U.S. patent application number 10/630044 was filed with the patent office on 2005-02-03 for flexible vibratory micro-electromechanical device.
Invention is credited to Chiou, Jen-Huang Albert.
Application Number | 20050024527 10/630044 |
Document ID | / |
Family ID | 33565198 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050024527 |
Kind Code |
A1 |
Chiou, Jen-Huang Albert |
February 3, 2005 |
FLEXIBLE VIBRATORY MICRO-ELECTROMECHANICAL DEVICE
Abstract
There is a sensor element (24) for an electronic sensor device
(20). The sensor element (24) may have a substrate (43), a pair of
proof masses (34a, 34b), a set of drive beams (44), and at least
one base beam (46). The pair of proof masses (34a, 34b) are
suspended above the substrate (43) and attached to the substrate
(43) at fixed anchor points (50). The set of drive beams (44) are
positioned between the proof masses (34a, 34b) and the anchor
points (50). Each drive beam (44) has a first longitudinal body
portion (62) that extends in a first direction and a first flexible
spring member (64) that extends along a second direction. The base
beam (46) interconnects the set of drive beams (44) and has a
second longitudinal body portion (72) and a second flexible spring
member (74). The second longitudinal body portion (72) extends
along the second direction and the second flexible spring member
(74) extends along the first direction. The first and second
flexible spring members (64, 74) may be serpentine in shape, such
as folded beam-columns or wrinkle springs.
Inventors: |
Chiou, Jen-Huang Albert;
(Libertyville, IL) |
Correspondence
Address: |
MOTOROLA, INC.
1303 EAST ALGONQUIN ROAD
IL01/3RD
SCHAUMBURG
IL
60196
|
Family ID: |
33565198 |
Appl. No.: |
10/630044 |
Filed: |
July 30, 2003 |
Current U.S.
Class: |
348/373 ; 396/14;
73/504.04; 73/504.12 |
Current CPC
Class: |
G01C 19/5719
20130101 |
Class at
Publication: |
348/373 ;
073/504.04; 073/504.12; 396/014 |
International
Class: |
G01P 003/44; G01P
009/00; H04N 005/225; G01P 015/08; G01C 019/00 |
Claims
1. A sensor element for a sensor device, the sensor element
comprising: a substrate; a pair of proof masses that are attached
to the substrate at fixed anchor points, the pair of proof masses
suspended above the substrate; and a set of drive beams positioned
between the proof masses and the anchor points, the drive beams
having a first body portion that includes a first flexible spring
member that extends along a first direction and a second body
portion that includes a flexible spring member that extends along a
second direction, the second direction being perpendicular to the
first direction, the first and second flexible spring members being
configured such that a drive frequency and a sense frequency of the
proof masses are substantially aligned.
2. The sensor element of claim 1 further comprising at least one
base beam that interconnects the set of drive beams, the base beam
having a second longitudinal body portion that extends along the
second direction and a second flexible spring member that extends
along the first direction.
3. The sensor element of claim 1, wherein the flexible spring
members are serpentine in shape.
4. The sensor element of claim 1, wherein the substrate is made of
glass and the proof masses and drive beams are made of silicon.
5. The sensor element of claim 1, wherein the sensor element is
used in sensing an externally induced angular rate in a
gyroscope.
6. The sensor element of claim 1 further comprising a first pair of
electrode combs that drives the proof masses in a first direction
of a first plane at the drive frequency.
7. The sensor element of claim 6 further comprising a second pair
of electrode combs and a pair of out-of-plane electrodes, the
second pair of electrode combs capable of sensing the movement of
the proof masses in the first plane, the pair of out-of-plane
electrodes capable of sensing the movement at the sense frequency
of the proof masses in a second plane, the second plane being
different from the first plane.
8. A sensor element for a sensor device, the sensor element
comprising: a substrate; a pair of proof masses that are attached
to the substrate at fixed anchor points, the pair of proof masses
suspended above the substrate; and a set of drive beams positioned
between the proof masses and the anchor points, each drive beam
having a first body portion that extends along a first direction in
a plane and a first flexible spring member therein and a second
body portion that includes a flexible spring member that extends
along a second direction, the second direction in the plane being
perpendicular to the first direction, the first and second flexible
spring members being configured such that a drive frequency of the
proof masses in the first direction of the lane and a sense
frequency of the proof masses out of the plane are substantially
aligned and not aligned with at least one vibrational frequency
that is in the second direction in the plane.
