U.S. patent application number 17/099264 was filed with the patent office on 2021-05-06 for micro-electro-mechanical system (mems) variable capacitor apparatuses and related methods.
The applicant listed for this patent is wiSpry, Inc.. Invention is credited to Norlito Baytan, Dana DeReus, Arthur S. Morris, III.
Application Number | 20210134532 17/099264 |
Document ID | / |
Family ID | 1000005340836 |
Filed Date | 2021-05-06 |
![](/patent/app/20210134532/US20210134532A1-20210506\US20210134532A1-2021050)
United States Patent
Application |
20210134532 |
Kind Code |
A1 |
Morris, III; Arthur S. ; et
al. |
May 6, 2021 |
MICRO-ELECTRO-MECHANICAL SYSTEM (MEMS) VARIABLE CAPACITOR
APPARATUSES AND RELATED METHODS
Abstract
Systems, devices, and methods for micro-electro-mechanical
system (MEMS) tunable capacitors can include a fixed actuation
electrode attached to a substrate, a fixed capacitive electrode
attached to the substrate, and a movable component positioned above
the substrate and movable with respect to the fixed actuation
electrode and the fixed capacitive electrode. The movable component
can include a movable actuation electrode positioned above the
fixed actuation electrode and a movable capacitive electrode
positioned above the fixed capacitive electrode. At least a portion
of the movable capacitive electrode can be spaced apart from the
fixed capacitive electrode by a first gap, and the movable
actuation electrode can be spaced apart from the fixed actuation
electrode by a second gap that is larger than the first gap.
Inventors: |
Morris, III; Arthur S.;
(Lakewood, CO) ; DeReus; Dana; (Santa Ana, CA)
; Baytan; Norlito; (Riverside, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
wiSpry, Inc. |
Irvine |
CA |
US |
|
|
Family ID: |
1000005340836 |
Appl. No.: |
17/099264 |
Filed: |
November 16, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16511899 |
Jul 15, 2019 |
10840026 |
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17099264 |
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14033434 |
Sep 20, 2013 |
10354804 |
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16511899 |
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61703595 |
Sep 20, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G 5/18 20130101; H01G
5/16 20130101; B81B 2201/0221 20130101; B81B 3/0051 20130101; B81B
3/0016 20130101; B81C 2201/013 20130101; B81C 1/00166 20130101;
B81C 1/00476 20130101; H01G 7/00 20130101 |
International
Class: |
H01G 5/16 20060101
H01G005/16; H01G 7/00 20060101 H01G007/00; B81B 3/00 20060101
B81B003/00; B81C 1/00 20060101 B81C001/00 |
Claims
1. A micro-electro-mechanical system (MEMS) variable capacitor,
comprising: a fixed capacitive electrode attached to a substrate; a
fixed actuation electrode attached to the substrate; a movable
component positioned above the substrate and movable with respect
to the fixed capacitive electrode and the fixed actuation
electrode, the movable component comprising: a movable capacitive
electrode positioned above the fixed capacitive electrode, wherein
at least a portion of the movable capacitive electrode is spaced
apart from the fixed capacitive electrode by a first gap; and a
movable actuation electrode positioned above the fixed actuation
electrode, wherein the movable actuation electrode is spaced apart
from the fixed actuation electrode by a second gap that is larger
than the first gap; and at least one standoff bump positioned
between the fixed actuation electrode and the movable actuation
electrode for maintaining a desired distance between the movable
actuation electrode and the fixed actuation electrode.
2. The micro-electro-mechanical system (MEMS) variable capacitor of
claim 1, wherein the movable capacitive electrode comprises: one or
more first capacitive portions spaced apart from the fixed
capacitive electrode by the first gap; and one or more second
capacitive portions spaced apart from the fixed capacitive
electrode by a distance greater than the first gap.
3. The micro-electro-mechanical system (MEMS) variable capacitor of
claim 2, wherein a size of each of the one or more first capacitive
portions is substantially similar to a size of the at least one
standoff bump.
4. The micro-electro-mechanical system (MEMS) variable capacitor of
claim 1, wherein the at least one standoff bump comprises one or
more first standoff bumps having a first dimension by which the one
or more first standoff bumps extends between the fixed actuation
electrode and the movable actuation electrode, the first dimension
being substantially equal to the difference between the dimensions
of the first gap and the second gap.
