U.S. patent application number 09/728474 was filed with the patent office on 2003-11-13 for mems optical switch actuator.
Invention is credited to Fu, Xiaodong R., Lambert, David W., Merchant, Paul P..
Application Number | 20030210851 09/728474 |
Document ID | / |
Family ID | 29401831 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030210851 |
Kind Code |
A1 |
Fu, Xiaodong R. ; et
al. |
November 13, 2003 |
MEMS OPTICAL SWITCH ACTUATOR
Abstract
A micro-electro-mechanical system (MEMS) optical switch actuator
and method for fabricating the actuator provide an anchor assembly
that functions as a second electrode. The actuator has a reflective
element assembly and a first electrode assembly for moving the
reflective element assembly from a first position to a second
position based on a switching signal. The actuator further includes
an anchor assembly coupled to the reflective element assembly such
that a spring force is generated in the reflective element assembly
when the reflective element assembly is in the second position. The
anchor assembly is electrically conductive such that the switching
signal generates an electrostatic force between the anchor assembly
and the first electrode assembly. The method for fabricating the
actuator includes the step of coupling a multi-level reflection
assembly to an optical circuit. The reflection assembly has an
electrically conductive anchor assembly positioned at a first level
with respect to the optical circuit and a mirror positioned at a
second level with respect to the optical circuit. An insulative
mirror beam layer is then coupled to the reflection assembly, and
an electrode assembly is coupled to the mirror beam layer. The
electrode assembly is coupled such that a voltage potential between
the anchor assembly and the electrode assembly causes the electrode
assembly to force the mirror beam layer and the mirror from the
first switching position to the second switching position.
Inventors: |
Fu, Xiaodong R.; (Painted
Post, NY) ; Lambert, David W.; (Corning, NY) ;
Merchant, Paul P.; (Corning, NY) |
Correspondence
Address: |
CORNING INCORPORATED
SP-TI-3-1
CORNING
NY
14831
|
Family ID: |
29401831 |
Appl. No.: |
09/728474 |
Filed: |
December 1, 2000 |
Current U.S.
Class: |
385/18 |
Current CPC
Class: |
G02B 6/357 20130101;
G02B 6/3546 20130101; G02B 6/358 20130101; G02B 6/3584 20130101;
G02B 6/3596 20130101; G02B 6/3514 20130101; G02B 6/3518
20130101 |
Class at
Publication: |
385/18 |
International
Class: |
G02B 006/26 |
Claims
What is claimed is:
1. A micro-electro-mechanical-system (MEMS) optical switch actuator
comprising: a reflective element assembly; a first electrode
assembly for moving the reflective element assembly from a first
position to a second position based on a switching signal; and an
anchor assembly coupled to the reflective element assembly such
that a spring force is generated in the reflective element assembly
when the reflective element assembly is in the second position, the
anchor assembly being electrically conductive such that the
switching signal generates an electrostatic force between the
anchor assembly and the first electrode assembly.
2. The actuator of claim 1 wherein the first electrode assembly
includes: an actuator beam; a contact stud coupled to the actuator
beam; and a pillar structure for supporting the actuator beam
adjacent to the reflective element assembly such that the contact
stud moves the reflective element assembly from the first position
to the second position in response to the switching signal.
3. The actuator of claim 2 wherein the pillar structure includes a
single pillar architecture for supporting the actuator beam at a
first end such that a second end of the actuator beam is free
standing.
4. The actuator of claim 2 wherein the pillar structure includes a
dual pillar architecture for supporting the actuator beam at a
first end and a second end.
5. The actuator of claim 1 wherein the anchor assembly includes: a
first anchor for supporting the reflective element assembly at a
first end; and a second anchor for supporting the reflective
element assembly at a second end.
6. The actuator of claim 5 wherein each anchor includes: an
electrode; and an extension coupled to the electrode and the
reflective element assembly.
7. The actuator of claim 1 wherein the reflective element assembly
includes: a non-electrically conductive mirror beam; and a mirror
coupled to the mirror beam.
