  132  is formed with the first substrate  100   a.    
         [0061]    Further, the first masking pattern is formed between the first support part  130   a  and the second support part  130   b,  and the second masking pattern is formed on the second support part  130   b.  Then, the first masking pattern  101   a  has a larger area than the second masking pattern  101   b . Accordingly, the second support part  130   b  has a smaller area than the first support part  130   a.    
         [0062]    Further, on one surface of the first substrate  100   a,  the first masking pattern  101   a  for forming the flexible beam  110 , the first mass  120   a  and the first support part  130   a  is formed facing the second substrate  100   b.    
         [0063]    Further, on one surface of the second substrate  100   b,  the second masking pattern  101   b  for forming the second mass  120   b  and the second support part  130   b  is formed facing a lower cover  140 . 
         [0064]    As described above, the acceleration sensor  100  according to the present invention is configured in multiple layers having the first substrate  100   a  and the second substrate  100   b  to form components through the first masking pattern  101   a  and the second masking pattern  101   b , respectively, thereby forming a flexible beam having a shallow etching depth and maintaining a piezo element  111  at the optimum position. Therefore, sensitivity can be improved and variation in sensitivity can be reduced, as well as maximally isolating external weight. 
         [0065]    Hereinafter, components of the acceleration sensor according to the preferred embodiment of the present invention and the relationship therebetween will be described in detail. 
         [0066]    More specifically, the flexible beam  110  has a plate shape and is a flexible substrate such as an elastic membrane or a beam to allow the mass  120  to be displaced. 
         [0067]    In addition, on one surface of the flexible beam  110 , a piezoresistive element  111  is formed. 
         [0068]    Further, the mass  120  is coupled with one surface of the flexible beam  110  and is displaced by inertial force, external force, Coriolis force, driving force and the like. 
         [0069]    Additionally, the support part  130  is coupled with one surface of the flexible beam and supports the mass  120  such that it is floated so as to be displaced. 
         [0070]    Here, the mass  120  is located at the center of the flexible beam  110 , the support part  130  has a hollow portion, such that the mass  120  is located in the hollow portion so that it is displaceable. Further, the support part  130  is located along the edge of the flexible beam  110  so as to give space for the mass  120  to be displaced. 
         [0071]    Further, the mass  120  may have a square pillar shape, and the support part  130  may have a cylinder or a square pillar shape. Further, the shapes of the mass  120  and the support part  130  are not limited thereto but they may have any shape known in the art. 
         [0072]    In the preferred embodiment of the present invention in which an inertial sensor is implemented as the acceleration sensor, when external force is applied, the mass  120  is moved by a moment generated by the external force and the resistance value of the piezoresistive element  111  on the flexible beam  110  is changed by the displacement of the mass  120 . Then, acceleration is calculated by detecting the resistance value. 
         [0073]    Further, the acceleration sensor  100  according to the preferred embodiment of the present invention may further include a lower cover  140  coupled with one surface of the support part  130  so as to cover the mass  120 . 
         [0074]    Further, the acceleration sensor  100  according to the preferred embodiment of the present invention may further include an upper cover (not shown) coupled with one surface of the support part  130  so as to cover the piezoresistive element  111 . 
         [0075]      FIG. 5A  is a simplified enlarged plan view of a stress isolating beam according to another preferred embodiment; and  FIG. 5B  is a simplified enlarged cross-sectional view of the stress isolating beam according to the another preferred embodiment. 
         [0076]    As shown, the support part  230  has a slit  231  formed therein, and stress isolating beam  232  are formed by the presence of the slit  231 . 
         [0077]    The stress isolating beam  232  includes a membrane part  232   a  and a stress isolating part  232   b.  The membrane part  232   a  is connected to the flexible beam  210  while the stress isolating part  232   b  is perpendicularly connected to the membrane part  232   a.    
         [0078]    Then, the coupling portion of the stress isolating part  232   b  coupled with the membrane part  232   a  has a smaller area than the membrane part  232   a.    
         [0079]    That is, the stress isolating part  232   b  of the stress isolating beam  232  according to the another preferred embodiment of the present invention has a smaller area than the stress isolating beam  132  according to the preferred embodiment shown in  FIG. 4B , thereby minimizing the rigidity of the stress isolating beam. 
