U.S. patent application number 09/727087 was filed with the patent office on 2001-06-07 for resonant element.
Invention is credited to Kawai, Hiroshi, Ohwada, Kuniki.
Application Number | 20010002551 09/727087 |
Document ID | / |
Family ID | 18370902 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010002551 |
Kind Code |
A1 |
Kawai, Hiroshi ; et
al. |
June 7, 2001 |
Resonant element
Abstract
A resonant element includes: a fixed substrate having a main
surface in orthogonal X- and Z-directions; a planar vibrating body
fixed via support beams so as to be vibratable in an X-direction,
the planar vibrating body having a weight portion which is isolated
from the fixed substrate; an exciter for vibrating the planar
vibrating body in the X-direction, and means for adjusting the
resonance frequency of said planar vibrating body by providing
electrostatic forces to said planar vibrating body, and for
correcting the tilt of said planar vibrating body with respect to
the substrate plane direction of said fixed substrate, the tilt
correcting means being provided at least opposing edge areas of
said planar vibrating body with a gap therebetween in the
X-direction, on the plane side and spaced from said planar
vibrating body in a Y-direction orthogonal to the X- and
Z-directions.
Inventors: |
Kawai, Hiroshi;
(Yokohama-shi, JP) ; Ohwada, Kuniki;
(Hachiojo-shi, JP) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Family ID: |
18370902 |
Appl. No.: |
09/727087 |
Filed: |
November 30, 2000 |
Current U.S.
Class: |
73/504.12 |
Current CPC
Class: |
G01P 15/0802 20130101;
G01C 19/5719 20130101 |
Class at
Publication: |
73/504.12 |
International
Class: |
G01P 003/44 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 1999 |
JP |
11-344648 |
Claims
What is claimed is:
1. A resonant element comprising: a fixed substrate having a main
surface extending in orthogonal X- and Z-directions; a planar
vibrating body connected to the fixed substrate via support beams
so as to be vibratable in the X-direction, the planar vibrating
body having a resonance frequency and a weight portion which is
isolated from the fixed substrate; an exciter for vibrating the
planar vibrating body in the X-direction, and tilt correcting means
providing electrostatic forces to said planar vibrating body to
adjust the resonance frequency of said planar vibrating body and to
correct the tilt of said planar vibrating body with respect to the
main surface of said fixed substrate.
2. A resonant element as claimed in claim 1, wherein: the tilt
correcting means is provided at least at opposing edge areas of
said planar vibrating body with a gap in the X-direction
therebetween and is spaced from said planar vibrating body in a
Y-direction orthogonal to said X- and Z-directions.
3. A resonant element as claimed in claim 1, wherein: said planar
vibrating body has a frame body disposed above and isolated from
the fixed substrate and wherein the weight portion is connected to
the inside of said frame body by connection beams.
4. A resonant element as claimed in claim 1, wherein: the tilt
correcting means comprises a first tilt correcting element and a
second tilt correction element, the first tilt correcting element
being provided at least at opposing edge areas of said weight
portion with a gap in the X-direction therebetween and being spaced
from said planar vibrating body in the Y-direction, and the second
tilt correcting element is provided at positions opposed to said
frame body and across said first vibrating body tilt correcting
means via gaps in the X-direction.
5. A resonant element as claimed in any one of claims 1-4, wherein:
stress canceling means are provided for directly or indirectly
applying to said support beams forces in a direction such as to
counteract any tensile stresses within said support beams caused by
electrostatic attractive forces given to said planar vibrating body
by said vibrating body tilt correcting means.
6. A resonant element as claimed in claim 5, wherein: said stress
canceling means are provided so as to be opposed to said vibrating
body tilt correcting means and so as to sandwich said vibrating
body between said stress canceling means and said vibrating body
tilt correcting means via gaps.
7. A resonant element as claimed in claim 6, wherein: said stress
canceling means are structured and arranged to cancel the tensile
stresses within said support beams by providing electrostatic
attractive forces to said vibrating body.
8. A resonant element as claimed in any one of claims 1 through 4,
wherein: a vertical movement side electrode is provided on at least
one of a front surface and a rear surface of said weight portion,
and a fixed opposing electrode is disposed on a side opposed to
said vertical movement side electrode and spaced from said weight
portion in the Y-direction, the set of said vertical movement side
electrode and said fixed opposing electrode functioning as a
detecting electrode for detecting a vibration amplitude of said
weight portion in the Y-direction due to an angular velocity being
applied to said vibrating body about the Z-direction, the vibration
amplitude corresponding to variation in the angular velocity of the
rotation around the Z-axis.
9. A resonant element as claimed in claim 8, wherein: said stress
canceling means are provided so as to be opposed to said vibrating
body tilt correcting means and so as to sandwich said vibrating
body between said stress canceling means and said vibrating body
tilt correcting means via intervals.
10. A resonant element as claimed in claim 9, wherein: said stress
canceling means are structured and arranged to cancel the tensile
stresses within said support beams by providing electrostatic
attractive forces to said vibrating body.
11. A resonant element as claimed in claim 8, wherein: said weight
portion is formed of silicon or polysilicon, and serves as the
movement side electrode.
12. A method for adjusting the vibration of a resonant element
comprising the steps of: providing a resonant element including a
fixed substrate having a main surface extending in orthogonal X-
and Z-directions, a planar vibrating body fixed via support beams
so as to be vibratable in the X-direction, the planar vibrating
body having a resonance frequency and a weight portion which is
isolated from the fixed substrate; an exciter for vibrating the
planar vibrating body in the X-direction, and tilt correcting means
providing electrostatic forces to said planar vibrating body to
adjust the resonance frequency of said planar vibrating body and to
correct the tilt of said planar vibrating body with respect to the
main surface of said fixed substrate; detecting a resonance
frequency of said planar vibrating body; adjusting said resonance
frequency to a desired value using said tilt correcting means;
detecting tilt of said planar body with respect to the main surface
of said fixed substrate; and correcting the tilt of said planar
body with respect to the main surface of said fixed substrate using
said tilt correcting means.
