U.S. patent number 8,983,097 [Application Number 13/408,971] was granted by the patent office on 2015-03-17 for adjustable ventilation openings in mems structures.
This patent grant is currently assigned to Infineon Technologies AG. The grantee listed for this patent is Alfons Dehe, Martin Wurzer. Invention is credited to Alfons Dehe, Martin Wurzer.
United States Patent |
8,983,097 |
Dehe , et al. |
March 17, 2015 |
Adjustable ventilation openings in MEMS structures
Abstract
A MEMS structure and a method for operation a MEMS structure are
disclosed. In accordance with an embodiment of the present
invention, a MEMS structure comprises a substrate, a backplate, and
a membrane comprising a first region and a second region, wherein
the first region is configured to sense a signal and the second
region is configured to adjust a threshold frequency from a first
value to a second value, and wherein the backplate and the membrane
are mechanically connected to the substrate.
Inventors: |
Dehe; Alfons (Reutlingen,
DE), Wurzer; Martin (Munich, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Dehe; Alfons
Wurzer; Martin |
Reutlingen
Munich |
N/A
N/A |
DE
DE |
|
|
Assignee: |
Infineon Technologies AG
(Neubiberg, DE)
|
Family
ID: |
48951021 |
Appl.
No.: |
13/408,971 |
Filed: |
February 29, 2012 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20130223654 A1 |
Aug 29, 2013 |
|
Current U.S.
Class: |
381/174; 381/191;
381/113 |
Current CPC
Class: |
H04R
1/222 (20130101); B81B 3/0078 (20130101); H04R
19/04 (20130101); H04R 7/26 (20130101); B81B
2203/0127 (20130101); H04R 19/005 (20130101); B81B
2201/0257 (20130101); H04R 2201/003 (20130101) |
Current International
Class: |
H04R
25/00 (20060101); H04R 3/00 (20060101) |
Field of
Search: |
;381/113,174,191
;257/416 ;361/283.4 ;438/53 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Eason; Matthew
Attorney, Agent or Firm: Slater & Matsil, L.L.P.
Claims
What is claimed is:
1. A MEMS structure comprising: a substrate; a backplate; and a
membrane comprising a first region and a second region, wherein the
first region is configured to sense a signal and the second region
is configured to adjust a threshold frequency from a first value to
a second value, wherein the backplate comprises a first electrode
and a second electrode, wherein the first region of the membrane
corresponds to the first electrode, and wherein the second region
of the membrane corresponds to the second electrode, and wherein
the backplate and the membrane are mechanically connected to the
substrate.
2. The MEMS structure according to claim 1, wherein the first
region is located in a center region of the membrane, and wherein
the second region is located in a periphery region of the
membrane.
3. The MEMS structure according to claim 1, wherein the first
region is located over an area encompassed by a rim, and wherein
second region overlies a portion of the substrate.
4. The MEMS structure according to claim 1, wherein the backplate
is electrically connected to a sense voltage V.sub.sense, wherein
the substrate is electrically connected to a tuning voltage
V.sub.tune, and wherein the membrane is electrically connected to
ground.
5. The MEMS structure according to claim 1, wherein the backplate
is electrically connected to a sense bias V.sub.sense, and to a
tuning voltage V.sub.tune, and wherein the membrane is electrically
connected to ground.
6. The MEMS structure according to claim 1, wherein the backplate
comprises a first region and a second region, wherein the first
region of the backplate corresponds to the first region of the
membrane, wherein the second region of the backplate corresponds to
the second region of the membrane, wherein the first region of the
backplate is electrically connected to a sense voltage V.sub.sense,
wherein the second region of the backplate is electrically
connected to a tuning voltage V.sub.tune, and wherein the membrane
is connected to ground.
7. A MEMS structure comprising: a substrate; a backplate; and a
membrane comprising an adjustable ventilation opening, wherein the
backplate and the membrane are mechanically connected to the
substrate, wherein the backplate is a structured backplate having a
first electrode and a second electrode, and wherein the adjustable
ventilation opening corresponds to the second electrode but not to
the first electrode.
8. The MEMS structure according to claim 7, wherein the membrane
comprises a central region and an outer region, the out region
encompassing the central region, and wherein the adjustable
ventilation opening is located in the outer region.
9. The MEMS structure according to claim 7, wherein the adjustable
ventilation opening is configured to move toward the substrate if
actuated.
10. The MEMS structure according to claim 7, wherein the adjustable
ventilation opening is configured to move toward the backplate if
actuated.
