Note: Descriptions are shown in the official language in which they were submitted.
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En 29 CA
Feb. 11, 2000
Capacitive Pressure Sensor Cells or Differential
Pressure Sensor Cells and Methods for
Manufacturing the Same
FIELD OF THE INVENTION
This invention relates to capacitive ceramic pressure
sensor cells or differential pressure sensor cells and to
methods for manufacturing the same.
BACKGROUND OF THE INVENTION
A capacitive ceramic pressure sensor cell commonly com-
prises a ceramic substrate and a ceramic diaphragm which
covers the substrate and is spaced from the latter to form
a sensing chamber between the diaphragm and a surface of
the substrate facing the diaphragm. The facing surfaces of
the substrate and the diaphragm are provided with elec-
trodes which together form a capacitor that provides an
electric signal which corresponds to a pressure of a pro-
cess medium acting on and deforming the diaphragm. Under
overload conditions, the substrate serves as a limiter for
the movement of the diaphragm.
To measure a difference between two pressures (differential
pressure), two sensing chambers are commonly used, one for
each pressure, the sensing chambers being spatially and
mechanically connected with one another and being provided
with one sensing capacitor each. In this manner it is pos-
sible to produce an electric signal which corresponds to
the difference between a pressure acting on one of the
sensing chambers and a pressure acting on the other sensing
chamber.
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A particular problem encountered with ceramic pressure
sensor cells is to fasten and join the diaphragm in its
edge area to the substrate in such a manner that the joint
is gasd and liquid-tight and can withstand high tensile and
compressive loads. In addition, the joint is to be long-
term-stable and free of relaxation effects.
Glass-frit joints used in conventional ceramic pressure
sensor cells do not fully meet the above requirements.
Therefore, a joint produced by means of an active brazing
solder has been used.
U.S. Patent 5,050,034, for example, discloses a capacitive
pressure sensor cell comprising
- a ceramic substrate having
-- a cylindrical surface and,
-- at a first major surface, a central area which
--- is provided with a first electrode and
--- has an electrical connection from the first electrode
through the substrate to a second major surface, and
- a ceranic diaphragm
-- which is joined to the substrate using a plane-parallel
ring of active brazing solder to form a high-vacuum-
tight sensing chamber,
--- with a second electrode being provided on a planar
inner surface of the diaphragm facing the substrate.
The joint produced by means of active brazing solder meets
the above-mentioned requirements for high stability, but in
certain cases where the diaphragm is subjected to overpres-
sure, it has turned out that the diaphragm cannot be sup-
ported on the substrate in a satisfactory manner. Because
of the "angular" shape of the ring of active brazing sol-
der, which serves as a spacer between the substrate and the
diaphragm, tensile stresses may occur, particularly in the
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edge region of the diaphragm, which result in a failure of
the diaphragm.
U.S. Patent 4,329,826 discloses a capacitive dif-ferential
pressure sensor cell comprising:
- a substrate having
-- an edge area and,
-- at a first major surface, a concave first central area
which
--- is provided with a first electrode,
--- has a first electrical connection to the first elec-
trode, and,
--- in the direction of the edge area, merges into a convex
first surface
---- which has a first vertex line intersecting the edge
area and
---- forms a first planar ring surface in the area of the
first vertex line,
-- said substrate further having, at a second major surface
opposite the first major surface, a concave second
central area
--- which is provided with a second electrode,
--- has a second electrical connection to the second
electrode, and,
--- in the direction of the edge area, merges into a convex
second surface which
---- has a second vertex line intersecting the edge area
and
---- forms a second planar ring surface in the area of the
second vertex line,
-- the substrate being provided with a connecting channel
between the first central area and the second central
area;
- a first ceramic diaphragm
-- which rests on and is fixed to the first ring surface of
the substrate,
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--- with a third electrode being provided on a planar inner
surface of the first diaphragm facing the substrate;
and
- a second ceramic diaphragm
-- which rests on and is fixed to the second ring surface
of the substrate,
--- with a fourth electrode being provided on a planar
inner surface of the second diaphragm facing the sub-
strate.
to
In the case of this prior-art differential pressure sensor
cell, the ring surfaces, which serve exclusively to join
the respective diaphragms to the substrate, extend up to
the cylindrical surface of the substrate. The way the joint
is produced is not explained.
