Patent Publication Number: US-2015059476-A1

Title: Acceleration sensor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2013-0103026, filed on Aug. 29, 2013, entitled “Acceleration Sensor”, which is hereby incorporated by reference in its entirety into this application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to an acceleration sensor. 
     2. Description of the Related Art 
     Generally, inertial sensors have been variously used in an automobile, an aircraft, a mobile communication terminal, a toy, and the like, and a three-axis acceleration and angular velocity sensor measuring X-axis, Y-axis, and Z-axis accelerations and angular velocities has been demanded and has been developed so as to have a high performance and a small size in order to detect a fine acceleration. 
     Among the inertial sensors as described above, an acceleration sensor has a technical feature of converting movement of a mass body and a flexible beam into an electrical signal, and is divided into a piezoresistive type acceleration sensor detecting the movement of the mass body from a resistance change of a piezoresistive element disposed in the flexible beam and a capacitive type acceleration sensor detecting the movement of the mass body from a capacitance change between the mass body and a fixed electrode. 
     In addition, in the piezoresistive type acceleration sensor, which uses an element having a resistance value changed by stress, for example, the resistance value is increased at a place at which tensile stress is distributed and is decreased at a place at which compressive stress is distributed. 
     Further, the piezoresistive type acceleration sensor according to the prior art including the Prior Art Document is vulnerable to impact since an area of the beam is decreased in order to increase sensitivity. 
     In addition, it is preferable that a piezoresistor is positioned at a distal end of a flexible part on which stress is concentrated in order to maximize sensitivity. However, when dispersion of a side wall angle is generated in an etching process for forming the flexible part, sensitivity is decreased at the distal end of the flexible part. Further, in order to improve sensitivity, a thickness of the mass body should be thick. However, the deeper the etching depth, the worse the dispersion of the side wall angle. 
     PRIOR ART DOCUMENT  
     Patent Document  
     (Patent Document 1) US 20060156818 A 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide an acceleration sensor capable of improving sensitivity and decreasing sensitivity dispersion by having a multi-layer structure of first and second substrates and including the respective components formed by first and second masking patterns to allow a flexible beam to be formed at a shallow etching depth and allow a piezoresistor to be maintained at an optimal position. 
     According to a preferred embodiment of the present invention, there is provided an acceleration sensor including: a mass body part; a flexible beam having an electrode or a piezoresistor disposed thereon and having the mass body part coupled thereto; and a support part having the flexible beam connected thereto and supporting the flexible beam, wherein the mass body part, the flexible beam, and the support part are formed by coupling first and second substrates to each other, one surface of the first substrate is provided with a first masking pattern corresponding to the flexible beam, the mass body part, and the support part, and one surface of the second substrate is provided with a second masking pattern corresponding to the mass body part and the support part. 
     The flexible beam may be formed of the first substrate. 
     The mass body part may include: a first mass body formed of the first substrate; and a second mass body formed of the second substrate. 
     The first mass body may have the first masking pattern formed on one surface thereof facing the second mass body, and the second mass body may have the second masking pattern formed thereon. 
     The first masking pattern may have an area wider than that of the second masking pattern. 
     The support part may include a first support part formed of the first substrate and a second support part formed of the second substrate. 
     The first and second support parts may have the first masking pattern formed therebetween, and the second support part may have the second masking pattern formed thereon. 
     The first masking pattern may have an area wider than that of the second masking pattern. 
     The second support part may have an area narrower than that of the first support part. 
     The first masking pattern may be formed so as to face the second substrate. 
     The acceleration sensor may further include a lower cover coupled to one surface of the support part, wherein the second masking pattern is formed so as to face the lower cover. 
     According to another preferred embodiment of the present invention, there is provided an acceleration sensor including: a mass body part; a flexible beam having an electrode or a piezoresistor disposed thereon and having the mass body part coupled thereto; and a support part having the flexible beam connected thereto and supporting the flexible beam, wherein the mass body part, the flexible beam, and the support part are formed by coupling first and second substrates to each other, and one surface of the first substrate is provided with a first masking pattern corresponding to the flexible beam, the mass body part, and the support part. 