13. A method for adjusting the vibration of a resonant element in
an angular velocity sensor and then determining angular velocity,
comprising: providing a resonant element including a fixed
substrate having a main surface in orthogonal X- and Z-directions,
a planar vibrating body fixed via support beams so as to be
vibratable in the X-direction, the planar vibrating body having a
weight portion which is isolated from the fixed substrate, an
exciter for vibrating the planar vibrating body in the X-direction,
tilt correcting means for providing electrostatic forces to said
planar vibrating body to adjust the resonance frequency of said
planar vibrating body and to correct the tilt of said planar
vibrating body with respect to the main surface of said fixed
substrate, a vertical movement side electrode is on at least one of
a front surface and a rear surface of said weight portion, and a
fixed opposing electrode is disposed on a side opposed to said
vertical movement side electrode and spaced from said weight
portion in the Y-direction, the set of said vertical movement side
electrode and said fixed opposing electrode functioning as a
detecting electrode for detecting a vibration amplitude of said
weight portion in the Y-direction due to an angular velocity being
applied to said vibrating body about the Z-direction, the vibration
amplitude corresponding to variation in the angular velocity of the
rotation around the Z-axis; detecting a resonance frequency of said
planar vibrating body; adjusting said resonance frequency to a
desired value using said tilt correcting means; detecting tilt of
said planar body with respect to the main surface of said fixed
substrate; correcting the tilt of said planar body with respect to
the main surface of said fixed substrate using said tilt correcting
means; applying an angular velocity to said resonant element about
a Y-axis orthogonal to said X- and Z- directions to cause said
resonant body to vibrate in the Z-direction due to a Coriolis
force; and detecting the vibrating amplitude of said weight portion
in the Y-direction using said detecting electrode to determine the
angular velocity of the rotation around the Z-axis.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a resonant element used as
an angular velocity sensor, filter, or the like.
[0003] 2. Description of the Related Art
[0004] FIG. 7A is a perspective view showing a previous resonant
element 16. The resonant element 16 is a microelement produced
utilizing a conventional silicon micromachining technique and the
like. More specifically, the resonant element 16 is produced by
forming a nitride film 7 on a silicon substrate 1, then forming a
polysilicon film 5 thereover, and forming the films 7 and 5 into a
predetermined pattern by dry etching or the like.
[0005] The substrate 1 functions as a fixed substrate of which the
substrate plane direction is an X-Z two-dimensional plane
direction. A weight portion 2 is disposed above the substrate in a
state isolated from the substrate 1. In the resonant element 16
shown in FIG. 7A, the weight portion functions as a planar
vibrating body 10. The planar vibrating body 10 is supported via
support beams 3 so as to be vibratable in the X-direction. One end
side of each of the support beams 3 is fixed to the substrate 1 via
a fixing portion 35.
[0006] Comb electrodes 6B are formed on both sides of the planar
vibrating body 10 outwardly in the transverse direction
(X-direction), and comb electrodes 6A are each disposed inwardly in
the transverse direction at positions opposed to and interdigitated
with the comb electrodes 6B. Conductive layers for driving 11A and
11B are connected to the comb electrodes 6A and 6B, respectively,
and are connected with outside electrode pads (not shown) via
conductor patterns (not shown), and thus form an exciter 4.
[0007] Once an AC voltage is applied to these conductive layers for
driving 11A and 11B of the exciter 4, an electrostatic force is
generated between the comb electrodes 6A and 6B, and the planar
vibrating body 10 is vibrated in the arrow F direction
(X-direction) by this electrostatic force.
[0008] When the resonant element 16 is rotated around the Z-axis
while the planar vibrating body 10 is vibrated in the X-direction
by driving the comb electrodes 6A and 6B, a Coriolis force occurs
in the Y direction orthogonal to the above-described X-Z
two-dimensional plane direction. The Coriolis force is applied to
the planar vibrating body 10 constituted of the weight portion 2,
and the planar vibrating body 10 vibrates in the direction of the
Coriolis force. By measuring an electric signal corresponding to
the magnitude of the vibration amplitude of the planar vibrating
body 10 due to the Coriolis force, for example, the magnitude of
the rotational angular velocity can be detected.
[0009] In the case where the resonant element 16 is used as an
angular velocity sensor, there is provided a detecting portion for
measuring the electric signal corresponding to the magnitude of the
vibration amplitude of the planar vibrating body 10 due to the
Coriolis force.
[0010] When the resonant element 16 is produced, the resonance
frequency of the planar vibrating body 10 in the direction of the
Coriolis force (Y-direction) is previously set at the design stage
to the resonance frequency in the X-direction, and the shape,
dimension, weight, etc. of the planar vibrating body 10 are
designed and produced so that the above-mentioned resonance
frequency is obtained. In many cases, however, the shape,
dimension, weight, etc. of the planar vibrating body 10 are not
achieved as designed, because of the machining accuracy of silicon
micromachining technique. Accordingly, deviation of the resonance
frequency of the planar vibrating body 10 from the designed
frequency often occurs. If the vibration of the planar vibrating
body 10 is in a resonant state, the amplitude is greatly amplified
by virtue of the value of the Q (quality factor) related to the
structure, but if the frequency deviates, a problem arises in that
the amplitude is not nearly amplified as much, resulting in the
sensitivity of the resonant element begin significantly reduced. It
is, therefore, necessary to perform trimming with respect to the
weight portion 2 and/or the support beams 3 by, for example, a
complicated machining process, to thereby adjust the resonance
frequency of the planar vibrating body 10 to the design
frequency.
[0011] Since the resonant element 16 is, however, a minute resonant
element 16, it is practically impossible because of the accuracy of
conventional mechanical trimming techniques to perform trimming of
the minute weight portion 2 and/or support beams 3 so as to have
the desired dimensions, shape, and weight, etc. It is, therefore,
very difficult to adjust the resonance frequency of the planar
vibrating body 10 to a set value.
[0012] Therefore, in the resonant element 16, as shown in FIG. 7B,
a conductive layer 12 for providing an electrostatic attractive
force 15 is located at a position opposed to the weight portion 2
in the Y-direction with a gap therebetween. As shown in FIG. 7A,
the conductive layer 12 is connected to a conductive pad 14 via a
conductive pattern 13. By controlling the voltage to be applied to
the conductive layer 12 via the conductive pattern 13 and
conductive pad 14, the resonance frequency of the resonant element
16 is adjustable to a set value.
[0013] Once a DC voltage is applied to the conductive layer 12, an
electrostatic force acts on the planar vibrating body 10 as an
electrostatic spring. Specifically, when the planar vibrating body
10 vibrates in the direction such that the planar vibrating body 10
approaches the substrate 1, an electrostatic force acts in the
direction such that the amplitude is increased, and hence the
application of the DC voltage to the conductive layer 12 has an
effect of generating a force in the opposite direction as if a
mechanical spring were being compressed. This results in a
reduction in the resonance frequency in the Y-direction. Since this
reduced amount of the resonance frequency varies in accordance with
the electrostatic attractive force 15, a fine-adjustment of the
resonance frequency of the planar vibrating body 10 from the
natural frequency thereof to the lower frequency side can be
performed by adjusting the magnitude of the DC voltage applied to
the conductive layer 12.
