JPH07113646B2 - Semiconductor acceleration sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a semiconductor acceleration sensor used in various fields such as industrial measurement, vehicles, and aircraft.

[Prior Art] In recent years, a semiconductor acceleration sensor capable of detecting acceleration in two-dimensional or three-dimensional directions has been developed. For example, as a sensor capable of detecting acceleration in a three-dimensional direction, as shown in FIG. 5, a sensor 2 having a cantilever capable of swinging in the X direction and a sensor capable of swinging in the Y direction are provided on the same semiconductor substrate 1. There is a sensor in which a sensor 3 having a cantilever beam and a sensor 4 having a cantilever beam that can swing in the Z direction are formed and the acceleration in each direction is measured. The semiconductor acceleration sensor shown in this figure is described in Japanese Patent Application No. 62-118260.

[Problems to be Solved by the Invention] In the conventional semiconductor acceleration sensor described above, a sensor having a cantilever that is swingable in one direction is provided separately in each direction. Due to this structure, there is a problem that the detection sensitivity varies unless the sensors are formed in the same shape. In order to solve this problem, it is necessary to increase the forming accuracy of the sensor, but it is technically difficult to increase the forming accuracy.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a semiconductor acceleration sensor that can improve detection accuracy without having to increase formation accuracy.

[Means for Solving Problems] In order to solve the above-mentioned problems, the present invention includes a weight portion formed in a central portion of a semiconductor substrate, and a support portion formed in a peripheral portion of the semiconductor substrate. A first beam part formed between one side of the weight part and the support part, and a second beam formed between the side of the weight part facing the one side and the support part. In a semiconductor acceleration sensor having a beam section, two strain gauges arranged at a connection section between the first beam section and the support section and a connection section between the second beam section and the support section. A first Wheatstone bridge constituted by two strain gauges arranged, two strain gauges arranged at a connecting portion between the second beam portion and the weight portion, and the second beam. Comprised of two strain gauges arranged at the connecting part between the support part and the support part And a second Wheatstone bridge.

[Operation] According to the above configuration, the acceleration sensor has a double-supported beam structure,
The first Wheatstone is composed of two strain gauges arranged at the connecting portion between the first beam portion and the supporting portion and two strain gauges arranged at the connecting portion between the second beam portion and the supporting portion. The bridge is configured to detect the acceleration component in the axial direction of the beam portion in the acceleration acting on the weight portion by the bridge.
On the other hand, 2 arranged at the connecting portion between the second beam portion and the supporting portion
A second Wheatstone bridge is constructed from the individual strain gauges and the two strain gauges arranged at the connecting portion between the second beam portion and the weight portion, and this bridge constitutes the axial direction of the beam portion. The acceleration component in the perpendicular direction is detected. In this way, the acceleration acting on the weight portion is divided into an axial component of the beam portion and a component perpendicular to the axial direction of the beam portion, and the axial component is detected by the first Wheatstone bridge,
The component perpendicular to the axial component is detected by the second Wheatstone bridge.

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

FIG. 1 is a plan view showing the structure of an embodiment of the present invention. In the figure, 5 is a semiconductor substrate (also serving as a supporting portion), and 6a and 6b are U-shaped notches formed in the semiconductor substrate 5. Cutouts 6a, 6b are configured to face each other, by the portion surrounded by these cutouts 6a, 6b,
The beam portions 5a and 5b and the weight portion 5c are configured. FIG. 2 is a sectional view taken along the line AA in FIG. 1. As shown in this figure, the beam portions 5a and 5b are thin and thin, and the weight portion 5c is thick. Strain gauges 7 and 8 are mounted on the beam portion 5a, respectively, and are arranged at the connecting portion between the semiconductor substrate 5 and the beam portion 5a. Reference numerals 9,10,11,12,13,14 are strain gauges mounted on the beam portion 5b.
13, 14 are arranged at the connecting portion between the beam portion 5b and the weight portion 5c, and the strain gauges 9, 10, 11, 12 are arranged at the connecting portion between the beam portion 5b and the semiconductor substrate 5.

According to the above configuration, since the beam portions 5a and 5b are structurally both-supported beams, when downward acceleration is applied to the weight portion 5c, the beam portions 5a and 5b are applied to the beam portions 5a and 5b. Has a stress distribution as shown in FIG. In this case, strain gauges 7-11
A tensile stress is applied to and the resistance value increases. Further, the strain gauges 13 and 14 are subjected to compressive stress, and the resistance value decreases.
In this way, by the acceleration acting on the weight portion 5c,
A stress is applied to the beam portions 5a and 5c according to the acting direction of acceleration. Further, the strain gauges 7 to 14 described above undergo a change in resistance value according to the stress of the attached portion.

FIGS. 4 (a) and 4 (b) are circuit diagrams showing the electrical configuration of this embodiment, respectively. Here, the two-dimensional directional component of the acceleration acting on the weight portion 5c can be obtained by detecting the change in the resistance value of the strain gauges 7 to 14 when the acceleration acts on the weight portion 5c. For example, as shown in FIG. 3A, when the acceleration α acts on the weight portion 5c, the axial component of the beam (hereinafter referred to as the X-direction component) αx and the component orthogonal to the axial component of the beam. It is possible to obtain αz (hereinafter, referred to as Z-direction component). Below, this acceleration α
As an example, a method of obtaining the X-direction component αx and the Z-direction component αz will be described.