8. A method for fabricating a micro-electro-mechanical-system
(MEMS) optical switch actuator, the method comprising the steps of:
coupling a multi-level reflection assembly to an optical circuit,
the reflection assembly having an electrically conductive anchor
assembly positioned at a first level with respect to the optical
circuit and a mirror positioned at a second level with respect to
the optical circuit; coupling an insulative mirror beam layer to
the reflection assembly; and coupling an electrode assembly to the
mirror beam layer such that a voltage potential between the anchor
assembly and the electrode assembly causes the electrode assembly
to force the mirror beam layer and the mirror from a first
switching position to a second switching position.
9. The method of claim 8 further including the steps of: generating
actuation anchor regions in a waveguide layer of the optical
circuit, the actuation anchor regions being defined by walls that
extend from a top surface of the waveguide layer to a top surface
of a substrate of the optical circuit; generating a mirror region
within a recess of the waveguide layer, the mirror region being
defined by walls that extend from the top surface of the waveguide
layer to an intermediate level within the waveguide layer;
disposing the anchor assembly within the actuation anchor regions;
and disposing the mirror within the mirror region.
10. The method of claim 9 further including the steps of:
depositing a plastic polymer layer on the top surface of the
waveguide layer and within the recess of the waveguide layer;
depositing a photoresist layer on the plastic polymer layer;
patterning the photoresist layer to open the mirror region and the
actuation anchor regions from the top surface of the waveguide
layer to the intermediate level; and etching the actuation anchor
regions to the top surface of the substrate.
11. The method of claim 10 further including the step of using
polyimide as the plastic polymer.
12. The method of claim 10 further including the steps of:
depositing a metallic layer on the top surface of the waveguide
layer and within the mirror region; and stripping the metallic
layer in an acid dip such that the actuation anchor regions are
etched to the top surface of the substrate.
13. The method of claim 12 further including the step of using
titanium as the metallic layer.
14. The method of claim 9 further including the steps of:
depositing an adhesive layer on the top surface of the waveguide
layer, within the mirror region, and within the actuation anchor
regions; etching the adhesive layer from the mirror region and a
portion of the top surface of the waveguide layer such that the
adhesive layer remains in the actuation anchor regions and in
reflective anchor regions, the reflective anchor regions defined by
the portion of the top surface of the waveguide layer having the
adhesive layer; depositing an optically reflective layer on the top
surface of the waveguide layer, within the actuation anchor
regions, within the mirror region, and within the reflective anchor
regions; etching the optically reflective layer from the top
surface of the waveguide layer; and depositing a metallic layer on
the remaining optically reflective layer.
15. The method of claim 14 further including the step of using gold
for the optically reflective layer.
16. The method of claim 14 further including the step of using
nickel for the metallic layer.
17. The method of claim 8 further including the steps of:
depositing the insulative mirror beam layer on the reflection
assembly under tensile stress; and etching the mirror beam layer
from a portion of a top surface of a waveguide layer of the optical
circuit such that a bridge is formed; said bridge suspending the
mirror of the multi-level reflection assembly at the first
level.
18. The method of claim 17 further including the step of using SiN
for the insulative mirror beam layer.
19. The method of claim 8 further including the steps of:
depositing a plastic polymer layer on a top surface of a waveguide
layer of the optical circuit and on the mirror beam layer; curing
the plastic polymer layer; depositing a metallic layer on the
plastic polymer layer; masking the metallic layer in a desired post
configuration; etching the metallic layer and the plastic polymer
layer such that electrode regions are generated, the electrode
regions being defined by walls extending from a top surface of the
plastic polymer layer to a top surface of the mirror beam layer;
depositing a seed layer on the top surface of the plastic polymer
layer and within the electrode regions; depositing an electrode
layer on the seed layer; masking the electrode layer in a desired
bridge configuration; etching the electrode layer such that the
electrode assembly is generated; and removing the plastic polymer
layer.
20. The method of claim 19 further including the step of using
polyimide for the plastic polymer layer.
21. The method of claim 19 further including the step of using
titanium for the metallic layer.
22. The method of claim 19 further including the step of reactive
ion etching the metallic layer.
23. The method of claim 19 further including the step of using
Cr/Ni for the seed layer.
24. The method of claim 19 further including the step of using
nickel for the electrode layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to optical
switching. More particularly, the present invention relates to a
micro-electro-mechanical- -system optical switch actuator having an
electrically conductive anchor assembly.
