JPH1172506A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the adjustment of the sensitivity while minimizing the bent by the weight of a weight movable electrode. SOLUTION: This acceleration sensor 100 is constituted of an anchor part 11, a weight movable electrode 12, beam parts 14-17, fixed electrodes 135-138 for detection and fixed electrodes 131-134 for adjusting sensitivity. In this acceleration sensor 100, when the weight movable electrode 12 is displaced by acceleration and comes into contact with any of the fixed electrodes 131-134 for sensing, energization is made between the movable electrode 12 and the fixed electrodes 131-134 and hence, the generation of the acceleration exceeding a fixed value is measured. A specified potential difference is applied between the weight movable electrode 12 and the fixed electrodes 131-134 for adjusting the sensitivity to generate a static attraction between the both to facilitate the adjustment of the sensitivity while minimizing bend as caused by the weight of the weight movable electrode 12.

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 example, a sensor built in a flow meter for gas or the like to detect vibrations such as an earthquake and closing a valve of a gas pipe, and a sensor built in a stove or the like. It can be used as a sensor that detects a vibration such as the above and cuts off the flame, or an acceleration sensor that detects acceleration in multiple directions in a two-dimensional plane with almost the same sensitivity.

[0002]

2. Description of the Related Art Conventionally, a sensor of this type has been disclosed in
There is an acceleration sensor disclosed in JP-A-145740. The acceleration sensor includes an anchor portion fixed on a substrate, a weight movable electrode supported on the anchor portion via a spiral beam portion and having a circumferential side surface, and a predetermined distance from the circumferential side surface of the weight movable electrode. A fixed electrode having a circumferential side surface facing away from the fixed electrode, and detecting that the movable weight electrode and the fixed electrode come into contact with each other when the movable weight electrode is displaced in a direction parallel to the surface of the substrate due to acceleration, thereby detecting occurrence of acceleration. It is supposed to.

[0003]

In the above-described acceleration sensor, if the weight movable electrode supported by the beam hangs down due to its own weight, the overlap between the weight movable electrode and the fixed electrode becomes very small or disappears. May not hold. In this case, as shown in an embodiment to be described later, if a predetermined potential difference is applied between the weight movable electrode and the fixed electrode, an electrostatic attractive force is generated between the weight movable electrode and the fixed electrode, and the weight drop is reduced. can do.

However, simply generating an electrostatic attraction between the weight movable electrode and the fixed electrode has a problem that it is difficult to adjust the detection sensitivity depending on the magnitude of the electrostatic attraction. For example, it is necessary to generate a certain amount of electrostatic attraction in order to reduce the above-mentioned sagging, but if the electrostatic attraction is too large, acceleration causes the weight to cause contact between the movable electrode and the fixed electrode. After that, there occurs a problem that the weight movable electrode remains in contact with the fixed electrode even if the acceleration is lost. That is, if the electrostatic attraction when the movable weight electrode and the fixed electrode come into contact with each other is larger than the spring force of the beam portion, the weight movable electrode is maintained in contact with the fixed electrode even when the acceleration is lost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to reduce the weight of a movable weight electrode and to easily adjust the detection sensitivity.

[0006]

In order to achieve the above object, the present invention employs specific means described in each claim. That is, in the first and second aspects of the invention,
It is characterized in that a sensitivity adjustment fixed electrode used for adjusting detection sensitivity by electrostatic attraction between the movable electrode and the weight is provided.

Accordingly, the weight of the movable weight electrode can be reduced by its own weight by the electrostatic attraction generated between the movable weight electrode and the fixed electrode for sensitivity adjustment, and the electrostatic attractive force can be adjusted by the fixed electrode for sensitivity adjustment. Thereby, the detection sensitivity can be easily adjusted. In this case, an independently adjustable potential difference is applied between the detection fixed electrode and the weight movable electrode and between the sensitivity adjustment fixed electrode and the weight movable electrode. By doing so, the above-described sensitivity adjustment can be easily performed.

According to the fourth aspect of the present invention, the potential difference between the fixed electrode for sensitivity adjustment and the weight moving electrode is determined by the above-mentioned electrostatic attraction when the weight movable electrode comes into contact with the detection fixed electrode. If it is set to be smaller than the spring force of the portion, the weight movable electrode can be returned to the original state after the application of the acceleration to the weight movable electrode is stopped.

Further, if the detection fixed electrode is provided with a protrusion which comes into contact with the weight movable electrode, the movable range of the weight movable electrode can be set. Thus, the detection sensitivity can be adjusted. In this case, as in the invention according to claim 6, when the weight movable electrode comes into contact with the projection of the detection fixed electrode,
If the weight movable electrode and the fixed sensitivity electrode are prevented from contacting by the projection, when the weight movable electrode comes into contact with the detection fixed electrode, the above-mentioned electrostatic attraction between the sensitivity adjustment fixed electrode and the weight movable electrode is reduced. Can be generated.

The length of the projection of the fixed electrode for detection is a value obtained by subtracting the above-mentioned electrostatic attraction from the spring force of the spring portion in the movable range of the weight movable electrode as in the invention according to claim 7. Can be defined as a region in which the weight increases simply, and as in the invention according to claim 8, a value obtained by subtracting the electrostatic attraction from the spring force of the spring portion in the movable range of the weight movable electrode. Can be defined so as to exceed the peak value and reach 0.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a plan view of an acceleration sensor 100 according to a first embodiment of the present invention, and FIG.
FIG. The acceleration sensor 100 shown in FIG. 1 configures a switch-type acceleration sensor including a substrate 30, an anchor portion 11, a movable weight electrode 12, four beams 14 to 17, and a fixed electrode 13.

