JPH11311633A - Semiconductor accelerometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor accelerometer, in which the deviation between a semiconductor accelerometer chip and a stopper is reduced and whose temperature characteristic is good. SOLUTION: In a semiconductor accelerometer constituted of a flexure part 1 which is composed of the central part 1a and a beam part 1b which is formed to extend in all the directions from the outer peripheral edge of the central part 1a, a plumb hob part 2b which is suspended from, and supported by, the central part 1a via a neck part 2a, a frame 2 in which the beam part 1b is connected to the inner peripheral side face, and a support member 5 which supports the rear surface of the frame 3 and which surrounds the outer peripheral edge of the plumb hob part 2b via a cut-out part 4 are provided. In addition, a piezoresistance 6 is formed at a prescribed place on the beam part 1b, and an interconnection 11 is formed so as to be connected electrically to the piezoresistance 6. In addition, a cut-out groove 7, which extens to the neck part 2a from the outer peripheral edge of the plumb hob part 2b, is formed between the beam part 1b and the plumb hob part 2b. Thereby, a semiconductor accelerometer chip is constituted. Then, a lopwer-part stopper 8 in which a recessed part 8a is formed in a place corresponding to the plumb hob part 2b and which is composed of a silicon substrate is bonded to the rear surface of the semiconductor accelerometer chip, i.e., the support member 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor having a double-supported beam structure used for automobiles, aircrafts, home electric appliances and the like.

[0002]

2. Description of the Related Art In general, a cantilever type and a doubly supported type have been proposed as acceleration sensors. As a detection method, there are a method of detecting mechanical strain as a change in electric resistance and a method of detecting a change in capacitance. For example, Japanese Patent Application Laid-Open No. 6-109755 discloses a double-supported beam acceleration sensor that detects mechanical strain as a change in electric resistance.

FIG. 3 is a schematic perspective view showing a conventional semiconductor acceleration sensor. This semiconductor acceleration sensor
A bending portion 1 comprising a central portion 1a and a beam portion 1b extending in all directions from the outer peripheral edge of the central portion 1a; a weight portion 2b suspended and supported by the central portion 1a via a neck portion 2a; A frame-shaped frame 3 having a beam portion 1b connected to a side surface, and a support member 5 that supports the lower surface of the frame 3 and surrounds the outer peripheral edge of the weight portion 2b via a cutout 4 is provided. ing.

A piezoresistor 6 is formed at a predetermined position of the beam portion 1b, and a wiring 11 is formed so as to be electrically connected to the piezoresistor 6. In addition, between the beam portion 1b and the weight portion 2b, the neck portion 2 extends from the outer peripheral edge of the weight portion 2b.
A notch 7 extending to a is formed to constitute a semiconductor acceleration sensor chip.

A lower stopper 10, which is a glass stopper having a recess 10a formed at a position corresponding to the weight 2b, is joined to the lower surface of the semiconductor acceleration sensor chip, that is, to the support member 5. The lower stopper 10 can prevent the sensor chip from being broken by limiting the displacement of the weight 2b when an unnecessarily large acceleration is applied to the weight 2b (downward). Further, by providing a gap between the weight portion 2b and the lower stopper 10 by the concave portion 10a, good frequency characteristics can be realized by utilizing the damping effect of air in this portion.

Generally, the semiconductor chip is made of silicon, and the lower stopper 10 is made of glass. The silicon and the glass are heated to about 400 ° C. and joined by anodic bonding.

In this semiconductor acceleration sensor, the weight 2b
When the acceleration is applied, the bending portion 1 interlocked with the weight portion 2b bends, and the bending changes the resistance value of the piezoresistor 6,
The acceleration is detected by converting the change in the resistance value into an electric signal.

[0008]

The semiconductor acceleration sensor having such a structure can ensure the maximum volume of the weight portion 2b within a fixed semiconductor chip volume, and
Since the effective length of the beam portion 1b can be increased, a small and highly sensitive semiconductor acceleration sensor can be realized.

However, on the other hand, since the effective length of the beam portion 1b is long, the beam portion 1b is very sensitive to a change in ambient temperature.

FIG. 4 shows the coefficient of thermal expansion of silicon and Pyrex glass (trademark of Corning Incorporated, USA) based on 400 ° C. As can be seen from FIG. 4, the thermal expansion coefficients of silicon and Pyrex glass are different, and silicon shrinks better.

FIG. 5 is a graph in which the difference between the expansion coefficients of silicon and Pyrex glass is plotted at each temperature.
Here, when one side of the chip is 5 mm, at 50 ° C.
0.5μm deviation, 0 ° C about 0.375μm deviation, -40 ° C about 0.25
μm displacement occurs.

FIG. 6 is a schematic diagram showing the effect of a shift between silicon and Pyrex glass on a semiconductor acceleration sensor. From FIG. 6, the portion where Pyrex glass and silicon are bonded (the portion where the lower stopper 10 and the support member 5 are bonded) has the same length at 400 ° C. (temperature at which anodic bonding is performed). As the temperature lowers, the above-described shift occurs between Pyrex glass and silicon.

However, since Pyrex glass and silicon are firmly bonded by anodic bonding, stress concentrates on the flexural portion 1 which is structurally flexible.
The bending portion 1 receives a tensile stress as shown in FIG.

