JPH08189937A - Acceleration sensor - Google Patents

Abstract

PURPOSE: To measure acceleration in a direction parallel to a substrate and perpendicular to a beam. CONSTITUTION: A weight 61 and beam 62 are displaced by acceleration Y which is parallel to a silicon substrate 50 and perpendicular to the beam 62 and another acceleration αZ which is perpendicular to the substrate 50. When piezo- resistors 64-1 and 64-2 are respectively strained by e1 and e2 , e1 -e2 =9.6mldY/ Ea<2> b, and e1 +e2 =12mlαZ/Eab<2> are established. Since the resistance of the piezo-resistor 64-1 varies proportionally to the displacement of the resistor 64-1 by the strain e1 , the variation of the resistance is measured as the output voltage of a detector. Similarly, the variation of the resistance of the piezo- resistor 64-2 is measured as the output voltage of the detector. A computing element calculates the acceleration αY by taking the difference between the outputs of the detector and multiplying the difference by a constant. The computing element, in addition, calculates the acceleration αZ by taking the sum of the outputs of the detector and multiplying the sum by a constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for detecting acceleration by using a piezoresistor arranged on a beam and detecting a change in resistance of the piezoresistor due to strain of the beam.

[0002]

2. Description of the Related Art Conventionally, techniques in such a field include:
For example, some documents were described in the following documents. Reference 1; Esashi, Fujita et al., "Micromachining and Micromechatronics", 1992, Baifukan Reference 2; IEEE TRANSACTION ON E
LECTRON DEVICES, ED-26, 197
9. Lynn Michelle Roylance, “A Batch-Fabricated
Silicon Accelerometer ", p. 1911-1917 Reference 3; Micro System Technologies 90-Proceedings o
f 1st International Conference on Micro Electro, Op
to, Mechanic System and Components Ed, H, Reichl.Berl
in, Sept. 10-13 (1990), J. Mohr et.l., `` Movable Mi
crostructures Manufactured by LIGA Process as Basi
c Element for Microsystems ", Springer-V
erlag, P.M. 529-537 Accelerometers have many uses for automobiles (airbags, navigation, ABS (anti-skid brake system) control, suspension control), and other robot control.

An acceleration sensor uses a structure in which a weight is supported by a beam and measures displacement of the weight due to acceleration. There are two types of strain gauges, one is to attach a strain gauge to the beam to know the displacement, and the other is to convert the displacement into a change in capacitance. 2 (a) and 2 (b) are views showing the acceleration sensor described in Documents 1 and 3, where FIG. 2 (a) is a plan view and FIG. 2 (b) is a sectional view taken along line AA. . In this acceleration sensor, a weight 2 is attached to a tip of a cantilever beam 3, and a change in diffusion resistance due to a piezoresistive effect of a piezoresistor 4 formed on the beam 3 is passed through a diffusion layer 5 to lead 6
By further detecting, the acceleration perpendicular to the silicon substrate 1 can be measured. In order to reduce the influence of the acceleration component parallel to the silicon substrate 1, the weight 2 is designed so that the centers of gravity of the weights 2 coincide with each other on the extension line of the beam 3 having the piezoresistor 4. The acceleration sensor is covered with a glass cover 8 in which the peripheral portion 7 of the weight 2 is removed by etching.

[0004]

However, the conventional acceleration sensor has the following problems. Most of the conventional acceleration sensors measure acceleration perpendicular to the substrate, and almost none measure acceleration parallel to the substrate. This is because it is difficult to manufacture a beam and a weight that vibrate only in a direction parallel to the substrate by micromachining, as shown below. FIG. 3 is a diagram showing a problem of the conventional acceleration sensor. Weight 12 in FIG.
Is weight m, and the beam 13 has width a, thickness b, and length l. The thickness b corresponds to the vertical direction of the substrate 11. X is the length direction of the beam 13, Y is the direction parallel to the substrate 11 and perpendicular to X, and Z is the direction perpendicular to the substrate 11. Beam 1 parallel to substrate 11
When the acceleration αY perpendicular to 3 is applied, the beam 13 bends in the −Y direction. The radius of curvature R _XY at a distance x from the fulcrum of the beam 13 at this time is R _XY = Ea ³ b / {12 × m (l−x) αY} (1). Here, E is Young's modulus.

The weight 12 and the beam 13 are bent in the -Z direction by the acceleration αZ perpendicular to the substrate 11. The radius of curvature R _ZX at this time is R _ZX = Eab ³ / {12 × m (l−x) αZ} (2) The magnitude of displacement of the beam 13 is inversely proportional to the radius of curvature. Therefore, the ratio of the magnitude of strain to the unit acceleration in the Y direction and the magnitude of strain to the unit acceleration in the Z direction is (1 / R _ZX αZ) / (1 / R _XY αY) = a ² / b ² ... (3) For example, if a structure with an aspect ratio b / a = 10 is created, the influence of the acceleration αZ can be suppressed within 1%, and the structure shown in FIG.
The acceleration αY parallel to the substrate 11 can be measured by the acceleration sensor having the weight 12 and the beam 13 having the structure shown in FIG. However, it is extremely difficult to obtain a structure with a large aspect ratio by micromachining.
As a method for obtaining a structure having a large aspect ratio by micromachining, the method described in L.
There is an IGA (Lithografie, Galvanoformung, Abformung) process. However, since the LIGA process requires synchrotron radiation, it is generally difficult to use, and mass productivity is poor.

