Title: Systems and methods for overcoming stiction
Abstract: A number of methods and systems for overcoming stiction are provided. The systems include electromechanical systems capable of exerting a variety of forces upon areas prone to stiction. The systems can be MEMS arrays or other types of devices where stiction related forces occur. The methods include a variety of ways of causing movement in areas prone to stiction forces. Such movement can be vibrational in nature and is sufficient to overcome stiction, allowing a trapped element to be moveed to a desired location.
Patent Number: 6,856,069 Issued on 02/15/2005 to Miller, et al.
| Inventors:
|
Miller; David (Louisville, CO);
Muller; Lilac (Nederland, CO);
Anderson; Robert L. (Boulder, CO)
|
| Assignee:
|
PTS Corporation (San Jose, CA)
|
| Appl. No.:
|
719858 |
| Filed:
|
November 20, 2003 |
| Current U.S. Class: |
310/311; 310/309; 310/328; 359/225; 385/18 |
| Intern'l Class: |
H02N 002//00 |
| Field of Search: |
310/309,311,328
359/225,291,295
385/18
335/79
|
References Cited [Referenced By]
U.S. Patent Documents
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|
| 5917625 | Jun., 1999 | Ogusu et al. | 359/130.
|
| 5999672 | Dec., 1999 | Hunter et al. | 385/37.
|
| 6028689 | Feb., 2000 | Michalicek et al. | 359/224.
|
| 6040935 | Mar., 2000 | Michalicek | 359/198.
|
| 6097859 | Aug., 2000 | Solgaard | 385/17.
|
| 6108471 | Aug., 2000 | Zhang et al. | 385/37.
|
| 6128122 | Oct., 2000 | Drake et al. | 359/224.
|
| 6701037 | Mar., 2004 | Staple et al. | 385/18.
|
| 6717715 | Apr., 2004 | Holl et al. | 359/291.
|
| 6738177 | May., 2004 | Gutierrez et al. | 359/298.
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| 6747786 | Jun., 2004 | Murakami et al. | 359/291.
|
| 6771851 | Aug., 2004 | Yang | 385/18.
|
| 6778304 | Aug., 2004 | Muller | 359/199.
|
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Levitation," Reprinted from Technical Digest IEEE Solid-State Sensor and
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dissertation by C. Keller, Fall 1998.
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dissertation by L. Muller; Spring 2000.
|
Primary Examiner: Dougherty; Thomas M.
Attorney, Agent or Firm: Townsend and Townsend and Crew LLP
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a divisional of and claims the benefit of U.S. patent
application Ser. No. 10/087,040 filed on Feb. 28, 2002, by David Miller,
et al., the entire disclosure of which is herein incorporated by reference
for all purposes.
Claims
What is claimed is:
1. An optical routing apparatus comprising a moveable micromirror, the
optical routing apparatus comprising:
a base layer;
a stop disposed over the base layer;
a structural plate supported above the base layer by a pivot, wherein the
structural plate is deflectable to contact the stop; and
an actuator disposed near the stop, wherein application of an AC voltage to
the actuator causes the stop to oscillate at a frequency at or about the
frequency of the AC voltage, and wherein the oscillation is sufficient to
overcome stiction related forces between the stop and the structural
plate.
2. The system of claim 1, wherein the oscillation comprises a combination
of horizontal and vertical movement relative to the base layer.
3. The system of claim 1, wherein the actuator is a first actuator, the
system further comprising a second actuator, wherein application of a
force to the second actuator causes the structural plate to deflect into
contact with the stop.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to the field of
micro-electrical-mechanical systems (MEMS), and in particular, to improved
MEMS devices and methods for their use with fiber-optic communications
systems.
The Internet and data communications are causing an explosion in the global
demand for bandwidth Fiber optic telecommunications systems are currently
deploying a relatively new technology called dense wavelength division
multiplexing (DWDM) to expand the capacity of new and existing optical
fiber systems to help satisfy this demand. In DWDM, multiple wavelengths
of light simultaneously transport information through a single optical
fiber. Each wavelength operates as an individual channel carrying a stream
of data. The carrying capacity of a fiber is multiplied by the number of
DWDM channels used. Today DWDM systems employing up to 80 channels are
available from multiple manufacturers, with more promised in the future.
In all telecommunication networks, there is the need to connect individual
channels (or circuits) to individual destination points, such as an end
customer or to another network Systems that perform these functions are
called cross-connects. Additionally, there is the need to add or drop
particular channels at an intermediate point. Systems that perform these
functions are called add-drop multiplexers (ADMs). All of these networking
functions are currently performed by electronics--typically an electronic
SONET/SDH system. However SONET/SDH systems are designed to process only a
single optical channel. Multi-wavelength systems would require multiple
SONET/SDH systems operating in parallel to process the many optical
channels. This makes it difficult and expensive to scale DWDM networks
using SONET/SDH technology.
The alternative is an all-optical network. Optical networks designed to
operate at the wavelength level are commonly called "wavelength routing
networks" or "optical transport networks" (OTN). In a wavelength routing
network, the individual wavelengths in a DWDM fiber must be manageable.
New types of photonic network elements operating at the wavelength level
are required to perform the cross-connect, ADM and other network switching
functions. Two of the primary functions are optical add-drop: multiplexers
(OADM) and wavelength-selective cross-connects (WSXC).
