U.S. patent application number 10/217714 was filed with the patent office on 2002-12-26 for direct acting 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 | 20020195674 10/217714 |
Document ID | / |
Family ID | 24645896 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020195674 |
Kind Code |
A1 |
Weaver, Billy L. ; et
al. |
December 26, 2002 |
Direct acting vertical thermal actuator
Abstract
A micrometer sized, single-stage, vertical thermal actuator
capable of repeatable and rapid movement of a micrometer-sized
optical device off the surface of a substrate. The 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 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 member
moves away from the substrate when current is applied to at least
the hot arm. The hot arm can optionally include a grounding tab to
minimize thermal expansion of the cold 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: |
24645896 |
Appl. No.: |
10/217714 |
Filed: |
August 13, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10217714 |
Aug 13, 2002 |
|
|
|
09659572 |
Sep 12, 2000 |
|
|
|
Current U.S.
Class: |
257/415 |
Current CPC
Class: |
G02B 6/3576 20130101;
B81B 2203/053 20130101; H01H 61/04 20130101; G02B 6/352 20130101;
B81B 2203/0109 20130101; B81B 2203/0118 20130101; G02B 6/358
20130101; B81B 3/0024 20130101; B81B 2201/045 20130101; H01G 5/18
20130101; B81B 2201/031 20130101; B81B 3/0037 20130101; H01H 1/0036
20130101; B82Y 15/00 20130101; H01H 2061/008 20130101; H01H
2061/006 20130101 |
Class at
Publication: |
257/415 |
International
Class: |
H01L 029/82 |
Claims
What is claimed is:
1. A microelectrical mechanical actuator, comprising: (a) a planar
substrate; (b) a first member having first and second ends and
wherein the first end of the first member is coupled to the
substrate and the first member has a first electrical conductivity;
(c) a second member having first and second ends and wherein the
first end of the second member is coupled to the substrate and the
second ends of the first and second member are coupled together and
the second member has a second electrical conductivity; and (d)
wherein electrical current is conducted along the first member and
the second member causing thermal expansion of the first and second
members and the first and second members expand at different rates
thereby causing the second ends of the members to move away from
the substrate.
2. The microelectrical mechanical actuator of claim 1 wherein the
first member includes a conductor material and a semiconductor
material.
3. The microelectrical mechanical actuator of claim 1 wherein the
first member includes a low resistivity layer coupled thereto along
a length thereof.
4. A microelectrical mechanical actuator comprising: (a) a planar
substrate; (b) a first member having first and second ends and a
first elongate portion located there between, wherein the first end
is fixedly coupled to the substrate and the first elongate portion
is arranged to extend over the substrate such that the longitudinal
axis of the first elongate portion is substantially parallel to the
plane of the substrate and is located a first distance above the
substrate; and (c) a second member having first and second ends and
a second elongate portion located there between, wherein the first
end is fixedly coupled to the substrate and the second elongate
portion is arranged to extend over the substrate such that the
longitudinal axis of the second elongate portion is substantially
parallel to the plane of the substrate and is located a second
distance above the substrate, and the second ends of the first and
second members are coupled so that electrical current can flow
through the first member to and through the second member; (d)
wherein the first distance of the first elongate portion is not
equal to the second distance of the second elongate portion; and
(e) wherein Joule heating occurs when electrical current flows
through the first and second members and the first member undergoes
a first amount of thermal expansion, and the second member
undergoes a second amount of thermal expansion that is not equal to
the first amount of thermal expansion of the first member, so that
the coupled second ends of the first and second members move
relative to the substrate.
5. The microelectrical mechanical actuator of claim 4 wherein the
second elongate portion comprises a first and second leg and the
first leg is located proximate a first side of the first member and
the second leg is located proximate a second side of the first
member.
6. The microelectrical mechanical actuator of claim 4 wherein the
second elongate portion comprises a first and second leg and the
first leg is located proximate and outboard a first side of the
first member and the second leg is located proximate and outboard a
second side of the first member.
7. The microelectrical mechanical actuator of claim 4 wherein the
first member includes a low electrical resistance layer so that an
electrical resistance of the first member is less than an
electrical resistance of the second member whereby less Joule
heating occurs in the first member than in the second member when
current is conducted along the first and second members.