[0014] Utilizing this effect, by designing the natural resonance
frequency of the planar vibrating body 10 in the Y-direction to be
slightly higher than the most sensitive resonance frequency (the
resonance frequency in the X-direction), i.e., by designing the
resonance frequency of the planar vibrating body 10 in the
detection direction to be higher than the resonance frequency
thereof by the exciter 4 in the vibrational direction, the
sensitivity of the resonant element 16 can be increased by
adjusting the DC voltage applied to the conductive layer 12.
[0015] In the resonant element 16, it is important to adjust the
resonance frequency thereof to a set value and to keep the
vibrating state of the planar vibrating body 10 on-target. FIGS. 6A
and 6B illustrate examples of movements of a planar vibrating body
10 in the X-Y plane without angular velocity around the Z-axis,
when the planar vibrating body 10 is vibrated in the X-direction.
In the resonant element 16 shown in FIGS. 7A and 7B, if the
vibration of the planar vibrating body 10 is deflecting in the
Y-direction, which is the detection direction, that is, if the
planar vibrating body 10 tilts with respect to the substrate plane,
a Coriolis force cannot be accurately measured if this tilt is
substantial, and the gyro characteristics of the angular velocity
sensor or the like deteriorates.
[0016] It is therefore desirable that the vibratory state of the
planar vibrating body 10 hardly exhibits any deflection in the
Y-direction, as shown in FIG. 6B.
[0017] Generally, the less the difference (.DELTA.f) in the
resonance frequency of the planar vibrating body 10 between the
vibrational direction and detection direction, the larger the
mechanical coupling between the two directions (the propagation of
a mechanical energy and the interaction between the two vibration
modes) becomes and the larger the deflection in the detection
direction while the resonant element 16 is driven becomes. In
particular, the dimensional error or the residual stress when the
resonant element is produced, increases this mechanical
coupling.
[0018] In the resonant element 16, therefore, even if the
difference (.DELTA.f) in the resonance frequency of the planar
vibrating body 10 between the vibrational direction and detection
direction is reduced in order to increase the sensitivity thereof,
a Coriolis force can not be accurately measured, if the deflection
amount in the detection direction increases. As a result, a
resonant element 16 having high sensitivity and accuracy can not be
obtained only by reducing the above-described difference (.DELTA.f)
in the resonance frequency through providing a conductive layer 12.
It has therefore been difficult to achieve a resonant element 16
wherein the difference (.DELTA.f) in the resonance frequency is
small and wherein the deflection in the detection direction is
small, and the yield of the resonant elements 16 capable of meeting
both characteristics has been very low.
[0019] In principle, it is possible to perform mechanical trimming
in a conventional resonant element 16 having a dimensional error or
the like so as to reduce the deflection amount of the planar
vibrating body 10 in the detection direction; however, from a
practical standpoint, it is not practicable to perform mechanical
trimming while evaluating the deflection amount of the planar
vibrating body 10.
[0020] It is also impractical and would take an extremely long time
to bring the deflection amount to zero by performing repeated
trimming operation in such a way that the deflection amount of the
planar vibrating body 10 is ascertained after trimming, and that
trimming is again performed. Accordingly, there is a need for a
resonant element 16 which allows the difference (.DELTA.f) in the
resonance frequency of the planar vibrating body 10 between the
vibrational direction and the detection direction to be small and
which allows the deflection in the detection direction to be small,
without the need for the above-described repetitive trimming.
SUMMARY OF THE INVENTION
[0021] The present invention has been made in order to solve the
above-described problems. It is an object of the present invention
to provide a resonant element allowing both the difference
(.DELTA.f) in the resonance frequency of the planar vibrating body
10 between the vibrational direction and the detection direction
and the deflection in the detection direction to be small, without
the need for troublesome trimming.
[0022] In order to achieve the above-described object, the present
invention has the following constitutions. In a first aspect, a
weight portion is disposed above a fixed substrate in a state
isolated from said fixed substrate, of which the substrate plane
direction is an X-Z two-dimensional plane direction; a planar
vibrating body comprising said weight portion is supported by said
fixed substrate via support beams so as to be vibratable in an
X-direction; an exciter for vibrating the planar vibrating body in
the X-direction is provided; and vibrating body tilt correcting
means for adjusting the resonance frequency of the planar vibrating
body by giving electrostatic forces to the planar vibrating body
thereby correcting the tilt of the planar vibrating body with
respect to the substrate plane direction of the fixed
substrate.
[0023] In accordance with another aspect, the tilt correcting means
are provided at least at the both edge areas of the planar
vibrating body with a gap therebetween in the X-direction and are
spaced from the vibrating body in a Y-direction orthogonal to the
X-Z two-dimensional plane direction.
[0024] In accordance with another aspect, the planar vibrating body
comprises a frame body disposed above the fixed substrate in a
state isolated from the fixed substrate, and a weight portion
connected to the inside of the frame body by connection beams.
First vibrating body tilt correcting means are provided at least at
the both edge areas of the weight portion with a gap therebetween
in the X-direction and spaced from the vibrating body in the
Y-direction. Second vibrating body tilt correcting means are
provided at positions opposed to the frame body and across the
first vibrating body tilt correcting means via gaps in the
X-direction.
[0025] In accordance with another aspect, the stress canceling
means are provided which directly or indirectly applies to the
support beams a force in a direction such that the tensile stresses
within the support beams are canceled, the tensile stresses being
caused by electrostatic attractive forces given to the planar
vibrating body by the vibrating body tilt correcting means.
[0026] In accordance with another aspect, the stress canceling
means are arranged so as to sandwich the planar vibrating body
between the stress canceling means and the vibrating body tilt
correcting means via gaps.
[0027] In accordance with another aspect, a vertical movement side
electrode is provided on at least one of the front surface and rear
surface of the weight portion, and a fixed opposing electrode is
provided on the side opposed to the vertical movement side
electrode with a gap interposed in the Y-direction; and the set of
the vertical movement side electrode and the fixed opposing
electrode are formed as a detecting electrode for detecting the
vibration amplitude of the weight portion in the Y-direction caused
by a variation in an angular velocity of rotation applied to the
resonant element around the Z-axis.
[0028] In accordance with another aspect, the weight portion is
formed of silicon or polysilicon, and constitutes a vertical
movement side electrode in itself.
[0029] In the present specification and claims, the term "both edge
areas" represents a wider concept including areas somewhat inside
both edge portions or areas somewhat outside both edge portions in
the planar vibrating portion or the weight portion.
[0030] In accordance with the present invention, both the
adjustment of the resonance frequency of the planar vibrating body
and the correction of the tilt of the planar vibrating body with
respect of the substrate plane direction of the fixed substrate can
be performed by the described vibrating body tilt correcting means.
