U.S. patent application number 09/814780 was filed with the patent office on 2001-07-26 for microsystem with a flexible membrane for a pressure sensor and manufacturing process.
This patent application is currently assigned to COMMISSARIAT A L'ENERGIE ATOMIQUE. Invention is credited to Delaye, Marie-Therese.
Application Number | 20010009112 09/814780 |
Document ID | / |
Family ID | 9506045 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009112 |
Kind Code |
A1 |
Delaye, Marie-Therese |
July 26, 2001 |
Microsystem with a flexible membrane for a pressure sensor and
manufacturing process
Abstract
Pressure sensor cell comprising: a substrate (12) comprising at
least a first electrode (10), a deformable membrane (22) fixed by a
peripheral edge to the substrate and defining a closed chamber (26)
around at least part of the first electrode (10), and a second
electrode (20) formed on a wall of the membrane (22) facing the
first electrode, the second being kept separate from the first
electrode if there is no pressure exerted on the membrane.
Inventors: |
Delaye, Marie-Therese;
(Grenoble, FR) |
Correspondence
Address: |
ANDERSON KILL & OLICK, P.C.
1251 Avenue of the Americas
New York
NY
10020
US
|
Assignee: |
COMMISSARIAT A L'ENERGIE
ATOMIQUE
|
Family ID: |
9506045 |
Appl. No.: |
09/814780 |
Filed: |
March 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09814780 |
Mar 22, 2001 |
|
|
|
09060607 |
Apr 15, 1998 |
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Current U.S.
Class: |
73/718 |
Current CPC
Class: |
G01L 9/0073 20130101;
G01L 9/0042 20130101; G06V 40/1306 20220101 |
Class at
Publication: |
73/718 |
International
Class: |
G01L 009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 1997 |
FR |
97 04767 |
Claims
1. Process for manufacturing a microsystem for a pressure sensor
comprising the following steps: a) deposit and forming of at least
a first conducting layer on a support, the conducting layer forming
at least a first electrode (10), b) deposit and forming of at least
one layer (18) of sacrificial material covering the first
conducting layer, c) deposit and forming of a second conducting
layer on the layer of sacrificial material in a region located
above the first conducting layer, the second conducting layer
forming a second electrode (20), d) formation of a first membrane
layer (22) covering and surrounding the layer of sacrificial
material and the second conducting layer, e) elimination of the
layer (18) of sacrificial material, f) forming of the first
membrane layer.
2. Process according to claim 1, in which a groove (11) is formed
in the first layer of conducting material to separate and delimit
two parts (10a, 10b), and in which the second conducting layer is
formed on the layer of sacrificial material in a region located
above at least one portion of the groove.
3. Process according to claim 1, in which elimination of the layer
(18) of sacrificial material may include opening of at least one
etching channel (24) in the first membrane layer (22), etching of
the layer of sacrificial material and the formation of a second
membrane layer (28) covering the first membrane layer and closing
the etching channel (24), the second membrane layer also being
formed during step f) in the process.
4. Process according to claim 3, in which the channel (24) is
formed in a region in the first membrane layer (22) located above a
peripheral part of the layer (18) of sacrificial material.
5. Process according to claim 1, in which the first membrane layer
(22) is formed before the sacrificial material layer (18) is
eliminated, in which formation of the first membrane layer
comprises etching of at least one channel in the form of a through
trench reaching the layer of sacrificial material, and in which the
layer of sacrificial material is eliminated by etching the said
channel.
6. Process according to claim 5, in which the trench shaped channel
is made above a peripheral part of the layer of sacrificial
material to release part of the first membrane layer.
7. Process according to claim 1 in which during step d), a first
conducting layer is formed in a recess made in the support such
that the first conducting layer and the support have flush
surfaces.
8. Process according to one of claims 1 to 7 in which the second
conducting layer is formed in a recess made in the layer of
sacrificial material in a region located above the first conducting
layer.
9. Process according to claim 1 in which in step b), a first layer
(18a) of sacrificial material is formed surrounding at least part
(9) of the first conducting layer and then the second layer (18b)
of sacrificial material is formed covered the first layer (18a) of
sacrificial material and the said part (9) of the first conducting
layer, and the first and second layers of sacrificial material are
formed.
