JP3036681B2 - Capacitive acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an acceleration sensor utilizing a change in capacitance capable of simultaneously detecting accelerations of two or more axes, and more particularly, to an outer peripheral portion of a beam supporting a flexible substrate so as not to face each other. By arranging and joining the weights only at the center of the flexible substrate and arranging the electrodes on the outer peripheral side of each substrate, the output with respect to the detected acceleration is affected even if the ambient temperature fluctuates. The present invention relates to a capacitance-type acceleration sensor that can be applied to applications such as automobiles that have a wide operating temperature range and that have no severe configuration.

[0002]

2. Description of the Related Art For example, Japanese Patent Application Laid-Open Nos. 4-148833 and 4-33743 disclose capacitive acceleration sensors.
No. 1, Japanese Patent Application Laid-Open No. 5-188079 discloses a method in which a plurality of capacitance elements are provided opposite to each other by attaching electrodes to opposite surfaces of a fixed substrate and a flexible substrate, and an XY plane parallel to the substrate surface is provided. And a change in acceleration in a three-dimensional direction of the X, Y, and Z axes of the Z axis orthogonal to the X axis is detected based on a change in capacitance between a plurality of capacitance elements. Has been proposed.

For example, as shown in a perspective view of FIG. 9A, a beam 11 (showing a center line) supporting a flexible substrate 10 is divided into a rectangular flexible substrate by dividing the rectangular flexible substrate into four parts except for a central part. In the configuration example in which the electrodes are arranged in a cross shape on a line, a fixed substrate (not shown) arranged at a predetermined interval in parallel with the flexible substrate and, as shown in FIG. ₁ , X ₂ , Y ₃ , Y ₄ , and Z are attached to form capacitance elements C _{1 to} C ₅ . Further, a glass weight body 12 having an appropriate mass is provided on the lower surface of the flexible substrate.

In detail, here, four electrodes are provided on the outer peripheral portion between the opposing surfaces and one electrode is provided on the central portion, and the capacitance element C is provided.
Configuration to form a ₁ -C _5, i.e., perpendicular with the electrode surface X, each two capacitances arranged on two axes of Y element C
And ₁ -C _4, consisting of construction of arranging the capacitive element C ₅ in the middle of the previous two axes.

In the above configuration, for example, when acceleration is applied in the X-axis direction, the distance between the electrodes between the opposing surfaces of the fixed substrate and the flexible substrate changes, so that each of the capacitance elements C ₁ to C ₁ the capacitance of C ₄ is changed. Similarly, when acceleration is applied in the Z-axis direction, the capacitance of each of the capacitance elements C _{1 to} C _{4 also} changes.

[0006] The detection of each component of the acceleration based on the change in the capacitance is performed, for example, as an output with respect to the acceleration in the X-axis direction, as a capacitance difference (C ₁ -C ₃ ) between the capacitance elements C ₁ and C ₃ , As outputs for the acceleration in the Y-axis direction, the capacitance elements C ₂ and C ₄
Is detected as the capacitance (C ₅ ) of the capacitance element C ₅ as an output with respect to the capacitance difference (C ₂ −C ₄ ) and acceleration in the Z-axis direction.

In such a capacitance type sensor, since the sensitivity of the sensor increases as the displacement of the flexible substrate with respect to the applied acceleration increases, a low-rigidity support structure is provided for the purpose of improving the detection sensitivity. In addition, a weight body having an appropriate mass whose center of gravity is shifted below the support structure of the flexible substrate is provided for the purpose of amplifying the applied acceleration.

For example, as a specific configuration of a capacitance type acceleration sensor having a high sensitivity, Japanese Unexamined Utility Model Publication No.
And Japanese Patent Application Laid-Open No. 5-264577. In these, it has been proposed to form the flexible portion with a thin and thin beam in order to obtain the above-described low-rigidity support structure.

[0009]

Since the flexible substrate is supported with low rigidity, it is very sensitive to disturbances other than acceleration. Specifically, there is a problem in that thermal stress is generated in the supporting structure due to a change in the ambient temperature, and the displacement of the flexible substrate due to the thermal stress is generated, so that an apparent output is generated despite no acceleration.