It is thereby possible, without the need for troublesome trimming,
to reduce the difference between the vibrational direction of the
planar vibrating body vibrating by a Coriolis force and the
detection direction thereof, as well as to reduce the deflections
in the detection direction, and to create thereby a superior
resonant element having a high sensitivity and a low noise
level.
[0031] In the resonant element wherein the planar vibrating body
comprises a frame body and a weight portion, and wherein first
vibrating body tilt correcting means are provided at least at both
edge areas of the weight portion, and wherein second vibrating body
tilt correcting means are provided at positions opposed to the
frame body and across the first vibrating body tilt correcting
means via a gap in the X-direction, the resonance frequency of the
planar vibrating body comprising the weight portion and the frame
body can be adjusted, and the tilt of the weight portion and the
frame body with respect to the plane of the substrate can be
individually corrected.
[0032] Furthermore, in the resonant element in accordance with the
present invention, when the weight portion is connected to the
inside of the frame body by the connection beams, the movement of
the frame body and the weight portion can be made independent of
each other by the construction of the connection beam so that, for
example, when the planar vibrating body vibrates in the X-direction
and rotates around the Z-axis, only the weight portion vibrates in
the Y-direction but the frame body hardly vibrates. This allows the
planar vibrating body to perform excitation vibration more stably
in the vibrational direction.
[0033] Moreover, in the resonant element in accordance with the
present invention wherein stress canceling means is provided, since
a force in a direction such that tensile stresses within the
support beams caused by electrostatic forces given to the planar
vibrating body by the vibrating body tilt correcting means are
counteracted can be applied to the support beams directly or
indirectly by the stress canceling means, the occurrence of various
problems caused by any troublesome tensile stresses within the
support beams can be reliably avoided. This allows a resonant
element having a higher sensitivity and a lower noises to be
provided.
[0034] Also, in accordance with the present invention wherein a
vertical movement side electrode is provided on at least one of the
front surface and rear surface of the weight portion (or where the
weight portion itself serves as the vertical movement side
electrode), and wherein a fixed opposing electrode is provided at
the side opposed to the vertical movement side electrode with a gap
interposed in the Y-direction, and wherein the set of the vertical
movement side electrode and the fixed opposing electrode are
constituted as a detecting electrode for detecting the vibration
amplitude of the weight portion in the Y-direction due to an
angular velocity around the Z-axis, a variation in an angular
velocity of the rotation around the Z-axis can be accurately
detected by the detecting electrode.
[0035] For the purpose of illustrating the invention, there is
shown in the drawings several forms which are presently preferred,
it being understood, however, that the invention is not limited to
the precise arrangements and instrumentalities shown.
[0036] Other features and advantages of the present invention will
become apparent from the following description of the invention
which refers to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0037] FIG. 1A is a perspective view showing the construction of
the main section of a resonant element in accordance with a first
embodiment of the present invention, and FIG. 1B is a cross
sectional view taken along the line A-A in FIG. 1A.
[0038] FIGS. 2A to 2D are explanatory cross sectional views showing
the production process of the resonant element in accordance with
the first embodiment.
[0039] FIG. 3A is a perspective view showing the construction of
the main section of a resonant element in accordance with a second
embodiment of the present invention, and FIG. 3B is a cross
sectional view taken along line B'-B' in FIG. 3B.
[0040] FIGS. 4A to 4C are explanatory views showing a resonant
element in accordance with a third embodiment of the present
invention.
[0041] FIG. 5A is a plane view showing a resonant element in
accordance with another embodiment of the present invention, and
FIG. 5B is a cross sectional view taken along line B'-B' in FIG.
5A.
[0042] FIGS. 6A and 6B are explanatory views illustrating examples
of movements of a planar vibrating body in the X-Y plan when the
planar vibrating body is vibrated in the X-direction in a resonant
element.
[0043] FIG. 7A a perspective view illustrating an example of a
conventional resonant element, and 7B is a cross sectional view
taken along line A-A in FIG. 7A.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0044] Hereinbelow, the embodiments in accordance with the present
invention will be explained based on the drawings. In the
descriptions of these embodiments, the same components as the
above-described previous resonant element are identified by the
same reference numerals and a repetition of detailed descriptions
thereof are omitted.
[0045] FIGS. 1 A and 1 B show a first embodiment of a resonant
element 16 in accordance with the present invention. As in the case
of the above-described previous resonant element 16, the first
embodiment of the resonant element 16 is a microelement produced
utilizing a silicon micromachining technique or the like, and is
used, for example, in an angular velocity sensor or the like.
[0046] As is the case with the previous resonant element 16 in
FIGS. 7A and 7B, the first embodiment of the resonant element 16
comprises a planar vibrating body 10 and an exciter 4 utilizing the
electrostatic forces of comb electrodes 6A and 6B.
[0047] It has been found that the above-described deflections of
the planar vibrating body 10 in the detection direction are
principally attributable to the tilt of the planar vibrating body
10 with respect to the substrate plane direction of the fixed
substrate 1. In this first embodiment, therefore, a vibrating body
tilt correcting means have been provided specifically for adjusting
the resonance frequency of the planar vibrating body and correcting
the tilt of the planar vibrating body 10 with respect to the
substrate plane direction of the fixed substrate 1.
[0048] More specifically, in this first embodiment, as shown in
FIG. 1B, two conductive layers 23 and 24 are provided at both edge
areas of the planar vibrating body 10 with a gap in the X-direction
therebetween, on the plane of the substrate 1 opposed to the plane
of the planar vibrating body 10 with a gap interposed in the
Y-direction, and these conductive layers 23 and 24 are used as
vibrating body tilt correcting means for adjusting the resonance
frequency of the planar vibrating body 10 by providing
electrostatic attractive forces 21 and 22 to the planar vibrating
body 10, and correcting the tilt of the planar vibrating body 10
with respect to the substrate plane direction of the fixed
substrate 1.
[0049] As shown in FIG. 1A, the conductive layer 23 is connected to
a conductive pad 27 via a conductive pattern 25, and the conductive
layer 24 is connected to a conductive pad 28 via a conductive
pattern 26.
[0050] In the first embodiment, the resonance frequency (fy= 5.5 Hz
for example) of the planar vibrating body 10 in the detection
direction is designed to be somewhat (500 Hz) higher than the
resonance frequency (fx= 5 kHz for example) of the planar vibrating
body 10 by an exciter 4 in the vibrational direction (i.e., the
X-direction).
[0051] FIGS. 2A to 2D show the production process of the resonant
element in accordance with the first embodiment. As shown in FIG.
