Abstract:
A gyro vibration piece detecting an angular velocity includes a supporting part, a driving part connected to the supporting part and performing vibration, and a detection part detecting vibration generated by Coriolis force generated by the rotation of the driving part. A connection part includes a connection portion having a fin and an end portion connected between at least one of a side of the driving part and a side of the supporting part and a side of the detection part and a side of the supporting part. The end portion includes a top surface and a side surface, whereby the side surface is substantially perpendicular to the top surface and includes a circular arc shape disposed along a bottom portion thereof opposite to a junction of the top surface and the side surface.

Description:
BACKGROUND 
   1. Technical Field 
   The present invention relates to a gyro vibration piece used in a gyro sensor detecting rotational angular velocity, and to a method of manufacturing the gyro vibration piece. 
   2. Related Art 
   A gyro vibration piece according to the related art will be described with reference to  FIG. 9 .  FIG. 9  illustrates an example of a gyro vibration piece, and is a partial plan view of a gyro vibration piece using a crystal. As shown in  FIG. 9 , a gyro vibration piece  210  includes driving parts  215 A and  215 C, and a detection part  216 A located at a central portion thereof. The driving parts  215 A and  215 C and the detection part  216 A are connected through individual connection parts  221  to a supporting part  212  in an X-Y plane which is a crystalline direction of a crystal. The connection part  221  of the driving parts  215 A and  215 C is formed in the same manner as the connection part  221  of the detection part  216 A, and the connection part  221  of the driving part  215 A will thus be described herein. The driving parts  215 A and  215 C and the detection part  216 A are formed in line symmetry with respect to an axis  228  located at a central portion of the supporting part  212  along the X-axis. That is, even though not shown in  FIG. 9 , a pair of the driving part  215 A, a pair of the driving part  215 C, and a pair of the detection part  216 A are formed with respect to the axis  228 . The gyro vibration piece  210  is formed by chemical etching by photolithography. An external shape, an electrode or the like is formed by the chemical etching. 
   Next, a chemical etching rate will be described.  FIG. 10  is a polar coordinate diagram showing the etching rate of a Z-cut crystal substrate in an X-Y plane. Referring to  FIG. 10 , the etching rate is zero at the center of a circle. In addition, the etching rate becomes higher as it becomes more distant from the center of the circle. It can be understood that the Z-cut crystal has anisotropy in the etching. Particularly, in-plane etching rate become higher in +X direction, +120° direction and −120° direction with respect to the X-axis, while in-plane etching rate become lower in −X direction, +30° direction and −30° direction with respect to the X-axis. On the other hand, the etching rate of Z direction becomes higher in −X direction, +30° direction and −30° direction with respect to the X-axis, while the etching rate of Z direction becomes lower in +X direction, +120° direction and −120° direction with respect to the X-axis. 
   Due to the anisotropy in the etching, a protrusion-shaped fin  220  is formed on a side of the connection part  221  between the driving parts  215 A and  21 C and the detection part  212 . 
   Since the fin  220  varies in size depending on the direction of the connection part  221 , the driving parts  215 A and  215 C and the detection part  216 A have an asymmetrical shape in width direction, causing the vibration performance of the gyro vibration piece  210  to be deteriorated. Examples of deterioration of the vibration performance of the gyro vibration piece include unstable vibration amplitude due to poor balance of vibration, unnecessary vibration, and the like. Thus, a processing method having a long etching time is employed in order to make the fin as small as possible. As the etching time becomes long, the connection part  221  between the driving parts  215 A and  215 C and the detection part  216 A and the supporting part  212  has a lateral shape formed such that a segment  222  having an angle of +60° (angle ‘a’) and a segment  223  having an angle of 30° (angle ‘b’) are continuously connected to each other. That is, the two segments  222  and  223  are connected to each other by performing an etching process for a long time. 
   The shape will be described in detail with reference to the driving part. A segment  226  of the driving part  215 A and a segment  224  of the supporting part  212  are connected to each other through a segment  222  forming an angle of +60° (angle ‘a’) with respect to X-axis and a segment  223  forming an angle of 30° (angle ‘b’) with respect to X-axis. In addition, a segment  227  of the driving part  215 A is connected to a segment of the supporting part  212  in line symmetry to the connection. In addition, a fin  220  is formed almost at a central portion of a thickness direction (Z-axis direction) on the side of the segment  226  of the driving part  215 A. Similarly to the driving part  215 A, the driving part  215 C and the detection part  216 A are connected to the supporting part  212  (for example, JP-A-10-96632). 