In order to obtain sufficient sensitivity, it is necessary to increase the deformation of the flexible substrate when acceleration is applied, so that it is necessary to increase the mass of the substrate. For this reason, it is necessary to increase the thickness of the flexible substrate. However, when this is performed, when manufacturing a support structure such as a thin beam, the substrate needs to be dug deeper from below, which is not practical in actual production. Normally, to obtain greater sensitivity, a configuration is adopted in which the weight is joined to a flexible substrate as a separate component, but if a material having a different thermal expansion coefficient from the substrate is used for the weight, the ambient temperature will fluctuate. Then, warping occurs in the flexible substrate due to the bimetal phenomenon at the joint surface, and as a result, there is a problem that the flexible substrate is displaced and an apparent output is generated despite no acceleration.

Usually, a capacitance type acceleration sensor is often manufactured by applying a so-called micro-machining technique for miniaturization. In general, Pyrex glass (trade name) is used for the above-mentioned weight, and anodic bonding is performed. However, when this method is implemented, a problem arises in that the above-mentioned flexible substrate is warped due to a difference in thermal expansion coefficient between silicon and glass, thereby causing displacement.

According to the present invention, there is provided an acceleration sensor utilizing a change in capacitance capable of simultaneously detecting accelerations of two or more axes, wherein the output with respect to the detected acceleration is not affected even if the ambient environmental temperature fluctuates. It is an object of the present invention to provide a capacitance type acceleration sensor which is most suitable for applications such as automobiles having a wide temperature range and severe.

[0013]

The inventor of the present invention has conducted various studies on the support structure of the flexible substrate with the beam for the purpose of a configuration in which the output with respect to the detected acceleration is not affected even if the ambient temperature fluctuates. By changing the support structure of the flexible substrate by the beam from the conventional arrangement on the center line of the flexible substrate to the configuration of arranging it on the outer peripheral portion, the thermal deformation of the flexible substrate due to the temperature change is caused by the rotation of the substrate plane. The present inventors have found that it is possible to escape in the direction and reduce the displacement of the substrate thickness in the vertical direction, and have completed the present invention.

Further, the inventor has paid attention to the fact that the sensor joins the substrate and the weight body to cause deformation due to the bimetal effect, and has an object to reduce the deformation or substantially have no adverse effect. As a result of various investigations, it was found that deformation by the bimetal effect can be reduced by changing the anodic bonding portion between the flexible substrate and the weight body, for example, from the conventional four lower surface of the substrate to only one central portion,
Furthermore, when materials having different coefficients of thermal expansion are joined assuming a predetermined difference in the coefficient of thermal expansion, the joint area at the central portion of the substrate is adjusted to an optimum value to reduce the bimetal effect and the thermal deformation of the beam. The interaction sets an increase and decrease area of the capacitance on the flexible substrate, and the increase and decrease of the capacitance becomes zero, thereby substantially reducing the influence of the bimetal effect and the displacement of the flexible substrate due to the thermal deformation of the beam. In other words, the central area of the substrate is set such that the area of increase and decrease of the capacitance are set substantially equal on the flexible substrate and the increase and decrease of the capacitance become zero. By adjusting the joint area between the flexible substrate and the weight at one location, it was found that displacement of the flexible substrate due to the bimetal effect and thermal deformation of the beam could be substantially prevented, and the present invention was completed.

Further, the inventor has made the support structure by the beam and the joint between the flexible substrate and the weight body according to the above-described structure of the present invention, and is affected by the thermal deformation of the flexible substrate due to a change in ambient temperature. As a result of diligent studies on the specific configuration, the four electrodes for the conventional X-axis and Y-axis acceleration detection were arranged on the outer periphery, and the configuration for the Z-axis acceleration detection was arranged at the center, The inventors have found that the object can be achieved by arranging all the electrodes for the X, Y, and Z axes on the outer peripheral portion except the central portion, and completed the present invention.

That is, according to the present invention, a plurality of capacitance elements are provided opposite to each other by attaching electrodes to respective opposing surfaces of a flexible substrate having a beam-supporting structure and a fixed substrate, and are provided in parallel with the substrate surface. X, Y, Z of the Z axis perpendicular to this
In a capacitance-type acceleration sensor that detects changes in acceleration in three-dimensional directions on the axis based on changes in capacitance between a plurality of capacitance elements, a beam is placed on the outer periphery of a flexible substrate. Anodic bonding to a flexible substrate
Of the weight body to be bonded is only one place at the center of the substrate
Or, electrodes are arranged on the outer peripheral part except the central part of the substrate
This is a capacitance type acceleration sensor having a configuration.