         [0080]      FIG. 6A  is a simplified enlarged plan view of a stress isolating beam according to yet another preferred embodiment;  FIG. 6B  is a simplified enlarged cross-sectional view of the stress isolating beam according to the yet another preferred embodiment; and  FIG. 6C  is a simplified enlarged perspective view of the stress isolating beam according to the yet another preferred embodiment. 
         [0081]    As shown, the support part  330  has a slit  331  formed therein, and a stress isolating beam  332  is formed by the presence of the slit  331 . 
         [0082]    The stress isolating beam  332  includes a membrane part  332   a  and a stress isolating part  332   b.  The membrane part  332   a  is connected to the flexible beam  310 , and the stress isolating part  332   b  is perpendicularly connected to the membrane part  332   a.    
         [0083]    Further, the stress isolating part  332   b  includes a beam part  332   b ′ and a protruding part  332   b″.    
         [0084]    Then, the coupling portion of the stress isolating part  332   b  coupled with the membrane part  332   a  has a smaller area than the membrane part  332   a.    
         [0085]    That is, the stress isolating beam  332  according to the yet another preferred embodiment of the present invention has a smaller area than the stress isolating beam  132  according to the preferred embodiment shown in  FIG. 4B , thereby minimizing the rigidity of the stress isolating beam as well as maximizing the sensitivity by locating a piezoresistive element  311  at an end of a flexible part. 
         [0086]      FIG. 7  is a simplified cross-sectional view of an acceleration sensor according to another preferred embodiment of the present invention. Compared to the acceleration sensor according to the preferred embodiment shown in  FIG. 1 , the acceleration sensor shown in  FIG. 7  has no remaining masking pattern exposed to the outside. 
         [0087]    As shown, an acceleration sensor  400  includes a flexible beam  410 , a mass  420  and a support part  430 . 
         [0088]    Specifically, the acceleration sensor  400  is formed by coupling a first substrate  400   a  with a second substrate  400   b  and performing etching in a predetermined pattern. 
         [0089]    To this end, on one surface of the first substrate  400   a,  a first masking pattern  401   a  corresponding to the flexible beam  410 , the mass  420  and the support part  430  is formed. 
         [0090]    In addition, the support part  430  has a stress isolating slit  431  formed therein, and the stress isolating beam  432  is formed by the presence of the stress isolating slit  431 . 
         [0091]    Further, the components of the acceleration sensor  400  may be formed with the first substrate  400   a  only or with the first substrate  400   a  and the second substrate  400   b.    
         [0092]    That is, the flexible beam  410  is formed with the first substrate  400   a,  and the mass  420  includes the first mass  420   a  formed with the first substrate  400   a  and the second mass  420   b  formed with the second substrate  400   b.    
         [0093]    In addition, the first masking pattern  401   a  is formed between the first mass  420   a  and the second mass  420   b.    
         [0094]    Then, the first mass  420   a  has a larger area than the second mass  420   b.    
         [0095]    Further, the support part  430  includes a first support part  430   a  formed with the first substrate  400   a  and a second support part  430   b  formed with the second substrate  400   b.    
         [0096]    In addition, the first support part  430   a  has a stress isolating slit  431  formed therein, and the stress isolating beam  432  is formed by the presence of the stress isolating slit  431 . That is, the stress isolating beam  432  is formed with the first substrate  400   a.    
         [0097]    In addition, the first masking pattern  401   a  is formed between the first support part  430   a  and the second support part  430   b.    
         [0098]    Then, the first support part  430   a  has a larger area than the second support part  430   b.    
         [0099]    Further, on one surface of the second substrate  400   b,  a second masking pattern (not shown) for forming the second mass  420   b  and the second support part  430   b  is formed facing a lower cover (not shown). 
         [0100]    The first masking pattern  401   a  and the second masking pattern thus configured and exposed to the outside are further etched, to produce the acceleration sensor  400  shown in  FIG. 4 . 
         [0101]    Further, in the acceleration sensor  400  according to another preferred embodiment of the present invention, the support part  430  may be implemented to form the stress isolating beam shown in  FIGS. 5 and 6 . 
         [0102]    As set forth above, according to the embodiments of the present invention, rigidity of a stress isolating beam can be lowered so that external weight is maximally isolated. Further, sensitivity can be improved and sensitivity variations can be lowered by way of configuring the acceleration sensor in multiple layers having first and second substrates to form components through first and second masking patterns, thereby forming a flexible beam having a shallow etching depth and locating a piezo element at the optimum position. 
         [0103]    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. 
         [0104]    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.