JPH05273231A - Capacity type acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain a capacity type acceleration sensor which can detect a failure correctly. CONSTITUTION:A silicon substrate 20 and a glass substrate 30 are bonded through anodic bonding in a capacity type acceleration sensor 10. The acceleration is measured by the change of the capacitance between a movable electrode 21 and a fixed electrode 31 formed on the substrates 20 and 30. A stopper 41 comprised of a conductive thin film 41a and an insulating thin film 41b is formed on the surface of the movable electrode 21. At the time of the anodic bonding, the conductive thin film 41a does not show polarization, whereas the insulating thin film 41b assumes considerably weak polarization. Before measurement, generally, a voltage is applied between the movable electrode 21 working also as a diagnostic electrode and a diagnostic electrode 32. The change of the output due to the change of the capacitance between the movable electrode 21 and the fixed electrode 31 is subsequently measured. Since a minute gap between the diagnostic electrodes is set to be small, the sensitivity at the checking time of failures is improved. Moreover, since a polarization is hardly brought about, the shifting amount between the electrodes in response to the application of the voltage for the purpose of checking failures is increased, thereby making it possible to detect a failure correctly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitive acceleration sensor formed by joining substrates having electrodes formed on each other.

[0002]

2. Description of the Related Art A capacitive acceleration sensor is arranged such that one electrode having a movable electrode and the other substrate having a fixed electrode face each other. The movable electrode formed on one of the substrates is supported from the periphery by a plurality of beams having spring properties. Then, when subjected to acceleration, the beams are bent and the distance between the movable electrode on one substrate and the fixed electrode formed on the other substrate changes. The capacitive acceleration sensor measures acceleration by a change in capacitance due to a change in the distance between the electrodes. Generally, the capacitance C is calculated by the following equation. C = εS / d (ε: dielectric constant, S: electrode area, d: electrode spacing)

[0003]

SUMMARY OF THE INVENTION Here, when the acceleration to be measured is extremely large and overloaded, excessive displacement such that electrodes having minute gaps are extremely close to each other is prevented to prevent mechanical damage such as a beam. Moreover, it is necessary to prevent electrical short circuit between electrodes having a minute gap so that electrical breakdown of the circuit does not occur. For this reason, as shown in FIG. 7, in the conventional capacitive acceleration sensor 90, the stopper 28 made of an insulating thin film is formed on the surface of the movable electrode 21.
The insulating thin film of the stopper 28 is usually PSG.
A (phosphorus glass) thin film 28a and a SiN (silicon nitride) thin film 28b are used.

Further, when a voltage (potential difference) V is applied between two diagnostic electrodes that are formed facing each other while sharing a small gap between the movable electrode and the fixed electrode, the following expression is given between both electrodes. An electrostatic force P _e is generated. ^{_{P e = εSV 2 / 2d 2}} ......... (1) (ε: dielectric constant, S: electrode area, d: distance between electrodes)

An anodic bonding method is used as a bonding method between the silicon substrate and the glass substrate. As the anodic bonding method, a silicon substrate and a glass substrate are stacked,
A DC voltage of about 800 to 1500V is applied with the silicon substrate side being positive and the glass substrate side being negative, by heating to about 300 to 400 ° C. At the time of this anodic bonding, strong polarization occurs in the PSG thin film 28a. The movable electrode 21 on which the polarized PSG thin film 28a is formed remains pulled to the fixed electrode 31 side even when the potential difference is zero. This is because the electrostatic force P _e acts even in the initial state where the potential difference is zero due to the charges in the film due to the polarization of the PSG thin film 28a during the anodic bonding. Then, as shown in the characteristics of the conventional product in FIG. 5, even if the voltage is used as a primary check applied voltage (V) which is an input signal for a failure check in a capacitive acceleration sensor with a power supply voltage of DC5V, the acceleration The amount of change in the primary sensitivity (%) with respect to the sensitivity was small, and apparently the result was that the movable electrode 21 hardly moved.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to determine the gap between the electrodes for acceleration measurement with respect to the applied voltage between the electrodes for diagnosis during failure diagnosis. It is an object of the present invention to provide a capacitive acceleration sensor capable of accurately performing a failure check with a large change.

[0007]

According to the structure of the invention for solving the above problems, a movable electrode formed on one substrate and a fixed electrode formed on the other substrate are opposed to each other with a minute gap. In the capacitive acceleration sensor, in which the two electrodes are joined together and the acceleration is measured by the change in capacitance between the two electrodes, the movable electrode and the fixed electrode are formed so as to face each other with a small gap shared therebetween. A pair of diagnostic electrodes, a conductive thin film formed by electrically short-circuiting the diagnostic electrode with a conductive material on at least one of the diagnostic electrode surfaces, and the conductive thin film surface or its periphery An insulating thin film formed so as to be closer to the facing electrode than the conductive thin film on the diagnostic electrode surface.

[0008]

According to the above means, the minute gap between the pair of diagnostic electrodes is reduced by the conductive thin film which is electrically short-circuited with the diagnostic electrode on the diagnostic electrode surface. In addition, the insulating thin film prevents the opposing electrodes from directly contacting each other.