First, in FIG. 4 (a), the bridge 15 is configured such that the strain gauge 7 and the strain gauge 8 and the strain gauge 9 and the strain gauge 10 are on opposite sides. According to such a circuit configuration, the direction of change in the resistance values of the strain gauges 7 and 8 is opposite to the direction of change in the resistance values of the strain gauges 9 and 10 with respect to the X-direction component αx of the acceleration α. , The output voltage Vx of the bridge 15 becomes a value corresponding to the X-direction component αx. Next, in the same figure (b), strain gauge 11 and strain gauge 12, strain gauge 13 and strain gauge 14
The bridge 16 is configured so that the two sides are opposite sides.
According to such a circuit configuration, the Z-direction component α of the acceleration α is
The direction in which the resistance values of the strain gauges 11 and 12 change with respect to z is opposite to the direction in which the resistance values of the strain gauges 13 and 14 change, so the output voltage Vz of the bridge 16 corresponds to the Z-direction component αz. It becomes a value.

Next, the respective output voltages Vx and Vz obtained from the bridges 15 and 16 are
It can be expressed as follows. In addition, strain gauge 7-10
Resistance value of R _{1 to} R _4, and the resistance value of strain gauges 11 to 14 R ₅ to
R ₈

The output voltages Vz and Vx of the bridges 15 and 16 are Becomes

Here, assuming that the resistance values of the respective strain gauges in the unstrained state are all equal, each value of R ₁ , R ₂ , ..., R ₈ is set as R. From the relationship between the stresses of the beam portions 5a and 5b described above, the change in the resistance value of each strain gauge has the following relationship.

ΔR ₁ = ΔR ₂ , ΔR ₃ = ΔR ₄ = ΔR ₅ = ΔR ₆ , ΔR ₇ = ΔR ₈ Therefore, the above equation is as follows.

In this case, since ΔR << R, the equation is as follows.

Next, the stress generated in each strain gauge is obtained. In this embodiment, since the weight 5c is provided at each tip of the beam portion 5a and the beam portion 5b both having the length l ₀ , the centralized load is approximately applied to the shaft and It can be regarded as a fixed beam with both ends receiving force in the direction of 2l ₀ .

Now, the stress generated in each strain gauge can be expressed by the following equation.

Of the stresses δ ₇ and δ ₈ generated in the strain gauges 7 and ₈ , the Z-direction component αz is Becomes Further, in the X-direction component αx, the reaction force on the support portion side at both ends is mαx / 2, Becomes Therefore, Becomes

Similarly, the stresses generated in the strain gauges 9, 10, 11, 12 δ ₉ , δ ₁₀ ,
δ ₁₁ and δ ₁₂ are And the stresses δ ₁₃ , δ ₁₄ generated in the strain gauges ₁₃ , ₁₄ are Becomes (A: width of beam, b: thickness of beam, m: weight of weight portion) Here, ΔR ₁ , ΔR ₃ and ΔR ₇ are proportional to strain, and the strain is proportional to stress. Therefore, since the stress is proportional to ΔR ₁ , ΔR ₃ , and ΔR ₇ , the above equation can be rewritten as follows.

(IIι: Strain gauge longitudinal piezoresistive coefficient) Therefore, substituting the equation into Becomes

As described above, the output voltages Vz and Vx are linear functions of αz and αx, and linear outputs can be obtained without mutual interference. Then, αz and αx can be obtained from the equation.

In this way, by using the double-supported beam structure, arranging the gauge resistors in the beam portions 5a and 5b, and connecting them by bridge connection, it is possible to detect each component of the acceleration in the two-dimensional direction at once. Therefore, it is completely unnecessary to form each sensor in the same shape as in the conventional case in which a sensor having a cantilever is separately provided for each direction to detect each component of acceleration in a two-dimensional direction. Becomes Further, since there is no variation due to the difference in the forming accuracy of each sensor, there is an advantage that the detecting accuracy is improved.

As described above, according to the present invention, the weight portion formed in the central portion of the semiconductor substrate, the support portion formed in the peripheral portion of the semiconductor substrate, and one side of the weight portion are provided. Semiconductor acceleration having a first beam portion formed between the support portion and a second beam portion formed between the support portion and a side of the weight portion facing the one side. In the sensor,
Consists of two strain gauges arranged at a connection portion between the first beam portion and the support portion and two strain gauges arranged at a connection portion between the second beam portion and the support portion. A first Wheatstone bridge, two strain gauges arranged at a connecting portion of the second beam portion and the weight portion, and a strain gauge arranged at a connecting portion of the second beam portion and the supporting portion. Since the second Wheatstone bridge configured by the two strain gauges described above is provided, it is possible to improve the detection accuracy without having to increase the formation accuracy.

[Brief description of drawings]

FIG. 1 is a plan view showing the external configuration of an embodiment of the present invention,
FIG. 2 is a sectional view taken along the line AA of FIG. 1, FIG. 3 is a diagram for explaining the same embodiment, FIG. 4 is a circuit diagram showing an electrical configuration of the same embodiment, and FIG. 5 is a conventional semiconductor. It is a perspective view which shows the external appearance structure of an acceleration sensor. 5 ... Semiconductor substrate (also serving as a supporting portion), 5a, 5b ... Beam portion, 5c ... Weight portion, 7 to 14 ... Strain gauge (Strain gauge 7,8,
9 and 10 compose the first Wheatstone bridge, and strain gauges 11, 12, 13 and 14 compose the second Wheatstone bridge).

Claims (1)

[Claims] 1. A weight portion formed in a central portion of a semiconductor substrate, and a supporting portion formed in a peripheral portion of the semiconductor substrate.
A first beam portion formed between one side of the weight portion and the support portion, and a second beam portion formed between a side of the weight portion facing the one side and the support portion. (B) two strain gauges arranged at a connecting portion between the first beam portion and the support portion, the second beam portion and the support portion, A first Wheatstone bridge composed of two strain gauges arranged in a connecting portion; and (c) two strain gauges arranged in a connecting portion of the second beam portion and the weight portion. And a second Wheatstone bridge constituted by two strain gauges arranged at a connecting portion between the second beam portion and the support portion.