JPH06163937A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To detect acceleration in three-dimensional coordinate system represented by X, Y, and Z axes. CONSTITUTION:When an acceleration sensor A is subjected to an acceleration G in X-axis direction, all piezo resistors RX1-RX4, RY1-RY4, RZ1-RZ4 are subjected to tensile stress and resistances of the piezo resistances RX1, RX3 decrease whereas resistances of other piezo resistors increase. When these resistors are constituted into a bridge, output is obtained only from a bridge for detecting the acceleration G in X-axis and zero output is produced from bridges for detecting the acceleration G in Y-axis and Z-axis. Similarly, output is obtained only from a bridge for detecting the acceleration G in Y-axis or Z-axis for the acceleration G functioning in Y-axis or Z-axis and zero output is produced from two other bridges. This constitution allows independent detection of acceleration in three axial directions.

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, and more particularly to a semiconductor acceleration sensor capable of detecting accelerations of three axes of X axis, Y axis and Z axis with a simpler structure.

[0002]

2. Description of the Related Art FIG. 9 shows a conventional acceleration sensor A ', in which a weight portion 2 is formed from one side of a substantially square-shaped support portion 4 formed by processing a semiconductor substrate 1 and a bending portion 3'. It is a thing. The acceleration sensor A'of this structure is
This is a so-called cantilever structure.

[0003]

In the conventional acceleration sensor A ', although it can detect acceleration in one axis, when viewed as a three-axis (X-axis, Y-axis, Z-axis) acceleration sensor, For example, consider a bridge configuration in which the stress in the flexure 3'appears only in tension or compression when acceleration is applied in the X-axis or Z-axis direction, and accelerations in the three axes are detected independently. However, there was a problem that it was impossible to realize.

Further, as another conventional example, there is, for example, Japanese Patent Laid-Open No. 63-169078. This conventional example is not a so-called cantilever structure type but a double-end fixed type, and there is a problem that it is difficult to achieve high sensitivity because the stress generated in the strain-generating part (beam part or diaphragm part) is small. It was The present invention has been provided in view of the above points, and provides a semiconductor acceleration sensor that is capable of detecting acceleration in a three-dimensional coordinate system represented by three axes of X, Y, and Z. To do.

[0005]

According to the present invention, a weight portion formed by processing a semiconductor substrate, a flexible portion integrally formed with the weight portion, and a support portion for supporting and fixing the flexible portion are provided. Placed in the flexure and bridged 4
In a semiconductor acceleration sensor having two piezoresistors, and a voltage proportional to the applied acceleration is taken out as the bridge output, a supporting portion is extended from both sides of one end of the weight portion toward the other end, A bridge connection is made in the above-mentioned flexure portion in order to detect an acceleration expressed as a vector component of the X-axis, Y-axis and Z-axis of the three-dimensional coordinate system,
Four types of piezoresistors, three types for X component detection, Y component detection, and Z component detection, are arranged so that each bridge does not output the acceleration with respect to the other axis.

Further, in the second aspect, the flexible portion is formed so as to be located above the weight portion.

[0007]

According to the present invention, the conventional acceleration sensor having a cantilever structure cannot detect acceleration in three axes, but in the present invention, three-dimensional coordinates represented by three axes of X, Y, and Z. The acceleration in the system can be detected. In addition, by using a cantilever structure, when compared with the same output sensitivity, the strain generating part (beam part or diaphragm part) can be made thicker than the double-end fixed type or diaphragm type, which is extremely easy to process. It will be easy. Conversely, if the thickness is the same, the cantilever structure has a larger stress generated in the strain-flexing portion, and thus a highly sensitive acceleration sensor can be configured.

Further, according to a second aspect of the present invention, the semiconductor acceleration sensor according to the first aspect has a higher output (high sensitivity) structure, and the flexure portion is formed above the weight portion. The weight portion can be maximized within the same chip area, and therefore, the sensitivity can be increased by the volume ratio of the weight portion with respect to the same acceleration.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an acceleration sensor A formed by processing a semiconductor substrate 1 to form a so-called cantilever structure, and a thick square-shaped weight portion 2 is formed in the center of the semiconductor substrate 1. A thin L-shaped flexible portion 3 is integrally formed with the weight portion 2 from both sides on the one end side of the weight portion 2. Further, a support portion 4 for supporting and fixing the flexible portion 3 is integrally formed, and the support portion 4 is formed in a substantially square shape.

