JP2713241B2 - Acceleration sensor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor,
In particular, the present invention relates to a structure and a manufacturing method of a capacitive acceleration sensor for measuring acceleration by detecting a change in distance between opposed electrodes due to acceleration as a change in capacitance of a capacitor formed by these electrodes. .

[0002]

2. Description of the Related Art A conventional capacitive acceleration sensor generally has a structure of a conventional example 1 shown in FIG. 4 or a conventional example 2 shown in FIG. 5 in order to extract a potential of a fixed electrode (Japanese Patent Application No. 4-130277).
No.).

In Conventional Example 1, a fixed electrode 12 is formed of a conductive film on a surface of a glass stopper 1 facing a movable electrode 21. A through hole 13 is made in the glass, and wiring between the fixed electrode 12 and the bonding pad is made through the hole. Si
The movable electrode portion 2 and the glass stopper 1 are bonded by an electrostatic bonding method. Reference numeral 40 in the drawing is a lead wire.

The prior art 2 (FIG. 5) uses an S electrode serving also as a fixed electrode.
The i-stopper 1 is bonded to the movable electrode section 2 via the insulating film 14. When glass is used for the insulating film 14, a stopper is bonded by electrostatic bonding, and the gap 3 between the fixed electrode 12 and the movable electrode 21 is controlled by the thickness of the insulating film 14. When an adhesive is used for the insulating film 14, microbeads having the same diameter as the gap 3 are mixed and mixed with the gap 3.
Is held, and the stopper 1 and the movable electrode unit 2 are bonded.

[0005]

In the structure of the capacitive acceleration sensor of the prior art example 1, since the bonding between the glass stopper and the movable electrode portion of Si uses an electrostatic bonding method, the glass surface is robust and highly reliable. The difference in the coefficient of thermal expansion between Si and Si caused a decrease in the temperature characteristics of the acceleration sensor. In addition, forming the entire stopper with glass has a problem that precise processing of glass is difficult and yield is low, such as formation of a through hole for wiring between a fixed electrode and a bonding pad and formation of a gap between a fixed electrode and a movable electrode. was there.

In the structure of the capacitive acceleration sensor of Conventional Example 2, there is a problem that a parasitic capacitance generated at a portion joined via an insulating film deteriorates the S / N ratio and increases the temperature dependency of the sensor output. there were. Also, it is difficult to form an insulator capable of electrostatic bonding to the thickness of the gap,
Even if a film is formed, leakage occurs because the film is thin, and it is difficult to perform electrostatic bonding. In the method of bonding the stopper and the movable electrode portion while maintaining the gap with an adhesive mixed with microbeads having a diameter equal to the gap, the coefficient of thermal expansion between Si and the adhesive having an adhesive strength enough to withstand dicing is greatly different. As a result, the temperature characteristics of the acceleration sensor are reduced.

An object of the present invention is to provide a capacitive acceleration sensor having good temperature characteristics, a high S / N ratio, and high reliability.

[0008]

A capacitive acceleration sensor according to the present invention has a stopper having an insulator frame arranged around a fixed electrode of a conductive plate, and the insulator frame and a support frame for a movable electrode. Are bonded.

Further, a method of manufacturing an acceleration sensor according to the present invention includes the following steps. 1) A step of electrostatically joining a fixed electrode and an insulator frame to form a laminated structure. 2) a step of cutting the laminated structure to a predetermined thickness; 3) A step of processing one of the cut surfaces of the laminated structure so smoothly as to enable electrostatic bonding. 4) a step of etching the fixed electrodes in the laminated structure to a depth equal to the distance between the electrodes. 5) a step of electrostatically joining the smoothly processed surface of the laminated structure and the movable electrode frame portion.

[0010]

According to the present invention, by arranging an insulator frame around a fixed electrode made of the same material as that of the movable electrode portion, portions having different coefficients of thermal expansion are reduced, so that the thermal distortion of the acceleration sensor is suppressed to a small value. The characteristics are improved. Furthermore, since the frame portion of the movable electrode portion to be joined to the stopper has a sufficiently thick insulator between the fixed electrode and the movable electrode portion, the parasitic capacitance is reduced, and the S / N ratio is improved.

An electrostatic bonding method is used for forming the structure of the stopper and bonding the stopper to the movable electrode portion, and a robust and highly reliable structure can be manufactured.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional perspective view of a first embodiment of the capacitive acceleration sensor according to the present invention. In the movable section 2, Si is etched with a KOH aqueous solution, hydrazine or the like to form a thin film section. One end of the thin film portion 23 is connected to the support portion 22, and the other end is connected to the movable electrode 21. The stopper 41 has a structure in which a glass frame 43 containing Na such as Pyrex glass (trade name of glass for physics and chemistry from Corning, USA) is bonded around a fixed electrode 42 made of Si having a high resistance and a low resistance containing impurities. It is. The gap 3 is formed on the surface of the fixed electrode 42 facing the movable electrode 21. The stopper 41 and the movable part 2 are bonded by an electrostatic bonding method.