The substrate 30 is a P-type silicon substrate. The anchor part 11 is formed on the substrate 30 in a cylindrical shape,
The weight movable electrode 12 is located at substantially the center of the substrate 30 and the four beams 1 capable of elastically deforming the weight movable electrode 12 substantially in parallel with the surface of the substrate 30.
4 to 17 are supported. The weight movable electrode 12 has a cylindrical shape, is provided in parallel with the substrate 30 at a predetermined interval, and is elastically deformable on the anchor portion 11.
It is supported by 4 to 17 and is displaced by the applied acceleration. Further, the weight movable electrode 12 has a substantially cylindrical side surface (circumferential side surface) perpendicular to the substrate 30, that is, a cylindrical outer peripheral surface serving as a conductive detection surface 18.

The beam portions 14 to 17 constitute a spring portion, and four beams are installed on the anchor portion 11 to move the weight movable electrode 1.
2 is formed in an elastically deformable shape that supports the support 2. In the present embodiment, the ratio of the vertical length to the horizontal length is increased so that the beam portions 14 to 17 can be elastically deformed in a substantially parallel direction with respect to the surface of the substrate 30. The shape is such that it becomes a part of an arc.

The fixed electrode 13 has a shape in which a column is hollowed out on the inside, and is formed on the substrate 30 at a predetermined interval outside the movable weight electrode 12. The cylindrical inner peripheral surface (circumferential side surface) facing the detection surface 18 of the weight movable electrode 12 is a conductive detection surface 19. As shown in FIG. 2, oxide films 21 and 22 are provided below the central anchor portion 11 and the fixed electrode 13, respectively, and are formed on the substrate 30.

Although not shown in FIG. 1, it is detected that the weight movable electrode 12 is displaced by the acceleration and the detection surface 18 of the weight movable electrode 12 and the detection surface 19 of the fixed electrode 13 are in contact with each other. There is a detection circuit that performs The detection circuit includes a detection surface 18 of the weight movable electrode 12, a fixed electrode 13
The conduction between the detection surface 19 and the detection circuit is established by wire bonding or the like. In the present embodiment, since the weight movable electrode 12, the beams 14 to 17, and the anchor 11 are all electrically connected, wire bonding may be performed from the anchor 11 to the detection circuit.

The term "substantially cylindrical side face" as used in the present invention means not only a side surface having a substantially cylindrical shape as shown in the detection surface 18 of FIG. Such an inner peripheral portion has a substantially cylindrical shape. Then, the weight movable electrode 12 and the fixed electrode 13
Are predetermined in each direction (i = 1 to
The relationship between the elastic modulus ki obtained by combining the beam portions along n) and the distance Di between the weight movable electrode 12 and the fixed electrode 13 is arranged as shown in Expression 1.

[0017]

D1 × k1 = D2 × k2 =... = Di × ki
=... = Dn × kn By arranging in this way, the acceleration isotropic even if the acceleration is generated in any direction (i = 1 to n) within a plane parallel to the substrate 30. Can be detected. For example, FIG.
In the description, the predetermined intervals are D1 (X direction in the drawing), D2 (Y direction in the drawing), and D3 (45 ° diagonal direction in the drawing), and the respective intervals obtained by integrating the four beam portions 14 to 17 are shown. Assuming that the elastic coefficients in the directions are k1, k2, and k3, in order to detect the acceleration F isotropically on a plane parallel to the substrate 30, the distances D1, D2, and D3 are equal to D1.
= F / k1, D2 = F / k2, D3 = F / k3.

When D1, D2, and D3 are set so as to satisfy Equation 1, k1 = k2 = k3. In the present embodiment, the weight movable electrode 12 is designed so as to satisfy Formula 1, and the weight movable electrode 12 has a cylindrical shape, and the fixed electrode 13 has a hollow cylindrical shape. And the acceleration sensor 1
00 is a vertically and horizontally symmetrical shape. Although not shown here, impurities are implanted into the surfaces of the anchor portion 11, the four beam portions 14 to 17, the weight movable electrode 12, and the fixed electrode 13 by a method such as ion implantation or phosphorus deposition. The resistivity of the surface of the structure may be reduced by introducing or depositing or plating a conductive material.

Next, a manufacturing process of the acceleration sensor 100 will be described with reference to FIGS. First, as shown in FIG.
An oxide film 20 is formed on a substrate 30, and a silicon film 1 is formed thereon.
0 is formed by film formation. The substrate 30 is made of SOI
(Silicon Insulator) substrate may be used. Next, as shown in FIG. 4, the silicon film 10 is etched, and the anchor portion 11, the beam portions 14 to 17 (the beam portions 14 and 16 are shown in FIG. 4), the weight movable electrode 1
2. The fixed electrode 13 is formed in a predetermined shape.

Thereafter, the weight movable electrode 12 and the beam portions 14 to
The movable portion is made movable by etching with a hydrogen fluoride-based liquid using the oxide film 20 immediately below 17 as a sacrificial layer, and the acceleration sensor 100 shown in FIGS. 1 and 2 is obtained. Next, the operation of the switch type acceleration sensor 100 will be described with reference to FIGS. In FIG. 5, beams 14 to 17 connecting the anchor portion 11 and the weight movable electrode 12 are omitted.

When no acceleration is applied to the acceleration sensor 100, the weight movable electrode 12 is stationary at a predetermined distance from the fixed electrode 13. The detection circuit (FIG. 6)
Are connected to the anchor portion 11 and the fixed electrode 13 at the center by wire bonding, respectively. As shown in FIG. 6, a potential difference V ₀ is applied between the terminal 1 and the terminal 2 via the detection circuit 20.

In FIG. 5, when acceleration is applied to the acceleration sensor 100 and the weight movable electrode 12 is displaced in the X-axis direction, the interval between the weight movable electrode 12 and the fixed electrode 13 becomes small, and if the acceleration exceeds a certain acceleration. The detection surface 18 of the weight movable electrode 12 and the detection surface 19 of the fixed electrode 11 are X
Contact on axis. At this time, as shown in FIG. 6, since the potential difference V ₀ is set between the weight movable electrode 12 and the fixed electrode 13, a current flows and the detection circuit 20 can detect the contact.