2A, first a nitride film 7 is formed on the outer periphery side on
the silicon substrate 1, and on the central portion of the
substrate 1, conductive layers 23 and 24 as vibrating body tilt
correcting means doped with phosphorus P or boron B, are formed
with a gap therebetween in the X-direction therebetween. The
formation positions of the conductive layers 23 and 24 are arranged
to be both edge areas of the weight portion 2 (planar vibrating
body 10) which is to be formed above the substrate 1 in an isolated
state at a later step.
[0052] Then, as illustrated in FIG. 2B, a sacrificial layer 8 such
as an oxide film is formed over the conductive layers 23 and 24 so
as to lie astride the nitride film 7 on the outer periphery
side.
[0053] Next, as illustrated in FIG. 2C, a polysilicon film is
formed over the nitride film 7 and the sacrificial film 8, and
forms the patterns of the weight portion 2 and the comb electrodes
6A and 6B. Then, as shown in FIG. 2D, the sacrificial layer 8 is
removed by, for example, dry etching, and the weight portion 2 is
formed so as to be isolated from the substrate 1 and constitutes
the planar vibrating body 10. By disposing these conductive layers
22 and 23 at both edge areas of the planar vibrating body 10 so as
to be opposed to each other, the resonant element 16 is
accomplished.
[0054] The first embodiment of the resonant element 16 is produced
as described above, and has a construction as shown in FIGS. 1A and
2B. As described with respect to the above-described previous
resonant element, the planar vibrating body 10 can be vibrated by
driving the exciter 4 in the X-direction orthogonal to the length
of the support beam 3. Once the resonant element 16 is rotated
around the Z-axis at this state, a Coriolis force occurs. This
Coriolis force is applied to the planar vibrating body 10, and the
planar vibrating body 10 vibrates in the direction of the Coriolis
force (Y-direction). Measurement of this vibration amplitude allows
the angular velocity to be detected.
[0055] Also, in the first embodiment, since the conductive layers
23 and 24 have been provided as means for correcting the tilt of
the planar vibrating body 10, it is possible, when vibrating the
planar vibrating body 10, to pull both edge areas opposed to the
conductive layers 23 and 24, as shown in FIG. 1B, toward the
substrate 1 by the electrostatic attractive forces 21 and 22 by
individually applying DC voltages to the conductive layers 23 and
24 via the conductive pads 27 and 28, respectively, and to thereby
perform a tilt correction with respect to the planar vibrating body
10. By performing a tilt correction, the vibrational deflections in
the detection direction of the planar vibrating body 10 can be
corrected.
[0056] Specifically, when the planar vibrating body 10 vibrates, if
the planar vibrating body 10 tilts downwardly to the right as
indicated by a broken line A in FIG. 1B, a DC voltage higher than
that applied to the conductive layer 24 is applied to the
conductive layer 23, and the edge region side of the planar
vibrating body 10 opposed to the conductive layer 23 is pulled
toward the substrate 1 side more strongly than the edge region of
the planar vibrating body 10 opposed to the conductive layer 24,
whereby the downward tilt to the right is corrected.
[0057] In contrast to this, if the planar vibrating body 10 tilts
downwardly to the left as indicated by a broken line B in FIG. 1B,
a DC voltage higher than that applied to the conductive layer 23 is
applied to the conductive layer 24. By pulling the edge region side
of the planar vibrating body 10 opposed to the conductive layer 24
toward the substrate 1 side more strongly than the edge region of
the planar vibrating body 10 opposed to the conductive layer 23,
the downward tilt to the left is corrected.
[0058] The conductive layer 23 and 24 each function for correcting
the tilt of the planar vibrating body 10, and simultaneously
function as means for adjusting the resonance frequency of the
planar vibrating body 10. That is, the conductive layer 23 and 24
can lower the resonance frequency of the planar vibrating body 10
in the detection direction by pulling the planar vibrating body 10
toward the substrate 1 side by the electrostatic forces 21 and 22
due to the application of DC voltages to the respective conductive
layers 23 and 24. Hence, by previously designing the resonance
frequency of the planar vibrating body 10 in the detection
direction to be slightly higher than that of the vibratory
frequency, and by lowering the resonance frequency of the planar
vibrating body 10 in the detection direction through pulling the
planar vibrating body 10 toward the substrate 1, the difference
(.DELTA.f) in the resonance frequency between the driving direction
and the detection direction of the planar vibrating body 10 can be
adjusted to be small.
[0059] In other words, in the first embodiment, by adjusting the DC
voltages applied to the conductive layers 23 and 24, it is possible
to correct the tilt of the planar vibrating body 10, and
simultaneously to adjust the difference (.DELTA.f) in the resonance
frequency between the driving direction and the detection direction
of the planar vibrating body 10 to be small by lowering the
resonance frequency of the planar vibrating body 10 in the
detection direction by an appropriate value.
[0060] Suppose, in the resonant element 16, the displacement
(deflection amount) in the detection direction (Y-direction) of the
planar vibrating body 10 with respect to the displacement in the
driving direction (X-direction) thereof is not less than 5 percent
when not applying DC voltages to the conductive layers 23 and 24,
or when applying equal DC voltages to the conductive layers 23 and
24. At this time, for example, the voltage to be applied to the
conductive layer 23 is set to 0, and the voltage to be applied to
the conductive layer 24 is varied from 0 to 20 V (or, conversely,
the voltage to be applied to the conductive layer 24 is set to 0,
and the voltage to be applied to the conductive layer 23 is varied
from 0 to 20 V). Thereby, an applied voltage value is found which
allows the tilt of the planar vibrating body 10 to be correct and
which allows the displacement in the detection direction of the
planar vibrating body 10 with respect to the displacement in the
driving direction thereof to be not more than 2 percent.
[0061] Suppose that the above-described displacement (deflection
amount) of not more than 2 percent can be achieved when the voltage
to be applied to the conductive layer 23 is set to 0, and the
voltage to be applied to the conductive layer 24 is set to 10 V. At
this time, a DC voltage (0+ a) V is applied to the conductive layer
23, and a DC voltage (10+ b) V is applied to the conductive layer
24 (where both a and b have positive values, and are adjusted to
make the difference (.DELTA.f) in the resonance frequency between
the driving and detection directions small. Thereby, the resonance
frequency of the planar vibrating body 10 in the detection
direction which has been designed to be rather higher than that in
the vibrational direction, can be adjusted to be smaller, so that
the difference (.DELTA.f) in the resonance frequency between the
driving direction and the detection direction can be adjusted to be
small.