11. The MEMS structure according to claim 7, wherein the adjustable
ventilation opening comprises a cantilever, and wherein the
cantilever is without ventilation openings.
12. The MEMS structure according to claim 7, wherein the adjustable
ventilation opening comprises a cantilever, and wherein the
cantilever comprises ventilation openings.
13. The MEMS structure according to claim 7, wherein the adjustable
ventilation opening comprises a plurality of adjustable ventilation
openings, and wherein the adjustable ventilation openings are
disposed in a periphery of the membrane placed in equidistant
distances.
14. A MEMS structure comprising: a substrate; a backplate; and a
membrane comprising a first region and a second region, wherein the
first region is configured to sense a signal and the second region
is configured to adjust a threshold frequency from a first value to
a second value, wherein the backplate and the membrane are
mechanically connected to the substrate, and wherein the backplate
is electrically connected to a sense voltage V.sub.sense, and to a
tuning voltage V.sub.tune, and wherein the membrane is electrically
connected to ground.
15. A MEMS structure comprising: a substrate; a backplate; and a
membrane comprising a first region and a second region, wherein the
first region is configured to sense a signal and the second region
is configured to adjust a threshold frequency from a first value to
a second value, wherein the backplate and the membrane are
mechanically connected to the substrate, and wherein the backplate
comprises a first region and a second region, wherein the first
region of the backplate corresponds to the first region of the
membrane, wherein the second region of the backplate corresponds to
the second region of the membrane, wherein the first region of the
backplate is electrically connected to a sense voltage V.sub.sense,
wherein the second region of the backplate is electrically
connected to a tuning voltage V.sub.tune, and wherein the membrane
is connected to ground.
16. A MEMS structure comprising: a substrate; a backplate; and a
membrane comprising an adjustable ventilation opening, wherein the
backplate and the membrane are mechanically connected to the
substrate, wherein the adjustable ventilation opening comprises a
cantilever, and wherein the cantilever is without ventilation
openings.
17. A MEMS structure comprising: a substrate; a backplate; and a
membrane comprising an adjustable ventilation opening, wherein the
backplate and the membrane are mechanically connected to the
substrate, wherein the adjustable ventilation opening comprises a
cantilever, and wherein the cantilever comprises ventilation
openings.
Description
TECHNICAL FIELD
The present invention relates generally to an adjustable
ventilation opening in a MEMS structure and a method for operating
a MEMS structure.
BACKGROUND
In general, microphones are manufactured in large numbers at low
cost. Due to these requirements, microphones are often produced in
silicon technology. Microphones are produced with different
configurations for their different field of applications. In one
example, microphones measure the change in capacity by measuring
the deformation or deflection of the membrane relative to a counter
electrode. The microphone is typically operated a setting a bias
voltage to an appropriate value.
A microphone may have operation and other parameters such as
signal-to-noise ratio (SNR), rigidity of the membrane or counter
electrode, or diameter of the membrane which often are set by the
manufacturing process. In addition, a microphone may have different
characteristics based on different materials used in the
manufacturing process.
SUMMARY OF THE INVENTION
In accordance with an embodiment of the present invention, a MEMS
structure comprises a substrate, a backplate, and a membrane
comprising a first region and a second region, wherein the first
region is configured to sense a signal and the second region is
configured to adjust a threshold frequency from a first value to a
second value, and wherein the backplate and the membrane are
mechanically connected to the substrate.
In accordance with another embodiment of the present invention, a
MEMS structure comprises a substrate, a backplate, and a membrane
comprising an adjustable ventilation opening. The backplate and the
membrane are mechanically connected to the substrate.
In accordance with an embodiment of the present invention, a method
for operating a MEMS structure comprises sensing an acoustic signal
by moving a sensing region of a membrane relative to a backplate
and opening or closing an adjustable ventilation opening in the
membrane if a high energy signal is detected.
