JP2004286652A - Acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a cantilever from being stuck by flow-in of moisture or the like, by simple structure without complicating structure itself of a movable electrode. <P>SOLUTION: A fluid 11 having elasticity, a shock absorbing property or viscosity such as gel is sealed between a fixed electrode 1 and a movable structure such as the movable electrode 2, and the sticking and binding are thereby prevented while moderating abrupt fluctuation of the movable structure such as the movable electrode. A through hole 20 is provided in the movable structure such as the movable electrode to enhance flowability of the fluid. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an acceleration sensor that detects acceleration based on a capacitance between a fixed electrode and a movable electrode.
[0002]
[Prior art]
4 and 5 show a schematic configuration of a conventional surface-processed G sensor, and are a perspective view including a cross section and a cross-sectional view, respectively. In this surface-processed G sensor, a plurality of pairs of fixed electrodes 1 and movable electrodes 2 are opposed to each other in an acceleration detection direction (X direction) by forming grooves in a semiconductor substrate (Si substrate) 10 and an oxide film (SiO ₂ ) 10a. To form a capacitor. A plurality of movable electrodes 2 are formed in a comb-like shape so as to extend in the ± Y direction with respect to the weight 3 extending in the X direction. At both ends of the weight 3, two beams 4 which can be displaced in the X direction are formed.
[0003]
In such a configuration, when an acceleration in the X direction is applied to this sensor, the beam 4 is displaced in the X direction, thereby causing the fixed electrode 1 and the movable electrode 2 to move as shown in FIGS. The distance between the electrodes changes and the capacitance between the fixed electrode 1 and the movable electrode 2 changes. Then, the acceleration can be detected by taking out the generated change in capacitance from the movable electrode 2 and converting it into a voltage.
[0004]
By the way, in such an acceleration sensor, as shown in FIGS. 6A and 6B, a change in the distance between the electrodes 1 and 2 is detected as a change in capacitance. Needs to have a fine structure because it is used as a capacitor. Further, in the conventional example, as shown in FIG. 7, a gas 5 such as a nitrogen atmosphere is sealed between a fixed electrode 1 and a movable structure such as a movable electrode 2 so that an influence from the outside world (for example, penetration of moisture or the like) is obtained. ) Is prevented. However, such a conventional structure has the following problems.
[0005]
-Operation failure caused by sticking (contact / adhesion) due to moisture adsorption (may occur even in the manufacturing process and after completion).
-Malfunctions caused by clogging between cantilevers due to particles (dust, etc.) (mainly in the manufacturing process).
Damage and sticking of the cantilever due to vibration due to resonance frequency, excessive impact, etc. (may occur even during the manufacturing process and after completion).
-The cantilever vibrates indefinitely due to the application of force (acceleration). If continuous vibration is applied, the vibration changes to large vibration or high-speed vibration, causing breakage or sticking of the cantilever.
・ Because of gas filling, the dielectric capacity is small, and the area between the cantilevers is required to be small while maintaining a large area.
[0006]
In order to solve the problem such as the adhesion of the movable electrode and the fixed electrode, Japanese Patent Application Laid-Open Publication No. H11-163,897 discloses a conventional beam structure and manufacturing method. Further, Japanese Patent Application Laid-Open No. H11-163,897 discloses a technique in which a stop portion of a movable electrode is formed to prevent a capacitance portion from adhering. Further, Patent Document 3 below discloses a technique in which a movable electrode is prevented from adhering by a cleaning step using a vapor phase.
[0007]
[Patent Document 1]
JP-A-11-51966 [Patent Document 2]
JP-A-11-68122 [Patent Document 3]
Japanese Unexamined Patent Publication No. Hei 8-510598
[Problems to be solved by the invention]
However, in the above conventional example, the structure of the movable electrode itself is devised in order to prevent the attachment of the movable electrode, and thus there is a problem that the structure itself of the movable electrode becomes complicated.
[0009]
The present invention has been made in view of the problems of the conventional example described above, and has a simple structure without complicating the structure of the movable electrode itself. It is an object of the present invention to provide an acceleration sensor capable of preventing a reduction in capacity of a cantilever due to resonance, and the like.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is characterized in that a viscous fluid is sealed between a movable structure including a movable electrode and a fixed electrode.