The present invention also relates to the capacitance type acceleration cell.
In the sensor, the beam is arranged on the outer periphery of the flexible substrate.
And a weight type body to be anodically bonded to the flexible substrate has only one bonding portion at the center of the substrate , and has a configuration in which electrodes are arranged on an outer peripheral portion excluding the center portion of the substrate. An acceleration sensor is also proposed.

[0018]

1A and 1B are a perspective view and a front view showing a flexible substrate of a capacitance type acceleration sensor according to the present invention, and FIG. 2 is a top view showing the arrangement of its electrodes. . A substantially square flexible substrate 1 made of silicon is supported on its outer periphery by four beams 2 whose position is indicated by a center line, and the lower surface of the flexible substrate 1 is a rectangular plate having an appropriate mass. The glass weight 3 is anodically bonded only at a central portion of the lower surface of the flexible substrate 1. Reference numeral 4 in FIG. 2 indicates a joint.

Electrodes are attached to the fixed substrate (not shown) arranged in parallel with the flexible substrate at a predetermined interval and the opposing surfaces of the flexible substrate 1 to form the capacitance elements C _{1 to} C ₅ . In this case, as shown in FIG.
The substantially trapezoidal electrodes X ₁ , X ₂ , Y ₃ , and Y ₄ for the Y axis are combined and arranged on the outer peripheral portion of the flexible substrate 1.
Is disposed between the X-axis electrode and the Y-axis electrode.

In the conventional structure shown in FIG. 9 described above, when the beam 11 is thermally deformed, these four beams are pushed and attracted to each other because two pairs of two beams are installed facing each other. As a result, the flexible substrate 10 is largely displaced up and down. That is, when the ambient temperature is changed from 20 ° C. to −40 ° C., the thermal deformation is F
FIGS. 11 and 12 show the results of simulation by EM analysis.
As shown in FIG. 7, the deformation of the beam and the bimetal phenomenon of the support structure can be observed, and it can be seen that the deformation amount is as large as 0.35 μm.

On the other hand, FIGS. 1 and 2 show a structure in which the above-described beam is arranged on the center line of the flexible substrate, and a structure in which the beam is arranged on the outer peripheral portion and a structure in which the joint is formed at one central portion.
In the present invention having the above structure, the deformation amount is 0.038 μm as shown in FIG. 3 and FIG. 4 in the simulation of the flexible substrate by the FEM analysis, and the deformation is largely suppressed. As shown in FIGS. 3 and 4, such an effect is obtained by deforming (elongating, elongating,
Due to the fact that no shrinkage occurs, they are pressed against each other and no attraction occurs, so that the flexible substrate is suppressed from being displaced in the thickness direction even when rotational movement occurs. It can be seen that the effect is also suppressed.

By changing the structure of the present invention described above, that is, the structure in which the support structure of the flexible substrate by the beam is arranged at the outer peripheral portion, the thermal deformation of the flexible substrate due to the temperature change is released in the rotation direction of the substrate plane. It is possible to suppress displacement in the thickness direction. Furthermore, if the joint is changed to one center and its area is adjusted to the optimum value, the influence of the warpage of the flexible substrate due to the bimetal effect can be suppressed, and the effect of the thermal deformation of the flexible substrate is greatly improved compared to the conventional structure. It became clear that it would be.

However, the structure of the present invention described above, that is, the structure in which the support structure of the flexible substrate by the beam is arranged at the outer peripheral portion is changed, and the joint is changed to one central portion to optimize the area. By adjusting the value to the above value, the influence of the thermal deformation of the flexible substrate is greatly improved as compared with the conventional structure, but the deformation amount is not completely zero, as shown in FIGS. . Further, according to the present invention, as shown in FIG. 2, the electrodes for X, Y and Z axes are all attached to the outer peripheral portion of the flexible substrate, as shown in FIG. The present invention is characterized in that a measure is taken by arranging over a region dividing line. This measure is described in detail below.

