U.S. patent application number 10/263117 was filed with the patent office on 2003-02-27 for combination horizontal and vertical thermal actuator.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Goetz, Douglas P., Hagen, Kathy L., Hamerly, Mike E., Smith, Robert G., Theiss, Silva K., Weaver, Billy L..
Application Number | 20030038703 10/263117 |
Document ID | / |
Family ID | 24644792 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030038703 |
Kind Code |
A1 |
Weaver, Billy L. ; et
al. |
February 27, 2003 |
Combination horizontal and vertical thermal actuator
Abstract
A micrometer sized, single-stage, horizontal and vertical
thermal actuator capable of repeatable and rapid movement of a
micrometer-sized optical device off the surface of a substrate. The
horizontal and vertical thermal actuator is constructed on a
surface of a substrate. At least one hot arm has a first end
anchored to the surface and a free end located above the surface. A
cold arm has a first end anchored to the surface and a free end.
The cold arm is located above and laterally offset from the hot arm
relative to the surface. The cold arm is adapted to provide
controlled bending near the first end thereof. A member
mechanically and electrically couples the free ends of the hot and
cold arms such that the actuator exhibits horizontal and vertical
displacement when current is applied to at least the hot arm.
Inventors: |
Weaver, Billy L.; (Eagan,
MN) ; Goetz, Douglas P.; (St. Paul, MN) ;
Hagen, Kathy L.; (Stillwater, MN) ; Hamerly, Mike
E.; (Vadnais Heights, MN) ; Smith, Robert G.;
(Vadnais Heights, MN) ; Theiss, Silva K.;
(Woodbury, MN) |
Correspondence
Address: |
Office of Intellectual Property Counsel
3M Innovative Properties Company
PO Box 33427
St. Paul
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
24644792 |
Appl. No.: |
10/263117 |
Filed: |
October 2, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10263117 |
Oct 2, 2002 |
|
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|
09659282 |
Sep 12, 2000 |
|
|
|
6483419 |
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Current U.S.
Class: |
337/335 ;
337/333 |
Current CPC
Class: |
H01H 2001/0068 20130101;
H01H 2061/008 20130101; H01H 2061/006 20130101; B81B 3/0024
20130101; H01H 61/01 20130101; B81B 2201/031 20130101; H01H 1/0036
20130101 |
Class at
Publication: |
337/335 ;
337/333 |
International
Class: |
H01H 037/52 |
Claims
What is claimed is:
1. A horizontal and vertical thermal actuator constructed on a
surface of a substrate consisting essentially of: one hot arm
having a first end anchored to the surface and a free end located
above the surface; a cold arm having a first end anchored to the
surface and a free end, the cold arm being located above and
laterally offset from the hot arm relative to the surface; and a
member mechanically and electrically coupling the free ends of the
hot and cold arms such that the actuator exhibits vertical
displacement and horizontal displacement when current is applied to
at least the hot arm.
2. The apparatus of claim 1 having a flexure formed in the cold arm
near the first end thereof adapted to provide controlled
bending.
3. The apparatus of claim 2 wherein the flexure comprises at least
one of a recess, depression, cut-out, hole, location of narrowed,
thinned or weakened material, alternate material or other
structural features or material change that decreases resistance to
bending in that location.
4. The apparatus of claim 1 further consisting essentially of a
grounding tab electrically coupling the hot arm to the
substrate.
5. The apparatus of claim 1 wherein the cold arm is electrically
isolated from the hot arm.
6. The apparatus of claim 1 wherein the hot arm and the cold arm
comprise a circuit through which electric current is passed.
7. The apparatus of claim 1 further consisting essentially of a
reinforcing member formed in the cold arm.
8. The apparatus of claim 7 wherein the reinforcing member is
integrally formed in the cold arm.
9. The apparatus of claim 1 comprising a metal layer extending
along the cold arm.
10. The apparatus of claim 1 comprising a plurality of horizontal
and vertical thermal actuators on the substrate.
11. The apparatus of claim 1 comprising at least one optical device
mechanically coupled to the horizontal and vertical thermal
actuator.
12. The apparatus of claim 11 wherein the optical device comprises
one of a reflector, a lens, a polarizer, a wave guide, a shutter,
or an occluding structure.
