U.S. patent application number 12/201211 was filed with the patent office on 2010-03-04 for pressure sensor featuring offset cancellation and method of making.
Invention is credited to Dubravka Bilic, Marco Fuhrmann, Thomas D. Ohe.
Application Number | 20100050776 12/201211 |
Document ID | / |
Family ID | 41723389 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100050776 |
Kind Code |
A1 |
Fuhrmann; Marco ; et
al. |
March 4, 2010 |
PRESSURE SENSOR FEATURING OFFSET CANCELLATION AND METHOD OF
MAKING
Abstract
A pressure sensor includes a first set of electrodes, a second
set of electrodes, and a common electrode. The first and second
sets of electrodes overlie an insulative surface, wherein the first
set of electrodes represent sense capacitor bottom electrodes and
the second set of electrodes represent reference capacitor bottom
electrodes. The second set of electrodes is configured in an
interleaved arrangement with the first set of electrodes, wherein
the geometry of individual electrodes of the first set of
electrodes substantially matches the geometry of individual
electrodes of the second set of electrodes. In addition, the common
electrode represents a sense and reference capacitor top electrode
that is (i) overlying, (ii) spaced from, and (iii) configured in
connection with the first and second sets of electrodes to form a
common pressure cavity, wherein the common electrode includes first
portions corresponding to sense membrane portions and second
portions corresponding to reference membrane portions, further
wherein an area of a sense membrane portion is greater than an area
of a reference membrane portion.
Inventors: |
Fuhrmann; Marco; (Gilbert,
AZ) ; Bilic; Dubravka; (Scottsdale, AZ) ; Ohe;
Thomas D.; (Tempe, AZ) |
Correspondence
Address: |
FREESCALE SEMICONDUCTOR, INC.;LAW DEPARTMENT
7700 WEST PARMER LANE MD:TX32/PL02
AUSTIN
TX
78729
US
|
Family ID: |
41723389 |
Appl. No.: |
12/201211 |
Filed: |
August 29, 2008 |
Current U.S.
Class: |
73/718 ;
29/592.1 |
Current CPC
Class: |
G01L 9/0073 20130101;
Y10T 29/49002 20150115 |
Class at
Publication: |
73/718 ;
29/592.1 |
International
Class: |
G01L 9/12 20060101
G01L009/12 |
Claims
1. A pressure sensor, comprising: a first set of electrodes
overlying an insulative surface; a second set of electrodes
overlying the insulative surface, the second set of electrodes
being configured in an interleaved arrangement with the first set
of electrodes, wherein a geometry of individual electrodes of the
first set of electrodes substantially matches a geometry of
individual electrodes of the second set of electrodes; and a common
electrode (i) overlying, (ii) spaced from, and (iii) configured in
connection with the first and second sets of electrodes to form a
common pressure cavity, wherein the common electrode includes first
portions corresponding to sense membrane portions and second
portions corresponding to reference membrane portions, further
wherein an area of a sense membrane portion is greater than an area
of a reference membrane portion.
2. The device of claim 1, wherein the geometry of individual
electrodes of the first set of electrodes matches the geometry of
the individual electrodes of the second set of electrodes.
3. The device of claim 2, further wherein the electrodes of the
first set of electrodes are each characterized by a length
dimension and a width dimension, the electrodes of the second set
of electrodes are each characterized by a length dimension and a
width dimension, and further wherein the length and width
dimensions of each of the electrodes in the first set of electrodes
equals the length and width dimensions of each of the electrodes in
the second set of electrodes.
4. The device of claim 1, wherein the first set of electrodes
comprise sense capacitor bottom plate electrodes, the second set of
electrodes comprise reference capacitor bottom plate electrodes,
and the common electrode comprises a capacitor top plate electrode
in common with the sense and reference capacitor bottom plate
electrodes.
5. The device of claim 1, wherein the first and second sets of
electrodes are configured in a layout including an axis of
substantial symmetry extending along one dimension of the common
electrode and a pattern of repeating first and second sets of
electrodes about another axis along another dimension of the common
electrode.
6. The device of claim 5, further comprising: a first conductive
runner electrically coupled to the first set of electrodes; and a
second conductive runner electrically coupled to the second set of
electrodes, wherein a geometry of the first conductive runner
substantially matches a geometry of the second conductive runner,
further wherein the first and second conductive runners extend in a
direction parallel to the axis of substantial symmetry.
7. The device of claim 6, wherein the geometry of the first
conductive runner substantially matches the geometry of the second
conductive runner.
8. The device of claim 1, wherein the first portions of the common
electrode corresponding to the sense membrane portions are each
characterized by a length dimension and a width dimension, the
second portions of the common electrode corresponding to the
reference membrane portions are each characterized by a length
dimension and a width dimension, wherein the length dimension of
the first portions equals the length dimension of the second
portions, and wherein the width dimension of the first portions is
greater than the width dimension of the second portions.
9. The device of claim 1, wherein the common electrode anchors to
the insulative surface for establishing (i) the first portions
corresponding to the sense membrane portions and (ii) the second
portions corresponding to the reference membrane portions.
10. The device of claim 1, wherein the common electrode is one of
(i) directly anchored to the dielectric surface or (ii) indirectly
anchored to the dielectric surface.
11. The device of claim 1, wherein the first set of electrodes
includes two electrodes, and wherein the second set of electrodes
includes two electrodes.
12. The device of claim 1, wherein the geometry of individual
electrodes of the second set of electrodes comprises an equivalent
geometry, wherein the equivalent geometry of each individual
electrode comprises a first half and a second half, wherein each of
the first half and second half is positioned opposite sides of a
corresponding electrode of the first set of electrodes along a
length dimension of the corresponding electrode.
13. The device of claim 12, further wherein the first portions of
the common electrode corresponding to the first half and the second
half equivalent geometry of individual electrodes of the second set
of electrodes effectively share a corresponding percentage of the
second portions of the common electrode.
14. The device of claim 13, further wherein each first half
equivalent geometry of the individual electrodes of the second set
of electrodes effectively shares a first half of a corresponding
second portion, and wherein the second half equivalent geometry of
the individual electrodes of the second set of electrodes
effectively shares a second half of the corresponding second
portion.
15. The device of claim 1, further comprising: a semiconductor
substrate including an doped well region, and wherein the
insulative surface comprises a surface of a dielectric layer
overlying the doped well region of the semiconductor substrate,
further wherein the first set of electrodes, the second set of
electrodes, and the common electrode also overly the doped well
region of the substrate.
16. A pressure sensor, comprising: a first set of electrodes
overlying an insulative surface; a second set of electrodes
overlying the insulative surface, the second set of electrodes
being configured in an interleaved arrangement with the first set
of electrodes, wherein a geometry of individual electrodes of the
first set of electrodes substantially matches a geometry of
individual electrodes of the second set of electrodes, further
wherein the first and second sets of electrodes are configured in a
layout including an axis of substantial symmetry; a first
conductive runner electrically coupled to the first set of
electrodes; a second conductive runner electrically coupled to the
second set of electrodes, wherein a geometry of the first
conductive runner substantially matches a geometry of the second
conductive runner, further wherein the first and second conductive
runners extend in a direction parallel to the axis of substantial
symmetry; and a common electrode (i) overlying, (ii) spaced from,
and (iii) configured in connection with the first and second sets
of electrodes to form a common pressure cavity, wherein the common
electrode includes first portions corresponding to sense membrane
portions and second portions corresponding to reference membrane
portions, wherein an area of a sense membrane portion is greater
than an area of a reference membrane portion, wherein the axis of
substantial symmetry extends along one dimension of the common
electrode and a pattern of repeating first and second sets of
electrodes extends about another axis along another dimension of
the common electrode, and wherein the common electrode anchors to
the insulative surface for establishing (i) the first portions
corresponding to the sense membrane portions and (ii) the second
portions corresponding to the reference membrane portions.
17. A method of making a pressure sensor, comprising: forming a
first set of electrodes overlying an insulative surface; forming a
second set of electrodes overlying the insulative surface, the
second set of electrodes being configured in an interleaved
arrangement with the first set of electrodes, wherein a geometry of
individual electrodes of the first set of electrodes substantially
matches a geometry of individual electrodes of the second set of
electrodes; and forming a common electrode (i) overlying, (ii)
spaced from, and (iii) configured in connection with the first and
second sets of electrodes to form a common pressure cavity, wherein
the common electrode includes first portions corresponding to sense
membrane portions and second portions corresponding to reference
membrane portions, further wherein an area of a sense membrane
portion is greater than an area of a reference membrane
portion.
18. The method of claim 17, wherein forming the first and second
sets of electrodes comprises configuring the first and second sets
of electrodes in a layout including an axis of substantial symmetry
extending along one dimension of the common electrode and repeating
a pattern of the first and second sets of electrodes along another
dimension of the common electrode.
19. The method of claim 18, wherein prior to forming the common
electrode, the method further comprises: forming a first conductive
runner electrically coupled to the first set of electrodes
overlying the insulative surface; and forming a second conductive
runner electrically coupled to the second set of electrodes
overlying the insulative surface, wherein a geometry of the first
conductive runner substantially matches a geometry of the second
conductive runner, further wherein the first and second conductive
runners extend in a direction parallel to the axis of substantial
symmetry.
20. The method of claim 19, wherein forming the common electrode
further includes anchoring the common electrode to the insulative
surface for establishing (i) the first portions corresponding to
the sense membrane portions and (ii) the second portions
corresponding to the reference membrane portions.
Description
BACKGROUND
[0001] 1. Field
[0002] This disclosure relates generally to pressure sensors, and
more specifically, to a pressure sensor featuring offset
cancellation and a method of making the same.
[0003] 2. Related Art
[0004] Leak detection and leak signal compensation are important
features for micro-electromechanical systems MEMS pressure sensors,
especially in automotive safety applications. A pressure leak in a
MEMS pressure sensor may occur, for example, in response to a
cracked membrane. In addition, time to market considerations foster
a need for better re-use options between inertial (e.g., gyroscope,
accelerometer, etc.) and pressure sensors. For example, a
differential pressure sensor that is more robust as a stand alone
P-Cell (pressure transducer) connected to any given ASIC
(application specific integrated circuit) design that was developed
for inertial or pressure sensors is desired.
[0005] Accordingly, there is a need for an improved method and
apparatus for overcoming the problems in the art as discussed
above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The present invention is illustrated by way of example and
is not limited by the accompanying figures, in which like
references indicate similar elements. Elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale.
[0007] FIG. 1 is a layout top view of a MEMS pressure sensor
featuring offset cancellation according to one embodiment of the
present disclosure;
[0008] FIG. 2 is a layout top view of the MEMS pressure sensor
featuring offset cancellation of FIG. 1, further showing
cross-section references, according to one embodiment of the
present disclosure;
[0009] FIG. 3 is a cross-section view of the MEMS pressure sensor
featuring offset cancellation of FIG. 2, taken along line 3-3 of
FIG. 2, according to one embodiment of the present disclosure;
[0010] FIGS. 4-13 are cross-section views of the MEMS pressure
sensor featuring offset cancellation of FIG. 2, taken along line
4-4 of FIG. 2, at different stages of manufacture, according to one
embodiment of the present disclosure;
[0011] FIG. 14 is a cross-section view of a MEMS pressure sensor
featuring offset cancellation, similar to the embodiment of FIG. 2
taken along line 3-3 of FIG. 2, according to another embodiment of
the present disclosure;
[0012] FIG. 15 is a cross-section view of a MEMS pressure sensor
featuring offset cancellation, similar to the embodiment of FIG. 2
taken along line 3-3 of FIG. 2, according to yet another embodiment
of the present disclosure; and
[0013] FIG. 16 is a top-down view of a MEMS pressure sensor
featuring offset cancellation, similar to the embodiment of FIG. 2,
according to still another embodiment of the present
disclosure.
DETAILED DESCRIPTION
[0014] As described herein, a semiconductor substrate can be any
semiconductor material or combinations of materials, such as
gallium arsenide, silicon germanium, silicon-on-insulator (SOI),
silicon, monocrystalline silicon, the like, and combinations of the
above. The embodiments of the present disclosure are not limited to
semiconductor substrates, but can include any suitable substrate
for a given pressure sensor application.
[0015] According to one embodiment, the pressure sensor
architecture of the present disclosure advantageously reduces
undesirable temperature effects and/or media effects. The
embodiments further allow for development of next generation combo
designs, including accelerometers and pressure sensor elements on a
single die, while reducing cost, as the pressure sensor itself does
not require a circuit on chip any more, but can advantageously
re-use existing capacitance-to-voltage (C2V) circuitry on the ASIC
side. The embodiments of the present disclosure also advantageously
provide offset cancellation for a dual-transducer pressure sensor.
In addition, the embodiments further provide for improved leak
detection.
[0016] According to the embodiments of the present disclosure, the
MEMS pressure sensor includes at least the following aspects: (i)
the MEMS pressure sensor design is substantially symmetric, (ii)
the MEMS pressure sensor design has interleaved reference and sense
elements, and (iii) the MEMS pressure sensor design has a common
chamber (or cavity), wherein the chamber can include a vacuum
chamber or a chamber filled with a suitable gas at a given
controlled pressure. Any offset drift needs to match between the
interleaved sensors, which is achieved by a substantially symmetric
layout of poly runners and substantially identical bottom plates.
In other words, matching of any offset drift between the
interleaved sensors is achieved by a substantially symmetric layout
of poly runners and substantially identical capacitor bottom
electrode plates (as will be discussed further herein). In
addition, the reference element of the MEMS pressure sensor design
is created with a smaller diaphragm width than that of the sense
element. Accordingly, this maintains a smallest possible die size
and allows for better temperature coefficient (TC) cancellation,
compared to increasing a thickness of a top capacitor electrode to
create a corresponding reference element.
[0017] Furthermore, the MEMS pressure sensor transducer according
to the embodiments of the present disclosure is designed to enable
differential sensing of pressure and keep capacitive offset drifts
substantially identical on both sides (i.e., on each of the sense
and reference sides). In one embodiment, the number of bottom
capacitor electrodes can include four (4) electrodes, two (2) for
the reference portion and two (2) for the sense portion of the
pressure transducer. The particular number of bottom electrodes (or
electrode plates) for reference and sense can be selected (or
adjusted as necessary) according to the requirements of a given
MEMS pressure sensor transducer implementation.
[0018] Referring now to the figures, FIG. 1 is a layout top view of
a MEMS pressure sensor 10 featuring offset cancellation according
to one embodiment of the present disclosure. MEMS pressure sensor
10 is fabricated on the surface of an insulative layer 12.
Insulative layer 12 can comprise any suitable insulative or
dielectric material layer, selected according to the requirements
of a given pressure sensor implementation. Electrodes 14, 16, 18
and 20 are formed overlying the surface of insulative layer 12,
wherein the electrodes are illustrated in phantom, due to the fact
that they are beneath a common electrode 22. Electrodes 16 and 20
represent a first set of sense capacitor bottom electrodes, while
electrodes 14 and 18 represent a second set of reference capacitor
bottom electrodes. The second set of electrodes (14,18) are
configured in an interleaved arrangement with the first set of
electrodes (16,20). In addition, in one embodiment, a geometry of
individual electrodes of the first set of electrodes (16,20)
substantially matches a geometry of individual electrodes of the
second set of electrodes (14,18), i.e., the geometries are
substantially similar. In another embodiment, the geometry of
individual electrodes of the first set of electrodes matches the
geometry of the individual electrodes of the second set of
electrodes, i.e., the geometries are identical.
[0019] In addition, the electrodes (16,20) of the first set of
electrodes can each be characterized by a length dimension and a
width dimension. The electrodes (14,18) of the second set of
electrodes can also be characterized by a length dimension and a
width dimension. For example, the length and width dimensions of
electrode 14 are represented by the dimension arrows 30 and 33,
respectively, in FIG. 1. Similarly, the length and width dimensions
of electrode 16 are represented by the dimension arrows 30 and 35,
respectively, in FIG. 1. In one embodiment, the length and width
dimensions of each of the electrodes (16,20) in the first set of
electrodes equals the length and width dimensions of each of the
electrodes (14,18) in the second set of electrodes.
[0020] Referring still to FIG. 1, common electrode 22 represents a
sense and reference capacitor top electrode. The top electrode 22
is (i) overlying, (ii) spaced from, and (iii) configured in
connection with the first and second sets of electrodes, (16,20)
and (14,18), respectively, to form a common vacuum cavity (as
indicated by reference numeral 90 in FIG. 3 and to be discussed
further herein). Common electrode 22 anchors to the surface of the
insulative layer 12 for establishing (i) first portions
corresponding to the sense membrane portions and (ii) second
portions corresponding to the reference membrane portions. For
example, in FIG. 1, common electrode 22 anchors to the insulative
surface 12 about a perimeter of the common electrode and at desired
locations internal to the perimeter, such as indicated by reference
numerals 24, 26, and 28, to establish the vacuum cavity and to
define the first and second portions. Accordingly, the common
electrode 22 includes first portions corresponding to the sense
membrane portions, as generally indicated by reference numerals 66
and 70 in FIG. 1 and discussed further herein with reference to
FIG. 3. The common electrode 22 also includes second portions
corresponding to reference membrane portions, as generally
indicated by reference numerals 64 and 68 in FIG. 1 and discussed
further herein with reference to FIG. 3. In addition, an area of a
sense membrane portion (e.g., portion 66) is greater than an area
of a reference membrane portion (e.g., portion 64).
[0021] The first portions (66,70) of the common electrode 22
corresponding to the sense membrane portions are each characterized
by a length dimension, as generally indicated by dimension arrow
30, and a width dimension, as generally indicated by dimension
arrows 34 and 38, respectively. The second portions (64,68) of the
common electrode 22 corresponding to the reference membrane
portions are each characterized by a length dimension, as generally
indicated by dimension arrow 30, and a width dimension, as
generally indicated by dimension arrows 32 and 36, respectively. In
one embodiment, the length dimension of the first portions (66,70)
equals the length dimension of the second portions (64,68). In
addition, the width dimension 34 of first portion 66 is greater
than the width dimension 32 of second portion 64. Furthermore, the
width dimension 38 of the first portion 70 is greater than the
width dimension 36 of second portion 68.
[0022] MEMS pressure sensor 10 further comprises a first conductive
node 40, a first conductive runner 42, a second conductive node 44,
and a second conductive runner 46. The first conductive runner 42
is electrically coupled to the first set of electrodes (16, 20) and
provides electrical access external to the sensor 10 at node 40.
The second conductive runner 46 is electrically coupled to the
second set of electrodes and provides electrical access external to
the sensor at node 44. In addition, the geometry of the first
conductive runner 42 substantially matches the geometry of the
second conductive runner 46. Furthermore, electrical access to
electrode 22 is provided at node 50. In the top view illustration
of FIG. 1, the first and second conductive runners, 42 and 46,
respectively, are insulated (not shown) from electrode 22 proximate
the perimeter of electrode 22 near nodes 40 and 44,
respectively.
[0023] As further illustrated in FIG. 1, the first and second sets
of electrodes, (16,20) and (14,18), respectively, are configured in
a layout including an axis of substantial symmetry 52 extending
along one dimension of the common electrode 22 and a pattern of
repeating first and second sets of electrodes, (16,20) and (14,18),
respectively, about another axis 54 along another dimension of the
common electrode 22. In one embodiment, the axis of substantial
symmetry 52 is perpendicular to axis 54. Furthermore, the first and
second conductive runners, 42 and 46, respectively, extend in a
direction parallel to the axis of substantial symmetry 52. Still
further, in one embodiment, the geometry of the first conductive
runner 42 substantially matches the geometry of the second
conductive runner 46.
[0024] Moreover, in the layout view illustration of FIG. 1,
pressure sensor 10 includes capacitors C1 and C2. Capacitor C1
substantially comprises bottom capacitor electrodes (14,18) and
corresponding reference membrane portions (64,68) of the common
capacitor top plate electrode 22. Capacitor C2 substantially
comprises bottom capacitor electrodes (16,20) and corresponding
sense membrane portions (66,70) of the common capacitor top plate
electrode 22. An important distinction of the MEMS pressure sensor
10 of FIG. 1 is that only the sensitivity between the reference
capacitor (C1) and the sense capacitor (C2) is different; whereas
offsets and parasitic capacitances (Cp) are ideally identical, and
in practice, they are roughly identical (i.e.,
Cp.sub.CB.apprxeq.Cp.sub.AB). The sensitivity differences is
achieved by using different top-plate widths (32,36) for C1 and
(34,38) for C2. For example, in FIG. 1, reference capacitor C1 has
less sensitivity than sense capacitor C2 because of the narrower
top-plate widths (i.e., corresponding to narrower reference
membrane portions compared to the sense membrane portions). In one
embodiment, the capacitance to voltage (C2V) transfer function for
the front end circuit is given by the expression: C2V=C2-C1. In
operation, deflection of the sense membrane portions and the
reference membrane portions of the common capacitor top plate
electrode occurs in response to changes in pressure experienced by
the respective membrane portions different from a pressure within
the cavity of the pressure sensor.
[0025] FIG. 2 is a layout top view of the MEMS pressure sensor 10
featuring offset cancellation of FIG. 1, further showing
cross-section references, according to one embodiment of the
present disclosure. FIG. 3 is a cross-section view of the MEMS
pressure sensor 10 featuring offset cancellation of FIG. 2, taken
along line 3-3 of FIG. 2, according to one embodiment of the
present disclosure. That is, in one embodiment, MEMS pressure
sensor 10 includes a substrate 56. Substrate 56 can comprise any
suitable substrate selected according to the requirements of a
given MEMS pressure sensor implementation. In one embodiment,
substrate 56 comprises a semiconductor substrate. In another
embodiment, a doped well region 58 is formed within substrate 56,
which underlies the insulative layer 12, the bottom electrodes
(14,16,18,20) and the top common electrode 22. As previously
discussed, the top electrode 22 is (i) overlying, (ii) spaced from,
and (iii) configured in connection with the first and second sets
of electrodes, (16,20) and (14,18), respectively, to form a common
vacuum cavity as indicated by reference numeral 90. Common
electrode 22 anchors to the surface of insulative layer 12 for
establishing (i) first portions (66,70) corresponding to the sense
membrane portions and (ii) second portions (64,68) corresponding to
the reference membrane portions. In particular, common electrode 22
anchors to the surface of insulative layer 12 about a perimeter of
the common electrode (indicated by reference numerals 60,62) and at
desired locations internal to the perimeter, such as indicated by
reference numerals 24, 26, and 28, to establish the vacuum cavity
and to define the first and second portions. In this embodiment,
the common electrode 22 is directly anchored to the surface of
insulative layer 12.
[0026] FIGS. 4-13 are cross-section views of the MEMS pressure
sensor featuring offset cancellation of FIG. 2, taken along line
4-4 of FIG. 2, at different stages of manufacture, according to one
embodiment of the present disclosure. While the cross-section is
taken along one of the conductive runners 46, the processing for
other features of sensor 10 such as the bottom electrodes
(14,16,18,20), and conductive runner (42) occur concurrently as
will be discussed but not illustrated, for brevity. The process of
making the MEMS pressure sensor includes forming a patterned
insulative layer 12 overlying substrate 56, for example, using any
suitable method known in the art. In one embodiment, the substrate
56 comprises an N-type lightly doped phosphorous wafer and
patterned insulative layer 12 comprises a field oxide. The field
oxide may comprise any suitable thickness, for example, on the
order of a few microns (i.e., in the range of 0.5-5.0 .mu.m). In
another embodiment, a well region 58 (FIG. 3) is formed within
substrate 56 prior or subsequent to formation of insulative layer
12.
[0027] Subsequent to formation of insulative layer 12, the
substrate and insulative layer are processed in preparation for the
formation of a substrate contact, for example, using a suitable
known HF etch. The process then includes deposition of a first
polysilicon layer 72 (or other suitable layer) to a suitable
thickness, for example, on the order of hundreds of nanometers (nm)
(i.e., in the range of 100-1000 nm). In addition, the first
polysilicon layer 72 can be doped according to the requirements of
the particular pressure sensor implementation (FIG. 4). For
example, in one embodiment, the polysilicon layer 72 is doped with
N-type dopant (31 P+, 80 keV, 5.05E15). Subsequently, layer 72 is
patterned according to the requirements of the given pressure
transducer implementation, including for example, to define bottom
electrode plates (14,16,18,20) and conductive runners (42,46). In
one embodiment, patterning includes providing an opening 74 in
layer 72, as will be discussed further herein.
[0028] Referring now to FIG. 5, an isolation material is deposited
and patterned to form isolation pads 76 and 78. As will be
understood herein, the isolation pads provide isolation of the top
electrode, as required, from the conductive runners and from the
substrate. For example, in one embodiment, the isolation material
deposition comprises a silicon rich low stress nitride deposition,
having a thickness on the order of hundreds of nanometers (nm)
(i.e., in the range of 100-1000 nm). The silicon rich nitride is
then patterned to define nitride isolation, such as isolation pads
76 and 78.
[0029] Referring now to FIG. 6, a sacrificial material is deposited
and patterned to form gap definition layer 80. Gap definition layer
80 overlies a region that includes a portion of isolation pads 76
and 78, as well as bottom electrode plates (14,16,18,20) and
conductive runners (42,46) which will underlie the subsequently
formed top electrode 22. In one embodiment, gap definition layer 80
is removed from regions corresponding to anchors (24,26,28) of the
top electrode plate 22 (FIGS. 2,3). In addition, in one embodiment,
the sacrificial material deposition comprises a phosphor silicate
glass (PSG) deposition, having a thickness in the range of 0.2-2.0
.mu.m. The PSG is then patterned to define gap definition layer
80.
[0030] Turning now to FIG. 7, a second polysilicon layer 82 (or
other suitable layer) is deposited to a suitable thickness, for
example, on the order of a few microns (i.e., 1-20 .mu.m). In
addition, the second polysilicon layer 82 can be doped according to
the requirements of the particular pressure sensor implementation.
For example, in one embodiment, the polysilicon layer 82 is doped
with N-type dopant (31 P+, 75 keV, 5E15). Subsequently, as
illustrated in FIG. 8, layer 82 is patterned according to the
requirements of the given pressure transducer implementation,
including for example, to define the pressure sensor top electrode
plate 22. In one embodiment, patterning includes providing openings
84,88 to define an outer perimeter of electrode plate 22. Openings
84,88 preferably land upon the isolation pads 76,78 so that the
portion of polysilicon layer 82 corresponding to the top electrode
plate 22 can be decoupled from other portions of layer 82 outside
of the perimeter of the top electrode plate 22. Patterning also
provides an opening 86 (or more openings as may be required) within
the electrode plate 22 which lands on sacrificial layer 80 to
provide access for removal of the sacrificial layer 80.
[0031] Turning now to FIG.9, the structure of FIG. 8 is subjected
to a suitable diaphragm release etch, wherein sacrificial material
80 is removed while other portions of the structure remain. Removal
of sacrificial material 80 creates a void 90, which will
subsequently become a sealed pressure cavity for pressure sensor
10. The portion of second polysilicon layer 82 corresponding to the
top electrode plate 20 thus becomes a diaphragm membrane for the
pressure sensor 10, with the exception of those regions of the top
electrode plate that are the anchored portions (24,26,28,60,62) of
the top electrode plate 22 (FIGS. 2,3).
[0032] Referring now to FIG. 10, a patterned membrane protection
layer 92 is formed overlying the top surface of the second
polysilicon layer 82. For example, forming the membrane protection
layer 92 can include depositing a tetra-ethyl-ortho-silicate (TEOS)
material (or other membrane layer protecting material) to a
suitable thickness, for example, on the order of a few microns
(i.e., 0.5-5.0 .mu.m). Deposition of layer 92 seals the cavity 90,
as well as, seals the openings (84,88) around a perimeter of the
top electrode plate 22. Sealing of the openings (84,88) around the
perimeter of the top electrode plate 22 also provides suitable
isolation of the top electrode plate 22 from regions external to
plate 22. Subsequently, as illustrated in FIG. 10, layer 92 is
patterned according to the requirements of the given pressure
transducer implementation, including for example, to define a
protected region of the pressure sensor top electrode plate 22 and
around a perimeter of the top electrode plate.
[0033] Turning now to FIG. 11, the pressure transducer 10 is
processed with a suitable metallization selected according to the
requirements of the pressure transducer implementation. For
example, in one embodiment, metallization includes deposition of an
aluminum silicide (AlSi) (or other metallization material) to a
suitable thickness, for example, on the order of a few microns
(i.e., 1-20 .mu.m). Subsequently, as illustrated in FIG. 11, the
metallization layer is patterned according to the requirements of
the given pressure transducer implementation, including for
example, to define a capacitor pad 94 of the conductive runner 46
and a substrate contact pad 96.
[0034] Referring now to FIG. 12, a patterned passivation layer 98
is formed overlying the top surface of membrane protection layer 92
and edge portions of metallization pads 94 and 96. For example,
forming the passivation layer 98 can include depositing a silicon
oxynitride (SiON) material (or other passivation layer material) to
a suitable thickness, for example, on the order of a few microns
(i.e., 0.5-5.0 .mu.m). Deposition of layer 98 passivates layer 92,
as well as, seals the edges between the metallization pads (94,96)
and layer 92 proximate the perimeter of the top electrode plate 22.
Subsequently, as illustrated in FIG. 12, layer 98 is patterned
according to the requirements of the given pressure transducer
implementation, including for example, to define an opening 100 to
the membrane protection layer 92 and openings for bond pads
(94,96). Subsequently, as shown in FIG. 13, the structure of FIG.
12 is further processed by patterning the membrane protection layer
92 to provide a suitable opening 102 (FIG. 13) via a suitable etch
of the exposed portion of membrane protection layer 92 through
opening 100 (FIG. 12). The second polysilicon layer 82, acting as a
membrane for pressure sensor 10, is thus exposed within opening
102.
[0035] FIG. 14 is a cross-section view of a MEMS pressure sensor
110 featuring offset cancellation, similar to the embodiment of
FIG. 2 taken along line 3-3 of FIG. 2, according to another
embodiment of the present disclosure. That is, in one embodiment,
MEMS pressure sensor 110 includes a substrate 56. Substrate 56 can
comprise any suitable substrate selected according to the
requirements of a given MEMS pressure sensor implementation. In one
embodiment, substrate 56 comprises a semiconductor substrate. In
another embodiment, a doped well region 58 is formed within
substrate 56, which underlies the insulative layer 12, the bottom
electrodes (14,16,18,20) and the top common electrode 23. The top
electrode 23 is (i) overlying, (ii) spaced from, and (iii)
configured in connection with the first and second sets of
electrodes, (16,20) and (14,18), respectively, to form a common
vacuum cavity as indicated by reference numeral 90. Common
electrode 23 anchors to the surface of insulative layer 12 via
standoff regions (21,25,27,29) for establishing (i) first portions
(66,70) corresponding to the sense membrane portions and (ii)
second portions (64,68) corresponding to the reference membrane
portions. In particular, in this embodiment, common electrode 23
anchors to the insulative surface of dielectric 12 via standoff
region 21 about a perimeter of the common electrode and at desired
locations internal to the perimeter via standoff regions, such as
indicated by reference numerals 25, 27, and 29, to establish the
vacuum cavity and to define the first and second portions. Standoff
regions 21, 25, 27, and 29 can comprise any suitable standoffs
selected according to the requirements of a given pressure
transducer implementation. In this embodiment, the common electrode
23 is indirectly anchored to the surface of insulative layer
12.
[0036] FIG. 15 is a cross-section view of a MEMS pressure sensor
120 featuring offset cancellation, similar to the embodiment of
FIG. 2 taken along line 3-3 of FIG. 2, according to yet another
embodiment of the present disclosure. This embodiment is similar to
the embodiment illustrated in FIG. 3, with differences as discussed
in the following. In particular, the bottom electrodes include a
plurality of sense capacitor bottom electrodes (16, 20, . . . ,
124) and a like plurality of reference capacitor bottom electrodes
(14, 18, . . . , 122). In addition, from a top layout view
perspective, the first and second sets of bottom electrodes are
configured in a layout including an axis of substantial symmetry
extending along one dimension of the common electrode and a pattern
of repeating first and second sets of electrodes about another axis
along another dimension of the common electrode 126. Referring
again to FIG. 15, MEMS pressure sensor 120 includes a substrate 56.
In one embodiment, the doped well region 58 is formed within
substrate 56, which underlies the insulative layer 12, the bottom
electrodes (14,16,18,20 . . . , 122,124) and the top common
electrode 126. The top electrode 126 is (i) overlying, (ii) spaced
from, and (iii) configured in connection with the first and second
sets of electrodes, (16,20, . . . , 124) and (14,18, . . . , 122),
respectively, to form a common vacuum cavity as indicated by
reference numeral 90. Common electrode 126 anchors to the surface
of insulative layer 12 for establishing (i) first portions (66,70,
. . . , 130) corresponding to the sense membrane portions and (ii)
second portions (64,68, . . . , 128) corresponding to the reference
membrane portions. In particular, common electrode 126 anchors to
the insulative surface 12 about a perimeter of the common electrode
(indicated by reference numerals 60,62) and at desired locations
internal to the perimeter, such as indicated by reference numerals
24, 26, 28, and 129, to establish the vacuum cavity and to define
the first and second portions. In this embodiment, the common
electrode 126 is directly anchored to the surface of insulative
layer 12.
[0037] FIG. 16 is a top-down view of a MEMS pressure sensor 140
featuring offset cancellation, similar to the embodiment of FIG. 2,
according to still another embodiment of the present disclosure.
This embodiment is similar to the embodiment of FIG. 2, with
differences as discussed in the following. In particular, the
geometry of individual electrodes of the second set of electrodes
((141,142),(181,182)) comprises an equivalent geometry. That is,
the equivalent geometry of each individual electrode (14 and 18 of
FIG. 2) comprises a first half (141 and 181, respectively of FIG.
16) and a second half (142 and 182, respectively of FIG. 16). Each
of the first half and second half is positioned opposite sides of a
corresponding electrode (16 or 20) of the first set of electrodes
(16,20) along a length dimension of the corresponding electrode. In
addition, the first portions (641, 642, 681, and 682) of the common
electrode 22 corresponding to the first half (141,181) and the
second half (142,182) equivalent geometry of individual electrodes
of the second set of electrodes (14 and 18 of FIG. 2) effectively
share a corresponding percentage of the second portions (66, 70) of
the common electrode 22. In other words, first half equivalent
geometry electrode 141 is within the first portion 641 of common
electrode 22 and second half equivalent geometry electrode 142 is
within the first portion 642 of common electrode 22, wherein first
portion 641 shares a left-hand side of second portion 66 of common
electrode 22 and second portion 642 shares a right-hand side of
second portion 66 of common electrode 22. The same applies to first
portion 681 and first portion 682 sharing left-hand and right-hand
sides, respectively, of second portion 70 of common electrode 22.
In one embodiment, each first half equivalent geometry of the
individual electrodes of the second set of electrodes effectively
shares a first half (e.g. on the order of fifty percent) of a
corresponding second portion, and wherein the second half
equivalent geometry of the individual electrodes of the second set
of electrodes effectively shares a second half (e.g. on the order
of fifty percent) of the corresponding second portion.
[0038] The inventors have found that changes in offset due to
changes in temperature are larger for individual capacitors than
for the difference of two capacitors, (i.e., a sense capacitor and
a reference capacitor. The capacitor can be modeled by the equation
of C=a*P2+b*P+c, where capacitance C is in units of (fF),
coefficients a, b and c in units of (fF/kPa.sup.2), (fF/kPa), and
(fF), respectively, and P is pressure in units of (kPa). In
addition, depositing a media protection coating (such as any
suitable gel) on a P-cell according to the embodiments of the
present disclosure results in a substantially uniform offset
change. In other words, offset deviation improves on the order of
approximately eighty percent (.about.80%) when taking a difference
of two capacitances of different sensitivities as compared to an
offset of one capacitor alone. Furthermore, leak detection can be
determined by the observation of any sensitivity change, caused,
for example, by a pressure leak. In response to detection of the
sensitivity change, the sensor output can be corrected
accordingly.
[0039] The embodiments of the present disclosure advantageously
combines offset cancellation and slow leak detection on a system
level. In particular, the embodiments provide a single sensor
architecture featuring offset cancellation and an option for system
level slow leak detection by matching an offset through the
interleaved pressure sensor element design as discussed herein. The
pressure sensor can be configured to implement pseudo differential
and differential pressure sensing is response to being coupled to a
differential circuit having a transfer function of C2-C1. In one
embodiment, the MEMS pressure sensor comprises an interleaving
arrangement of two pressure sensor elements with different
sensitivity, wherein the pressure sensor elements share the same
pressure cavity. In other words, in one embodiment, a single
pressure cavity is common to all of the pressure sensor elements of
the MEMS pressure sensor.
[0040] The embodiments of the present disclosure further provide
for a more robust design that yields improved performance over a
life time in harsh environments and improved fault detection
capability on a system level with possible self correction. The
embodiments also provide for better re-use of ASIC front end
circuit designs between inertial and pressure sensors. For example,
the embodiments of the present disclosure can be implemented into
any given pressure sensor or combo device (e.g., accelerometer plus
pressure sensor elements on one die without circuitry).
[0041] By now it should be appreciated that there has been provided
a pressure sensor comprising: a first set of electrodes overlying
an insulative surface; a second set of electrodes overlying the
insulative surface, the second set of electrodes being configured
in an interleaved arrangement with the first set of electrodes,
wherein a geometry of individual electrodes of the first set of
electrodes substantially matches a geometry of individual
electrodes of the second set of electrodes; and a common electrode
(i) overlying, (ii) spaced from, and (iii) configured in connection
with the first and second sets of electrodes to form a common
pressure cavity, wherein the common electrode includes first
portions corresponding to sense membrane portions and second
portions corresponding to reference membrane portions, further
wherein an area of a sense membrane portion is greater than an area
of a reference membrane portion.
[0042] In one embodiment, the geometry of individual electrodes of
the first set of electrodes matches the geometry of the individual
electrodes of the second set of electrodes. In another embodiment,
the electrodes of the first set of electrodes are each
characterized by a length dimension and a width dimension, the
electrodes of the second set of electrodes are each characterized
by a length dimension and a width dimension, and the length and
width dimensions of each of the electrodes in the first set of
electrodes equals the length and width dimensions of each of the
electrodes in the second set of electrodes.
[0043] In another embodiment, the first set of electrodes comprise
sense capacitor bottom plate electrodes, the second set of
electrodes comprise reference capacitor bottom plate electrodes,
and the common electrode comprises a capacitor top plate electrode
in common with the sense and reference capacitor bottom plate
electrodes. In yet another embodiment, the first and second sets of
electrodes are configured in a layout including an axis of
substantial symmetry extending along one dimension of the common
electrode and a pattern of repeating first and second sets of
electrodes about another axis along another dimension of the common
electrode. Still further, the device comprises: a first conductive
runner electrically coupled to the first set of electrodes, and a
second conductive runner electrically coupled to the second set of
electrodes, wherein a geometry of the first conductive runner
substantially matches a geometry of the second conductive runner,
further wherein the first and second conductive runners extend in a
direction parallel to the axis of substantial symmetry. Moreover,
the geometry of the first conductive runner substantially matches
the geometry of the second conductive runner.
[0044] In yet another embodiment, the first portions of the common
electrode corresponding to the sense membrane portions are each
characterized by a length dimension and a width dimension, the
second portions of the common electrode corresponding to the
reference membrane portions are each characterized by a length
dimension and a width dimension, wherein the length dimension of
the first portions equals the length dimension of the second
portions, and wherein the width dimension of the first portions is
greater than the width dimension of the second portions. In a
further embodiment, the common electrode anchors to the insulative
surface for establishing (i) the first portions corresponding to
the sense membrane portions and (ii) the second portions
corresponding to the reference membrane portions. In addition, the
common electrode is one of (i) directly anchored to the dielectric
surface or (ii) indirectly anchored to the dielectric surface. In
one embodiment, the first set of electrodes includes two
electrodes, and wherein the second set of electrodes includes two
electrodes.
[0045] In a still further embodiment, the geometry of individual
electrodes of the second set of electrodes comprises an equivalent
geometry, wherein the equivalent geometry of each individual
electrode comprises a first half and a second half, wherein each of
the first half and second half is positioned opposite sides of a
corresponding electrode of the first set of electrodes along a
length dimension of the corresponding electrode. The first portions
of the common electrode correspond to the first half and the second
half equivalent geometry of individual electrodes of the second set
of electrodes effectively share a corresponding percentage of the
second portions of the common electrode. In another embodiment,
each first half equivalent geometry of the individual electrodes of
the second set of electrodes effectively shares a first half of a
corresponding second portion, and wherein the second half
equivalent geometry of the individual electrodes of the second set
of electrodes effectively shares a second half of the corresponding
second portion.
[0046] In yet another embodiment, the device further comprises: a
semiconductor substrate including an doped well region, and wherein
the insulative surface comprises a surface of a dielectric layer
overlying the doped well region of the semiconductor substrate,
further wherein the first set of electrodes, the second set of
electrodes, and the common electrode also overly the doped well
region of the substrate.
[0047] In another embodiment, a pressure sensor, comprises: a first
set of electrodes overlying an insulative surface; a second set of
electrodes overlying the insulative surface, the second set of
electrodes being configured in an interleaved arrangement with the
first set of electrodes, wherein a geometry of individual
electrodes of the first set of electrodes substantially matches a
geometry of individual electrodes of the second set of electrodes,
further wherein the first and second sets of electrodes are
configured in a layout including an axis of substantial symmetry; a
first conductive runner electrically coupled to the first set of
electrodes; a second conductive runner electrically coupled to the
second set of electrodes, wherein a geometry of the first
conductive runner substantially matches a geometry of the second
conductive runner, further wherein the first and second conductive
runners extend in a direction parallel to the axis of substantial
symmetry; and a common electrode (i) overlying, (ii) spaced from,
and (iii) configured in connection with the first and second sets
of electrodes to form a common pressure cavity, wherein the common
electrode includes first portions corresponding to sense membrane
portions and second portions corresponding to reference membrane
portions, wherein an area of a sense membrane portion is greater
than an area of a reference membrane portion, wherein the axis of
substantial symmetry extends along one dimension of the common
electrode and a pattern of repeating first and second sets of
electrodes extends about another axis along another dimension of
the common electrode, and wherein the common electrode anchors to
the insulative surface for establishing (i) the first portions
corresponding to the sense membrane portions and (ii) the second
portions corresponding to the reference membrane portions.
[0048] In yet another embodiment, a method of making a pressure
sensor, comprises: forming a first set of electrodes overlying an
insulative surface; forming a second set of electrodes overlying
the insulative surface, the second set of electrodes being
configured in an interleaved arrangement with the first set of
electrodes, wherein a geometry of individual electrodes of the
first set of electrodes substantially matches a geometry of
individual electrodes of the second set of electrodes; and forming
a common electrode (i) overlying, (ii) spaced from, and (iii)
configured in connection with the first and second sets of
electrodes to form a common pressure cavity, wherein the common
electrode includes first portions corresponding to sense membrane
portions and second portions corresponding to reference membrane
portions, further wherein an area of a sense membrane portion is
greater than an area of a reference membrane portion. In one
embodiment, forming the first and second sets of electrodes
comprises configuring the first and second sets of electrodes in a
layout including an axis of substantial symmetry extending along
one dimension of the common electrode and repeating a pattern of
the first and second sets of electrodes along another dimension of
the common electrode. In addition, in another embodiment, prior to
forming the common electrode, the method further comprises: forming
a first conductive runner electrically coupled to the first set of
electrodes overlying the insulative surface; and forming a second
conductive runner electrically coupled to the second set of
electrodes overlying the insulative surface, wherein a geometry of
the first conductive runner substantially matches a geometry of the
second conductive runner, further wherein the first and second
conductive runners extend in a direction parallel to the axis of
substantial symmetry. Furthermore, forming the common electrode
further includes anchoring the common electrode to the insulative
surface for establishing (i) the first portions corresponding to
the sense membrane portions and (ii) the second portions
corresponding to the reference membrane portions.
[0049] Because the apparatus implementing the present invention is,
for the most part, composed of electronic components and circuits
known to those skilled in the art, circuit details will not be
explained in any greater extent than that considered necessary as
illustrated above, for the understanding and appreciation of the
underlying concepts of the present invention and in order not to
obfuscate or distract from the teachings of the present
invention.
[0050] Although the invention has been described with respect to
specific conductivity types or polarity of potentials, skilled
artisans appreciated that conductivity types and polarities of
potentials may be reversed.
[0051] Moreover, the terms "front," "back," "top," "bottom,"
"over," "under" and the like in the description and in the claims,
if any, are used for descriptive purposes and not necessarily for
describing permanent relative positions. It is understood that the
terms so used are interchangeable under appropriate circumstances
such that the embodiments of the invention described herein are,
for example, capable of operation in other orientations than those
illustrated or otherwise described herein.
[0052] Although the invention is described herein with reference to
specific embodiments, various modifications and changes can be made
without departing from the scope of the present invention as set
forth in the claims below. For example, the embodiments of the
present disclosure could be implemented in connection with any
capacitive pressure sensor implementation (e.g., MEMS and other
than MEMS), whether stand-alone or in a combination (inertial and
pressure sensor) implementation. Accordingly, the specification and
figures are to be regarded in an illustrative rather than a
restrictive sense, and all such modifications are intended to be
included within the scope of the present invention. Any benefits,
advantages, or solutions to problems that are described herein with
regard to specific embodiments are not intended to be construed as
a critical, required, or essential feature or element of any or all
the claims.
[0053] The term "coupled," as used herein, is not intended to be
limited to a direct coupling or a mechanical coupling. Furthermore,
the terms "a" or "an," as used herein, are defined as one or more
than one. Also, the use of introductory phrases such as "at least
one" and "one or more" in the claims should not be construed to
imply that the introduction of another claim element by the
indefinite articles "a" or "an" limits any particular claim
containing such introduced claim element to inventions containing
only one such element, even when the same claim includes the
introductory phrases "one or more" or "at least one" and indefinite
articles such as "a" or "an." The same holds true for the use of
definite articles.
[0054] Unless stated otherwise, terms such as "first" and "second"
are used to arbitrarily distinguish between the elements such terms
describe. Thus, these terms are not necessarily intended to
indicate temporal or other prioritization of such elements.
* * * * *