In order to perform wavelength routing functions optically today, the light
stream must first be de-multiplexed or filtered into its many individual
wavelengths, each on an individual optical fiber. Then each individual
wavelength must be directed toward its target fiber using a large array of
optical switches commonly called an optical cross-connect (OXC). Finally,
all of the wavelengths must be re-multiplexed before continuing on through
the destination fiber. This compound process is complex, very expensive,
decreases system reliability and complicates system management. The OXC in
particular is a technical challenge. A typical 40-80 channel DWDM system
will require thousands of switches to fully cross-connect all the
wavelengths. Conventional optomechanical switches providing acceptable
optical specifications are too big, expensive and unreliable for
widespread deployment.
In recent years, micro-electrical-mechanical systems (MEMS) have been
considered for performing functions associated with the OXC. Such MEMS
devices are desirable because they may be constructed with considerable
versatility despite their very small size. In a variety of applications,
MEMS component structures may be fabricated to move in such a fashion that
there is a risk of stiction between that component structure and some
other aspect of the system. One such example of a MEMS component structure
is a micromirror, which is generally configured to reflect light from two
positions. Such micromirrors find numerous applications, including as
parts of optical switches, display devices, and signal modulators, among
others.
In many applications, such as may be used in fiber-optics applications,
such MEMS-based devices may include hundreds or even thousands of
micromirrors arranged as an array. Within such an array, each of the
micromirrors should be accurately aligned with both a target and a source.
Such alignment is generally complex and typically involves fixing the
location of the MEMS device relative to a number of sources and targets.
If any of the micromirrors is not positioned correctly in the alignment
process and/or the MEMS device is moved from the aligned position, the
MEMS device will not function properly.
In part to reduce the complexity of alignment, some MEMS devices provide
for individual movement of each of the micromirrors. An example is
provided in FIGS. 1A-1C illustrating a particular MEMS micromirror
structure that may take one of three positions. Each micromirror 116 is
mounted on a base 112 that is connected by a pivot 108 to an underlying
base layer 104. Movement of an individual micromirror 116 is controlled by
energizing actuators 124a and/or 124b disposed underneath base 112 on
opposite sides of pivot 108. Hard stops 120a and 120b are provided to
limit movement of base 112. Energizing left actuator 124a causes
micromirror 116 to tilt on pivot 108 towards the left side until one edge
of base 112 contacts left hard stop 120a, as shown in FIG. 1A. In such a
titled position, a restorative force 150, illustrated as a direction
arrow, is created in opposition to forces created when left actuator 124a
is energized.
Alternatively, right actuator 124b may be energized to cause the
micromirror 116 to tilt in the opposite direction, as shown in FIG. 1B. In
such a titled position, a restorative force 160, illustrated as a
direction arrow, is created in opposition to forces created when right
actuator 124b is energized. When both actuators 124 are de-energized, as
shown in FIG. 1C, restorative forces 150, 160 cause micromirror 116 to
assume a horizontal static position. Thus, micromirror 116 may be moved to
any of three positions. This ability to move micromirror 116 provides a
degree of flexibility useful in aligning the MEMS device, however,
alignment complexity remains significant.
In certain applications, once the micromirror is moved to the proper
position, it may remain in that position for ten years or more. Thus, for
example, one side of an individual mnicromirror may remain in contact with
the hard stop for extended periods. Maintaining such contact increases the
incidence of dormancy related stiction. Such stiction results in the
micromirror remaining in a tilted position after the actuators are
de-energized. Some theorize that stiction is a result of molecule and/or
charge build-up at the junction between the micromirror and the hard stop.
For example, it has been demonstrated that an accumulation of H.sub.2 O
molecules at the junction increases the incidence of stiction.
In "Ultrasonic Actuation for MEMS Dormancy-Related Stiction Reduction",
Proceedings of SPIE Vol. 4180 (2000), Ville Kaajakari et al. describe a
system for overcoming both molecule and charge related stiction. The
system operates by periodically vibrating an entire MEMS device to
overcome stiction forces. While there is evidence that vibrating the
entire MEMS device can overcome stiction, such vibration causes temporary
or even permanent misalignment of the device. Thus, freeing an individual
micromirror often requires performance of a costly alignment procedure.
Even where the device is not permanently misaligned by the vibration, it
is temporarily dysfunctional while the vibration is occurring.
Thus, there exists a need in the art for systems and methods for increasing
alignment flexibility of MEMS devices and for overcoming stiction in MEMS
devices without causing misalignment.
SUMMARY OF THE INVENTION
The present invention provides improved MEMS devices for use with all
optical networks, and methods of using and making the same. Therefore,
some embodiments of the invention include a structural plate comprising a
micromirror. For example, the present invention may be used with the
exemplary wavelength routers described in co-pending U.S. patent
application Ser. No. 09/422,061, filed Nov. 16, 1999, the complete
disclosure of which is herein incorporated by reference.
Embodiments of the present invention comprise methods and apparatus related
to overcoming stiction in electromechanical devices. For example, some
embodiments provide methods for overcoming stiction electromechanical
systems. The methods can include providing a base layer with a contact
area or with a stop disposed on the base layer. A structural plate is
disposed above the base layer with one side of the structural plate in
contact with the contact area or stop. At the point where the structural
plate contacts the contact area, a stiction force impedes movement of the
structural plate away from the contact area. To overcome this stiction
force, a local vibration is created at or near the contact area.
In some embodiments, the local vibration is caused by mechanical contact at
or near the contact area. In other embodiments, the local vibration is
caused by exciting a mass near the contact area at a frequency at or near
the resonant frequency of the mass. In yet other embodiments, the local
vibration is caused by activating and deactivating an actuator such that a
serpentine structure or other spring structure is repetitively moved
resulting in a vibration.