[0006]

In order to solve the above-mentioned problems, the acceleration sensor of the first invention has a weight and a beam that supports the weight, and the weight and the silicon around the beam are used. A vibrator having a substrate as a penetrating portion and a plurality of piezos arranged on the beam (e.g., symmetric with respect to the center line in the length direction of the beam) and having resistance varying according to the magnitude of displacement of the beam due to acceleration. Have resistance. Furthermore, based on the change in resistance measured by the piezoresistive measurement circuit for measuring the change in resistance of the piezoresistor, the direction parallel to the substrate and perpendicular to the direction of the beam. And an arithmetic unit for calculating acceleration.

[0007]

According to the first aspect of the invention, since the acceleration sensor is constructed as described above, the resistance of the piezoresistor changes due to the displacement of the beam due to the acceleration parallel to the substrate. Since the piezoresistor is composed of multiple pieces and is arranged on the beam,
The amount of displacement of each piezoresistor is different. When the piezoresistors are arranged symmetrically with respect to the center of the beam length, the difference between the displacements of the two piezoresistors is the acceleration component in the direction parallel to the substrate and perpendicular to the beam, and other constants. And the product. Therefore, the piezoresistance measurement circuit measures the displacement amount of the piezoresistance, and the calculator calculates the difference and multiplication with respect to the displacement amount of the piezoresistance measured by the piezoresistance circuit. And the acceleration component in the direction perpendicular to the beam is calculated. Therefore, the above problem can be solved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIGS. 1 (a) and 1 (b) are acceleration sensors showing a first embodiment of the present invention. FIG. 1 (a) is a plan view and FIG. It is a side view. This acceleration sensor differs from the conventional acceleration sensor in that two piezoresistors 64-1 and 64-2 are arranged at different positions in the width direction of the beam 62, and the piezoresistor 6
4-1 and the piezoresistors 71-1 to 71-3 arranged on the fixed part of the silicon substrate 50 form a bridge circuit, and the piezoresistors 64-2 and the piezoresistors 72-1 to 72 arranged on the fixed part of the silicon substrate 50. The bridge circuits are respectively constituted by 3 and 3, and the arithmetic unit for calculating the outputs of the detectors of the two bridge circuits to calculate the acceleration component parallel to the silicon substrate 50 is provided. As shown in FIG. 1A, in this acceleration sensor, a vibrator 60 that oscillates in the vertical direction (± Z direction) and parallel (± Y direction) with respect to the silicon substrate 50 is provided in the central portion of the silicon substrate 50. are doing.
The vibrator 60 includes a weight 61 and a beam 62 that supports the weight 61. Peripheral portions of the weight 61 and the beam 62 are penetrating portions 63 formed by penetrating etching of the silicon substrate 50, and the vibrator 60 can vibrate in the ± Z direction and the ± Y direction. Piezoresistors 64-1 and 64-2, which are formed by diffusion resistors introduced with impurities having a concentration of about 1 × 10 ¹⁸ to 2 × 10 ²¹ cm ^−3, are arranged in the length direction of the beam 62. .

FIG. 4 is an enlarged view of portion A in FIG. As shown in FIG. 4, the piezoresistors 64-1 and 64
-2 is arranged at a position symmetrical with respect to a straight line that bisects the beam 62 in the Y direction at the base of the beam 62, and at a position of 8 μm (0.4a, a is the width of the beam 62) from the center line. is there. One terminals of the piezoresistor 64-1 and the piezoresistor 64-2 are connected by an aluminum wiring 65 in order to commonly supply power. As shown in FIG. 1A, the fixed portion of the silicon substrate 50 is formed of diffused resistors, and the piezoresistors 71-1 to 71-1 are formed of diffused resistors having the same impurity concentration as the piezoresistors 64-1 and 64-2. 3,72-
1 to 72-3 are arranged. 5 (a)-(b)
FIG. 4 is a diagram showing a connection between piezoresistors. As shown in FIG. 5A, the resistance of the piezoresistor 64-1 and each of the piezoresistors 71-1 to 71-3 in the non-displaced state is equal to about 10 kΩ, and these four piezoresistors make It constitutes a stone bridge. One terminal of the short-circuited piezoresistors 64-1 and one terminal of the piezoresistors 71-1, one terminal of the short-circuited piezoresistors 71-2 and one terminal of the piezoresistors 71-3 are used as a power supply branch, A constant power is supplied. The other terminal of the shorted piezoresistor 64-1 and the other terminal of the piezoresistor 71-3, the other terminal of the shorted piezoresistor 71-1 and the piezoresistor 71.
The voltage is measured by the detector with the other terminal of −2 as the detection branch.

Further, as shown in FIG. 5B, the piezoresistors 64-2 and the respective piezoresistors 72-1 in the non-displaced state.
The resistance of ˜72-3 is equal to about 10 kΩ, and these four piezoresistors form a Wheatstone bridge. One terminal of the short-circuited piezoresistors 64-2 and one terminal of the piezoresistors 72-1, one terminal of the short-circuited piezoresistors 72-2 and one terminal of the piezoresistors 72-3 are used as a power supply branch, A constant power is supplied. The other terminal of the short-circuited piezoresistor 64-2 and the other terminal of the piezoresistor 72-3, and the short-circuited piezoresistor 72
The voltage is measured by the detector with the other terminal of -1 and the other terminal of the piezoresistor 72-2 as detection branches. Piezoresistors 64-1 and 64-2 to form a bridge
And piezoresistors 71-1 to 71-3, 72-1 to 72-3
The connection between the two is made by aluminum wiring. The output side of the detector is connected to a calculator (not shown) that performs calculation such as difference and multiplication on the output.