In accordance with an embodiment of the present invention, a method
comprises sensing an acoustic signal by moving a membrane relative
to a backplate, and opening or closing an adjustable ventilation
opening in the membrane if an application setting of the MEMS
structure is changed.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, and the
advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
FIG. 1a shows a top view of a MEMS structure;
FIG. 1b shows a detailed perspective view of a connection region of
a MEMS structure;
FIG. 1c shows a cross sectional view of a connection region of a
MEMS structure;
FIGS. 2a-2c show cross-sectional views of an embodiment of an
adjustable ventilation opening;
FIG. 2d shows a top view of an embodiment of an adjustable
ventilation opening;
FIG. 2e shows a diagram for a corner or threshold frequency;
FIGS. 3a-3d show embodiments and configuration of an adjustable
ventilation opening;
FIG. 4a shows a cross-sectional view of an embodiment of a MEMS
structure, wherein the membrane is pulled toward the backplate;
FIG. 4b shows a cross-sectional view of an embodiment of a MEMS
structure, wherein the membrane is pulled toward the substrate;
FIG. 5a shows a cross-section view of an embodiment of a MEMS
structure;
FIG. 5b shows a top-view of an embodiment of the MEMS structure of
FIG. 5a;
FIG. 6a shows a cross-section view of an embodiment of a none
actuated MEMS structure;
FIG. 6b shows a cross-section view of an embodiment of an actuated
MEMS structure;
FIG. 7a shows a cross-section view of an embodiment of a none
actuated MEMS structure;
FIG. 7b shows a cross-section view of an embodiment of an actuated
MEMS structure;
FIG. 7c shows a top-view of an embodiment of the MEMS structure of
FIG. 7a;
FIG. 8a shows a flow chart of an operation of a MEMS structure,
wherein the adjustable ventilation opening is originally
closed;
FIG. 8b shows a flow chart of an operation of a MEMS structure,
wherein the adjustable ventilation opening is originally open;
FIG. 8c shows a flow chart of an operation of a MEMS structure,
wherein the adjustable ventilation opening is opened to switch from
a first application setting to a second application setting;
and
FIG. 8d shows a flow chart of an operation of a MEMS structure,
wherein the adjustable ventilation opening is closed to switch from
a first application setting to a second application setting.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The making and using of the presently preferred embodiments are
discussed in detail below. It should be appreciated, however, that
the present invention provides many applicable inventive concepts
that can be embodied in a wide variety of specific contexts. The
specific embodiments discussed are merely illustrative of specific
ways to make and use the invention, and do not limit the scope of
the invention.
The present invention will be described with respect to embodiments
in a specific context, namely sensors or microphones. The invention
may also be applied, however, to other MEMS structures such as
pressure sensors, RF MEMS, accelerometers, and actuators.
Microphones are realized as parallel plate capacitor on a chip. The
chip is packaged enclosing a given back-volume. A movable membrane
vibrates due to pressure differences such as acoustic signals. The
membrane displacement is translated into an electrical signal using
capacitive sensing.
FIG. 1a shows a top view of a MEMS device 100. A backplate or
counter electrode 120 and a movable electrode or membrane 130 are
connected via connection regions 115 to the substrate 110. FIGS. 1b
and 1c show detailed perspective views of one connection regions
115 of the MEMS device 100. A backplate or counter electrode 120 is
arranged over a membrane or movable electrode 130. The backplate
120 is perforated to avoid or mitigate damping. The membrane 130
comprises a ventilation hole 140 for low frequency pressure
equalization.
In the embodiment of FIGS. 1a-1c the membrane 130 is mechanically
connected to the substrate 110 in the connection regions 115. In
these regions 115 the membrane 130 cannot move. The backplate 120
is also mechanically connected to the substrate 110 in the
connection region 115. The substrate 110 forms a rim 122 to provide
space for the back-volume. The membrane 130 and the backplate 120
are connected to the substrate at or close to the rim 122. In this
embodiment the rim 122 and the membrane 120 form a circle.
Alternatively, the rim 122 and the membrane 120 may comprise a
square or may comprise any other suitable geometrical form.
In general, designing and manufacturing a sensor requires a high
signal-to-noise ratio (SNR). Among other things, this can be
achieved when the change in capacitances to be measured is as great
as possible and when the parasitic capacitances are as small as
possible. The greater the parasitic portion of the capacitance is
relative to the overall capacitance, the smaller the SNR.
The compliance of the back-volume and the resistance of the
ventilation path through the ventilation hole define the RC
constant of the sensor. If the ventilation hole is large the corner
frequency is a relatively high frequency and if the ventilation
hole is small the corner frequency is a relatively lower frequency.
Both back-volume and the diameter of the ventilation hole are given
by construction and hence the corner frequency is given by
construction. Accordingly, the corner frequency cannot be changed
during operation.
A problem with a fixed size ventilation hole is that high energetic
signals that have a frequency higher than the corner frequency of
the ventilation hole distort or overdrive the sensor even with the
application of electrical filters. Moreover, if a sensor is used
for more than one application two sensors must be integrated into
one sensor system which doubles the system costs.