5. The micro-electro-mechanical system (MEMS) variable capacitor of
claim 4, wherein the at least one standoff bump comprises one or
more second standoff bumps having a second dimension by which the
one or more second standoff bumps extends between the fixed
actuation electrode and the movable actuation electrode, the second
dimension being greater than the first dimension of the one or more
first standoff bumps.
6. The micro-electro-mechanical system (MEMS) variable capacitor of
claim 5, wherein the one or more first standoff bumps are
positioned relatively closer to the fixed capacitive electrode than
the one or more second standoff bumps.
7. The micro-electro-mechanical system (MEMS) variable capacitor of
claim 1, wherein one or more of the at least one standoff bump is
attached to the substrate at or near the fixed actuation
electrode.
8. The micro-electro-mechanical system (MEMS) variable capacitor of
claim 1, wherein one or more of the at least one standoff bump is
attached to the movable component at or near the movable actuation
electrode.
9. The micro-electro-mechanical system (MEMS) variable capacitor of
claim 1 wherein a difference between the dimensions of the first
gap and the second gap measured in microns is greater than a value
of a ratio between an actuation voltage V.sub.actuation and a
maximum electric field E.sub.max generated between the movable
actuation electrode and the fixed actuation electrode, wherein
V.sub.actuation is between 10 and 100V, and wherein E.sub.max is
between 100 and 1000 V/.mu.m.
10. The micro-electro-mechanical system (MEMS) variable capacitor
of claim 1, wherein the difference between the dimensions of the
first gap and the second gap is selected such that a self-actuation
voltage between the movable actuation electrode and the fixed
actuation electrode is above a predetermined threshold value.
11. The micro-electro-mechanical system (MEMS) variable capacitor
of claim 10, wherein the difference between the dimensions of the
first gap and the second gap is less than or equal to one quarter
of the dimension of the second gap.
12. The micro-electro-mechanical system (MEMS) variable capacitor
of claim 1, wherein the difference between the dimensions of the
first gap and the second gap is between about 10 nm and 500 nm.
13. A micro-electro-mechanical system (MEMS) variable capacitor,
comprising: a fixed capacitive electrode attached to a substrate; a
first fixed actuation electrode and a second fixed actuation
electrode attached to the substrate on opposing sides of the fixed
capacitive electrode; a movable component comprising a first end
that is fixed with respect to the substrate and a second end
opposite the first end that is fixed with respect to the substrate,
a center portion of the movable component being positioned above
the substrate and movable with respect to the fixed capacitive
electrode, the first fixed actuation electrode, and the second
fixed actuation electrode, the movable component comprising: a
first movable actuation electrode positioned above the first fixed
actuation electrode; a second movable actuation electrode
positioned above the second fixed actuation electrode; and a
movable capacitive electrode positioned above the fixed capacitive
electrode; and at least one standoff bump positioned between the
fixed actuation electrode and the movable actuation electrode for
preventing contact of the movable actuation electrode with the
fixed actuation electrode; wherein at least a portion of the
movable capacitive electrode is spaced apart from the fixed
capacitive electrode by a first gap; wherein the first movable
actuation electrode and the second movable actuation electrode are
spaced apart from the first fixed actuation electrode and the
second fixed actuation electrode, respectively, by a second gap
that is larger than the first gap; and wherein a first dimension by
which one or more of the at least one standoff bump extends between
the fixed actuation electrode and the movable actuation electrode
is substantially equal to the difference between the dimensions of
the first gap and the second gap.
14. The micro-electro-mechanical system (MEMS) variable capacitor
of claim 13, wherein the at least one standoff bump comprises one
or more additional standoff bumps having a second dimension by
which the one or more additional standoff bumps extends between the
fixed actuation electrode and the movable actuation electrode, the
second dimension being greater than the first dimension.
15. The micro-electro-mechanical system (MEMS) variable capacitor
of claim 14, wherein the one or more of the at lest one standoff
bump are positioned relatively closer to the fixed capacitive
electrode than the one or more additional standoff bumps.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to co-pending U.S. patent
application Ser. No. 16/511,899, filed Jul. 15, 2019, which is a
continuation of issued U.S. patent application Ser. No. 14/033,434,
filed Sep. 20, 2013, which claimed priority to U.S. Provisional
Patent Application Ser. No. 61/703,595, filed Sep. 20, 2012, the
disclosures of which are incorporated herein by reference in their
entireties.