As shown in FIG. 1B, the periphery 82 of the vibrator 60 is covered with etched glass covers 80 and 81. The beam 62 has a width a = 20 μm and a thickness b =
50 μm, length l = 1000 μm, long and thin, ± Z direction,
It has a structure that vibrates in the ± Y direction. In order to increase the sensitivity, an additional weight of several mg may be added to the weight 61. In that case, it is necessary to consider that the center of gravity of the entire weight 61 is on the extension line of the beam 62. When the additional weight is not attached to the weight 62, the weight 62 has a mass of 0.1 mg. In this case, according to this design, the natural frequency of the vibrator 60 in the ± Y directions is 463.5 Hz, and the natural frequency of the vibration in the ± Z directions is 1159 Hz. These natural frequencies are obtained by vibration simulation by the finite element method. The vibrator 60 has a displacement of 1.48 μm in the ± directions and 0.28 μm in the ± Z directions due to acceleration 1G. The operation of the acceleration sensor according to the first embodiment of the present invention will be described below with reference to these drawings.

The weight 61 and the beam 62 are formed on the silicon substrate 50.
And the acceleration of the silicon substrate 50 that is parallel to
It is displaced by the acceleration αZ perpendicular to. A change in resistance of the piezoresistors 64-1 and 64-2 at this time will be seen. Figure 6
FIG. 3 is a diagram showing displacement of a beam of the acceleration sensor of FIG. 1. As shown in FIG. 6, when only the acceleration αY moves, the inertia moment (-m · l · αY) of the weight 61 and the bending moment of the beam 62 are equal (ignoring the mass of the beam 62). The radius of curvature at P is R _XY = Ea ³ b / (mlαY × 12) (4). At this time, as shown in the figure,
The radii of curvature at the portions 1 and 64-2 are R _XY +
0.4a and R _XY -0.4a. Therefore, the piezoresistor 64-1 feels a tensile strain of e _Y1 = 0.4a / R _XY = 4.8 ml αY / (Ea ² b) (5), and the piezoresistor 64-2 has e _Y2 = -0.4a / R _XY = -4.8 ml αY / (Ea ² b) ··· Feel the compressive strain of (6).

Next, the acceleration α perpendicular to the silicon substrate 50
Consider when only Z worked. The radius of curvature at the neutral point in this case is R _ZX = Eab ³ / (mlαZ × 12) (7) The radius of curvature is R _ZX + for both piezoresistors 64-1 and 64-2.
Since it is 0.5b, the strains are both e _Z1 = e _Z2 = 0.5b / R _ZX = 6 ml αZ / (Eab ² ) (8). General acceleration vector (αZ,
αY, αZ), the strains felt by the piezoresistors 64-1 and 64-2 are e ₁ = e _Y1 + e _Z1 = 4.8 ml αY / (Ea ² b) +6 ml αZ / Eab ² ... ( 9) e ₂ = e _Y2 + e _Z2 = −4.8 ml αY / (Ea ² b) +6 ml αZ / Eab ² (10)

From these, e ₁ −e ₂ = 9.6 ml αY / (Ea ² b) (11) e ₁ + e ₂ = 12 ml αZ / (Eab ² ) (12) When strain is small, strain Is piezoresistors 64-1 and 6
It is proportional to the rate of change of the resistance of 4-2. That is, by measuring the difference in strain at the positions of the piezoresistors 64-1 and 64-2 through changes in the resistance of the piezoresistors 64-1 and 64-2, the αY component of acceleration is The αZ component of the acceleration can be detected by the equation (12) by measuring the sum of The measurement is performed by forming a Hoystone bridge as shown in FIG. When the piezoresistor 64-1 is not distorted, the four piezoresistors 64-
Since 1 and 71-1 to 71-3 have the same resistance, the output from the detector is 0 even when an input voltage is applied to the bridge. When strain is applied to the piezoresistor 64-1,
The resistance changes in proportion to the amount of displacement of the strain, and the amount of change is measured as an output voltage from the detector. Similarly,
The resistance changes in proportion to the magnitude of the strain of the piezoresistor 64-2, and the detector measures the amount of change as an output voltage. An arithmetic unit calculates the acceleration αY by multiplying the difference between the outputs of the detectors and the difference result by a constant. Further, the output of the detector is added and the addition result is multiplied by a constant to calculate the acceleration αZ.

As described above, the first embodiment has the following advantages. (A) A position symmetrical to a straight line bisecting a cantilever beam vibrating in both the Z direction (direction perpendicular to the substrate) and the Y direction (direction perpendicular to the substrate and perpendicular to the beam) in the Y direction. Since the piezoresistors 64-1 and 64-2 are formed on the
The difference in strain between the resistance positions of 1 and 64-2 is measured through the resistance and further calculated to separate the acceleration component parallel to the substrate and perpendicular to the beam from the acceleration component perpendicular to the substrate. Can be detected. (B) By measuring the sum of strains, it is possible to detect an acceleration component perpendicular to the substrate without mixing the accelerations of other axes. Further, since the detection is based on piezo resistance, the linearity is high, so that the acceleration can be accurately measured. (C) Since it is not necessary to create a structure with an extremely high aspect ratio, there is no need to use the LIGA process, and a simple structure can be created using a normal semiconductor process, which is inexpensive and mass-producible. Are better.

Method of Manufacturing Acceleration Sensor of FIG . 1 FIG. 7 is a manufacturing process diagram showing a method of manufacturing the acceleration sensor of FIG. Hereinafter, a method for manufacturing the acceleration sensor of FIG. 1 will be described with reference to the drawings. (1) Step of FIG. 7A An n-type silicon substrate having a thickness of 50 μm is prepared. If the substrate is too thin to obtain sufficient strength, only the periphery of the vibrator is etched from the back side with a concentrated KOH aqueous solution to a thickness of 50 microns. (2) Step of FIG. 7B The oxide film of 0.5 micron is formed on the substrate in 1200 ° C. oxygen. (3) Step of FIG. 7C The piezoresistive portion is formed by etching the piezoresistive portion by photolithography and further by diffusing boron. (4) Step of FIG. 7D After vapor deposition of aluminum on the entire surface, patterning is performed to form wiring between piezoresistors and aluminum electrodes for input / output to form a Wheatstone bridge.