Yet other embodiments of the present invention provide systems capable of
overcoming stiction forces. Such systems can include a base layer with a
structural plate supported above the base layer by a pivot. The structural
plate is moveable along a movement path until it contacts a stop located
at a position along the movement path. Stiction forces can result at the
contact between the structural plate and the stop. To overcome the
stiction forces, a local vibration element is provided at or near the
contact between the stop and the structural plate. The vibration element
provides local vibration sufficient to overcome the stiction forces.
The summary provides only a general outline of the embodiments according to
the present invention. Many other objects, features and advantages of the
present invention will become more fully apparent from the following
detailed description, the appended claims and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
A further understanding of the nature and advantages of the present
invention may be realized by reference to the FIGS. which are described in
remaining portions of the specification. In the figures, like reference
numerals are used throughout several to refer to similar components. In
some instances, a sub-label consisting of a lower case letter is
associated with a reference numeral to denote one of multiple similar
components. When reference is made to a reference numeral without
specification to an existing sub-label, it is intended to refer to all
such multiple similar components.
FIGS. 1A, 1B, and 1C are cross-sectional diagrams of a tilting micromirror
controlled by actuation of different actuators;
FIG. 2A is a cross-sectional diagram of a tilting structural plate
surrounded on either side by actuators including overlying vibrational
structures according to embodiments of the present invention;
FIGS. 2B and 2C are cross-sectional diagrams illustrating movement the
overlying vibrational structures of FIG. 2A according to embodiments of
the present invention;
FIGS. 3A and 3B are cross-sectional diagrams illustrating embodiments of
the actuators of FIG. 2 according to the present invention;
FIG. 4 is a cross-sectional diagram of a tilting structural plate
surrounded on either side by vibrating stops according to embodiments of
the present invention;
FIG. 5A is a cross-sectional diagram illustrating an embodiment of the
stops of FIG. 4 which are capable of vibrating both horizontally and
vertically and either passively or actively according to embodiments of
the present invention;
FIGS. 5B and 5C are cross-sectional diagrams illustrating an embodiment of
the stops of FIG. 4 which are capable of vibrating vertically according to
embodiments of the present invention
FIGS. 6A and 6B are cross-sectional diagrams illustrating embodiments of
the actuators of FIG. 4 which are capable of vibrating horizontally
according to embodiments of the present invention;
FIG. 7 illustrates an amplitude curve for a mass excited at or near its
natural frequency;
FIG. 8A is a cross-sectional diagram of a tilting structural plate
including vibrational elements integral thereto according to embodiments
of the present invention;
FIG. 8B is a top level diagram of the tilting structural plate of FIG. 8A;
FIG. 8C illustrates the tilting structural plate of FIG. 8A in a left tilt
position with the vibrational element flexed according to embodiments of
the present invention;
FIGS. 8D and 8E illustrate an embodiment of the present invention including
connected vibrational and movement actuators;
FIG. 9 is a cross-sectional diagram of a tilting structural plate system
including a vibrational beam according to embodiments of the present
invention;
FIG. 10 is a top level diagram of a plurality of vibrational actuators
interconnected according to embodiments of the present invention;
FIGS. 11A, 11B, and 11C are schematic top, side, and end views,
respectively, of one embodiment of a wavelength router that uses spherical
focusing elements;
FIGS. 12A and 12B are schematic top and side views, respectively, of a
second embodiment of a wavelength router that uses spherical focusing
elements; and
FIG. 13 is a schematic top view of a third embodiment of a wavelength
router that uses spherical focusing elements; and
FIGS. 14A and 14B are side and top views of an implementation of a
micromirror retroreflector array.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
1. Definitions
For purposes of this document, a structural plate refers to a substantially
planar structure disposed on a pivot The structural plate can be a
rectangular plate, or other such member, capable of movement on the pivot.
Such flexure movement from a static position is opposed by a restoring
force developed near the contact between the pivot and the structural
plate. Thus, the structural plate can be deflected by applying a force to
the beam and when the force is removed, the structural plate returns to a
static position. Such structural plates can include a cantilever beam
where one edge of the structural plate is closer to the pivot than an
opposite edge.
The pivot can be any member capable of supporting the structural plate in a
way that allows the structural plate to deflect or tilt to one or more
sides. For example, the pivot can be a post disposed near the center of a
rectangular shaped structural plate. Alternatively, the pivot can be a
rectangular shaped plate disposed across a pivot axis of the structural
plate. Yet another alternative includes a series of two or more posts
disposed across a pivot axis of the structural plate. Pivots can also be a
complex structure allowing for the movement of a supported structural
plate. For example, a pivot can be a bending or torsion element, or a
hinged element. Thus, one of ordinary skill in the art will recognize a
number of other members and/or geometries which are suitable as pivots.
2. Introduction
Embodiments of the invention are directed to MEMS methods and devices which
use localized vibration to overcome stiction forces. Such methods of
localized vibration can include creating a mechanical vibration at or near
locations prone to stiction forces. Such areas prone to stiction forces
can include, for example, areas where a tilted structural plate contacts a
base layer or a hard stop formed above a base layer. In some embodiments
vibration is localized to a particular structural plate, while in other
embodiments, vibration is localized to a group of structural plates. The
localized vibration can include vibration along a vertical vector, a
horizontal vector, or a combination of vertical and horizontal vectors.
In various embodiments, vibrational structures are formed at or near
locations prone to stiction forces. Such vibrational structures can be
actuated to create localized vibration, which is useful for overcoming
stiction forces. The vibrational structures can include a mass which is
excited by an external force, such that the mass vibrates. Other
vibrational structures can include elements formed to utilize the elastic
properties of the elements to generate vibrations local to the element.
Such vibrational structures can be coupled to or integral with either a
base layer, a structural plate, or a combination thereof. Structures
according to the present invention can be fabricated according to MEMS
fabrication techniques known in the art, or any other applicable
techniques known in the art.
In other embodiments, localized vibration can be created by tapping a
mechanical element at or near the area prone to stiction forces. Such
tapping can be done at a variety of frequencies. Thus, the present
invention provides a number of systems and methods for overcoming stiction
through use of localized vibration. As will be apparent to anyone of
ordinary skill in the art, the systems and methods of the present
invention are applicable to a wide variety of applications where stiction
forces are involved.
3. Vibration through Excitation by a Direct Current (DC) Potential
FIG. 2A illustrates an embodiment of the present invention applied to a
structural plate micromirror system 200. Specifically, FIG. 2A illustrates
structural plate micromirror system 200 with a structural plate 220 in a
static horizontal position. Structural plate 220 is supported above a base
layer 210 by a pivot 224 and a micromirror 222 is disposed on structural
plate 220. Structural plate 220, including micromirror 222, can be
deflected to either the right or the left about a pivot point 226, which
in some embodiments is located at the junction of structural plate 220 and
pivot 224. Pivot 224, similar to other pivots discussed herein, can be a
complex structure allowing for the movement of a supported structural
plate. For example, pivot 224 can be a bending or torsion element, or a
hinged element.
A left actuator 230 is used to deflect structural plate 220 to the left and
a right actuator 232 is used to deflect structural plate 220 to the right.
Structural plate 220 can be deflected to the left such that it contacts a
left stop 260. Left stop 260 includes a left vibrational actuator 250 and
a left overlying structure 240. Similarly, structural plate 220 can be
deflected to the right such that it contacts a right stop 262 which
includes a right vibrational actuator 252 and a right overlying structure
242.
In operation, left actuator 230 is actuated, along with right vibrational
actuator 252, by application of a DC voltage, VR. The potential difference
between VR and structural plate 220, which is electrically connected to a
common ground, creates an electric field which causes structural plate 220
to tilt, or otherwise deflect, to the left until the end of structural
plate 220 contacts left overlying structure 240. In addition, as
illustrated in FIG. 2B, contact by structural plate 220 causes the
horizontal portion of left overlying structure 240 to bow until the center
of the horizontal portion nears left vibrational actuator 250.
Contact between structural plate 220 and left overlying structure 240 is
eliminated as structural plate 220 is returned from the left tilt position
to the horizontal static position illustrated in FIG. 2A. Return to the
horizontal static position is achieved by removing VR from left actuator
230 and right vibrational actuator 252. Under normal circumstances,
restoring forces associated with the interaction of structural plate 220
and pivot 224 cause structural plate 220 to return to the horizontal
static position. However, in some instances, stiction related forces are
sufficient to overcome the restoring forces and structural plate 220
remains tilted to the left even after VR is removed.
The present embodiment of the invention disrupts such stiction related
forces through vibration of left overlying structure 240. Such vibration
is produced coincident with the removal of VR. More specifically, when VR
is removed, the horizontal portion of left overlying structure 240
elastically snaps from the bowed position (illustrated in FIG. 2B) to the
non-bowed position (illustrated in FIG. 2A). This movement, or localized
vibration, of left overlying portion 240 disrupts any stiction forces,
such that the restoring forces associated with structural plate 220 and
pivot 224 are sufficient to cause structural plate 220 to return to the
static horizontal position illustrated in FIG. 2A. In this embodiment, the
localized vibration is primarily along a vertical vector.
In some embodiments, left overlying structure 240 is engineered such that
movement of the horizontal portion of left overlying structure 240 from
the bowed position illustrated in FIG. 2B to the non-bowed position
illustrated in FIG. 2A involves a damped oscillation between a bowed down
position and a bowed up position. Thus, by removing VR, the horizontal
portion of overlying structure 240 oscillates between the positions
illustrated in FIGS. 2B and 2C until damping forces stop the oscillation
and the left overlying structure comes to rest in the horizontal position
illustrated in FIG. 2A. Such oscillation, or localized vibration,
sufficiently disrupts any stiction forces such that the restorative forces
associated with structural plate 220 are sufficient to return structural
plate 220 to the horizontal static position.
At this juncture, it should be recognized that a similar tilt to the right
can be achieved and stiction forces resulting from such tilt can be
overcome using right actuator 232 and right stop 262.
In some embodiments, left actuator 230 and right vibrational actuator 252
are electrically connected and are thus both actuated when VR is applied.
Similarly, right actuator 232 and left vibrational actuator 250 can be
electrically connected, such that both are actuated by the application of
a voltage potential, VL. Thus, in some embodiments, the functionality of
the actuators can be provided with minimal wiring and/or control logic.
Alternatively, in some embodiments, left actuator 230 and left vibrational
actuator 250, as well as, left actuator 232 and left vibrational actuator
252 are not electrically connected and can be actuated individually. This
provides a degree of flexibility when operating structural plate
micromirror system 200. In yet other embodiments, left actuator 230 and
left vibrational actuator 250 are electrically connected and are thus both
actuated when VL is applied. Similarly, right actuator 232 and right
vibrational actuator 252 can be electrically connected, such that both are
actuated by the application of a voltage potential, VR.