10. Process according to claim 3, in which step f) comprises
partial elimination of the second membrane layer and thinning of
the first membrane layer in a region surrounding the second
electrode.
11. Process according to claim 10 in which the formation of the
first membrane layer (22) comprises the successive deposit of three
sublayers (22a, 22b, 22c) of material, of which at least one
sublayer (22b) forms an etching stop sublayer and in which the
first membrane layer (22) is thinned by etching with an etching
stop on the etching stop sublayer (22b).
12. Pressure sensor comprising at least one microsystem made
according to a process conform with claim 1.
13. Pressure sensor according to claim 12, in which the support
comprises an electronic measurement circuit connected to the first
and second layers of the conducting material.
14. Pressure sensor cell comprising: a substrate (12) comprising at
least a first electrode (10), a deformable membrane (22) fixed by a
peripheral edge to the substrate and defining a closed chamber (26)
around at least part of the first electrode (10), and a second
electrode (20) formed on a wall of the membrane (22) facing the
first electrode, the second being kept separate from the first
electrode if there is no pressure exerted on the membrane.
15. Sensor cell according to claim 14, also comprising an
electronic measurement circuit (14) integrated into the substrate
and connected to the first and second electrodes (10, 20).
16. Cell according to claim 15 in which the electronic circuit (14)
is placed in the substrate under the first electrode.
17. Cell according to claim 15 in which the integrated circuit (14)
is of the CMOS type or the BICMOS type.
18. Cell according to claim 14, in which the membrane comprises a
rigid part above the second electrode (20).
19. Cell according to claim 15 in which the measurement circuit
comprises a capacitance meter for measuring a variation in the
electrical capacitance between the first and the second
electrodes.
20. Cell according to claim 14, in which the first electrode (10)
comprises a first and second parts (10a, 10b) separated by a groove
(11) and in which the second electrode (20) is located at least
partly above the groove (11) so that it is kept in contact with the
first and second parts to connect them electrically when sufficient
pressure is applied on the membrane (22).
21. Fingerprints sensor comprising a number of adjacent sensor
cells according to claim 14.
22. Sensor according to claim 21 in which all cells are made on the
same substrate (12).
Description
TECHNICAL DOMAIN
[0001] This invention relates to a microsystem with a flexible
membrane for a pressure sensor and its manufacturing process.
[0002] A microsystem with a flexible membrane refers to a pressure
sensor cell, for example of a capacitive measurement type, or a
switch cell triggered by pressure.
[0003] The invention has applications in the manufacture of
microsensors, microswitches, variable microcapacitors, and more
generally micro-components that can be integrated with an
associated electronic circuit. One particular application of the
invention is the manufacture of a fingerprints sensor.
STATE OF PRIOR ART
[0004] Document (1), the reference of which is given at the end of
this description, describes the manufacture of pressure
micro-sensors with a deformable silicon membrane.
[0005] Due to their manufacturing process, compatibility
difficulties occur when making this type of microsensor jointly
with CMOS type integrated circuits. Furthermore, these sensors
include a generally conducting membrane, which may cause electrical
insulation problems when components are miniaturized.
[0006] Insulating membrane sensors made on glass substrates are
also known. For example, this type of sensor is described in
document (2), the reference of which is given at the end of this
description.
[0007] Document (3), the reference of which is also given at the
end of this description, describes the manufacture of sensors
associated with electronic circuits and adjacent to each other on
the same substrate. This type of design is particularly attractive
for production manufacturing.
[0008] However, it has a number of limitations concerning
interconnection problems between sensors and the corresponding
electronic circuits. The electrical connections between the sensors
and integrated circuits placed on the same substrate generate
harmful parasite capacitance effects. Furthermore, the electrical
connections are cumbersome and form an obstacle to increased
miniaturization of the devices.
[0009] Finally, separate manufacturing of sensors and associated
electronic circuits result in high manufacturing costs.
DESCRIPTION OF THE INVENTION
[0010] The purpose of this invention is to propose a process for
manufacturing microsystems with a flexible membrane that do not
have the limitations mentioned above. In particular, one purpose is
to propose microsystems with a flexible membrane made integrally on
a substrate according to a process compatible with the manufacture
of MOS integrated circuits in the same substrate.
[0011] Another purpose is to significantly reduce the size of the
microsystems and the associated electronic circuits.
[0012] Another purpose is to propose pressure sensors or integrated
microswitches that can be laid out in the form of a large number of
adjacent cells, for example in the form of a matrix.
[0013] Another purpose is to propose a fingerprints detector using
this type of sensor.
[0014] Finally, another purpose is to reduce the manufacturing cost
of microsystems with flexible membranes.
[0015] In order to achieve these objectives, the purpose of the
invention is more precisely a process for manufacturing a
microsystem for a pressure sensor comprising the following
steps:
[0016] a) deposit and forming of at least a first conducting layer
on a support, the conducting layer forming at least a first
electrode,
[0017] b) deposit and forming of at least one layer of sacrificial
material covering the first conducting layer,
[0018] c) deposit and forming of a second conducting layer on the
layer of sacrificial material in a region located above the first
conducting layer, the second conducting layer forming a second
electrode,
[0019] d) formation of a first membrane layer covering and
surrounding the layer of sacrificial material and the second
conducting layer,
[0020] e) elimination of the layer of sacrificial material,
[0021] f) forming the first membrane layer.
[0022] The steps in the process are preferably carried out in the
order mentioned above. However the order of steps e) and f) can be
reversed. Furthermore, in one special embodiment, the layers
mentioned in steps b) and c) may be formed at the same time.
[0023] In particular, when major cutting or thinning operations are
necessary on the first membrane layer, it is useful to not release
it by eliminating the sacrificial layer, until it has been
completely formed.
[0024] The layer of sacrificial material is formed so as to define
the shape and size of a closed chamber, in which one wall is formed
by the first membrane layer.
[0025] The process according to the invention can be used to make
simple and inexpensive Microsystems, and particularly cells for
pressure sensors suitable for common integration with CMOS or
BICMOS type circuits on the same substrate. This aspect will be
described in more detail in the rest of the description.
[0026] Beneficially, with the process according to the invention,
the first and second conducting layers forming the electrodes are
not separated by any material layer. After the layer of sacrificial
material has been eliminated, the second conducting layer is kept
separated from the first conducting layer by means of the flexible
membrane layer, when there is no pressure exerted on this membrane
layer.
[0027] A particularly sensitive sensor cell can be made by
adjusting the thickness of the layer of sacrificial material.
[0028] Furthermore, the first and second layers of conducting
material may be separated by a very small distance only, for
example of the order of about 0.1 .mu.m to 5 .mu.m. This
characteristic is also useful for making sensitive sensors. For
example, the first and second layers could form the armatures of a
capacitor in which the capacitance varies as a function of a
deformation of the membrane layer.
[0029] In other applications, the microsystem obtained by the
process according to the invention could also form a microswtich.
The first and second conducting layers may in this case form the
terminals of the switch. For example, this type of switch is open
when the deformation of the membrane layer is insufficient for the
first and second conducting layers to come into contact with each
other, and is closed when the conducting layers are pressed in
contact with each other.
[0030] According to one alternative embodiment of the microsystem
for use as a switch, a groove is formed in the first layer of
conducting material to separate and delimit two electrodes, and the
second conducting layer is then formed on the layer of sacrificial
material in a region above at least one portion of the groove.
[0031] In a microsystem made according to this alternative, when
the membrane layer is deformed, the second conducting layer
electrically connects the two electrodes in the first conducting
layer which thus form the terminals of the switch.
[0032] According to one specific embodiment of the process
according to the invention, elimination of the layer of sacrificial
material may include opening of at least one etching channel
through the first membrane layer, etching of the layer of
sacrificial material and the formation of a second membrane layer
covering the first membrane layer and closing the etching channel,
the second membrane layer also being formed during step f) in the
process.
[0033] For example, step f) may include partial elimination of the
second membrane layer and thinning of the first membrane layer in a
region surrounding the second electrode.
[0034] Thinning of the first membrane can precisely adjust its
suppleness or flexibility and therefore the sensitivity of the
microsystem.
[0035] Preferably, thinning takes place in a region surrounding the
electrode formed in the second conducting layer but not above this
electrode. This characteristic increases the stiffness of the
membrane in the region of the second electrode and thus prevents
excessive deformation of this electrode when pressure is applied to
the membrane.
[0036] Preferably, formation of the first membrane layer may
include the successive deposit of three sublayers of material, in
which at least one sublayer forms an etching stop sublayer. The
first membrane layer is then thinned by etching, stopping the
etching on the etching stop sublayer.
[0037] Thus the final thickness of the membrane layer may be very
small without risking penetration during etching. Furthermore, the
thickness may be determined very accurately.
[0038] According to another advantageous aspect, the channel for
eliminating the layer of sacrificial material can be formed in a
region in the first membrane layer located above a peripheral part
of the layer of sacrificial material.
[0039] This arrangement avoids the need to increase the stiffness
of the membrane if the material in the second membrane layer enters
the channel and forms a plug supported on the support of the first
conducting layer. Formation of a plug in a peripheral region of the
membrane only very slightly affects the flexibility of the
membrane.
[0040] According to one particular embodiment of the process
according to the invention, forming of the first membrane layer may
also take place before the layer of sacrificial material is
eliminated. In this case, forming of the membrane layer may include
etching of one or several channels in the form of through trenches
reaching the layer of sacrificial material.
[0041] These trenches are used to eliminate the layer of
sacrificial material.
[0042] They can also be used to partly release part of the membrane
layer, when the sacrificial material has been eliminated. The
trenches may be laid out to define part of the perimeter of a
portion of the membrane layer. The trenches are then preferably
above a peripheral part of the layer of sacrificial material.
[0043] The first conducting layer may be made flush with the
support surface. In this case, in step a) the first conducting
layer is formed in a recess formed in the support such that the
first conducting layer and the support have flush surfaces.
[0044] This type of construction may be beneficial when the
microsystem is used as a sensor cell with capacitive measurement of
the membrane deformation.
[0045] However, when the microsystem is used as a switch, it is
preferable that at least the first or the second electrode projects
above its support.
[0046] This can be done, for example by forming the second
conducting layer in a recess formed in the layer of sacrificial
material, in a region located above the first conducting layer.
[0047] According to one possible alternative, step b) includes the
formation of a first layer of sacrificial material surrounding at
least part of the first conducting layer and then a second layer of
sacrificial material is formed covering the first layer of
sacrificial material and the said part of the first conducting
layer, and the first and second layers of sacrificial material are
formed. Due to this arrangement, the second layer of sacrificial
material has a recess on its free upper surface that is filled by
the second conducting layer. Thus after the sacrificial material
has been eliminated, the second conducting layer projects on the
surface of the membrane layer facing towards the support.
[0048] The invention also relates to a pressure sensor cell
comprising:
[0049] a substrate comprising at least a first electrode,
[0050] a deformable membrane fixed by an edge around the periphery
of the substrate and defining a closed chamber around at least part
of the first electrode,
[0051] a second electrode formed on a wall of the deformable
membrane facing towards the first electrode and kept separate from
the first electrode in the lack of any pressure exerted on the
membrane.
[0052] The pressure sensor cell may also comprise or be associated
with an electronic measurement circuit integrated into the
substrate and connected to the first and second electrodes.
[0053] Beneficially, the electronic circuit may be placed in the
substrate under the first electrode.
[0054] A better integration of the cell and the integrated circuit
may be obtained due to this characteristic.
[0055] In particular, this means that a fingerprints sensor
comprising a large number of adjacent sensor cells can be made, for
example in the form of a matrix. All cells and the associated
electronic circuits can then be made on or in the same support.
[0056] Note that Microsystems and cells according to the invention
are particularly suitable for use with CMOS (Complementary Metal
Oxide Semiconductor) or BiCMOS (BipolarCMOS) type integrated
circuits.
[0057] Other characteristics and advantages of the invention will
become clear from the following description with reference to the
figures in the attached drawings. This description is given for
illustration purposes only and is in no way restrictive.
BRIEF DESCRIPTION OF THE FIGURES
[0058] FIGS. 1 to 8 are schematic sections showing the successive
steps in a process for manufacturing a microsystem according to the
invention.
[0059] FIGS. 9 and 10 show a sectional view of a step in which a
sacrificial material layer is thinned locally,
[0060] FIGS. 11 and 12 show a sectional view of an alternative of
the step for making the layer of sacrificial material,
[0061] FIGS. 13 and 14 show a sectional view of another alternative
of the step for making the layer of sacrificial material,
[0062] FIG. 15 is a schematic section at a larger scale of a
microsystem according to the invention, forming an alternative to
that shown in FIG. 8,
[0063] FIG. 16 is a schematic section at a larger scale of a
microsystem according to the invention, forming an alternative to
that shown in FIG. 15.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0064] FIG. 1 shows a first step in a process according to the
invention. A first layer 10 of a conducting material such as for
example titanium, titanium nitride, chromium or any other
compatible conductor, is deposited on a support 12. The layer 10 is
deposited for example by cathodic spraying or by evaporation under
vacuum to a thickness of the order of 100 nm to a few micrometers.
The layer 10 may also be formed by any other deposition technique,
for example such as electrolysis.
[0065] Support 12 may be a substrate plate, for example made of
silicon or glass, and particularly an integrated circuit board.
Beneficially, support 12 contains one or several electronic
circuits such as measurement circuits to be used in Microsystems
made according to the invention. These circuits, preferably of the
CMOS or BiCMOS type are represented schematically as reference 14
in the figure. Reference 16 denotes an electrical connection
between the electronic circuit 14 and the first conducting layer
10.
[0066] A photolithography and dry or chemical etching step forms
the first layer of conducting material 10 as shown in FIG. 2. The
conducting layer 10 formed makes up a first electrode in the
microsystem denoted by the same reference 10 for simplification
reasons.
[0067] A subsequent step shown in FIG. 3 comprises the deposition
and forming of a layer 18 of sacrificial material. The shape and
thickness of this layer define the dimensions of a chamber in the
microsystem enabling the deformation of a flexible membrane
described later. The thickness of the sacrificial layer may be for
example between 0.1 .mu.m and 5 .mu.m. The layer of sacrificial
material is made from a material with a good etching selectivity
compared with other materials used to make the microsystem. The
material in the sacrificial layer is also chosen for its
etchability over long distances starting from a given location.
[0068] The sacrificial layer may be made from a metal such as
tungsten or aluminium, from an organic material such as
photosensitive resins or polyimide, from a dielectric material such
as silicon oxide (SiO.sub.2) or any material with the qualities
indicated above.
[0069] A second layer of conducting material is formed above the
layer of sacrificial material and is then formed by etching to form
a second electrode.
[0070] This second electrode is shown in FIG. 4 as reference 20. It
is located at least partially above the first electrode 10 and is
separated from it by a layer of sacrificial material. The second
layer of conducting material is made for example from Ti, TiN or Cr
with a thickness of the order of 100 nm to a few .mu.m. It is made
using cathodic spraying, evaporation or electrolysis
techniques.
[0071] A subsequent step in the process shown in FIG. 5 includes
the formation of a first layer 22 called the membrane layer. The
membrane layer 22 covers the second electrode 20, the layer of
sacrificial material 18 and extends at least partly over the
surface of support 12.
[0072] The first layer membrane 22 may be a single coat of an
electrically insulating material. For example it may be a 0.8 .mu.m
thick Si.sub.3N.sub.4 layer deposited using a plasma aided chemical
vapor deposition (PECVD) technique. It may also have a flaky
structure with three sublayers 22a, 22b and 22c, as shown in FIG.
5. The median sublayer 22b is an etch stop sublayer used during
subsequent thinning of the first membrane layer. This thinning is
described in the rest of the text.
[0073] For example, a membrane layer 22 with a total thickness of
0.76 may comprise a sublayer 22a consisting of 0.3 .mu.m of
Si.sub.3N.sub.4, a stop sublayer 22b consisting of 0.06 .mu.m of
SiO.sub.2 and a sublayer 22c of 0.4 .mu.m of Si.sub.3N.sub.4. The
etch stop sublayer may also be a metallic layer. It is then
preferably insulated from the second electrode 20 by a first
sublayer 22a made of an electrically insulating material.
[0074] As shown in FIG. 6, an opening 24 forming an etching channel
is made in membrane 22 to reach a peripheral region in the layer of
sacrificial material. The sacrificial layer is completely
eliminated through this opening 24, for example by chemical attack.
Elimination of the sacrificial material opens up a chamber 26 in
the microsystem that enables deformation of the membrane layer 22.
The second electrode 20 remains bonded to the membrane layer 22
which keeps it separate from the first electrode 10.
[0075] A second membrane layer 28 is then deposited on the first
membrane layer 22 to close the opening 24 and thus close chamber
26.
[0076] The second membrane layer is preferably a layer of
SiO.sub.2, Si.sub.3N.sub.4, or metal. For example it may be a 0.8
.mu.m thick layer of Si.sub.3N.sub.4 deposited by a plasma aided
chemical vapor deposition (PECVD) technique.
[0077] The thickness of the second membrane layer 26 is generally
chosen to be sufficient to close opening 24 made in the first
membrane layer. Note on FIG. 7 the formation of a plug 27 that may
be supported on the surface of support 12. When opening 24 is made
in a peripheral region, this type of plug does not compromise the
flexibility of the membrane layer(s).
[0078] Preferably, the second membrane layer 28 may be formed under
a vacuum to obtain a vacuum sealed chamber 26.
[0079] A next step shown in FIG. 8 consists of eliminating the
second membrane layer 26 in a region surrounding the second
electrode 20 and thinning the first membrane layer in the same
region.
[0080] For example, thinning may be done by etching, stopping on
the stop sublayer 22b described above.
[0081] The remaining thickness of the first membrane layer is then
of the order of 0.3 to 0.4 .mu.m. This thickness may be adjusted as
a function of the size of chamber 26, the nature of the materials
used for the membrane layer and as a function of a sensitivity of
the microsystem made.
[0082] Adjustment of the thickness affects the flexibility of the
membrane. However, the first membrane layer is preferably kept
sufficiently thick to prevent collapse into chamber 26,
particularly when chamber 26 is kept under a vacuum.
[0083] Furthermore, a part 32 of the first membrane layer and
possibly of the second membrane layer may be kept above the second
electrode 20 to prevent its deformation.
[0084] Similarly, part of the second membrane layer is also kept in
the region of the opening 24 and the plug 27.
[0085] Finally, note that an electrical connection 17 shown very
schematically as a chain dotted line in FIG. 8 may also be provided
between the second electrode 20 and the electronic circuit 14.
[0086] The electronic circuit 14 may for example be equipped with
means of measuring an electric capacitance between the first and
second electrodes 10, 20. Pressure exerted on the membrane causes
its deformation and modifies the distance separating the
electrodes, and consequently an electric capacitance measured
between these electrodes.
[0087] The first and second electrodes may also make up contact
terminals when the microsystem is used as a microswitch.
[0088] In this case, it is useful if at least one of the first and
second electrodes project above their support surface, to make good
contact between the first and the second electrodes when the
microswitch is activated.
[0089] The shape of the second electrode depends on the shape of
the second conducting layer formed on the layer of sacrificial
material and consequently on the shape given to the upper surface
of the layer of sacrificial material.
[0090] In the case shown in FIG. 9, a layer of sacrificial material
18 is formed above a first electrode 10, the surface of which is
flush with the surface of support 12. Therefore the surface of the
sacrificial layer is plane. For better readability, the thickness
of the layer of sacrificial material is shown larger in FIGS. 9 to
14.
[0091] A recess 19 etched in the upper surface of layer 18 of the
sacrificial material as shown in FIG. 10, is used to form a second
layer of conducting material in a later step that projects towards
the first electrode 10.