8. The microelectrical mechanical actuator of claim 4 wherein the
first member comprises conductor material and semiconductor
material.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of U.S.
application Ser. No. 09/659,572, filed on Sep. 12, 2000.
FIELD OF THE INVENTION
[0002] The present invention relates generally to micro-mechanical
devices, and more particularly, to a micrometer sized,
single-stage, vertical thermal actuator capable of repeatable and
rapid movement of a micrometer-sized device off the surface of a
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
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 directed to a micrometer sized
vertical thermal actuator capable of repeatable and rapid movement
of a micrometer-sized optical device off the surface of the
substrate.
[0012] The 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 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 member moves away from the substrate when
current is applied to the at least one hot arm.
[0013] 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] One or more of the free ends optionally include a dimple
supporting the member above the surface of the substrate. The cold
arm can be located directly over the hot arm. The first end of the
hot arm can be attached to the substrate adjacent to the first end
of the cold arm or offset from the first end of the cold arm. A
metal layer optionally extends along the cold arm. In one
embodiment, the at least one hot arm comprises two hot arms each
having a first end anchored to the surface and free ends located
above the surface.
[0015] In another embodiment, the vertical thermal actuator has a
first beam with 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 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, such that current supplied to the first and
second contacts causes the first and second beams to thermally
expand and the member to move in an arc away from the
substrate.
[0016] In one embodiment, the third beam is located generally over
the first and second beams. The third beam may optionally include a
metal layer. The first and second beams are generally parallel to
the first surface in an unactivated configuration. Electric current
is applied to the first and second electrical contacts in an
activated configuration so that the first and second beams curved
upward away from the surface of the substrate.
[0017] In one embodiment, the first end of the third beam is
electrically isolated from the substrate. In another embodiment, at
least a portion of the current in the first and second beams passes
through the third beam. The first and second beams can optionally
be electrically coupled to the substrate by a grounding tab.
[0018] A plurality of vertical thermal actuators can be formed on a
single substrate. At least one optical device can be mechanically
coupled to the 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. In another embodiment, a
wave-guide is formed on second beam. The wave-guide is preferably
integrally formed on second beam using micro-electro-mechanical
systems processing.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0019] 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.
[0020] FIG. 1 is a side view of a vertical thermal actuator prior
to backbending.
[0021] FIG. 2 is a side view of the vertical thermal actuator of
FIG. 1 after backbending.
[0022] FIG. 3 is a top view of a vertical thermal actuator in
accordance with the present invention.
[0023] FIG. 4 is a side view of the vertical thermal actuator of
FIG. 3.
[0024] FIG. 5 is a sectional view of the vertical thermal actuator
of FIG. 3.
[0025] FIG. 6 is a sectional view of the vertical thermal actuator
of FIG. 3.
[0026] FIG. 7 is a side view of the vertical thermal actuator of
FIG. 4 in an actuated position.
[0027] FIG. 8 is a top view of an alternate vertical thermal
actuator in accordance with the present invention.
[0028] FIGS. 9-11 are top views of vertical thermal actuators with
various anchor configurations in accordance with the present
invention.
[0029] FIG. 12 top view of a two-beam vertical thermal actuator in
accordance with the present invention.
[0030] FIG. 13 is a side view of the vertical thermal actuator of
FIG. 12.
[0031] FIG. 14 is a side view of an alternate two-beam vertical
thermal actuator in accordance with the present invention.
[0032] FIGS. 15-17 are various views of a vertical thermal actuator
including a wave guide in accordance with the present
invention.
[0033] FIG. 18 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 single-stage, vertical
thermal actuator for micro-mechanical devices. The micrometer
sized, single-stage, vertical thermal actuator is capable of
repeatable and rapid movement of a micrometer-sized device off the
surface of a substrate.