TECHNICAL FIELD
[0002] The subject matter disclosed herein relates generally to
micro-electro-mechanical system (MEMS) devices and methods for the
fabrication thereof.
[0003] More particularly, the subject matter disclosed herein
relates to systems, devices, and methods for MEMS variable
capacitors.
BACKGROUND
[0004] Micro-electro-mechanical systems (MEMS) can be used to
create variable capacitors. Specifically, for example, as shown in
FIG. 1a, a variable capacitor 1 can include a substrate 10 on which
one or more fixed actuation electrodes 11 and one or more fixed
capacitive electrodes 12 can be positioned. A movable component 20
can be suspended above substrate 10, movable component 20 being
fixed with respect to substrate 10 at either end. Movable component
20 can include one or more movable actuation electrodes 21 and one
or more movable capacitive electrodes 22. In this configuration, by
controlling a potential difference between fixed actuation
electrodes 11 and movable actuation electrodes 21, movable
component 20 can be selectively moved toward or away from substrate
10. In this way, the capacitance between fixed capacitive electrode
12 and movable capacitive electrode 22 can be selectively varied.
In some aspects, a layer of dielectric material can be deposited to
cover the actuation electrode 11 and capacitive electrode 12. The
dielectric material can be planarized to provide a flat
surface.
[0005] In some aspects, the substrate 10 and moveable component can
be fixed by two anchor or support structures 23 on both ends as
illustrated in FIG. 1B. In such configuration, however, applying a
potential difference between fixed actuation electrodes 11 and
movable actuation electrodes 21 can cause movable component 20 to
flex toward substrate 10 unevenly, which can cause issues with
charging in the actuator dielectric and wear. Furthermore, although
it is desirable for movable capacitive electrode 22 to be able to
move fully downward so that it can contact fixed capacitive
electrode 12 to maximize the capacitance range, it can be
undesirable for fixed actuation electrodes 11 and movable actuation
electrodes 21 to get too close to one another since the electrodes
can be subject to suddenly "snapping down" together after moving
close enough to one another, as illustrated in FIG. 1B, and the
device can suffer from dielectric damages and stiction caused by
high electric fields between the actuator electrode for spacings
that are too close.
[0006] Accordingly, it would be desirable for systems, devices, and
methods for MEMS variable capacitors to more consistently bring its
capacitor electrodes into close proximity while maintaining
sufficient spacing of the adjacent actuator(s).
SUMMARY
[0007] In accordance with this disclosure, systems, devices, and
methods for micro-electro-mechanical system (MEMS) tunable
capacitors are provided. In one aspect, a MEMS variable capacitor
is provided having a fixed actuation electrode attached to a
substrate, a fixed capacitive electrode attached to the substrate,
and a movable component positioned above the substrate and movable
with respect to the fixed actuation electrode and the fixed
capacitive electrode. The movable component can include a movable
actuation electrode positioned above the fixed actuation electrode
and a movable capacitive electrode positioned above the fixed
capacitive electrode. At least a portion of the movable capacitive
electrode can be spaced apart from the fixed capacitive electrode
by a first gap, and the movable actuation electrode can be spaced
apart from the fixed actuation electrode by a second gap that is
larger than the first gap.
[0008] In some aspects, a MEMS variable capacitor can include a
fixed capacitive electrode attached to a substrate, a first fixed
actuation electrode and a second fixed actuation electrode attached
to the substrate on opposing sides of the fixed capacitive
electrode, and a movable component comprising a first end that can
be fixed with respect to the substrate and a second end opposite
the first end that can be fixed with respect to the substrate, a
center portion of the movable component being positioned above the
substrate and movable with respect to the fixed capacitive
electrode, the first fixed actuation electrode, and the second
fixed actuation electrode. The movable component can include a
first movable actuation electrode positioned above the first fixed
actuation electrode, a second movable actuation electrode
positioned above the second fixed actuation electrode, and a
movable capacitive electrode positioned above the fixed capacitive
electrode. At least a portion of the movable capacitive electrode
can be spaced apart from the fixed capacitive electrode by a first
gap, and wherein the first movable actuation electrode and the
second movable actuation electrode can be spaced apart from the
first fixed actuation electrode and the second fixed actuation
electrode, respectively, by a second gap that is larger than the
first gap.
