Abstract:
A tuning fork vibrator includes: a vibration arm including one or more grooves extending depthwise in a first direction; and exciting electrodes configured to provide a level of driving force required for vibrations of the vibration arm, wherein the one or more grooves have a cross-sectional shape in which a depth of the one or more grooves decreases from a first point toward a second point, and the depth of the one or more grooves at the second point is 30% or more of the depth of the groove at the first point.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2014-0187104 filed on Dec. 23, 2014, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The following description relates to a tuning fork vibrator capable of having equivalent series resistance (ESR) characteristics. 
         [0004]    2. Description of Related Art 
         [0005]    A tuning fork vibrator is an example of one type of vibrator. The tuning fork vibrator includes one or more grooves formed in an arm in which vibrations are generated. 
         [0006]    In order to increase efficiency of the tuning fork vibrator, a distance between electrodes needs to be significantly reduced. Therefore, the grooves need to be formed at a deep depth in the arm. 
         [0007]    However, in a case in which the grooves are formed at an excessively deep depth, there is a problem in which grooves formed in different surfaces connect to each other. In addition, in a case in which a depth of a groove is deep, there is a problem in which equivalent series resistance (ESR) characteristics of the vibrator are deteriorated. 
         [0008]    Therefore, the development of a tuning fork vibrator capable of improving both of vibration efficiency and ESR characteristics is desirable. 
       SUMMARY 
       [0009]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0010]    According to one general aspect, a tuning fork vibrator includes: a vibration arm including one or more grooves extending depthwise in a first direction; and exciting electrodes configured to provide a level of driving force required for vibrations of the vibration arm, wherein the one or more grooves have a cross-sectional shape in which a depth of the one or more grooves decreases from a first point toward a second point, and the depth of the one or more grooves at the second point is 30% or more of the depth of the one or more grooves at the first point. 
         [0011]    The depth of the one or more grooves at the first point may be 30% or more of a height of the vibration arm in the first direction. 
         [0012]    The one or more grooves may have a cross-sectional shape including lines having an angle of inclination with respect to a vertical line in the first direction. 
         [0013]    The one or more grooves may be formed, respectively, in first and second surfaces of the vibration arm that are perpendicular to the first direction. 
         [0014]    The one or more grooves may be formed in first and second surfaces of the vibration arm that are perpendicular to the first direction to be symmetrical to each other. 
         [0015]    The one or more grooves may be formed lengthwise in a second direction, which is a length direction of the vibration arm. 
         [0016]    The one or more grooves may be formed at predetermined gaps in a third direction, which is a width direction of the vibration arm. 
         [0017]    The cross-sectional shape of the one or more grooves may satisfy the following Conditional Expression: 0.3&lt;Dmin/Dmax&lt;0.45, wherein Dmax is the depth of the one or more grooves at the first point and Dmin is the depth of the one or more grooves at the second point. 
         [0018]    The cross-sectional shape of the one or more grooves may satisfy the following Conditional Expression: Dmin/W&lt;2.0, wherein Dmin is the depth of the one or more grooves at the second point and W is a maximum width of the one or more grooves. 
         [0019]    The cross-sectional shape of the one or more grooves may satisfy the following Conditional Expression: 0.16&lt;Dmin/h&lt;0.36, wherein Dmin is the depth of the one or more grooves at the second point. 
         [0020]    The vibration arm may be formed of crystal. 
         [0021]    The tuning fork vibrator may include a mass member formed on the vibration arm. 
         [0022]    According to another general aspect, a tuning fork vibrator may include: a vibration arm including one or more grooves extending depthwise in a first direction; and mask patterns formed on the vibration arm at predetermined gaps between the mask patterns to form the one or more grooves, wherein a minimum depth of the one or more grooves is greater than a gap between the mask patterns. 
         [0023]    The minimum depth (Dmin) of the one or more grooves may satisfy the following Conditional Expression with respect to the gap (G) between the mask patterns: 3.0&lt;Dmin/G. 
         [0024]    A maximum depth (Dmax) of the one or more grooves may satisfy the following Conditional Expression with respect to the gap (G) between the mask patterns: 4.0&lt;Dmax/G. 
         [0025]    The vibration arm may be formed of a material having mechanical directionality. 
         [0026]    According to another general aspect, a method of manufacturing a tuning fork vibrator includes: forming mask patterns on at least one of an upper surface and a lower surface of a member forming a vibration arm; and etching the member to form a groove extending between the mask patterns along a length of the member, wherein the groove has a width in a direction corresponding to a direction of a gap between the mask patterns on the upper surface of the member or the lower surface of the member, and wherein the gap between the mask patterns is narrower than the width of the groove. 
         [0027]    The groove may have a cross-sectional shape in which the depth of the groove decreases from a first point toward a second point, wherein the depth of the groove is perpendicular to the width of the groove. 
         [0028]    Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a plan view illustrating an example of a tuning fork vibrator. 
           [0030]      FIG. 2  is a cross-sectional view of the tuning fork vibrator taken along line A-A′ of  FIG. 1 , according to an example. 
           [0031]      FIG. 3  is a cross-sectional view of the tuning fork vibrator taken along line B-B′ of  FIG. 1 . 
           [0032]      FIG. 4  is an enlarged view of part C illustrated in  FIG. 3 . 
           [0033]      FIG. 5  is a graph illustrating a relationship between a minimum depth Dmin of a groove and equivalent series resistance (ESR). 
           [0034]      FIG. 6  is a graph illustrating a relationship between a ratio (Dmin/Dmax) of a minimum depth of a groove to a maximum depth of the groove and ESR. 
           [0035]      FIG. 7  is a view illustrating a process of forming grooves in the tuning fork vibrator. 
           [0036]      FIG. 8  is an enlarged view of part D of  FIG. 7  illustrating a change in a size of the groove depending on an etching time. 
           [0037]      FIG. 9  is a cross-sectional view of another form of the tuning fork vibrator taken along line B-B′ of  FIG. 1 , according to an example. 
       
