JPH05264573A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain a higher performance and low cost semiconductor acceleration sensor which has improved detection sensitivity without requiring any special process whose interference output and offset output with a passivation film are lowered. CONSTITUTION:A weight 1 is supported with beams 2 and 3 and 4 and 5 from the left and right and strain gauges 2A, 3A, 4A and 5A are formed on the beams 2, 3, 4 and 5 in the longitudinal direction of the top surface thereof on the side of a coupled part of the beams and a support body 6 while strain gauges 2B, 3B, 4B and 5B are formed in the longitudinal direction of the top surface thereof on the side of the coupled part of the beams and the weight 1. The strain gauges 2A and 5A, 3A and 4A, 2B and 5B, and 3B and 4B are arranged respectively symmetrically with respect to the center O of the weight 1 to form a Wheatstone bridge and a passivation film 10 is formed on the top surface of the strain gauges.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor miniaturized acceleration sensor.

[0002]

2. Description of the Related Art FIGS. 8 and 9 show an example of a conventional semiconductor acceleration sensor, FIG. 8 is a plan view and FIG. 9 is a side view. 8 and 9, a square thick-walled weight 1 made of semiconductor, for example, 400 μm in thickness, a square thick-walled support 6 having a predetermined distance from one side of the weight, and a weight. 1 is composed of a thin-walled beam 7 having a thickness of, for example, 20 to 40 μm, which connects the one side surface of the support body 6 to the side surface of the support body 6 facing the one side surface.
C and 7D are formed. Among these strain gauges, the strain gauges 7A and 7C are formed in the length direction of the beam 7 on the upper surface of the beam 7 and the support 6 on the side of the connecting portion, and the strain gauges 7B and 7D are on the connecting portion side of the beam 7 and the weight 1. Is formed on the upper surface of the beam 7 in the width direction of the beam 7. And these strain gauges 7A, 7B, 7C, 7D
As shown in FIG. 12, the strain gauges 7A and 7C and 7B and 7D are opposed to each other to form a Wheatstone bridge. E is a power supply terminal, G is a ground terminal, and S1 and S2 are signal output terminals.

Now, the weight 1 is in the direction of arrow V in FIG. 9, that is, the direction perpendicular to the weight 1 (which is the acceleration detection direction).
When the acceleration of is applied to the beam 7, the beam 7 is moved to the weight 1 as shown in FIG.
Receives a vertical force F _v and bends in the direction of arrow M. At this time, tensile stress acts on the beam 7 on the upper surface of the beam 7 and the support 6 on the side of the joint portion and on the upper surface of the beam 7 and the weight 1 on the side of the joint portion, and the beam 7 is formed in the longitudinal direction of the beam 7. The strain gauges 7A and 7C have increased resistance values.
The resistance values of the strain gauges 7B and 7D formed in the width direction do not change. In this way, the detection signal having a magnitude proportional to the acceleration is output from the signal output terminals S1 and S2 of the Wheatstone bridge.

Since the strain gauges 7A, 7B, 7C and 7D are usually formed by a diffusion technique, the weight 1, the beam 7 and the upper surface of the support 6 are protected by SiO ₂ or Si.
A passivation film 10 of N or the like is provided.

[0005]

In the acceleration sensor described above, there is a distance L between the deflection center line 9 of the beam 7 and the center of gravity W of the weight 1 as shown in FIG. When the acceleration is applied to the weight 1 in the lateral direction (which is the direction in which the acceleration is not detected), the distance L between the deflection center line 9 and the center of gravity W of the weight 1 and the lateral direction generated in the weight 1 by the acceleration. A force is generated by the force F _h and the beam 7 bends in the direction of arrow M as in the case where acceleration is applied in the vertical direction, as shown in FIG. The Wheatstone bridge also outputs a signal due to this bending, and this signal becomes an interference output and reduces detection accuracy.

For this reason, as shown in FIGS. 10 and 11, an additional weight 8 made of, for example, glass is joined to the upper surface of the weight 1 to form a center of gravity W of the weight composed of the weight 1 and the additional weight 8.
It is conceivable to just match the bending center line 9 of the beam 7 and set the distance L between them to zero, but the special step of joining the additional weight increases and the cost rises. Furthermore, in the aforementioned acceleration sensor, the strain gauge formed in the width direction of the beam on the upper surface at the side where the beam and the weight are connected does not cause resistance change when acceleration is applied, so that the detection sensitivity is low. There is.