The acceleration sensor 100 operates only when a certain acceleration or more is applied.
Electric current is applied between the fixed electrodes 13 to operate as a sensor. That is, the interval between the movable weight electrode 12 and the fixed electrode 13 is set to be in contact when a certain constant in-plane acceleration is applied. Therefore, the shape of the detection surface 18 of the weight movable electrode 12 and the shape of the detection surface 19 of the fixed electrode 13 are cylindrical, and the spring formed by the beams 14 to 17 is isotropic with respect to the in-plane direction. Since it has a proper spring constant, acceleration can be detected uniformly in a plane parallel to the surface of the substrate 30. In this case, if one detection circuit 20 that detects that the detection surface 18 of the weight movable electrode 12 and the detection surface 19 of the fixed electrode 13 are in contact is used, the detection acceleration can be detected.

In addition, since the weight movable electrode 12 is formed of an annular member, the annular inner side and the annular outer side can be used effectively. In addition, since the anchor section 11 is arranged inside the annular section, the anchor section 11 is arranged. Therefore, it is not necessary to prepare a special area, and the area of the acceleration sensor can be reduced. Further, since the anchor portion 11, the beam portions 14 to 17, the weight movable electrode 12 and the fixed electrode 13 are integrally formed of the same semiconductor material, they can be formed in the same process in a semiconductor process. Since it is not necessary to assemble it, it can be manufactured at low cost.

Further, when no acceleration is applied,
Since the distance between the detection surface 18 and the detection surface 19 is kept substantially uniform, even if the acceleration is applied in any direction substantially parallel to the surface of the substrate 30, the magnitude of the acceleration is The distance between the detection surface 18 and the detection surface 19 can be reduced by almost the same amount. Thereby, the acceleration can be detected isotropically.

When the acceleration sensor 100 described above detects vibration such as an earthquake, the magnitude of the earthquake that must be activated is about 0.2 G when converted to acceleration, and the spring constant of the beam with respect to the mass part is very small. Become smaller.
When such an acceleration sensor is manufactured, as shown in FIG. 7, droop occurs considerably due to the weight of the sensor element, and the overlap between the mass portion (weight movable electrode) 12 and the fixed electrode 13 is very small or eliminated. There is a possibility that the sensor will not be established. Further, when such a sensor is formed, there is a possibility that the sensitivity is largely changed due to processing variations.

Therefore, in this embodiment, a potential difference V ₀ is set between the movable weight electrode 12 and the fixed electrode 13, and an electrostatic attraction is generated between the movable weight electrode 12 and the fixed electrode 13.
We try to reduce the weight drop. Hereinafter, this point will be described. The capacitance C between the weight movable electrode 12 and the fixed electrode 13 is expressed by Expression 2.

[0028]

[Number 2] ^{_{C = 2πε 0 h / cosh -1}} ((r 1 2 + r 2
^2- d ² ) / 2r ₁ r ₂ ) where r ₁ and r ₂ are the fixed electrode 13 and the weight movable electrode 1
A radius of 2; d is an amount of displacement of a center point of the weight movable electrode 12;
h indicates the thickness of the weight movable electrode 12 (r ₁ , r ₂ , d
See FIG. 5). In this case, for example, r ₁ = 20
Assuming that 0 μm, r ₂ = 220 μm, and h = 10 μm, the capacitance C is different from the displacement d of the weight movable electrode 12 in FIG.
And when d = 0 μm, C = 0.006 pF
Becomes From FIG. 8, it can be seen that the capacitance increases as the weight movable electrode 12 approaches the fixed electrode 13.

Here, the weight movable electrode 12 and the fixed electrode 1
3, a potential difference V ₀ is applied between the weight movable electrode 12 and the fixed electrode 13.
The electrostatic force Fe 2 is represented by Expression 3.

[0030]

[Equation 3] Fe = ∂ / ∂d (１ ／ CV ₀ ² ) Here, assuming that the potential difference V ₀ is 5 V, the electrostatic attractive force Fe is
It changes as shown in FIG. 9 with respect to the displacement d of the weight movable electrode 12. FIG. 10 is an enlarged view of a region where the displacement d is small. 9 and 10 that when the displacement d is 0, the electrostatic attractive force Fe does not act on the movable portion.

This will be described with reference to a model shown in FIG. Spring with spring constant k at fixed end (beams 14-17)
Is supported, and the other end has a weight movable electrode 1 having a mass m.
2 are connected. The fixed electrode 13 is formed at a certain distance from the weight movable electrode 12. Further, a potential difference V ₀ is externally applied between the fixed electrode 13 and the spring.

In this system, when acceleration (absolute value) a is applied to the weight movable electrode 12, the force F applied to the weight movable electrode 12 is determined by the balance between Fk due to the restoring force of the spring and force Fe due to the electrostatic force. . Assuming that the electrostatic force Fe is proportional to the displacement d when the displacement d is small, a relationship of ma = Fk-Fe = kd-bd = (kb) d holds. Here, k is a spring constant of the spring, and b is a proportional constant. Therefore, when the weight movable electrode 12 is eccentric due to the acceleration, an electrostatic attraction as shown in the figure acts, and the spring constant apparently decreases by b.

By utilizing this effect, a large spring constant is set to reduce the self-weight and the spring constant in the horizontal direction is apparently reduced by applying the voltage V ₀ .
Great sensitivity can be obtained. Note that, in the above-described embodiment, the manufacturing method using the steps shown in FIGS. 3 and 4 is described. However, the acceleration sensor 100 may be manufactured using an SOI substrate having a low-resistance bonding layer. it can. The manufacturing process in this case is shown in FIGS.
Shown in

First, as shown in FIG. 12, a single crystal silicon substrate as the first semiconductor substrate 40 is prepared. Then, an alignment groove 40a is formed in the silicon substrate 40 by trench etching. Thereafter, a silicon oxide film 41 as a thin film for a sacrificial layer is formed on the silicon substrate 40 including the groove 40a by a CVD method or the like. further,
The silicon oxide film 41 is partially etched through photolithography to form a concave portion 41a. This is formed in order to prevent the beam structure from being adhered to the substrate due to surface tension or the like after the beam structure is released in a sacrificial layer etching step described later, and to form a projection that reduces the adhered area.