[0009] In another aspect, a method for manufacturing a MEMS
variable capacitor is provided. The method can include depositing a
fixed actuation electrode on a substrate, depositing a fixed
capacitive electrode on the substrate, depositing a sacrificial
layer over the fixed actuation electrode and the fixed capacitive
electrode, etching the sacrificial layer to form a recess in a
region of the sacrificial layer above the fixed capacitive
electrode, depositing a movable actuation electrode on the
sacrificial layer above the fixed actuation electrode, depositing a
movable capacitive electrode in the recess of the sacrificial layer
above the fixed capacitive electrode, depositing a structural
material layer on the movable actuation electrode and the movable
capacitive electrode, and removing the sacrificial layer such that
the movable actuation electrode, the movable capacitive electrode,
and the structural material layer define a movable component
suspended above the substrate and movable with respect to the fixed
actuation electrode and the fixed capacitive electrode. At least a
portion of the movable capacitive electrode can be spaced apart
from the fixed capacitive electrode by a first gap, and the movable
actuation electrode can be spaced apart from the fixed actuation
electrode by a second gap that is larger than the first gap.
[0010] In yet another aspect, a micro-electro-mechanical system
(MEMS) variable capacitor can include a fixed actuation electrode
attached to a substrate, a fixed capacitive electrode attached to
the substrate, and a movable component positioned above the
substrate and movable with respect to the fixed actuation electrode
and the fixed capacitive electrode. The movable component can
include a movable actuation electrode positioned above the fixed
actuation electrode, a movable capacitive electrode positioned
above the fixed capacitive electrode, and at least one standoff
bump attached to the movable component at or near the movable
actuation electrode. Where at least a portion of the movable
capacitive electrode can be spaced apart from the fixed capacitive
electrode by a first gap. Furthermore, the movable actuation
electrode can be spaced apart from the fixed actuation electrode by
a second gap that is larger than the first gap, and the at least
one standoff bump can protrude from the movable actuation electrode
a distance that is substantially equal to the difference between
the dimensions of the first gap and the second gap.
[0011] Although some of the aspects of the subject matter disclosed
herein have been stated hereinabove, and which are achieved in
whole or in part by the presently disclosed subject matter, other
aspects will become evident as the description proceeds when taken
in connection with the accompanying drawings as best described
hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The features and advantages of the present subject matter
will be more readily understood from the following detailed
description which should be read in conjunction with the
accompanying drawings that are given merely by way of explanatory
and non-limiting example, and in which:
[0013] FIGS. 1A through 1D are side views of conventional variable
capacitor configurations;
[0014] FIGS. 2A through 2H are side views of variable capacitor
configurations according to various embodiments of the presently
disclosed subject matter;
[0015] FIGS. 3A through 3H are side views of various variable
capacitor configurations according to an embodiment of the
presently disclosed subject matter;
[0016] FIGS. 4A through 4D are side views of various variable
capacitor configuration according to an embodiment of the presently
disclosed subject matter;
[0017] FIGS. 5A to 5E are cross sectional views of standoff bumps
located in movable actuation regions of a MEMS device according to
an embodiment of the presently disclosed subject matter; and
[0018] FIGS. 5F and 5G are side views illustrating standoff bumps
as they are placed in movable actuation regions of a MEMS device
according to an embodiment of the presently disclosed subject
matter.
DETAILED DESCRIPTION
[0019] The present subject matter provides systems, devices, and
methods for MEMS variable capacitors. In one aspect, the present
subject matter provides configurations for MEMS variable capacitors
that exhibit improved cycling lifetimes, allow improved capacitor
contact, enable a snap pull-in characteristic that can be desirable
for stable two-state operation, and reduce actuator stiction,
contact forces, charging, breakdown, cycling, and/or hold down. To
achieve these benefits, a MEMS variable capacitor can be configured
to have different gap distances between the capacitor electrodes
compared to the actuator electrodes. In such a configuration, the
capacitor electrodes can be brought together while maintaining the
actuator electrodes at desirable distances apart.
[0020] In some aspects, as illustrated in FIG. 1C, the movable
component 20 can have additional actuation 21 and/or capacitive 22
electrodes on its top surface. This may form a mechanical structure
that is balanced in stress and over temperature leading to a stable
beam shape in fabrication and in operation. Electrical current can
be connected to the electrodes located on the top surface and this
can contribute to lower resistive losses and a more robust movable
component 20 under high current conditions. In some other aspects,
the entire movable component 20 can be made out of metal, as
illustrated in FIG. 1D. According to this particular setup, a shunt
capacitor can be constructed by coupling the actuation electrodes
11 and capacitive electrode 12 to a grounded moveable component
20.