    
    
       [0038]    Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. 
       DETAILED DESCRIPTION 
       [0039]    The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be apparent to one of ordinary skill in the art. The sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Also, descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted for increased clarity and conciseness. 
         [0040]    The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided so that this disclosure will be thorough and complete, and will convey the full scope of the disclosure to one of ordinary skill in the art. 
         [0041]    A tuning fork vibrator  100 , according to an example, will be described with reference to  FIG. 1 . 
         [0042]    The tuning fork vibrator  100 , includes a support body  110  and a vibration arm  120 . For example, the support body  110  may be configured to not be vibrated, and vibration arms  120  and  121  may be configured to be vibrated with respect to the support body  110 . In addition, the tuning fork vibrator  100  includes mass members  130  configured to adjust a vibration frequency of the vibration arm  120 . 
         [0043]    The support body  110  is configured to be fixed to a substrate (not shown) or another member. For example, the support body  110  may be firmly fixed to the substrate by an adhesive or another means. 
         [0044]    Connection electrodes  142  and  144  are formed in the support body  110 . For example, the first connection electrode  142  may be formed on a portion of the support body  110 , and the second connection electrode  144  may be formed on another portion of the support body  110 . 
         [0045]    The connection electrodes  142  and  144  are connected to exciting electrodes  152  and  154 . For example, the first connection electrode  142  may be connected to the first exciting electrode  152 , and the second connection electrode  144  may be connected to the second exciting electrode  154 . 
         [0046]    The vibration arms  120  and  121  may be configured to be vibrated by a level of driving force. For example, each of the vibration arms  120  and  121  may be configured so that one end (hereinafter referred to as a “fixed end”) thereof is fixed to the support body  110  and the other end (hereinafter referred to as a “free end”) thereof may freely move. For example, a pair of vibration arms  120  and  121  may extend lengthwise from one side of the support body  110  in a length direction of the tuning fork vibrator  100  (vertically in  FIG. 1 ). The vibration arms  120  and  121  configured as described generate a predetermined frequency while the other ends thereof are vibrated in the one direction by an electrical signal. 
         [0047]    One or more grooves  122  are formed in the vibration arms  120  and  121 . For example, the one or more grooves  122  may be formed in at least one of first and second surfaces of the vibration arms  120  and  121 . The configuration of the grooves  122  described facilitates vibrations of the vibration arms  120  and  121 . In addition, the configuration of the grooves  122  described facilitates formation of the exciting electrode. 
         [0048]    The vibration arms  120  and  121  may be formed of a material having a piezoelectric property. For example, the vibration arms  120  and  121  may be formed of crystal. As another example, the vibration arms  120  and  121  may be formed of a material having mechanical directionality. 
         [0049]    The exciting electrodes  152  and  154  are formed on the vibration arms  120  and  121 . For example, the first exciting electrodes  152  may be formed on portions of the vibration arms  120  and  121 , and the second exciting electrodes  154  may be formed on other portions of the vibration arms  120  and  121 . 
         [0050]    The first and second exciting electrodes  152  and  154  substantially face each other. For example, the first exciting electrodes  152  may be formed on both side surfaces of the vibration arm  120 , and the second exciting electrode  154  may be formed on the groove  122 . 
         [0051]    Positions of the first and second exciting electrodes  152  and  154  may be different from each other depending on the vibration arm  120 . For example, forms of the exciting electrodes  152  and  154  formed on the first and second vibration arms  120  and  121  may be opposite to each other. For example, the first exciting electrodes  152  may be formed on both side surfaces of a first vibration arm  120 , and the second exciting electrodes  154  may be formed on the groove  122  of the first vibration arm  120 . As another example, the second exciting electrodes  154  may be formed on both side surfaces of the second vibration arm  121 , and the first exciting electrode  152  may be formed on the groove  122  of the first vibration arm  120 . The exciting electrodes  152  and  154  having the form as described above may be easily connected to the connection electrodes  142  and  144 . 