   However, in the above-mentioned gyro vibration piece, the segment  226  of the driving part  215 A and the segment  224  of the supporting part  212  are connected to each other through the segment  222  forming an angle of +60° (angle ‘a’) with respect to X-axis and the segment  223  forming an angle of 30° (angle ‘b’) with respect to X-axis. In this case, vertices P 1 , P 2 , and P 3  are formed on portions in which the segments  226 ,  222 ,  223 , and  224  intersect each other. For example, when an impact, such as dropping, is applied to the gyro vibration piece, stress concentration due to the impact occurs one of the vertices P 1 , P 2 , and P 3 . Due to the stress concentration, the driving parts  215 A and  215 C, or the detection part  216 A may be broken. 
   SUMMARY 
   An advantage of some aspects of the invention is that it provides a gyro vibration piece that prevents breakdown of a driving part or a detection part due to an impact, such as dropping, applied from the outside of the gyro vibration piece and has an improved impact resistance. 
   According to an aspect of the present invention, there is provided a gyro vibration piece detecting an angular velocity, including: a supporting part; a driving part connected to the supporting part and performing vibration; a detection part connected through the driving part and the supporting part and detecting detection vibration generated by Coriolis force generated by the rotation of the driving part; and a connection part including a connection portion having a plurality of steps formed between a side of a width direction of the driving part or a side of a width direction of the detection part and a side of another portion connected to the driving part or the detection part, which are continuously connected, in which the connection part has a first end portion which is located on an innermost side of the connection part among the connection portion and has a circular arc shaped wall portion that connects a side of a width direction of the driving part or a side of a width direction of the detection part to a side of another portion connected to the driving part or the detection part, and a bottom surface having a predetermined depth. 
   In the gyro vibration piece, the driving part or the detection part is connected to another part through a connection part including the first end portion having a circular arc shaped wall portion formed on the innermost side of the connection part. Since the circular arc shaped wall portion of the first end portion does not have vertices, stress concentration due to an external impact seldom occurs. Accordingly, it is possible to prevent breakdown due to the stress concentration. In addition, since the first end portion has a bottom surface and the central portion has a wall portion on the outside than the first end portion, it is possible to increase the sectional area. That is, it is possible to improve the intensity of the connection part by increasing the volume of the connection part. As a result, it is possible to provide a gyro vibration piece that prevents breakdown of a driving part or a detection part due to an impact, such as dropping, applied from the outside of the gyro vibration piece and has an improved impact resistance. 
   Preferably, the supporting part includes a base part and a supporting member extended from the base part, the driving part is connected to the supporting member, and the detection part is extended from the base part. 
   The gyro vibration piece may include a second connection part having a second connection portion having a plurality of steps formed between a side of the base part and a side of the supporting member, which are continuously connected, in which the second connection part has a second end portion which is located on an innermost side of the second connection part among the second connection portion and has a circular arc shaped wall portion that connects a side of the base part to a side of the supporting member, and a bottom surface having a predetermined depth. 
   Accordingly, since the circular arc shaped wall portion of the second end portion does not have vertices, stress concentration due to an external impact seldom occurs. Accordingly, it is possible to prevent breakdown due to the stress concentration. In addition, since the second end portion has a bottom surface and the central portion has a wall portion on the outside than the second end portion, it is possible to increase the sectional area. That is, it is possible to improve the intensity of the second connection part by increasing the volume of the second connection part. As a result, it is possible to provide a gyro vibration piece that prevents breakdown of a driving part or a detection part due to an impact, such as dropping, applied from the outside of the gyro vibration piece and has an improved impact resistance. 
   Preferably, at least one connection portion having the plurality of steps has a fin part projected on the outside of a central portion of a thickness direction of the connection portion, and a third end portion that is continuously connected to the fin part and has a wall portion on an inner side of the connection part than the fin part, and the first or second end portion is formed on an inner side of the connection part than the wall portion of the third end portion. 
   Accordingly, since the first or second end portion is formed on an inner side than the fin part and the third end portion, the wall portion continuously connected to the driving part, the detection part, or the surface of the supporting member roughly has a circular arc shape without vertices. Accordingly, stress concentration due to an external impact seldom occurs, thereby preventing breakdown due to the stress concentration. 