An embodiment of the invention provides tunable ventilation
openings in a MEMS structure. The tunable ventilation openings may
be switched between an open position and a closed position. The
tunable ventilation holes may also be set in an intermediate
position. Another embodiment of the invention provides a variable
ventilation opening cross-section. An embodiment of the invention
provides a tunable ventilation opening in a sensing region close to
a rim of the substrate. A further embodiment provides a tunable
ventilation opening in a tuning region outside the sensing region
of the membrane.
FIGS. 2a-2c show a cross sectional views of a backplate or
counter-electrode 250 and a membrane or movable electrode 230
having an air gap 240 between them. The backplate 250 is perforated
252 and the membrane 230 comprises an adjustable ventilation
opening 238. FIG. 2d shows a top view of this arrangement with the
circles indicating the perforated back plate 250, 252 and dark
plane being the underlying membrane 230. In this embodiment the
movable portion 237 of the adjustable ventilation hole 238 is
formed as a U shaped slot 239. The adjustable ventilation opening
238 may comprise of rectangular, square or semicircle form.
Alternatively, the adjustable ventilation opening 238 may comprise
any geometrical form as long as the form is able to provide a
ventilation path. The movable portion 237 of the adjustable
ventilation opening 238 may be a cantilever, a bridge or a spring
supported structure.
The FIG. 2a shows a configuration where the actuation voltage (bias
voltage) V.sub.bias=0. The adjustable ventilation opening 238 is
closed forming a small slot 239 in the membrane 230. No actuation
voltage provides a minimal ventilation path and therefore a low
threshold frequency. The adjustable ventilation opening 238 is in a
closed or OFF (non-activated) position. An example of such a low
threshold frequency can be seen as frequency "A" in FIG. 2e.
FIG. 2b shows a configuration where the actuation voltage
V.sub.bias is increased, i.e. is different than 0 V but lower than
the pull-in voltage V.sub.pull-in. The adjustable ventilation
opening 238 opens and provides a larger ventilation path than in
the configuration of FIG. 2a. The threshold frequency can be seen
as frequency "B" in FIG. 2e. It is noted that adjustable
ventilation opening 238 may provide a sizable ventilation path when
displacement of the movable portion 237 is larger than the
thickness of the membrane 230.
FIG. 2c shows a configuration where the actuation voltage
V.sub.bias is larger than pull-in voltage V.sub.pull-in. The
adjustable ventilation opening 238 is completely open and a large
ventilation path is created. The threshold frequency can be seen as
frequency "C" in FIG. 2e. By adjusting the actuation voltage the RC
constant can be decreased or increased and the threshold frequency
can be set according to a desired value. It is noted that the
adjustable ventilation opening may already open completely for
actuation voltages below the pull-in voltage.
Referring now to FIG. 2e, in one embodiment the threshold frequency
"A" may be about 10-50 Hz and may be moved to about 200-500 Hz as
threshold frequency "C." Alternatively, the threshold frequency in
"A" is about 10-20 Hz and is moved to about 200-300 Hz in "C."
The threshold frequency in position "A" may also depend on the
number of adjustable ventilation openings and the gap distance a
slot forms in the membrane. The threshold frequency in position "A"
is higher for a MEMS structure with more adjustable ventilation
openings (e.g. 32 adjustable ventilation openings) than for a MEMS
structure with less adjustable ventilation openings (e.g., 2, 4 or
8 adjustable ventilation openings). The threshold frequency is also
higher for MEMS structures with a larger slot gap (larger slot
width and/or larger slot length) defining the adjustable
ventilation opening than for those with a smaller slot gap.
The embodiment of FIG. 3a shows a configuration of an actuation
voltage (tuning or switching voltage) wherein the actuation voltage
is identical to the sensing bias. The MEMS structure comprises a
single electrode on the backplate 350, an air gap 340 and a
membrane 330. The electrode of the backplate 350 is set to an
actuation potential and the membrane 330 is set to ground. The
adjustable ventilation opening 338 is closed with a low actuation
voltage (OFF position) and open with a high actuation voltage (ON
position). A low actuation voltage results in a low corner or
threshold frequency and a low sensitivity of the MEMS structure,
and a high actuation voltage results in a high corner or threshold
frequency and a high sensitivity.