Furthermore, Si for protecting the strain gauge
A passivation film such as O ₂ or SiN is usually formed at a high temperature and then returned to room temperature. However, since the thermal expansion coefficient of the passivation film is different from that of the silicon semiconductor, stress is applied to the surface of the silicon semiconductor when the temperature is returned to room temperature. As a result, the beam 7 may be bent as shown in FIG. When the beam is deflected in this way, the voltage is output from the Wheatstone bridge in the same manner as when acceleration is applied. This voltage is called an offset output and reduces the SN ratio of the sensor output to reduce the detection accuracy.

An object of the present invention is to solve the above-mentioned problems, to provide an acceleration sensor which does not require a special process, has improved detection sensitivity, and has reduced interference output. Another object of the present invention is to provide an acceleration sensor in which the offset voltage due to the passivation film is reduced.

[0009]

In order to achieve the above-mentioned object, a semiconductor acceleration sensor of the present invention is made of a semiconductor and has a quadrangular thick-walled weight and a predetermined distance from the weight,
And a thick-walled support having a square inner hole formed so as to surround the weight, both ends of each of the outer sides of the pair of facing outer sides of the weight, and a support that faces these both ends. It is composed of four thin-walled beams that connect each inner side of the body, and a strain gauge is formed on each of the beams. Alternatively, it is made of a semiconductor and has four square thick walls formed at the positions of the regular square thick central portion and the sides of the central portion that coincide with each other by 90 ° rotational movement about the central portion. And a thick-walled support having a quadrangular inner hole formed so as to surround the weight, and a weight consisting of a convex portion having a predetermined shape, an outer side of each convex portion of the weight, and a predetermined distance. Connect one side of each convex portion of the weight, which coincides with each other by 90 ° rotational movement around the center of the weight, and each inner side of the support, which faces each one of these convex sides 4 Each of the beams has a thin gauge beam, and a strain gauge is formed on each of the beams.
Further, the strain gauges formed on each of the four beams of these semiconductor acceleration sensors have four strain gauges on the first side formed on the upper surfaces of the beams in the length direction of the beams and on the joint side of the beam and the support. The strain gauge and the four strain gauges on the second side formed on the upper surface of the beam and the connecting portion side of the weight,
Of the four strain gauges on the side of, the two strain gauges that are symmetrical with respect to the center point of the weight are opposed to each other, and the center point of the weight of the four strain gauges on the second side Wheatstone bridges are formed by making two strain gauges symmetrical to each other face each other. Then, in the semiconductor acceleration sensor in which the strain gauges formed on each of the four beams are formed on the upper surfaces of the beams in the length direction of the beams on the joint side of the beams and the support, A passivation film is provided on the upper surface.

[0010]

In the semiconductor acceleration sensor according to the first aspect of the present invention, a quadrangular thick-walled weight made of a semiconductor and a quadrangle formed at a predetermined distance from the weight and surrounding the weight are included. A thick-walled support having holes, each end of each outer edge of the pair of outer edges facing each other, and each inner edge of the support that faces these both edges are connected to each other 4
It consists of individual thin-walled beams, and the strain gauges are formed on each of the beams, so the weights are supported by the beams from the left and right, so when the lateral (non-detection) acceleration is applied, The deflection is significantly smaller than that in the case of being supported by a conventional beam on one side, and the interference output is significantly reduced.

According to another aspect of the semiconductor acceleration sensor of the present invention, each of the sides of the central portion is made of a semiconductor and has a square thick-walled central portion and the central portions that are mutually rotated by 90 ° about the central portion. A weight having four quadrangular thick-walled convex portions formed at the respective positions, and a predetermined distance from the outer edge of each convex portion of the weight, and formed so as to surround the weight. A thick support having a quadrangular inner hole, one side of each convex portion of the weight which is rotated by 90 ° about the central portion of the weight, and each of these convex sides It is composed of four thin-walled beams that connect each inner side of the supporting body facing each other, and a strain gauge is formed on each beam, so that each beam is attached to each side of the center portion of the weight. Will be formed along and can lengthen their length direction It will bend more easily. As a result, the detection sensitivity can be further improved in addition to the effect of the first aspect.