9. The sensor element of claim 8, wherein the flexible spring
members of the drive beams are serpentine in shape.
10. (cancel).
11. The sensor element of claim 8, wherein the substrate is made of
glass and the proof masses, drive beams, and base beam are made of
silicon.
12. The sensor element of claim 8, wherein the sensor element is
used in sensing an externally induced angular rate in a
gyroscope.
13. The sensor element of claim 8 further comprising a first pair
of electrode combs that drives the proof masses in a first
direction of a first plane at the drive frequency.
14. The sensor element of claim 13 further comprising a second pair
of electrode combs and a pair of out-of-plane electrodes, the
second pair of electrode combs capable of sensing the movement of
the proof masses in the fit plane, the pair of out-of-plane
electrodes capable of sensing the movement at the sense frequency
of the proof masses in a second plane, the second plane being
different from the first plane.
15. An electronic sensor comprising: a digital processing unit; and
a sensor element, the sensor element comprising: a substrate; a
pair of proof masses that are attached to the substrate at fixed
anchor points, the pair of proof masses suspended above the
substrate; a set of drive beams positioned between the proof masses
and the anchor points, each drive beam having a first longitudinal
body portion that extends along a first direction in a plane and a
first flexible spring member therein and a second body portion that
includes a flexible spring member that extends along a second
direction in the plane, the second direction being perpendicular to
the first direction, the first and second flexible spring members
being configured such that a drive frequency of the proof masses in
the first direction of the plane and a sense frequency of the proof
masses out of the plane are substantially aligned and not aligned
with at least one vibrational frequency that is in the second
direction in the plane; and at least one base beam that
interconnects the set of drive beams, the base beam having a second
longitudinal body portion that extends along the second direction
and a second flexible spring member that extends along the first
direction.
16. The electronic sensor of claim 15, wherein the flexible spring
members of the drive beams are serpentine in shape.
17. (cancel).
18. The electronic sensor of claim 15, wherein the substrate is
made of glass and the proof masses, drive beams, and base beam are
made of silicon.
19. The electronic sensor of claim 15, wherein the sensor element
is used in sensing an externally induced angular rate in a
gyroscope.
20. The electronic sensor of claim 15, wherein the sensor element
further comprises a first pair of electrode combs that drives the
proof masses in a first direction of a first plane at the drive
frequency, the first pair of electrode combs receiving a signal
from the digital processing unit.
21. The electronic sensor of claim 20, wherein the sensor element
further comprises a second pair of electrode combs and a pair of
out-of-plane electrodes, the second pair of electrode combs capable
of sensing the movement of the proof masses in the first plane, the
pair of out-of-plane electrodes capable of sensing the movement at
the sense frequency of the proof masses in a second plane, the
second plane being different from the first plane, the second pair
of electrode combs and the pair of out-of-plane electrodes further
capable of sending signals to the digital processing unit.
Description
FIELD OF THE INVENTION
[0001] This invention in general relates to micro-electromechanical
systems (MEMS) in sensors such as gyroscopes and, more
particularly, to the use of flexible vibratory members in the
devices.
BACKGROUND OF THE INVENTION
[0002] Electronic sensor devices manufactured by MEMS technology
are playing key roles in many areas. For instance, micro mechanical
gyroscopes have enabled several important control systems in
transportation and commercial applications. Other microdevices such
as pressure sensors, accelerometers, actuators, and resonators
fabricated by MEMS technology are also used in many areas.
[0003] One type of micro gyroscope contains two movable proof
masses. The proof masses are suspended above a substrate by a
support structure. The proof masses are vibrated in the same plane
(in-plane) at a predetermined frequency by a motor in the
gyroscope. The motor may include electrodes that drive the proof
masses in the same plane in an oscillatory manner. The oscillation
of the proof masses is controlled to a frequency near the resonant
frequency of the proof masses.
