JPH07218534A - Capacitance type acceleration sensor and its manufacture - Google Patents

Abstract

PURPOSE:To prevent drop of the sensing accuracy of an acceleration sensor caused by the deadweight of a weight by forming it from a quadriangular plate of electrically insulative material, and furnishing movable electrodes, stationary electrodes, etc., on a fixing frame of an insulative substance which are located on the sides apart from one another. CONSTITUTION:When a lateral acceleration is applied to a weight 5, a sideways movement takes place so that the distance between a movable electrode 51 and a stationary electrode 61 varies to cause a change in the electrostatic capacitance, and thus the acceleration is sensed. Even though the weight 5 moves down by its deadweight, the distances between the electrodes 51, 52 and 61, 62 do not change because of parallelism, and because the lengths in vertical direction of the electrodes 51, 52 and ones 61, 62 are good larger than the distance for which the weight 5 normally moves downward due to its deadweight, change in the mating areas of electrodes 51, 52 and ones 61, 62 is lesser. Accordingly there is no risk that the deadweight of the weight 5 deteriorates the sensing accuracy. If the vertical length of one of the electrodes is made smaller than that of the other, change in the mating area of these electrodes will further lessen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-compact capacitive acceleration sensor which is used for various controls, for example, by detecting an acceleration condition and a shaking condition of an automobile and processing the detection signal.

[0002]

2. Description of the Related Art A silicon layer made of, for example, polysilicon and a PSG (Phosp) are formed on the surface of a silicon substrate.
ho Silicate Glass, phosphosilicate glass)
A technique (hereinafter, referred to as a multi-layer micro-machine technique) for forming an ultra-small multi-layer structure by forming a multi-layer sacrificial layer made of, and removing the sacrificial layer with hydrofluoric acid after processing by the micro-machine technique has been developed. An ultra-small capacitive acceleration sensor has been developed using such a technique.

FIG. 8 shows an example of a conventional capacitive acceleration sensor manufactured by a multi-layer micromachine technique.
(A) is a perspective view, (b) is a CC cross-sectional view of (a), which is composed of a semiconductor substrate 1 and polysilicon, respectively.
Supports 21A, 21B, 21C and 21D provided on the upper surface of the semiconductor substrate 1 at respective corners of a quadrangle via an insulating layer 1A, and one ends of the supports 21A, 21B, 21C,
This rectangular diagonal beam 24A, 24B, 2 which is connected to 21C and 21D and is fitted in a 90 ° rotational movement
4C and 24D and these beams 24A, 24B, 24
A weight 23 coupled to the other ends of C and 24D, the upper and lower surfaces of which form movable electrodes 23A and 23B, and a lower surface of the movable electrode 23B of the weight 23, which is spaced apart by a predetermined distance, from the upper surface of the silicon substrate 1. The fixed electrode 31 provided via the insulating layer 1A and the insulating layer 1 on the upper surface of the silicon substrate 1.
Supports 42A and 42B provided through A, and their peripheries are coupled to these supports 42A and 42B,
A fixed electrode 41 provided at a predetermined distance on one side of the movable electrode 23A of the weight 23, that is, on the upper surface on the left side in FIG.
From the movable electrodes 23A and 23B, the terminal M is drawn out via the beam 24B and the support 21B, the fixed electrode 31 is drawn out from the terminal S ₁ , and the fixed electrode 41 is drawn out from the terminal S ₂ via the support 42A.

Here, the polysilicon is doped with impurities, and its specific resistance is lowered to, for example, about 1 to 10 ⁻³ Ωcm, which makes it conductive. Of course, it is possible to use single crystal silicon made conductive by doping impurities instead of polysilicon, but the cost of polysilicon is lower than that of single crystal silicon. The operation of this capacitive acceleration sensor is as follows. When vertical acceleration is applied to the weight 23, the movable electrodes 23A and 23B move in the vertical direction. By the vertical movement of the movable electrodes 23A and 23B, for example, the movable electrode 23B and the fixed electrode 31 come close to each other, and the electrostatic capacitance therebetween increases, and the movable electrode 23A and the fixed electrode 41 are separated from each other. During this time, the capacitance decreases. The values of these capacitances are taken out from between the terminals M and S _{1 and} between the terminals M and S ₂ , and signal processing is performed by a differential amplifier or the like to detect the applied acceleration.