Further, in each of the semiconductor acceleration sensors as described in claim 3, the strain gauges formed on each of the four beams are arranged in the lengthwise direction of the beams on the side where the beams and the support are connected. The four strain gauges on the first side formed on the upper surface of the first side and the four strain gauges on the second side formed on the upper surface on the side where the beams and weights are connected, Of the four strain gauges, the two strain gauges that are symmetrical with respect to the center point of the weight are opposed to each other, and
Of the four strain gauges on the side of, the two strain gauges that are symmetrical with respect to the center point of the weight are made to face each other to form the Wheatstone bridge, so that, for example, in the lateral direction (non-detection direction) When acceleration is applied, two strain gauges on each of the first side and the second side, which are symmetric with respect to the center point of the weight, have two strain gauges. Tensile stress is applied to the gauges, they act to cancel out the change in resistance value, and no signal is output from the Wheatstone bridge. When acceleration in the vertical direction (detection direction) is applied, all strain gauges on the first side and the second side are strained on the other side when compressive stress is applied to the strain gauge on one side. A tensile stress is applied to the gauge, and a detection signal is output from the Wheatstone bridge due to changes in the resistance values of all these strain gauges. This reduces interference output and improves detection sensitivity.

Further, as in the semiconductor acceleration sensor according to a third aspect of the present invention, the strain gauges are provided in the beam length direction on the upper surface of the beam-supporting joint side and on the upper surface of the beam-weight coupling side, respectively. In this semiconductor acceleration sensor, when a passivation film is provided on the upper surface of the beam on which the strain gauge is formed as described in claim 4, stress is applied to the surface of the silicon semiconductor due to the difference in thermal expansion coefficient between the passivation film and the silicon semiconductor. However, when the strain gauges on the upper surface of these beams all have the same resistance change and are connected to the Wheatstone bridge, these resistance changes do not cancel each other out to generate an offset output.

[0014]

1 and 2 show an embodiment of a semiconductor acceleration sensor of the present invention, FIG. 1 is a plan view, and FIG. 2 is A- of FIG.
It is sectional drawing in A. FIG. In FIG. 1 and FIG. 2, a weight 1 made of a semiconductor and having a quadrangular thickness, for example, a thickness of 400 μm, is formed so as to surround the weight 1 with a predetermined distance from the weight 1. The thick-walled support body 6 having a square inner hole, the respective end portions of the outer edges of the pair of outer edges of the weight 1 which are opposed to each other, and the inner edges of the support element 6 which face these end portions are connected to each other. It is composed of four thin-walled beams 2, 3, 4, 5 having a thickness of, for example, 20 to 40 μm, and strain gauges 2A,
2B, 3A, 3B, 4A, 4B, 5A, 5B are formed. Of these strain gauges, strain gauges 2A, 3A,
4A and 5A are formed in the length direction of these beams on the upper surface of the side of the connection between the support 6 and the beams 2, 3, 4, and 5 on which these strain gauges are formed, and the strain gauges 2B, 3B and 4B are formed. ，
5B is formed in the length direction of the weight 1 and the upper surface of the side where the beams 2, 3, 4, 5 on which the strain gauges are formed are connected. Now, four strain gauges 2A, 3 are formed on the upper surface of each beam on the side of the joint between the beam and the support.
A, 4A, and 5A are referred to as first side strain gauges, and four strain gauges 2B, 3B, 4B, and 5B formed on the upper surface of each beam and weight coupling side are referred to as second side strain gauges. , The four strain gauges 2A, 3A, 4A, 5A on the first side
Of the two strain gauges 2A, 5A and 3A, 4A that are symmetric with respect to the center point O of the weight 1, respectively, and face each other, and the four strain gauges 2B, 3B, 4B on the second side,
Of the 5B, two strain gauges 2B, 5B and 3B, 4B which are symmetrical with respect to the center point O of the weight 1 are opposed to each other to form a Wheatstone bridge as shown in FIG. In addition, V is a power supply terminal, G is a ground terminal, S1, S2
Is a signal output terminal.

Now, for the weight 1, in the direction of arrow V in FIG.
That is, when acceleration is applied to the weight 1 in the vertical direction (which is the direction of detecting the acceleration), the weight 1 receives the vertical force F _v and moves downward as shown in FIG. , 5 supported. At this time, a tensile stress is generated on the upper surface of the beam and the support 6 on the side of the connecting portion, and a compressive stress is generated on the upper surface of the beam and the weight 1 on the side of the connecting portion. Therefore, the resistance values of the strain gauges 2A, 3A, 4A, 5A on the first side increase, the resistance values of the strain gauges 2B, 3B, 4B, 5B on the second side decrease, and the signal output terminal S1 of the Wheatstone bridge. , S2 outputs a detection signal having a magnitude proportional to the acceleration.