Further, a bridge is connected to the flexible portion 3.
4 piezoresistors R_X1~ R_X4, R _Y1~ R_Y4, R_Z1~ R
_Z4Is applied and, as will be described later, the applied acceleration
To take out a voltage proportional to the degree as a bridge output
is doing. In addition, piezo resistance R_X1~ R_X4It consists of
The bridge output corresponding to the X axis is output by the ridge circuit.
Piezo resistance R_Y1~ R_Y4In the bridge circuit configured in
Output the bridge output corresponding to the Y axis, and
Anti-R_Z1~ R_Z4Supports Z-axis with bridge circuit configured in
It is designed to output the bridge output.

Here, as shown in FIG. 1, the X axis and the Y axis are
The Z axis is taken perpendicular to these two axes. In this Figure 1.
As shown, piezo resistance R_X1~ R_X4, R_Y1~ R_Y4, R_Z1
~ R _Z4When is arranged, each direction (X-axis direction, Y-axis direction)
Direction, Z-axis direction)
The operation of the sensor A will be described. First, before that,
The anti-effect will be described. As shown in FIG. 7, n-type silicon
<100> for the plane orientation of the controller and <110 for the X and Y directions.
The piezoresistors arranged as> are shown in Fig. 7 (a).
If it is arranged like, resistance to tensile stress +
The value R increases as R + ΔR. Conversely, it receives compressive stress
Then, R-ΔR and the resistance value decrease.

In the case of FIG. 7B, the resistance value R decreases to R-ΔR with respect to the tensile stress +, and conversely, when the compressive stress is applied, the resistance value increases to R + ΔR. That is, FIG.
In (a) and (b), opposite resistance values change with respect to the same stress. In n-type silicon, in the 100 plane and the 110 direction, almost the same resistance change occurs with respect to the same stress in FIGS. 7A and 7B.

FIG. 2 shows a perspective view of the acceleration sensor A,
When the acceleration G is applied to the acceleration sensor A from each of the X-axis, Y-axis, and Z-axis directions, the stress applied to the flexible portion 3 is expressed as + tensile stress and − as compressive stress.
It becomes like FIG. Here, FIG. 3 shows the flexure of the flexure 3 when the acceleration G is applied to the acceleration sensor A in the X-axis direction, and FIG. 4 shows the flexure of the flexure 3 when the acceleration G is applied in the Y-axis direction. 5 shows the flexure of the flexure portion 3 when the acceleration G is applied in the Z-axis direction. In FIGS. 4 and 5, 0 indicates the case where the stress is 0.

First, as shown in FIG. 3, when acceleration G is applied to the acceleration sensor A from the X-axis direction, all the piezoresistors R _{X1 to} R _X4 , R _{Y1 to} R _Y4 , and R _{Z1 to} R _Z4 are pulled. When stress is applied, the resistance values of the piezoresistors R _X1 and R _X3 decrease and the resistance values of the other piezoresistors increase, so if these resistances are configured in a bridge as shown in FIG. The output is obtained only from the bridge that detects G, and the output of the bridge that detects the acceleration G of the Y axis and the Z axis becomes zero. In FIG. 6, R _{1 to} R ₄ represent resistances when the X axis, the Y axis, and the Z axis are common.

Next, as shown in FIG. 4, when acceleration G is applied from the Y-axis direction, theoretically, the piezo resistances R _{X1 to} R _X4.
The resistance value of the piezoresistors does not change, and the other piezoresistors are subjected to stress as shown in FIG. 4, and as a result, the piezoresistors R _Y1 , R _Y3 ,
R _Z1 and R _Z4 are increased, and piezo resistances R _Y2 , R _Y4 , R _Z2 and R
_Z3 is reduced. If this is configured in a similar bridge, Y
Only the output of the bridge that detects the acceleration G of the axis is obtained,
The outputs of the other two bridges are zero.

Finally, as shown in FIG. 5, when the acceleration G is applied from the Z-axis direction, the resistance values of the piezoresistors R _{X1 to} R _X4 do not change and the piezo-resistance R R does not change as in the Y-axis. _Y2 ,
R _Y3 , R _Z2 , and R _Z4 increase, and the piezo resistances R _Y1 , R _Y4 , and R
_Z1 and R _Z3 are reduced. As a result, only the output of the bridge that detects the acceleration G in the Z-axis direction is obtained, and the outputs of the other two bridges are zero.