[0005]

The above-mentioned capacitive acceleration sensor has a structure in which the movable electrodes provided on the upper surface and the lower surface of the weight are provided with the fixed electrodes at intervals, respectively. Due to the weight of the weight, the distance between the movable electrode and the fixed electrode on the upper surface side of the weight or the distance between the movable electrode and the fixed electrode on the lower surface side changes, which causes a problem that the detection accuracy decreases. In addition, a silicon layer made of, for example, polysilicon and a sacrifice layer made of, for example, PSG are formed in multiple layers on the surface of a silicon substrate, and the sacrifice layer is removed by hydrofluoric acid or the like after processing by the micromachine technique. However, in the multi-layer micromachine technology, there is a problem that transfer and etching of a plurality of masks on a silicon substrate are required and the number of manufacturing steps is increased.

An object of the present invention is to provide a highly accurate capacitive acceleration sensor which prevents the detection accuracy from being lowered due to the weight of the weight. Another object of the present invention is to provide a low-cost manufacturing method that reduces the number of manufacturing steps.

[0007]

In order to achieve the above-mentioned object, the capacitive acceleration sensor of the present invention is provided with an insulating weight composed of a quadrangular plate and each side surface of the weight with a space therebetween. And an insulative fixed frame, each beam provided between the opposite one side surfaces of this weight and each inner side surface of the fixed frame facing each of these both side surfaces, and the other opposite side surfaces of the weight And each fixed electrode provided on the inner side surface of the fixed frame so as to face each of the movable electrodes. It is desirable that each of the beams be composed of four beams provided between a portion near both ends of one opposite side surface of the weight and each inner side surface of the fixed frame facing these portions. . Further, in the above capacitive acceleration sensor, the weight, the fixed frame, and each beam are made of insulating silicon having a high specific resistance, and each movable electrode and each fixed electrode are doped with impurities in the insulating silicon having a high specific resistance. Then, it is preferable to use conductive silicon having a reduced specific resistance, or the weight, the fixing frame and each beam may be made of an insulating resin.
When it is made of resin, it is preferable to form the weight, the fixing frame, and each beam by irradiating an uncured ultraviolet curable resin with ultraviolet rays.

[0008]

In the capacitive acceleration sensor of the present invention, the weight moves by its own weight in the direction parallel to the movable electrode and the fixed electrode, so that the distance between the movable electrode and the fixed electrode does not change. Further, since the length of the movable electrode and the fixed electrode in the direction in which the weight moves due to its own weight is usually larger than the length of the weight moved due to its own weight, the change in the area where the movable electrode and the fixed electrode face each other is small. Therefore, the detection accuracy does not decrease due to the weight of the weight. Note that it is preferable to make the length of the weight of one electrode in the direction in which the weight moves by its own weight shorter than the length of the other electrode because the change in the area where these electrodes face each other is reduced.

Further, each of the beams is composed of four beams provided between a portion of the weight close to both ends of one opposite side surface of the weight and each inner side surface of the fixed frame opposed to these portions. In this case, if the supporting force of the weight is equal when supporting with two beams and when supporting with four beams, the width of the beam becomes 1/2 when supporting with four beams. As a result, the rigidity becomes low, the amount of movement of the weight when acceleration is applied is large, and the detection sensitivity is improved. In addition, by supporting with four beams, twisting during movement of the weight is prevented, and the detection operation is stabilized.