The embodiment of FIG. 3b shows a configuration wherein the
actuation voltage (tuning or switching voltage) is independent from
the sensing bias. The MEMS structure comprises a structured
backplate 350, e.g., a backplate that has at least two electrodes,
an air gap 340 and a membrane 330. The second electrode 352 of the
backplate 350 is set to an actuation potential and the first
electrode 351 is set to a sense potential. The membrane 320 is set
to ground. The two electrodes are isolated from each other. For
example, the backplate 350 may comprise the structured electrode
and an isolation support 355. The isolation support 355 may face
toward the membrane 320 or may face away from the membrane 320. The
tuning or switching voltage does not influence the sensitivity of
the MEMS structure.
The adjustable ventilation opening is 338 closed with a low
actuation voltage (OFF position) and open with a high actuation
voltage (ON position). A low actuation voltage results in a low
corner or threshold frequency and a high actuation voltage results
in a high corner or threshold frequency. The sense bias is
independent from the actuation voltage and can be kept constant or
independently decreased or increased.
The embodiment of FIG. 3c shows a configuration of an actuation
voltage (tuning or switching voltage) wherein the actuation voltage
is identical to the sensing bias. The MEMS structure comprises a
single electrode in the backplate 350, an air gap 340 and a
membrane 330. The adjustable ventilation opening 338 is closed with
a high actuation voltage (ON position) and is open with a low
actuation voltage (OFF position). The movable portion 337 of the
adjustable ventilation opening 338 touches the backplate 350 when
activated and is in plane with the rest of the membrane when not
activated. A low actuation voltage results in a high corner or
threshold frequency and a low sensitivity of the MEMS structure,
and a high actuation voltage results in low corner or threshold
frequency and a high sensitivity of the MEMS structure. The
backplate 350 comprises ventilation openings 357 and the movable
portion 337 of the adjustable ventilation opening 338 comprises
ventilation openings 336. The ventilation openings 336 in the
movable portion 337 of the adjustable ventilation opening 338 are
closed in an ON (or activated) position. There is no ventilation
path through the adjustable ventilation opening 338 when the
adjustable ventilation opening is in the ON (or activated)
position.
The embodiment of FIG. 3d shows the actuation voltage (tuning or
switching voltage) wherein the actuation voltage is independent
from the sensing bias. This MEMS structure comprises a structured
backplate 350, e.g., the backplate may comprise a first electrode
351 and a second electrode 352, an air gap 340 and a membrane 330.
Alternatively, the structured backplate 350 may comprise more than
two electrodes. The second electrode 352 of the backplate 350 is
set to an actuation potential and the first electrode 351 is set to
a sense potential. The membrane 330 is set to ground. The first
electrode 351 and the second electrode 352 are isolated from each
other. For example, the backplate 350 may comprise the structured
electrode and an isolation support 355. The isolation support 355
may face toward the membrane 330 or may face away from the membrane
330. The tuning or switching voltage does not influence the
sensitivity of the MEMS structure.
The adjustable ventilation opening is closed with a high actuation
voltage (ON position) and is open with a low actuation voltage (OFF
position). A low actuation voltage (OFF position) results in a high
corner or threshold frequency and a low actuation voltage (ON
position) results in a high corner or threshold frequency. The
sense bias is independent from the actuation voltage and can be
kept constant or independently decreased or increased.
The backplate 350 comprises ventilation openings 357 and the
movable portion 337 of the adjustable ventilation opening 338
comprises also ventilation openings 336. The ventilation openings
336 in the adjustable ventilation opening 338 are closed in the ON
position. There is no ventilation path through the ventilation
openings 357 of the backplate 338 and the ventilation openings 336
of the adjustable ventilation opening 338 when the adjustable
ventilation opening 338 is open. There is no ventilation path
through the ventilation openings 357 of the backplate 338 and the
ventilation openings 336 of the adjustable ventilation opening 338
when the adjustable ventilation opening 338 is closed or in an OFF
position.
The embodiment of FIG. 4a shows a cross-sectional view of a MEMS
structure 400. The MEMS structure comprises a substrate 410. The
substrate 410 comprises silicon or other semiconductor materials.
Alternatively, the substrate 410 comprises compound semiconductors
such as GaAs, InP, Si/Ge, or SiC, as examples. The substrate 410
may comprise single crystal silicon, amorphous silicon or
polycrystalline silicon (polysilicon). The substrate 410 may
include active components such as transistors, diodes, capacitors,
amplifiers, filters or other electrical devices, or an integrated
circuit. The MEMS structure 400 may be a stand-alone device or may
be integrated with and IC into a single chip.