[0021] Furthermore, FIGS. 2A through 2H illustrate a variety of
variable capacitor configuration that each decouple the dimensions
of the air gaps between the capacitor plates and the actuator
plates. As shown in FIG. 2a, for instance, for a variable
capacitor, generally designated 100, a substrate 110 can include
one or more fixed actuation electrodes 111 and at least one fixed
capacitive electrode 112 positioned thereon. A movable component
120 can be suspended above substrate 110 and include one or more
movable actuation electrodes 121 and at least one movable
capacitive electrode 122. Movable component 120 can comprise a
first end that is fixed with respect to substrate 110 and a second
end opposite the first end that is fixed with respect to substrate
110. In this way, movable capacitive electrode 122 can be movable
in a direction substantially perpendicular to a surface of
substrate 110 to which fixed capacitive electrode 112 is
attached.
[0022] Rather than fixed actuation electrodes 111 and fixed
capacitive electrode 112 being arranged coplanar as in FIG. 1D,
fixed capacitive electrode 112 can be raised above the surface of
substrate 110 relative to fixed actuation electrodes 111). To
accomplish this offset, an insulating pedestal 115 (e.g., an oxide
material layer) is provided on substrate 110 prior to fixed
capacitive electrode 112 being positioned over substrate 110. In
some other aspects, this can be accomplished by depositing metal
over the pedestal 115 and patterning the metal layer. In this
configuration, movable capacitive electrode 122 is spaced apart
from fixed capacitive electrode 112 by a first gap, and movable
actuation electrodes 121 are spaced apart from fixed actuation
electrodes 111 by a second gap that is larger than the first gap.
In this way, movable capacitive electrode 122 can be moved into
close proximity with fixed capacitive electrode 112 while
maintaining a desired distance between movable actuation electrodes
121 and fixed actuation electrodes 111.
[0023] Similarly, in an alternative configuration shown in FIG. 2b,
for example, a protrusion 125 can be provided between movable
component 120 and movable capacitive electrode 122. In this way,
movable capacitive electrode 122 can be offset toward fixed
capacitive electrode 112 with respect to movable actuation
electrodes 121.
[0024] In yet a further alternative configuration shown in FIG. 2c,
for example, movable actuation electrodes 121 can be at least
partially embedded in movable component 120. For example, in a
process for manufacturing variable capacitor 100, fixed actuation
electrodes 111 and fixed capacitive electrodes 112 can be deposited
or otherwise attached to substrate 110. A sacrificial layer can be
provided over fixed actuation electrodes 111 and fixed capacitive
electrode 112, and the sacrificial layer can be etched to form a
recess in a region of the sacrificial layer above fixed capacitive
electrode 111. Movable actuation electrodes 121 can be provided on
the sacrificial layer above fixed actuation electrodes 111, and
movable capacitive electrode 122 can be provided in the recess of
the sacrificial layer above fixed capacitive electrode 112. Movable
component 120 can be formed by providing a structural material
layer on movable actuation electrodes 121 and movable capacitive
electrode 122. The sacrificial layer can be removed such that
movable actuation electrodes 121, movable capacitive electrode 122,
and the structural material layer define movable component 120
suspended above substrate 110 and movable with respect to fixed
actuation electrodes 111 and fixed capacitive electrode 112.
[0025] In still a further alternative configuration shown in FIG.
2d, for example, fixed actuation electrodes 111 can be at least
partially embedded in substrate 110. In addition, although FIGS. 2a
through 2d each only show one mechanism by which the first gap
between movable capacitive electrode 122 and fixed capacitive
electrode 112 is reduced relative to the second gap between movable
actuation electrodes 121 and fixed actuation electrodes 111, those
having skill in the art should recognize that the different ways of
offsetting the capacitive electrodes with respect to the actuation
electrodes can be combined in any of a variety of ways to further
define the differentiation in gap sizes.
[0026] In some aspects, the fixed capacitive electrode 112 can be
made thicker than the fixed actuation electrodes 111, as
illustrated in FIG. 2E. In this way, movable capacitive electrode
122 can be offset toward fixed capacitive electrode 112 with
respect to movable actuation electrodes 121. In some aspects, the
movable capacitive electrode 122 can be placed closer or further to
the fixed capacitive electrode 112 depending on the deposition
depth of the electrode metal and the depth of the recess etched on
the movable component 120. For example, FIG. 2C illustrates a setup
where the depth of the recess is equal to the depth of the metal
deposited. Otherwise, as illustrated in FIG. 2F, the depth of the
recess can be deeper than the depth of the metal deposited, and the
movable capacitive electrode 122 can be placed closer to the fixed
capacitive electrode 112. The thickness of the electrode 112 can be
taller than or equal to the thickness of the electrodes 111.