[0004] In addition to a set of proof masses and drive electrodes,
the gyroscope also contains sensing electrodes around the proof
masses that report signals indicative of the movement of each proof
mass. In particular, certain electrodes sense the in-plane movement
of the proof masses. Other electrodes sense the out-of-plane
movement of the proof masses. With appropriate signal processing
and extraction circuitry, an angular rate component can be
recovered from the reported signal of the electrodes sensing the
out-of-plane movement of the proof masses.
[0005] The proof masses and support structure in conventional
gyroscopes are extremely thin. The thickness of beams in the
support structure is known to be below 10 .mu.m and the width of
the beams below 5 .mu.m, with very tight process tolerances. There
is a need to make the proof masses thicker to improve yield in mass
production and a need to relax process tolerances. This is
particularly important in low cost gyroscope devices for automobile
applications. Making the proof masses thicker, however, generates
other problems. For instance, certain frequencies of various
vibration modes become undesirable and may become more susceptive
to signal noise.
[0006] A need exists for improved mechanisms to realign frequencies
of different vibration modes of a gyroscope that uses movable proof
masses. The mechanism should allow the sensor device to use thicker
movable proof masses and support structures, which improves yield
in mass production applications. It is, therefore, desirable to
provide an improved mechanism in a sensor to overcome most, if not
all, of the preceding problems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a high-level block diagram of one embodiment of an
electronic sensor of the present invention;
[0008] FIG. 2 is a top view of one embodiment of a sensor element
of the present invention;
[0009] FIG. 3A-3B is a top view of one embodiment of the present
invention where a set of proof masses in the sensor element are
moving in a drive mode (proof masses moving in opposite direction
in the x-axis);
[0010] FIG. 4A-4B is a perspective view of one embodiment of the
present invention where a set of proof masses in the sensor element
are moving in a sense mode (proof masses moving in opposite
direction in the z-axis);
[0011] FIG. 5A-5B is a top view of one embodiment of the present
invention where a set of proof masses in the sensor element are
moving in a hula mode (proof masses moving together in the x-axis
direction);
[0012] FIG. 6A-6B is a perspective view of one embodiment of the
present invention where a set of proof masses in the sensor element
are moving in a trampoline mode (proof masses moving together in
the z-axis direction);
[0013] FIG. 7A-7B is a perspective view of one embodiment of the
present invention where a set of proof masses in the sensor element
are moving in a twist mode (proof masses twisting in the y-axis
plane);
[0014] FIG. 8A-8B is a perspective view of one embodiment of the
present invention where a set of proof masses in the sensor element
are moving in a flip-flap mode (proof masses twisting about the
y-axis); and
[0015] FIGS. 9 and 10 are diagrams illustrating relative
frequencies that may be obtained by using various embodiments of
the present invention.
[0016] While the invention is susceptible to various modifications
and alternative forms, specific embodiments have been shown by way
of example in the drawings and will be described in detail herein.
However, it should be understood that the invention is not intended
to be limited to the particular forms disclosed. Rather, the
invention is to cover all modifications, equivalents and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION
[0017] What is described are improved mechanisms and structures in
a sensor element of an electronic sensor device that allows for the
realignment of relative frequencies at various vibration modes.
This allows the sensor device to use thicker movable proof masses,
which improves yield in mass production applications and allows
process tolerances to be relaxed. To this end, in one embodiment
there is a sensor element for a sensor device comprising a
substrate, a pair of proof masses, and a set of drive beams. The
pair of proof masses is suspended above the substrate and is
attached to the substrate at fixed anchor points. The set of drive
beams is positioned between the proof masses and the anchor points.
The drive beams have a longitudinal body portion that extends along
a first direction and a flexible spring member that extends along a
second direction. The second direction may be perpendicular to the
first direction and the flexible spring members may be serpentine
in shape, such as folded beam-columns or wrinkle springs.
[0018] The sensor element may further comprise at least one base
beam that interconnects the set of drive beams. The base beam may
have its own longitudinal body portion that extends along the
second direction and a second flexible spring member that extends
along the first direction. The flexible spring members of the base
beam may also be serpentine in shape, such as folded beam-columns
or wrinkle springs. The sensor element may further comprise a first
pair of electrode combs that drives the proof masses in a first
plane. The sensor element may also comprise a second pair of
electrode combs and a pair of out-of-plane electrodes. The second
pair of electrode combs would be capable of sensing the movement of
the proof masses in the first plane. The pair of out-of-plane
electrodes would be capable of sensing the movement of the proof
masses in a second plane where the second plane is different from
the first plane.
