JP2741861B2 - Vibrator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microscopic vibrator, and more particularly to a vibrator suitable for a physical quantity sensor using a displacement on the order of μm or less.

[Conventional technology]

A conventional vibrator is described in Japanese Patent No. 938959 or Japanese Patent Application Laid-Open No. 61-97572, and includes a support portion 101, a beam portion 102, and a mass portion 103 as shown in the sectional view of FIG. It had a cantilever type structure in which the parts were fixed.

[Problems to be solved by the invention]

The above prior art focuses on increasing the amount of deflection deformation of the beam. When bending vibration is caused by an external force, the mass portion 103 is inclined by an angle θ with respect to the reference position 104 as shown in FIG. As a result, assuming that the length of the mass part is a, an amplitude difference of Δh = a · θ occurs between the root and the tip of the mass part. As described above, the prior art does not consider the occurrence of the above-described amplitude difference due to the inclination of the mass part, and improves the sensitivity when detecting vibration due to a change in capacitance between the mass part and the opposing wall surface. There was a problem. Also,
In the prior art oscillator, a silicon single crystal is formed by anisotropic etching, so that the cross section 106 of the beam has a trapezoidal shape as shown in FIG. There is a problem that it is difficult to form the electrostrictive material and the resistance element symmetrically above and below the portion. Further, in FIG. 6, when an external force acts in the y direction, the center of gravity of the mass part and the axis in the y direction of the beam part are displaced from each other, so that there is a problem that a bending is applied due to a moment.

An object of the present invention is to provide a vibrator capable of translating a mass part in parallel with an external force only in the z direction.

Another object of the present invention is to provide a vibrator capable of accurately detecting vibration due to a change in capacitance.

[Means for solving the problem]

MEANS TO SOLVE THE PROBLEM In order to achieve the said objective, the vibrator of this invention is a mass part which receives an external force, two beams which bend and deform according to the said external force, and supports the said mass part cantilever via the two beams. A cantilever-type vibrator comprising a support portion, wherein one surface of the surface receiving the external force of the mass portion has a first electrode, the other surface has a second electrode, and the first electrode A third electrode is formed on a surface facing the second electrode, and a fourth electrode is formed on a surface facing the second electrode. The area of the surface receiving the external force of the mass part is the surface receiving the external force. Are larger than the area of the surface of the two beams on the same plane, and each of the two beams is formed of a pair of parallel plates in a direction perpendicular to the direction of the external force. A plate spring, wherein each of the pair of parallel plates is formed with a strain gauge; Characterized in that it is arranged apart by a desired distance from each other.

[Action]

Since the mass portion is cantilevered by a pair of parallel leaf springs, the beam portion can be a flexible beam that guides the mass portion in parallel. Also, by making this structure from silicon single crystal, the pair of beams can be made symmetrical with respect to the central axis of the vibrator, so that the beam is deflected by a moment due to an external force in the y direction, which is the neutral axis of the vibrator. No deformation.

Furthermore, by forming the same pattern on the front and back surfaces of one silicon single crystal and performing anisotropic etching, a pair of parallel and symmetric beams is formed. An electrostrictive element can be formed.

Embodiment An embodiment of the present invention will be described below with reference to FIG. A symmetrical pattern is formed on both sides of the silicon wafer by using a lithography technique to form a symmetrical pattern on the front and back surfaces to form a desired oscillator planar shape. Next, an etching resistant mask is formed of an oxide film by using it. Finally, when the anisotropic etching treatment is performed using a 40% aqueous solution of KOH, the vibrator of the present invention is obtained.

In this structure, the mass part 4 is supported from the support part 1 via the beam parts 2 and 3. The normal direction of mass part 4 is silicon single crystal ｛10
The 0 ° axis and the central axis y direction of the mass part 4 are {110} axes. The thickness of the mass part 4 and the support part 1 is 400 μm, the area of the mass part is 2 × 2 mm, the thickness of the beam parts 2 and 3 is 20 μm and the length is 200 μm. FIG. 2 is a cross-sectional view on the y-axis of the present invention.
The same parts as those in the drawings are denoted by the same reference numerals. The support portion 1 of the vibrator is bonded to an external fixed base 5. The beams 2 and 3 are symmetrical with respect to the center axis of the vibrator in the y direction. FIG. 3 shows a state in which the external force F is applied and the mass part 4 moves by h. Since the beams 2 and 3 act as parallel leaf spring guides, the mass 4 can only perform parallel translation.

In FIG. 2, when an external compressive force is applied in the y direction, the moment of the center of gravity G is equally applied to the beam portions 2 and 3, so that there is an advantage that the bending deformation does not occur as in the conventional example of FIG. .