Next, as shown in FIG. 13, a silicon nitride film 42 serving as an etching stopper at the time of etching the sacrificial layer is formed.
Is formed. Then, an opening is formed in the anchor portion forming region of the stacked body of the silicon nitride film 42 and the silicon oxide film 41 by dry etching or the like through photolithography. This opening is made up of the beam structure and the substrate (lower electrode).
And fixed electrode (and electrode extraction part)
And a wiring pattern. Subsequently, a polysilicon thin film 43 is formed on the silicon nitride film including the opening. Since this polysilicon thin film 43 also serves as an anchor (fixing portion) and wiring, impurities are introduced during or after film formation. Further, a wiring pattern, a lower electrode, and an anchor portion are formed through photolithography. Thus, an impurity-doped polysilicon thin film 43 as a conductive thin film is formed in a predetermined region on the silicon nitride film 42 including the opening. The thickness of the polysilicon thin film 43 is 0.5
About 2 μm.

Next, as shown in FIG. 14, a silicon nitride film 44 is formed on the polysilicon thin film 43, and a silicon oxide film 45 is formed on the silicon nitride film 44.
Thereafter, as shown in FIG. 15, a polysilicon thin film 46 as a bonding thin film is formed on the silicon oxide film 45,
For bonding, the surface of the polysilicon thin film 46 is planarized by mechanical polishing or the like.

Next, as shown in FIG. 16, a single-crystal silicon substrate (supporting substrate) 47 different from the silicon substrate 40 is prepared, and the surface of the polysilicon thin film 46 and the silicon substrate 47 as a second semiconductor substrate are prepared. And stick them together. After this,
The silicon substrates 40 and 47 are turned upside down, and the silicon substrate 40 side is thinned by mechanical polishing or the like. That is, the silicon substrate 40 is polished to a desired thickness. At this time, FIG.
As shown in FIG. 2, when polishing is performed to the depth of the groove 40a formed by trench etching, a layer of the silicon oxide film 41 appears, so that the hardness in polishing changes, and the end point of polishing can be easily detected. .

Thereafter, as shown in FIG. 17, aluminum electrodes 48a and 48b are formed and patterned. Then, as shown in FIG. 18, the structure (anchor portion 11,
Weight movable electrode 12, fixed electrode 13, beams 14 to 17)
The structure is formed through photolithography of the above pattern. The structure may be etched using a soft mask such as a photoresist or a hard mask such as an oxide film.

Finally, as shown in FIG. 19, the silicon oxide film 41 is removed by etching with an HF-based etchant, and the beam structure having the weight movable electrode 12 is made movable. That is, the silicon oxide film 41 in a predetermined region is removed by sacrifice layer etching using an etchant, so that the silicon substrate 40 has a movable structure. At this time, in order to prevent the movable portion from sticking to the substrate during the drying process after the etching,
A sublimation agent such as valadichlorobenzene is used.

In the etching of the sacrificial layer, since the polysilicon thin film 43 is used in the anchor portion 11, the etching is stopped in the anchor portion 11 and there is no variation. That is, since the silicon oxide film 41 is used as the thin film for the sacrificial layer and the polysilicon thin film 43 is used for the anchor portion 11, when the HF-based etchant is used, the silicon oxide film 41 is dissolved in Since the silicon thin film 43 does not melt, it is not necessary to accurately control the concentration and temperature of the HF-based etchant or to perform the end of the etching with precise time management, thereby facilitating manufacture.

Since the anchor portion 11 can be formed in this manner, it is not necessary to control the end point by time control in the sacrifice layer etching step when releasing the beam structure, thereby facilitating the control of the spring constant and the like. It becomes possible.
In the acceleration sensor 100 manufactured by the steps shown in FIGS. 12 to 19, the lower electrode 49 is formed by the polysilicon thin film 43 connected to the anchor 11 below the weight movable electrode 12 and the beams 14 to 17. For example, by setting the weight movable electrode 12, the beams 14 to 17, and the lower electrode 49 to, for example, the same potential, the weight movable electrode 12 and the substrate 30 can be placed between the weight movable electrode 12 and the substrate 30 by electrostatic force. Can be avoided.

In a sensor element having a cross-sectional structure as shown in FIG. 1, when the potential of the weight movable electrode 12 is taken, it must be taken out to the center, that is, the anchor portion 11, by wire bonding or the like.
By forming the lower electrode 49, it is possible to bring the element from the center to the edge of the element through the lower electrode 49 and take it out to the element surface. Normally, when wire bonding is performed, it is necessary to have a diameter of about 200 μm.
Since it can be reduced from m to several tens μm, the sensor element can be reduced in size.

In the above embodiment, the structure in which the structure is formed on the semiconductor substrate has been described. However, the structure may be formed on the glass substrate to manufacture the acceleration sensor 100. The manufacturing process in this case is shown in FIGS.
3 is shown. First, as shown in FIG. 20, a Pyrex glass substrate 230 (Pyrex is a trade name) and a low-resistance silicon substrate 210 are bonded by anodic bonding. At this time, if necessary, the surface of the silicon substrate 210 may be thinned by polishing or etching.

Next, as shown in FIG.
10 by etching, anchor portion 211, beam portion 21
4, 216, the weight movable electrode 212, and the fixed electrode 213 are formed in a predetermined shape. Finally, as shown in FIG. 22, the Pyrex glass substrate 230 immediately below the weight movable electrode 212 and the beam portions 214 and 216 is etched with a hydrogen fluoride-based liquid to make the movable portion movable. Although a Pyrex glass substrate has been described here, the present invention is not limited to Pyrex, and any glass can be used as long as it can be anodically bonded to silicon and can be etched with a hydrogen fluoride-based liquid. (Second Embodiment) According to the first embodiment described above, FIG.
As shown in (2), contact between the weight movable electrode 12 and the fixed electrode 13 can be detected even if the weight movable electrode 12 is displaced in any direction within a plane parallel to the surface of the substrate 30.

