JP2006177675A - Capacitance acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance frequency responsiveness without lowering sensitivity. <P>SOLUTION: In this capacitance acceleration sensor, a substrate 20 is mounted on a base 30, and a frame part 21, a mass part 22, and a diaphragm 23 are integrally formed on the substrate 20, with the diaphragm 23 supporting the mass part 22 on the frame part 21. A prescribed air gap 51 is formed between the mass part 22, the diaphragm 23, and the base 30. A fixed electrode 41 for detecting the displacement of the mass part 22 as a change in capacitance is formed on the base 30. The air gap 51 is extended/formed on an inner circumferential-side portion of the frame part 21 to form a groove 24 in the circumferential-side portion engaged on the air gap 51. Air damping can be reduced without decreasing an area for detecting capacitance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a capacitance detection type acceleration sensor.

FIG. 6 shows a configuration described in Patent Document 1 as a conventional configuration example of this type of acceleration sensor. A frame portion 12, a mass portion 13 and a diaphragm 14 are integrally formed on a substrate 11 made of single crystal silicon. Has been.
The mass portion 13 is located in the center of the frame portion 12 having a rectangular frame shape and is connected to the frame portion 12 by a diaphragm 14. The mass portion 13 is displaced by being supported by an elastic diaphragm 14 on the entire circumference. It is possible.
An upper fixed substrate 15 and a lower fixed substrate 16 made of an insulating material such as glass are respectively disposed on the upper and lower surfaces of the substrate 11, and the upper and lower surfaces of the frame portion 12 are respectively connected to the upper fixed substrate 15 and the lower fixed substrate 16. As a result, a closed space is formed inside the acceleration sensor.

In this example, the mass portion 13 is formed to be slightly thinner than the frame portion 12, thereby forming a required gap between the mass portion 13 and the upper fixed substrate 15 and the lower fixed substrate 16. The mass portion 13 functions as a movable electrode, and in this example, a fixed electrode 17 facing the mass portion 13 is formed on the inner surface of the upper fixed substrate 15.
In the acceleration sensor configured as described above, when acceleration is input in the input axis direction (perpendicular to the plate surface of the substrate 11), the mass unit 13 is displaced by an inertial force according to the input acceleration. And the fixed electrode 17 change, the capacitance between the mass portion 13 and the fixed electrode 17 changes, and the input acceleration can be detected by detecting the change in the capacitance.

In addition, the displacement of the mass portion 13 is hindered (air-damped) by a fluid (for example, air) existing in the gap between the mass portion 13 and the upper fixed substrate 15 and the lower fixed substrate 16, thereby deteriorating responsiveness. Therefore, in this example, in order to reduce such air damping, a plurality of grooves 18 are formed on the upper and lower surfaces of the mass portion 13, respectively.
JP-A-8-254544

Since the capacitance is proportional to the electrode area and inversely proportional to the distance between the electrodes, the sensitivity of this type of capacitive acceleration sensor is determined by the following conditions (1) to (4) including these items. .
(1) Mass of mass part (2) Electrode area (3) Diaphragm spring constant (4) Distance between electrodes On the other hand, a capacitive acceleration sensor can be downsized or increased in sensitivity while maintaining its size. When considering, there is a limit in terms of size in increasing the mass of the mass part (1) and the area of the electrode (2). In addition, reducing the spring constant of the diaphragm in (3) also has a limit because the diaphragm cannot be made extremely thin from the viewpoint of impact resistance. Therefore, it is necessary to reduce the distance between the electrodes in (4), but this causes a problem that air damping becomes large.

For example, in a capacitance type acceleration sensor, in order to reduce the size and increase the sensitivity, the distance between the electrodes, that is, the distance between the mass portion and the fixed electrode needs to be set to at least several microns. Since it becomes extremely large and causes the frequency response to deteriorate, conventionally, a groove 18 is provided on the surface of the mass portion 13 as in the above-described example.
However, when the groove is provided on the surface of the mass part in this way, the area as an electrode for detecting the capacitance is reduced accordingly, and thus the sensitivity is lowered by the amount of the area reduction.

  In view of this problem, an object of the present invention is to provide a capacitive acceleration sensor that can reduce air damping without reducing the capacitance detection area, and thus has excellent frequency response and excellent sensitivity. It is to provide.