[0062] Such an adjustment allows the deflection amount due to the
tilt of the of the planar vibrating body 10 with respect of the
plane of the substrate 1 to be not more than 2 percent, and allows
the difference (.DELTA.f) in the resonance frequency between the
driving direction and the detection direction to be made small. It
has been experimentally verified that the detection sensitivity of
the resonant element 16 increases from about 0.9 degree/sec. to
about 0.3 degree/sec. That is, about a three-fold (0.9/0.3)
increase in detection sensitivity (resolution) has been achieved.
Furthermore, an increase of even more than three-fold can be
attained depending on conditions of the planar vibrating body 10,
the support beams 3, or the magnitude of the DC voltage to be
applied to the conductive layers 23 and 24.
[0063] In accordance with this first embodiment, as described
above, the conductive layers 23 and 24 as vibrating body tilt
correcting means for performing the resonance frequency adjustment
and the tilt correction with respect to the planar vibrating body
10 are disposed with a gap in the X-direction therebetween, at the
positions on the substrate 1 opposed to the planar vibrating body
10. By appropriately adjusting the value of the DC voltage to be
applied to these conductive layers 23 and 24, the difference in the
resonance frequency between the driving direction and the detection
direction of the planar vibrating body 10 can be adjusted to be
small and the tilt of the planar vibrating body 10 can be reduced.
It is therefore possible to make this resonant element 16 a
superior resonant element 16 having a high sensitivity and a low
noise level, without being bound by errors occurring during the
production process or a change in use circumstances, and without
the need for mechanical trimming of the planar vibrating body 10 or
support beams 3.
[0064] In particular, in this first embodiment, the conductive
layers 23 and 24 are provided at both edge areas of the planar
vibrating body 10 with a gap in the X-direction therebetween,
thereby the distance between the gravity position of the weight
portion 2 which is the planar vibrating body 10, and the position
where the electrostatic forces 21 and 22 are applied, may be
increased. This provides increased leverage, therefore, the tilt of
the planar vibrating body 10 can be corrected even by small
electrostatic forces 21 and 22, and the magnitude of the voltage
applied to the conductive layers 23 and 24 via the conductive pads
27 and 28 can be reduced. As a result, the upsizing of the resonant
element 16 is rendered unnecessary, and a small resonant element 16
can be achieved.
[0065] Also, in this first embodiment, if a vertical movement side
electrode 30 is provided on the surface of the weight portion 2, as
shown in FIG. 2D, for example, and a fixed opposing electrode 31 is
provided on the side opposed to the vertical movement side
electrode 30 with a gap interposed in the Y-direction, and if the
set of the vertical movement side electrode and the fixed opposing
electrode are constituted as a detection electrode for angular
velocity around the Z-axis for detecting the vibration amplitude of
the weight portion in the Y-direction corresponding to the
variation in the angular velocity of the rotation around the
Z-axis, it is possible to detect the angular velocity by detecting
the Coriolis force in the Y-direction generated by the rotation
around the Z-axis, as described above.
[0066] When the fixed opposing electrode 31 is thus disposed on the
opposite side of the substrate 1 side, the resonant element 16 can
be formed, as indicated by the chain line in FIG. 2(D), by fixing
the fixed opposing electrode 31 on a cover 32 made of e.g. glass
and by bonding the glass cover to a polysilicon film 5 at a bonded
portion 34 by means of anode bonding. Alternatively, the resonant
element 16 can be formed by previously vapor depositing a metal
such as gold on the bonded portion 34, and performing eutectic
bonding with respect to the bonded portion 34.
[0067] In FIG. 3A, the construction of the main section of a
resonant element 16 in accordance with a second embodiment of the
present invention is shown as a perspective view. In FIG. 3B, a
sectional view taken along the line B-B in FIG. 3A is shown. In the
descriptions of this second embodiment, the same components as the
above-described first embodiment are identified by the same
reference numerals, and repeated explanations thereof are
omitted.
[0068] The resonant element 16 in accordance with the second
embodiment is an angular velocity sensor. The difference between
this second embodiment and the above-described first embodiment is
characterized in that, firstly, as shown in FIG. 3A, the planar
vibrating body 10 is constructed so as to have a frame body 36
disposed above the substrate 1 in a isolated state, and have the
weight portion 2 connected to the inside of the frame body 36 by
connection beams 40, and that, secondly, as shown in FIG. 3B, the
resonant element 16 is constructed by providing the conductive
layers 23A and 24A as the first vibrating body tilt correcting
means, and the conductive layers 23B and 24B as the second
vibrating body tilt correcting means. The conductive layers 23A and
24A are disposed at both edge areas of the weight portion 2 with a
gap in the X-direction therebetween, on the side of substrate 1
opposed to the planar vibrating body 10, and the conductive layers
23B and 24B are disposed at the positions across the conductive
layers 23A and 24A via a gap in the X-direction.
[0069] The conductive layers 23A, 24A, 23B, and 24B are each
connected to conductive pads (not shown) via individual patterns
(not shown). In this second embodiment, by adjusting the DC voltage
to be applied to each of the conductive pads and, thereby,
providing electrostatic forces 21A, 22A, 21B, and 22B to the planar
vibrating body 10, the resonance frequency of the planar vibrating
body 10, and the tilt of the planar vibrating body 10 with respect
to the substrate plane direction of the substrate 1 can be
adjusted.
[0070] In this second embodiment, the weight portion 2 is formed of
e.g. silicon or polysilicon, thereby, weight portion 2 itself
performs the function of a vertical movement side electrode 30. On
the substrate 1 opposed to the weight portion 2 with a gap
interposed in the Y-direction, a fixed opposing electrode 31 is
provided, the set of the weight portion 2 (vertical movement side
electrode 30) and the fixed opposing electrode 31 is constituted as
a detecting electrode for angular velocity around the Z-axis for
detecting the vibration amplitude of the weight portion in the
Y-direction, the vibration amplitude corresponding to the variation
in the angular velocity of the rotation around the Z-axis.
[0071] Also, in this second embodiment, the substrate 1 is made of
glass. A vibrator, fixation portion, etc. having a planar vibrating
body 10 and support beams 3 are formed on the substrate 1 by
micromachining a silicon layer having a thickness of 50 mm.
Furthermore, in this second embodiment, as in the cases of the
above-described previous resonant element and the first embodiment,
conductive layers for driving (not shown) are each connected to the
comb electrodes 6a and 6B, and are connected to external electrode
pads (not shown) via conductive patterns to form an exciter 4.
[0072] The two connection beams 40 are disposed along the
Z-direction orthogonal to the X-direction which is the vibrational
direction on the right-side of the weight portion 2. The weight
portion 2 is connected to the right side (as viewed in FIGS. 2A and
2B) of the rectangular frame body 36 by the connection beams 40.