As schematically shown in FIG. 5B, the deformed state of the flexible substrate 1 is a state in which the deformation due to the expansion or contraction of the beam and the deformation due to the bimetal effect are combined. Therefore, by changing the structure in which the support structure by the beam is arranged on the outer peripheral portion and adjusting the bonding area of the flexible substrate 1 with the glass weight 3, as shown in FIG. Area dividing line 5 (2
For example, when the temperature rises, the outside deforms upward (the capacitance value increases) from the initial state, and the inside deforms downward (the capacitance value decreases). At the time of lowering, by configuring so as to deform in the opposite direction, an area where the capacitance increases and an area where the capacitance decreases are set on the flexible substrate 1, and the increase and decrease of the capacitance becomes zero. It can be substantially zero.

Here, in FIG. 5A, it is assumed that the plane of the flexible substrate 1 is on the XY axis and the substrate thickness direction is the Z axis direction.
Assuming that a portion where the deformation state of the flexible substrate 1 due to heat is Z = 0 in the Z-axis direction is displayed, the portion is indicated by a two-dot chain line on the substrate 1. In the present invention, such a portion indicated by a two-dot chain line is referred to as a region dividing line 5.

That is, as shown in FIG. 6A, the bonding area of the flexible substrate 1 with the glass weight 3 is adjusted so that the region dividing line passes slightly outside the center of the substrate 1 and the center of each side. Substantially trapezoidal electrodes X ₁ , X ₂ , Y ₃ , X and Y axes
Y ₄ , and the arrangement of the Z-axis electrode Z disposed between the X-axis electrode and the Y-axis electrode are arranged so as to straddle the region dividing line 5 and the area outside and inside the region dividing line 5. Were set approximately equal. Even if thermal deformation occurs in one electrode by such a configuration, in the example of the behavior at the time of temperature rise, the capacitance value on the outer side of the region dividing line 5 increases, and the capacitance value on the inner side decreases, so that subtraction is performed. It is possible to realize a sensor which becomes substantially zero and is not substantially affected by thermal deformation.

Another embodiment of the electrode arrangement according to the present invention will be described. The electrode arrangement in FIG. 6B is different from the configuration in which a rectangular Z-axis electrode Z is arranged at the center of the substantially trapezoidal electrodes X ₁ , X ₂ , Y ₃ , and Y ₄ for the X axis and Y axis in FIG. 6A. In this case as well, the area outside and inside the region dividing line 5 of each electrode disposed across the region dividing line 5 is set to be substantially equal.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1 and 2, a beam 2 is arranged on an outer peripheral portion of a flexible substrate 1, and a joint portion of the flexible substrate 1 with a glass weight 3 is changed to one central portion to reduce the area. Is adjusted to an optimum value, and furthermore, the ambient temperature is actually varied by the capacitance type acceleration sensor according to the present invention having a configuration in which the electrodes for the X, Y, and Z axes are all arranged on the outer periphery of the flexible substrate. FIG. 7 shows the relationship between the temperature and the zero-point temperature drift by measuring the change in the capacitance value due to the ambient temperature fluctuation and converting the value into acceleration.

Further, in the above-described configuration of FIGS. 1 and 2,
Only the electrode arrangement was the conventional arrangement shown in FIG. 9B, and the change in the capacitance value due to the ambient temperature fluctuation of the capacitance type acceleration sensor in which the beam arrangement and the joining of the glass weight were configured according to the present invention was measured. FIG. 8 shows the relationship between the temperature and the zero-point temperature drift in terms of acceleration.

Further, a change in capacitance value due to a change in ambient temperature of the conventional capacitance type acceleration sensor shown in FIG. 9 is measured, converted into acceleration, and the relationship between temperature and zero point temperature drift is shown in FIG. Shown in The flexible substrate material used for the above three types of sensors is silicon, and the weight material is Pyrex glass.

In the above-described conventional structure shown in FIG. 9, as shown in FIG. 10, it can be seen that the capacitance value fluctuates due to the fluctuation in temperature and apparent acceleration occurs. In addition, when the beam arrangement and the joining of the glass weight are configured according to the present invention, as shown in FIG. 8, it can be seen that the configuration according to the present invention works effectively and the temperature characteristics are improved. Further, when the beam arrangement, the bonding of the glass weight body, and the electrode arrangement in FIGS. 1 and 2 are configured according to the present invention, as shown in FIG. It turns out that it is not affected.