When acceleration is applied to the acceleration sensor of the first embodiment, the thin film portion 23 having one end fixed to the support portion 22 is bent, and the gap 3 between the fixed electrode 42 and the movable electrode 21 changes. The magnitude of the acceleration is measured from the change in capacitance between these electrodes.

FIG. 2 is a diagram showing a second embodiment of the present invention. In this embodiment, the shape of the stopper 44 is slightly different from that of the first embodiment, and the other points are the same as those of the first embodiment. That is, the stopper 44 has a structure in which a glass frame 46 is adhered to at least one pair of opposing surfaces of a fixed electrode 45 made of a short Si having a low resistance and containing a high concentration of impurities.
The surface facing the movable electrode 21 is recessed from the end of the glass frame 46 by the depth of the gap 3.

Next, a method of manufacturing the stopper 44 according to the second embodiment will be described. As shown in FIG. 3A, a glass wafer 5 having a width equal to that of the glass frame 46 is electrostatically bonded to both surfaces of the low-resistance Si wafer 4 having a thickness equal to the width of the fixed electrode 45 to form a laminated structure. (FIG. 3A). The laminated structure is cut to a thickness obtained by adding a polishing margin to the thickness of the stopper 44, and the cut surface 15 of the glass wafer 5 is polished so smoothly that electrostatic bonding can be performed (FIG. 5B). The Si portion 4 serving as the fixed electrode 45 in the laminated structure is etched to the depth of the gap 3 by using an etching solution such as hydrazine which does not etch SiO ₂ but etches Si (FIG. 5 (c)). . The polished surface of the glass frame 46 and the movable electrode frame portion 22 are electrostatically bonded (FIG. 5D).
When a bias voltage at the time of electrostatic bonding is applied from the fixed electrode 45, the fixed electrode 45 and the movable electrode 21 are prevented from contacting the fixed electrode 45 and the movable electrode 21 to prevent leakage.
It is preferable to form an insulating film or form small protrusions of an insulating material on one or both of the surfaces.

Since the electrostatic bonding can bond the glass and the aluminum foil, the material forming the fixed electrode 45 and the movable portion 2 is not limited to Si, and may be replaced with a material having an aluminum thin film formed on the surface of a conductive material. It is possible.

[0017]

As described above, by arranging the insulator frame around the fixed electrode made of the same material as the movable electrode portion, the portions having different coefficients of thermal expansion are reduced, and the thermal distortion of the acceleration sensor is reduced. It is suppressed and sensitivity temperature characteristics are improved. Furthermore, since the frame portion of the movable electrode portion to be joined to the stopper has a sufficiently thick insulator between the fixed electrode and the movable electrode portion, the parasitic capacitance is reduced, and the S / N ratio is improved. Since the fixed electrode also serves as the stopper, it is not necessary to form a through hole in the stopper and to perform wiring, and processing is easy.

An electrostatic bonding method is used for forming the structure of the stopper and bonding the stopper to the movable electrode portion, and a robust and highly reliable structure can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional perspective view of a first embodiment of the present invention.

FIG. 2 is a sectional perspective view of a second embodiment of the present invention.

FIG. 3 is an explanatory view of a manufacturing process according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view of Conventional Example 1 of an acceleration sensor.

FIG. 5 is a sectional view of a second conventional example of the acceleration sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stopper 2 Movable part 3 Gap 4 Si wafer 5 Glass wafer 11 Stopper insulating frame 12 Fixed electrode 13 Capacitance take-out hole 14 Insulator bonding layer 15 Polished surface 21 Movable electrode 22 Movable part support frame 23 Movable part thin film part 40 Lead wire 41 Stopper 42 Fixed electrode 43 Glass frame 44 Stopper 45 Fixed electrode 46 Glass frame

Claims (5)

(57) [Claims] 1. A capacitive acceleration sensor comprising a movable electrode and a fixed electrode opposed to each other with a gap therebetween, and measuring an acceleration by detecting a change due to acceleration of the electrode gap as a change in capacitance. An acceleration sensor having a structure in which a frame of a green material is arranged around or partially around the fixed electrode, and the frame of the green material is bonded to a support frame of the movable electrode. 2. The acceleration sensor according to claim 1, wherein the fixed electrode is rectangular, and the insulator frame is adhered to a pair of opposing surfaces. 3. The acceleration sensor according to claim 1, wherein the movable electrode and the fixed electrode are made of the same material. 4. The movable electrode includes a movable portion, a thin film portion,
The acceleration sensor according to any one of claims 1 to 3, wherein the acceleration sensor is formed integrally with a support portion, and the insulator frame is bonded to the support portion. 5. The method for manufacturing an acceleration sensor according to claim 1, wherein at least 1) a step of forming a laminated structure by electrostatically bonding the fixed electrode and an insulator; A step of cutting the laminated structure to a predetermined thickness; 3) a step of processing at least one of the cut surfaces of the laminated structure so smoothly as to enable electrostatic bonding; and 4) etching a fixed electrode in the laminated structure. 5) A method of manufacturing an acceleration sensor, comprising: a step of electrostatically bonding a smoothly processed surface of the laminated structure to a movable electrode support frame portion.