Further, the weight, the fixed frame and each beam are made of insulating silicon having a high specific resistance, and each movable electrode and each fixed electrode are doped with impurities in the insulating silicon having a high specific resistance to obtain a specific resistance. It is convenient to use silicon having reduced conductivity because it can be manufactured by a normal semiconductor manufacturing process. In addition, the weight, the fixed frame, and each beam may be made of an insulating resin (the movable electrode and the fixed electrode are to be attached later). In this case, the weight, the fixed frame, and each beam are uncured by UV curing. When the resin is formed by irradiating ultraviolet rays, it is not necessary to transfer and etch the mask in the semiconductor manufacturing process, and the number of manufacturing steps is reduced.

[0011]

1 is a perspective view showing an embodiment of a capacitive acceleration sensor of the present invention. In FIG. 1, the capacitive acceleration sensor includes an insulating weight 5 made of a quadrangular plate, an insulating fixing frame 6 provided on each side surface of the weight 5 with a space, and the weight 5 faces each other. Each of the beams 7A provided between one side, for example, the central portion of both side surfaces in the depth direction and each inner side surface of the fixed frame 6 facing the both side surfaces,
7B, the movable electrodes 51 and 52 provided on the other side of the weight 5, for example, on both side surfaces in the lateral direction, and on the inner side surface of the fixed frame 6 facing the movable electrodes 51 and 52, respectively. Each of the fixed electrodes 61 and 62 is
The movable electrodes 51 and 52 are movably drawn to terminals M ₁ and M ₂ , respectively, and the fixed electrodes 61 and 62 are drawn to terminals S ₁ and S ₂ , respectively.

Here, the weight 5, the fixed frame 6 and the respective beams 7
A and 7B are made of, for example, insulating silicon having high purity and high specific resistance, and the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 are formed by doping the insulating silicon having high specific resistance with impurities. It is made of conductive silicon with reduced specific resistance. Alternatively, the weight 5, the fixed frame 6 and the beams 7A and 7B are made of, for example, resin, and the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 are made of electrodes such as a conductive metal that is attached later.

The operation of this capacitive acceleration sensor is as follows. When a lateral acceleration is applied to the weight 5, the weight 5 moves in the lateral direction, and the movable electrode 51 and the fixed electrode 61 come close to each other, for example, and the electrostatic capacitance therebetween increases, so that the movable electrode 52 and the fixed electrode 52 are fixed. On the contrary, the electrode 62 is separated from the electrode 62, and the capacitance therebetween decreases. The values of these capacitances are used as the terminals M ₁ and S ₁
Taken out from between and between terminals M _2, S _2, to detect the acceleration applied to the signal processing such as by a differential amplifier.

In this capacitive acceleration sensor, the distance between the movable electrode and the fixed electrode does not change even if the weight 5 moves downward due to its own weight. In addition, the movable electrodes 51, 52
Since the vertical lengths of the fixed electrodes 61 and 62 are usually sufficiently larger than the downward distance in which the weight 5 moves by its own weight, there is little change in the facing area between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62. . Therefore, the detection accuracy does not decrease due to the weight of the weight 5. Note that it is preferable to make the vertical length of one electrode shorter than the vertical length of the other electrode, because the change in the area where these electrodes face each other becomes smaller.

FIG. 2 is a perspective view showing another embodiment of the capacitive acceleration sensor of the present invention. The embodiment shown in FIG. 2 is shown in FIG.
1 is different from the embodiment shown in FIG. 1 in that it is provided between the facing one of the weights 5 in FIG. 1, for example, the central portion of both side surfaces in the depth direction and the inner side surfaces of the fixed frame 6 facing these respective side surfaces. In place of the beams 7A, 7B, the beams 7C, 7D are provided between the portions of the weight 5 close to both ends of the opposite side surfaces and the inner surface of the fixed frame 6 facing these portions. 7E, 7
F is provided, and the width of each of the beams 7C, 7D, 7E, and 7F is set to be half that of each of the beams 7A and 7B of the embodiment of FIG. 1 (the supporting force of the weight 5 is the same as that of the embodiment of FIG. 1). To be the same).