It has turned out that the joint produced solely by means
of the ring surfaces is insufficient, particularly~if great
axially parallel forces act on these surfaces. In addition,
such a joint is not high-vacuum-tight and not long-term-
stable.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide capa-
citive pressure sensor cells or capacitive differential
pressure sensor cells in which the joint between the sub-
strate and the diaphragms is both pressure- and/or tension-
proof and high-vacuum-tight and long-term-stable.
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To attain this object, a first variant of the
invention provides a capacitive pressure sensor cell
comprising: a ceramic substrate having a cylindrical
surface, a first major surface and a second major surface,
5 said second major surface being opposite said first major
surface, said first major surface including a concave
central area which, as the concave central area extends
towards said cylindrical surface, merges into a convex
surface having a vertex line, said convex surface forming a
planar ring surface proximate to said vertex line, a first
electrode located in said concave central area of said first
major surface, and an electrical connection extending from
said first electrode through said substrate to said second
major surface; and a ceramic diaphragm having a planar inner
surface, a second electrode located on said planar inner
surface of said diaphragm, said planar inner surface of said
diaphragm resting on said planar ring surface of said first
major surface of said substrate, said diaphragm being joined
to said substrate by an active brazing solder which is
located in a circumferential wedge zone formed between said
diaphragm and said substrate and between said planar ring
surface and said cylindrical surface, a high-vacuum-tight
sensing chamber being formed between said planar inner
surface of said diaphragm and said first major surface of
said substrate, and electrical connection to said second
electrode being made through said circumferential wedge
zone.
To attain the above object, a second variant of
the invention provides a capacitive differential pressure
sensor cell comprising: a ceramic substrate having a
cylindrical surface and, at a first major surface, a concave
first central area which is provided with a first electrode,
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has a first electrical connection from the first electrode
through the substrate to a second major surface, and, as the
concave first central area extends towards the cylindrical
surface, merges into a convex first surface having a first
vertex line, said convex first surface forming a first
planar ring surface proximate to the first vertex line,
which substrate further has, at a second major surface
opposite the first major surface, a concave second central
area which is provided with a second electrode, has a second
electrical connection from the second electrode through the
substrate to the cylindrical surface, and, as the concave
second central area extends towards the cylindrical surface,
merges into a convex second surface having a second vertex
line, said convex second surface forming a second planar
ring surface proximate to the second vertex line, said
substrate further having a connecting channel between the
first central area and the second central area; a first
ceramic diaphragm which rests on the first ring surface of
the substrate, and which is joined to the substrate on the
2C first ring surface and between the cylindrical surface and
the first ring surface by means of active brazing solder
forming a first circumferential wedge zone, to form a first
high-vacuum-tight sensing chamber, with a third electrode
being provided on a planar inner surface of the first
diaphragm facing the substrate, to which third electrode
contact is made through the first wedge zones and a second
ceramic diaphragm which rests on the second ring surface of
the substrate, and which is joined to the substrate on the
second ring surface and between the cylindrical surface and
the second ring surface by means of active brazing solder
forming a second circumferential wedge zone, to form a
second high-vacuum-tight sensing chamber, with a fourth
electrode being provided on a planar inner surface of the
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second diaphragm facing the substrate, to which fourth
electrode contact is made through the second wedge zone.
To attain the above object, a third variant of the
invention provides a capacitive differential pressure sensor
cell comprising: a first ceramic substrate having a first
cylindrical surface and, at a first major surface, a concave
first central area which is provided with a first electrode,
has an electrical connection from the first electrode
through the first ceramic substrate to a second major
surface opposite the first major surface, and, as the
concave first central area extends towards the cylindrical
surface, merges into a convex first surface having a first
vertex line, said convex first surface forming a first
planar ring surface proximate to the first vertex line; a
second ceramic substrate having second cylindrical surface
and, at a first major surface, a concave central area which
is provided with a second electrode, has a second electrical
connection from the second electrode through the second
ceramic substrate to a second major surface opposite the
first major surface, and, as the concave second central area
extends towards the second cylindrical surface, merges into
a convex second surface having a second vertex line, said
convex second surface forming a second planar ring surface
proximate to the second vertex lined and a ceramic substrate
which rests with a first surface on the first ring surface
of the first substrate, is joined to the first substrate on
the first ring surface and between the first cylindrical
surface and the first ring surface of the first substrate by
means of active brazing solder forming a first
circumferential wedge zone, to form a first
high-vacuum-tight sensing chamber, rests with a second
surface on the second ring surface of the second substrate,
is joined to the second substrate on the second ring surface
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and between the second cylindrical surface and the second
ring surface of the second substrate by means of active
brazing solder forming a second circumferential wedge zone,
to form a second high-vacuum-tight sensing chamber, the
first surface of the diaphragm being provided with a third
electrode to which contact is made through the first wedge
zone, and the second surface being provided with a fourth
electrode to which contact is made through the second wedge
zone.
