JPH09243654A - Accelerometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an accelerometer whose frequency responsivity is good and whose reliability is high. SOLUTION: In a sensor chip 11, glass substrates 2, 3 which comprise fixed electrodes are bonded to both sides of a silicon substrate 1 comprising a weight part equipped with a moving electrode which is displaced due to an acceleration. The sensor chip is fixed onto a base plate 13, a cover 14 is put on the upper part of the base plate, and both the base plate 13 and the cover 14 are sealed hermetically and sealed up. When the sealing-up treatment is executed inside a reduced-pressure space, the inside of a package can be set to a reduced- pressure state. The circumference and the inside of the sensor chip 11 are set to conduction via a through hole 9 formed in the sensor chip 11. However, the interior of the sensor chip 11 is set to the reduced-pressure state inside the package 12. As a result, when the weight part is displaced, it is hardly subjected to the viscosity of a gas, and the frequency responsivity of an accelerometer becomes good. In addition, an inner space is stable irrespective of the state of an atmosphere at the outside of the package 12, and it is possible to obtain a stable characteristic over a long period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly to an acceleration sensor used for detecting acceleration and vibration of an automobile or the like.

[0002]

2. Description of the Related Art As a conventional acceleration sensor, for example,
There is a structure as shown in FIG. The one shown in the figure is a capacitive acceleration sensor, in which a first glass substrate 2 is bonded to the lower surface of a silicon substrate 1 and a second glass substrate 2
The glass substrate 3 is bonded. First glass substrate 2
Has a substantially same planar shape as the silicon substrate 1, and the second glass substrate 3 is shorter than the silicon substrate 1 in the long side direction. As a result, a part of the upper surface of the silicon substrate 1 is exposed.

Then, as shown in FIG. 1B, the silicon substrate 1 has a support frame 1a whose plane is formed in a square shape by an etching process, and a weight portion 1b supported by a cantilever through a beam portion 1c. Are connected to each other. further,
Both upper and lower surfaces of the weight portion 1b and both glass substrates 2 and 3 facing each other
A predetermined gap is formed between the surface and the opposing surface. As a result, when acceleration is applied, the beam portion 1c bends and the weight portion 1b
Is displaced, and the distance of the gap is changed.

Both surfaces of the weight portion 1b are movable electrodes 5
It has become. First, so as to face the movable electrode 5,
The first fixed electrode 6 and the second fixed electrode 7 are formed on the inner surfaces of the glass substrate 2 and the second glass substrate 3, respectively. Therefore, as described above, when the weight portion 1b is displaced and the distance of the gap is changed, the movable electrode 5 and the first fixed electrode 6 are
The distance between them and the distance between the movable electrode 5 and the second fixed electrode 7 change, and the capacitance between them also changes. Therefore, by detecting the change in the capacitance, the displacement amount of the weight portion 1b, that is, the acceleration can be detected.

As a structure for extracting a signal based on a change in electrostatic capacitance between the electrodes to the outside, first, the movable electrode 5 is electrically connected to the bonding wire 8a connected to the integrated silicon substrate 1. , And can be connected to an external circuit (such as a signal processing circuit) via the bonding wire 8a. Further, the first fixed electrode 6 is electrically connected to the electrode thin film 10a formed on the lower surface of the first glass substrate 2 through the through hole 9 formed in the first glass substrate 2,
By mounting the lower surface of the first glass substrate 2 on the substrate, it becomes possible to connect to an external circuit. Further, the second fixed electrode 7 is electrically connected to the electrode thin film 10b formed on the upper surface of the first glass substrate 3 through the through hole 9 formed in the second glass substrate 3, and its second It can be connected to an external circuit via a bonding wire 8b connected to the electrode thin film 10b of the glass substrate 3. In the sensor having this structure, the inside of the sensor is open to the atmosphere through the through hole 9.

In addition, another structure of the capacitive acceleration sensor is
An example is also shown in FIG. Unlike the type shown in FIG. 6 described above, the sensor shown in the figure is a sealed type whose inside is shielded from the outside air.

That is, as shown in the figure, the first glass substrate 2 and the second glass substrate 3 are formed on both sides of the silicon substrate 1.
Are common in that they are integrated by anodic bonding. And
The movable electrode 5 and both fixed electrodes 6 and 7 are connected to the electrode thin film 10 formed on the upper surface of the second glass substrate 3 through the through holes 9a, 9b, ... Formed in the glass substrate,
Bonding wire 8 connected to the electrode thin film 10
It is adapted to be electrically connected to an external circuit via a, 8b and the like.