13. The apparatus of claim 11 comprising an optical communication
system including at least one optical device.
14. A horizontal and vertical thermal actuator constructed on a
surface of a substrate comprising: at least two hot arms, each
having a first end anchored to the surface and a free end located
above the surface; a cold arm having a first end anchored to the
surface and a free end and a first major side and a second major
side, the cold arm being located above and laterally offset from
the at least two hot arms relative to the surface and the at least
two hot arms are laterally offset from the same side of the cold
arm; electrical contacts electrically coupled to the first ends of
the at least two hot arms; and a member mechanically and
electrically coupling the free ends of the hot and cold arms.
15. The apparatus of claim 14 comprising a flexure formed in the
cold arm near the first end thereof adapted to provide controlled
bending.
16. The apparatus of claim 15 wherein the flexure comprises at
least one of a recess, depression, cut-out, hole, location of
narrowed, thinned or weakened material, alternate material or other
structural features or material change that decreases resistance to
bending in that location.
17. The apparatus of claim 14 comprising a grounding tab
electrically coupling the hot arms to the substrate.
18. The apparatus of claim 14 wherein the cold arm is electrically
isolated from the hot arms.
19. The apparatus of claim 14 wherein at least one hot arm and the
cold arm comprise a circuit through which electric current is
passed.
20. The apparatus of claim 14 comprising a reinforcing member
formed in the cold arm.
21. The apparatus of claim 20 wherein the reinforcing member is
integrally formed in the cold arm.
22. The apparatus of claim 14 comprising a metal layer extending
along the cold arm.
23. The apparatus of claim 14 further comprising at least one hot
arm laterally offset from the side of the cold arm opposite the
side laterally offset from the at least two hot arms.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 09/659,282, filed Sep. 12, 2000, now allowed.
FIELD OF THE INVENTION
[0002] The present invention relates generally to micro-mechanical
devices, and more particularly, to a micrometer sized horizontal
and vertical thermal actuator that is capable of repeatable and
rapid movement of a micrometer-sized device off the surface of the
substrate.
BACKGROUND OF THE INVENTION
[0003] Fabricating complex micro-electro-mechanical systems (MEMS)
and micro-optical-electro-mechanical systems (MOEMS) devices
represents a significant advance in micro-mechanical device
technology. Presently, micrometer-sized analogs of many macro-scale
devices have been made, such as for example hinges, shutters,
lenses, mirrors, switches, polarizing devices, and actuators. These
devices can be fabricated, for example, using Multi-user MEMS
processing (MUMPs) available from Cronos Integrated Microsystems
located at Research Triangle Park, N.C. Applications of MEMS and
MOEMS devices include, for example, data storage devices, laser
scanners, printer heads, magnetic heads, micro-spectrometers,
accelerometers, scanning-probe microscopes, near-field optical
microscopes, optical scanners, optical modulators, micro-lenses,
optical switches, and micro-robotics.
[0004] One method of forming a MEMS or MOEMS device involves
patterning the device in appropriate locations on a substrate. As
patterned, the device lies flat on top of the substrate. For
example, the hinge plates of a hinge structure or a reflector
device are both formed generally coplanar with the surface of the
substrate using the MUMPs process. One challenge to making use of
these devices is moving them out of the plane of the substrate.
[0005] Coupling actuators with micro-mechanical devices allows for
moving these devices out of the plane of the substrate. Various
types of actuators, including electrostatic, piezoelectric, thermal
and magnetic have been used for this purpose.
[0006] One such actuator is described by Cowan et al. in "Vertical
Thermal Actuator for Micro-Opto-Electro-Mechanical Systems",
v.3226, SPIE, pp. 137-46 (1997). The actuator 20 of Cowan et al.
illustrated in FIG. 1 uses resistive heating to induce thermal
expansion. The hot arm 22 is higher than the cantilever arm 24, so
that thermal expansion drives the actuator tip 26 toward the
surface of the substrate 28. At sufficiently high current, the
downward deflection of the actuator tip 26 is stopped by contact
with the substrate 28 and the hot arms 22 bow upward. Upon removal
of the drive current the hot arms 22 rapidly "freeze" in the bowed
shape and shrink, pulling the actuator tip 26 upward, as
illustrated in FIG. 2.