[0009]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is a central longitudinal sectional view showing a capacitive acceleration sensor 10 which is a capacitive sensor according to the present invention. 2 is a silicon substrate 20 of the capacitive acceleration sensor 10 of FIG.
FIG. 6 is a plan view of the above as viewed from the movable electrode 21 side. FIG. 3 is a plan view of the glass substrate 30 of the capacitive acceleration sensor 10 of FIG. 1 viewed from the fixed electrode 31 side. Capacitive acceleration sensor 1
Reference numeral 0 denotes a silicon substrate 20 which is one substrate on which the movable electrode 21 and the like are formed, a glass substrate 30 which is the other substrate on which the fixed electrode 31 is formed, and a base 40 made of glass.
It has a three-layer structure. The movable electrode 21 and the fixed electrode 31 are opposed to each other so as to have a minute gap, and the two substrates 20 and 30 are bonded to each other.
Bonded on top. The movable electrode 21 is the silicon substrate 2
A weight 22 is formed on the surface of 0 as an impurity by phosphorus diffusion, and a weight 22 that moves by acceleration is provided below the weight. or,
The silicon substrate 20 is provided with four thin beams 23a, 23b for supporting the movable electrode 21 from its surroundings with a spring property.
23c and 23d are formed. In addition, the fixed electrode 3
1 is formed by depositing a metal such as Al (aluminum) on a glass substrate 30. The weight 22 and the beams 23a, 23b, 23c, 2 below the movable electrode 21.
3d and the like are achieved by etching the silicon substrate 20.

An IC 50 using a CMOS circuit is provided outside the glass substrate 30 bonded at the peripheral portion of the silicon substrate 20.
Are arranged. Further, a wiring 25 is formed at the same time as the movable electrode 21 by phosphorus diffusion on the surface of the silicon substrate 20, and the wiring 25 connects the movable electrode 21 and the IC 50. The movable electrode 21 formed on the silicon substrate 20 also serves as one diagnostic electrode. Further, at the center of the fixed electrode 31 formed on the glass substrate 30, the other diagnostic electrode 32 is formed facing the movable electrode 21 formed on the silicon substrate 20. Furthermore, the movable electrode 2
A conductive thin film 41a made of a conductive material, Al, is formed on one surface so as to face the surface of the diagnostic electrode 32, and is electrically short-circuited with the movable electrode 21. An insulating thin film 41b made of SiN, which is an insulating material, is formed on the surface of the conductive thin film 41a. Then, the glass substrate 3 and the silicon substrate 20 are bonded to each other to form the glass substrate 3
Terminal part 31a of fixed electrode 31 on the 0 side and diagnostic electrode 32
The terminal portion 32a is connected to the IC 50 via the terminal portions 26 and 27 facing each other on the silicon substrate 20 side.

The glass substrate 30 and the silicon substrate 20 are bonded by anodic bonding as described above. At the time of this anodic bonding, since the conductive thin film 41a on the surface of the movable electrode 21 is made of a conductive material Al, no polarization occurs. The insulating thin film 41b on the surface of the conductive thin film 41a is made of SiN, which is an insulating material and is hardly polarized, so that the polarization can be made extremely weak. Further, this polarization action becomes larger as the thickness of the thin film becomes thicker, but since the height is made of a conductive material and an insulating thin film made of SiN is formed on the outside thereof, the polarization action is made as small as possible. ing.

FIG. 4 is a block diagram showing the electrical construction of the capacitive acceleration sensor 10 of the present invention. The capacitive acceleration sensor 10 has a capacitance C _V depending on the area of the electrodes where the movable electrode 21 and the fixed electrode 31 face each other, the electrode spacing at that time, and the like.
Is determined. Moreover, the capacitance C _P is determined by the area of the electrodes and the electrode interval where the movable electrode 21 and the diagnostic electrode 32 face each other. The capacitance type acceleration sensor 10 in the normal measurement of the acceleration, the state switch S _W is shown by a solid line, i.e., it is to be no effect on the measurement is connected to the power supply V _DD. Then, the constant current circuit I _1, I ₂ , the transistor T
_The C / f converter composed of _r1 , T _r2 , the Schmitt trigger circuit 61, and the inverter circuits 62, 66 converts the terminal voltage waveform at the time of charging and discharging the capacity C _V at that time into the frequency f _S. This frequency f _S is converted into a voltage V _S1 by the f / V converter 63. This voltage V _S1 is input to a high frequency pass filter (HPF) 65 and converted into a voltage V _S2 in which low frequencies are cut. This voltage V _S2 is input to the differential amplifier 64, and the capacitance C _V when the acceleration of the capacitive acceleration sensor 10 is zero from the differential amplifier 64.
The voltage V _out, which is an analog output, is output as a measurement signal in accordance with the difference from the voltage V ₁ corresponding to.