Similarly, as illustrated in FIG. 2G, sometimes the depth of the
recess can be shallower than the depth of the deposited metal, and
the movable capacitive electrode 122 can appear to be semi-embedded
into the movable component 120, and placed further away from the
fixed capacitive electrode 112.
[0027] Alternatively, movable actuation electrodes 121 and
capacitive electrodes 122 can all be deposited on top a sacrificial
layer, resulting in the movable electrodes being embedded in the
movable component 120 as illustrated in FIG. 2H. in addition, fixed
actuation electrodes 111 can be embedded in the substrate 110 via
a, for example, etch and metal deposition sequence. As such, a
larger gap can be created between the fixed actuation electrodes
111 and movable actuation electrodes 121.
[0028] In addition to configuring the relative gap sizes, variable
capacitor 100 can further include additional features that can help
to improve cycling lifetimes, improve capacitor contact, enable a
snap pull-in characteristic, and reduce actuator stiction, contact
forces, charging, breakdown, cycling, and/or hold down. In
particular, for example, as shown in FIGS. 3a and 3b, a thin
dielectric layer 113 can be provided over fixed actuation
electrodes 111 and fixed capacitive electrode 112 to help reduce
contact forces between the elements in the "closed" state, to
prevent shorting of the capacitor and to provide a more stable
capacitance. In addition, at least one standoff bump 130 can be
attached to movable component 120 at or near movable actuation
electrodes 121. At least one standoff bump 130 can protrude from
movable actuation electrodes 121 towards fixed actuation electrodes
111 for further preventing contact of movable actuation electrodes
121 with fixed actuation electrodes 111. In particular, for
example, at least one standoff bump 130 can protrude from movable
actuation electrodes 121 a distance that is substantially equal to
the difference between the dimensions of the first gap and the
second gap. Specifically, where the distance between fixed
capacitive electrode 112 and movable capacitive electrode 122 when
in an "open" state can be defined by a gap having a first dimension
a, and the distance between fixed actuation electrodes 111 and
movable actuation electrodes 121 when in the "open" state can be
defined by a gap having a second dimension b that is larger than
first dimension a, at least one standoff bump 130 can protrude from
movable actuation electrodes 121 a distance equal to second
dimension b minus first dimension a. In this arrangement, when
movable component 120 is moved toward substrate 110 such that
movable capacitive electrode 122 contacts fixed capacitive
electrode 112, at least one standoff bump 130 can likewise contact
fixed actuation electrodes 111, which can help to support movable
component 120 above substrate 110 and minimize stress related to
the attraction between fixed actuation electrodes 111 and movable
actuation electrodes 121. Furthermore, gaps 123 can be formed due
to the height difference between b and a. Such gaps 123 can improve
device reliability by reducing actuator electric field under high
voltage conditions, and the gap width can be designed to avoid
significantly reducing self-actuation voltage.
[0029] Furthermore, a dielectric layer 114 can be deposited on the
movable component 120 as shown in FIGS. 3C and 3D. In this setup,
fixed actuation electrode 111 and fixed capacitive electrode 112
can be deposited directly on top of the substrate 110 to reduce the
gap space between the fixed and movable electrodes. In addition, a
dielectric layer 113 can be deposited on top of the fixed
electrodes 111, 112 in conformity to the existing surface
topography. As such, standoff bumps 130 can be shorter in height
yet gap spaces 123 can still be formed between the movable
component 120 and the substrate 110, resulting in improved device
reliability under high electric field conditions.
[0030] While FIGS. 3C-3F show dielectric layers on both movable
beam and fixed electrodes, it is understood that the dielectric
layer may be on either or both surfaces.
[0031] Alternatively, standoff bumps can be placed on top of the
dielectric layer 113 and the fixed capacitive 111 and actuation 112
electrodes, as illustrated in FIG. 3E. According to another aspect
shown in FIG. 3F, a layer of dielectric material 115 can be
deposited before depositing the fixed capacitive electrode 112,
therefore being placed at an elevated position compared to fixed
actuation electrodes 111. As such, the gap distance a is further
reduced compared to the gap distance b, resulting in larger gap
spaces 123 when the device is in a "closed" position.