[0007] The deformation of the hot arm 22 is permanent and the
actuator tip 26 remains deflected upward without applied power,
forming a backbent actuator 32. Further application of the drive
current causes the backbent actuator 32 to rotate in the direction
30 toward the surface of the substrate 28. The backbent actuator 32
of FIG. 2 is typically used for setup or one-time positioning
applications. The actuators described in Cowan et al. are limited
in that they cannot rotate or lift hinged plates substantially more
than forty-five degrees out-of-plane in a single actuation
step.
[0008] Harsh et al., "Flip Chip Assembly for Si-Based Rf MEMS"
Technical Digest of the Twelfth IEEE International Conference on
Micro Electro Mechanical Systems, IEEE Microwave Theory and
Techniques Society 1999, at 273-278; Harsh et al., "The Realization
and Design Considerations of a Flip-Chip Integrated MEMS Tunable
Capacitor" 80 Sensors and Actuators 108-118 (2000); and Feng et
al., "MEMS-Based Variable Capacitor for Millimeter-Wave
Applications" Solid-State Sensor and Actuator Workshop, Hilton Head
Island, S.C. 2000, at 255-258 disclose various vertical actuators
based upon a flip-chip design. During the normal release-etching
step, the base oxide layer is partially dissolved and the remaining
MEMS components are released. A ceramic substrate is then bonded to
the exposed surface of the MEMS device and the base polysilicon
layer is removed by completing the etch of the base oxide layer
(i.e., a flip chip process). The resultant device, which is
completely free of the polysilicon substrate, is a capacitor in
which the top plate of the capacitor is controllably moved in a
downward fashion toward an opposing plate on the ceramic substrate.
The device is removed from the polysilicon substrate because stray
capacitance effects of a polysilicon layer would at a minimum
interfere with the operation of the device.
[0009] Lift angles substantially greater than forty-five degrees
are achievable with a dual-stage actuator system. A dual-stage
actuator system typically consists of a vertical actuator and a
motor. The vertical actuator lifts the hinged micro-mechanical
device off of the substrate to a maximum angle not substantially
greater than forty-five degrees. The motor, which has a drive arm
connected to a lift arm of the micro-mechanical device, completes
the lift. One such dual-stage assembly system is disclosed by Reid
et al. in "Automated Assembly of Flip-Up Micromirrors", Transducers
'97, Int'l Conf. Solid-State Sensors and Actuators, pp. 347-50
(1997). These dual stage actuators are typically used for setup or
one-time positioning applications.
[0010] The dual-stage actuator systems are complex, decreasing
reliability and increasing the cost of chips containing MEMS and
MOEMS devices. As such, there is a need for a micrometer sized
horizontal and vertical thermal actuator that is capable of
repeatable and rapid movement of a micrometer-sized device off the
surface of the substrate.
BRIEF SUMMARY OF THE INVENTION
[0011] The present invention is direct to a micrometer sized
horizontal and vertical thermal actuator capable of repeatable and
rapid movement of a micrometer-sized optical device off the surface
of the substrate.
[0012] The horizontal and vertical thermal actuator is constructed
on a surface of a substrate. At least one hot arm has a first end
anchored to the surface and a free end located above the surface. A
cold arm has a first end anchored to the surface and a free end.
The cold arm is located above and laterally offset from the hot arm
relative to the surface. A member mechanically and electrically
couples the free ends of the hot and cold arms such that the
actuator exhibits vertical displacement and horizontal displacement
when current is applied to at least the hot arm.
[0013] The flexure comprises at least one of a recess, depression,
cut-out, hole, location of narrowed, thinned or weakened material,
alternate material or other structural features or material change
that decreases resistance to bending in that location. In one
embodiment, the hot arm and the cold arm comprise a circuit through
which electric current is passed. In another embodiment, a
grounding tab electrically couples the hot arm to the substrate. In
the embodiment with the grounding tab, the cold arm can optionally
be electrically isolated from the hot arm.