Next, when an acceleration is applied to the weight 1 in the direction of the arrow H in FIG. 2, that is, in the lateral direction (which is the non-detection direction of acceleration) with respect to the weight 1, the deflection center line 9 of the beam and the weight 1 are applied. 7 by the distance L between the center of gravity W of the weight and the lateral force F _h generated in the weight 1 by the acceleration.
Beam 2 on the side that is deformed as shown in and is pushed by the weight 1.
In No. 3, compressive stress is generated on the upper surface of each beam-supporting joint side, and tensile stress is generated on the upper surface of each beam-weight joint side.
In the beams 4 and 5 on the side pulled by the weight 1, tensile stress is generated on the upper surface of each beam-supporting joint side, and compressive stress is generated on the upper surface of each beam-weight joint side.

Therefore, the four strain gauges 2A on the first side,
Of the two strain gauges 2A, 5A and 3A, 4A which are symmetrical with respect to the center point O of the weight 1 among the strain gauges 3A, 4A, 5A, the strain gauges 2A, 5A have a resistance value of 2A, 5A.
Becomes an increase in the resistance value and the changes in the resistance value cancel each other out, and in the strain gauges 3A and 4A, 3A decreases the resistance value, 4A
Becomes an increase in resistance value and the changes in resistance value cancel each other out.
Also, the four strain gauges 2B, 3B, 4B, 5 on the second side
Similarly, the B's cancel each other out the change in their resistance values, and no signal is output from the Wheatstone bridge.

In this semiconductor acceleration sensor, since the weight 1 is supported by the beams 2, 3 and 4, 5 from the left and right, the weight is supported by the left and right beams when a lateral (non-detection direction) acceleration is applied. , Compared with the case of being supported by a conventional beam on one side, the deflection itself of the beam becomes smaller,
As described above, the strain gauges cancel each other out the change in their resistance values, so that the interference output is significantly reduced.

When acceleration in the vertical direction (detection direction) is further applied, a signal is output to the Wheatstone bridge due to a change in the resistance value of all strain gauges, so that the signal output increases. 3 and 4 show different embodiments of the semiconductor acceleration sensor of the present invention, FIG. 3 is a plan view, and FIG. 4 is FIG.
It is sectional drawing in BB of FIG. In FIGS. 3 and 4, a quadrangular thick wall made of semiconductor, for example, a thickness of 400
Four quadrangular thick-walled convex portions 1 formed on the respective sides of the central portion 1A of the micron and the central portion 1A which coincide with each other by a 90 ° rotational movement about the central portion 1A.
A weight 1 composed of A, 1B, 1C and 1D, and a quadrangle formed so as to surround the weight 1 with a predetermined distance from the outer sides of the respective convex portions 1A, 1B, 1C and 1D of the weight 1. A thick-walled support 6 having an inner hole and one side of each of the protrusions 1A, 1B, 1C, 1D of the weight 1 which are fitted to each other by a rotational movement of 90 ° about the central portion 1A of the weight 1. , Four thin walls, for example, 20 to 40 micron beams 2, 3, 4, 5 which connect the inner sides of the support 6 facing the one side, respectively.
Strain gauges 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B are formed on the beams 2, 3, 4, 5 respectively. Of these strain gauges, strain gauge 2
A, 3A, 4A and 5A are formed on the upper surface of the side where the beams and the support are connected, and the strain gauges 2B, 3B, 4B and 5B are connected to the beams and the weights. It is formed in the length direction of these beams on the upper surface on the part side. These strain gauges form a Wheatstone bridge as in the embodiment shown in FIGS. 1 and 2, and their operation is also shown in FIG.
And is completely the same as the embodiment shown in FIG.

In this semiconductor acceleration sensor, each beam 2, 3,
Since the weights 4 and 5 are formed along each side of the central portion 1A of the weight 1, they can be elongated in the lengthwise direction, so that they can be bent more easily, and the detection sensitivity can be further improved. In addition, the convex portions 1A, 1 provided on each side of the weight 1
As shown in FIG. 1, B, 1C, and 1D are provided at one end of each side, and the beam 2 is provided on one side of the two sides of these protrusions, which has a longer distance from the inner side of the supporting body 6 facing each other. , 3, 4, 5
The length of these beams can be made longer by forming the beam.