In yet other embodiments, the functionality of left actuator 230 is
provided by left vibrational actuator 250, which allows left actuator 230
to be eliminated. Similarly, in some embodiments, the functionality right
actuator 232 is provided by right vibrational actuator 252 and right
actuator 232 is eliminated. Thus, for example, a left tilt of structural
plate 220 is effectuated by applying VL to left vibrational actuator 250
only, in the absence of left actuator 230. Such elimination of left
actuator 230 and/or right actuator 232 can provide similar functionality
to systems including both actuators, while reducing the number of
actuators, wiring, and/or the complexity of any control logic.
FIGS. 3A and 3B illustrate two embodiments where dimples and standoff
structures are used to promote the longevity of left stop 260, and
similarly right stop 262. Referring to FIG. 3A, left overlying structure
240 includes standoff structures 245a, 245b formed above dimple areas
251a, 251b. Dimple areas 251a, 251b are formed by cutting out portions of
left vibrational actuator 250. Formation of dimples 251a, 251b can include
removal of small portions of left vibrational actuator 250 to provide
clearance for standoff structures 245a, 245b. One purpose of standoff
structures 245a, 245b is to prevent contact between overlying structure
240 and the underlying actuator, thus avoiding a short. For embodiments
where standoff structures 245a, 245b are posts, dimple areas 251a, 251b
can be circular or rectangular cut out areas of left vibrational actuator
250. Such cut out areas leave left vibrational actuator 250 contiguous,
less only relatively small dimple areas 251a, 251b.
Alternatively, standoff structures 245a, 245b can be bars formed across the
length of left overlying structure 240, in which case, dimple areas 251a,
251b are formed across the length of left vibrational actuator 250.
Formation of such expansive dimples 251a, 251b, effectively sub-divides
left vibrational actuator into sub-parts 250a, 250b, 250c.
Standoff structures 245a, 245b contact base layer 210 at dimple areas 251a,
251b when the horizontal portion of left overlying structure 240 is bowed
toward left vibrational actuator 250 (similar to that illustrated in FIG.
2A). By contacting base layer 210, standoff structures 245a, 245b prevent
left overlying layer 240 from contacting and potentially damaging left
vibrational actuator 250. Further, standoff structures 245a, 245b prevent
an electrical short between left overlying structure 240 and left
vibrational actuator 250. In this way, the longevity of left stop 260 can
be increased. Of course, it is recognized that using, such standoffs and
dimples is similarly applicable to right stop 262.
FIG. 3B illustrates an alternative embodiment where standoffs 246a, 246b
are formed in dimple areas 251a, 251b on base layer 210. Similar to the
embodiment described in relation to FIG. 3A, standoff structures 246a,
246b prevent left overlying structure 240 from physically contacting left
vibrational actuator 250. Also, electrical shorting between left overlying
structure 240 and left vibrational actuator 250 is prevented.
FIG. 4 illustrates an embodiment of the present invention applied to a
structural plate micromirror system 500. Specifically, FIG. 4 illustrates
structural plate micromirror system 500 with a structural plate 520 in a
static horizontal position. Structural plate 520 is supported above a base
layer 510 by a pivot 524 and a micromirror 522 is disposed on structural
plate 520. Structural plate 520, including micromirror 522, can be
deflected to either the right or the left about a pivot point 526, which
in some embodiments is located at the junction of structural plate 520 and
pivot 524.
A left vibrational stop 560 is located next to a left actuator 590 used to
deflect structural plate 522 to the left and a right vibrational stop 562
is located next to a right actuator 591 used to deflect structural plate
520 to the right. Structural plate 520 can be deflected to the left such
that it contacts left vibrational stop 560. Similarly, structural plate
520 can be deflected to the right such that it contacts a right
vibrational stop 562.
In operation, left stop 560 is actuated by application of a (DC) voltage,
VL. The potential difference between VL and structural plate 520, which is
electrically connected to a common ground, creates an electric field which
causes structural plate 520 to tilt, or otherwise deflect, to the left
until the end of structural plate 520 contacts left stop 560. In addition,
as will be more fully described in relation to FIGS. 5 through 6, the
electric field created by applying VL to left actuator 590 causes an
elastic displacement of left stop 560.
Contact between structural plate 520 and left stop 560 is eliminated as
structural plate 520 is returned from the left tilt position to the
horizontal static position illustrated in FIG. 4. Return to the horizontal
static position is achieved by removing VL from left actuator 590. Under
normal circumstances, restoring forces associated with structural plate
520 and pivot 524 cause structural plate 520 to return to the horizontal
static position. However, in some instances, stiction related forces are
sufficient to overcome the restoring forces and structural plate 520
remains tilted to the left even after VL is removed.
The present embodiment of the invention disrupts such stiction related
forces by vibrating left stop 560. Such vibration is produced coincident
with the removal of VL. More specifically, when VL is removed, left stop
560 elastically snaps from the displaced position to a static position.
This movement, or localized vibration of left stop 560 disrupts any
stiction forces, such that the restoring forces associated with structural
plate 520 are sufficient to cause structural plate 520 to return to the
static horizontal position. In various embodiments, the localized
vibration can be primarily along a vertical vector, primarily along a
horizontal vector, or any other vector. Further, such vibration can be
actively created by applying an alternating force, or passively created by
relying on the elasticity of the materials comprising the structural plate
and/or the stop.
