JPH05340956A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain a cantilever acceleration sensor in which sensitivity can be enhanced while suppressing increase of size and weight. CONSTITUTION:When masses 6, 6 disposed at the free ends of cantilever beams 5, 5 are displaced, the cantilever beams 5, 5 flex to cause variation in the resistance of four distortion gauges carried on each cantilever beam. The four distortion gauges are carried on each cantilever beam 5, 5 such that they detect variation of resistance due to force in the acceleration detecting direction to offset variation of resistance due to force in perpendicular direction. Consequently, a bridge circuit comprising four distortion gauges outputs a signal voltage which is sensitive only to the force, i.e., acceleration, in the acceleration detecting direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor.
The present invention is applied to, for example, a semiconductor type acceleration sensor.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 8, there is provided a dual-supported acceleration sensor in which the left and right ends of a mass 90 are supported by beams 91 to 94, and a pair of strain gauges are provided for each beam 91 to 94. It is known to provide (not shown). In this semiconductor type acceleration sensor, the resistance values change in the acceleration detection direction in the same direction, and the resistance value changes of the strain gauges in the direction perpendicular to the acceleration detection direction cancel each other out.

[0003]

However, the above-mentioned conventional acceleration sensor has a small output sensitivity, that is, a change in resistance value, and thus improvement in sensitivity is demanded. It should be noted that an increase in the mass weight improves the sensitivity, but it also increases the overall size and weight, which is disadvantageous for downsizing. The present invention has been made in view of the above problems, and an object thereof is to provide a cantilever beam type acceleration sensor capable of improving sensitivity while suppressing an increase in body size and weight.

[0004]

The acceleration sensor according to the present invention comprises a first and a second cantilevered beam which extends from a fixed end in a predetermined direction and has a mass fixed at the other end, and the two beams different from each other. Each of the strain gauges has four strain gauges arranged in a predetermined direction on the upper side, and detects a change in resistance value of each strain gauge due to acceleration in a predetermined direction, and detects the change in the direction perpendicular to the direction. An acceleration sensor, comprising: a bridge circuit that cancels a change in resistance value of each strain gauge due to the acceleration.

[0005]

When the mass provided at the free ends of both cantilever beams is displaced by acceleration, each cantilever beam bends, and the resistance value of each of the four strain gauges arranged on each cantilever beam. Changes. Each of these four strain gauges is arranged on each cantilever beam so as to detect the resistance value change due to the force in the acceleration detection direction and cancel the resistance value change due to the force in the direction perpendicular to the acceleration detection direction, Further, since they are bridge-connected, the bridge circuit composed of these four strain gauges outputs a signal voltage sensitive only to the force in the acceleration detection direction, that is, acceleration.

That is, according to the present invention, by using the cantilever beam type acceleration sensor, it is possible to realize an acceleration sensor which is sensitive only to the acceleration in the detection direction while maintaining high sensitivity. Further, although the acceleration sensor of the present invention uses two cantilever beam type acceleration sensors, the sensitivity is higher than that of the double-sided beam type acceleration sensor having twice the mass of one of the two cantilever beam type acceleration sensors. If it is fixed, the mass can be remarkably downsized.

[0007]

【Example】

(Embodiment 1) The present invention will be described below with reference to an embodiment shown in the drawings. FIG. 1 is a partially cutaway sectional view showing an embodiment of the acceleration sensor of the present invention. The package of this acceleration sensor is composed of a plate-shaped stem 1 and a shell 2 having a lower end opening, and a square thick portion 11 is formed in the center of the stem 1, and a step portion 12 around the thick portion 11 is formed. The shell 2 is fitted and welded. A pedestal 4 on which two cantilevers 3a and 3b are placed is fixed in the package, and a damping liquid is enclosed. Twelve through holes are formed in the thick portion 11 of the stem 1, and sealing glass that seals the through holes fixes the lead terminals 14. Reference numeral 15 is a mounting hole.

A cross-sectional view of the cantilever 3a and the pedestal 4 is shown in FIG. The cantilever 3a is composed of a rectangular plate chip made of an N-type silicon single crystal substrate, and has a rectangular frame-shaped support portion 31 and a base end fixed to one short side of the support portion 31 and extended toward the other short side. It consists of an existing cantilever beam 5 and a mass 6 fixed to the tip (free end) of the cantilever beam 5.
The U-shaped groove 32 that separates the cantilever beam 5 and the mass 6 from the support portion 31 is formed by double-sided etching, and the lower portion of the lower portion of the cantilever beam 5 is for thinning the cantilever beam 5. The recess 33 is etched. The lower surface of the support portion 31 is adhered to the upper surface of the pedestal 4 by a base layer 34 made of a Ni layer or the like.

As shown in FIG. 3, on the surface of the cantilever beam 5, four semiconductor strain gauges 71 are formed by a known semiconductor processing technique, for example, thermal diffusion or ion implantation of P-type impurities such as boron. ~ 74 are formed. Further, in the same step as the formation of the semiconductor strain gauges 71 to 74, P-type impurities are introduced into the cantilever beam 5 at a high concentration to form respective wiring layers (not shown) for extraction, and these wiring layers are formed. The wiring members (not shown) made of Al vapor deposition film and the like are connected to each other, and the end portions of the respective wiring members are connected to pad portions (not shown) for external drawing. These pad portions are electrically connected to the lead terminals 14 by bonding wire wires 16, and the sensor element is bonded to the stem 1 by soldering or the like. Reference numeral 35 is a protective film such as a silicon oxide film.