Further, as shown in FIG. In the semiconductor acceleration sensor shown in FIG. 2 or the semiconductor acceleration sensor shown in FIGS. 3 and 4, a passivation film 10 such as SiO ₂ or SiN is provided to protect the strain gauge formed on the upper surface.
To form. This passivation film is usually formed at a high temperature of several hundreds of degrees and then returned to room temperature, but since the coefficient of thermal expansion is different from that of the silicon semiconductor, stress remains on the surface of the silicon semiconductor, which causes strain gauges 2A , 2
Although the resistance values of B, 3A, 3B, 4A, 4B, 5A and 5B change, these strain gauges are all beams 2, 3, 4, 5
Since it is provided in the upper surface longitudinal direction, the same resistance change occurs. Then, when these strain gauges are connected to the Wheatstone bridge shown in FIG. 5, all the strain gauges have the same resistance change, and therefore these resistance changes do not cancel each other out to generate an offset output.

[0022]

According to the present invention, depending on the shape of the semiconductor device and the number, position and connecting method of the strain gauges formed on the device, no additional process is required.
Since the detection sensitivity is improved and the interference output and the offset output are reduced, a high-performance semiconductor acceleration sensor can be supplied at low cost. This kind of semiconductor acceleration sensor is widely used in various applications including automobiles, and the effect that a high-performance semiconductor acceleration sensor can be supplied at low cost is extremely large.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a semiconductor acceleration sensor of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a plan view showing another embodiment of the semiconductor acceleration sensor of the present invention.

FIG. 4 is a sectional view taken along line BB in FIG.

5 is a connection diagram of the semiconductor acceleration sensor of the present invention shown in FIG.

6 is a sectional view for explaining the operation of the semiconductor acceleration sensor of the present invention shown in FIG.

FIG. 7 is a sectional view for further explaining the operation of the semiconductor acceleration sensor of the present invention shown in FIG.

FIG. 8 is a plan view showing an example of a conventional semiconductor acceleration sensor.

9 is a side view of FIG.

FIG. 10 is a plan view showing another embodiment of the conventional semiconductor acceleration sensor.

11 is a side view of FIG.

FIG. 12 is a connection diagram of the conventional semiconductor acceleration sensor shown in FIG.

13 is a side view for explaining the operation of the conventional semiconductor acceleration sensor shown in FIG.

14 is a side view further explaining the operation of the conventional semiconductor acceleration sensor shown in FIG.

15 is a side view further explaining the operation of the conventional semiconductor acceleration sensor shown in FIG.

[Explanation of symbols]

 1 Weight 1A Central part 1B Convex part 1C Convex part 1D Convex part 1E Convex part 2 Beam 2A Strain gauge (on the first side) 2B Strain gauge (on the second side) 3 Beam 3A Strain gauge (on the first side) ) 3B Strain gauge (second side) 4 Beam 4A Strain gauge (first side) 4B Strain gauge (second side) 5 Beam 5A Strain gauge (first side) 5B Strain gauge (first) 2 side) 6 support 10 passivation film O center point (of weight 1)

Claims (4)

[Claims] 1. A thick-walled support made of a semiconductor, having a quadrangular thick-walled weight and a quadrangular inner hole formed so as to surround the weight with a predetermined distance from the weight. And four thin-walled beams connecting each end of each outer edge of the pair of outer edges facing each other and each inner edge of the support facing these both ends, A semiconductor acceleration sensor, wherein a strain gauge is formed on each beam. 2. A thick square central portion made of a semiconductor and four pieces formed at positions of respective sides of the central portion which coincide with each other by a rotational movement of 90 ° about the central portion. A weight having a quadrangular thick-walled convex portion, a thick wall-shaped having a quadrangular inner hole formed so as to surround the weight with a predetermined distance from the outer side of each convex portion of the weight. A support,
Connect one side of each convex portion of the weight, which coincides with each other by 90 ° rotational movement around the center of the weight, and each inner side of the support, which faces each one of these convex sides 4 A semiconductor acceleration sensor, comprising a plurality of thin-walled beams, and a strain gauge is formed on each beam. 3. The semiconductor acceleration sensor according to claim 1 or 2, wherein the strain gauges formed on each of the four beams are provided on the upper surface of the beam in the length direction of the beam and on the joint side of the support. Four strain gauges on the first side to be formed and four strain gauges on the second side to be formed on the upper surface of the connecting portion side of these beams and weights.
Of the four strain gauges on the first side, two strain gauges symmetrical with respect to the center point of the weight are opposed to each other, and the strain gauges on the second side are Each of the two strain gauges is symmetrical about the center point of the weight.
A semiconductor acceleration sensor characterized in that a Wheatstone bridge is formed by making individual strain gauges face each other. 4. The semiconductor acceleration sensor according to claim 3, wherein a passivation film is provided on the upper surface of the beam on which the strain gauge is formed.