By supporting each side surface of the weight 5 by the two beams, that is, the four beams 7C, 7D, 7E, and 7F in total, each side surface of the weight 5 is set to 1 as in the embodiment of FIG. Beams,
The amount of horizontal movement of the weight 5 can be increased as compared with the case of using two beams 7A and 7B in total. 3 and 4 respectively show the weight 5 in the embodiment shown in FIG.
Each side has one beam, and a total of two beams 7A, 7B
2 when each side surface of the weight 5 in the embodiment shown in FIG. 2 is supported by four beams 7C, 7D, 7 in total.
It is a model figure which shows the result of having analyzed the moving amount of the horizontal direction of the weight 5 when supporting by E and 7F. In FIG. 3, FIG. 3A shows a state in which no acceleration is applied,
When acceleration is applied laterally from this state, the weight 5 moves laterally, for example, a distance L, as shown in FIG. 3B.
Similarly, in FIG. 4, FIG. 4A shows a state in which no acceleration is applied, and when acceleration is applied laterally from this state, in this case, the weight 5 moves a distance 2L in the lateral direction. That is, compared with the case of supporting with two beams 7A and 7B,
When supported by the four beams 7C, 7D, 7E, 7F, the beam width is halved, so that the rigidity is low and the movement amount of the weight 5 is large.

Further, by supporting the four beams 7C, 7D, 7E and 7F, twisting of the weight 5 during movement is prevented and the detection operation is stabilized. In the capacitive acceleration sensor of the present invention shown in FIGS. 1 and 2, the weight 5, the fixed frame 6
And each beam 7A, 7B or 7C, 7D, 7E, 7F
Is made of insulating silicon having a high specific resistance, for example, about 10 ⁶ ohm-cm, and the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 are doped with impurities having high specific resistance to obtain the specific resistance. For example, when it is made of conductive silicon having a thickness lowered to about 1 to 10 ⁻³ Ωcm, it can be manufactured by a normal semiconductor manufacturing process. When the weight 5, the fixed frame 6 and the beams 7A, 7B or 7C, 7D, 7E, 7F are made of resin,
It is preferable to manufacture by a manufacturing method using an ultraviolet curable resin as the resin shown in FIGS. 5 and 6 because the number of manufacturing steps is reduced. FIG. 5 shows a manufacturing apparatus in this manufacturing method,
In FIG. 5, the ultraviolet laser light emitted from the laser oscillator 81 passes through a mirror 83 and a beam condensing lens 84 and hits a resin tank 85 containing an ultraviolet curable resin (not shown). The table 89 is located at a position having a slight gap with the window plate 86 provided on the lower surface of the resin tank 85, and this gap is filled with the ultraviolet curable resin. First, the laser beam scans the lower surface of the window plate 86 in the X direction by the XY stage 87. At this time, it is possible to open the shutter 82 at a portion where the resin is desired to be cured and to close the shutter 82 at a portion where the resin is not desired to be cured to form a cross section having an arbitrary shape. After scanning one line in the X direction, the laser light is then moved in the Y direction. After repeating this X-direction scan and Y-direction movement an arbitrary number of times, Z
The table 89 and the cured resin are lifted by moving the stage 88 in the Z direction. As a result of the lifting, the gap between the window plate 86 and the table 89 is filled with the ultraviolet curable resin again.

FIG. 6 shows the scanning state of the ultraviolet laser light. At the place where the weight 5, the fixed frame 6, and the beams 7C, 7D, 7E, and 7D are formed, the shutter is opened to irradiate the ultraviolet laser light and Y Move in the direction. FIG. 7 shows the weight 5, the fixed frame 6, and the beams 7C, 7D, and 7 thus made.
E and 7F are shown, and the resin is sequentially cured for each layer in the Z direction indicated by the dotted line to form a predetermined thickness. In this manufacturing method, the manufacturing can be performed only by repeating the laser scanning in the X direction, the movement in the Y direction, and the movement in the Z direction, and it is not necessary to transfer or etch the mask in the semiconductor manufacturing process, and the number of manufacturing steps is reduced.