Specifically, the movable electrode 5 is connected to the bonding wire 8a through a through hole 9a connected to the integrated support frame 1a. Then, the bottom surface of the through hole 9a is closed by the support frame 1a. Further, the second fixed electrode 7 is connected to the bonding wire 8b via the through hole 9b. And through hole 9
The bottom surface of b is closed by the sealing block 1d formed at the same time when the silicon substrate 1 is processed. Further, although not shown in the drawings, the first fixed electrode 6 has the first fixed electrode 6 through the through hole formed at a predetermined position of the first glass substrate 2 which does not face the through hole 9b like the first fixed electrode 6 as shown in FIG. The glass substrate 2 is connected to the electrode thin film on the lower surface thereof, and the through hole is closed with a sealing block.

Since the sealing block is made of silicon and has conductivity, the electrical connection between the fixed electrode and the through hole is more reliably performed through the contact surface of the sealing block. Furthermore, since the sealing block has a function of a part of the connection path between the fixed electrode and the through hole, a through hole for connecting the first fixed electrode 6 to the outside may be provided on the second glass substrate side. it can. Thereby, the extraction surface of each electrode can be unified with the upper surface of the second glass substrate 3.

And, whichever configuration is adopted,
As described above, the through hole that connects the inside and the outside of the sensor is closed by the support frame 1a and the sealing block 1d, so the inside of the sensor is sealed. Therefore, it is possible to bring the inside of the sensor into a depressurized state by performing it in a depressurized room when assembling the sensor.

[0011]

However, the above-mentioned conventional capacitive acceleration sensor has the following problems. That is, in the capacitive acceleration sensor shown in FIG. 6, the inside of the sensor is open, and gas such as air exists inside the sensor. Therefore, when the weight portion 1b is displaced due to acceleration, the displacement is delayed due to the viscosity of the gas, and the frequency response characteristic is deteriorated. Further, since the viscosity depends on the state of the gas, that is, the surrounding atmosphere, the output may vary depending on the state of the surrounding atmosphere even if the same acceleration is applied.

On the other hand, the closed capacitive acceleration sensor shown in FIG. 7 is less affected by the atmosphere around the sensor, and therefore the characteristics are more stable than those of the structure shown in FIG.
When the pressure inside the sensor is reduced, the effect of gas viscosity is reduced and the response characteristics are improved.

However, the silicon substrate 1 and the glass substrate 2,
When the anodic bonding of No. 3 is performed, a voltage may not be uniformly applied (current does not flow) to the entire bonding surface of the opposing substrate, and a defective bonding portion may exist. Then, with the passage of time, the gas around the sensor gradually enters the inside of the sensor from the defective joint. Then, the state becomes an open state, and the same problem as described above occurs.

The present invention has been made in view of the above background, and an object of the present invention is to solve the above problems and reduce the pressure inside the sensor to improve the frequency response characteristics. An object of the present invention is to provide a capacitive acceleration sensor that can maintain the reduced pressure state and increase the reliability of the acceleration sensor for a long period of time.

[0015]

In order to achieve the above object, an acceleration sensor according to the present invention has a weight portion that is displaced by receiving acceleration, and can output a signal according to the amount of displacement of the weight portion. The sensor chip is sealed in a sealed package, and the inside of the package is held in a reduced pressure state (claim 1).

The sensor chip may have any structure as long as it can detect the acceleration based on the displacement of the weight portion, and the displacement amount is easily influenced by the air resistance (viscosity). A semiconductor sensor such as a resistance type semiconductor acceleration sensor is particularly preferable. Further, as illustrated in the third embodiment as an example, the present invention effectively functions even in the case where the parts are assembled and the size is small and the leaf spring is easily deformed.

The acceleration to be detected is, of course, not only the acceleration that occurs when an object literally moves,
Various types are included, such as one that detects continuously generated acceleration such as vibration in time series, and one that detects gravitational acceleration such as inclination.

Further, preferably, the sensor chip has a structure in which the weight portion is enclosed in a sealed state, and the inside of the sensor chip is also kept in a predetermined depressurized state (claim 2). ). The degree of pressure reduction inside the sensor chip and the degree of pressure reduction inside the package may be the same or different.