[0003] 2. Technical Background
[0004] In the development of communications technologies, the
primary objectives have always included the improvement of
transmission fidelity, the increase of data rates, and the increase
of distance between relay stations. The speed at which light
travels and its potential to address all of these concerns
logically led to attempts at optical communication. Early
experiments with optical communications suggested the feasibility
of modulating a coherent optical carrier wave at very high
frequencies, but were commercially impractical because of the
installation expense and the tremendous cost of developing the
necessary components. The combination of semiconductor technology,
which provided the necessary light sources and photodetectors, and
optical waveguide technology, however, eventually enabled the
development and use of optical fiber-based systems despite these
initially perceived difficulties.
[0005] Optical networking involves the management and coordination
of various functions such as optical transport and optical
switching. Earlier approaches to optical switching actually
involved the conversion of optical signals into electrical signals
and the switching of the electrical signals. This type of
electrical/optical conversion proved to be both difficult to
implement and costly due to the required transformation into and
out of the electrical domain. As a result, more recent approaches
have attempted to perform switching in the optical domain.
[0006] Optical switching in the networking context presents its own
set of unique concerns. For example, in order to efficiently manage
the increasing number of optical signals and wavelength channels,
optical switches must be significantly reduced in size.
Micro-electro-mechanical-- systems (MEMS) have recently been
developed based on semiconductor processes, and applied in the
areas of medicine, life science, sensors, aerospace,
micro-satellites and data storage. MEMS technology allows
conventionally large components to be reduced to sizes not
previously available. While some attempts have been made at
applying MEMS technology to optical switching in the networking
context, certain concerns still remain.
[0007] One such concern is the design of the actuator for the
optical switch. For example, thermal actuation schemes have been
attempted, but often lead to difficult heating issues. In fact, the
type of driving force that is used to operate the actuator is a
crucial factor. It is therefore desirable to provide a MEMS optical
switch actuator that does not use heat as a driving force.
[0008] While certain attempts have been made using electrostatic
forces to actuate the optical switch, there is considerable room
for improvement. For example, in the conventional electrostatic
actuator approach, a pair of electrodes and various anchoring
structures will be used to force a reflective element into and out
of the path of an optical signal. The anchoring structures serve to
attach the actuator to the optical circuit and provide the
requisite stability for actuation. These approaches have typically
been quite complex and require several fabrication steps in order
to create the relatively high number of anchors and complex
electrodes. It is therefore desirable to provide a MEMS optical
switch actuator that operates in response to electrostatic driving
forces, but does not require separate electrode and anchor
assemblies.
[0009] As noted above, fabrication of MEMS actuators has proven to
be quite difficult. For example, in order to generate sufficient
force to manipulate a mirror (or reflective element), it is often
necessary to provide a multi-level reflection assembly.
Specifically, anchoring of the entire structure as well as
manipulation of the mirror require widely varying amounts of
structural support. Conventional actuators, however, have not
addressed this issue to a sufficient level of specificity. It is
therefore desirable to provide a method for fabricating a
multi-level reflection assembly having an anchor assembly that also
functions as an electrode.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, a
micro-electro-mechanica- l-system (MEMS) optical switch actuator is
provided. The actuator has a reflective element assembly and a
first electrode assembly for moving the reflective element assembly
from a first position to a second position based on a switching
signal. The actuator further includes an anchor assembly coupled to
the reflective element assembly such that a spring force is
generated in the reflective element assembly when the reflective
element assembly is in the second position. The anchor assembly is
electrically conductive such that the switching signal generates an
electrostatic force between the anchor assembly and the first
electrode assembly. Using the anchor assembly as an effective
second electrode allows simplification of the actuator in a manner
unachievable under conventional approaches.
[0011] In another aspect of the invention, a method for fabricating
a MEMS optical switch actuator is provided. The method includes the
step of coupling a multi-level reflection assembly to an optical
circuit. The reflection assembly has an electrically conductive
anchor assembly positioned at a first level with respect to the
optical circuit, and a mirror positioned at a second level with
respect to the optical circuit. An insulative mirror beam layer is
then coupled to the reflection assembly, and an electrode assembly
is coupled to the mirror beam layer. The electrode assembly is
coupled such that a voltage potential between the anchor assembly
and the electrode assembly causes the electrode assembly to force
the mirror beam layer and the mirror from a first switching
position to a second switching position. Positioning the anchor
assembly at a different level from the mirror reduces the overall
number of components and allows the fabrication process to be
simplified beyond that available under conventional approaches.