[0014] In one embodiment, a reinforcing member is formed in the
cold arm. The reinforcing member typically extends from proximate
the flexure to proximate the free end thereof. The reinforcing
member can be integrally formed in the cold arm. In one embodiment,
the reinforcing member extends longitudinally along the cold arm,
such as one or more ridges extending longitudinally along the cold
arm.
[0015] In one embodiment, the least one hot arm comprises two or
more hot arms each having a first end anchored to the surface and
free ends located above the surface. The plurality of hot arms can
optionally be arranged laterally offset and symmetrical with the
cold arm.
[0016] In another embodiment, the horizontal and vertical thermal
actuator constructed on a surface includes a first beam having a
first end anchored to the surface and a free end located above the
surface. A second beam has a first end anchored to the surface and
a free end located above the surface. A member electrically and
mechanically couples the free end of the first beam to the free end
of the second beam. A third beam has a first end anchored to the
surface and a free end mechanically coupled to the member. The
third beam is located above and laterally offset from the first and
second beams relative to the surface. First and second electrical
contacts are electrically coupled to the first ends of the first
and second beams, respectively. The actuator exhibits vertical
displacement and horizontal displacement when current is applied to
the first and second beams.
[0017] A plurality of horizontal and vertical thermal actuators can
be formed on a single substrate. At least one optical device can be
mechanically coupled to the horizontal and vertical thermal
actuator. The optical device comprises one of a reflector, a lens,
a polarizer, a wave-guide, a shutter, or an occluding structure.
The optical device can be part of an optical communication
system.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0018] Further features of the invention will become more apparent
from the following detailed description of specific embodiments
thereof when read in conjunction with the accompany drawings.
[0019] FIG. 1 is a side view of a vertical thermal actuator prior
to backbending.
[0020] FIG. 2 is a side view of the vertical thermal actuator of
FIG. 1 after backbending.
[0021] FIG. 3 is a top view of a horizontal and vertical thermal
actuator in accordance with the present invention.
[0022] FIG. 4 is a side view of the horizontal and vertical thermal
actuator of FIG. 3.
[0023] FIG. 5 is a sectional view of the horizontal and vertical
thermal actuator of FIG. 3.
[0024] FIG. 6 is a sectional view of the horizontal and vertical
thermal actuator of FIG. 3 in the activated position.
[0025] FIG. 7 is a side view of the horizontal and vertical thermal
actuator of FIG. 3 in an actuated position.
[0026] FIG. 8 is a top view of a two-beam horizontal and vertical
thermal actuator in accordance with the present invention.
[0027] FIG. 9 is a side view of the horizontal and vertical thermal
actuator of FIG. 8.
[0028] FIG. 10 is a sectional view of the horizontal and vertical
thermal actuator of FIG. 8.
[0029] FIG. 11 is a side view of a two-beam horizontal and vertical
thermal actuator in accordance with the present invention.
[0030] FIG. 12 is a top view of horizontal and vertical thermal
actuator with multiple hot arms in accordance with the present
invention.
[0031] FIG. 13 is a side view of the horizontal and vertical
thermal actuator of FIG. 12.
[0032] FIG. 14 is an end view of the horizontal and vertical
thermal actuator of FIG. 12.
[0033] FIG. 15 is a schematic illustration of an optical switch in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0034] The present invention relates to a horizontal and vertical
thermal actuator for micro-mechanical devices. The micrometer sized
horizontal and vertical thermal actuator is capable of repeatable
and rapid movement out of plane.
[0035] As used herein, "micro-mechanical device" refers to
micrometer-sized mechanical, opto-mechanical, electro-mechanical,
or opto-electro-mechanical device. Various technology for
fabricating micro-mechanical devices is available using the
Multi-User MEMS Processes (MUMPs) from Cronos Integrated
Microsystems located at Research Triangle Park, N.C. One
description of the assembly procedure is described in "MUMPs Design
Handbook", revision 5.0 (2000) available from Cronos Integrated
Microsystems.
[0036] Polysilicon surface micromachining adapts planar fabrication
process steps known to the integrated circuit (IC) industry to
manufacture micro-electro-mechanical or micro-mechanical devices.
