Inertia force sensor

Details Inertia force sensor Inertia force sensor

2002-11-21

2004-05-18

Kwok, Helen C. (Department: 2856)

Measuring and testing

Speed, velocity, or acceleration

Angular rate using gyroscopic or coriolis effect

C073S504020, C073S504120

Reexamination Certificate

active

06736008

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an inertia force sensor including a silicon structure formed on an insulating substrate and, more particularly, to an accelerometer or an angular velocity sensor used for vehicle posture control of automobile or collision detection in an air bag system.
2. Description of the Related Art
FIG. 10
is an exploded perspective view showing an example of the structure of an inertia force sensor I of the prior art.
The inertia force sensor I includes a silicon structure
2
, a lower glass substrate
7
that has a recess
7
a
that forms a clearance space on the surface thereof and an upper glass substrate
6
that has a recess
6
a
on the surface thereof. The inertia force sensor has such a constitution as the silicon structure
2
is sandwiched by the lower glass substrate
7
and the upper glass substrate
6
that are bonded with the silicon structure, so that the recess
6
a
and the recess
7
a
face inward. The inertia force sensor is hermetically sealed. The upper glass substrate
6
has electrode lead-out portions
8
,
9
that penetrate the substrate and are used for connection with an external circuit. The electrode lead-out portions
8
,
9
make contact with metallic electrodes
331
,
421
of the silicon structure
2
, respectively, thereby establishing electrical continuity. Surface of the recess
6
a
of the upper glass substrate
6
is covered with a metal film
10
that prevents movable electrode portions to be described later from sticking onto the upper glass substrate when applying anodic bonding of the silicon structure
2
and the upper glass substrate
6
.
The silicon structure
2
includes a movable portion
3
and a fixed portion
4
, that are functional sections, and a frame portion
5
that surrounds and protects the two functional sections, as shown FIG.
11
. The movable portion
3
includes a movable electrode portion
31
, a pair of beam portions
32
that support the movable electrode portion
31
in the air, and a pair of support portions
33
,
33
that support the beam portion
32
and are bonded to the lower glass substrate
7
. The movable electrode portion
31
includes a base portion
311
, a comb-shaped electrode portion for the movable part
312
that consists of a plurality of cantilever electrodes
312
a
disposed at equal intervals on both sides of the base portion
311
in the longitudinal direction and extending over the recess
7
a
from the base portion
311
, and a pair of weights
313
,
313
that are connected to both ends of the base portion
311
and increase the displacement of the movable portion
3
due to inertia force, with these components being formed in a single piece.
Each of the pair of fixed portions
4
,
4
includes a fixed electrode portion
41
and a support portion
42
that supports the fixed electrode portion
41
and is bonded onto the lower glass substrate
7
. The fixed electrode portion
41
has a comb-shaped electrode portion for the fixed part
411
including a plurality of cantilever electrodes
411
a
that extend over the recess
7
a
and are disposed to oppose, with a very small distance, the plurality of cantilever electrodes
312
a
of the movable electrode section
31
. Each pair of the cantilever electrode
312
a
and the cantilever electrode
411
a
forms a capacitive electrode.
Reference numeral
11
denotes a first stopper portion that restricts the movable portion
3
from making an excessive displacement in the direction of the inertia force, and includes a movable protruding portion
313
a
consisting of corners of the weight portion
313
and a fixed protruding portion
42
a
disposed on the support portion
42
. When the movable portion
3
is displaced, the movable protruding portion
313
a
and the fixed protruding portion
42
a
of the support portion
42
are brought into contact with each other, thereby restricting an excessive displacement. Reference numeral
12
denotes a second stopper portion that functions similarly to
11
, and includes the movable protruding portion
313
a
consisting of corners of the weight portion
313
and a fixed protruding portion
33
a
consisting of the protruding portion disposed in the support portion
33
. An example of a cantilever type accelerometer provided with a stopper portion is disclosed in Japanese Laid-open Patent Publication No. 6-308151, Japanese Laid-open Patent Publication No. 8-43436 and Japanese Laid-open Patent Publication No. 11-94872.
FIG. 12
is a longitudinal sectional view taken along lines XII-XII′ in
FIG. 11
, showing the silicon structure
2
bonded with the upper glass substrate
6
and the lower glass substrate
7
.
Silicon is machined to form the silicon structure by reactive ion etching (hereinafter referred to as ICP-RIE) that uses inductively coupled plasma (ICP) as an activation energy source. Since the ICP-RIE process is free from anisotropy of etching due to the crystal orientation of silicon, degree of freedom in the design of the silicon structure configuration can be made much higher than in the case of conventional alkaline wet process, thereby allowing etching operation with high accuracy. An example of angular velocity sensor fabricated by employing the ICP-RIE process is described by S. Kobayashi et al., “Double-frame Silicon Gyroscope Packaged Under Low Pressure By Wafer Bonding”, Proc. of Transducers, ′99, pp. 910-913.
SUMMARY OF THE INVENTION
The present inventors have found out the problems described below in the inertia force sensor of the prior art.
FIG. 13
is a schematic plan view showing an example of the state of the inertia force sensor I under an excessive inertia force F. While the movable protruding portion
313
a
and the fixed protruding portion
42
a
that constitute the first stopper portion
11
shown at the left-hand side of drawing make contact with each other, the movable protruding portion
313
a
and the fixed protruding portion
33
a
that constitute the second stopper portion
12
shown at the left-hand side of drawing make contact with each other, thereby restricting the movable portion
3
from making an excessive displacement under the inertia force F. FIG.
14
and
FIG. 15
are schematic plan views showing the first stopper portion
11
and the second stopper portion
12
in
FIG. 13
, respectively, in enlarged view. As shown in
FIG. 14
, there have been such cases as the movable protruding portion
313
a
and the fixed protruding portion
42
a
make violent contact and break in the first stopper portion
11
. This leads to such problems as the movable portion
3
being cracked or chips of broken silicon entering minute gaps of the silicon structure, thus resulting in lower reliability of the sensor due to malfunction or failure of the sensor. Also as shown in
FIG. 15
, the same problem as in the first stopper portion
11
can occur in the second stopper portion
12
. Also the corner of the weight portion
313
of the movable electrode portion
31
may hit the cantilever electrode
411
a
disposed at the distal end of the fixed electrode portion
41
thereby cutting off the cantilever electrode
411
a
, resulting in lower reliability of the sensor due to malfunction or failure of the sensor.
An object of the present invention is to solve the problems described above and to provide an inertia force sensor that has higher reliability by preventing the sensor from being damaged by excessive displacements due to inertia force.
The inertia force sensor of the invention, in order to achieve the object described above, includes insulating substrates and a silicon structure that is bonded between the insulating substrates with clearance space secured therebetween, wherein the silicon structure has a movable portion and a fixed portion, with the movable portion having a movable electrode portion that is capable of making displacement in the direction of inertia force, a pair of beam structures for the movable portion that are connected to both ends of the movable electrode portion and support the m

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