[0019] In another embodiment, there is a sensor element for a
sensor device comprising a substrate, a pair of proof masses, a set
of drive beams, and at least one base beam. The pair of proof
masses are suspended above the substrate and attached to the
substrate at fixed anchor points. The set of drive beams are
positioned between the proof masses and the anchor points. Each
drive beam has a first longitudinal body portion that extends in a
first direction and a first flexible spring member that extends
along a second direction. The base beam interconnects the set of
drive beams and has a second longitudinal body portion and a second
flexible spring member. The second longitudinal body portion
extends along the second direction and the second flexible spring
member extends along the first direction. Here, the first and
second flexible spring members may be serpentine in shape, such as
folded beam-columns or wrinkle springs.
[0020] There is also an electronic sensor that comprises a digital
processing unit and a sensor element. The sensor element may
comprise a substrate, a pair of proof masses, a set of drive beams,
and at least one base beam. The pair of proof masses are suspended
above the substrate and attached to the substrate at fixed anchor
points. The set of drive beams are positioned between the proof
masses and the anchor points. Each drive beam has a first
longitudinal body portion that extends in a first direction and a
first flexible spring member that extends along a second direction.
The base beam interconnects the set of drive beams and has a second
longitudinal body portion and a second flexible spring member. The
second longitudinal body portion extends along the second direction
and the second flexible spring member extends along the first
direction.
[0021] The sensor element may further comprise a first pair of
electrode combs that drives the proof masses in a first plane. The
first pair of electrode combs may be configured to receive a signal
from the digital processing unit. The sensor element may further
comprise a second pair of electrode combs and a pair of
out-of-plane electrodes. The second pair of electrode combs may be
capable of sensing the movement of the proof masses in the first
plane and then sending a signal to the digital processing unit. The
pair of out-of-plane electrodes may be capable of sensing the
movement of the proof masses in another plane and then sending
another signal to the digital processing unit. The signals that are
reported to the digital processing unit may be used by the device
to extract an angular rate component reflective of the angular rate
externally induced to the device.
[0022] Now, turning to the drawings, FIG. 1 illustrates one
embodiment of an electronic sensor 20 having a digital processing
unit 22 and a sensor element 24. To illustrate the present
invention, a micro gyroscope sensor will be used as an exemplary
embodiment of the electronic sensor 20.
[0023] In one embodiment, the digital processing unit 22 may be
implemented in a digital signal processor (DSP) controller that
includes a number of functional blocks such as those described in a
patent application entitled Method and Apparatus for Signal
Extraction in an Electronic Sensor by Stephen J. Rober, filed Oct.
18, 2003, Ser. No. 10/273,805, commonly assigned to the assignee of
the present application and incorporated herein by reference in its
entirety. Generally, in one embodiment, the digital processing unit
22 may control the movement of proof masses of the sensor element
24 in one plane by sending a motor drive signal 26 to the sensor
element 24. Alternatively, a separate analog system could be used
to control the movement of the proof masses of the sensor element
24 as known to those of ordinary skill in the art. The digital
processing unit 22 may also extract and report an angular rate 28
that is reflective of the angular rate that is externally induced
to the sensor element 24. To extract and report the angular rate
28, the present invention uses the digital processing unit 22 to
receive a first signal 30 and a second signal 32 from the sensor
element 24. As will be described further below, the first signal 30
is reported from sensing electrodes that are in the same plane as
the proof masses. The second signal 32 is reported from sensing
electrodes that are not in the same plane as the proof masses.
[0024] Referring to FIG. 2, the sensor element 24 generally
includes a pair of movable proof masses 34a, 34b, a pair of outer
combs 36a, 36b, a pair of inner combs 38a, 38b, a pair of
out-of-plane sensing electrodes 40a, 40b, and a support structure
42. The support structure 42 is attached between the movable proof
masses and an underlying substrate 43. In one embodiment, the
underlying substrate 43 is made of glass and the proof masses 34a,
34b and support structure 42 are made of silicon.
[0025] In one embodiment of the present invention, as shown in FIG.