(5) Step of FIG. 7 (e) Silicon oxide film 5 μm as a mask by CVD,
Further, a tungsten silicon sand film of 0.5 micron is deposited. Using the tungsten silicide as a mask, the silicon oxide film is etched to form a mask for silicon wafer through etching in the next step. (6) Step of FIG. 7 (f) A mixed gas of SF ₃ and CCl ₂ F ₂ is used as a reaction gas,
The reactive ion etching vertically etches the silinco substrate. (7) Step of FIG. 7G The mask is removed, and the manufacturing of the vibrator shown in FIG. 1 is completed.
As described above, in the present embodiment, the acceleration sensor shown in FIG. 1 for measuring the acceleration in the direction parallel to the silicon substrate and perpendicular to the beam (Y direction) and the direction perpendicular to the silicon substrate (Z direction) is the LIGA. Since it is not necessary to use a process and can be formed by using an ordinary semiconductor process, it is inexpensive and excellent in mass productivity.

Second Embodiment FIGS. 8A and 8B are views showing an acceleration sensor according to a second embodiment of the present invention. FIG. 8A is a plan view and FIG. 8B is a view. Is a side view. The difference between the acceleration sensor of the second embodiment and the acceleration sensor of the first embodiment is that the vibrator 1
10 is composed of both-supported beams 112-1 and 112-2, and piezoresistors 114-1 and 114-2 are provided at positions symmetrical with respect to the center of gravity O of the weight 111. FIG.
As shown in (a), in this acceleration sensor, a vibrator 110 is arranged on a silicon substrate 100. Oscillator 11
0 is the weight 111 arranged in the center and this weight 1
Support beams 112-1 and 112- arranged on the left and right of 11
2 and. Weight 11 of oscillator 110
1 and the peripheries of the beams 112-1 and 112-2 are penetrating portions 1 formed by penetrating etching of the silicon substrate 100.
It is 13. Point-symmetric about the center of gravity O of the weight 111,
The concentration of impurities is 1 × at the roots of the beams 112-1 and 112-2.
Piezoresistors 114-1 and 114-2 formed by diffusion resistances of about 10 ^{18 to} 2 × 10 ²¹ cm ⁻³ are arranged.

FIG. 9 is an enlarged view of portion B in FIG. 8 (a). As shown in FIG. 9, the piezoresistor 114-2 is connected to the beam 1
At the base of 12-2, in the length direction of the beam 112-2, 4 μm from the symmetry axis in the Y direction (0.4a, a is the beam 112-1, 11
2-2 thickness). The piezoresistor 114-2 is another piezoresistor 122-1 formed by a diffusion resistance having the same concentration as that of the piezoresistor 114-2 on the fixed portion of the silicon substrate 100 by the aluminum wiring 115, as shown in FIG. 8A. To 122-3. FIG. 10 is a diagram showing the connection between the piezoresistors in FIG. As shown in FIG. 10A, the piezoresistor 11
4-1 and the piezoresistors 121-1 to 121-3 form a Wheatstone bridge. A constant power is supplied to the power branch of the Hoystone bridge, and a detector is connected to the detection branch. Then, the output side of the detector is connected to an arithmetic unit for obtaining the acceleration in the direction parallel to the silicon substrate and perpendicular to the beam 112-1.

Further, as shown in FIG. 10B, the piezoresistor 114-2 and the piezoresistors 122-1 to 122-3 form a Wheatstone bridge. A constant power is supplied to the power branch of the Hoystone bridge, and a detector is connected to the detection branch. Then, the arithmetic unit is connected to the output side of the detector. As shown in FIG. 8B, the left and right beams 112-1 and 112-2 have a width a.
= 10 μm, thickness b = 30 μm, length l = 500 μm
Thus, both ± Z directions (directions perpendicular to the substrate 100) and ± Y directions (directions perpendicular to the substrate 100 and perpendicular to the beams 112-1 and 112-2) are vibrated. Weight 111
Has a lower part made of silicon 111a and an upper part made of gold 111b, and the weight 111 as a whole weighs 2 mg. The upper gold 11 is the added weight. The center of gravity O of the entire weight 111 is designed to be on the extension of the beams 112-1 and 112-2.

The operation of the acceleration sensor shown in FIG. 8 will be described below. The weight 111 and the beams 112-1 and 112-2 are displaced by an acceleration αY parallel to the silicon substrate 100 and perpendicular to the beams 112-1 and 112-2 and an acceleration αZ perpendicular to the silicon substrate 100. When only acceleration αY works,
The curvature at the neutral point of the roots of the beams 112-1 and 112-2 is R _XY = Ea ³ b / (mlαY × 3) (13). Further, when only the acceleration αZ works, the beam 112
The curvature at the neutral point of the root of −1, 112-2 is R _YZ = Eab ² / (mlαZ × 3) (14). After that, considering the same as in the first embodiment, when the general acceleration vector (αX, αY, αZ) is given to the sensor, the strains felt by the piezoresistors 114-1 and 114-2 are e ₁ , respectively. When _{e 2, e 2 -e 1 =} 1.2mlαY / (Ea 2 b) ··· (15) e 1 + e 2 = 1.5mlαZ / (Eab 2) is related to (16), The accelerations αY and αZ can be detected.