[0032]

According to the capacitance type acceleration sensor of the present invention, the beams supporting the flexible substrate are arranged on the outer peripheral portion so as not to face each other, and the weight is joined only to the central portion of the flexible substrate. In addition, by arranging the electrodes on the outer peripheral side of each substrate, even if the ambient temperature fluctuates, the output with respect to the detected acceleration is not affected, and it can be used in applications with large ambient temperature fluctuations such as automobiles A highly accurate sensor can be provided. Further, according to the present invention, temperature compensation by an electric circuit, which is required in a conventional sensor, is not required, and thus a sensor having a simple configuration can be provided at low cost.

[Brief description of the drawings]

FIG. 1A is a perspective view illustrating a flexible substrate of a capacitive acceleration sensor according to the present invention, and FIG. 1B is a side view illustrating a flexible substrate.

FIG. 2 is an explanatory plan view showing an arrangement of electrodes on a flexible substrate of the capacitive acceleration sensor according to the present invention.

FIG. 3 is an explanatory view showing the result of simulating the thermal deformation of the capacitance type acceleration sensor according to the present invention due to the temperature change by FEM analysis, wherein A is a perspective view and B is an explanatory view of a planar direction; is there.

FIG. 4 is an explanatory view showing the result of simulating the thermal deformation of the capacitance type acceleration sensor according to the present invention due to the temperature change by FEM analysis, where A is a temperature of 20 ° C., and B is a temperature of −40 ° C. At this time, it shows a deformation in a state where 1 G (earth gravity) is applied to the Z axis (vertical direction in the figure).

FIGS. 5A and 5B are explanatory diagrams schematically showing a deformation state of the capacitance type acceleration sensor accompanying a temperature change, wherein A shows a plane and B shows a deformation in a thickness direction.

FIGS. 6A and 6B are explanatory plan views showing another arrangement of the electrodes on the flexible substrate of the capacitive acceleration sensor according to the present invention.

FIG. 7 is a graph showing a relationship between a temperature and a zero-point temperature drift obtained by measuring a change in capacitance value due to a change in ambient temperature of a capacitance type acceleration sensor according to the present invention and converting the measured value into acceleration.

FIG. 8 is a graph showing a relationship between a temperature and a zero-point temperature drift obtained by measuring a change in capacitance value due to a change in ambient temperature of a capacitance type acceleration sensor according to the present invention and converting the measured value into acceleration.

FIG. 9A is a perspective view illustrating a flexible substrate of a conventional capacitive acceleration sensor, and FIG. 9B is a plan view illustrating an arrangement of electrodes.

FIG. 10 measures a change in capacitance value due to a change in ambient temperature of a conventional capacitance-type acceleration sensor, converts the measured value into acceleration,
It is a graph shown as a relationship between temperature and zero point temperature drift.

11A and 11B are explanatory diagrams showing the results of simulating the thermal deformation of a conventional capacitance-type acceleration sensor due to a temperature change by FEM analysis, where A is an explanatory diagram of a perspective direction and B is an explanatory diagram of a planar direction. is there.

FIG. 12 is an explanatory view showing the result of simulating the thermal deformation of a conventional capacitive acceleration sensor due to a temperature change by FEM analysis, where A is a temperature of 20 ° C. and B is a temperature of -4.
At 0 ° C, 1G (Earth gravity) on the Z axis (vertical direction in the figure)
3 shows the deformation in the state of being shaded.

[Explanation of symbols]

1,10 flexible substrate 2,11 beam 3,12 glass weight body 4 junction 5 region division line _{X 1, X 2, Y 3} , Y 4, Z electrodes _{C 1, C 2, C 3} , C 4, C ₅ capacitive element

Claims (3)

(57) [Claims] 1. A capacitive acceleration sensor disposed facing the flexible substrate fixing substrate having a support structure by the beam, a configuration of placing a beam on an outer peripheral portion of the flexible substrate, variable
The joint of the weight body that is anodically bonded to the flexible substrate is at the center of the substrate
A capacitance type acceleration sensor that is only one place . 2. A flexible substrate having a beam support structure.
And a fixed substrate facing each other.
And the beam is arranged on the outer periphery of the flexible substrate.
An electrostatic capacitance type acceleration sensor in which electrodes are arranged on the outer peripheral part except the central part of the plate . 3. A flexible substrate having a beam support structure.
And a fixed substrate facing each other.
And the beam is arranged on the outer periphery of the flexible substrate.
The joint of the weight body that is anodically bonded to the flexible substrate is
An electrostatic capacitance type acceleration sensor in which electrodes are arranged only in a central portion and on an outer peripheral portion excluding a central portion of a substrate.