2, the support structure 42 comprises a series of drive beams 44,
base beams 46, and torsion beams 48. The components of the sensor
element 24 are mounted to the substrate 43, via the support
structure 42, at fixed anchor points 50. The components of the
sensor element 24 are preferably housed within a vacuum-sealed
cavity.
[0026] The proof masses 34a, 34b are suspended above the substrate
43. As described in more detail below, the beams 44, 46, 48 of the
support structure 43 permit the proof masses 34a, 34b to move in
relation to a series of anchor points 50. The anchor points 50 are
rigidly attached to the substrate 43. The proof masses 34a, 34b are
permitted to move in different planes. The first plane (in-plane)
is defined by an x-axis as shown in FIG. 2. The other planes
(out-of-planes) are defined by a y-axis and a z-axis.
[0027] The pair of outer combs 36a, 36b are electrodes that drive
the proof masses 34a, 34b in the first plane defined by the x-axis.
An exaggerated view of this movement (drive mode) is shown in FIGS.
3A and 3B. In the drive mode, the motion is driven by the
electrodes to create Coriolis forces on the proof masses 34a, 34b.
The pair of outer combs 36a, 36b may be mounted to the substrate
and provide electrostatic forces with varying input voltages to
drive the proof masses.
[0028] The pair of inner combs 38a, 38b are in the same plane as
the proof masses 34a, 34b. The pair of inner combs 38a, 38b may be
mounted to the substrate. The pair of inner combs 38a, 38b may be
electrodes that sense the movement of the proof masses 34a, 34b in
the x-axis. The pair of inner combs 38a, 38b are used to report the
first signal 30 to the digital processing unit 22.
[0029] The pair of out-of-plane sensing electrodes 40a, 40b sense
the out-of-plane movement of the proof masses 34a, 34b. For
instance, an exaggerated view of one of the main types of
out-of-plane movements (sense mode) is shown in FIGS. 4A and 4B.
This is when the proof masses 34a, 34b move opposite to each other
in a z-axis direction. The pair of out-of-plane sensing electrodes
40a, 40b may be positioned beneath the pair of proof masses 34a,
34b. The pair of out-of-plane sensing electrodes 40a, 40b are used
to report the second signal 32 to the digital processing unit 22.
The second signal 32 contains an angular rate component that
reflects the angular rate externally induced to the sensor element
24. The digital processing unit 22 receives the second signal 32
and extracts the angular rate component to report the angular rate
28.
[0030] As mentioned above, FIGS. 3A, 3B, 4A, 4B show exaggerated
views of the oscillatory movement of the proof masses 34a, 34b for
a drive mode (FIGS. 3A and 3B) and a sense mode (FIGS. 4A and 4B).
The frequency at which the proof masses 34a, 34b oscillate need to
be near each other to avoid other vibration modes and signal noise.
Currently, it has been known to use very thin proof masses and
support structures, with very limited process thickness ranges, to
keep the frequencies of these two modes near each other. The use of
thin structures and limited process tolerances generates lower
yields in the manufacturing process. It would be advantageous to
use proof masses that are thicker to improve yield in mass
production and to relax process tolerances.
[0031] The use of thicker proof masses, however, creates other
problems. For instance, the frequencies of oscillation in the drive
mode (shown FIGS. 3A and 3B) and a sense mode (shown in FIGS. 4A
and 4B) will become too far apart from each other. Moreover, other
undesired vibration modes such as the ones described below may
result. Without the mechanisms described in this invention, these
other vibration modes may separate the frequencies of the drive
mode and sense mode and the device will not function correctly.
[0032] For instance, one vibration mode that may occur, when
thicker structures are used, is a vibration mode that we will call
the hula mode. An exaggerated view of the movement of the proof
masses 34a, 34b in the hula mode is shown in FIGS. 5A and 5B. Here,
the proof masses 34a, 34b may move in the same direction in the
x-axis direction. Another vibration mode that can occur is what we
will call the trampoline mode. An exaggerated view of the movement
of the proof masses 34a, 34b in the trampoline mode is shown in
FIGS. 6A and 6B. Here, the proof masses 34a, 34b may move together
in the z-axis direction. A further vibration mode that can occur is
what we will call the twist mode. An exaggerated view of the
movement of the proof masses 34a, 34b in the twist mode is shown in
FIGS. 7A and 7B. Here, the proof masses 34a, 34b may twist in the
y-axis plane and rotate about the z-axis. Yet another vibration
mode that can occur is what we will call the flip-flap mode. An
exaggerated view of the movement of the proof masses 34a, 34b in
the flip-flap mode is shown in FIGS. 8A and 8B. Here, the proof
masses 34a, 34b may rotate about the y-axis.