     The flexible beam may be formed of the first substrate. 
     The mass body part may include: a first mass body formed of the first substrate; and a second mass body formed of the second substrate. 
     The first and second mass bodies may have the first masking pattern formed therebetween. 
     The first mass body may have an area wider than that of the second mass body. 
     The support part may include a first support part formed of the first substrate and a second support part formed of the second substrate. 
     The first and second support parts may have the first masking pattern formed therebetween. 
     The first support part may have an area wider than that of the second support part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a plan view schematically illustrating 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 the line A-A of  FIG. 1 ; 
         FIG. 3  is a schematic cross-sectional view of the acceleration sensor taken along the line B-B of  FIG. 1 ; and 
         FIG. 4  is a schematic cross-sectional view of an acceleration sensor according to another preferred embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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. 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. 
       FIG. 1  is a plan view schematically illustrating 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 the line A-A of  FIG. 1 ; and  FIG. 3  is a schematic cross-sectional view of the acceleration sensor taken along the line B-B of  FIG. 1 . 
     As illustrated in  FIGS. 1 to 3 , the acceleration sensor  100  is configured to include a flexible beam  110 , a mass body part  120 , and a support part  130 . 
     More specifically, the acceleration sensor  100  is formed by coupling first and second substrates  100   a  and  100   b  to each other and etching predetermined patterns. 
     To this end, one surface of the first substrate  100   a  is provided with a first masking pattern  101   a  corresponding to the flexible beam  110 , the mass body part  120 , and the support part  130 , and one surface of the second substrate  100   b  is provided with a second masking pattern  101   b  corresponding to the mass body part and the support part. 
     In addition, the respective components of the acceleration sensor  100  are formed only of the first substrate  100   a  or are formed of the first and second substrates  100   a  and  100   b.    
     That is, the flexible beam  110  is formed of the first substrate  100   a,  and the mass body part  120  may include a first mass body  120   a  formed of the first substrate  100   a  and a second mass body  120   b  formed of the second substrate  100   b.    
     In addition, the first mass body  120   a  has the first masking pattern  101   a  formed on one surface thereof facing the second mass body  120   b,  and the second mass body  120   b  has the second masking pattern  101   b  formed thereon. 
     Further, the first masking pattern  101   a  has an area wider than that of the second masking pattern  101   b . Therefore, the first mass body has an area wider than that of the second mass body. 
     The reason is that etching is performed by the second masking pattern and is then performed by the first masking patter, such that sequential etching is performed. 
     Further, the support part  130  includes a first support part  130   a  formed of the first substrate  100   a  and a second support part  130   b  formed of the second substrate  100   b.    
     Further, the first and second support parts  130   a  and  130   b  have the first masking pattern formed therebetween, and the second support part has the second masking pattern formed thereon. In addition, the first masking pattern  101   a  has an area wider than that of the second masking pattern  101   b.  Therefore, the second support part  130   b  has an area narrower than that of the first support part  130   a.    
     In addition, the first masking pattern  101   a  for forming the flexible beam  110 , the first mass body  120   a,  and the first support part  130   a  is formed on one surface of the first substrate  100   a  so as to face the second substrate  100   b.    
     In addition, the second masking pattern  101   b  for forming the second mass body  120   b  and the second support part  130   b  is formed on one surface of the second substrate  100   b  so as to face a lower cover  140 . 
     As described above, the acceleration sensor  100  according to the preferred embodiment of the present invention has a multi-layer structure of the first and second substrates  100   a  and  100   b  and includes the respective components formed by the first and second masking patterns  101   a  and  101   b  to allow the flexible beam to be formed at a shallow etching depth and allow a piezoresistor  111  to be maintained at an optimal position, thereby making it possible to improve sensitivity and decrease sensitivity dispersion. 
     Hereinafter, the respective components of the acceleration sensor according to the preferred embodiment of the present invention and organic coupling between the respective components will be described in more detail. 
     More specifically, the flexible beam  110  has a plate shape and is formed of a flexible substrate such as a membrane, a beam, or the like, having elasticity so that the mass body part  120  may be displaced. 