  According to the present invention, a substrate in which a frame portion, a mass portion located in the frame portion, and a diaphragm that supports the mass portion on the frame portion are integrally formed is mounted on the base, and the diaphragm is mounted on the base of the substrate. Capacitance in which a predetermined gap is formed between the mass part and the diaphragm and the base located on the opposing surfaces, and a fixed electrode is formed on the base to detect displacement of the mass part as a change in the capacitance. In the type acceleration sensor, the gap is formed to extend in the inner peripheral portion of the frame portion, and the groove facing the gap is formed in the inner peripheral portion.

  According to the present invention, the air damping can be reduced without sacrificing the area for detecting the capacitance, and thus the frequency response can be improved without causing a decrease in sensitivity.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an embodiment of a capacitive acceleration sensor according to the present invention. FIG. 1A shows an external appearance, and FIG. 1B shows a cross-sectional structure. 2A and 2B show a CC section and a DD section in FIG. 1A, respectively.
In this example, the capacitive acceleration sensor includes a substrate 20 on which a frame portion, a mass portion, a diaphragm, and the like are formed, and a base 30 on which the substrate 20 is mounted. 3 and 4 show the configurations of the substrate 20 and the base 30, and FIG. 5 shows the substrate 20 viewed from the bottom side. First, the structure of the substrate 20 and the base 30 will be described.

As shown in FIG. 3, the substrate 20 has a frame portion 21 having a rectangular frame shape, a mass portion 22 located in the center of the frame portion 21, and a mass located between the frame portion 21 and the mass portion 22. A diaphragm 23 for supporting the portion 22 on the frame portion 21 so as to be displaceable is integrally formed. The substrate 20 is made of, for example, single crystal silicon, and the frame portion 21 and the mass portion are formed by anisotropic etching. 22 and a diaphragm 23 are formed. The diaphragm 23 is located on the bottom surface 20 a side of the substrate 20.
As shown in FIG. 5, four elongated grooves 24 are formed on the bottom surface 20 a of the substrate 20 so as to form four sides of the square, and the grooves 20 communicate with the longitudinal center of one of the grooves 24. A wide groove 25 is formed outside 24, that is, on the side surface side of the substrate 20. The four grooves 24 are located in the inner peripheral side portion of the frame portion 21 as shown in FIG. In addition, the groove | channel 25 is not open | released by the side surface of the board | substrate 20, but is stopped in front of the side surface. These grooves 24 and 25 are formed by anisotropic etching of single crystal silicon.

  On the other hand, the base 30 is made of, for example, an insulating material such as glass and has a rectangular plate shape that is longer than the substrate 20 as shown in FIG. The upper surface of the base 30 has a shape that is slightly recessed, leaving a rectangular frame shape with the center of one side cut out. That is, a concave surface 30a is formed on the upper surface of the base 30 by etching or the like. A recess 32 surrounded by a rectangular frame-shaped step 31 by 30a, a terminal forming portion 33 located outside the step 31 and located on one short side of the base 30, and a recess 32 and a terminal forming portion 33. And a wiring lead-out portion 34 is formed. The step portion 31 has a shape corresponding to the frame portion 21 of the substrate 20, and the concave portion 32 reaches a position facing the inner peripheral side portion of the frame portion 21 as shown in FIG. 2, that is, a position facing the groove 24. The size is assumed.

A fixed electrode 41 is formed in the center of the recess 32 of the base 30 having the above-described structure, and the terminal 42 and the fixed electrode 41 formed in the terminal forming portion 33 have a lead wire 43 passing through the wiring lead portion 34. Connected through. The fixed electrode 41, the terminal 42, and the lead wire 43 are formed by sputtering, for example. Note that the square fixed electrode 41 has a shape facing the mass portion 22.
The base 30 and the substrate 20 are assembled by mounting and fixing the substrate 20 on the step portion 31 of the base 30, thereby completing the capacitive acceleration sensor shown in FIG. 1. The base 30 and the substrate 20 are fixed by, for example, anodic bonding. In addition, it can also be set as adhesive fixation. The terminal forming portion 33 in which the terminal 42 of the base 30 is formed is protruded to the side of the substrate 20 as shown in FIG.