[0012] It is to be understood that both the foregoing general
description and the following detailed description are merely
exemplary of the invention, and are intended to provide an overview
or framework for understanding the nature and character of the
invention as it is claimed. The accompanying drawings are included
to provide a further understanding of the invention, and are
incorporated in and constitute part of this specification. The
drawings illustrate various features and embodiments of the
invention, and together with the description serve to explain the
principles and operation of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The various advantages of the present invention will become
apparent to one skilled in the art by reading the following
specification and appended claims, and by referencing the following
drawings, in which:
[0014] FIG. 1 is a side view of an optical switch actuator in
accordance with the principals of one embodiment of the present
invention;
[0015] FIG. 2 is a side view of an optical switch actuator in
accordance with the principals of an alternative embodiment of the
present invention;
[0016] FIG. 3 is a plan view of an optical circuit in accordance
with the present invention;
[0017] FIG. 3A is a cross sectional view taken along lines 3A-3A
shown in FIG. 3 of the present invention;
[0018] FIG. 3B is a cross sectional view taken along lines 3B-3B
shown in FIG. 3 of the present invention;
[0019] FIG. 4 is a plan view of the optical circuit shown in FIG. 3
having actuation anchor regions and a mirror region in accordance
with the present invention;
[0020] FIG. 4A is a cross sectional view taken along lines 4A-4A
shown in FIG. 4 of the present invention;
[0021] FIG. 4B is a cross sectional view taken along lines 4B-4B
shown in FIG. 4 of the present invention;
[0022] FIG. 5 is a plan view of the optical circuit shown in FIG. 4
having a metallic layer in accordance with the present
invention;
[0023] FIG. 5A is a cross sectional view taken along lines 5A-5A
shown in FIG. 5 of the present invention;
[0024] FIG. 5B is a cross sectional view taken along lines 5B-5B
shown in FIG. 5 of the present invention;
[0025] FIG. 6 is a plan view of the optical circuit shown in FIG. 5
having the actuation anchor regions etched to the top surface of a
substrate in accordance with the present invention;
[0026] FIG. 6A is a cross sectional view taken along lines 6A-6A
shown in FIG. 6 of the present invention;
[0027] FIG. 6B is a cross sectional view taken along lines 6B-6B
shown in FIG. 6 of the present invention;
[0028] FIG. 7 is a plan view of the optical circuit shown in FIG. 6
having an adhesive layer disposed within actuation anchor regions
and reflective anchor regions in accordance with the present
invention;
[0029] FIG. 7A is a cross sectional view taken along lines 7A-7A
shown in FIG. 7 of the present invention;
[0030] FIG. 7B is a cross sectional view taken along lines 7B-7B
shown in FIG. 7 of the present invention;
[0031] FIG. 8 is a plan view of the optical circuit shown in FIG. 7
having an optically reflective layer deposited on the top surface
of the waveguide layer, the actuation anchor regions, the mirror
region, and the reflective anchor regions in accordance with the
present invention;
[0032] FIG. 8A is a cross sectional view taken along lines 8A-8A
shown in FIG. 8 of the present invention;
[0033] FIG. 8B is a cross sectional view taken along lines 8B-8B
shown in FIG. 8 of the present invention;
[0034] FIG. 9 is a plan view of the optical circuit shown in FIG. 8
having a metallic layer deposited on an optically reflective layer
in accordance with the present invention;
[0035] FIG. 9A is a cross sectional view taken along lines 9A-9A
shown in FIG. 9 of the present invention;
[0036] FIG. 9B is a cross sectional view taken along lines 9B-9B
shown in FIG. 9 of the present invention;
[0037] FIG. 10 is a plan view of the optical circuit shown in FIG.