Next, the operation of the above-mentioned C / f converter during normal measurement will be described in detail. When the power is turned on, first, the transistor T _r1 is turned on, and the discharge of the capacitance C _V is started. Capacitance C _V is the output voltage Lo level when the discharge becomes higher than a predetermined voltage Schmitt trigger circuit 61, the output voltage of the inverter circuit 66 becomes Hi level, to turn on the transistor T _r2. Then, when the capacitance C _V is charged and becomes lower than a predetermined voltage, the output voltage of the Schmitt trigger circuit 61 becomes Hi level and the output voltage of the inverter circuit 66 becomes Lo level. Then, by repeating the above operation, a pulse signal proportional to the capacitance C _V and the capacitance C _P is output.

Next, the operation during the primary check, which is a normal or failure operation check before the capacitive acceleration sensor 10 enters the normal acceleration measurement state, will be described. During the primary check, the primary check signal S _P is V _H becomes a Hi level from Lo level V _L, is switched to a state in which the switch S _W is indicated by a broken line. Then, one diagnostic electrode 32 side is grounded, and the other movable electrode 21 side is, for example, a predetermined voltage 5
V is applied. Here, an electrostatic force P _e calculated by the equation (1) is generated between the movable electrode 21 having a minute gap and the diagnostic electrode 32. At this time, polarization hardly occurs in the conductive thin film 41a and the insulating thin film 41b formed between both electrodes as described above. Therefore, FIG.
As shown in, the change amount of the primary sensitivity (%) with respect to the acceleration sensitivity becomes large at the primary check applied voltage (V), that is, the displacement of the movable electrode 21 with respect to the primary check applied voltage becomes large. As a result, the capacitive acceleration sensor 10 of the present invention can accurately determine whether the sensor is normal or failed each time the primary check signal is output before the normal measurement.

Next, the configuration of a capacitive acceleration sensor 70 which is another embodiment of the present invention will be described with reference to FIG. The same components as those in the above-described embodiment are designated by the same reference numerals, and the description thereof will be omitted. In this capacitive acceleration sensor 70, a PSG thin film 71 having high polarizability similar to the conventional one is formed on the surface of the movable electrode 21, and a conductive thin film 72 made of an Al thin film is formed on the surface. The peripheral end surface of the conductive thin film 72 is electrically short-circuited with the movable electrode 21, thereby eliminating the polarization effect of the PSG thin film 71. Then, PS is formed on the surface of the movable electrode 21 around the conductive thin film 72.
Stopper 7 consisting of G thin film 78a and SiN thin film 78b
8 is formed. The stopper 78 prevents the electrically conductive thin film 72 from contacting the diagnostic electrode 32 facing the electrically conductive thin film 72 at the time of an overload and electrically short-circuiting. As a result, the capacitive acceleration sensor 70 of the present invention has a large change amount of the primary sensitivity with respect to the acceleration sensitivity, and the capacitive acceleration sensor 10 described above is used.
It becomes easy to check the primary as well.

[0016]

Since the present invention is configured as described above, the conductive thin film reduces the minute gaps between the diagnostic electrodes and improves the sensitivity in fault diagnosis.
Further, the insulating thin film formed on or around the conductive thin film surface prevents excessive displacement between the electrodes at the time of overload and can prevent damage. Further, the insulating thin film prevents the electrodes from directly contacting each other, preventing an electrical short circuit between the electrodes and preventing the circuit from being destroyed.

[Brief description of drawings]

FIG. 1 is a central longitudinal sectional view showing a configuration of a capacitive acceleration sensor according to a specific example of the present invention.

FIG. 2 is a plan view of the silicon substrate of the capacitive acceleration sensor according to the embodiment as seen from the movable electrode side.

FIG. 3 is a plan view of the glass substrate of the capacitive acceleration sensor according to the embodiment as seen from the fixed electrode side.

FIG. 4 is a block diagram showing an electrical configuration of the capacitive acceleration sensor according to the embodiment.

FIG. 5 is a characteristic diagram showing a relationship between a primary check applied voltage and primary sensitivity with respect to acceleration sensitivity.

FIG. 6 is a central longitudinal sectional view showing a second embodiment of the capacitive acceleration sensor according to the present invention.

FIG. 7 is a central longitudinal sectional view showing the configuration of a conventional capacitive acceleration sensor.

[Explanation of symbols]

10-capacitance type acceleration sensor 20-silicon substrate 21-movable electrode (diagnostic electrode) 22-weights 23a, 23b, 23c, 23d-beam 30-glass substrate 31-fixed electrode 32-diagnostic electrode 40-base
41-Stopper 41a-Conductive thin film 41b-Insulating thin film 50-
IC

Claims (1)

[Claims] 1. A movable electrode formed on one substrate and a fixed electrode formed on the other substrate are opposed to each other so as to have a minute gap, and the two substrates are joined to each other to change the capacitance between the two electrodes. In a capacitive acceleration sensor that measures acceleration by means of a pair of diagnostic electrodes formed on both substrates so as to face each other with a small gap shared by the movable electrode and the fixed electrode, at least one of the diagnostic electrode surfaces And a conductive thin film formed by electrically short-circuiting the diagnostic electrode with a conductive material, and an electrode facing the conductive thin film on the conductive thin film surface or on the periphery of the diagnostic electrode surface. And an insulating thin film formed so as to come close to the capacitive acceleration sensor.