         [0052]    The mass members  130  are formed on the vibration arms  120  and  121 . For example, the mass members  130  may be formed at the free ends of the vibration arms  120  and  121 . The mass members  130  may have a predetermined mass. For example, masses of the mass members  130  may be greater than those of the vibration arms  120  and  121 . However, a relationship between masses of the mass members  130  and the vibration arms  120  and  121  is not limited to the foregoing example. As another example, masses of the mass members  130  may be the same as or lesser than those of the vibration arms  120  and  121 . 
         [0053]    The mass member  130  may have a form in which an inner portion thereof is empty. For example, the mass member  130  may be manufactured in a hollow form. The mass member  130  may be formed of a material different from that of the vibration arms  120  and  121 . For example, the mass member  130  may be formed of a metal, a resin, or the like. 
         [0054]    An example structure of a cross section of the tuning fork vibrator  100  taken along line A-A′ will be described with reference to  FIG. 2 . 
         [0055]    As shown in  FIG. 2 , the support body  110  of the tuning fork vibrator  100  may be manufactured to be easily bonded to a substrate or a fixing body. For example, the support body  110  may have a rectangular cross-sectional shape. Since the support body  110  having this shape has a cross section of which a height is low and a width is wide, the support body  110  may be firmly fixed to the substrate or the fixing body. In addition, the support body  110  having this shape may be advantageous in making the tuning fork vibrator  100  thin. 
         [0056]    An example structure of a cross section of the tuning fork vibrator  100  taken along line B-B′ will be described with reference to  FIG. 3 . 
         [0057]    As shown in  FIG. 3 , two grooves  122  are formed in each of first surfaces (upper surfaces in  FIG. 3 ) of the vibration arms  120  and  121 , and two grooves  124  are formed in each of second surfaces (lower surfaces in  FIG. 3 ) of the vibration arms  120  and  121 . The grooves  122  and  124  may be formed depthwise in a first direction (a vertical direction in  FIG. 3 ). 
         [0058]    The first and second grooves  122  and  124  may have substantially the same shape. For example, the first and second grooves  122  and  124  may be symmetrical to each other in relation to a horizontal line bisecting the vibration arms  120  and  121  in  FIG. 3 . 
         [0059]    A depth of each of the grooves  122  and  124  may have a predetermined ratio with respect to a height h of each of the vibration arms  120  and  121 . For example, a maximum depth Dmax of each of the grooves  122  and  124  may satisfy the following Conditional Expression with respect to the height h of each of the vibration arms  120  and  121 : 
         [0000]      0.4&lt; D max/ h.   [Conditional Expression]
 
         [0060]    In a case in which the above Conditional Expression is satisfied, areas of the first and second exciting electrodes  152  and  154  facing each other on the vibration arms  120  and  121  may be increased, such that driving efficiency of the tuning fork vibrator  100  may be improved. 
         [0061]    An example form of the grooves  122  and  124  of the tuning fork vibrator  100  will be described with reference to  FIG. 4 . 
         [0062]    The depths of the grooves  122  and  124  may be varied in the vibration arms  120  and  121 . For example, a depth of the grooves  122  and  124  may decrease from a first point toward a second point. As another example, the grooves  122  and  124  may have a cross-sectional shape in which three straight lines are connected to each other. Each surface may have a gradient of 45 degrees or less with respect to a vertical line in the first direction (the height direction of the vibration arms  120  and  121 ). 
         [0063]    A depth of the grooves  122  and  124  may have a predetermined ratio with respect to a height h of each of the vibration arms  120  and  121 . For example, a minimum depth Dmin of the grooves  122  and  124  may satisfy the following Conditional Expression: 
         [0000]      0.17&lt; D min/ h.   [Conditional Expression]
 