[0092] A second technique is used to make the recess 19. This
technique, as shown in FIG. 11, consists of forming firstly a first
layer of sacrificial material 18a that surrounds at least part 9 of
the first conducting layer 10. The surface of part 9 of the first
conducting layer thus forms a pattern recessed from the free
surface of the first layer of sacrificial material 18a.
[0093] A second layer of sacrificial material 18b is then formed on
the first layer of sacrificial material 18a and on part 9 of the
conducting layer left uncovered. Thus the pattern with a recess 19
is reproduced on the surface of the second layer of sacrificial
material 18b. This recess, visible in FIG. 12, is used in the rest
of the process to make a second conducting layer forming a
projection.
[0094] FIGS. 13 and 14 show the formation of the layer of
sacrificial material 18 when the first electrode 10 formed on the
support 12 projects above this surface. The prominence formed by
the conducting layer 10, as shown in FIG. 13 is located on the
upper surface of the layer of sacrificial material 18. It is
indicated as reference 17. This type of prominence would cause a
recessed formation of the second conducting layer in a region
located above the first conducting layer 10.
[0095] To prevent this phenomenon, it is possible to flatten the
upper surface of the sacrificial layer 18 as shown in FIG. 14,
before formation of the second conducting layer.
[0096] FIG. 15 shows an alternative embodiment of a microsystem
according to the invention at a larger scale. For simplification
reasons, identical references are used to denote parts identical to
or similar to parts shown on previous figures. Therefore, the
previous description is valid.
[0097] The microsystem made on a substrate 12 comprises a first
electrode 10 supported by this substrate. The first electrode
comprises two parts 10a and 10b separated by a groove 11. Thus
parts 10a and 10b that are formed on an insulating substrate 12 are
electrically isolated by the substrate and by the groove 11. The
groove is located approximately in the middle of a chamber 26 in
the microsystem, delimited at the sides and the top by a flexible
membrane 22.
[0098] A second electrode 20 fixed to the membrane 22 is located
approximately above a region of the electrode 10 comprising the
groove 11.
[0099] Thus, when sufficient pressure is applied to membrane 22,
the electrode 20 comes into contact with parts 10a and 10b of the
first electrode 10 and electrically connects them together.
[0100] The microsystem in FIG. 15 can thus be used as a
microswitch, in which the terminals are parts 10a and 10b of the
second electrode 10.
[0101] The microsystem in FIG. 15 can also be used as a pressure
sensor with an On/Off type detection.
[0102] Parts 10a and 10b of the first electrode are connected to a
circuit 14 integrated in substrate 12 under the microsystem. This
circuit and the electrical connections 16, 17 that connect it to
part parts 10a and 10b of the first electrode are shown very
schematically.
[0103] Note also that membrane 22 is thinned locally to make it
more flexible.
[0104] In FIG. 15, the layer forming the membrane 22 is shown in
contact with the first electrode. However, it may also be in direct
contact with substrate 12, for example as shown in FIG. 6.
[0105] FIG. 16 shows another possible embodiment of the microsystem
usable particularly as a microswitch.
[0106] The first and second electrodes 10, 20 located under the
substrate 12 and the membrane 22 respectively, each extends into
another region approximately in the middle of chamber 26.
[0107] The second electrode 20, initially kept apart from the first
electrode 10 by the flexible membrane 22, comes into contact with
the first electrode 10 in the overlap area under the effect of
sufficient pressure applied to membrane 22.
[0108] Thus the first and second electrodes can form the terminals
of a switch. The first and second electrodes are electrically
connected to an electronic circuit 14 which may for example be
located in substrate 12.
[0109] In this respect, the second layer of conducting material in
which the second electrode is formed preferably extends as far as
substrate 12.
REFERENCED DOCUMENTS
[0110] (1)
[0111] FR-A-2 700 003
[0112] (2)
[0113] CA-A-2 130 505
[0114] (3)
[0115] A surface micromachined miniature switch for
telecommunication applications with signal frequencies from DC up
to 4 GHz from J. Jason and F. Chang, International Conference on
Solid State, Sensors and Actuators, Stockholm, Sweden June 25-29,
1995.
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