When a sensor chip having a function of detecting acceleration is enclosed in a package whose inside is in a reduced pressure state,
Even if the sensor chip is open and expectations around the sensor chip allow it to enter the inside of the sensor, the internal state of the sensor chip becomes the same reduced pressure state inside the package.

Therefore, the viscosity of the air is reduced without being exposed to the atmosphere. Therefore, the weight portion can quickly react (move) to a given acceleration, and the frequency response characteristic of the acceleration sensor becomes good.

Further, the package can be easily and surely sealed as compared with the case where the sensor chip itself is sealed. Therefore, long-term reliability can be secured as compared with the conventional closed type acceleration sensor.

Further, according to the second aspect, the sensor chip itself is in a depressurized state, so that the frequency response is improved similarly to the first aspect. Further, since the sensor chip and the package form a double decompressed closed space, the reliability of the decompressed state is increased. And
Even if the airtight state of the sensor chip is released, it is not immediately opened to the atmosphere as in the conventional case because the reduced pressure state formed by the package is formed around the sensor chip.

[0023]

1 and 2 show a first embodiment of an acceleration sensor according to the present invention. In this embodiment, the sensor chip 11 is enclosed by the package 12.

The sensor chip 11 is formed by bonding and integrating glass substrates 2 and 3 having fixed electrodes 6 and 7 above and below a silicon substrate 1 on which a weight portion 1c with a movable electrode 5 is formed. The structure is similar to that of the conventional sensor chip shown in FIG. The sensor chip 11 is of a type in which the inside is opened to the outside through the through hole 9. Since the detailed structure of the specific sensor chip is the same as the conventional one described above, the same reference numerals are given and the description thereof is omitted.

The package 12 includes a base plate 13 on which the sensor chip 11 is installed, and the base plate 13
And a cover 14 that closes the upper space of the base plate 13.

The base plate 13 is a flat plate having a substantially square plane, and the outer peripheral edge 13a of the upper surface is 1
It is getting lower. Then, lead pins 15 are attached in the vicinity of the four corners of the base plate so as to penetrate vertically. The slight gap formed between the lead pin 15 and the base plate 13 is sealed with, for example, resin or sealed with an adhesive or solder for fixing the two to ensure airtightness.

The sensor chip 11 has a base plate 13
Is fixed to the center of the upper surface of the device using a conductive adhesive or the like. The lower surface of the first glass substrate 2 is surface-mounted, and is directly connected to a printed wiring pattern formed on the upper surface of the base plate 13, and is electrically connected to a predetermined lead pin through the printed range line pattern. It is like this. The other ends of the bonding wires 8a and 8b connected to predetermined positions of the sensor chip 11 are bonded to the upper ends of predetermined lead pins 15, respectively. As a result, the change in capacitance between the movable electrode 5 of the sensor chip 11 and the first and second fixed electrodes 6 and 7 can be taken out to the outside via the lead pin 15.

On the other hand, the cover 14 is in the form of a rectangular box having an open bottom, and a bottom surface thereof is formed with a flange portion 14a projecting outward over the entire circumference. Then, the flange portion 14 a is the outer peripheral edge 13 of the base plate 13.
It is formed so as to be in surface contact with a.

The base plate 1 having the above structure
When integrating 3 and the cover 14, the base plate 13 on which the sensor chip 11 is installed is placed in a depressurized work space, and the cover 14 is covered on the upper surface of the base plate 13. At this time, the flange portion 14a and the base plate 1
The outer peripheral edge 13b of 3 is brought into surface contact. Then, by hermetically sealing the joint portion, they are joined and integrated in a close contact state. As a result, the package 12 that completely seals the base plate 13 and the cover 14 and completely seals the arrangement space of the sensor chip 11 is formed.

The method of airtightly integrating the base plate 13 and the cover 14 is not limited to the above, but for example, an adhesive is used, or the both surfaces 13a and 14a are heated with a predetermined pressure to heat the contact surface. Various methods such as melting and then cooling to be integrated, soldering, and welding can be adopted. Then, in consideration of the materials of the base plate 13 and the cover 14, etc., a material that can easily and surely maintain the airtight state for a long period of time is appropriately selected.

Since the above-mentioned work is performed in a depressurized space, the inside of the package 12 is hermetically sealed in a depressurized state. Therefore, the inside of the sensor chip 11 is also in a depressurized state due to the through hole 9, so that the weight portion 1b on which the movable electrode 5 is formed is unlikely to be affected by the viscosity of air. Therefore, when the acceleration sensor is subjected to acceleration or vibration, the position is instantly changed, and the frequency response characteristic is improved.

Further, since there is no unbonded portion in the package 12, air outside the package 12 does not enter the inside of the package 12 with the passage of time, and the capacitance type acceleration sensor has high reliability. .

FIG. 3 shows a second acceleration sensor according to the present invention.
The embodiment of is shown. In the present embodiment, the sensor chip 11 'constituting the conventional acceleration sensor (a type in which the inside of the sensor is hermetically sealed) shown in FIG. 7 is included in the package 12 used in the first embodiment.

In the present embodiment, although the sensor chip 11 'itself has a depressurized state, even if the depressurized state is released due to various causes, the same operation principle as that of the first embodiment described above is used. Accordingly, the package 12 holds the reduced pressure state. Therefore, the reduced pressure state in the sensor chip 11 'is more reliably maintained for a long period of time, and the reliability is improved.

Further, if the depressurized state inside the sensor chip 11 'is made higher (atmospheric pressure is lower), high-performance sensing is possible at first in the high depressurized state held by the sensor chip 11' itself, and thereafter. For some reason,
Even if the airtightness of the sensor chip 11 'is lost, the decompressed state is formed in the package 12, so that the sensor chip 11' is not immediately exposed to the atmosphere as in the conventional case, and relatively high-performance sensing is possible.

FIG. 4 shows a third acceleration sensor according to the present invention.
The embodiment of is shown. The above-mentioned respective embodiments are
Although the silicon substrate is processed using the semiconductor process and the mechanism for displacing the weight portion by acceleration is integrally formed, in the present embodiment, the sensor chip 20 is formed by mechanically assembling various parts. I am trying to configure it.

Specifically, the sensor chip 20 includes a support member 2 made of an insulator between two fixed substrates 21 and 22.
A leaf spring 24 having elasticity is supported via 3 via a sandwich. Then, the weight portions 25 are welded to the centers of the upper surface and the lower surface of the leaf spring 24 to be integrated. Further, the fixed substrates 21 and 22 and the weight portion 25 are both made of a metal plate having a predetermined thickness.

With this structure, when the sensor chip 20 receives an acceleration, the weight portion 25 tries to move in a predetermined direction, and the leaf spring 24 elastically deforms accordingly, and the displacement of the weight portion 25 is allowed. Then, the interval between the weight portion 25 and the fixed substrates 21 and 22 arranged above and below changes.

At this time, since the fixed substrates 21 and 22 and the weight portion 25 are made of metal, the surfaces of both the substrates 21 and 22 function as fixed electrodes 26 and 27, and the surface of the weight portion 25 is the movable electrode 28. Function as. Therefore, the capacitance between the two electrodes changes based on the displacement of the weight portion 25, and the acceleration can be detected according to the same principle as that of the sensor chips 11 and 11 '.

Further, on the upper surface of the second fixed board 22, a circuit board 32 on which a signal processing circuit 31 is mounted is attached via a washer 30. The signal processing circuit 31 and each of the electrodes 26 to 28 are directly connected to each other via the lead wire 33 connected to the leaf spring 24 and the first fixed substrate 25 and from the upper surface of the second fixed substrate 26. Further, the signal processing circuit 31 is connected to an external circuit through two power supply lines 35a and one signal line 35b.

Here, in this embodiment, the sensor chip 20 is used.
Are housed in a sealed package 40 under a reduced pressure. The package 40 used in this example has a cup-shaped container body 41 that is open at the top and a cup-shaped lid body 42 that is opened downward, and the upper edge of the container body 41 and the lower edge of the lid body 42 are respectively Flange portions 41a and 42a having the same shape and protruding outward are formed. Further, an insulating pedestal 43 is fixed to the bottom surface of the container body 41. Further, the through hole 42 is provided at the center of the top surface of the lid 42.
b is formed.