[0019]

According to the capacitive acceleration sensor of the present invention, the detection accuracy is improved because the decrease of the detection accuracy due to the weight of the weight is prevented. Further, the weight, the fixed frame, and each beam are made of insulating silicon having a high specific resistance, and each movable electrode and each fixed electrode are doped with impurities in the insulating silicon having a high specific resistance to reduce the specific resistance. Since it is made of conductive silicon, it can be manufactured by a normal semiconductor manufacturing process. In addition, the weight, the fixed frame, and each beam may be made of an insulating resin. In this case, the weight, the fixed frame, and each beam are formed by irradiating an uncured ultraviolet curable resin with ultraviolet rays. There is no need to transfer or etch a mask in the process, which reduces the number of manufacturing steps and costs.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a capacitive acceleration sensor of the present invention.

FIG. 2 is a perspective view showing another embodiment of the capacitive acceleration sensor of the present invention.

3A and 3B show analysis results of a horizontal movement amount of a weight in the embodiment shown in FIG. 1, where FIG. 3A is a model diagram before application of acceleration, and FIG. 3B is a model diagram after application of acceleration.

4A and 4B show analysis results of a horizontal movement amount of a weight in the embodiment shown in FIG. 2, where FIG. 4A is a model diagram before application of acceleration, and FIG. 4B is a model diagram after application of acceleration.

FIG. 5 is a perspective view of a manufacturing apparatus used in the manufacturing method of forming the weight, the fixing frame, and each beam by irradiating an uncured ultraviolet curable resin with ultraviolet rays in the embodiment shown in FIG. 1 or FIG.

6 is a model diagram showing a scanning state of ultraviolet laser light in the manufacturing apparatus shown in FIG.

FIG. 7 is a model diagram showing a state in which a weight, a fixed frame, and each beam are formed by the manufacturing apparatus shown in FIG.

FIG. 8 shows an example of a conventional capacitive acceleration sensor,
(A) is a perspective view, (b) is a C-C sectional view of (a)

[Explanation of symbols]

 5 Weight 51 Movable electrode 52 Movable electrode 6 Fixed frame 61 Fixed electrode 62 Fixed electrode 7A Beam 7B Beam 7C Beam 7D Beam 7E Beam 7F Beam

Claims (5)

[Claims] 1. An insulative weight made of a quadrangular plate, an insulative fixing frame provided on each side surface of the weight at a distance from each other, one opposite side surface of the weight and both side surfaces thereof. To each inner surface of the fixed frame facing each other, each movable electrode provided to each of the other opposite side surfaces of the weight, and the fixed frame facing each of these movable electrodes. A capacitive acceleration sensor, comprising: each fixed electrode provided on an inner surface thereof. 2. The beam according to claim 1, wherein each beam is provided between a portion of one side surface of the weight close to both ends of the opposite side surface and each inner side surface of the fixed frame which faces these portions. Four
A capacitive acceleration sensor characterized by comprising individual beams. 3. The device according to claim 1 or 2,
The weight, the fixed frame, and each beam are made of insulating silicon having a high specific resistance, and each movable electrode and each fixed electrode are formed by doping the insulating silicon having a high specific resistance with impurities to reduce the specific resistance. A capacitive acceleration sensor, which is made of silicon. 4. The method according to claim 1 or 2,
A capacitive acceleration sensor characterized in that the weight, fixed frame and each beam are made of insulating resin. 5. The method of manufacturing a capacitive acceleration sensor according to claim 4, wherein the weight, the fixing frame and the respective beams are formed by irradiating an uncured ultraviolet curable resin with ultraviolet rays.