         [0064]    In a case in which the above Conditional Expression is satisfied, areas of the first and second exciting electrodes  152  and  154  facing each other on the vibration arms  120  and  121  may be increased, such that driving efficiency of the tuning fork vibrator  100  may be improved. 
         [0065]    Depths Dmax and Dmin of the grooves  122  and  124  may have a predetermined ratio with respect to a width W of the grooves  122  and  124 . For example, a maximum depth Dmax of the groove  122  may satisfy at least one of the following Conditional Expressions with respect to the width W of the grooves  122  and  124 : 
         [0000]      3.3&lt; D max/ W   [Conditional Expression]
 
         [0000]      3.30&lt; D max/ W&lt; 3.75.  [Conditional Expression]
 
         [0066]    As another example, a minimum depth Dmin of the grooves  122  and  124  may satisfy at least one of the following Conditional Expressions with respect to the width W of the grooves  122  and  124 : 
         [0000]      1.3&lt; D min/ W   [Conditional Expression]
 
         [0000]      1.3&lt; D min/ W&lt; 2.0.  [Conditional Expression]
 
         [0067]    The minimum depth Dmin of the groove  122  and  124  may have a predetermined ratio with respect to the maximum depth Dmax of the grooves  122  and  124 . For example, the minimum depth Dmin of the grooves  122  and  124  may satisfy at least one of the following Conditional Expressions with respect to the maximum depth Dmax of the grooves  122  and  124 : 
         [0000]      0.3&lt; D min/ D max  [Conditional Expression]
 
         [0000]      0.3&lt; D min/ D max&lt;0.45.  [Conditional Expression]
 
         [0068]    A relationship between a minimum depth Dmin of a grooves  122  and  124  and an equivalent series resistance (ESR) will be described with reference to  FIG. 5 . 
         [0069]    The tuning fork vibrator  100 , according to the example of  FIG. 5 , may be configured to have low ESR. For example, the minimum depth Dmin of the grooves  122  and  124  formed in the vibration arms  120  and  121  may be 15 μm or more. 
         [0070]    The minimum depth Dmin of the grooves  122  and  124  described above may be advantageous in lowering ESR in vibration arms having the same form as confirmed from a graph of  FIG. 5 . 
         [0071]    A relationship between a ratio (Dmin/Dmax) of a minimum depth of the grooves  122  and  124  to a maximum depth of the grooves  122  and  124  and an ESR will be described with reference to  FIG. 6 . 
         [0072]    In the tuning fork vibrator  100  according to the example of  FIG. 6 , the minimum depth Dmin of the groove  122  or  124  may have a predetermined ratio with respect to the maximum depth Dmax of the grooves  122  and  124 . For example, the minimum depth Dmin of the grooves  122  and  124  may satisfy the following Conditional Expression with respect to the maximum depth Dmax of the grooves  122  and  124 . For reference, a horizontal axis in  FIG. 6  is a maximum depth of the grooves  122  and  124 . 
         [0000]      0.3&lt; D min/ D max&lt;0.45  [Conditional Expression]
 