The standard building-block processes for polysilicon surface
micromachining are deposition and photolithographic patterning of
alternate layers of low-stress polycrystalline silicon (also
referred to as polysilicon) and a sacrificial material (e.g.,
silicon dioxide or a silicate glass). Vias etched through the
sacrificial layers at predetermined locations provide anchor points
to a substrate and mechanical and electrical interconnections
between the polysilicon layers. Functional elements of the device
are built up layer-by-layer using a series of deposition and
patterning process steps. After the device structure is completed,
it can be released for movement by removing the sacrificial
material using a selective etchant such as hydrofluoric acid (HF)
which does not substantially attack the polysilicon layers.
[0037] The result is a construction system generally consisting of
a first layer of polysilicon which provides electrical
interconnections and/or a voltage reference plane, and additional
layers of mechanical polysilicon which can be used to form
functional elements ranging from simple cantilevered beams to
complex electro-mechanical systems. The entire structure is located
in-plane with the substrate. As used herein, the term "in-plane"
refers to a configuration generally parallel to the surface of the
substrate and the terms "out-of-plane" refer to a configuration
greater than zero degrees to about ninety degrees relative to the
surface of the substrate.
[0038] Typical in-plane lateral dimensions of the functional
elements can range from one micrometer to several hundred
micrometers, while the layer thicknesses are typically about 1-2
micrometers. Because the entire process is based on standard IC
fabrication technology, a large number of fully assembled devices
can be batch-fabricated on a silicon substrate without any need for
piece-part assembly.
[0039] FIGS. 3 through 5 illustrate a first embodiment of a
horizontal and vertical thermal actuator 50 in accordance with the
present invention. As used herein, "horizontal and vertical thermal
actuator" refers to a micro-mechanical device capable of repeatably
moving between an in-plane position and an out-of-plane position
that includes both a horizontal and a vertical component. The
horizontal and vertical thermal actuator 50 is disposed in-plane on
a surface of a substrate 52 typically comprising a silicon wafer 54
with a layer of silicon nitride 56 deposited thereon. The actuator
50 includes a first layer 60 of polysilicon located on the layer of
silicon nitride 56. A second layer of polysilicon 62 is configured
to have first and second anchors 64, 66 and a pair of beams 68, 70
arranged in a cantilever fashion from the anchors 64, 66
respectively.
[0040] In the embodiment illustrated in FIG. 3, the anchors 64, 66
include electrical contacts 76, 78 formed on the substrate 52
adapted to carry electric current to the beams 68, 70. The traces
76, 78 typically extend to the edge of the substrate 52.
Alternatively, a wide variety of electric contact devices and/or
packaging methods such as a ball grid array (BGA), land grid array
(LGA), plastic leaded chip carrier (PLCC), pin grid array (PGA),
edge card, small outline integrated circuit (SOIC), dual in-line
package (DIP), quad flat package (QFP), leadless chip carrier
(LCC), chip scale package (CSP) can be used to deliver electric
current to the beams 68, 70.
[0041] The beams 68, 70 are electrically and mechanically coupled
at their respective free ends 71, 73 by member 72 to form an
electric circuit. The beams 68, 70 are physically separated from
the first layer 60 so that the member 72 is located above the
substrate 52. In an unactivated configuration illustrated in FIG.
4, the beams 68, 70 are generally parallel to the surface of the
substrate 52. As used herein, the "unactivated configuration"
refers to a condition in which substantially no current is passed
through the circuit formed by the beam 68, the member 72 and the
beam 70.
[0042] A third layer 80 of polysilicon is configured with an anchor
82 attached to the substrate 52 near the anchor 64, 66. The third
layer 80 forms upper beam 84 cantilevered from the anchor 82 with a
free end 83 mechanically coupled to the member 72 above the beams
68, 70.
[0043] As best illustrated in FIG. 5, the beam 68, 70 are located
below and laterally offset from the beam 84 relative to the
substrate 52. FIG. 5 illustrates an axis 81 extending perpendicular
to the substrate 52 and through the center of the beam 84. The
center of mass of the beams 68, 70 is not located along the axis
81.
[0044] A via 88 is formed at the member 72 and/or free end 83 to
mechanically couple the free end 83 of the upper beam 84 to the
member 72. Other structures may be used to mechanically couple the
upper beam 84 to the member 72. The upper beam 84 is generally
parallel to surface of the substrate 52 in the unactivated
configuration.