Here, the weight movable electrode 12 and the fixed electrode 1
In order to make the contact with No. 3 preferably, the following configuration is preferably adopted. In other words, as shown in FIG. 23, the protrusions 301 to 308 move in the direction of the weight movable electrode on the fixed electrode 13 side.
Is provided. Thereby, the weight movable electrode 12
Can receive an acceleration and can be displaced and contact pressure with the fixed electrode 13 can be increased.

FIG. 23 shows the projection shape inclined with respect to the fixed electrode 13, but the projection 30 shown in FIG.
9, the projection 310 shown in FIG. 25, and the projection 311 shown in FIG.
The shape may be I-type, T-type, or rhombus for the fixed electrode 13 as shown in FIG. Here, the embodiment in which the protrusion is formed on the fixed electrode 13 side is shown.
Further, it may be formed on both sides of the fixed electrode 13 and the weight movable electrode 12.

Here, as shown in FIG. 27, a metal, preferably a noble metal 312 such as Au or Pt, is formed on the surface of the weight movable electrode 12 on the fixed electrode 13 side and the surface of the fixed electrode 13 on the weight movable electrode 12 side. Thereby, the contact resistance between the weight movable electrode 12 and the fixed electrode 13 can be reduced. This surface treatment is the same for the projection shapes shown in FIGS.

The same applies to the case where the projections are formed on the weight movable electrode 12 side and on both the weight movable electrode 12 and the fixed electrode 13. In the second embodiment, similarly to the first embodiment, the weight movable electrode 12 and the fixed electrode 13 are used.
And a predetermined potential difference is applied between them to detect acceleration. (Third Embodiment) Next, a third embodiment in which the position of the beam portion in the first embodiment is changed will be described below. FIG. 31 is a plan view of an acceleration sensor according to a third embodiment of the present invention, and FIG. 32 is a sectional view taken along line BB in FIG.

The acceleration sensor shown in FIG. 31 includes a cylindrical movable weight electrode 52 displaced by acceleration, a cylindrical fixed electrode 51 located at the center of the substrate 30, an anchor portion 53 for supporting the weight movable electrode 52 from the outside, It is composed of four beams 54 to 57. The inner peripheral surface of the cylinder of the weight movable electrode 52 is a conductive detection surface 58, and the outer peripheral surface of the fixed electrode 51 is a conductive detection surface 59.

In FIG. 1, the movable weight electrode 12 is supported by the anchor portion 11 located at the center of the structure, and the fixed electrode 13 is located outside the movable weight electrode 12. In FIG. 52 is a weight movable electrode 52
Part 53 located at a predetermined interval outside
Further, it is supported above the substrate 30 at predetermined intervals by the beams 54 to 57. Also, the weight movable electrode 52
Inside the cylindrical fixed electrode 51 at a predetermined interval.
Is arranged. Central fixed electrode 51 and anchor 5
3 have oxide films 21 and 22, respectively.
Connected to 0.

Although not shown here, the anchor portion 51, the four beam portions 54 to 57, the weight movable electrode 5
2. Impurities may be introduced into the surface of the fixed electrode 53 by a method such as ion implantation or phosphorus deposition, or a conductive material may be deposited, plated or formed into another film to lower the resistivity of the structure. good. As described above, if the position of the fixed electrode 51 is changed from the outside to the inside of the cylindrical weight movable electrode 52, an acceleration sensor with higher sensitivity can be manufactured using the beam having the same cross-sectional shape as the first embodiment.

Further, in addition to the effects of the first embodiment, since the fixed electrode 51 is provided inside the annular portion, it is not necessary to provide a special area for providing the fixed electrode 51, and the area of the acceleration sensor is reduced. Can be reduced. In the third embodiment, similarly to the first embodiment, the weight movable electrode 12 and the fixed electrode 13 are used.
And a predetermined potential difference is applied between them to detect acceleration. (Fourth Embodiment) FIG. 33 is a plan view of an acceleration sensor according to a fourth embodiment of the present invention, and FIG.
FIG.

In the fourth embodiment, the detected surface 19 of the fixed electrode 13 is different from the first embodiment shown in FIG.
The difference is that projections 13a to 13d for sensitivity adjustment (for contacts) are formed. These projections 13a to 13d are formed of the same material as the fixed electrode 13. By providing such projections 13a to 13d, the distance between the weight movable electrode 12 and the fixed electrode 13 is adjusted, and the weight movable electrode 1 is adjusted.
The sensitivity of this sensor can be adjusted by taking into account the electrostatic force generated when 2 is displaced toward the fixed electrode 13 side.

In FIG. 33, four protrusions are formed on the fixed electrode 13, but the number of protrusions may be other than that.
In this case, the detection accuracy varies depending on the number of projections, but in order to ensure the operation as a sensor, it is preferable to set the number so that the weight movable electrode 12 does not contact the fixed electrode 13 other than the projection. Further, the protrusion is a fixed electrode 1
Instead of the third side, it can be formed on the weight movable electrode 12 side. That is, as shown in FIGS. 35 and 36, contact protrusions 12 a to 12 a are formed on the detection surface 18 of the weight movable electrode 12.
forming d. FIG. 35 is a plan view of the acceleration sensor, and FIG. 36 is a cross-sectional view taken along line DD in FIG.

Furthermore, a projection for sensitivity adjustment can be provided in the third embodiment shown in FIG. That is, as shown in FIGS. 37 and 38, the contact projections 51 a to 51 a are formed on the detection surface 59 of the fixed electrode 51.
forming d. FIG. 37 is a plan view of the acceleration sensor, and FIG. 38 is a sectional view taken along line EE in FIG. Also,
In the configuration shown in FIG. 37, a protrusion may be formed on the weight movable electrode 42 side. That is, as shown in FIG. 39 and FIG. 40, contact projections 52 a to 52 d are formed on the detection surface 58 of the weight movable electrode 52. 39 is a plan view of the acceleration sensor, and FIG. 40 is a cross-sectional view taken along line FF in FIG. (Fifth Embodiment) FIG. 41 is a plan view of an acceleration sensor according to a fifth embodiment of the present invention, and FIG.
FIG.