9 having an insulative mirror beam layer deposited on a reflection
assembly in accordance with the present invention;
[0038] FIG. 10A is a cross sectional view taken along lines 9A-9A
shown in FIG. 10 of the present invention;
[0039] FIG. 10B is a cross sectional view taken along lines 10B-10B
shown in FIG. 10 of the present invention;
[0040] FIG. 11 is a plan view of the optical circuit shown in FIG.
10 having a mirror beam layer etched from a portion of the top
surface of a waveguide layer in accordance with the present
invention;
[0041] FIG. 11A is a cross sectional view taken along lines 11A-11A
shown in FIG. 11 of the present invention;
[0042] FIG. 11B is a cross sectional view taken along lines 11B-11B
shown in FIG. 11 of the present invention;
[0043] FIG. 12 is a plan view of the optical circuit shown in FIG.
11 having a plastic polymer layer deposited on a top surface of a
waveguide layer and a mirror beam layer in accordance with the
present invention;
[0044] FIG. 12A is a cross sectional view taken along lines 12A-12A
shown in FIG. 12 of the present invention;
[0045] FIG. 12B is a cross sectional view taken along lines 12B-12B
shown in FIG. 12 of the present invention;
[0046] FIG. 13 is a plan view of the optical circuit shown in FIG.
12 having an etched metallic layer and plastic polymer layer such
that electrode regions are generated in accordance with the present
invention;
[0047] FIG. 13A is a cross sectional view taken along lines 13A-13A
shown in FIG. 13 of the present invention;
[0048] FIG. 13B is a cross sectional view taken along lines 13B-13B
shown in FIG. 13 of the present invention;
[0049] FIG. 14 is a plan view of the optical circuit shown in FIG.
13 having a seed layer deposited on the top surface of the plastic
polymer layer and electrode regions in accordance with the present
invention;
[0050] FIG. 14A is a cross sectional view taken along lines 14A-14A
shown in FIG. 14 of the present invention;
[0051] FIG. 14B is a cross sectional view taken along lines 14B-14B
shown in FIG. 14 of the present invention;
[0052] FIG. 15 is a plan view of the optical circuit shown in FIG.
15 having an electrode layer deposited on the seed layer in
accordance with the present invention;
[0053] FIG. 15A is a cross sectional view taken along lines 15A-15A
shown in FIG. 15 of the present invention;
[0054] FIG. 15B is a cross sectional view taken along lines 15B-15B
shown in FIG. 15 of the present invention;
[0055] FIG. 16 is a plan view of the optical circuit shown in FIG.
15 having the electrode layer masked and etched such that an
electrode assembly is generated in accordance with the present
invention;
[0056] FIG. 16A is a cross sectional view taken along lines 16A-16A
shown in FIG. 16 of the present invention;
[0057] FIG. 16B is a cross sectional view taken along lines 16B-16B
shown in FIG. 16 of the present invention;
[0058] FIG. 17 is a plan view of the optical circuit shown in FIG.
16 having the plastic polymer layer removed in accordance with the
present invention;
[0059] FIG. 17A is a cross sectional view taken along lines 17A-17A
shown in FIG. 17 of the present invention; and
[0060] FIG. 17B is a cross sectional view taken along lines 17B-17B
shown in FIG. 17 of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0061] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numerals will be used throughout the drawings to
refer to the same or like parts.
[0062] Turning now to FIG. 1, a micro-electro-mechanical-system
(MEMS) optical switch actuator 20 is shown. Generally, the actuator
20 has a reflective element assembly 30, a first electrode assembly
40, and an anchor assembly 50. The first electrode assembly 40
moves the reflective element assembly 30 from a first position to a
second position based on an applied switching signal. The
reflective element assembly 30 is shown as being in the first
position. The anchor assembly 50 is coupled to the reflective
element assembly 30 such that a spring force is generated in the
reflective element assembly 30 when the reflective element 30 is in
the second position. It is important to note that the anchor
assembly 50 is electrically conductive such that the switching
signal generates an electrostatic force between the anchor assembly
50 and the first electrode assembly 40.
[0063] It can be seen that the reflective element assembly 30
preferably includes a non-electrically conductive (i.e.,
insulative) mirror beam 32 and a mirror 34 coupled to the mirror
beam 32. The dielectric nature of the mirror beam 32 allows an
electric field to be generated between the first electrode assembly
40 and the anchor assembly 50 when the switching signal is applied.