     In addition, the flexible beam  110  has the piezoresistor  111  formed on one surface thereof. 
     Further, the mass body part  120  is coupled to one surface of the flexible beam  110  and is displaced by inertial force, external force, Coriolis force, driving force, or the like. 
     Further, the support part  130  is coupled to one surface of the flexible beam and supports the flexible beam in a floated state so that the mass body part  120  may be displaced. 
     Here, the mass body part  120  is positioned at a central portion of the flexible beam  110 , the support part  130  has a hollow shape, such that the mass body part  120  is positioned in a hollow part so as to be displaceable, and the support part  130  is positioned at an edge portion of the flexible beam  110  to secure a space in which the mass body part  120  may be displaced. 
     In addition, the mass body part  120  may have a square pillar shape, and the support part  130  may have a cylindrical shape. Further, the mass body part  120  and the support part  130  are not limited to having the above-mentioned shape, but may have all shapes known in the art. 
     In the case in which an inertial sensor according to the preferred embodiment of the present invention is configured as described above and is implemented by the acceleration sensor and external force is generated, a moment is generated by the external force, such that the mass body part  120  is moved, a resistance value of the piezoresistor  111  of the flexible beam  110  is changed by the displacement of the mass body part  120 , and the resistance value is detected to calculate an acceleration. 
     In addition, the acceleration sensor  100  according to the preferred embodiment of the present invention may further include a lower cover  140  coupled to one surface of the support part  130  so as to cover the mass body part  120 . 
     In addition, the acceleration sensor  100  according to the preferred embodiment of the present invention may further include an upper cover (not illustrated) coupled to one surface of the support part  130  so as to cover the piezoresistor  111 . 
       FIG. 4  is a schematic cross-sectional view of an acceleration sensor according to another preferred embodiment of the present invention. As illustrated in  FIG. 4 , the acceleration sensor according to another preferred embodiment of the present invention is different from the acceleration sensor according to the preferred embodiment of the present invention illustrated in  FIG. 1  in that a masking pattern exposed to the outside does not remain. 
     As illustrated in  FIG. 4 , the acceleration sensor  200  is configured to include a flexible beam  210 , a mass body part  220 , and a support part  230 . 
     More specifically, the acceleration sensor  200  is formed by coupling first and second substrates  200   a  and  200   b  to each other and etching predetermined patterns. 
     To this end, one surface of the first substrate  200   a  is provided with a first masking pattern  201   a  corresponding to the flexible beam  210 , the mass body part  220 , and the support part  230 . 
     Therefore, the respective components of the acceleration sensor  200  are formed only of the first substrate  200   a  or are formed of the first and second substrates  200   a  and  200   b.    
     That is, the first flexible beam  210  is formed of the first substrate  200   a,  and the mass body part  220  may include a first mass body  220   a  formed of the first substrate  200   a  and a second mass body  220   b  formed of the second substrate  200   b.    
     In addition, the first and second mass bodies  220   a  and  220   b  have the first masking pattern  201   a  formed therebetween. 
     In addition, the first mass body  220   a  may have an area wider than that of the second mass body  220   b.    
     Further, the support part  230  includes a first support part  230   a  formed of the first substrate  200   a  and a second support part  230   b  formed of the second substrate  200   b.    
     In addition, the first masking pattern  201   a  is formed between the first and second support parts  230   a  and  230   b.    
     In addition, the first support part  230   a  may have an area wider than that of the second support part  230   b.    
     In addition, a second masking pattern (not illustrated) for forming the second mass body  220   b  and the second support part  230   b  is formed on one surface of the second substrate  200   b  so as to face a lower cover (not illustrated). 
     The first masking pattern  201   a  exposed to the outside and the second masking pattern are additionally etched, such that the acceleration sensor  200  illustrated in  FIG. 4  is completed. 
     According to the preferred embodiment of the present invention, it is possible to obtain an acceleration sensor capable of improving sensitivity and decreasing sensitivity dispersion by having a multi-layer structure of first and second substrates and including the respective components formed by first and second masking patterns to allow a flexible beam to be formed at a shallow etching depth and allow a piezoresistor to be maintained at an optimal position. 
     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. 
     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.