The fifth embodiment is different from the first embodiment shown in FIG. 1 in that the fixed electrode 13 is divided into fixed electrodes 131-134 for sensitivity adjustment and fixed electrodes 135-138. Fixed electrodes 131 to 131 for sensitivity adjustment
Insulation separation films (or insulation separation means such as gaps) 139 to 146 are formed between 134 and fixed electrodes 135 to 138.

The fixed electrodes 135 to 138 are provided with contact projections 135a to 138a, respectively, and these projections are formed of the same material as the fixed electrodes 135 to 138. Here, since a voltage is applied to the weight movable electrode 12 via the anchor portion 11 and the beam portions 14 to 17,
Between the weight movable electrode 12 and the fixed electrodes 135 to 138,
As shown in FIG. 43, voltage V ₀ is applied. In addition, the weight movable electrode 12 and the sensitivity adjustment fixed electrodes 131 to 134
, A voltage V _R is applied.

[0058] In this case, with the sensitivity adjustment by the projection 135a~138a formed on the fixed electrode 135-138 to adjust the voltage V _0, V _R independently by the power supply means voltage V _0, V _R shown in FIG. Thereby, the sensitivity can be adjusted after manufacturing the sensor. The potential difference V _R between the fixed electrodes 131 to 134 for sensitivity adjustment and the weight movable electrode 12.
When the weight movable electrode 12 comes into contact with the fixed electrodes 135 to 138, the electrostatic attraction generated between the sensitivity adjustment fixed electrodes 131 to 134 and the weight movable electrode 12 causes the beam portions 14 to 1
7 is set to be smaller than the spring force.

As a result, the weight movable electrode 12 and the fixed electrodes 135 to 138 come into contact with each other due to the occurrence of acceleration,
Thereafter, when the acceleration stops, the weight movable electrode 12 can be returned to the original state by the spring force of the beams 14 to 17. Hereinafter, this point will be described in detail. The electrostatic attractive force acting between the sensitivity adjustment electrodes 131 to 134 and the weight movable electrode 12 has a relationship represented by Expressions 1 to 3, and a distance between the sensitivity adjustment electrodes 131 to 134 and the weight movable electrode 12. And the potential difference has an effect. In this case, the electrostatic attraction is
As shown in FIGS. 9 and 10, the displacement d of the weight movable electrode 12 increases, that is, increases as the distance between the weight movable electrode 12 and the sensitivity adjustment electrodes 131 to 134 decreases.

FIG. 44 shows the relationship between the spring force Fk and the electrostatic attraction Fe with respect to the displacement d of the weight movable electrode 12. As shown in the drawing, the electrostatic attraction Fe increases as the displacement d increases and the electrostatic attraction exceeds the spring force Fk. Here, the spring force F
The value (Fk-Fe) obtained by subtracting the electrostatic attractive force Fe from k, the displacement d gradually increases from 0 to a and peaks at the point a, and when the displacement d is between a and b, the electrostatic attractive force Fe sharply increases. (Fk-Fe) suddenly decreases due to a slight increase, and becomes a negative value beyond point b. That is, when the displacement d exceeds the point b, the electrostatic attractive force Fe exceeds the spring force Fk, and the weight movable electrode 12 remains attached to the fixed electrode side,
Even if the acceleration received by the vibration such as the earthquake disappears, the movable electrode 12 cannot be separated from any of the projections 135a to 138a of the fixed electrode.

Therefore, the amount of displacement of the weight movable electrode 12 is
It is necessary to set an area where the electrostatic attractive force Fe does not exceed the spring force as shown in FIG. That is, the weight movable electrode 1
2 is in contact with any one of the projections 135a to 138a of the fixed electrode and approaches the sensitivity adjusting electrodes 131 to 134, so that the electrostatic attractive force Fk does not exceed the spring force Fe. Protruding length, sensitivity adjustment fixed electrodes 131 to 134 and weight movable electrode 12
Setting the potential difference V _R between.

In FIG. 44, (Fk-Fe) simply increases in a range where the displacement d is 0 to a. Therefore, when the displacement of the weight movable electrode 12 is set to be smaller than a, a predetermined value is obtained. When the weight movable electrode 12 comes into contact with any of the projections 135a to 138a of the fixed electrode under the acceleration,
When the applied acceleration to the weight movable electrode 12 becomes smaller than the predetermined acceleration, the weight movable electrode 12
Are separated from the projections 135a to 138a of the fixed electrode.

In the region where the displacement d is ab, (Fk-Fe) has a peak value at point a, and when it is larger than a, (Fk-Fe) becomes smaller. The magnitude of the acceleration for contacting any of the protrusions 135a to 138a differs from the magnitude of the acceleration at which the weight movable electrode 12 separates from the protrusions 135a to 138a of the fixed electrode. That is, at a certain acceleration, the weight movable electrode 1
2 contacts the fixed electrode protrusions 135a to 138a, the weight movable electrode 12 is fixed to the fixed electrode protrusion 13 until the acceleration becomes smaller than the acceleration by a certain value.
5a to 138a. Accordingly, by setting the amount of displacement of the weight movable electrode 12 between the regions a and b, the weight movable electrode 12 can be fixed to the projection 135a of the fixed electrode.
138a can be made longer than when the displacement d is set in the range of 0 to a, and the acceleration can be detected more reliably.

The amount of displacement of the weight movable electrode 12, that is, whether the movable range of the weight movable electrode 12 is set to the range of 0 to a or the range of a to b is determined by the projection 135 of the fixed electrode.
a to 138a. The projections 135a to 138a of the fixed electrode may have shapes as shown in FIGS.