[0033] To allow thicker structures for the sensing element 24, the
present invention advantageously includes a mechanism as described
below. In particular, the support structure 42 has a set of drive
beams 44 that are positioned between the proof masses 34a, 34b and
the anchor points 50. Each drive beam 44 has a longitudinal body
portion 62 that extends along a first direction and a flexible
spring member 64 that extends along a second direction. In the
embodiment shown in FIGS. 3-8, the first direction is along the
y-axis and the second direction is along the x-axis. One skilled in
the art with the benefit of this disclosure will realize that the
actual definition of the axes is implementation specific. However,
the first direction should be different from the second direction.
The embodiment shown in FIGS. 3-8 shows the second direction
perpendicular to the first direction. Moreover, in one embodiment,
the flexible spring members 64 are formed in a serpentine shape, or
folded beam-columns or wrinkle springs, and uniform along a portion
of the longitudinal body portion 62.
[0034] Using thicker proof masses than found in conventional
devices, FIG. 9 shows the relative frequencies of the various
vibration modes for one embodiment of the present invention. The
dashed boxes show the relative frequencies of the various vibration
modes using the flexible spring members 64 on the drive beams 44.
The solid line boxes reflect the relative frequencies of the
various vibration modes without the flexible spring members 64. It
is noted that the use of the flexible spring member 64 on the drive
beams 44 will allow the relative frequencies of the drive mode and
the sense mode to be more closely aligned. Moreover, in a further
embodiment, the base beam 46 of the support structure 42 is used to
interconnect the drive beams 44. The base beams 46 have a
longitudinal body portion 72 that extends along the second
direction and a flexible spring member 74 that extends along the
first direction. As mentioned above, the second direction is along
the x-axis and the first direction is along the y-axis. Again, one
skilled in the art with the benefit of this disclosure will realize
that the actual definition of the axes is implementation specific.
However, the first direction should be different from the second
direction. The embodiment shown in FIGS. 3-8 shows the second
direction perpendicular to the first direction. In this embodiment,
the flexible spring members 74 are formed in a serpentine shape, or
folded beam-columns or wrinkle springs, and uniform along a portion
of the longitudinal body portion 72.
[0035] Using thicker proof masses than found in conventional
devices, FIG. 10 shows the relative frequencies of the various
vibration modes for an embodiment that uses both the flexible
spring members 64 in the drive beams 44 and the flexible spring
members 74 in the base beams 46. In particular, the dotted-dashed
boxes show the relative frequencies of the various vibration modes
using both flexible spring members 64, 74. In effect, the use of
the flexible spring members 74 will shift the frequency of the
sense mode closer to the frequency of the drive mode. The dashed
line boxes reflect the relative frequencies of the various
vibration modes with just the flexible spring members 64 in the
drive beams 44. It is noted that with the flexible spring members
64, 74 provide a further improvement to existing devices and allow
the relative frequencies of the drive mode and the sense mode to be
more closely aligned.
[0036] What has been described are improved mechanisms and
structures in a sensor element that allow for the realignment of
frequencies at various vibration modes. This allows the sensor
device to use thicker movable proof masses and structures, which
improves yield in mass production applications and allows process
tolerances to be relaxed. As a result, the present invention has
the benefit of reducing manufacturing costs for a sensor device.
The mechanism and structure allows more flexibility by using
serpentine, or folded beam-columns or wrinkle springs, to more
closely align the frequencies for the drive mode and the sense mode
without interference by other unwanted vibration modes. The
mechanism allows flexibility to a designer by allowing the number
of serpentine loops, the width of loops, and the gap between loops
to be adjusted to fine-tune the stiffness and adjust the overall
frequencies of the structure.
[0037] The above description of the present invention is intended
to be exemplary only and is not intended to limit the scope of any
patent issuing from this application. The present invention is
intended to be limited only by the scope and spirit of the
following claims.
* * * * *