The measurement is carried out by constructing a Hoystone bridge as shown in FIG. When the piezoresistor 114-1 is not distorted, the four piezoresistors 114-1, 121-1 to 121-3 forming the bridge have the same resistance, so that the output is 0 even if an input voltage is applied to the bridge. . On the other hand, when strain is applied to the piezoresistor 114-1,
The resistance of the piezoresistor 114-1 changes and an output voltage is obtained. Similarly, when strain is applied to the piezoresistor 114-2, the resistance of the piezoresistor 114-2 changes and an output voltage is obtained. So, by the arithmetic unit,
The difference between the output voltages of the bridge and the result of this difference are multiplied by a constant to obtain the acceleration αY. Further, the output voltage of the bridge is added and the result of this addition is multiplied by a constant to obtain the acceleration αZ. As explained above,
The second embodiment has the same advantages as the first embodiment.

Method of Manufacturing Acceleration Sensor of FIG . 8 Next, a method of manufacturing the acceleration sensor of FIG. 8 will be described. First, a silicon substrate having a thickness of 400 μm is used. After forming a piezoresistor having an impurity concentration of about 1 × 10 ¹⁸ to 2 × 10 ²¹ cm ⁻³ on the silicon substrate by a diffusion method, the periphery of the vibrator is left with a concentrated KOH solution while leaving the weight portion. Etch from the back. After that, by reactive ion etching, vertical etching is performed using a mixed gas of SF ₆ and CCl ₂ F ₂ until it penetrates around the beam and the weight. Then add additional weight.

Third Embodiment FIG. 11 is a diagram showing an acceleration sensor according to a third embodiment of the present invention. The acceleration sensor according to the third embodiment of the present invention is different from the conventional acceleration sensor in that it is a three-dimensional acceleration sensor that measures acceleration in three-dimensional directions by using two transducers that are orthogonal to each other. This acceleration sensor has two oscillators 250 and 270 which are orthogonal to each other and are obtained by etching the silicon substrate 200. Oscillator 250 and 2
Reference numeral 70 has exactly the same structure as the vibrator 60 of the acceleration sensor of the first embodiment except that the direction is different. 12
11A and 11B are diagrams showing the vibrator 250 in FIG. 11, FIG. 11A is a plan view, and FIG. 11B is a side view. As shown in FIG. 12A, the vibrator 250 is composed of a weight 251 and a beam 252. Weight 2
The periphery of 51 and the beam 252 is a through portion 253 formed by through etching of the silicon substrate 200. Piezoresistor 254 along the length of beam 252
-1 and 254-2 are arranged.

FIG. 13 is an enlarged view of portion C in FIG. 12 (a). As shown in FIG. 13, the piezoresistor 254-1 and the piezoresistor 254-2 are symmetrical with respect to a straight line that bisects the beam 252 in the Y direction at the root of the beam 252, and is 8 degrees from the center line.
It is located at the position of μm (0.4a). Piezo resistance 254-1
And one of the terminals 252-2 has an aluminum wiring 255
Connected by. As shown in FIG.
The fixed portion of the silicon substrate 200 has a piezoresistor 261-.
1-261-3 are arranged. FIG. 14 (a),
FIG. 12B is a diagram showing wiring between the piezoresistors in FIG. As shown in FIG. 14A, the piezoresistor 25
A Wheatstone bridge circuit is configured by 4-1 and the piezo resistors 261-1 to 261-3. A detector is arranged between the terminals of the short-circuited piezoresistors 254-1 and 261-3 and the terminals of the short-circuited piezoresistors 261-1 and 261-2. A calculator is not installed. Similarly, as shown in FIG.
Piezoresistor 254-2 and piezoresistors 262-1 to 262
-3 constitutes a Hoystone bridge circuit. A detector is arranged between the terminals of the short-circuited piezoresistors 254-2 and 262-3 and the terminals of the short-circuited piezoresistors 262-1 and 262-2, and the above calculation is performed on the output side of the detector. Are placed.

The beam 252 has a width a = 20 μm and a thickness b = 50.
μm, length l = 1000 μm, long and thin, ± Z direction, ± Y
It has a structure that can vibrate in two directions. As shown in FIG. 12B, the acceleration sensor is covered with glass covers 211 and 212 in which upper and lower peripheral portions 213 and 214 of the vibrator 250 are etched. Further, an n-type silicon substrate whose plane orientation of the silicon substrate 200 is (011) is used. The beam direction of the oscillator 250 is
It matches (-2 ^1/2 , 1, -1), and the oscillator 270
The direction of the beam of is in agreement with the (-2 ^1/2 , -1, 1) direction. Note that the directions (-2 ^1/2 , 1, -1) and (-
It can be seen that ^21/2 , -1, 1) are orthogonal by taking the inner product of the vectors. The direction of these beams is the silicon substrate 2
The orientation flat direction of 00 is used as a reference. Further, hereinafter, when it is stated that the direction of the beam coincides with (l, m, n), the beam is (l, m, n) and (-l,-).
It does not matter which of the m, -n) direction it is facing. That is, it does not matter which direction the weight is facing.

The operation of the acceleration sensor shown in FIG. 11 will be described below. First, the operation of the vibrator 250 will be described. First
In the same manner as in the above example, when only the acceleration αY parallel to the substrate 200 and perpendicular to the beam 252 moves, the radius of curvature at the neutral point of the fulcrum of the beam is R _XY = Ea ³ b / (mlαY × 12).・ ・ (17) At this time, the piezo resistors 254-1 and 254-2
The radii of curvature at the part of are R _XY + 0.4a, R _XY
It becomes −0.4a. Therefore, the piezoresistor 254-1 feels a tensile strain of e _Y1 = 0.4a / R _XY = 4.8 ml αY / (Ea ² b) (18), and the piezoresistor 254-2 evaluates e _Y2 = -0.4a / R _XY = -4.8 ml αY / (Ea ² b) ··· Feel a compressive strain of (19).