In the above-described embodiment, the case where the voltages V ₀ and V _R are set by two power supply means has been described.
As shown in FIG. 45, the fixed electrode 135 to the divided voltage of the external power supply V ₁ by the resistors R1, R2 and weight movable electrode 12
138 may be applied. With such a configuration, one power source can be used. In addition, the weight movable electrode 12 and the sensitivity adjustment fixed electrodes 131 to
When lowering the voltage between the resistors 134, the voltage divided by the resistors R3 and R4 is applied between the weight movable electrode 12 and the sensitivity adjustment fixed electrodes 131 to 134 as shown in FIG. do it.

In the example shown in FIG. 43, the sensitivity adjustment fixed electrode and the fixed electrode are each divided into four, but the number of divisions may be other. FIG.
Also in the third embodiment shown in (1), an electrode configuration in which the fixed electrode is divided into a fixed electrode for sensitivity adjustment and a fixed electrode can be used. That is, as shown in FIGS. 47 and 48, the fixed electrode 51 is fixed to the fixed electrodes 151 to 15 for sensitivity adjustment.
4. The electrode configuration is divided into fixed electrodes 155 and 156, and the electrodes are insulated and separated by insulating separation films 157 to 160. In addition, the fixed electrodes 155 and 156 have a structure protruding from the fixed electrodes 151 to 154 for sensitivity adjustment, so that the sensitivity can be adjusted at the protruding portions in the same manner as the above-described contact projection. Has become. FIG. 47 is a plan view of the acceleration sensor, and FIG.
It is HH sectional drawing in 7. In this case, between the weight movable electrode 12 and the sensitivity adjustment fixed electrodes 151 to 154, and between the weight movable electrode 12 and the fixed electrodes 155 and 156, FIG.
3, independent voltages can be applied using any of the configurations shown in FIGS. 45 and 46.

In the above-described second to fifth embodiments, the structure manufactured by the steps shown in FIGS. In this case, by using the lower electrode 49, each potential can be easily extracted. However, in the above-described fifth embodiment, the fixed electrodes 131 to 134 for sensitivity adjustment and the fixed electrodes 135 to 1
38 is separated by the insulating separation means 139 to 146, so that the manufacturing method is slightly different from the other embodiments. In this case, the manufacturing method includes the sensitivity adjustment fixed electrodes 131 to 1.
There is a slight difference between a case where an insulating separation film is formed between the fixed electrode 34 and the fixed electrodes 135 to 138 and a case where only a gap is formed.

In the former case, first, when forming the alignment groove 40a shown in FIG. 12, a groove for separating the sensitivity adjustment fixed electrodes 131 to 134 and the fixed electrodes 135 to 138 is formed at the same time. That is, trench etching by dry etching is performed. Thereafter, when the silicon oxide film 41 is formed, the fixed electrode 1 for sensitivity adjustment is simultaneously formed.
The grooves formed between the fixed electrodes 31 to 134 and the fixed electrodes 135 to 138 are buried with a silicon oxide film.
9 to 146 are formed.

In this case, when the silicon oxide film 41 shown in FIG. 19 is removed by etching, the insulating separation means is a silicon oxide film formed between the fixed electrodes 131-134 for sensitivity adjustment and the fixed electrodes 135-138. 139-146
Must be protected by a mask or the like so as not to be removed. In the latter case, as shown in FIGS. 18 and 19, the anchor portion 11, the weight movable electrode 12, and the beam portion 13 are formed and simultaneously the sensitivity adjustment fixed electrodes 131 to 134 and the fixed electrode 1 are formed.
What is necessary is just to separate from 35-138. This can also be performed by dry etching. Alternatively, as another method, the silicon oxide film formed between the fixed electrodes 131 to 134 for sensitivity adjustment and the fixed electrodes 135 to 138 by the former method is simultaneously removed by etching the silicon oxide film 41 shown in FIG. Even if they are removed by etching, the sensitivity adjustment fixed electrodes 131 to 134 and the fixed electrodes 135 to 138 are used.
Can form a gap between them.

[Brief description of the drawings]

FIG. 1 is a plan view of an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA in FIG.

FIG. 3 is a process chart showing a manufacturing process of the acceleration sensor shown in FIG. 1;

FIG. 4 is a process chart showing a manufacturing process following FIG. 3;

FIG. 5 is an explanatory diagram for explaining the operation of the acceleration sensor shown in FIG. 1;

FIG. 6 is a diagram showing a configuration for detecting acceleration by the acceleration sensor shown in FIG. 1;

FIG. 7 is a diagram for explaining a problem when a spring constant is small in the acceleration sensor shown in FIG. 1;

FIG. 8 is a characteristic diagram showing a relationship between a displacement of a weight movable electrode and a capacitance in the acceleration sensor shown in FIG. 1;

9 is a characteristic diagram showing a relationship between displacement of the weight movable electrode and capacitance when a voltage of 5 V is applied between the movable weight electrode and the fixed electrode in the acceleration sensor shown in FIG.

FIG. 10 is an enlarged view of a region where displacement is small in the characteristic diagram shown in FIG. 9;

FIG. 11 is a model diagram for explaining a relationship between a force applied to a weight movable electrode, a force due to a restoring force of a spring, and a force due to an electrostatic force.

FIG. 12 is a process chart showing another method for manufacturing the acceleration sensor shown in FIG. 1;

FIG. 13 is a process drawing following FIG. 12;

FIG. 14 is a process drawing following FIG. 13;

FIG. 15 is a process drawing following FIG. 14;

FIG. 16 is a process drawing following FIG. 15;

FIG. 17 is a process drawing following FIG. 16;

FIG. 18 is a process drawing following FIG. 17;

FIG. 19 is a process drawing following FIG. 18;

FIG. 20 is a process chart showing still another method of manufacturing the acceleration sensor shown in FIG. 1;

FIG. 21 is a process drawing following FIG. 20;

FIG. 22 is a process drawing following FIG. 21;

FIG. 23 is a plan view of an acceleration sensor according to a second embodiment of the present invention.