Further, a piezoresistor 6 is formed in the bending portion 1, and this change in stress is detected as sensitivity.
Since this stress (deviation) changes depending on the temperature, there is a problem that the temperature characteristic is greatly affected.

The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor acceleration sensor having good temperature characteristics by reducing a deviation between a semiconductor acceleration sensor chip and a stopper. It is in.

[0016]

According to the first aspect of the present invention,
A weight, a flexure for suspending and supporting the weight, a support for supporting the flexure, a piezoresistor for converting a resistance change due to flexure formed in the flexure into an electrical signal, the weight, and the flexure; In a semiconductor acceleration sensor having a semiconductor acceleration sensor chip having a notch groove formed between the semiconductor acceleration sensor chip and a stopper joined to the semiconductor acceleration sensor chip, a silicon substrate is used as the stopper. It is characterized by the following.

According to a second aspect of the present invention, in the semiconductor acceleration sensor according to the first aspect, the semiconductor acceleration sensor chip and the silicon substrate are joined via a thin film joining layer.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic sectional view showing a semiconductor acceleration sensor according to an embodiment of the present invention. The semiconductor acceleration sensor according to the present embodiment is different from the semiconductor acceleration sensor shown in FIGS. 3 and 6 as a conventional example in that a concave portion 8a is formed at a position corresponding to the weight 2b instead of the lower stopper 10 which is a glass stopper. In addition, the configuration uses a lower stopper 8 made of a silicon substrate. Here, the support member 5 and the lower stopper 8 are joined by a silicon-silicon joining technique.

Therefore, in the present embodiment, since the silicon substrate is used as the lower stopper, no displacement occurs between the semiconductor acceleration sensor chip and the lower stopper.
Temperature characteristics can be improved.

Embodiment 2 FIG. 2 is a schematic sectional view showing a semiconductor acceleration sensor according to another embodiment of the present invention. The semiconductor acceleration sensor according to the present embodiment is the same as the semiconductor acceleration sensor shown in FIG.
Are bonded via a thin film bonding layer 9.

The thin film bonding layer 9 includes a glass thin film, a gold thin film, and a water glass thin film formed by sputtering. Here, when a glass thin film is used, the semiconductor acceleration sensor chip and the lower stopper 8 are joined by anodic bonding, and when a gold thin film is used, the semiconductor acceleration sensor chip and the lower stopper 8 are gold eutectic. When a water glass thin film is used, the semiconductor acceleration sensor chip and the lower stopper 8 are joined by solidifying the water glass thin film by heating.

Therefore, in this embodiment, since the thin film bonding layer 9 is interposed between the semiconductor acceleration sensor chip and the lower stopper 8, the thin film bonding layer 9 can be easily bonded by anodic bonding or the like. Since the layer 9 is formed thin, the deviation between the semiconductor acceleration sensor chip and the lower stopper 8 can be reduced as compared with the conventional example, and the temperature characteristics can be improved.

[0024]

According to the first aspect of the present invention, a change in resistance due to a weight, a flexure for suspending and supporting the weight, a support for supporting the flexure, and a flexure formed in the flexure is converted into an electric signal. A semiconductor comprising: a semiconductor acceleration sensor chip having a piezoresistor to be converted; a notch formed between the weight portion and the bending portion; and a stopper joined to the semiconductor acceleration sensor chip. In the acceleration sensor, since the silicon substrate is used as the stopper, no deviation occurs between the semiconductor acceleration sensor chip and the stopper, the temperature characteristics can be improved, and the deviation between the semiconductor acceleration sensor chip and the stopper is reduced. Thus, a semiconductor acceleration sensor having good temperature characteristics can be provided.

According to a second aspect of the present invention, in the semiconductor acceleration sensor according to the first aspect, the semiconductor acceleration sensor chip and the silicon substrate are joined via a thin film joining layer. In addition, the semiconductor acceleration sensor chip and the stopper can be easily bonded by anodic bonding or the like.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a semiconductor acceleration sensor according to one embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a semiconductor acceleration sensor according to another embodiment of the present invention.

FIG. 3 is a schematic perspective view showing a semiconductor acceleration sensor according to a conventional example.

FIG. 4 is a characteristic diagram showing a coefficient of thermal expansion of silicon and Pyrex glass with respect to temperature.

FIG. 5 is a characteristic diagram showing a difference in heat shrinkage with respect to the temperature of silicon and Pyrex glass.

FIG. 6 is a schematic diagram showing the effect of a shift between silicon and Pyrex glass on a semiconductor acceleration sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Deflection part 1a Central part 1b Beam part 2a Neck part 2b Weight part 3 Frame 4 Cut part 5 Support member 6 Piezoresistor 7 Cut groove 8 Lower stopper 8a Depression 9 Thin film bonding layer 10 Lower stopper 10a Depression 11 Wiring

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Takuro Ishida 1048 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Works Co., Ltd.

Claims (2)

[Claims] 1. A weight, a flexure for suspending and supporting the weight, a support for supporting the flexure, a piezoresistor for converting a resistance change caused by flexure formed in the flexure into an electric signal, and the weight. A semiconductor acceleration sensor chip having a notch groove formed between the semiconductor acceleration sensor chip and the bending portion; and a stopper joined to the semiconductor acceleration sensor chip. A semiconductor acceleration sensor using a substrate. 2. The semiconductor acceleration sensor according to claim 1, wherein said semiconductor acceleration sensor chip and said silicon substrate are bonded via a thin film bonding layer.