         [0073]    The above Conditional Expression may be one condition for optimizing vibration efficiency of the vibration arms  120  and  121  formed of crystal. For example, in a case in which Dmin/Dmax is outside of a lower limit value of the above Conditional Expression, areas of the first and second exciting electrodes facing each other on the vibration arms are substantially small, such that vibration efficiency may be low. As another example, in a case in which Dmin/Dmax is outside of an upper limit value of the above Conditional Expression, it may be substantially difficult to manufacture the vibration arms, and it may not be easy to form the exciting electrodes on the grooves  122  and  124 . 
         [0074]    A process of forming the grooves  122  and  124  in the tuning fork vibrator  100  will be described with reference to  FIG. 7 . 
         [0075]    The grooves  122  and  124  of the vibration arms  120  and  121  may be formed through the following operations. 
         [0076]    1) Operation of Forming Mask Pattern (First Drawing of  FIG. 7 ) 
         [0077]    In a first operation, mask patterns  162  and  164  are formed on a member (for example, a crystal member) forming the vibration arm  120 . For example, mask patterns  162  and  164  may be formed on first and second surfaces (upper and lower surfaces in  FIG. 7 ) of the member forming the vibration arm  120 . 
         [0078]    The mask patterns  162  and  164  may be spaced apart by predetermined gaps. For example, the mask patterns  162  and  164  may be spaced apart by a gap that is narrower than a width of the grooves  122  and  124 . Forms of the mask patterns  162  and  164  disposed as described above may be advantageous in deeply forming the grooves  122  and  124 . 
         [0079]    2) Etching Operation (Second to Fourth Drawings in  FIG. 7 ) 
         [0080]    In a subsequent operation, the members configuring the vibration arm  120  is etched to form the grooves  122  and  124  between adjacent mask patterns  162  and  164 . For example, the members configuring the vibration arm  120  may be etched for several tens of hours or several hours by a wet etching scheme. 
         [0081]    The vibration arm  120  formed of crystal may be etched to have directionality. For example, the grooves  122  and  124  of the vibration arm  120  may include both of deeply etched portions and shallowly etched portions, as seen in  FIG. 7 . Therefore, performance of the vibration arm  120  may depend on a minimum depth of the grooves  122 . 
         [0082]    A relationship between a mask pattern and a size of a grooves  122  and  124  will be described with reference to  FIG. 8 . 
         [0083]    As shown in  FIG. 8 , a gap G between first and second mask patterns  162  and  164  may be adjusted to optimize depths Dmax and Dmin of the grooves  122  and  124 . For example, the depth of the grooves  122  and  124  formed in the vibration arm  120  may have a predetermined ratio with respect to the gap G between the mask patterns  162  and  164 . For example, the minimum depth Dmin of the grooves  122  and  124  may satisfy one or more of the following Conditional Expressions with respect to the gap G between the mask patterns  162  and  164 : 
         [0000]      3.0&lt; D min/ G   [Conditional Expression]
 
         [0000]      3.0&lt; D min/ G&lt; 6.0.  [Conditional Expression]
 
         [0084]    As another example, the maximum depth Dmax of the grooves  122  and  124  may satisfy one or more of the following Conditional Expressions with respect to the gap G between the mask patterns  162  and  164 : 
         [0000]      4.0&lt; D max/ G   [Conditional Expression]
 
         [0000]      8.0&lt; D max/ G&lt; 11.0.  [Conditional Expression]
 
         [0085]    The above Conditional Expressions may be optimized conditions for forming the grooves  122  and  124  having a predetermined depth in the vibration arm  120 . For example, in a case in which Dmin/G and Dmax/G are outside of lower limit values of the above Conditional Expressions, the mask patterns  162  and  164  may shorten an etching time required for forming the grooves  122  and  124 , but may be disadvantageous in enlarging the minimum depth Dmin of the grooves  122  and  124 . 
         [0086]    The gap G between the first and second mask patterns  162  and  164  may satisfy the following Conditional Expression with respect to the height h of the vibration arm  120 . For reference, in the example of  FIG. 8 , the gap G between the first and second mask patterns  162  and  164  may be 5.0 μm, and a height of the member configuring the vibration arm  120  may be 102 μm. In addition, the minimum depth Dmin of the grooves  122  and  124  may be 18 μm, and the maximum depth Dmax of the grooves  122  and  124  may be 45 μm. 
         [0000]        G/h&lt; 0.05  [Conditional Expression]
 
         [0087]    Next, other forms of the tuning fork vibrator  100  will be described. 
         [0088]    Another form of the tuning fork vibrator  100 ′ will be described with reference to  FIG. 9 . 
         [0089]    The tuning fork vibrator  100 ′, according to an example, is similar to the tuning fork vibrator  100  described above, except that the tuning fork vibrator  100 ′ includes a vibration arm  120 ′ The vibration arm  120 ′ is similar to the previously described vibration arm  120 , except that the number the grooves  122  and  124  formed in the first and second surfaces of the vibration arm  120 ′ is less than the number of grooves  122  and  124  formed in the first and second surfaces of the vibration arm  120 . For example, there may be only one groove  122  formed in the first surface of the vibration arm  120 ′ and only one groove  124  formed in the second surface of the vibration arm  120 ′. The tuning fork vibrator  100 ′ having this form may be advantageous in being miniaturized. 
         [0090]    As set forth above, according to examples disclosed herein, ESR characteristics of a tuning fork vibrator may be improved. 
         [0091]    While this disclosure includes specific examples, it will be apparent to one of ordinary skill in the art that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure.