JP2011047821A - Acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration sensor capable of heightening shock resistance by suppressing the maximum stress without concentrating a stress on an intersection angle, and without lowering sensor sensitivity. <P>SOLUTION: This acceleration sensor 100 includes: a frame section 111; a weight section 112; a beam section 113 for connecting the frame section 111 to the weight section 112; an acceleration detection section formed on the beam section 113; a fillet section 116 spread toward a connecting section between the beam section 113 and the weight section 112 or the frame section 111; and a stress relaxing section 117 formed circularly or elliptically under the connecting section 115, and having a depth in a separating direction from the connecting section 115. The stress relaxing section 117 is formed so as to satisfy following conditions: L≥100 μm, 30 μm≤W≤60 μm, and 10 μm≤O≤40 μm, where W is a beam width, L is an intersection width, and O is the depth. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an acceleration sensor that detects acceleration in the X-, Y-, and Z-axis directions using a piezoresistive element.

  In recent years, acceleration sensors are used in various fields such as automobiles and home appliances. Accelerometers are roughly classified into piezoresistive, piezoelectric, and capacitive types. Each of them has a flexible portion that is deformed in a state where acceleration is applied, and a displacement amount of the flexible portion is obtained as a piezoresistor or a piezoelectric element, and a change in capacitance is obtained as an electrical signal. The use of the acceleration sensor was mainly for detection in the plane direction such as an air bag and vehicle control in the automobile field. As an acceleration sensor for these applications, the detection direction may be one axis or two axes, and since high acceleration values are detected, high resolution is rarely required.

  The high-sensitivity type acceleration sensor is formed so that the flexible portion is easily deformed to ensure sensitivity. For this reason, if an impact force that greatly deviates from the measurement range is applied to the acceleration sensor, the flexible portion may be deformed excessively and may be destroyed, and high sensitivity and high impact resistance conflict.

  Patent Document 1 describes an acceleration sensor having a structure in which a notch portion is provided in a weight plate portion and a support frame portion, and the weight plate portion and the support frame portion are not in contact with the flexible portion. The acceleration sensor described in Patent Document 1 can increase the fracture resistance of the acting portion and the flexible portion of the acceleration sensor element and the boundary portion between the fixed portion and the flexible portion even when an abnormal impact force is applied. .

JP 2004-198280 A

  However, since the acceleration sensor described in Patent Document 1 has a stress relaxation structure in which the beam portion does not have a fillet shape (fillet: R = 0) as a measure against impact resistance, stress is concentrated on the fillet portion to reduce the maximum stress. There are issues that cannot be done.

  FIG. 1 is a view showing the structure of a beam having no fillet shape of an acceleration sensor (fillet: R = 0).

  As shown in FIG. 1, in the acceleration sensor described in Patent Document 1, the beam portion 11 does not have a fillet shape (fillet: R = 0). In addition, there is a conventional technique in which the beam portion 11 is provided with a fillet shape. FIG. 1 shows the shape of the intersection in the case of fillet: R = 30. This intersection shape is a combination of a straight line 21 and a circle 22. Stresses 31 to 33 are generated at the intersections of the beam portions 11 upon impact.

  Conventionally, as a method for reducing the maximum stress of the acceleration sensor, it has been considered to (1) reduce the weight, (2) increase the beam width, and (3) increase the beam thickness. However, any of these methods lowers the sensitivity of the sensor, which is contrary to the requirement for high sensitivity. Further, as shown in FIG. 1, the stresses 31 and 32 can be alleviated to some extent by increasing the width and depth of the intersection. However, the intersecting portion shape is a combination of the straight line 21 and the semicircle 22, and the stress 33 is concentrated particularly on the straight line 21 portion, which is not a preferable shape.

  The present invention has been made in consideration of such points, and can suppress the maximum stress without lowering the sensitivity of the sensor and without concentrating the stress at the intersection angle, thereby improving the impact resistance. An object is to provide an acceleration sensor.

  The acceleration sensor according to the present invention includes a frame portion, a weight portion, a beam portion connecting the frame portion and the weight portion, an acceleration detection portion formed on the beam portion, and the weight portion to the weight portion. Or a fillet portion that expands as it approaches the frame portion, and a stress relaxation portion that is formed in an arc shape or an elliptical shape in the weight portion or the frame portion and has a depth in a direction away from the beam portion, A structure is provided that includes a beam portion and a connecting portion that connects the weight portion or the frame portion.

  According to the present invention, it is possible to increase the impact resistance by suppressing the maximum stress without reducing the sensor sensitivity and without concentrating the stress on the intersection angle.

The figure which shows the structure of the beam of the conventional acceleration sensor without the fillet shape (fillet: R = 0) The perspective view seen from the surface of the acceleration sensor concerning an embodiment of the invention The perspective view seen from the back surface of the acceleration sensor which concerns on the said embodiment The enlarged view of the crossing part of the acceleration sensor which concerns on the said embodiment The image figure as a cantilever beam explaining the structure of the crossing part of the acceleration sensor which concerns on the said embodiment The figure which shows the structure of the cross | intersection part of the beam part of the acceleration sensor which concerns on the said embodiment, and a weight part The figure which shows the relationship between the beam width and depth of the acceleration sensor which concerns on the said embodiment. The perspective view seen from the surface in case weight is added to the weight part of the acceleration sensor which concerns on the said embodiment The enlarged view of the crossing part of the acceleration sensor which concerns on the said embodiment The figure which shows the stress change by the difference in the cross | intersection part width | variety of the acceleration sensor which concerns on the said embodiment. The figure which shows the stress change by the difference in the depth of the acceleration sensor which concerns on the said embodiment. The figure explaining the effect of the acceleration sensor which concerns on the said embodiment The enlarged view of the intersection of the acceleration sensor which concerns on other embodiment

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment)
FIG. 2 is a perspective view seen from the front surface of the acceleration sensor according to the embodiment of the present invention, and FIG. 3 is a perspective view seen from the back surface of the acceleration sensor. FIG. 4 is an enlarged view of the intersection of the acceleration sensor shown in FIG. 3A. FIG. 5 is an image diagram as a cantilever for explaining the structure of the intersection of the acceleration sensors. The present embodiment is an example applied to a triaxial acceleration sensor.

  As shown in FIGS. 2 to 4, the acceleration sensor 100 includes a frame part 111 (111 a to 111 d), a weight part 112 (112 a to 112 d) provided in the frame part 111, a frame part 111 and a weight part 112. And a cross-shaped beam portion 113 (113a to 113d) connecting the two and an acceleration detection element formed on the beam portion 113.

  The weight portion 112 has a center portion 112e (FIG. 3) connected to the center non-movable portion 114, and weight portions 112a to 112b are connected to the center portion 112e and formed in a clover shape.

  Each beam 113a-113d which comprises the beam part 113 is a thin flexible member which has a piezoresistive element. The beam portion 113 is connected to the clover-shaped weight portion 112 at the center portion. The central portion of the beam portion 113 is not movable because the thin and flexible beam portion 113 bends in response to acceleration while the weight portion 112 is not bent even when acceleration is applied. This will be referred to as part 114.

  The beam portion 113 is disposed between the weight portions 112a and 112b, 112b and 112c, 112c and 112d, and 112d and 112a, and is connected to the center non-movable portion 114.

  As shown in FIG. 5, the acceleration sensor has a structure in which a weight portion 112 is connected to a cantilever portion 113 and the beam portion 113 bends when a load is applied.

  This embodiment is characterized by the structure of the connecting portion between the beam portion and the weight portion of the acceleration sensor 100.

  FIG. 6 is a diagram illustrating the structure of the intersection of the beam portion 113 and the weight portion 112 of the acceleration sensor 100.

  As shown in FIG. 6, the acceleration sensor 100 includes a connecting portion 115 that is an intersection of the beam portion 113 and the weight portion 112, and both sides of the beam portion 113, and the beam portion 113 and the weight portion 112 or the frame portion 111. A fillet portion 116 that expands as it approaches the connection portion 115, and a concave stress relaxation portion 117 that has an arc shape at the intersection of the fillet portion 116 and the weight portion 112.

  The stress relaxation portion 117 is formed below the connecting portion 115 and has a circular arc shape or an elliptical shape and has a depth in a direction away from the connecting portion 115.

  The depth of the stress relaxation portion 117 is formed by uniformly cutting the central portion 112e between the weight portions 112a and 112b into an arc shape or an elliptical shape from the lower end surface of the weight portion 112 to the center non-movable portion 114. The weight portions 112b and 112c, 112c and 112d, and 112d and 112a are formed in the same manner.

  When the stress relaxation portion 117 is formed in an elliptical shape, the intersection width is the major axis of the ellipse and the depth is the minor axis of the ellipse. The stress relaxation part 117 has a fan shape.

  The intersection width is a width in contact with the end of the beam portion 113 and the weight portion 112, and the depth is a length from the end of the beam portion 113 to the weight portion 112. The depth of the stress relaxation portion 117 is smaller than the intersection width of the stress relaxation portion 117. The present embodiment is characterized in that an appropriate length intersection width and depth are formed according to the beam width of the acceleration sensor 100. Specifically, the stress relaxation portion 117 is formed in the following shape.

  When the beam width W, the fillet portion 116 in the connecting portion 115 and the beam crossing width L, and the depth O of the stress relaxation portion 117 from the connecting portion 115, the shape satisfies the following expression (1).

L ≧ 100 μm
30μm ≦ W ≦ 60μm
10 μm ≦ O ≦ 40 μm (1)
The above L ≧ 100 μm is set from L ≧ beam width + (fillet × 2) + (error) × 2. This error depends on the manufacturing accuracy described later.

  The lower limit value 30 μm of the above 30 μm ≦ W ≦ 60 μm is set according to the mounting request for wiring and the like. The upper limit value 60 μm is set from the required accuracy such as sensitivity.

  FIG. 7 is a diagram showing the relationship between the beam width W and the depth O. As shown in FIG.

  As shown in FIG. 7, the beam width W and the depth O are set to optimum intermediate values in a range that falls within the range of the maximum value (MAX) and the minimum value (MIN) of manufacturing accuracy.

  Considering the manufacturing accuracy (± 5 μm), it may be between the manufacturing accuracy (MAX) and the manufacturing accuracy (MIN). Further, even if the intersection width and depth are changed, the sensor sensitivity is not affected.

  In the stress relaxation portion 117 of FIG. 6, when the intersection width is equal to or greater than the beam width + fillet × 2 + 5 μm (manufacturing accuracy) × 2, that is, when the curve of the fillet portion 116 ends and intersects at the straight portion, the depth O Set the length to the optimum value for. For example, when the beam width is 40 μm + fillet 30 μm (one side) × 2 + 5 μm (one side) × 2 (manufacturing accuracy) = 110 μm, the depth O is set to the length indicated by the optimum value in FIG. Thereby, the stress at the point B in FIG. 6 which is a corner portion can be suppressed while the maximum stress at the point A in FIG. 6 is relaxed. The stress can be relieved and the impact resistance can be improved by setting the width and depth of the crossing portion to an appropriate length according to the beam width of the acceleration sensor 100. That is, it is possible to increase the impact resistance by reducing the maximum stress without reducing the sensor sensitivity, which has been a problem of the conventional example, and without concentrating the stress on the intersection angle.

  FIG. 8 is a perspective view seen from the surface when a weight is applied to the weight 112 of the acceleration sensor 100. FIG. 9 is an enlarged view of the intersection of the acceleration sensor shown in FIG. 8A.

  As shown in FIG. 8, the acceleration sensor 100 includes a beam portion 113 and a weight portion 112. When high acceleration (for example, 2000 G) is applied, the beam portion 113 is bent and a maximum stress is applied to the beam end portion on the weight portion 112 side. appear. The bending of the beam portion 113 is detected as acceleration by an acceleration detection element (not shown).

  However, as a result of the impact test, breakage has occurred from the end portion of the beam on the weight 112 side, and if this part is subjected to stress relaxation, the impact resistance is improved. FIG. 9 shows the stress at the end of the beam on the weight 112 side.

  The present inventors performed simulation by changing the width and depth of the intersection. As a result, it was found that there is an optimum length for each beam width. An explanation will be given by taking a beam width of 40 μm as an example.

  The simulation was performed using ANSYS and the conditions were static analysis and 2000G in the X-axis direction.

  FIG. 10 is a diagram showing a stress change due to a difference in intersection width (ellipse major axis). The depth is fixed at 20 μm, the intersection width is changed by changing the intersection width, and the stress at the intersection angle with respect to the maximum stress. The ratio is shown.

  Basically, the wider the intersection, the better. As shown in FIG. 10, the maximum stress changed by 50 MPa between 90 μm and 110 μm and the ratio exceeded 90%, whereas the maximum stress change after 110 μm was about 20 MPa and the ratio suddenly decreased. There is a music point. This is due to the fact that the intersection has moved to the straight line instead of the fillet curve. As described above, there is no problem if the crossing width is 40 μm beam + 30 μm fillet × 2 + 5 μm (one side) × 2 (manufacturing accuracy) = 110 μm or more.

  FIG. 11 is a diagram showing the stress change due to the difference in depth (short axis of the ellipse), and shows the ratio of the stress at the intersection angle when the depth is changed with the intersection width fixed at 130 μm.

  As shown in FIG. 11, it can be seen that the maximum stress has a bottom from 25 μm to 40 μm. The stress may be in that range. However, taking the ratio into account, the optimum value is 25 μm. By performing the same analysis for each beam width, the optimum values of the intersection width and depth can be determined.

  12A and 12B are diagrams for explaining the effects of the conventional example and the present embodiment in comparison. FIG. 12A is an enlarged view of an intersection of a conventional acceleration sensor, and FIG. It is an enlarged view of the cross | intersection part of the acceleration sensor 100 of the form. FIG. 12A shows the same conventional example as FIG.

  As shown in FIG. 12A, when the intersection shape of the acceleration sensor is a combination of a straight line 21 and a circle 22, stresses 31 to 33 are generated at the intersection of the beam 11 at the time of impact. In particular, the stress 33 concentrates on the straight line 21 portion of the beam 11. Further, the stresses 31 and 32 are concentrated at the intersection angle. On the other hand, in the present embodiment, as shown in FIG. 12B, the acceleration sensor 100 forms a fan-shaped stress relaxation portion 117, so that only the intersection angle is compared to the conventional example. Only extremely small stresses 121 and 122 are generated.

  As shown in FIG. 12A, in the conventional example, when the beam width is 40 μm, the maximum stress was 1559 MPa and the impact resistance was 1400 G in the X-axis 2000G analysis.

  On the other hand, as shown in FIG. 12B, in the present embodiment, the maximum stress is 1358 MPa in the X-axis 2000G analysis in the case of the optimum value, here, when the intersection width is 130 μm and the depth is 25 μm. An improvement of about 10% is seen compared to the conventional example. Considering the impact resistance from the stress value, it is expected to be 1600G, and an improvement in impact resistance of 200G is obtained.

  The stress relaxation at the intersection occurs at high acceleration, and at the low acceleration actually used, the sensitivity does not change even if the intersection is changed.

  As described above in detail, the acceleration sensor 100 according to the present embodiment is formed on the frame portion 111, the weight portion 112, the beam portion 113 that connects the frame portion 111 and the weight portion 112, and the beam portion 113. The acceleration detection unit, the fillet unit 116 that expands as it approaches the connection part between the beam part 113 and the weight part 112 or the frame part 111, and the connection part 115 is formed in an arc shape or an ellipse shape on the lower side. And a stress relaxation portion 117 having a depth in a direction away from the portion 115, where the stress relaxation portion 117 is L ≧ 100 μm, 30 μm ≦ W ≦ 60 μm, 10 μm ≦ when the beam width W, the intersection width L, and the depth O are provided. O ≦ 40 μm is formed. Thereby, as shown in FIG. 6, the stress at the point B in FIG. 6 which is a corner portion can be suppressed while the maximum stress at the point A in FIG. 6 is relaxed. As a result, it is possible to increase the impact resistance by reducing the maximum stress without reducing the sensor sensitivity and without concentrating the stress on the intersection angle.

(Other embodiments)
FIG. 13 is an enlarged view of a crossing portion of an acceleration sensor according to another embodiment.

  As shown in FIG. 13, the stress relaxation portion 117 </ b> A of the acceleration sensor 100 is formed on the lower side of the connecting portion 115 and has a shape combining an ellipse and a straight line.

  If the depth of the stress relaxation portion 117A is an optimum value, a shape combining an ellipse and a straight line can be taken. By forming the stress relaxation portion 117A having a shape combining an ellipse and a straight line, stresses 131 to 133 are generated at the intersection angle and the straight line portion, but are within an allowable range.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, Various changes are possible based on the technical idea of this invention, and this invention covers these. It is natural.

  Although the above embodiment is an example applied to a triaxial acceleration sensor, it can be applied to all semiconductor acceleration sensors with the same configuration.

  In the above embodiment, the name “acceleration sensor” is used. However, this is for convenience of explanation, and a three-axis acceleration sensor, a semiconductor acceleration sensor, or the like may be used.

  The acceleration sensor of the present invention can be widely applied to various devices such as toys such as game controllers, automobile impact detection devices, hard disk drop detection devices, and mobile phone input devices.

DESCRIPTION OF SYMBOLS 100 Acceleration sensor 111,111a-111d Frame part 112,112a-112d Weight part 113,113a-113d Beam part 115 Connection part 116 Fillet part 117,117A Stress relaxation part

Claims (3)

A frame,
A weight part;
A beam portion connecting the frame portion and the weight portion;
An acceleration detector formed on the beam;
A fillet portion that expands from the beam portion as it approaches the weight portion or the frame portion, and a stress relaxation portion that is formed in an arc shape or an elliptical shape in the weight portion or the frame portion and has a depth in a direction away from the beam portion. And a connecting part that connects the beam part and the weight part or the frame part, and
An acceleration sensor comprising:   When the width between the end of the beam and the weight is the intersection width, and the length from the end of the beam to the weight or the frame is the depth, the depth is greater than the width of the intersection. The acceleration sensor according to claim 1, which is small. The stress relaxation part has a beam width W, a crossing part width L, and a depth O, and has a shape satisfying the following: L ≧ 100 μm
30μm ≦ W ≦ 60μm
10μm ≦ O ≦ 40μm
The acceleration sensor according to claim 2.