Various embodiments which provide such localized vibration are illustrated
in FIGS. 5 through 6. Referring to FIG. 5A, an embodiment of left stop 560
according to the present invention is illustrated. In this embodiment,
left stop 560 includes: an actuator mass 561 supported above base layer
510 by a number of serpentine structures 564. In some embodiments,
serpentine sturctures 564 are vertical serpentine structures. In addition,
left stop 560 comprises an actuator 590 disposed above base layer 510 and
next to stop mass 561.
In operation, VL is applied to actuator 590. Application of VL creates an
electric field between left stop 560 and structural plate 520 (not shown)
and between stop mass 561 and actuator 590. The electric field causes
structural plate 520,to deflect to the left until an end of structural
plate 520 contacts stop mass 561. In addition, the electric field causes
stop mass 561 to displace toward actuator 590. Such displacement can be
both horizontal and vertical depending upon the placement of actuator 590
relative to stop mass 561. Stop mass 561 remains in this displaced
position until VL is removed.
When VL is removed from actuator 590, the attraction between stop mass 561
and actuator 590 is eliminated and actuator mass elastically snaps back to
a static position. This involves a combination of horizontal and vertical
movement, or localized vibration which disrupts any stiction related
forces allowing the restorative forces associated with structural plate
520 to return structural plate 520 to the static horizontal position.
In some embodiments, the combination of stop mass 561 and serpentine
structures 564 are engineered such that removal of VL results in a damped
oscillation of stop mass 561. During such oscillation, or localized
vibration, stop mass 561 repeatedly moves away from actuator 590 and
subsequently back toward actuator 59O until the oscillation is entirely
damped out and stop mass 561 comes to rest in a static position. This
localized vibration occurring along various vectors, including a
combination horizontal and vertical vector, provides sufficient disruption
of any stiction related forces to allow structural plate 520 to return to
the horizontal static position.
FIGS. 5B and 5C illustrate embodiments of the present invention where the
localized vibration occurs primarily along a vertical vector. Referring to
FIG. 5B, an embodiment of left stop 560 according to the present invention
is illustrated. In this embodiment, left stop 560 includes actuator 590
which is operable to cause structural plate 520 (not shown) to deflect
into contact with a deformable pad 1510.
In operation, VL is applied to actuator 590. Application of VL creates an
electric field between actuator 590 and structural plate 520 (not shown).
The electric field causes structural plate 520 to deflect to the left
until an end of structural plate 520 contacts deformable stop 1510 as
illustrated in FIG. 5C. Deformable stop 1510 bends to accommodate movement
of structural plate 520 toward base layer 510.
When VL is removed from actuator 590, the attraction between actuator 590
and structural plate 520 is eliminated. Elimination of the attractive
force allows deformable pad 1510 to elastically snap back to the static
position illustrated in FIG. 5B. This involves primarily vertical
movement, or localized vibration which disrupts any stiction related
forces acting between deformable stop 1510 and structural plate 520 and
allowing the restorative forces associated with structural plate 520 to
return structural plate 520 to the static horizontal position.
In some embodiments, deformable stop 1510 is engineered such that removal
of VL results in a damped oscillation of deformable stop 1510 along a
primarily vertical vector. During such oscillation, or localized
vibration, deformable stop 1510 repeatedly moves away from base layer 510
and subsequently back toward base layer 510 until the oscillation is
entirely damped out and deformable stop 1510 comes to rest in the static
position. This localized vibration provides sufficient disruption of any
stiction related forces to allow structural plate 520 to return to the
horizontal static position.
FIGS. 6A and 6B illustrate embodiments of the present invention where the
localized vibration occurs primarily along a horizontal vector. Referring
to FIG. 6A, an embodiment of left stop 560 according to the present
invention is illustrated. In this embodiment, left stop 560 includes an
actuator mass 565 which is moveable across base layer 510 and is tethered
by a serpentine structure 566 to an anchor mass 567. In some embodiments,
actuator mass 565 is supported above base layer 510 by dimples (not
shown). The dimples can be useful to reduce friction between actuator mass
565 and base layer 510. Further, in some embodiments, serpentine structure
566 can be a comb drive actuator.
In operation, VL is applied to anchor mass 567. Application of VL creates
an electric field between left stop 560 and structural plate 520 (not
shown) and between actuator mass 565 and anchor mass 567. The electric
field causes structural plate 520 to deflect to the left until an end of
structural plate 520 contacts actuator mass 565. In addition, the electric
field causes actuator mass 565 to displace horizontally toward actuator
590. Actuator mass 565 remains in this displaced position until VL is
removed.
When VL is removed from anchor mass 567, the attraction between actuator
mass 565 and anchor mass 567 is eliminated and actuator mass 565
elastically snaps back to a static position. This involves substantially
horizontal movement, or localized vibration which disrupts any stiction
related forces allowing the restorative forces associated with structural
plate 520 to return structural plate 520 to the static horizontal
position. In some embodiments significant horizontal forces between
actuator mass 565 and structural plate 520 can cause structural plate 520
to break. Thus, in some embodiments, the amount of horizontal movement of
actuator mass 565 is limited.
In some embodiments, a combination of actuator mass 565 and serpentine
structure 566 are engineered such that removal of VL results in a damped
oscillation of actuator mass 565 along a primarily horizontal vector.
During such oscillation, or localized vibration, actuator mass 565
repeatedly moves away from anchor mass 567 and subsequently back toward
anchor mass 567 until the oscillation is entirely damped out and actuator
mass 565 comes to rest in a static position. This localized vibration
provides sufficient disruption of any stiction related forces to allow
structural plate 520 to return to the horizontal static position.