Next, consider a case where only the acceleration αZ perpendicular to the silicon substrate 200 is applied. The radius of curvature at the neutral point in this case is R _ZX = Eab ³ / (mlαZ × 12) (20) The radius of curvature is R for both piezoresistors 254-1 and 254-2.
_ZX + because it is 0.5b strain _{together, e Z1 = e Z2 = 0.5b} / R ZX = 6mlαZ / (Eab 2) a ... (21). A general acceleration vector (αX,
.alpha.Y, .alpha.Z) is given, the piezoresistor 254-1
And the strains felt by 254-2 are e ₁ = e _Y1 + e _Z1 = 4.8 ml αY / Ea ² b + 6 ml αZ / (Eab ² ) ... (22) e ₂ = e _Y2 + e _Z2 = −4.8 ml αY / Ea ² b + 6 ml αZ / (Eab ² ) ... (23) From these, e ₁ −e ₂ = 9.6 ml αY / (Ea ² b) ・ ・ ・ (24) e ₁ + e ₂ = 12 ml αZ / (Eab ² ) ・ ・ ・(25) When the strain is small, the strain is proportional to the rate of change of the resistance of the piezoresistors 254-1 and 254-2. Piezo resistance 25
Supposing that the outputs of the detector of the Hoystone bridge connected with 4-1 and 254-2 are V _o ¹ and V _o ² , V _o ¹ = πe ₁ V _i × E / 4 (26) V _o ² = πe ₂ V _i × E / 4 (27) From formulas (24), (25), (26) and (27), V _o ¹ -V _o ² = π 2.4 ml αYV _i / (a ² b) (28) V _o ¹ + V _o ² = −π3 ml αZV _i / (ab ² ) (29)

Here, π is the apparent piezoresistive coefficient in the (−2 ^1/2 , −1, 1) direction, and V _i is the input voltage to each bridge. As a result, αY and αZ are obtained. Therefore, the difference between the outputs of the detectors is calculated by the arithmetic unit according to the equation (28), and the difference result and the apparent piezo coefficient π
The acceleration αY is calculated by performing multiplication with a constant such as. In addition, the computing unit calculates the acceleration αZ according to the equation (29). Similarly, the oscillator 27
0, accelerations αX and αZ are obtained by a Hoiston bridge circuit including a piezoresistor arranged on the beam of the vibrator 270 and a calculator. The advantages of the third embodiment of the present invention will be described below. In the third embodiment, the substrate 200
Using an n-type silicon substrate with a plane orientation (011) as
The direction of the beam length of the oscillators 250 and 270 is the direction (-2
^1/2, 1, -1), (- consistent ^21/2, -1,1) direction. Generally, in the (l, m, n) direction (l ² + m ² +
The change in piezoresistance when the stress T is applied to (n ² = 1) is Δρ / ρ = {π ₁₁ +2 (π ₄₄ + π ₁₂ −π ₁₁ ) (l ² m ² + m ² n ² + n ² l ² )} T ... (30) The apparent piezoresistive coefficient is shown in parentheses.

FIG. 15 shows p calculated by the equation (30).
It is a figure which shows the apparent piezoresistive coefficient of the typical crystal plane of room-temperature silicon at room temperature, and the figure (a) is (001).
Plane, (b) in the figure, (011) plane, and (c) in the figure, (11)
1) The apparent piezoresistive coefficient in the plane. The length from the origin in the figure represents the magnitude of the piezoresistance coefficient, and the orientation from the origin represents the crystal orientation. FIG. 16 is a diagram showing the relationship between the gauge factor and the specific resistance of silicon.
From this figure, the relationship between the sensitivity due to the strain of the crystal plane in the p-type and the n-type and the piezoresistance can be understood. That is, the larger the absolute value of the gauge factor, the better the sensitivity when the piezoresistor having the gauge factor is used in the acceleration sensor. As shown in FIG. 15, the plane orientation of silicon (011)
In the case of, the maximum piezoresistance coefficient is (-
The direction of the beam is the (1,1, -1) direction and the (-1, -1,1) direction, and the length of the beam maximizes the sensitivity of the acceleration sensor having the vibrator in this direction. However, these directions are not orthogonal. In order to obtain uniform sensitivity from any direction of acceleration horizontal to the substrate, the sensitivities of two orthogonal sensors must be equal. In order to satisfy this condition and further maximize the piezoresistance coefficient, silicon having a plane orientation of (011) is used as the substrate, and the oscillators 250 and 270 are used.
As the direction of the length of each beam of (-2 ^1/2 , 1,-
1) and the (-2 ^1/2 , -1, 1) direction orthogonal thereto. This makes it possible to realize a sensor having high sensitivity in both the X and Y directions.

Fourth Embodiment This fourth embodiment differs from the third embodiment in that (001) -plane n-type silicon is used as a silicon substrate and two oscillators 250 and 270 which are orthogonal to each other are used. To (-1, 1,
0), (1, 1, 0) direction and piezoresistor p
That is the diffusion resistance of the mold. The acceleration sensor of the fourth embodiment operates similarly to the acceleration sensor of the third embodiment. The advantages of the fourth embodiment will be described below. FIG.
As shown in (1), in the p-type silicon having the (001) plane orientation, the piezoresistance coefficients are (-1, 1, 0) and (1,
It becomes maximum in the direction of (1, 0). Therefore, the n-type silicon substrate having the (001) plane orientation is used as the substrate, and the directions of the beam lengths of the two oscillators orthogonal to each other are (−1, 1,
0) and the (1, 1, 0) direction orthogonal thereto, it is possible to realize a sensor with high sensitivity in any of the X and Y directions.

