Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
1998-02-18
2001-03-13
Saadat, Mahshid (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
C257S417000, C438S050000, C438S052000
Reexamination Certificate
active
06201284
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a capacitance detecting type acceleration sensor and a manufacturing method thereof, capable of simultaneously measuring acceleration along either two axes or three axes, applicable to a vibration measurement, a vehicle control, and a motion control.
2. Description of Related Art
As sensors for detecting acceleration applied to a moving object, there are various sorts of sensors such as piezoelectric type sensors, distortion gauge type sensors, magnetic type sensors for using differential transformers, and capacitance type sensors for detecting capacitance changes in capacitors. Very recently, especially, as the acceleration sensors with utilizing the micromachining technique in the semiconductor field, a great attention is paid to the acceleration sensors with using the piezoelectric effect, the electric resistance value of which is varied in response to external mechanical force, and the acceleration sensor for calculating the acceleration by detecting changes in the capacitors. These sensors own various merits such as compactness of devices, mass-productivity, higher precision, and higher reliability. In particular, the acceleration sensor for electrically detecting the acceleration based on the changes in the capacitance value of the capacitor is disclosed in, for example, J-P-A 8-32090 (J-P-A: Japanese Patent unexamined publication.
FIG. 9
is an explanatory diagram for showing an example of the conventional capacitance type acceleration sensor described in J-P-A 8-32090. FIG.
9
(
a
) is a plan view, and FIG.
9
(
b
) is a sectional view. The variable electrode
1
corresponding to the silicon mass body is supported via the beam
3
by an anchor portion
2
. The fixed electrodes
4
and
5
b
are formed with defining a constant space on the side surface of this mass body. The capacitors
10
and
11
are formed by the mass body
1
and the fixed electrodes
4
and
5
b
. As seen from the A—A sectional view of
FIG. 9
, the sensor structure containing these auxiliary supporting unit
7
is jointed to the glass substrate
8
a
and the glass substrate
9
b
by the anode jointing method, and the region used to form the capacitors is hermetically sealed. These capacitors
10
and
11
constitute the sensor element
12
. When inertial force caused by acceleration is exerted along the x-direction of the mass body
1
, the mass body
1
is displaced along the x-direction. One electric capacitance defined between the mass body
1
and the fixed electrodes
4
,
5
is increased (C×1=C+&Dgr;C) by the displacement, whereas the other capacitance defined between the mass body
1
and the fixed electrodes
4
,
5
is decreased (C×2=C−&Dgr;C) by the displacement.
This capacitance change is converted into the voltage output by the IC-formed detecting chip (ASIC), so that this acceleration can be derived as the voltage output. This IC-formed detecting chip owns the capacitance-to-voltage converting circuit having:
Vout=
C×
1/(
C×
1
+C×
2)·
Vs
In this formula, symbol “Vout” indicates the voltage output, and symbol “Vs” shows the input voltage.
In the case that the above-described acceleration sensor, this acceleration sensor is limited to the acceleration measurement of the one axial direction (x direction). Accordingly, when the acceleration along the two axial directions, or the three axial directions is measured, two sets of the sensor elements and of the ASICs are required, so that the dimension of the package for storing the sensor elements and the ASICs is increased. Therefore, there is a problem that the manufacturing cost is increased.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-described conventional problems, and has an object to provide a low-cost multi-axis acceleration sensor and a manufacturing method thereof, capable of measuring acceleration along either two axial directions or three axial directions.
A first aspect of the present invention is a multi-axis acceleration sensor for detecting acceleration along directions of plural axes of the present invention which comprises:
at least one mass body made of a single crystal silicon wafer and arranged within a plane of said silicon wafer;
at least two cantilever beams arranged in parallel to each other, capable of displacing said mass body along a plurality of directions and of holding said mass body in such a manner that vibration forms of said mass body are defined to be parallel moved along said wafer plane direction;
at least one fixed electrode which is electrically insulated from said cantilever beams and said mass body, and is arranged each direction, opposite to each other via a constant space every acceleration detecting direction of said each mass body so as to detect displacement of said mass body caused by the acceleration along the plural directions; and
displacement detecting means for detecting the displacement of said mass body by applying a constant voltage between said fixed electrode and said mass body.
A second aspect of the present invention is the multi-axis acceleration sensor according to the first aspect of the present invention, wherein:
the mass body comprises two mass bodies are arranged within said wafer plane in such a manner that said cantilever beams are positioned perpendicular to each other;
said fixed electrode is arranged opposite to said mass body along the acceleration detecting direction within said wafer plane; and
the acceleration along the two axial directions within said wafer plane is detected.
A third aspect of the present invention is the multi-axis acceleration sensor according to the first aspect of the present invention, wherein:
first and second mass bodies are arranged within said wafer plane in such a manner that said cantilever beams are positioned perpendicular to each other; and
said fixed electrode contains a first fixed electrode arranged opposite to said first mass body along the acceleration detecting direction within said wafer plane, and a second fixed electrode arranged opposite to said second mass body along an acceleration detecting direction outside said wafer plane; whereby:
a detection is made of the acceleration of two axes along the detection directing within the wafer plane, and of one axis along the detecting direction outside the wafer plane.
A fourth aspect of the present invention is the multi-axis acceleration sensor according to the first aspect of the present invention, wherein
wherein a multi-axis acceleration detecting sensor is comprised of: a mass body “a” displaced with respect to one axis within the wafer plane, and a beam structure holding this mass body “a”; an edge portion of this beam structure is connected to a mass body “b” formed at a peripheral portion of the mass body “a”; in which the beam structure for holding the mass body “b” owns such a structure that the beam structure is displaced perpendicular to a displacement direction of the mass body “a”; more than one fixed electrodes are provided via a constant space and positioned opposite to the acceleration detecting directions within the wafer plane of the respective mass bodies; and the respective fixed electrodes are electrically insulated from the beam and the mass bodies to thereby detect the acceleration of two axes along the detecting directions within the wafer plane.
According to a fifth structure of the present invention, a multi-axis acceleration detecting sensor is comprised of: a mass body “a” displaced with respect to one axis within the wafer plane, and a beam structure holding this mass body “a”; an edge portion of this beam structure is connected to a mass body “b” formed at a peripheral portion of the mass body “a”; in which the beam structure for holding the mass body “b” owns such a structure that the beam structure is displaced perpendicular to a displacement direction of the mass body “a”; an edge portion of a beam of the mass body “b” is connected to amass body “c” formed
Hirata Yoshiaki
Konno Nobuaki
Tsugai Masahiro
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
Saadat Mahshid
Wilson Allan R.
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