   According to another aspect of the present invention, there is provided a method of manufacturing a gyro vibration piece including a supporting part; a driving part connected to the supporting part and performing vibration; a detection part connected through the driving part and the supporting part and detecting detection vibration generated by Coriolis force generated by the rotation of the driving part; and a connection part including a connection portion having a plurality of steps formed between a side of a width direction of the driving part or a side of a width direction of the detection part and a side of another portion connected to the driving part or the detection part, which are continuously connected, the method including: forming a first mask on a surface of a piezoelectric substrate; forming a first external shape by performing a first etching process to remove the piezoelectric substrate on an opening of the first mask; forming a second mask on a surface of the first external shape; and forming a second external shape, in which part of the first external shape is removed, by performing a second etching process to remove the piezoelectric substrate on an opening of the second mask, in which, in the step of forming a second external shape, a first end portion, which has a circular arc shaped wall portion that connects a side of a width direction of the driving part or a side of a width direction of the detection part to a side of another portion connected to the driving part or the detection part, and a bottom surface having a predetermined depth, is formed on an inner side than a wall portion formed on the innermost side among the connection portion formed by the process of forming the first external shape. 
   According to the method of manufacturing the gyro vibration piece, the first end portion is formed by performing the second etching process on the inner side than the wall portion formed on the innermost side of the connection portion formed by the first etching process. The first end portion has a circular arc shaped wall portion on the inner side than the wall portion formed on the innermost side of the connection portion formed by the process of forming the first external shape. Accordingly, the wall portion having vertices formed by the first etching process is removed, and vertices are not formed on a portion close to the surface, such that stress concentration due to an external impact seldom occurs. Accordingly, it is possible to prevent breakdown due to the stress concentration. 
   Preferably, the second etching process is performed in a shorter process time than the first etching process. 
   Since the second etching process is performed in a shorter time than the first etching process, an uneven shape is seldom generated. Thus, the end portion formed by the second etching process does not have uneven shape very much, such that the connection part has a stable shape. Accordingly, it is possible to prevent problems generated due to the uneven planar shape of the connection part. For example, it is possible to prevent the vibration of the driving part from leaking to the outside such as the detection part, or to reliably detect the angular velocity. 
   According to another aspect of the present invention, there is provided a gyro sensor including: a holding unit; and a gyro vibration piece according to the first aspect that is mounted in the holding unit. 
   In the gyro sensor, the gyro vibration piece is mounted in the holding unit. Accordingly, it is possible to provide a one-package-type gyro sensor having an excellent impact resistance. 
   According to another aspect of the present invention, there is provided a gyro sensor including: a holding unit; a gyro vibration piece that is mounted in the holding unit; and a circuit element mounted in the holding unit and having at least a function of driving the gyro vibration piece. 
   The gyro sensor includes the gyro vibration piece and a mounted circuit element having at least a function of driving the gyro vibration piece in the holding unit. Accordingly, it is possible to provide a small-sized one-package-type gyro sensor which has an excellent impact resistance and in which oscillation and drive can be performed by one gyro sensor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
       FIG. 1A  is a plan view schematically illustrating the structure of a gyro vibration piece according to a first embodiment of the invention. 
       FIG. 1B  is a partially enlarged view of Q shown in  FIG. 1A  and a left-side view thereof. 
       FIG. 2  is a plan view for explaining the driving vibration of a gyro vibration piece. 
       FIG. 3  is a plan view for explaining the detection vibration of a gyro vibration piece. 
       FIG. 4  is a plan view showing an example of a connected shape. 
       FIG. 5  is a plan view showing an example of applying a connected shape to another connection part. 
       FIG. 6  is a process flow showing a method of manufacturing a gyro vibration piece according to a second embodiment of the invention. 
       FIG. 7  is a front cross-sectional view showing the structure of a gyro sensor according to a third embodiment of the invention. 
       FIG. 8  is a front cross-sectional view showing the structure of a gyro sensor according to a fourth embodiment of the invention. 
       FIG. 9  is a partial plan view of a gyro vibration piece according to the related art. 
       FIG. 10  is a polar coordinate diagram showing the etching rate of a Z-cut crystal substrate in an X-Y plane. 
   

   DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Preferred embodiments of a gyro vibration piece, a method of manufacturing the gyro vibration piece, and a gyro sensor according to the present invention will be described with reference to the accompanying drawings. 
   First Embodiment 
   A gyro vibration piece according to a first embodiment of the present invention will be described with reference to the accompanying drawings.  FIG. 1A  is a plan view schematically illustrating a structure of a gyro vibration piece according to a first embodiment of the invention, and  FIG. 1B  is a partially expanded view of Q shown in  FIG. 1A  and a left-side view thereof. 