The connection beams 40 formed so that the thickness in the
Y-direction which is the detecting vibration direction of the
weight portion 2, is less than 50 mm, and so that the rigidity in
the Y-direction is smaller than that in the X-direction which is
the vibrational direction of the planar vibrating body 10. On the
other hand, the support beams 3 are formed so that the rigidity in
the X-direction which is the vibrational direction of the planar
vibrating body 10 is smaller than that in the Y-direction which is
the detecting vibration direction of the weight portion 2.
[0073] In FIGS. 3A and 3B, reference numeral 50 designates a recess
constituting a cavity, reference numeral 20 designates a connection
electrode for the weight portion 2 (i.e., for the vertical movement
side electrode 30), and reference numeral 33 designates a
connection electrode for the fixed opposing electrode 31.
[0074] The second embodiment is constituted so that conductive
layers 23A and 24A are provided at the positions corresponding to
both edge areas of the weight portion 2 of the planar vibrating
body 10 for pulling the weight portion 2 toward the substrate 1
side by the electrostatic attractive forces 21A and 22A, and so
that conductive layers 23B and 24B are provided at the positions
across the conductive layers 23A and 24A corresponding to the frame
body 36 for pulling the frame body 36 toward the substrate 1 side
by the electrostatic attractive forces 21B and 22B. This allows the
resonance frequency in the Y-direction of the planar vibrating body
10 having the weight portion 2 and the frame body 36 to be
adjusted, and also allows the tilts of the weight portion 2 and the
frame body 36 with respect to the plane of the substrate 1 to be
individually corrected.
[0075] The second embodiment can, therefore, exert a similar
effects to the above-described first embodiment.
[0076] Moreover, in the second embodiment, the planar vibrating
body 10 is constructed so as to have the frame body 36 and the
weight portion 2, and the planar vibrating body 10 is formed so
that the rigidity of connection beams 40 for connecting the frame
body 36 and the weight portion 2 with respect to the Y-direction is
smaller than the rigidity thereof with respect to the X-direction,
and that the rigidity of support beams 3 for supporting the planar
vibrating body 10 and with respect to the X-direction is smaller
than the rigidity thereof with respect to the Y-direction. Thereby,
it becomes possible that, when the planar vibrating body 10
vibrates in the X-direction and rotates around the Z-axis, only the
weight portion vibrates in the Y-direction and the frame body
hardly vibrates in the Y-direction. As a result, there is no risk
that the comb electrode 6B is displaced in the Y-axis direction
with respect to the comb electrode 6A, so that the planar vibrating
body 10 always can stably perform an excitation vibration
maintaining the magnitude of the amplitude corresponding to the
voltage applied to the above-described conductive layers for
driving, and can detect the angular velocity around the Z-axis with
a higher accuracy.
[0077] In addition, in the second embodiment, since the connection
beams 40 are provided along the Z-direction orthogonal to the
X-direction which is the vibrational direction of the planar
vibrating body 10, there is no risk that movement due to
acceleration caused by the vibration of the planar vibrating body
10 occurs in the torsional direction of the weight portion 2,
causing fluctuating components in the vertical direction. As a
result, this moment does not affect the Coriolis force generated in
the Y-direction, which leads to a detection of the rotational
angular velocity with a higher accuracy.
[0078] Now a third embodiment will be described hereinbelow with
reference to FIGS. 4A to 4C. The third embodiment is characterized
in that stress canceling means are provided. Other constructions
are similar to the above-described first and second embodiments. In
the descriptions of this third embodiment, the same components as
the above-described first and second embodiments are identified by
the same reference numerals and repeated descriptions thereof are
omitted.
[0079] When the vibrating body tilt correcting means (conductive
layers 23 and 24) are provided as described above, and the planar
vibrating body 10 is pulled toward the substrate 1 by electrostatic
forces, tensile stresses are generated within the support beams 3.
This raises concerns that these tensile stresses of the support
beams 3 cause the vibration amplitude of the planar vibrating body
10 to be somewhat reduced, resulting in a reduction in the
sensitivity thereof, or that the tensile stresses within the
support beams 3 momentarily disturb the planar vibrating body 10,
resulting in the generation of noise in an electric signal for
detection.
[0080] Accordingly, the third embodiment is arranged so that forces
which counteract the tensile stresses, are applied to the support
beams 3 by providing the above-described stress canceling means.
FIG. 4A shows an example in the case where the above-described
stress canceling means is added to the resonant element 16 shown in
FIG. 1, while FIG. 4B shows an example in the case where the
above-described stress canceling means is added to the resonant
element 16 shown in FIGS. 3A and 3B. As illustrated in FIGS. 4A and
4B, in this third embodiment, conductive layers 41 and 42 (41A,
41B, 42A, and 42B) which are stress canceling means, are disposed
so as to be opposed to the above-described vibrating body tilt
correcting means (conductive layers 23 and 24 (23A, 23B, 24A, and
24B)) with the plane of the planar vibrating body 10 interposed,
and so as to sandwich the planar vibrating body between these
conductive layers and the vibrating body tilt correcting means via
gaps.
[0081] The conductive layers 41 and 42 (41A, 41B, 42A, and 42B) are
constructed so that a DC voltage is applied to them via conductive
patterns (not shown), and once a DC voltage is applied to these
conductive layers 41 and 42 (41A, 41B, 42A, and 42B), electrostatic
attractive forces attracting each other occur between the
conductive layers 41 and 42 (41A, 41B, 42A, and 42B) and the planar
vibrating body 10, and the planar vibrating body 10 is pulled up,
in the upward direction in FIGS. 4A to 4C.
[0082] Thereby, forces in directions to counteract the tensile
stresses, are indirectly applied to the support beams 3, the forces
being caused by the above-described vibrating body tilt
corresponding means. Hence, it is possible to substantially cancel
the above-described tensile stresses of the support beams 3 by
adjusting the magnitudes of the DC voltages to be applied to the
above-described conductive layers 41, 42 (41A, 41B, 42A, and 42B).
For example, letting the magnitudes of the electrostatic attractive
forces applied to the planar vibrating body 10 when DC voltages are
applied to the conductive layers 23, 24, 41, and 42 be F23, F24,
F41, and F42, respectively, the magnitudes of the DC voltages to be
applied to the conductive layers 23, 24, 41, and 42 are determined
so that the equation F23+ F24= F41+ F42 holds. Thereby, the
above-described tensile stresses within the support beams can be
substantially canceled.
[0083] In accordance with this third embodiment, since any
troublesome tensile stresses within the support beams 3 are
canceled by the stress canceling means, the occurrence of various
problems caused by the tensile stresses within the support beams 3
can be reliably avoided. This allows the planar vibrating body 10
to make an ideal vibration, and allows a resonant element having a
higher sensitivity and lower noise to be provided.