[0032] In some aspects, the movable component 120 can accommodate
standoff bumps with at least two different sizes, as illustrated in
FIGS. 3G and 3H. For example, standoff bumps 130 closer to the
capacitive electrodes 112 and 122 can be smaller in height (e.g.,
0.2 .mu.m) with this height approximately equal to the gap
difference, if present, and one or more additional standoff bumps
131 closer to the support/anchor structures 124 can be taller in
height (e.g. 0.5 .mu.m). As demonstrated in FIG. 3H, the taller
additional standoff bumps 131 can limit the deflection of the
movable component 120, thus improving device stability and
reliability. It should be noted that those having skill in the art
should recognize that the standoff bumps can alternatively be
conveniently placed on the fixed surface to achieve the same
purpose.
[0033] Furthermore, at least one standoff bump 130 can be formed in
a manner substantially similar to the formation of a protruding
movable capacitive electrode 122. Specifically, after positioning a
sacrificial layer over substrate 110, one or more recesses
corresponding to each of at least one standoff bump 130 can be
formed in the sacrificial layer. It can be desirable to form at
least one standoff bump 130 and the recess for the capacitor
electrode using a single etch step into the sacrificial material.
However, etch rates have a pattern dependence. As a result, etching
cavities for both movable capacitive electrode 122 and at least one
standoff bump 130 into the sacrificial layer can produce unequal
depths if their geometries are too different in some processes. To
address this issue, movable capacitive electrode 122 can be
provided as an array of electrode portions that are substantially
similar in size to at least one standoff bump 130. In particular,
as shown in FIGS. 4a and 4b, for example, movable capacitive
electrode 122 can be provided as one or more protruding capacitive
portions 122a spaced apart from fixed capacitive electrode 112 by
the first gap (i.e., having a first dimension a) and one or more
recessed capacitive portions 122b spaced apart from fixed
capacitive electrode 112 by a distance greater than the first gap
(e.g., spaced by a second dimension b). As shown in FIGS. 4a and
4b, protruding capacitive portions 122a and recessed capacitive
portions 122b can be provided in an alternating arrangement across
movable component 120. In this way, even though the portions are
arranged at different heights with respect to fixed capacitive
electrode 112, all of the portions can together cover substantially
the same footprint as a single electrode. Although this
configuration can lower the maximum capacitance density, it can
also improve manufacturability. For example, patterning protruding
capacitive portions 122a each having a size that is substantially
similar to a size of at least one standoff bump 130 can enable
similar pattern factors and thus a depth into the sacrificial layer
that is more closely matched to at least one standoff bump 130. As
a result, the manufacture of variable capacitor 100 can be more
consistent.
[0034] Alternatively, as shown in FIGS. 4C and 4D, metal
thicknesses of the fixed actuation electrodes 111 and capacitive
electrode 112 can be taller than their corresponding recesses,
resulting in an uneven surface topography. As such, dielectric
layer 113 deposited in conformity to the surface topography will
have dips between the electrodes as illustrated in FIGS. 4C and 4D.
In addition, movable actuation electrodes 121 and movable
capacitive electrodes 122a and 122b can be formed from a single
etch on the sacrificial layer. This way the depth between the
electrodes can be more closely matched, resulting in a similar
vertical dimension between the capacitor gap offset (b-a) and the
standoff bumps 130. Such device structure can be desirable because
the closed capacitor is then held flat, as shown in FIG. 4D, and
can also improve device manufacturability.