FIG. 6B illustrates another embodiment of left stop 560 according to the
present invention. In this embodiment, left stop 560 includes an stop mass
569 which is supported above base layer 510 by a number of support dimples
591, 592 and tethered by a serpentine structure 580 to an actuator mass
570.
In operation, VL is applied to actuator mass 570. Application of VL creates
an electric field between left stop 560 and structural plate 520 (not
shown) and between stop mass 569 and actuator mass 570. The electric field
causes structural plate 520 (not shown) to deflect to the left until an
end of structural plate 520 (not shown) contacts stop mass 569. In
addition, the electric field causes stop mass 569 to displace primarily
along a horizontal axis toward actuator mass 570. Stop mass 569 remains in
this displaced position until VL is removed.
When VL is removed from stop mass 569, the attraction between stop mass 569
and actuator mass 570 is eliminated and stop mass 569 elastically snaps
back to a static position. This involves primarily horizontal movement, or
localized vibration which disrupts any stiction related forces allowing
the restorative forces associated with structural plate 520 to return
structural plate 520 to the static horizontal position.
Similar to the embodiment discussed in relation to FIG. 6B, some of the
present embodiments involve a damped oscillation which provides the
localized vibration sufficient to overcome any stiction related forces.
4. Vibration through Excitation by an Alternating Current (AC) Potential
The preceding embodiments each involve creation of localized vibration
through application and removal of a DC voltage potential. At this
juncture, it should be noted that in any of the embodiments described in
relation to FIGS. 2 through 6, localized vibration can be created by
application of an AC potential. For example, by using an AC voltage or a
pulsed DC voltage for VL in the embodiment described in relation to FIG.
2, the frequency at which the horizontal portion of left overlying
structure 240 bows and subsequently returns to the static position can be
selected by controlling the frequency of VL. It should be recognized that
in various embodiments, the present invention can incorporate either a DC
voltage in the place of an AC voltage. Thus, for example, where VL is a
voltage potential alternating between ground and ten (10) volts at a
frequency of. 60 Hz, left overlying structure 240 will bow and return to a
static position at a rate of 60 Hz. Such voltages and frequencies can be
tailored to a particular application. Of course, the elasticity of the
material forming left overlying structure 240 can affect the rate and
therefore should be selected accordingly. In such embodiments, the
localized vibration is provided at a frequency corresponding to the
frequency of the applied AC voltage.
Yet further embodiments of the present invention provide localized
vibration by exciting an actuator mass and/or a hard stop with an AC
voltage alternating at or near the natural frequency of the actuator mass
and/or a hard stop. FIG. 7 illustrates an amplitude curve 700 for the
vibration of a mass excited by a driving force. The amplitude of a
vibration is noted on a vertical axis 705 and the frequency of the driving
force is noted on a horizontal axis 710. The peak of amplitude curve 700
occurs at an amplitude value 715 where a frequency 720 of the driving
force is close to the natural frequency of the vibrating mass. Frequency
720 is often referred to as the resonant frequency. At the resonant
frequency, the amplitude of the vibration is maximized, however, vibration
is ongoing for frequencies on either side of frequency 720. By exciting
the vibrating mass at or near the resonant frequency, the amplitude of the
vibration can be made very large through repeated application of a
relatively small force.
Additionally, significant vibration can be achieved by exciting a mass
using a driving frequency at or near one of the harmonic frequencies of
the material comprising the actuator and/or hard stop. Thus, one of
ordinary skill in the art will recognize that a number of different
driving frequencies may be used to excite the mass.
Such an approach of creating localized vibration through application of a
driving force at or near the natural frequency of a material can be
applied to the embodiments described in relation to FIGS. 2 through 6. For
example, an AC voltage, VL, can be applied to left stop 560 of FIG. 4.
Where the frequency of VL is at or near the natural frequency of the
material comprising left stop 560, it will oscillate. Such oscillations
provide the localized vibration sufficient to overcome stiction related
forces. While the preceding example is described using an AC voltage
potential to excite the mass, it should be recognized by one skilled in
the art that other energy types may be used to excite the actuator. For
example, a sound wave with a frequency at or near the natural frequency of
the material comprising the actuator may be used to excite the actuator to
vibrate.
FIGS. 8A and 8B illustrate yet another embodiment of the present invention
which is describe herein to provide localized vibration by application of
an AC voltage with a frequency at or near the natural frequency of the
vibrating mass. However, it will be recognized by any one of skill in the
art that the present embodiment can be used to provide localized vibration
by application of a DC voltage or by an AC voltage not necessarily at or
near the natural frequency of the material. Such localized vibration is
provided consistent with methods and operations of the previously
described embodiments.
More specifically, FIG. 8A illustrates a structural plate micromirror
system 800 with a structural plate 820 in a static horizontal position.
Structural plate 820 includes left serpentine structures 840 and right
serpentine structures 842, which are designed to promote vibration of
structural plate 820. In some embodiments, structural plate 820 is
vibrated according to the principles discussed in relation to FIG. 7.
Similar to prior embodiments, structural plate 820 is supported above a
base layer 810 by a pivot 824 and a micromirror 822 is disposed on
structural plate 820. Structural plate 820, including micromirror 822, can
be deflected to either the right or the left about a pivot point 826,
which in some embodiments is located at the junction of structural plate
820 and pivot 824.
A left actuator 860 is used to deflect structural plate 822 to the left and
a right actuator 862 is used to deflect structural plate 820 to the right.
Structural plate 820 can be deflected to the left such that it contacts
base layer 810 or a hard stop disposed thereon. Similarly, structural
plate 820 can be deflected to the right such that it contacts base layer
810 or a hard stop disposed thereon. FIG. 8B provides a top level
schematic diagram of structural plate 820, including left and right
serpentine structures 840, 842 and micromirror 822.