[0045] FIGS. 6 and 7 illustrate the horizontal and vertical thermal
actuator 50 of FIGS. 3-5 in an out-of-plane or activated
configuration. The "activated configuration" refers to applying
electrical current to one or more of the beams. In the illustrated
embodiment, the activated configuration comprises applying current
to the circuit formed by the beam 68, the member 72, and the beam
70 (see FIG. 3). The beams 68, 70 are the "hot arms" and the beam
84 is the cold arm. As used herein, "hot arm" or "hot arms" refer
to beams or members that have a higher current density than the
cold arm(s) when a voltage is applied. "Cold arm" or "cold arms"
refer to beams or members that have a lower current density than
the hot arm(s) when a voltage is applied. In some embodiments, the
cold arm(s) has a current density of zero. Consequently, the hot
arms have greater thermal expansion than the cold arms.
[0046] The electric current heats the hot arms 68, 70 and causes
them to increase in length in the direction 90. Since the hot arms
68, 70 are laterally offset and below the cold arm 84, expansion in
the direction 90 causes horizontal and vertical displacement of the
cold arm 84 (and the member 72) along an axis 91 that passes
generally through the center of mass of the arms 68, 70, 84. As
used herein, "horizontal and vertical displacement" refers to a
displacement with a component parallel to the substrate and a
component perpendicular to the substrate.
[0047] With regard to horizontal displacement, expansion of the hot
arms 68, 70 causes horizontal displacement 93 of the cold arm 84
parallel to the substrate 52 a distance 79, as illustrated in FIG.
6. As used herein, "horizontal displacement" refers to the
displacement parallel to the plane of the substrate. The section of
FIG. 6 is taken near the member 72 and approximates the total
lateral displacement thereof.
[0048] With regard to vertical displacement, expansion of the hot
arms 68, 70 causes the cold arm 84 to move in an upward arc 92 a
distance 95, as illustrated in FIG. 7. Vertical displacement 97 is
perpendicular to the plane of the substrate 52.
[0049] The combination of horizontal and vertical displacement
generates lifting force 94. Due to the height difference between
the cold arm 84 and the hot arms 68, 70, a moment is exerted on the
cold arm 84 near the anchors 64, 66. The hot arms 68, 70 bend
easily, offering little resistance to the motion 92 of the cold arm
84. The cold arm 84, however, is fixed at the anchor 82 and
electrically isolated so that the current entirely or substantially
passes through the circuit formed by the hot arms 68, 70 and the
member 72. In the illustrated embodiment, the displacement 95 can
be about 1 micrometers to about 5 micrometers. When the current is
terminated, the horizontal and vertical thermal actuator 50 returns
to its original, unactivated configuration illustrated in FIG.
4.
[0050] In an alternate embodiment, the anchor 82 and the cold arm
84 are electrically coupled to the member 72. At least a portion of
the current flowing through the hot arms 68, 70 flows along the
cold arm 84 to the anchor 82. It is also possible that all of the
current flowing through the hot arms 68, 70 exits the horizontal
and vertical thermal actuator 50 through the cold arm 84. The
material and/or geometry of the cold arm 84 is adapted to have a
lower current density than the hot arms 68, 70, even when the same
voltage is applied. In one embodiment, the cold arm 84 is formed
from a material with a coefficient of linear thermal expansion less
than the coefficient of linear thermal expansion of the hot arms
68, 70. In yet another embodiment, the cold arm 84 is provided with
a lower electrical resistivity by having a larger cross sectional
area. In another embodiment, a conductive layer is provided on the
cold arm 84. Suitable conductive materials include metals such as
aluminum, copper, tungsten, gold, or silver, semiconductors, and
doped organic conductive polymers such as polyacetylene,
polyaniline, polypyrrole, polythiophene, polyEDOT and derivatives
or combinations thereof. Consequently, the net expansion of the hot
arms 68, 70 is greater than the expansion of the cold arm 84.