   In the first embodiment, a double T-type gyro vibration piece will be described as an example of the gyro vibration piece. As shown in  FIG. 1A , the gyro vibration piece  10  is formed of a crystal substrate as an example of a piezoelectric substrate. Crystal forming the crystal substrate has an X-axis, which is called an electrical axis, a Y-axis, which is called a mechanical axis, and a Z-axis, which is called an optical axis. The gyro vibration piece  10  is formed in an X-Y plane of Z-cut crystal substrate that is cut in a direction of a plane formed by the X-axis and Y-axis of the crystal. The gyro vibration piece  10  is formed of a crystal substrate having a predetermined thickness. The plane of the gyro vibration piece  10  is formed in an X-Y plane along the crystalline axis of crystal, and is formed in point symmetry of 180° with respect to a central point G. The central point G indicates a central position of the gyro vibration piece  10 . 
   The gyro vibration piece  10  includes a supporting part  11  at its central portion. The supporting part  11  consists of a base part  12  and two connection arms  13  and  14 . The base part  12  has a rectangular shape having a section parallel to the X-axis and Y-axis. The base part  12  is connected to the connection arms  13  and  14  each extended from a central portion of two sections of the base part  12  parallel to the Y-axis of the base part  12  toward a direction parallel to the X-axis. In addition, the base part  12  is connected to detection parts extended from a central portion of two sections parallel to the X-axis of the base part  12  toward a direction parallel to the Y-axis, i.e., a detection arm  16 A extended in a plus direction of Y-axis and a detection arm  16 B extended in a minus direction of Y-axis. End portions of the connection arms  13  and  14  are connected to driving arms  15 A,  15 B,  15 C, and  15 D, which are extended in a diagonal direction of the connection arms  13  and  14 . That is, the end portion of the connection arm  13  is connected to the driving arm  15 A extended in a plus direction of Y-axis and to the driving arm  15 B extended in a minus direction of Y-axis. In addition, the end portion of the connection arm  14  is connected to the driving arm  15 C extended in a plus direction of Y-axis and to the driving arm  15 D extended in a minus direction of Y-axis. 
   The driving arms  15 A,  15 B,  15 C, and  15 D have a width or length set so that driving vibration having a predetermined resonance frequency is generated. In addition, the driving arms  15 A,  15 B,  15 C, and  15 D have recesses  17 A,  17 B,  17 C, and  17 D on a central portion of each of the driving arms to improve vibration performance. The detection arms  16 A and  16 B and the connection arms  13  and  14  have a width or length set so that detection vibration having a predetermined resonance frequency is generated. In addition, the detection arms  16 A and  16 B have recesses  18 A and  18 B on a central portion of each of the detection arms to improve detection vibration performance. 
   Next, a connection portion  30  between the driving arms  15 A,  15 B,  15 C, and  15 D and the connection arms  13  and  14 , a connection portion  40  between the detection arms  16 A and  16 B and the base part  12 , and a second connection portion  35  between the connection arms  13  and  14  and the base part  12  will be described. The connection portions  30  and  40 , and the second connection portion  35  have the same structure, and  FIG. 1B  is thus used as part of Q shown in  FIG. 1A . 
   A connection on a left side of a plan view shown in  FIG. 1B  will be described. As shown in  FIG. 1B , a side having a segment  16 L of the detection arm  16 A and a side having a segment  12 L of the base part  12  are connected to each other at a connection part  22 . A fin  19  having a projected shape is formed almost at a central portion of a side of the connection part  22  in the thickness direction. The fin  19  is formed by anisotropy of the etching process described in the Background. A third end portion  27  connected to the fin  19  is formed around the fin  19 . The third end portion  27  has a wall portion in which the segment  16 L of the detection arm  16 A and the segment  12 L of the base part  12  are continuously connected to each other by a segment  24  of about 60° (denoted by angle θ 1 ) with respect to X-axis and a segment  21  of about 30° (denoted by angle θ 2 ) with respect to X-axis. Points C 1 , C 2 , and C 3  each having an angle of about 150° are formed on a connection portion between the segment  16 L and the segment  24 , a connection portion between the segment  24  and the segment  21 , a connection portion between the segment  21  and the segment  12 L, respectively. A wall portion of the third end portion  27  is connected to a first end portion or a second end portion  20  (The first end portion indicates the connection part  22  formed on the connection portions  30  and  40 , and the second end portion indicates a second connection part (not shown) formed on the second connection portion  35 . The first and second end portions have the same structure, and the first end portion  20  will thus be described and the second end portion will not be described). The third end portion  27  and the first end portion  20  are connected to each other such that the wall portion of the third end portion  27  and the bottom surface of the first end portion  20  are continuously connected to each other. The first end portion  20  has a circular arc shaped wall portion R 1  that continuously connects the segment  16 L and the segment  12 L as tangent lines. In other words, the wall portion R 1  is formed by a curved line in which the segments  16 L and  12 L do not have vertices. In addition, the wall portion R 1  may be formed by connecting the segment  16 L and the segment  12 L without vertices, or, for example, by using a curved line (not shown) having irregular curvature between the segment  16 L and the segment  12 L. The wall portion R 1  of the first end portion  20  is continuously connected to a surface of the connection part  22 . 
   Next, a connection on a right side of a plan view shown in  FIG. 1B  will be described. A side having a segment  16 R of the detection arm  16 A and a side having a segment  12 R of the base part  12  are connected to each other at a connection part  22 ′. A third end portion  27 ′ is formed almost at a central portion of a side of the connection part  22 ′ in the thickness direction. The third end portion  27 ′ connects the segment  16 R of the detection arm  16 A to the segment  12 R of the base part  12 . The third end portion  27 ′ has a wall portion formed of a segment  24 ′ and a segment  21 ′ which are formed in line symmetry to the segment  24  and the segment  21  of the third end portion  27 . The segment  16 R of the detection arm  16 A and the segment  12 R of the base part  12  are continuously connected to each other by the wall portion formed by the segments  24 ′ and  21 ′. The wall portion of the third end portion  27 ′ is connected to the first end portion  20 ′ having a bottom surface. The first end portion  20 ′ has a circular arc shaped wall portion R 2  that continuously connects the segment  16 R and the segment  12 R as tangent lines. In other words, the wall portion R 2  is formed by a curved line in which the segments  16 R and  12 R do not have vertices. In addition, the wall portion R 2  may be formed by connecting the segment  16 R and the segment  12 R without vertices, or, for example, by using a curved line (not shown) having irregular curvature between the segment  16 R and the segment  12 R. The wall portion R 2  of a first end portion  20 ′ is continuously connected to a surface of the connection part  22 ′. The fin  19  formed on the left side is not formed on the right side of the connection part  22 ′. The connection part  22 ′ on the right side is formed almost in line symmetry to the connection part  22  with respect to a central line of the detection arm  16 A in width direction, except the fin  19 . 
   The vibrating operation of the gyro vibration piece  10  will be described.  FIGS. 2 and 3  are plan views for explaining the operation of the gyro vibration piece  10  according to the first embodiment of the present invention. In  FIGS. 2 and 3 , each of vibration arms is simplified to a line to easily represent the vibrating shape. The same components as those of  FIG. 1  are denoted by the same reference numerals, and a detailed description thereof will thus be omitted herein. 
     FIG. 2  is a view for explaining driving vibration. In  FIG. 2 , the driving vibration indicates that the driving arms  15 A,  15 B,  15 C, and  15 D vibrate in a direction of an arrow ‘A’ in a predetermined frequency in which vibration represented by a solid line and a dash-dot line is repeated. At this time, since the driving arms  15 A and  15 B and the driving arms  15 C and  15 D vibrate in line symmetry in Y-axis passing through the central point G, the base part  12 , the connection arms  13  and  14 , and the detection arms  16 A and  16 B seldom vibrate. 
     FIG. 3  is a view for explaining detection vibration. In  FIG. 3 , the detection vibration indicates that vibration represented by a solid line and a dash-dot line is repeated in the frequency of the driving vibration. The detection vibration is generated by Coriolis force applied in a direction of an arrow ‘B’ to the driving arms  15 A and  15 B, and  15 C and  15 D when angular velocity ω around Z-axis is applied to the gyro vibration piece  10  performing the driving vibration shown in  FIG. 2 . 
   As a result, the driving arms  15 A,  15 B,  15 C, and  15 D vibrate as shown in the arrow ‘B’. The vibration represented by the arrow ‘B’ indicates vibration occurring in a circumferential direction with respect to the central point G. Simultaneously, as shown in the arrow ‘C’, the detection arms  16 A and  16 B vibrate in a direction opposite to the arrow ‘B’ in the circumferential direction in response to the vibration of the arrow ‘B’. 
   At this time, a fringe of the base part  12  does not vibrate when the driving arms  15 A,  15 B,  15 C and  15 D and the detection arms  16 A and  16 B vibrate as shown in  FIG. 2 . Accordingly, even though a supporting member for supporting the gyro vibration piece  10  is fixed to the base part  12 , it will not affect the vibration of the gyro vibration piece  10 . 
   The gyro vibration piece  10  according to the first embodiment has the first end portions  20  and  20 ′ having circular arc shaped wall portions R 1  and R 2  on the innermost side of the connection parts  22 ,  22 ′ of the connection portion  40  between the detection arm  16 A and the base part  12 . Due to the first end portions  20  and  20 ′, the wall portions R 1  and R 2  continuously connected to the surface of the detection arm  16 A are roughly formed in a circular arc shape without vertices. Accordingly, stress concentration due to external impact seldom occurs, thereby preventing breakdown due to the stress concentration. 
   Also, the first end portions  20  and  20 ′ have bottom surfaces, and the third end portions  27  and  27 ′ are formed on a central side in a thickness direction than the bottom surface. The third end portions  27  and  27 ′ have wall portions formed of segments  21  and  21 ′ and segments  24  and  24 ′ on an outer side than the wall portions R 1  and R 2  of the first end portions  20  and  20 ′. Accordingly, it is possible to increase a sectional area in the vicinity of a central portion in the thickness direction. That is, it is possible to improve the intensity of the connection parts  22  and  22 ′ by increasing the volume of the connection parts  22  and  22 ′. 
   Also, other connection parts of the gyro vibration piece  10 , for example, the connection portion  30  between the driving arms  15 A,  15 B,  15 C, and  15 D and the connection arms  13  and  14 , and the second connection portion  35  between the connection arms  13  and  14  and the base part  12 , have the same structure and same effect. As a result, it is possible to prevent breakdown of the driving arms  15 A,  15 B,  15 C, and  15 D, the connection arms  13  and  14 , and the detection arms  16 A and  16 B due to impact such as dropping, and to provide a gyro vibration piece having an improved impact resistance. 
   Also, as shown in  FIG. 4 , the first end portion  20  in the connection portion  40  between a side of the detection arm  16 A and a side of the base part  12  may have circular arc shaped wall portions L 1  and L 2  formed by connecting a plurality of short lines  23 . As a result, since the wall portions L 1  and L 2  have a plurality of intersecting points, stress concentration seldom occurs such that the detection arm  16 A is seldom broken. 
   Also, the structure of the connection parts  22  and  22 ′ can be applied in addition to the connection portions  30  and  40 , and the second connection portion  35  shown in  FIG. 1 . For example, as shown in  FIG. 5 , the structure of the connection parts  22  and  22 ′ can be applied to a connection portion  45  in which weight-shaped members  25 C and  26 A formed on the end portions of the driving arm  15 C and the detection arm  16 A are formed. The connection portion  45  has the same effect as that of the first embodiment. 
   While the double T-type gyro vibration piece has been described in the above-mentioned embodiment, the present invention is not limited thereto. For example, the present invention can be applied to a tuning fork type gyro vibration piece or an H-type gyro vibration piece. 
   Second Embodiment 
   A method of manufacturing a gyro vibration piece according to the present invention will be described with reference to the drawings.  FIG. 6  is a process flow of a method of manufacturing a gyro vibration piece. In the second embodiment, a method of forming a gyro vibration piece using a crystal substrate as a piezoelectric substrate will be described. 
   A metal layer  51  is formed as a corrosion-resisting film on a surface of a crystal substrate  50 . The metal layer  51  is formed of, for example, a chrome (Cr) layer as a base metal, and an aurum (Au) layer as a corrosion-resisting metal formed on the Cr layer. The Cr layer has a thickness of tens of nanometers and the Au layer has a thickness of hundreds of nanometers. The Cr layer having good adherence to the crystal substrate  50  and the Au layer is formed as a base metal layer since the crystal layer  50  has bad adherence to the Au layer. Also, in  FIG. 6 , the Cr layer and the Au layer are not depicted and a combination of the Cr layer and Au layer is depicted as the metal layer  51 . A positive-type photoresist layer  52  is formed on the metal layer  51  (S 102 ). 
   Next, a pattern for forming a first outer shape of the gyro vibration piece is subjected to photo-finishing by exposure of ultraviolet ray or the like. Subsequently, the pattern is subjected to a development process, and a mask  53  corresponding to the outer shape of the gyro vibration piece is formed by removing an unnecessary portion of the photoresist layer  52  (S 104 ). Next, a metal layer  54  corresponding to the first outer shape is formed by performing an etching process on an exposed portion of the metal layer  51  (S 106 ). Next, the mask  53  is removed, such that the metal layer  54  is exposed as a first mask having the first outer shape on the surface of the crystal substrate  50  (S 108 ). 
   Next, a positive-type photoresist layer  55  is formed on the exposed surface of the crystal substrate  50  and the metal layer  54  to form a second outer shape pattern (S 110 ). The pattern for the second outer shape is subjected to photo-finishing on the photoresist layer  55  by the exposure of ultraviolet ray or the like. Subsequently, the pattern is subjected to a development process, and a mask  56  corresponding to the second outer shape is formed by removing an unnecessary part of the photoresist layer  55  (S 112 ). 
   Next, the crystal substrate  50 , in which the metal layer  54  is used as a mask, is soaked in etching solution using hydrogen fluoride or ammonium fluoride, such that the crystal substrate  50  is subjected to a first etching process. An unnecessary part (depicted in a dashed line) of the crystal substrate  50  is removed by the etching process, such that the first outer shape, such as the detection arm  16 A, is formed (S 114 ). A main outer shape of the gyro vibration piece is formed by forming the first outer shape. 
   Next, in order to form a second outer shape, the metal layer  54  is etched while the mask  56  is used as a mask, such that a metal mask  57  is formed as a second mask (S 116 ). By this etching process, the metal layer  54  on an area corresponding to a processing portion in the first outer shape is removed, thereby forming the metal mask  57 . Next, the crystal substrate  50 , in which the metal mask  57  is used as a mask, is soaked in etching solution using hydrogen fluoride or ammonium fluoride, such that the crystal substrate  50  is subjected to a second etching process. By this etching process, a second outer shape is formed by performing an additional process on the first outer shape (S 118 ). The second outer shape is formed by, for example, additionally processing a first end portion  20  that has a circular wall surface and a bottom surface of a predetermined depth connected to the surface of the detection arm  16 A shown in  FIG. 1  and the recess  18 A of the detection arm  16 A. The second etching process is performed for a shorter time than the processing time of the first etching process. The etching process is performed for a short time, and thus the shape having the bottom surface can be processed in the middle of the depthwise direction. 
   Next, the mask  56  is removed and the metal mask  57  is removed (S 120 ). By this process, the shape of the gyro vibration piece is formed. 
   According to the method of manufacturing the gyro vibration piece of the second embodiment, the first end portion  20  is formed by performing the second etching process (S 118 ) on the inner side of the wall portion formed on the innermost side of the connection portion formed by the first etching process (S 114 ). The first end portion  20  has a circular arc shaped wall portion on the inner side of the wall portion formed on the innermost side of the connection portion formed with the process of forming the first outer shape (for example, detection arm  16 A). Thus, since the wall portion having vertices formed by the first etching process (S 114 ) is removed, stress concentration due to external impact seldom occurs. Accordingly, for example, it is possible to prevent breakdown of the detection arm  16 A. 
   Also, since the second etching process (S 118 ) is performed in a shorter time than the first etching process (S 114 ), the removed amount is small and an uneven shape is seldom generated. Thus, the first end portion  20  formed by the second etching process (S 118 ) does not have uneven shape very much, such that the connection part has a stable shape. Accordingly, it is possible to prevent problems generated due to the uneven shape of the connection part. For example, it is possible to prevent the vibration of the vibration part from leaking to the outside such as the detection part, or to reliably detect the angular velocity. 
   Third Embodiment 
   A gyro sensor according to a third embodiment will be described with reference to  FIG. 7 .  FIG. 7  is a front cross-sectional view of the structure of the gyro sensor according to the third embodiment. 
   As shown in  FIG. 7 , the gyro sensor  150  according to the present invention includes a gyro vibration piece  10 , supporting arms  151  and  152  of the gyro vibration piece  10  located within a package  154  serving as a holding unit, a supporting substrate  153 , and a cover  155  of the package  154 . 
   The package  154  is formed of, for example, a ceramic. The supporting substrate  153 , on which a circuit pattern and the like is formed, is fixed on a hollow formed on a central portion of the package  154 . An end portion of each of the supporting arms  151  and  152  is connected to a surface of the supporting substrate  153 . The supporting arms  151  and  152  are formed of a flexible metal thin film. The gyro vibration piece  10  is connected to an end portion located on an opposite side of an end portion connected to the supporting substrate  153 . The supporting arms  151  and  152  are formed to be bent upward on a portion projected from the supporting substrate  153  in order to prevent contact between the supporting substrate  153  and the gyro vibration piece  10 . The supporting arms  151  and  152  are further bent in the vicinity of the end portion in the bent direction, in which the gyro vibration piece  10  is connected. The gyro vibration piece  10  described in the first embodiment is used. The opening of the package  154  is covered with the cover  155  which is fixed, for example, by seam welding, metal heat fusion, or the like. The cover  155  is fixed while the hollow of the package  154  is in a vacuum state. The hollow of the package  154  is sealed in a vacuum state by fixing the cover  155 . 
   In the gyro sensor  150  according to the third embodiment, the gyro vibration piece  10  described in the first embodiment is mounted in the package  154  and is sealed in a vacuum state. Accordingly, it has the same effect as the gyro vibration piece  10  described in the first embodiment. Also, since the gyro vibration piece  10  is supported in the vacuum state, it is possible to reduce the effect of temperature of components other than the package  154  and to provide a gyro sensor having stable vibration performance. 
   Fourth Embodiment 
   A fourth embodiment will be described with reference to  FIG. 8 .  FIG. 8  is a front cross-sectional view of the structure of a gyro sensor according to the fourth embodiment of the present invention. 
   As shown in  FIG. 8 , a gyro sensor  170  according to the present invention includes a plurality of components in a package  174 . The components in the package  174  are a gyro vibration piece  10 , supporting arms  171  and  172  of the gyro vibration piece  10 , a supporting substrate  173 , and a circuit element  176 . An opening of the package  174  is sealed with a cover  175 . 
   The package  174  is formed of, for example, a ceramic. The supporting substrate  173 , on which a circuit pattern and the like is formed, is fixed to a hollow formed on a central portion of the package  174 . An end portion of each of the supporting arms  171  and  172  is connected to the surface of the supporting substrate  173 . The supporting arms  171  and  172  are formed of a flexible metal thin film or the like. The gyro vibration piece  10  is connected to an end portion located on an opposite side of an end portion connected with the supporting substrate  173 . The supporting arms  171  and  172  are formed to be bent upward on a portion projected from the supporting substrate  173  in order to prevent contact between the supporting substrate  173  and the gyro vibration piece  10 . The supporting arms  171  and  172  are further bent in the vicinity of the end portion in the bent direction, in which the gyro vibration piece  10  is connected. The gyro vibration piece  10  described in the first embodiment is used. The circuit element  176  is fixed with a conductive adhesive (not shown) on a bottom surface of the hollow of the package  174 . The circuit element  176  is electrically connected to a connection wire (not shown) formed on the package  174  or the supporting substrate  173  by wire-bonding or the like. The circuit element  176  has various functions such as a function of driving the gyro vibration piece  10 , or a function of detecting angular velocity. The opening of the package  174  is covered with the cover  175  which is fixed, for example, by seam welding, metal heat fusion, or the like. The cover  175  is fixed while the hollow of the package  174  is in a vacuum state. The hollow of the package  174  is sealed in a vacuum state by fixing the cover  175 . 
   According to the fourth embodiment, the gyro vibration piece  10  is mounted in the package  174  in a vacuum state. Accordingly, it has the same effect as the gyro vibration piece  10  described in the first embodiment. In addition, since all components such as the circuit element  176  and the like are provided in the package  174 , an external attaching component is not necessary. In addition, since the gyro vibration piece  10  is supported in a vacuum state, it is possible to reduce the effect of temperature of components other than the package  174  and to provide a gyro sensor having stable vibration performance. 
   Also, the method of fixing the package and the cover described in the third and fourth embodiments may be performed using other fixing material such as low melting point glass or thermal curing type adhesive. 
   Also, even though a double T-type gyro vibration piece has been described as an example of a gyro vibration piece in the above-mentioned embodiments, the present invention does not limited thereto. For example, the present invention can be applied to an electrode of a gyro vibration piece such as a tuning fork type gyro vibration piece or an H-type gyro vibration piece. 
   The entire disclosure of Japanese Patent Application No. 2005-97590, filed Mar. 30, 2005 is expressly incorporated by reference herein.