In operation, left actuator 860 is actuated by application of a voltage,
VL. In some embodiments, VL is initially a DC voltage potential which
creates an electric field attracting structural plate 820 to tilt, or
otherwise deflect to the left until an edge of structural plate 820
contacts base layer 810 or a hard stop disposed thereon. Similar to
previously described embodiments, VL is then removed allowing structural
plate 820 to return to the static horizontal position illustrated in FIG.
8A. Again, however, stiction related forces occasionally prevent such a
return of structural plate 820 to the static horizontal position.
To overcome these stiction related forces, an AC voltage, VL', is applied
to left actuator 860. The frequency of VL' is chosen to be at or near the
natural frequency of left serpentine structures 840. The alternating
potential difference between VL' and the common ground coupled to
structural plate 820 creates an alternating electric field and causes left
serpentine structures to oscillate according the principles discussed in
relation to FIG. 7. The alternating electric field is insufficient to
maintain structural plate 820 in contact with base layer 810, but does
create sufficient localized vibration to disrupt stiction related forces
and allow the restorative forces associated with structural plate 820 to
return structural plate 820 to the horizontal static position.
As previously discussed, the embodiment described in relation to FIGS. 8A
through 8B can also be used to create localized vibration through the
application of either a DC voltage or an AC voltage not necessarily near
the natural frequency of any of the structures. For example, FIG. 8C
illustrates an embodiment where structural plate 820 is designed to flex
at serpentine elements 840, 842. Thus, for example, when VL is applied to
left actuator 860 causing structural plate 820 to tilt to the left,
structural plate 820 flexes at serpentine structures 840 as the end of
structural plate 820 contacts base layer 810. The flex point associated
with serpentine structures 840 stores energy which is released when VL is
removed from left actuator 860. This release of energy causes structural
plate 820 to return to its straight static position. In returning to the
static position, the end of structural plate 820 moves relative to base
layer 810. Such movement, or local vibration, is sufficient to overcome
stiction related forces, and the restorative forces associated with
structural plate 820 and pivot 824 act to return structural plate 820 to
the static horizontal position.
In some embodiments, the release of energy from the flexure associated with
serpentine elements 840 results in a damped oscillation as serpentine
elements 840 repeatedly bow toward base layer 810 and away from base layer
810 until the oscillation is finally damped out and structural plate 820
comes to rest in a straight position. Such oscillation results in a
localized vibration at the point where structural plate 820 contacts base
layer 810. This localized oscillation disrupts stiction related forces and
allows the restorative forces to return structural plate 820 to the static
horizontal position.
Referring to FIGS. 8D and 8E, a system 2000 including a structural plate
2012 disposed above pivot 2008 is disclosed. Structural plate 2012
includes a right vibration mass 2043 attached via a right serpentine
structure 2042. Similarly, a left vibration mass 2041 is attached via a
left serpentine structure 2040. Structural plate 2012 can be deflected to
the right by energizing right actuator 2062 and similarly deflected to the
left by energizing left actuator 2060. When deflected to the right,
structural plate 2012 contact a stop 2072. In addition, a right vibration
electrode 2063 and a left vibration electrode 2061 are disposed under the
respective right and left vibration masses 2043, 2041.
In some embodiments, right vibration electrode 2063 is electrically
connected to right actuator 2062. Similarly, left actuator 2060 is
electrically connected to left vibration electrode 2061. In other
embodiments, left actuator 2060 is electrically connected to right
vibration electrode 2063, while right actuator 2062 is electrically
connected to left vibration electrode 2061. In yet other embodiments, all
vibration electrodes 2061, 2063 are connected via a common bond pad (not
shown).
As illustrated in FIG. 8D, structural plate 2012 is stuck due to stiction
in a right tilt position with all actuators and vibration electrodes
de-energized. To overcome the stiction between structural plate 2012 and
stop 2072, right vibration electrode is energized using an AC voltage or a
pulsed DC voltage. Application of this voltage causes right vibration mass
2043 to be attracted toward right vibration electrode 2063 and release.
This is repeated as the applied voltage changes state causing right
vibration mass 2043 to vibrate. Such vibration increases until the
stiction between stop 2072 and structural plate 2012 is overcome.
In embodiments where right vibration electrode 2063 is electrically
connected to left actuator 2060, left actuator 2060 is energized in unison
with the energization of right vibration electrode 2063. Energization of
left actuator 2060 creates attraction between the actuator and structural
plate 2012 which aids in overcoming the stiction. With the stiction
overcome, restorative forces associated with structural plate 2012 and
pivot 2008 cause the structural plate to return to a static state as
illustrated in FIG. 8E.
5. Vibration through Mechanical Excitation
FIG. 9 illustrates an embodiment of a micromirror system 900 according to
the present invention where an external element is used to create
localized vibration at a point susceptible to stiction related forces.
Micromirror system 900 includes a structural plate 920 deflected to a
right tilt position. Structural plate 920 is supported above a base layer
910 by a pivot 924 and includes a micromirror 922 disposed over it. A left
actuator 960 and a right actuator 962 are included on either side of pivot
924. When activated, left and right actuators 960, 962 cause structural
plate 920 to tilt, or otherwise deflect in the direction of the respective
left or right actuator 960, 962.
In addition, micromirror system 900 includes a vibration beam 980 supported
above base layer 910 by a pivot 984. Vibration beam 980 can be brought
into co