[0035] Regardless of the particular configuration of elements, a
common feature of each of the configurations discussed herein above
is that movable capacitive electrode 122 is spaced apart from fixed
capacitive electrode 112 by a first gap, and movable actuation
electrodes 121 are spaced apart from fixed actuation electrodes 111
by a second gap that is larger than the first gap. The particular
gap sizes can be specifically selected to address any of a variety
of performance criteria. For example, the difference between the
size of the first gap (i.e., first dimension a) and the size of the
second gap (i.e., second dimension b) can be designed to be large
enough to reduce the electric field generated between fixed
actuator electrodes 111 and movable actuator electrodes 121, which
can provide for high reliability. At the same time, the difference
between the gap sizes can be selected to be small enough to avoid
significantly reducing self-actuation voltage. Accordingly, the
difference between the dimensions of the first gap and the second
gap measured in microns can be selected to be greater than a value
of a ratio between an actuation voltage V.sub.actuation (e.g.,
between about 10 and 100V) and a maximum electric field E.sub.max
generated between movable actuation electrodes 121 and fixed
actuation electrodes 111 (e.g., between about 100 and 1000
V/.mu.m). Furthermore, the difference between the dimensions of the
first gap and the second gap can be selected such that a
self-actuation voltage between movable actuation electrodes 121 and
fixed actuation electrodes 111 is above a predetermined threshold
value. For example, the difference between the dimensions of the
first gap and the second gap can be less than or equal to one
quarter of the dimension of the second gap. In particular exemplary
configurations, for instance, the difference between the dimensions
of the first gap and the second gap can be between about 10 nm and
500 nm.
[0036] FIG. 5A illustrates a cross sectional view of standoff bumps
530 located in the movable actuation region of a MEMS device,
generally designated 500. The bumps 530 can be square, round,
octagonal or any general shape that can be formed in a mask. In
some aspects, the standoff bumps 530 can be in contact with a
dielectric layer 510, and isolated from the actuation metals 540.
The standoff bumps 530 can be dielectric in nature (e.g., oxide
material) and deposited into dips of a sacrificial layer. A
planarization process can be performed to provide a even surface,
and actuation metal 540 can be then deposited on top of the
sacrificial layer. The actuation metal 540 is patterned to remove
it from above the standoff bumps. The dielectric layer 510 can then
be deposited between the actuation metal 540 and onto the standoff
bumps 530. In some aspects, the dielectric layer 540 can be a same
type of material as the standoff bumps 530 (e.g., oxide
material).
[0037] FIG. 5B illustrates the MEMS device in a "closed" position,
where the standoff bumps 530 lays flat on a fixed dielectric
surface 550. The fixed dielectric surface 550 can rest on top of a
substrate 520, and the gap spaces 555 between the actuation metal
540 and dielectric layer 550 can reduce actuator electric field
under high voltage conditions and improve device reliability. The
actuator metal 540 absent above the standoff bumps 530 also greatly
reduces the electric fields within the bumps and nearby dielectric
layers.
[0038] Alternatively, recesses can be etched into the sacrificial
layer, and standoff bumps 530 can be formed by depositing
dielectric material (e.g., oxide material) into the recesses, as
illustrated in FIG. 5C. Additional dielectric layer 510 can be
deposited on top of the standoff bumps 530 between the actuation
metal. In some other aspects, actuation metal 540 can be deposited
and recesses can be etched between the metals. Standoff bumps 530
can be formed by a single deposition of dielectric material into
the recesses and between the metals, as illustrated in FIG. 5D.
[0039] In some aspects, recesses can be first etched into the
sacrificial layer, and a layer of dielectric material 560 can be
deposited to cover the entire surface including the recesses.
Actuation metal 540 can be deposited between the recesses, followed
by a deposition of dielectric material layer 510 between the metals
540, as illustrated in FIG. 5E
[0040] FIGS. 5F and 5G are side views illustrating of standoff
bumps 530 in the actuation electrode region as they are placed on
the bottom surface of the movable component of the MEMS device 500
Standoff bumps 530 can be square, round, octagonal or any general
shape that can be formed in a mask. As shown in FIGS. 5F and 5G,
standoff bumps 530 may be arranged in a pattern which may be evenly
spaced as shown, unevenly spaced or may be in other arrangements
such as hexagonally packed. Surrounding the bumps 530 are another
layer of dielectric material 540, and actuation metals 540 are
electrically isolated from the standoff bumps 530. In some aspects,
the standoff bumps 530 can be 50 nm to 1.0 .mu.m in height and 0.1
.mu.m to 5 .mu.m in diameter. The actuation metal thicknesses range
from 0.1 .mu.m to 0.5 .mu.m. The lateral gap between the edge of
the bump and the patterned edge of the surrounding actuator metal
should be as large or larger than the height of the standoff
bump.
[0041] The present subject matter can be embodied in other forms
without departure from the spirit and essential characteristics
thereof. The embodiments described therefore are to be considered
in all respects as illustrative and not restrictive. Although the
present subject matter has been described in terms of certain
preferred embodiments, other embodiments that are apparent to those
of ordinary skill in the art are also within the scope of the
present subject matter.
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