FIG. 8 shows a conventional example of moving the mass part in parallel. The mass part 207 is supported via the beam parts 205 and 206 from the support parts 203 and 204 fixed to the fixing parts 201 and 202. Since this structure is a support structure at both ends, when using beams having the same cross section, in order to achieve the same amount of deflection as compared with the present invention having a cantilever structure, the length of the beam portion in the y direction is required. It becomes two parts and large. This is disadvantageous in reducing the size of the vibrator. Further, since the rotational moment due to the y-direction force applied to the center of gravity G cannot be prevented, the mass 207 is inclined.

FIG. 4 shows a second embodiment of the present invention. It comprises a support portion 31, two pairs of beam portions 32, 33, 34, 35, and a mass portion 36. Since the beam portions 32 and 33 and the beam portions 34 and 35 are provided at a predetermined distance in the x direction, the rigidity against external forces such as rotation α around the y-axis and rotation β around the z-axis is improved, Ensure only translation in the z-direction.

FIG. 5 shows an embodiment of an acceleration sensor using the vibrator of the present invention. This is a structure in which a vibrator made up of a support portion 41, beam portions 42 and 43, and a mass portion 44 is sandwiched and fixed between glass members 45 and 46, which are insulators. On the pair of beams 42 and 43, silicon diffusion type strain gauges 47 and 48 are formed. Since the shapes of the beams 42 and 43 are symmetrical with respect to the axis of the vibrator, it is easy to equalize the output characteristics of the strain gauges with respect to acceleration in both positive and negative directions. Glasses 45 and 46 have shallow grooves formed by chemical etching, and electrodes 49 and 50 are formed therein. Electrodes 51 and 52 are also formed on the surface of the mass section 44 facing these electrodes. The detection system of the acceleration sensor of the present invention has z
It amplifies the output of the strain gauges 47 and 48 due to the acceleration input from the direction, advances the phase, and applies a potential between the electrodes 49 and 51 or 50 and 52 to form a system that suppresses the vibration of the vibrator. ing. The acceleration is specified from the power required for the vibration suppression. Since the vibrator mass 44 translates, the electrodes 49 and 5
The distance between 1, 50 and 52 can be made extremely small, and in this example, it was set to 2 μm. Further, since the mass portion 44 moves in parallel, it is possible to use a damping effect by a squeezing action of a thin air layer when the electrodes approach each other.

In the method of manufacturing a pair of parallel beams described in the present invention, a predetermined opening of a SiO ₂ film mask is provided on the front and back of the (100) wafer, and the frame structure is formed by symmetrically etching from both sides. Is an application of the technology for making
87.3.11, 16th EM Symposium "Micromechanics Technology on Si Chips" by Sato et al.
Reported by IEICE).

Further, as a method of damping the vibrator, it is possible to fill the viscoelastic material VEM or a lead-based damping metal inside the beam portion of the present invention. By making the electrode larger than the beam part, it is possible to make the mass part that can be displaced by electrostatic force when the electrode is formed, electrostatic vibration detection and vibration suppression, and damping action by squeeze effect by air film Can be performed effectively. Therefore, a small, high-performance vibrator suitable for an acceleration sensor can be manufactured.

[Brief description of the drawings]

FIG. 1 is a bird's-eye view of one embodiment of the present invention, FIG. 2 is a cross-sectional view passing through the y-axis of FIG. 1, and FIG. 3 is a cross-sectional view similar to FIG. FIG. 4 shows the second embodiment of the invention.
FIG. 5 is a cross-sectional view of a third embodiment of the present invention, FIG. 6 is a cross-sectional view of a conventional example, FIG. 7 is a cross-sectional view of a conventional example, and FIG. FIG. 9 is a sectional view of an example, and FIG. 9 is a sectional view of a beam portion. 1 ... support part, 2 ... beam part, 3 ... beam part, 4 ... mass part.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Koide 1-280 Higashi Koikebo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-62-118259 (JP, A) JP-A-54-36771 (JP, A) Real opening 57-14811 (JP, U)

Claims (1)

(57) [Claims] 1. A cantilever beam type comprising a mass portion receiving an external force, two beams that bend and deform in accordance with the external force, and a support portion that cantileverly supports the mass portion via the two beams. A vibrator, a first electrode on one surface of the mass portion that receives an external force, a second electrode on the other surface, and a third electrode on a surface facing the first electrode. A fourth electrode is formed on a surface facing the second electrode, and an area of a surface of the mass portion that receives an external force is the two beams that are on the same surface as the surface that receives the external force. Each of the two beams is a parallel leaf spring composed of a pair of parallel plates in a direction perpendicular to the direction of the external force. Are each formed with a strain gauge, and the two beams are arranged at a desired distance from each other. A vibrator characterized by being made.