[0084] The present invention is not limited to the above-described
embodiments. Various embodiments can be adopted. For example, in
the above-described first embodiment, the conductive layers 23 and
24 are provided only at both edge areas of the planar vibrating
body 10, but the conductive layers 23 and 24 may be provided at
least at both edge areas, that is, the conductive layers 23 and 24
may be provided at some portions other than both edge areas. Also,
in the above-described first embodiment, the planar vibrating body
10 (weight portion 2) is formed of polysilicon, but may be formed
of silicon. When using the resonant element 16 shown in the first
embodiment as an angular velocity sensor, the vertical movement
side electrode 30 is disposed at the weight portion 2, but the
present invention may be arranged so that the weight portion 2
itself functions as a vertical movement side electrode.
[0085] In the above-described second embodiment, the conductive
layers 23A and 24A as the first vibrating body tilt correcting
means are provided only at both edge areas of the weight portion 2,
but the conductive layers 23A and 24A may be provided at least at
the weight portion 2, that is, the conductive layers 23A and 24A
may be provided at some portions other than both edge areas.
However, as shown in FIG. 3A, when the fixed opposing electrode 31
is provided under the weight portion 2, the conductive layers 23A
and 24A are each disposed at positions which do not interfere with
the position of the fixed opposing electrode 31.
[0086] Also, in the above-described second embodiment, the
connection beams 40 are disposed at the right side of the weight
portion 2, and the weight portion 2 is connected to the right side
of the frame body 36 by the connection beams 40. However, the
connection beams 40 may be disposed at the left side of the weight
portion 2, and the weight portion 2 may be connected to the frame
body 36 in a straddle-mounted beam state by disposing the
connection beams 40 on both sides of the weight portion. Also, the
connection beams may be disposed along the X-direction. However, it
is preferable that the connection beams be disposed along the
Z-direction in order to detect the rotational angular velocity
around the Z-axis without being subjected to the effect of
acceleration generated by vibration by disposing the connection
beams 40 along the Z-direction.
[0087] In addition, when the frame body 36 and the planar vibrating
body 10 are connected to one another using L-letter shaped
connection beams 40, as shown in FIGS. 5A and 5B, the tips of the
shorter sides 46 of the L-letter shaped connection beams 40 are
each connected to the four comers of the weight portion 2, and the
longer sides 47 of the L-letter shaped connection beams 40 are each
extended from the comers where the tips of the L-letter shaped
shorter sides 46 are connected, along the sides of the weight
portions 2 via a gap to the sides of the frame body 36 where the
tips of the longer sides 47 are connected to the sides of the frame
body 36.
[0088] In this case also, as in the case of the above-described
second embodiment, by providing the conductive layers 23A, 24A,
23B, and 24B, the conductive patterns 25A, 26A, 25B, and 26B
connected to the conductive layers 23A, 24A, 23B, and 24B, and the
conductive pads 27A, 28A, 27B, and 28B, as shown in Figs SA and 5B,
and by pulling the weight portion 2 toward the substrate 1 side by
the electrostatic attractive forces 21A and 22A, as well as by
pulling the frame body 36 toward the substrate 1 side by the
electrostatic attractive forces 21B and 22B, a similar effect to
that of the above-described second embodiment can be achieved. Also
in the resonant element 16 having the configuration shown in FIGS.
5A and 5B, by providing the conductive layers 41A, 1B, 42A, and
42B, as shown in FIG. 4C, which are the stress canceling means as
described with reference to the above described third embodiment, a
similar effect to that of the third embodiment can be exerted.
[0089] In the above-described first and second embodiments, the
conductive layers 23 and 24 are extended along the sides of both
edges of the planar vibrating body 10, but the arrangement may be
such that a plural of minute conductive layers are formed so as to
be arranged along the sides of both edges of the planar vibrating
body 10. In this case, it is preferable that the plurality of
minute conductive layers include minute conductive layers opposed
to the four comers of the rectangular planar vibrating body 10.
[0090] Furthermore, in the above-described second embodiment,
although the weight portion 2 performs itself functions as a
vertical movement side electrode, another vertical movement side
electrode 30 may be provided on at least one of the surface side
and the rear side of the weight portion 2. If a vertical movement
side electrode 30 is disposed on the surface side of the weight
portion 2, for example, in the same state as that shown in FIG. 2D,
a cover 32 or the like opposed to the weight portion 2 is provided,
and a fixed opposing electrode is disposed on the cover 32 or the
like.
[0091] In the above-described first embodiment, a vertical movement
side electrode 30 may be disposed on the rear surface of the weight
portion 2, and a fixed opposing electrode 31 may be disposed at the
position opposed to the weight portion 2 above the substrate 1.
[0092] Also, in each of the above-described first and second
embodiments, the conductive layers 23 and 24 (23A, 23B, 24A, and
24B) each performing the functions of vibrating body tilt
correcting means are disposed on the substrate 1, but when the
cover 32 covering the planar vibrating body 10 is provided, these
conductive layers 23 and 24 (23A, 23B, 24A, and 24B) may be
disposed on the cover 32 in place of the substrate. In this case
also, as is the case with the above-described embodiments, the
conductive layers 23 and 24 are disposed at both edge areas of the
planar vibrating body 10. When the conductive layers 23 and 24
(23A, 23B, 24A, and 24B) each performing the functions of vibrating
body tilt correcting means are thus disposed on the cover 32, if
the conductive layers 41 and 42 which are stress canceling means
shown in the above-described third embodiment are provided, these
the conductive layers 41 and 42 are disposed so as to be opposed to
the substrate 1 with the plane of the substrate 1 interposed so as
to sandwich the planar vibrating body 10 between the conductive
layers 41 and 42 and the above-mentioned conductive layers 23 and
24.
[0093] In the above-described third embodiment, the arrangement is
such that forces in a direction such that tensile stresses within
the support beams are counteracted, are applied to the support beam
3, but, for example, conductive layers which are stress canceling
means may be provided so that electrostatic attractive forces may
be directly given to the support beams 3.
[0094] In each of the above-described embodiments, the planar
vibrating body 10 is a structure fixed at opposite ends, but the
planar vibrating body 10 may be constructed by a one-side fixed
method (e.g., cantilever method).
[0095] Also, in each of the above-described embodiments, the
resonant element 16's were described as being used in angular
velocity sensors, but the planar vibrating body 10 in accordance
with present invention can also be used in other type devices.
[0096] While preferred embodiments of the invention have been
disclosed, various modes of carrying out the principles disclosed
herein are contemplated as being within the scope of the following
claims. Therefore, it is understood that the scope of the invention
is not to be limited except as otherwise set forth in the
claims.
* * * * *