The MEMS structure 400 further comprises a first insulating layer
or spacer 420 disposed over the substrate 410. The insulating layer
420 may comprise an insulting material such a silicon dioxide,
silicon nitride, or combinations thereof.
The MEMS structure 400 further comprises a membrane 430. The
membrane 430 may be a circular membrane or a square membrane.
Alternatively, the membrane 430 may comprise other geometrical
forms. The membrane 430 may comprise conductive material such as
polysilicon, doped polysilicon or a metal. The membrane 430 is
disposed above the insulating layer 420. The membrane 430 is
physically connected to the substrate 410 in a region close to the
rim of the substrate 410.
Moreover, the MEMS structure 400 comprises a second insulating
layer or spacer 440 disposed over a portion of the membrane 430.
The second insulating layer 440 may comprise an insulting material
such as a silicon dioxide, silicon nitride, or combinations
thereof.
A backplate 450 is arranged over the second insulating layer or
spacer 440. The backplate 450 may comprise a conductive material
such as polysilicon, doped polysilicon or a metal, e.g., aluminum.
Moreover, the backplate 450 may comprise an insulating support or
insulating layer regions. The insulating support may be arranged
toward or away from the membrane 430. The insulating layer material
may be silicon oxide, silicon nitride or combinations thereof. The
backplate 450 may be perforated.
The membrane 430 may comprise at least one adjustable ventilation
opening 460 as described above. The adjustable ventilation openings
460 may comprise a movable portion 465. In one embodiment the
adjustable ventilation openings 460 are located in a region close
to the rim of the substrate 410. For example, the adjustable
ventilation openings 460 may be located in the outer 20% of the
radius of the membrane 430 or the outer 20% of the distance from a
center point to the membrane 430 edge of a square or a rectangle.
In particular, the adjustable ventilation openings 460 may not be
located in a center region of the membrane 430. For example, the
adjustable ventilation openings 460 may not be located in the inner
80% of the radius or the distance. The adjustable ventilation
openings 460 may be located in equidistant distances from each
other along a periphery of the membrane 430.
The embodiment of FIG. 4a is configured so that the adjustable
ventilation openings 460 open toward the backplate 450. The
membrane 430 and the backplate 450 may have any of the
configurations as described in FIGS. 2a-2d and 3a-3d. The backplate
450 is set to a sense voltage V.sub.sense and an actuation voltage
V.sub.p (sense voltage and actuation voltage can be the same or
different as described above) and the membrane 430 is set to
ground, or vice versa.
The MEMS structure 400 of the embodiment of FIG. 4b shows a similar
structure to that of the embodiment in FIG. 4a. However, the
configuration is different, e.g., the movable portion 465 of the
adjustable ventilation opening 460 is pulled toward the substrate
410. The backplate is set to a sense voltage V.sub.sense, the
substrate is set to the actuation voltage V.sub.p and the membrane
is set to ground. In this configuration of the MEMS structure 400
the actuation voltage (tuning or switching voltage) is independent
of the sensing voltage.
The embodiment of FIG. 5a shows a cross sectional view and FIG. 5c
shows a top view of a MEMS structure 500 having a membrane 530
extending over a portion of the substrate 510 and outside a sensing
region 533. The MEMS structure 500 comprises a substrate 510, a
connection region 520, a membrane 530 and a backplate 540 which
comprise similar materials as described with respect to the
embodiment in FIG. 4a. The membrane 530 comprises a sensing region
533 and a tuning region 536. The sensing region 533 is located
between the opposite rims of the substrate 510 or between the
opposite connection regions 520. The tuning region 533 extends over
a portion of the substrate 510 and is located outside the sensing
region 533. The sensing region 536 may be located on a first side
of the connection region 520 and the tuning region 533 may be
located on a second side of the connection region 520. A recess 515
(under etch) is formed between the membrane 530 and the substrate
510 in the tuning region 536. The backplate 540 overlies only the
sensing region 533 but not the tuning region 536 of the membrane
530. The backplate 540 may be perforated. The backplate 540 is set
to a bias voltage V.sub.sense, the substrate 510 is set to a tuning
voltage V.sub.p and the membrane is set to ground. In this
configuration of the MEMS structure 500 the tuning voltage is
independent of the sensing voltage.
The tuning region 536 of the membrane 530 comprises at least one
adjustable ventilation openings 538 which provide a ventilation
path in a non-actuated position (OFF position) and which does not
provide a ventilation path in an actuated position (ON positioni).