Fifth Embodiment The fifth embodiment is different from the third embodiment in that an n-type silicon substrate having a (111) plane orientation is used as a silicon substrate and a diffusion method is applied to two oscillators orthogonal to each other. Is to form a p-type piezoresistor. The orientation in which the oscillator is formed does not matter. The acceleration sensor of the fifth embodiment operates similarly to the acceleration sensor of the third embodiment. The advantages of the fifth embodiment will be described below. As shown in FIG.
1) In plane-oriented p-type silicon, the piezoresistance coefficient is the same in all orientations. Therefore, if a (111) plane orientation n-type silicon substrate is used as a substrate and p-type piezoresistors are formed on two orthogonal oscillators, an acceleration sensor having the same sensitivity in the horizontal direction can be obtained. To be Therefore, since it is not necessary to accurately align the orientation of the vibrator, there is an advantage that the orientation does not need to be taken into consideration when aligning the mask for forming the piezoresistor, the beam, and the like with the silicon substrate.

The present invention is not limited to the above embodiment, and various modifications can be made. The following are examples of such modifications. (1) In this embodiment, the single crystal silicon substrate is used, but polycrystalline silicon, another semiconductor (p-type Ge, n-type Ge, p-type InSb, n-type InSb, etc.), metal, or the like. The material of the vibrator of does not matter. (2) In this embodiment, the piezoresistance of silicon formed by the diffusion method is used, but a thin film type may be used. (3) In this embodiment, the resistance change of the piezoresistor is measured by the bridge circuit, but it may be measured by a circuit other than the bridge circuit. (4) As the silicon substrate 50 in FIG. 1, n-type silicon having the (011) plane orientation is used, and the direction of the beam 62 of the vibrator 60 is (1, -1,1) or (1,1, -1). Alternatively, p-type diffusion resistors may be used as the piezoresistors 64-1 and 64-2. (5) n-type silicon having a (011) plane orientation is used as the silicon substrate 50 in FIG. 1, and the direction of the beam 62 of the vibrator 60 is (2, -1,1) or (2,1, -1). Alternatively, p-type diffusion resistors may be used as the piezoresistors 64-1 and 64-2. At this time, there is a point that the beam 62 can be manufactured by wet etching using a KOH solution or the like instead of the reactive ion etching. That is, when the beam 62 is taken in this direction, the side surface of the beam 62 is in the same direction as the (111) plane. Since the (111) plane has a property of being less likely to be etched than other planes, the portion of the beam 62 is made of SiO 2.
_A vertical beam 62 can be manufactured by masking with ₂ etc. and etching with KOH. This method is simpler than reactive ion etching. Further, there is no need to use CFC gas that destroys the ozone layer.

(6) A p-type silicon substrate having a (001) plane orientation is used as the silicon substrate 200 in FIG.
Arranged in the (1,0,0) and (0,1,0) directions as the direction of the length of each beam of the two orthogonal oscillators,
You may form an n-type piezoresistor by the diffusion method. FIG.
FIG. 7 is a diagram showing an apparent piezoresistive coefficient of a typical crystal plane of n-type silicon at room temperature calculated by the equation (30). As shown in FIG. 16, in the n-type silicon, when the plane orientation of silicon is (001) and its orientation is the same, the gauge factor becomes maximum and the sensitivity becomes highest. Is. Therefore, as a silicon substrate, (100)
A plane-oriented n-type silicon substrate is used. Further, as shown in FIG. 17, in the case of the plane orientation of silicon (001), the maximum piezoresistance coefficient is in the (1,0,0) and (0,1,0) directions, and The length of is the maximum sensitivity of the acceleration sensor having the vibrator in this direction. Therefore, it is possible to obtain an acceleration sensor which is uniformly sensitive to any direction of acceleration horizontal to the substrate. (7) As the silicon substrate 200 in FIG.
Using the p-type silicon of the (11) plane, two orthogonal oscillators 250 and 270 are (0, 1, -1), (1, 0,
The piezoresistors may be n-type diffused resistors by arranging in the 0) direction. (8) As the silicon substrate 200 in FIG.
The piezoresistor may be an n-type diffused resistor by using p-type silicon of the 11) plane.

[0035]

As described above in detail, the first to the first
According to the invention of claim 6, since a plurality of piezoresistors are arranged at different positions in the width direction of the beam of the vibrator, a change in resistance due to the displacement of the piezoresistive beam is detected, and the piezoresistance is parallel to the substrate and perpendicular to the beam. Acceleration in various directions can be measured.

[Brief description of drawings]

FIG. 1 is a diagram of an acceleration sensor showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a conventional acceleration sensor.

FIG. 3 is a diagram showing a problem of a conventional acceleration sensor.

FIG. 4 is an enlarged view of part A in FIG.

5 is a diagram showing a connection between piezoresistors in FIG.

FIG. 6 is a diagram showing bending of a beam of the acceleration sensor of FIG.

7A to 7C are manufacturing process diagrams showing a method of manufacturing the acceleration sensor of FIG.

FIG. 8 is a diagram showing an acceleration sensor according to a second embodiment of the present invention.

9 is an enlarged view of part B in FIG.

10 is a diagram showing a connection between piezoresistors in FIG.

FIG. 11 is a diagram showing an acceleration sensor according to a third embodiment of the present invention.

12 is a diagram showing a vibrator 250 in FIG.

13 is an enlarged view of part C in FIG.

14 is a diagram showing a connection between piezoresistors in FIG.

FIG. 15 is a diagram showing a piezoresistance coefficient of p-type silicon at room temperature.