[0035] As used herein, "micro-mechanical device" refers to
micrometer-sized mechanical, opto-mechanical, electromechanical, 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 electromechanical 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 6 illustrate a first embodiment of a
vertical thermal actuator 50 with controlled bending in accordance
with the present invention. As used herein, "vertical thermal
actuator" refers to a micro-mechanical device capable of repeatably
moving an optical device between an in-plane position and an
out-of-plane position. The 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 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. In an alternate embodiment, beams 68, 70 are
electrically coupled to grounding tab 77. The grounding tab 77
electrically couples the beams 68, 70 to an electrical contact 79
on the substrate 52 in both the unactivated configuration (see FIG.
4) and the activated configuration (see FIG. 7). The grounding tab
77 can be a flexible member or a spring member that is adapted to
maintain contact with the substrate 52. A grounding tab can be used
with any of the embodiments disclosed herein.
[0042] The beams 68, 70 are physically separated from the first
layer 60 so that the member 72 is located above the substrate 52.
One or more dimples 74 may optionally be formed in the member 72 to
support the beams 68, 70 above the substrate 52. In an alternate
embodiment, the dimples or bumps 74 can be formed on 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.
[0043] 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. In one embodiment, a metal layer is optionally applied to
the upper beam 84.
[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] FIG. 7 is a side sectional view of the vertical thermal
actuator 50 of FIGS. 3-6 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, electric current is applied 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. Expansion of the
beams 68, 70 causes the free end 83 of the vertical thermal
actuator 50 to move in an upward arc 92, generating lifting force
94 and displacement 95. 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.
[0047] 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 cold arm 84 bends along its length. The hot
arms 68, 70 also bend easily, offering little resistance to the
motion 92 of the cold arm 84. In the illustrated embodiment, the
displacement 95 can be from about 0.5 micrometers to about 4
micrometers. When the current is terminated, the vertical thermal
actuator 50 returns to its original, unactivated configuration
illustrated in FIG. 4.
[0048] 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 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.
[0049] In another alternate embodiment, all or a portion of the
current flowing through the hot arms 68, 70 flows through grounding
tab 77 to the substrate 52. The grounding tab 77 maintains physical
contact with the substrate 52 as the vertical thermal actuator 50
moves from the unactivated position to the activated position
illustrated in FIG. 7.
[0050] FIG. 8 illustrates an alternate embodiment of a vertical
thermal actuator 50' in which the anchor 82' and the beam 84' are
not electrically isolated from the member 72'. Current flows in the
direction of the arrows 96' from the beams 68', 70', through the
member 72' and back to the anchor 82' along the beam 84'. The
material and/or geometry of the beam 84' is controlled so that it
experiences a lower current density than the beams 68', 70'. In one
embodiment, the beam 84' is formed from a material with a
coefficient of linear thermal expansion less than the coefficient
of linear thermal expansion of the beams 68', 70'. In yet another
embodiment, the beam 84' is provided with a lower electrical
resistivity by having a larger cross sectional area. In another
embodiment, a conductive layer 98' is provided on the beam 84'.
Consequently, the net expansion of the beams 68', 70' is greater
than the expansion of the beam 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.
[0051] FIG. 9 illustrates an alternate vertical thermal actuator
200 having first and second anchors 202, 204 for the beams 206, 208
located further from the member 210 than the anchor 212 for the
beam 214. The vertical thermal actuator 200 of FIG. 9 provides a
greater lifting force, with a reduction in total displacement.
[0052] FIG. 10 illustrates an alternate vertical thermal actuator
220 having first and second anchors 222, 224 for the beams 226, 228
located closer to the member 230 than the anchor 232 for the beam
234. The vertical thermal actuator 220 of FIG. 10 provides a
greater displacement, with a reduction in total lifting force.
[0053] FIG. 11 illustrates an alternate vertical thermal actuator
240 having first anchor 242 for the beam 246 further from the
member 250 than the anchor 252 for the beam 254. The second anchors
244 for the beams 248 is located closer to the member 250 than the
anchor 252. The thermal expansion for the beams 246, 248 is still
greater than any expansion of the beam 254 so that a net lifting
force is generated when current is applied to the beams 246, 248.
Assuming that the expansion per unit length is the same for the
beams 246, 248, the net expansion of the beam 246 will be greater
than the expansion of the beam 248. Consequently, the vertical
thermal actuator 240 will rise from the substrate with a twisting
motion, causing a lateral displacement of the member 250 in a
direction 256.