The non-actuated or open position (OFF position) is a position
wherein the adjustable ventilation openings 538 are in the same
plane as the membrane 530 in the sensing region 533 in in its
resting position. The actuated or closed position (ON position) is
a position wherein the adjustable ventilation openings 538 are
pressed against the substrate 510 and the ventilation path is
blocked. Intermediate positions may be set by pulling the
adjustable ventilation openings 538 towards the substrate 510 but
where the adjustable ventilation openings 538 are not pressed
against the substrate 510. It is noted that the sensing region 533
may or may not comprise adjustable ventilation openings 538.
The embodiment of FIGS. 6a and 6b show a cross sectional view of a
MEMS structure 600 having a membrane 630 extending over a portion
of the substrate 610 outside a sensing region 633. The MEMS
structure 600 comprises a substrate 610, a connection region 620, a
membrane 630 and a backplate 640 which comprise similar materials
as described with respect to the embodiment in FIG. 4a. The
membrane 630 comprises a sensing region 633 and a tuning region
636. The sensing region 633 is located between the opposite rims of
the substrate 610 or between the opposite connection regions 620.
The tuning region 636 extends over a portion of the substrate 610
and is located outside the sensing region 633. The sensing region
633 may be located on a first side of the connection region 620 and
the tuning region 636 may be located on a second side of the
connection region 620. A recess 615 is formed between the membrane
630 and the substrate 610 in the tuning region 636. The backplate
640 overlies the sensing region 633 and the tuning region 636 of
the membrane 630. The backplate 640 may be perforated in the
sensing region 633 and the tuning region. Alternatively, the
backplate 640 may be perforated in the sensing region 633 but not
in the tuning region 636. The backplate 640 comprises a first
electrode 641 and a second electrode 642. Alternatively, the
backplate 640 comprise more than two electrodes. The first
electrode 641 is isolated from the second electrode 642. The first
electrode 641 is disposed in the sensing region 633 and the second
electrode 642 is disposed in the tuning region 636. The first
electrode 641 is set to a bias voltage V.sub.sense, and the second
electrode 642 is set to the tuning voltage V.sub.p. The membrane
630 is set to ground. In this configuration of the MEMS structure
600 the tuning voltage is independent of the sensing voltage.
The tuning region 636 of the membrane 630 comprises one or more
adjustable ventilation openings 638 which provide a ventilation
path in an non-actuated position (OFF position) in FIG. 6a and
which does not provide a ventilation path in an actuated position
(ON position) in FIG. 6b. The open position or non-actuated (OFF
position) is a position wherein the adjustable ventilation openings
638 are in the same plane as the membrane 630 in the sensing region
633 in its resting position. The closed position or actuated
position (ON position) is a position wherein the adjustable
ventilation openings 638 are pressed against the backplate 640 and
the ventilation path is blocked. The MEMS structure 600 provides a
ventilation path and a high corner frequency when it is not in an
actuated position (OFF position). The MEMS structured 600 provides
a closed ventilation path and a low corner frequency when it is in
an actuated position (ON position). Intermediate positions may be
set by pulling the adjustable ventilation openings 638 toward the
backplate 640 but where the adjustable ventilation openings 638 are
not pressed against the backplate 640. It is noted that the sensing
region 633 may or may not comprise adjustable ventilation openings
638.
The backplate 640 comprises ventilation openings 639 and the
membrane 630 comprises adjustable ventilation openings 638 in the
tuning region 636. In one embodiment the ventilation openings 639
and the adjustable ventilation openings 638 are reversely aligned
with respect to each other.
The embodiment of FIGS. 7a and 7b show a cross sectional view and
FIG. 7c shows a top view of a MEMS structure 700 having a membrane
730 extending over a portion of the substrate 710 and outside a
sensing region 733. The MEMS structure 700 comprises a substrate
710, a connection region 720, a membrane 730 and a backplate 740
which comprise similar materials as described with respect to
embodiment of FIG. 4a. The backplate 740 may comprise a sensing
backplate (e.g. circular or rectangle) 741 and a backplate bridge
742.
The membrane 730 comprises a sensing region 733 and a tuning region
736. The sensing region 733 is located between the opposite rims of
the substrate 710 or between the opposite connection regions 720.
The tuning region 733 extends over a portion of the substrate 710
and is located outside the sensing region 733. The sensing region
736 may be located on a first side of the connection region 720 and
the tuning region 733 may be located on a second side of the
connection region 720. A recess 715 (under etch) is formed between
the membrane 730 and the substrate 710 in the tuning region 736.