With the above configuration, a viscous fluid is sealed between the movable structure including the movable electrode and the fixed electrode, so that the structure of the movable electrode itself is simple without complicating the structure itself, and the sticking of the cantilever due to the inflow of moisture or the like. Further, it is possible to prevent the cantilever from being damaged due to excessive acceleration, the capacity between the cantilevers from being reduced, and the cantilever from being damaged due to resonance.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a main part of an embodiment of an acceleration sensor according to the present invention, FIG. 2 is a process diagram showing an example of a method for producing a fluid in FIG. 1, and FIG. 3 is a modified example of the acceleration sensor in FIG. FIG.
[0012]
In FIG. 1, the movable electrode 11 shown in FIGS. 4 and 5 and a movable structure such as the movable electrode 2 are filled with an elastic, shock-absorbing, or viscous fluid 11 such as a gel so as to be movable. While alleviating sudden fluctuations of the electrode 2, sticking and clogging are prevented. When the fluid 11 having a high dielectric constant ε is used, C = ε · S / d (C is the capacitance between the electrodes, S is the facing area between the electrodes, and d is the distance between the electrodes), so that even a fine force (acceleration) can be obtained. The capacitance change ΔC increases, and the detection sensitivity increases. In addition, by improving the sensitivity, the distance d between the electrodes 1 and 2 can be increased, clogging by particles is improved, and processing becomes easier. In addition, since it is not a gas, sticking and clogging of the electrodes 1 and 2 due to moisture (due to particles or the like) can be improved.
[0013]
Next, a method of sealing the fluid 11 will be described. After creating a movable structure including the movable electrode 2 and the like, a buffer material 12 such as a gel is poured and sealed. However, if the buffer material 12 is a fluid, there is a possibility of sticking at the time of pouring. 1. A method of spraying the gel in a fine crystal (solid) state at a low temperature onto a cantilever and then returning the temperature to normal temperature. 2. Method of spraying the cantilever in a high temperature steam state to return to normal temperature A method of returning the sticking portion by ultrasonic waves after enclosing the buffer material may be considered.
The buffer material 12 may be in a fine solid state, but since it is difficult to embed the buffer material uniformly, a liquid having fluidity is preferable because the change in capacitance becomes clear. Further, as a material of the fluid 11, it is desirable that the fluid 11 has as small a change in viscosity, a change in volume, and a change in volume as possible even when the temperature changes.
[0014]
FIG. The following shows the method of encapsulation. First, as shown in FIG. 2A, a movable structure such as a fixed electrode 1 and a movable electrode 2 is formed, and then, as shown in FIG. The buffer material 12 is vapor-deposited in between, and then the temperature is returned to normal temperature as shown in FIG.
[0015]
Further, according to the above configuration, as shown in FIG. 3, by providing the through hole 20 in the movable structure such as the movable electrode 2, the fluidity of the fluid 11 is improved, which is more effective.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a main part of an embodiment of an acceleration sensor according to the present invention.
FIG. 2 is a process chart showing an example of a method for producing the fluid of FIG.
FIG. 3 is a configuration diagram showing a modification of the acceleration sensor of FIG. 1;
FIG. 4 is a perspective view showing a schematic configuration of a conventional surface-processed G sensor, including a cross section.
5 is a cross-sectional view of the surface-processed G sensor of FIG.
FIG. 6 is an explanatory diagram showing the principle of detecting the capacitance of the acceleration sensor.
FIG. 7 is a configuration diagram showing a main part of a conventional acceleration sensor.
[Explanation of symbols]
Reference Signs List 1 fixed electrode 2 movable electrode 5 gas 10 semiconductor substrate (Si substrate)
10a oxide film (SiO ₂ )
11 fluid 12 cushioning material 20 through hole

Claims (2)

In an acceleration sensor that detects acceleration based on a capacitance between a fixed electrode and a movable electrode,
An acceleration sensor, wherein a viscous fluid is sealed between a movable structure including the movable electrode and the fixed electrode. The acceleration sensor according to claim 1, wherein a through hole through which the fluid can flow is formed in the movable electrode.

Images