[0051] In another alternate embodiment, all or a portion of the
current flowing through the hot arms 68, 70 flows through grounding
tab (see FIG. 9) to the substrate 52. The grounding tab maintains
electrical contact with a contact pad the substrate 52 as the
thermal actuator 50 moves from the unactivated position to the
activated position.
[0052] FIGS. 8 through 10 illustrate a horizontal and vertical
thermal actuator 150 with two beams 152, 154 in accordance with the
present invention. The cold arm or beam 152 extends from anchor 156
in a cantilever fashion above and to the side of the hot arm or
beam 154 and the substrate 158. The hot arm 154 optionally extends
from the anchor 156 or from a separate anchor (see FIG. 11). Free
ends 160, 162 of the beams 152, 154, respectively, are mechanically
and electrically coupled at member 164. Reinforcing member 166
optionally extends along a portion of the cold arm 152. Flexure 170
is optionally formed in the cold arm 152 near the anchor 156.
[0053] When current is applied to the circuit formed by the beams
152, 154, and the member 164, the thermal actuator 150 moves along
displacement vector 177 that extends through the center of mass of
the beams 152, 154. The displacement vector 177 comprises a
vertical component 174 and a horizontal component 173. The
magnitude of the respective components 173, 174 can be adjusted by
altering the position of the hot arm 154 relative to the cold arm
152. The flexure 170 will also determine, in part, the magnitude of
the components 173, 174. In one embodiment, the flexure provides
asymmetrical resistance to bending, thereby increasing the
magnitude of one of the components 173, 174.
[0054] As used herein, "reinforcing member" refers to one or more
ridges, bumps, groove or other structural features that increase
resistance to bending. The reinforcing members are preferably
integral with the cold arm 152. In the illustrated embodiment, the
reinforcing member 166 is a curvilinear ridge (see FIG. 10)
extending along a portion of the cold arm 152, although it could be
rectangular, square, triangular or a variety of other shapes.
Additionally, the reinforcing member 166 can be located in the
center of the cold arm 152 or along the edges thereof. Multiple
reinforcing members may also be used.
[0055] As used herein, "flexure" refers to a recess, depression,
hole, slot, cut-out, location of narrowed, thinned or weakened
material, alternate material or other structural features or
material change that provides controlled bending in a particular
location. As used herein, "controlled bending" refers to bending
that occurs primarily at a discrete location, rather than being
distributed along the beams of the horizontal and vertical thermal
actuator. Alternate materials suitable for use as a flexure include
polysilicon, metal or polymeric material. As best illustrated in
FIGS. 3 and 5, the flexure 87 is a recess 89. The flexure 170
comprises the weakest section of the cold arm 152, and hence, the
location most likely to bend during actuation of the horizontal and
vertical thermal actuator 150.
[0056] The rigidity of the cold arm 152 relative to the rigidity of
the flexure 170 determines to a large extend the magnitude
(location and direction) of the controlled bending of the
horizontal and vertical thermal actuator 150. In one embodiment,
the reinforcing member 166 is used in combination with the flexure
170. In another embodiment, the reinforcing member 166 extends
along a portion of the cold arm 152, but no flexure is used. The
portion of the cold arm 152 without the reinforcing member 166 is
the location of controlled bending. In yet another alternate
embodiment, the flexure 170 is formed in the cold arm 152 without
the reinforcing member 166 such that the flexure 170 is the
location of controlled bending.
[0057] In one embodiment, the cold arm 152, the member 164 and the
hot arm 154 form a circuit. The material and/or geometry of the
cold arm 152 is controlled so that it experiences a lower current
density than the hot arm 154 when a voltage is applied to the
circuit, as discussed above.
[0058] In another embodiment, a grounding tab 163 electrically
couples the hot arm 154 to contact pad 165 on the substrate 158.
The grounding tab 163 is preferably flexible or a spring member so
that its electrical coupling with the substrate 158 is maintained
in the activated state (see generally FIG. 9). Consequently, less
current (or no current) flows through the cold arm 152, thereby
increasing the total displacement of the horizontal and vertical
thermal actuator 150.
[0059] FIG. 11 is a side view of a horizontal and vertical thermal
actuator 180 with cold arm or beam 182 located generally above and
to the side of the hot arm or beam 184, such as illustrated in FIG.