The diaphragm 23 located on the bottom surface 20a side of the substrate 20 is opposed to the base 30, and as shown in FIG. 1B and FIG. 2, the concave portion 32 formed in the base 30 allows the diaphragm 23 and the mass portion 22 to be separated from the base 30. A predetermined gap 51 is formed. The gap 51 extends to the inner peripheral side portion of the frame portion 21, and the groove 24 formed in the frame portion 21 faces the gap 51. The wide groove 25 formed on the bottom surface 20 a of the substrate 20 is positioned on the wiring lead-out portion 34 of the base 30.
In the structure as described above, when the dimension (amount of gap) of the gap 51 is a and the depth of the grooves 24 and 25 is b as shown in FIG. 2A,
b> a
Preferably, the groove depth b is at least 10 times the gap dimension a. In FIGS. 1 and 2 and the like, the gap 51 is exaggerated for easy understanding. When the thickness of the diaphragm 23 is c and the thickness between the groove 24 and the inner wall surface (inclined surface) of the frame portion 21 is d,
d> c
It is said.

In the acceleration sensor having the above-described configuration, when acceleration is input in the input axis direction (perpendicular to the plate surface of the substrate 20), the mass portion 22 is displaced and the fixed electrode 41 is displaced as in the conventional acceleration sensor shown in FIG. The distance between and changes. Therefore, the input acceleration can be detected by detecting a change in capacitance between the mass portion 22 and the fixed electrode 41.
In this example, air damping of the mass portion 22 can be reduced by the presence of the grooves 24 and 25 communicating with the gap 51. For example, when the groove depth b is 10 times or more of the gap dimension a as described above, the flow velocity around the diaphragm 23 and the gap 51 of the wiring lead-out portion 34 is 1/10 or less before the grooves 24 and 25 are provided. Become. Since the loss due to the viscosity of the fluid is proportional to the flow velocity, the loss around the diaphragm 23 and in the wiring lead-out portion 34 is 1/10 or less that before the grooves 24 and 25 are provided. In the example, the air damping of the entire sensor can be reduced. Unlike the conventional example shown in FIG. 6, in this example, a groove is not provided on the surface of the mass portion 22 that faces the fixed electrode 41, so the capacitance detection area does not decrease, and therefore the sensitivity decreases. Does not occur.

Next, the results of evaluating various types of prototypes will be described.
The following three types of prototypes were made in an acceleration sensor having an outer dimension (the size of the base 30) of 4 mm × 5 mm and a gap dimension a of 1.4 μm. The mass of the mass part 22, the area of the fixed electrode 41, and the diaphragm 23 were the same.
Prototype 1 (comparative example): When grooves 24 and 25 are not provided Prototype 2 (comparative example): On the surface of the mass portion 22 facing the fixed electrode 41, a lattice shape as described in FIG. Prototype 3 (Example): When grooves 24 and 25 are provided (groove depth b: 25 μm)

The results of measuring the cut-off frequencies of these prototypes 1 to 3 are shown below.
Prototype 1 (comparative example): 10.6 Hz
Prototype 2 (comparative example): 11.8 Hz
Prototype 3 (Example): 26.5 Hz
As is clear from the above results, in the prototype 3 which is an embodiment of the present invention, the cut-off frequency was greatly improved, and it was confirmed that there was an extremely excellent effect for reducing air damping. The sensitivity of prototype 3 was the same as that of prototype 1, but the sensitivity of prototype 2 was about 15% lower than the sensitivity of prototype 1. In the structure in which the groove is provided on the surface of the mass portion facing the fixed electrode, the sensitivity is reduced in this way, and it is clear from the above results that a significant reduction effect of air damping cannot be expected.

  In the embodiment described above, the groove 25 is provided in addition to the groove 24. However, the groove 25 is not necessarily provided, and only the groove 24 may be provided. Even in this case, the same effect as described above can be obtained.

The figure which shows one Example of the capacitive acceleration sensor by this invention, A is a perspective view which shows an external appearance, B is a perspective view which shows a cross-section. 1A is a CC cross-sectional view of FIG. 1A, and B is a DD cross-sectional view of FIG. 1A. The perspective view of the board | substrate in FIG. 1A. The perspective view of the base in FIG. 1A. The perspective view which looked at the board | substrate of FIG. 3 from the bottom face side. The figure which shows the prior art structural example of a capacitive acceleration sensor, A is a top view partly notched, B is sectional drawing.

Claims (1)

A substrate on which a frame part, a mass part located in the frame part, and a diaphragm that supports the mass part on the frame part are integrally formed is mounted on a base, and the diaphragm faces the base of the substrate A predetermined gap is formed between the mass part and the diaphragm and the base, and a fixed electrode for detecting a displacement of the mass part as a change in capacitance is formed on the base. In capacitive acceleration sensors,
A capacitive acceleration sensor, wherein the gap is formed to extend in an inner peripheral side portion of the frame portion, and a groove facing the gap is formed in the inner peripheral side portion.

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