The membrane 730 comprises an adjustable ventilation opening 738
formed by a slot 735. The slot 735 forms a movable portion as
described in FIGS. 2a-2c for the adjustable ventilation opening
738
The backplate 740 overlies the sensing region 733 and the tuning
region 736 of the membrane 730. For example, the sensing backplate
741 (first electrode) overlies the sensing region 733 and the
backplate bridge 742 (second electrode) overlies the tuning region
736. Alternatively, the backplate 740 comprise more than two
electrodes. The first electrode 741 is isolated from the second
electrode 742. The first electrode 741 is set to a bias voltage
V.sub.sense and second electrode 742 is set to a tuning voltage
V.sub.p. The membrane 730 is set to ground. In this configuration
of the MEMS structure 700 the tuning voltage is independent of the
sensing voltage. The backplate 740 may be perforated in the sensing
region 733 and the tuning region 736. Alternatively, the backplate
740 may be perforated in the sensing region 733 but not in the
tuning region 736. The backplate bridge 742 comprises ventilation
openings 749.
The tuning region 736 of the membrane 730 comprises one or more
adjustable ventilation openings 738 which provide a ventilation
path in an actuated position (ON position) in FIG. 7b and which do
not provide a ventilation path in a non-actuated position (OFF
position) in FIG. 7a. The closed or non-actuated position (OFF
position) is a position wherein the adjustable ventilation openings
738 are in the same plane as the membrane 730 in the sensing region
733 in its resting position. The open or actuated position (ON
position) is a position wherein the adjustable ventilation openings
738 are pressed against the backplate 740 and the ventilation path
is open. The MEMS structure 700 provides a ventilation path and a
high corner frequency when it is in an actuated position (ON
position). The MEMS structured 700 provides a closed ventilation
path and a low corner frequency when it is in none actuated
position (OFF position). Intermediate positions may be set by
pulling the adjustable ventilation openings 738 toward the
backplate 740 but where the adjustable ventilation openings 738 are
not pressed against the backplate 740. It is noted that the sensing
region 733 may or may not comprise adjustable ventilation openings
738.
FIG. 8a shows an embodiment of operating a MEMS structure. In a
first step 810, an acoustic signal is sensed by moving a membrane
relative to a backplate. The adjustable ventilation opening is in a
closed position. In a next step 812, a high energy signal is
detected. The adjustable ventilation opening is moved from a closed
position to an open position, 814. The open position may be a
completely open position or a partially open position.
FIG. 8b shows an embodiment of operating a MEMS structure. In a
first step, 820, an acoustic signal is sensed by moving a membrane
relative to a backplate. The adjustable ventilation opening is in
an open position. In a next step 822, a high energy signal is
detected. The adjustable ventilation opening is moved from the open
position to a closed position, 824. The closed position may be a
completely closed position or a partially closed position.
FIG. 8c shows an embodiment of operating a MEMS structure. In a
first step, 830, the MEMS structure is in a first application
setting sensing acoustic signals by moving a membrane relative to a
backplate. The adjustable ventilation opening is in a closed
position. In a second step, 832, the MEMS structure is in a second
application setting sensing acoustic signals by moving a membrane
relative to the backplate. The adjustable ventilation opening is
moved from a closed position to an open position. The open position
may be a completely open position or a partially open position.
FIG. 8d shows an embodiment of operating a MEMS structure. In a
first step, 840, the MEMS structure is in a first application
setting sensing acoustic signals by moving a membrane relative to a
backplate. The adjustable ventilation opening is in an open
position. In a second step, 842, the MEMS structure is in a second
application setting sensing acoustic signals by moving a membrane
relative to the backplate. The adjustable ventilation opening is
moved from an open position to an closed position. The closed
position may be a completely closed position or a partially closed
position.
Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims.
Moreover, the scope of the present application is not intended to
be limited to the particular embodiments of the process, machine,
manufacture, composition of matter, means, methods and steps
described in the specification. As one of ordinary skill in the art
will readily appreciate from the disclosure of the present
invention, processes, machines, manufacture, compositions of
matter, means, methods, or steps, presently existing or later to be
developed, that perform substantially the same function or achieve
substantially the same result as the corresponding embodiments
described herein may be utilized according to the present
invention. Accordingly, the appended claims are intended to include
within their scope such processes, machines, manufacture,
compositions of matter, means, methods, or steps.
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