Suspending the mirror 34 from a dielectric material provides a much
more compact configuration than available under conventional
approaches.
[0064] It can further be seen that the first electrode assembly 40
has an actuator beam 42, and a contact stud 44 coupled to the
actuator beam 42. A pillar structure supports the actuator beam 42
adjacent to the reflective element assembly 30 such that the
contact stud 44 moves the reflective element assembly 30 from the
first position (shown in FIG. 1) to the second position in response
to the switching signal. The preferred pillar structure includes a
dual pillar architecture 46 for supporting the actuator beam 42 at
a first end and a second end.
[0065] FIG. 2 demonstrates a MEMS optical switch actuator 60 with
an alternative pillar structure. In this embodiment, the pillar
structure includes a single pillar architecture 48 for supporting
the actuator beam 42 at a first end 62 such that a second end 64 of
the actuator beam 42 is free standing. This approach requires
greater stress control in the actuator beam 42, but may provide
enhanced torque and therefore improved actuation.
[0066] The contact stud 44' is larger in size than in the preferred
embodiment, and may optionally have a non-cubical shape (e.g.
rounded). Rounding the contact stud 44' will allow the first
electrode assembly 40' to accommodate for the additional moments
associated with the single pillar design.
[0067] Returning now to FIG. 1, it will be appreciated that the
dual pillar architecture 46 need not be deposited directly upon the
light wave optical circuit (LOC) substrate 22. In fact, it is
important to note that the LOC substrate 22 must be made of a
dielectric material in order to maintain electrical isolation
between the first electrode assembly 40 and the anchor assembly 50
if substrate deposition is chosen. As will be discussed below,
another approach could be to deposit the dual pillar architecture
46 directly upon the mirror beam 32.
[0068] The anchor assembly 50 will now be described in greater
detail. Specifically, the anchor assembly 50 preferably includes a
first anchor 52 for supporting the reflective element assembly 30
at a first end, and a second anchor 54 for supporting the
reflective element assembly 30 at a second end. Each anchor 52, 54
preferably includes an electrode 56, and an extension 58 coupled to
the electrode 56 and the reflective element assembly 30.
[0069] In operation, light will propagate along core portions 24a
and 24b when the reflective element assembly 30 is in the first
position (i.e., at equilibrium). When a voltage potential is
applied between the first electrode assembly 40 and the anchor
assembly 50, the actuator beam 42 and the contact stud 44 will be
drawn in the downward direction towards the LOC substrate 22. The
contact stud 44 will therefore come into contact with the mirror
beam 32 such that the mirror beam 32 and the mirror 34 are forced
downward. The mirror 34 will intersect the propagation path of the
light traveling through the core portions 24. Thus, if the light is
traveling from left to right, the reflective surface of the mirror
34 will direct the light away from core portion 24b. Thus, with
proper design of the core portions, optical switching can be
performed in any number of configurations.
[0070] It will also be appreciated that the present invention
provides a method for fabricating a MEMS optical switch actuator.
Generally, FIGS. 3-17B demonstrate one approach to such a
fabrication in accordance with the present invention. Specifically,
FIGS. 3, 3a and 3b show an optical circuit 70 to which the switch
actuator of the present invention is coupled. The optical circuit
70 has a waveguide layer 72 and a recess 74. The waveguide layer 72
is coupled to a substrate 76, which has a plurality of protrusions
78 extending through the waveguide layer 72 to the top surface of
the waveguide layer 72. The waveguide layer 72 also has a cladding
portion 80 and a core portion 82. The cladding portion 80 and the
core portion 82 have indices of refraction that enable light to
propagate along the core portion 82 in a desired path.
[0071] As will be discussed in greater detail below, the MEMS
optical switch actuator is generally fabricated by coupling a
multi-level reflection assembly to the optical circuit 70, where
the reflection assembly has an electrically conductive anchor
assembly positioned at a first level with respect to the optical
circuit 70 and a mirror positioned at a second level with respect
to the optical circuit 70. An insulative mirror beam layer is then
coupled to the reflection assembly such that the mirror is
suspended within the recess 74, and an electrode assembly is
coupled to the mirror beam layer. The electrode assembly is coupled
such that a voltage potential between the anchor assembly and the
electrode assembly causes the electrode assembly to force the
mirror beam layer and the mirror from a first switching position
(at the first level) to a second switching position (in the path of
the light).