As described above, in the present invention, the accelerations G in the three axis directions can be detected independently. (Embodiment 2) FIG. 8 shows another embodiment. Unlike the previous embodiment, the flexure portion 3 of the acceleration sensor A is integrally formed with the support portion 4 by passing above the weight portion 2 so as to form a weight. The volume of the part 2 is set to be large. By increasing the volume of the weight portion 2, it is possible to detect the acceleration with higher sensitivity.

[0018]

As described above, the present invention has a weight portion formed by processing a semiconductor substrate, a flexible portion integrally formed with the weight portion, and a support portion for supporting and fixing the flexible portion. A semiconductor accelerometer having four piezoresistors arranged in a flexure section and bridge-connected, wherein a voltage proportional to an applied acceleration is taken out as the bridge output. Extending the support part toward the side, in the flexible part,
A bridge connection is made to detect accelerations expressed as vector components of the X-axis, Y-axis, and Z-axis of the three-dimensional coordinate system, and four types each of three types for X component detection, Y component detection, and Z component detection are provided. Since the piezoresistors are arranged so that each bridge does not output the acceleration of the other axis, the conventional cantilever type acceleration sensor cannot detect the acceleration of the three axes. In the present invention, it is possible to detect the acceleration in the three-dimensional coordinate system represented by the three axes of X, Y and Z. In addition, by using a cantilever structure, when compared with the same output sensitivity, the strain generating part (beam part or diaphragm part) can be made thicker than the double-end fixed type or diaphragm type, which is extremely easy to process. It will be easy. Conversely, with the same thickness, the cantilever structure has a larger stress generated in the strain-flexing portion, so that an acceleration sensor with high sensitivity can be configured.

According to a second aspect of the present invention, the semiconductor acceleration sensor according to the first aspect has a higher output (high sensitivity) structure, and the flexure portion is formed above the weight portion. The weight portion can be maximized within the same chip area, and therefore, the sensitivity can be increased by the volume ratio of the weight portion with respect to the same acceleration.

[Brief description of drawings]

FIG. 1A is a plan view of an acceleration sensor according to an embodiment of the present invention. (B) is a perspective view of the acceleration sensor of the embodiment of the present invention.

FIG. 2 is a perspective view of the above acceleration sensor.

FIG. 3 is a diagram illustrating a case where an acceleration is applied to the acceleration sensor in the above-described direction from the X-axis direction.

FIG. 4 is a diagram illustrating a case where acceleration is applied to the acceleration sensor in the same direction as the Y-axis.

FIG. 5 is a description of a case where acceleration is applied to the acceleration sensor in the same direction from the Z-axis direction.

FIG. 6 is an equivalent circuit diagram in the case where the above piezoresistor has a bridge configuration.

FIG. 7 is an explanation of the piezoresistor of the above.

FIG. 8A is a plan view of an acceleration sensor of another embodiment of the above. (B) is a perspective view of an acceleration sensor same as the above.

FIG. 9A is a plan view of a conventional acceleration sensor. (B) is a perspective view of the conventional acceleration sensor.

[Explanation of symbols]

1 Semiconductor substrate 2 Weight part 3 Deflection part 4 Support part A Accelerometer R _{X1 to} R _X4 piezoresistor R _{Y1 to} R _Y4 piezoresistor R _{Z1 to} R _Z4 piezoresistor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Hamaoka, 1048 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Works Co., Ltd. (72) Naohiro Taniguchi, 1048, Kadoma, Kadoma City, Osaka Matsushita Electric Works, Ltd.

Claims (2)

[Claims] 1. A weight portion formed by processing a semiconductor substrate, a flexure portion integrally formed with the weight portion, a support portion for supporting and fixing the flexure portion, and a bridge connection disposed on the flexure portion. Equipped with four piezoresistors,
In a semiconductor acceleration sensor configured to take out a voltage proportional to an applied acceleration as the bridge output, a support portion is extended from both sides of one end of the weight portion toward the other end, and a three-dimensional shape is formed on the flexible portion. The X axis of the coordinate system,
Bridge connections are made to detect accelerations expressed as Y-axis and Z-axis vector components, and three types of piezoresistors for X-component detection, Y-component detection, and Z-component detection are provided for each bridge. A semiconductor acceleration sensor, which is arranged so that output is not output for accelerations of other axes. 2. The semiconductor acceleration sensor according to claim 1, wherein the flexible portion is formed above the weight portion.