10. The cold arm 182 is attached to substrate 186 by anchor 188.
Reinforcing member 192 is optionally located on the cold arm 182. A
flexure 194 is optionally located on the cold arm 182 near the
anchor 188.
[0060] The hot arm 184 is attached to substrate 186 by anchor 190.
In one embodiment, the beams 182, 184 are electrically and
mechanically coupled at member 193. By locating the anchor 188
further from the member 193 than the anchor 190, the horizontal and
vertical thermal actuator 180 of FIG. 11 is capable of greater
displacement in the direction 194, but generates a lower lifting
force. In an alternate embodiment, the hot arm 184 can be
electrically coupled to the substrate by a grounding tab such as
discussed in connection with FIG. 9.
[0061] FIGS. 12 through 14 illustrate another embodiment of a
horizontal and vertical thermal actuator 200 in accordance with the
present invention. Cold arm 202 is cantilevered from anchor 206
above substrate 204. A first pair of hot arms 208, 210 are
cantilevered from anchors 212, 214, respectively, along a first
side of the cold arm 202. A second pair of hot arms 216, 218 are
cantilevered from anchors 220, 222, respectively, above the
substrate 204 along a second side of the cold arm 202. Distal ends
of the arms 202, 208, 210, 216 and 218 are mechanically coupled by
member 224.
[0062] As best illustrated in FIG. 14, the hot arms 208, 210 are
located below and to the side of (or laterally offset from) the
cold arm 202 relative to the substrate 204. Similarly, the hot arms
216, 218 are located below and to the other side of the cold arm
202. In the illustrated embodiment, the center of mass of the hot
arms 208, 210, 216, 218 are centered under the cold arm 202. That
is, the plurality of hot arms 208, 210, 216, 218 are laterally
offset but symmetrically arranged relative to the cold arm 202.
[0063] By selectively applying current to the hot arms 208, 210,
216, 218, the actuator 200 can be made to move out of plane in
various directions. In one embodiment, the hot arms 208, 210 form
an electric circuit that causes the cold arm 202 to be displaced
both horizontally and vertically in the direction 226. In another
embodiment, the hot arms 216, 218 form an electric circuit that
causes the cold arm 202 to be displaced both horizontally and
vertically in the direction 228. Alternatively, electric current is
applied to all of the hot arms 208, 210, 216, 218 to move the cold
arm 202 vertically off of the substrate 204. The cold arm 202 may
also be part of the electric circuit, as discussed above.
[0064] FIG. 15 is schematic illustration of an optical switch 350
utilizing a 4.times.4 array of optical devices 352. As used herein,
"optical device" refers to reflectors, lenses, polarizing devices,
wave guides, shutters, or occlusion devices. Each of the optical
devices 352 is mechanically coupled to one or more horizontal and
vertical thermal actuators illustrated herein. In the in-plane
position, the optical devices 352 do not extend into the optical
path of input optical fibers 354a-354d. In the out-of-plane
configuration the optical devices 352 extend into the optical path
of the input optical fibers 354a-354d. The array of vertical
mirrors 352 are arranged to permit an optical signal from any of
the input fibers 354a-354d to be optically coupled with any of the
output fibers 356a-356d through selective actuation of the
horizontal and vertical thermal actuators. The optical switch 350
illustrated in FIG. 15 is for illustration purposes only. The
present horizontal and vertical thermal actuators may be used in
any of a variety of optical switch architectures, such as an on/off
switch (optical gate), 2.times.2 switch, one.times.n switch, or a
variety of other architectures. The optical device can be part of
an optical communication system.
[0065] All of the patents and patent applications disclosed herein,
including those set forth in the Background of the Invention, are
hereby incorporated by reference. Although specific embodiments of
this invention have been shown and described herein, it is to be
understood that these embodiments are merely illustrative of the
many possible specific arrangements that can be devised in
application of the principles of the invention. Numerous and varied
other arrangements can be devised in accordance with these
principles by those of ordinary skill in the art without departing
from the scope and spirit of the invention. For example, any of the
flexures, reinforcing structures, anchor locations and beam
configurations disclosed herein can be combined to produce numerous
horizontal and vertical thermal actuators.
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