[0054] FIGS. 12 and 13 illustrate a vertical thermal actuator 260
with two beams 262, 264 in accordance with the present invention.
The beams 262, 264 extend from anchor 266 in a cantilever fashion
above substrate 268. Free ends 270, 272 of the beams 262, 264,
respectively, are mechanically and electrically coupled at member
274. In one embodiment, the cold arm or beam 262, the member 274
and the hot arm or beam 264 form a circuit.
[0055] The material and/or geometry of the cold arm 262 is
controlled so that it experiences a lower current density than the
hot arm 264. In one embodiment, the cold arm 262 is formed from a
material with a coefficient of linear thermal expansion less than
the coefficient of linear thermal expansion of the hot arm 264. In
yet another embodiment, the cold arm 262 is provided with a lower
electrical resistivity by having a larger cross sectional area
and/or a conductive layer 276. Consequently, the net expansion of
the hot arm 264 is greater than the expansion of the cold arm 262.
When current is applied to the beams 262, 264, the vertical thermal
actuator 260 curves upward in direction 278 and generates lifting
force 280.
[0056] In another embodiment, a grounding tab 273 electrically
couples the hot arm 264 to the substrate 268. The grounding tab 273
is preferably flexible or a spring member so that its electrical
coupling with the substrate 268 is maintained in the activated
state (see generally FIG. 7). Consequently, less current (or no
current) flows through the cold arm 262, thereby increasing the
total displacement of the vertical thermal actuator 260.
[0057] FIG. 14 is a side view of a vertical thermal actuator 290
with cold arm or beam 292 located generally above hot arm or beam
294, such as illustrated in FIG. 13. The cold arm 292 is attached
to substrate 296 by anchor 298. The hot arm 294 is attached to
substrate 296 by anchor 300. In one embodiment, the beams 292, 294
are electrically and mechanically coupled at member 302. By
locating the anchor 298 further from the member 302 than the anchor
300, the vertical thermal actuator 290 of FIG. 14 is capable of
greater displacement in the direction 304, but generates a lower
lifting force. In an alternate embodiment, the hot arm 294 can be
electrically coupled to the substrate by a grounding tab such as
discussed in connection with FIG. 13.
[0058] FIGS. 15 through 17 illustrate an optical switch 310 using a
vertical thermal actuator 312 generally as illustrated in FIG. 3
with a wave guide 314 attached to the cold arm or beam 316 in
accordance with the present invention. The wave guide 314 can be
formed as part of the fabrication process or added as a separate
component, such as an optical fiber. The wave guide 314 can be
effectively located on the cold arm 316 since it experiences little
or no thermal expansion. The cold arm 316 is preferably
electrically isolated from the hot arms 324, 326.
[0059] As best illustrated in FIG. 16, when the vertical thermal
actuator 312 is in the deactivated or in-plane configuration, the
wave guide 314 is optically coupled with an adjacent wave guide
318. In the activated or out-of-plane configuration illustrated in
FIG. 17, the wave guide 314 can be aligned with any of a plurality
of other wave guides 320, 322. Consequently, the wave guide 314 can
be selectively coupled to any of the wave guides 318, 320, 322 by
varying the current applied to the vertical thermal actuator
312.
[0060] FIG. 18 is schematic illustration of an optical switch 150
utilizing a 4.times.4 array of optical devices 152. As used herein,
"optical device" refers to reflectors, lens, polarizing devices,
wave guides, shutters, or occlusion devices. Each of the optical
devices 152 is mechanically coupled to one or more vertical thermal
actuators. In the in-plane position, the optical devices 152 do not
extend into the optical path of input optical fibers 154a-154d. In
the out-of-plane configuration the optical devices 152 extend into
the optical path of the input optical fibers 154a-154d. The array
of vertical mirrors 152 are arranged to permit an optical signal
from any of the input fibers 154a-154d to be optically coupled with
any of the output fibers 156a-156d through selective actuation of
the vertical thermal actuators.
[0061] The optical switch 150 illustrated in FIG. 18 is for
illustration purposes only. Any of the present vertical thermal
actuators may be used in 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 switch 150 can be part of an optical communication
system.
[0062] 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.
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