The cantilevers 3b have the same structure as the above cantilevers 3a, and are adhered to the pedestal 4 in parallel with each other in opposite directions. However, semiconductor strain gauges 81 to 84 are formed on the cantilever beam 5b of the cantilever 3b (see FIG. 3). When acceleration is applied to the mass 6, the cantilever beams 5a and 5b are distorted, and the semiconductor strain gauges 71 to 74 and 81 are deformed according to the magnitude and direction of the acceleration.
The resistance value of ~ 84 changes.

Next, FIG. 3 shows the arrangement direction of the gauges 71 to 74 and 81 to 84, and FIG. 4 shows the bridge connection method. The long direction of the cantilevers 3a and 3b is x, the width direction is y, and the direction perpendicular to them is z. The acceleration detection direction is the z-axis direction. As shown in FIG. 3, a gauge 71,
73, 83, 81 in the y direction (sideways) to the gate 7
2, 74, 84 and 82 are extended in the x direction (longitudinal direction), and the gauges 71, 72, 81 and 82 are arranged on the left side when facing the mass 6 from the supporting portion 31. , Gauge 7
3, 74, 83, 84 are arranged on the right side when facing the mass 6 from the support portion 31. Each gauge 71-74,
As shown in FIG. 4, each of 81 to 84 constitutes a pair resistance, and a bridge is formed by four pair resistances. That is, the gages 71 and 81, the gages 72 and 82, the gages 73 and 83, and the gages 74 and 84 respectively form a pair resistance.

Next, the resistance change when acceleration occurs will be shown. First, in FIG. 1, downward from the paper surface (z direction)
When acceleration is generated in the cans 6, the masses 6 and 6 are displaced downward, and the cantilever beams 6 and 6 are distorted.
2, 84, the resistance value increases, and the gauges 71, 73, 81,
The resistance value of 83 decreases and an output voltage is generated.

Here, the x and y directions are directions in which acceleration is not desired to be detected, but when acceleration occurs in the x direction, the resistance values of the resistors 71, 73, 82 and 84 increase and the resistors 72 and 72,
The resistance values of 74, 81 and 83 decrease. When acceleration occurs in the y direction, the resistance values of the resistors 71, 74, 81, 84 increase and the resistance values of the resistors 72, 73, 82, 83 decrease.

Therefore, when the resistors 72 and 82 are regarded as one resistance, the output voltage when acceleration in the x direction occurs is canceled out by the resistance value change, and the combined resistance (resistance value of resistance).
Does not seem to change. Similarly, resistors 73 and 83,
Similarly, the combined resistance of the resistors 71 and 81 and the resistors 74 and 84 does not change. The output voltage when acceleration in the y-direction is generated is the resistance 72, 82 and the resistance 73, 83.
Decrease, the resistances 71 and 81 and the resistances 74 and 84 increase,
After all, the output voltage does not change. The results are summarized in Table 1.

[0015]

[Table 1] As a result, the output voltage of the bridge responds only to the acceleration in the x direction. (Embodiment 2) Another embodiment is shown in FIG.

In this embodiment, cantilevers 3a and 3b are provided on one chip with a common support portion 31, and the cantilevers 3a and 3b are arranged in a line.
In FIG. 6, the cantilevers 3a and 3b are arranged in parallel, and the chip size can be reduced as compared with the case of FIG. (Embodiment 3) Another embodiment is shown in FIG.

In this embodiment, the arrangement order of the gauges 71 to 74 and 81 to 84 on the cantilever beams 5 and 5 is changed, and the operation and effect are the same. Further, when acceleration occurs in the z direction, the resistance values of the gauges 72, 82, 71, 81 increase or decrease in the same direction, and the gauges 73, 83,
The resistance values of 74 and 84 are gauges 72, 82, 71 and 81.
Arranged so that it changes in the opposite direction to each resistance value of
When acceleration is generated in the x direction and the y direction, the gauges may be arranged or wired so as to cancel the resistance value of the gauge.

[Brief description of drawings]

FIG. 1 is a partially cutaway plan view showing an embodiment of the present invention,

2 is a cross-sectional view of the cantilever of FIG. 1,

FIG. 3 is an enlarged plan view of a cantilever beam portion of the cantilever shown in FIG.

FIG. 4 is a bridge connection diagram of FIG.

FIG. 5 is a partially cutaway plan view showing another embodiment,

FIG. 6 is a plan view showing another embodiment of FIG.

FIG. 7 is a partially enlarged plan view showing another embodiment,

FIG. 8 is a plan view of a main part of a conventional acceleration sensor.

[Explanation of symbols]

5 is a cantilever beam, 6 is a mass, 71-74, 81-84
Is a strain gauge

Claims (1)

[Claims] 1. A first and a second cantilever beam extending from a fixed end in a predetermined direction and having a mass fixed to the other end, and each of the beams being arranged on the different beams in the predetermined direction. It has four strain gauges, each of the strain gauges detects a change in resistance value of each strain gauge due to acceleration in a predetermined direction, and detects a change in resistance value of each strain gauge due to acceleration in a direction perpendicular to the direction. An acceleration sensor comprising: a bridge circuit that cancels out.