[0072] Multi-Level Reflection Assembly
[0073] Turning now to FIGS. 4, 4a, and 4b, it can be seen that
actuation anchor regions 84 are generated in the waveguide layer
72. The actuation anchor regions 84 are defined by walls 86, 88,
90, 92, 94, 96, 98, and 100 that extend from the top surface of the
waveguide layer 72 to a top surface of the substrate 76. It is
important to note that the walls defining the actuation anchor
regions 84 extend only to an intermediate level within the
waveguide layer 72 at this stage of the fabrication process.
Subsequent steps, to be discussed below, will extend the actuation
anchor regions 84 all the way to the top surface of the substrate
76 without modifying the walls that define a mirror region 102.
[0074] It can further be seen that the mirror region 102 is
generated within the recess 74, and is defined by walls 104, 106,
108, and 110. The walls of the mirror region 102 extend from the
top surface of the waveguide layer 72 to the intermediate level
within the waveguide layer 72. As will be described in greater
detail below, subsequent steps of the fabrication process dispose
the anchor assembly within the actuation anchor regions 84, and
dispose the mirror within the mirror region 102.
[0075] In order to generate the actuation anchor regions 84 and the
mirror region 102, it is preferred that a plastic polymer layer be
deposited on the top surface of the waveguide layer 72 and within
the recess 74 of the waveguide layer 72. Approximately 20
micrometers of polyimide (PI) should be sufficient for this
purpose. PI can withstand temperatures up to 400.degree. F. and is
an excellent insulator. A photoresist layer is then deposited on
the PI layer, and the photoresist layer is patterned to open the
mirror region 102 and the actuation anchor regions 84 from the top
surface of the waveguide layer 72 to the intermediate level.
Residual PI 150 remains in the recess 74 and will serve as a
resting surface for the mirror to be described below.
[0076] Turning now to FIGS. 5, 5a, and 5b, it can be seen that the
actuation anchor regions 84 are etched to the top surface of the
substrate 76 by depositing a metallic layer 112 (such as titanium)
on the top surface of the waveguide layer 72 and within the mirror
region 102. The metallic layer 112 is then stripped in an acid dip
(e.g., HF) to obtain the configuration shown in FIGS. 6, 6a, and
6b. Thus, the walls 86, 88, 90, 92, 94, 96, 98, and 100 extend from
the top surface of the waveguide layer 72 to the top surface of the
substrate 76. On the other hand, the walls 104, 106, 108, and 110
defining the mirror region 102 extend only to the intermediate
level above the core portion 82 of the waveguide layer 72.
[0077] Turning now to FIGS. 7, 7a, and 7b, the beginning of the
process of disposing the anchor assembly within the actuation
anchor regions 84 and disposing the mirror within the mirror region
102 is shown. Specifically, an adhesive layer 114 is deposited on
the top surface of the waveguide layer 72, within the mirror region
102, and within the actuation anchor regions 84. The preferred
material for the adhesive layer 114 is Cr due to its ability to
bond to glass. The adhesive layer 114 is then etched from the
mirror region 102 and a portion of the top surface of the waveguide
layer 72 such that the adhesive layer 114 remains in the actuation
anchor regions 84 and in reflective anchor regions 116. The
location of the reflective anchor regions 116 is essentially
dictated by the location of the protrusions 78 of the substrate 76.
This will ultimately allow all anchoring structures to be coupled
to the substrate 76 which provides more structural support than the
waveguide layer 72. In any event, the reflective anchor regions 116
are defined by the portion of the top surface of the waveguide
layer 72 having the adhesive layer 114.
[0078] FIGS. 8, 8a, and 8b demonstrate the deposition of an
optically reflective layer 118 on the top surface of the waveguide
layer 72, within the actuation anchor regions 84, within the mirror
region 102, and within the reflective anchor regions. The optically
reflective layer 118 is preferably gold, and can be sputtered on at
an approximately 2000 angstrom thickness. It is important to note
that the optically reflective layer 118 will ultimately serve as
the reflective surface for the mirror.
[0079] Turning now to FIGS. 9, 9a, and 9b, it can be seen that the
optically reflective layer 118 is etched from the top surface of
the waveguide layer, and a metallic layer 120 is deposited on the
remaining optically reflective layer 118. The metallic layer 120
can be 3-4 micrometers of nickel, which can be wet etched in
accordance with well-known fabrication techniques.
[0080] Mirror Beam Layer
[0081] FIGS. 10, 10a, and 10b demonstrate the process of depositing
the insulative mirror beam layer 122 on the reflection assembly. It
is important to note that the mirror beam layer is deposited under
tensile stress in order to increase actuation forces. The mirror
beam layer 122 is preferably approximately one micrometer thick and
includes PECVD SiN. The mirror beam layer 122 is insulative in
order to isolate the anchor regions 84, 116 (which also act as an
electrode) from the electrode assembly to be described below.
[0082] As shown in FIGS. 11, 11a, and 11b, the mirror beam layer
122 is etched from a portion of the top surface of the waveguide
layer 72 of the optical circuit 70 such that a bridge is formed.
The bridge suspends the mirror of the multi-level reflection
assembly at the first level with respect to the optical
circuit.
[0083] Electrode Assembly
[0084] Turning now to FIGS. 12, 12a, and 12b, a plastic polymer
layer 124 is deposited on the top surface of the waveguide layer 72
and on the mirror beam layer 122. Spinning on 12 micrometers of PI
should be sufficient for this step. This thickness will ultimately
determine the actuation distance of the electrode assembly. The PI
layer 124 is then cured, and a metallic layer is deposited on the
PI layer 124. The metallic layer can then be masked in a desired
post-configuration. FIGS. 13, 13a, and 13b show that this allows
the metallic layer and the PI layer 124 to be reactive ion etched
such that electrode regions 126 are generated. The electrode
regions 126 are defined by walls, 128, 130, 132, 134, 136, 138, 140
and 142 extending from the top surface of the PI layer 124 to the
top surface of the mirror beam layer 122. An alternative to the
above masking and etching steps would be to spin on a thick
photoresist layer. This would allow the elimination of the need for
masking as well as the metallic layer.
[0085] Turning now to FIGS. 14, 14a, and 14b, it can be seen that a
seed layer 144 is deposited on the top surface of the PI layer 124
and within the electrode regions 126. The preferred seed layer 144
is approximately 3000 angstroms thick and includes Cr/Ni. Using
Cr/Ni enables the seed layer to also act as an adhesive layer.
[0086] FIGS. 15, 15a, and 15b demonstrate the deposition of an
electrode layer 146 on the seed layer by plating approximately 2
microns of nickel. As best seen in FIGS. 16, 16a, and 16b, the
electrode layer 146 can then be masked in a desired bridge
configuration and etched such that the electrode assembly 148 is
generated. Finally, FIGS. 17, 17a, and 17b demonstrate that the PI
layer can be removed to obtain a completed actuator. Another
approach to the above "seeding" steps would be to plate the
electrode layer, photoresist, and strip the unwanted portion.
[0087] In operation, a voltage potential is applied to the
electrode layer 146 and the electrically conductive anchor
assembly. The anchor assembly concludes the adhesive layer 114, the
optically reflective layer 118, and the metallic layer 120. An
electrostatic field is therefore created across the mirror beam
layer 122 which forces the electrode layer 146 in a downward
direction. Thus, light propagating down core portion 82a would be
allowed to pass directly through to core portion 82d until the
switching signal is applied. Upon application of the switching
signal, the electrode layer 146 forces the mirror defined by
optically reflective layer 118 and metallic layer 120 into the
recess 74. This causes the light to be reflected down core portion
82b instead of core portion 82d. It is important to note that other
waveguide configurations can be designed without parting from the
spirit and scope of the invention.
[0088] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the present
invention can be implemented in a variety of forms. Therefore,
while this invention has been described in connection with
particular examples thereof, the true scope of the invention should
not be so limited since other modifications will become apparent to
the skilled practitioner upon a study of the drawings,
specification, and following claims.
* * * * *