FIG. 24 is a partial configuration diagram showing a modified example of the acceleration sensor shown in FIG.

25 is a partial configuration diagram showing another modification of the acceleration sensor shown in FIG.

FIG. 26 is a partial configuration diagram showing still another modified example of the acceleration sensor shown in FIG.

FIG. 27 is a partial configuration diagram showing still another modified example of the acceleration sensor shown in FIG.

FIG. 28 is a partial configuration diagram showing still another modified example of the acceleration sensor shown in FIG.

FIG. 29 is a partial configuration diagram showing still another modified example of the acceleration sensor shown in FIG.

30 is a partial configuration diagram showing still another modified example of the acceleration sensor shown in FIG.

FIG. 31 is a plan view of an acceleration sensor according to a third embodiment of the present invention.

FIG. 32 is a sectional view taken along line BB in FIG. 31;

FIG. 33 is a plan view of an acceleration sensor according to a fourth embodiment of the present invention.

34 is a sectional view taken along the line CC in FIG. 33.

FIG. 35 is a plan view showing a modification of the acceleration sensor according to the fourth embodiment of the present invention.

36 is a sectional view taken along line DD in FIG. 35.

FIG. 37 is a plan view showing another modification of the acceleration sensor according to the fourth embodiment of the present invention.

38 is a sectional view taken along the line EE in FIG. 37.

FIG. 39 is a plan view showing still another modified example of the acceleration sensor according to the fourth embodiment of the present invention.

40 is a sectional view taken along the line FF in FIG. 39.

FIG. 41 is a plan view of an acceleration sensor according to a fifth embodiment of the present invention.

42 is a sectional view taken along line GG in FIG. 41.

FIG. 43 is a diagram showing a configuration for detecting acceleration by the acceleration sensor shown in FIG. 41.

FIG. 44 is a diagram showing a relationship between a spring force Fk and an electrostatic attraction Fe with respect to a displacement d of the weight movable electrode 12.

FIG. 45 is a diagram showing another configuration for performing acceleration detection by the acceleration sensor shown in FIG. 41.

FIG. 46 is a diagram showing still another configuration in which acceleration is detected by the acceleration sensor shown in FIG. 41.

FIG. 47 is a plan view showing a modification of the acceleration sensor according to the fifth embodiment of the present invention.

FIG. 48 is a sectional view taken along line HH in FIG. 47;

[Explanation of symbols]

11, 51 ... anchor portion, 12, 52 ... weight movable electrode, 13, 53 ... fixed electrode, 14-17, 54-57 ...
Beam part, 30 ... substrate, 100 ... acceleration sensor.

Claims (8)

[Claims] 1. A substrate (30), an anchor portion (11, 53) fixed on the substrate, a movable weight electrode (12, 52), one end is fixed to the anchor portion, and the other end is the other end. A spring portion (14 to 14) which is fixed to the weight movable electrode and elastically deforms when an acceleration is generated in a direction parallel to the surface of the substrate to displace the weight movable electrode in a direction parallel to the surface of the substrate. 17, 54 to 57) and a fixed electrode for detection (135 to 138, 1) which comes into contact with the movable weight electrode when the movable movable weight electrode is displaced in the parallel direction by the acceleration.
55, 156) and fixed electrodes for sensitivity adjustment (131 to 134, 151 to 154) fixed on the substrate and used to adjust detection sensitivity by electrostatic attraction between the weight movable electrode. An acceleration sensor, comprising: 2. A substrate (30), and anchor portions (11, 5) fixedly disposed on the substrate.
3) and a weight movable electrode (1) having a circumferential side surface (18, 58).
2, 52); one end is fixed to the anchor portion and the other end is fixed to the weight movable electrode, and when acceleration is generated in a direction parallel to the surface of the substrate, the weight is elastically deformed and the weight is movable. A spring portion (14 to 17, 54 to 57) for displacing an electrode in a direction parallel to the surface of the substrate; and a fixed portion disposed on the substrate, and a predetermined distance from the circumferential side surface of the weight movable electrode. Circumferential side faces (1
9, 59) fixed electrodes (131 to 138, 151)
To 156), wherein the fixed electrode is a detection fixed electrode (135 to 138, 155, 155) that comes into contact with the weight movable electrode when the weight movable electrode is displaced in the parallel direction by the acceleration.
156), and a sensitivity adjustment fixed electrode (131-1) which is insulated and separated from the detection fixed electrode and is used for adjusting the detection sensitivity by electrostatic attraction between the weight movable electrode.
34, 151 to 154). 3. A means for giving independently adjustable potential differences between the fixed electrode for detection and the movable weight electrode and between the fixed sensitivity adjustment electrode and the movable weight electrode, respectively. The acceleration sensor according to claim 1 or 2, wherein: 4. The potential difference (V _R ) between the fixed electrode for sensitivity adjustment and the movable electrode with weight is determined when the movable electrode for weight contacts the fixed electrode for detection with the fixed electrode for sensitivity adjustment and the weight. The acceleration sensor according to claim 3, wherein an electrostatic attraction generated between the movable portion and the movable electrode is set to be smaller than a spring force of the spring portion. 5. The acceleration sensor according to claim 1, wherein the detection fixed electrode has projections (135a to 138a) that come into contact with the weight movable electrode. 6. The acceleration sensor according to claim 5, wherein, when the weight movable electrode contacts the projection, the projection prevents the weight movable electrode from contacting the sensitivity fixed electrode. . 7. The projection length of the projection is defined so that a value obtained by subtracting the electrostatic attraction from the spring force simply increases in a movable range of the weight movable electrode. The acceleration sensor according to claim 6, wherein 8. The projection length of the projection is set so that a value obtained by subtracting the electrostatic attractive force from the spring force exceeds a peak value and becomes zero in a movable range of the weight movable electrode. The acceleration sensor according to claim 6, wherein the acceleration sensor is defined.