Then, the sensor chip 20 is packaged in the package 4.
In order to store the sensor chip in 0, the sensor chip 20 is first fixed on the pedestal 43 of the container body 21. In addition, the power line 35a,
The signal line 35b is passed through the through hole 42b formed in the lid 42, the tip of the signal wire 35b is pulled out of the lid 42, and the through hole 42b is filled with a resin 44 or the like to be hermetically sealed. Then, similarly to each of the above-described embodiments, while covering the upper side of the container body 41 with the lid body 42 in the working space in a reduced pressure state,
The two flange portions 41a, 42a are brought into surface contact with each other. And
Hermetically seals and flanges 41a, 42a
The surface-contacted portions of are bonded without any gap to form a completely sealed package 40.

Since the above-mentioned work is performed under reduced pressure, the inside of the package 40 is reduced in pressure. Therefore, as in the first embodiment, the inside of the sensor chip 20 is also in a depressurized state, the weight portion 25 is not affected by the viscosity of air, and the frequency response characteristic of the acceleration sensor becomes good.

FIG. 5 shows a fourth embodiment of the present invention. In the present embodiment, the base plate 1 that constitutes the package 12 used in the second embodiment
A substrate 45 on which a predetermined circuit is printed is arranged on the upper surface of 3. Then, the closed sensor chip 11 ′ and the signal processing circuit 46 are arranged on the upper surface of the substrate 45. And
The circuit elements forming the sensor chip 11 ′ and the signal processing unit 46 are connected by bonding wires 47 or printed wiring formed on the substrate 45. Further, it is also connected to the lead pin 15 by a bonding wire 47 so that the signal processed by the signal processing unit 46 is sent to the outside and the power is supplied from the outside.

Also in this embodiment, since the reduced pressure state is maintained inside the package 12, the state of good responsiveness is maintained for a long period of time. The sensor chip 11 '
In addition, the configuration, operation, and effect of the package 12 are the same as those in the above-described respective embodiments, and thus detailed description thereof will be omitted.

Further, the structure of the sensor chip for enclosing the signal processing circuit in this way is not limited to the sealed type shown in the figure, but may be the open type shown in FIG. Further, in the third embodiment, the sensor chip 2
Although 0 and the signal processing circuit 31 are enclosed in the package 40, only the sensor chip 20 may be sealed.

Furthermore, the semiconductor type acceleration sensor is not limited to the capacitance type sensor described above, but a piezo element is installed at a deformed portion such as a beam portion and the acceleration is detected from a change in resistance of the piezo element. Such a type may be used, and other types of structures may be used.

In each of the above-mentioned embodiments, the capacitance type sensor having two sets of movable electrodes and fixed electrodes is shown, but a sensor chip having a pair of movable electrodes and fixed electrodes may be used. Of course.

[0049]

As described above, in the capacitive acceleration sensor according to the present invention, the sensor for detecting acceleration is included in the package, and the inside of the package is in a depressurized state. The space in which the movable electrode is placed is also in a reduced pressure state, and the position of the movable electrode changes rapidly, so that the frequency response characteristic can be improved.

When a sensor chip whose inside is hermetically sealed and depressurized is used (Claim 2), even if the sensor chip loses its airtightness and becomes open, the sensor chip Since the periphery of the package is in a reduced pressure state formed by the package, air outside the package does not enter the inside of the sensor, and reliability is ensured for a long period of time.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of a capacitive acceleration sensor according to the present invention.

FIG. 2 is a sectional view of FIG.

FIG. 3 is a sectional view showing a second embodiment of the capacitive acceleration sensor according to the present invention.

FIG. 4 is a diagram showing a third embodiment of the capacitive acceleration sensor according to the present invention.

FIG. 5 is a diagram showing an example of a capacitive acceleration sensor according to the present invention.

FIG. 6A is a diagram showing one form of a conventional capacitive acceleration sensor. (B) is a sectional view thereof.

FIG. 7 is a diagram showing one form of a conventional capacitive acceleration sensor.

[Explanation of reference numerals] 1b, 25 Weight portion 11, 11 'Sensor chip 12, 40 Package

Claims (2)

[Claims] 1. A weight portion that is displaced in response to acceleration,
An acceleration sensor characterized in that a sensor chip capable of outputting a signal according to the amount of displacement of the weight portion is enclosed in a sealed package, and the package is held in a reduced pressure state. 2. The acceleration according to claim 1, wherein the sensor chip has a structure in which the weight portion is enclosed in a sealed state, and the inside of the sensor chip is also kept in a predetermined depressurized state. Sensor.