FIG. 16 is a diagram showing a relationship between a gauge factor and a specific resistance in silicon.

FIG. 17 is a diagram showing a piezoresistance coefficient of n-type silicon at room temperature.

[Explanation of symbols]

50, 100, 200
Silicon substrate 60, 110, 250, 270
Transducer 61,111,251
Weight 62,112-1,112-2,252
Beam 63,113,253
Penetration part 64-1, 64-2, 114-1
Piezoresistor 114-2, 254-1, 254-2
Piezoresistors 71-1 to 71-3, 72-1 to 72-3
Piezoresistors 121-1 to 121-3, 122-1 to 122-3
Piezoresistors 261-1 to 261-3, 262-1 to 262-3
Piezo resistance

Claims (16)

[Claims] 1. A weight and a beam for supporting the weight,
A vibrator having a substrate in a peripheral portion of the weight and the beam as a penetrating portion; a plurality of piezoresistors arranged on the beam, the resistance of which changes according to the magnitude of strain of the beam due to acceleration; A piezoresistance measuring circuit for measuring a change in resistance of the, and a calculation for calculating an acceleration in a direction parallel to the substrate and perpendicular to the beam direction, based on the change in resistance measured by the resistance measuring circuit. An acceleration sensor characterized by comprising: 2. Two vibrators each having a weight and a beam supporting the weight, a substrate in a peripheral portion of the weight and the beam being a penetrating portion, and length directions of the beams being orthogonal to each other. And a plurality of piezoresistors arranged on the beams of each of the two vibrators, the resistance of which changes according to the magnitude of strain of the beams due to acceleration, and a piezoresistance measuring circuit for measuring the change of resistance of the piezoresistors. And an arithmetic unit that calculates acceleration in two directions parallel to the substrate and perpendicular to the beam direction based on a change in resistance measured by the resistance measurement circuit. And an acceleration sensor. 3. The piezoresistance measuring circuit constitutes a bridge circuit with each of the piezoresistances, supplies power to a power supply branch of the bridge, and detects a change in resistance of the piezoresistance by a detector of a detection branch. The acceleration sensor according to claim 1, wherein the acceleration sensor is configured to measure. 4. The beam is a cantilever beam, and the piezoresistor is arranged at a position symmetrical with respect to a center line in the length direction of the beam. Acceleration sensor. 5. The vibrator has a weight in the center and a doubly supported beam symmetrically arranged with respect to the weight, and the piezoresistor is arranged point-symmetrically with respect to the center of gravity of the vibrator. The acceleration sensor according to claim 1, wherein 6. The acceleration according to claim 1, wherein the directions of the substrate and the beam are selected so that the rate of change of the resistance of the piezoresistor with respect to the strain due to the acceleration of the beam is large. Sensor. 7. The direction of each beam of the substrate and the two vibrators is such that a rate of change of resistance of the piezoresistor arranged on the beam of each vibrator is relative to strain due to acceleration of each beam. The acceleration sensor according to claim 2, wherein both are selected to be large. 8. The acceleration sensor according to claim 1, wherein the substrate is made of silicon crystal, and the piezoresistance is an n-type or p-type impurity diffusion resistance. 9. The substrate is an n-type silicon substrate having a (011) plane orientation, and the beam length directions of the vibrator are (1, -1,1) direction, (-1,1,1,) -1) direction,
The (1, 1, -1) direction or the (-1, -1, 1) direction is made to match, and the piezoresistance is a p-type impurity diffusion resistance. Acceleration sensor. 10. The substrate is an n-type silicon substrate having a (011) plane orientation, and the length direction of the beam of the oscillator is (2, -1,1) direction, (-2,1,) -1) direction, (-
The (2, -1,1) direction or the (2,1, -1) direction is matched, and the piezoresistance is a p-type impurity diffusion resistance, The acceleration according to claim 1, wherein Sensor. 11. The substrate is an n-type silicon substrate having a (011) plane orientation, and the beam length directions of the two oscillators are (−2 ^1/2 , 1, −1). Direction or (2 ^1/2 , -1, 1)
Direction and the (-2 ^1/2 , -1, 1) direction or (2 ^1/2 ,
The acceleration sensor according to claim 2, wherein the piezoresistor is a p-type impurity diffused resistor so that the piezoresistor is aligned with the (1, -1) direction. 12. The substrate is an n-type silicon substrate having a (001) plane orientation, and a length direction of each beam of the two vibrators is a (−1,1,0) direction or a (1 , -1, 0) direction,
The (1,1,0) direction or the (-1, -1,0) direction is made to coincide with each other, and the piezoresistance is a p-type impurity diffusion resistance. Acceleration sensor. 13. The substrate is a p-type silicon substrate having a (011) plane orientation, and a length direction of each beam of the two vibrators is a (0,1, −1) direction or a (0,1) direction. , -1, 1) direction,
The (1, 0, 0) direction or the (-1, 0, 0) direction is made to coincide with each other, and the piezo resistance is an n-type impurity diffusion resistance. Sensor. 14. The substrate is a p-type silicon substrate having a (001) plane orientation, and a length direction of each beam of the two vibrators is a (0,1,0) direction or a (0,1,0) direction. -1,0) direction and (1,0,0) direction or (-1,0,0) direction, and the piezoresistance is an n-type impurity diffusion resistance. The acceleration sensor according to claim 2. 15. The substrate is an n-type silicon substrate having a (111) plane orientation, and the piezoresistor is a p-type impurity diffusion resistor.
The acceleration sensor described. 16. The substrate is a p-type silicon substrate having a (111) plane orientation, and the piezoresistor is an n-type impurity diffusion resistor.
The acceleration sensor described.