To attain the above object, a fourth variant of
the invention provides a method for manufacturing a
capacitive pressure sensor cell comprising the steps of:
providing a ceramic substrate having a cylindrical surface,
a first major surface and a second major surface, said
second major surface being opposite said first major
surface, said first major surface including a concave
central area which, as the concave central area extends
towards said cylindrical surface, merges into a convex
surface having a vertex line, said convex surface being
formed into a planar ring surface proximate to said vertex
line; depositing a first electrode on said concave area
forming an electrical connection from said first electrode
through said substrate to said second major surface:
providing a ceramic diaphragm having a planar inner surface;
depositing a second electrode on the central portion of said
planar inner surface of said diaphragm such that, when said
diaphragm is placed on said substrate, said second electrode
extends up to said planar ring surface of said substrate;
applying an active brazing solder to said convex portion of
said substrate between said cylindrical surface and said
planar ring surface; placing said diaphragm on said planar
ring surface of said substrate such that said second
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electrode of said diaphragm extends up to said planar ring
surface, and said second electrode faces said first
electrode; heating said substrate and said diaphragm in a
vacuum or inert-gas atmosphere until the active brazing
solder has melted; and allowing said substrate and said
diaphragm to cool down.
To attain the above object, a fifth variant of the
invention provides a method for manufacturing a capacitive
differential pressure sensor cell comprising the steps of:
providing a ceramic substrate, at the first major surface
thereof, with a concave first central area which, as the
concave first central area extends towards a cylindrical
surface, merges into a convex first surface having a first
vertex line, said convex first surface being formed as a
first planar ring surface proximate to the first vertex
line; depositing a first electrode on the first central area
and providing an electrical connection from the first
electrode through the substrate to the cylindrical surface
of the substrate; providing the substrate, at a second major
surface opposite the first major surface, with a concave
second central area which, as the concave second central
area extends towards a cylindrical surface of the substrate,
merges into a convex second surface having a second vertex
line, said convex second surface being formed as a second
planar ring surface proximate to the second vertex line;
depositing a second electrode on the second central area and
providing an electrical connection from the second electrode
through the substrate to the cylindrical surface of the
substrate; providing a first ceramic diaphragm congruent
with the first major surface of the substrate, on a planar
inner surface thereof, with a third electrode dimensioned so
that, after the first diaphragm has been placed on the first
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ring surface of the substrate, the third electrode extends
up to said first ring surface; providing a second ceramic
diaphragm congruent with the second major surface of the
substrate, on a planar inner surface thereof, with a fourth
5 electrode dimensioned so that, after the second diaphragm
has been placed on the second ring surface of the substrate,
said fourth electrode extends up to said second ring
surface: applying respective quantities of active brazing
solder sufficient to braze the first and second diaphragms
10 to the substrate to portions of the convex first surface of
the substrate located between the first ring surface and the
cylindrical surface and to portions of the convex second
surface of the substrate located between the second ring
surface and the cylindrical surface: placing the surface of
the first diaphragm provided with the third electrode on the
first ring surface of the substrate: placing the surface of
the second diaphragm provided with the fourth electrode on
the second ring surface of the substrate; and heating the
substrate and the diaphragm in a vacuum or inert-gas
atmosphere until the active brazing solder has melted, and
then allowing them to cool down.
To attain the above object, a sixth variant of the
invention provides a method for manufacturing a capacitive
differential pressure sensor cell comprising the steps of:
providing a first ceramic substrate, at a first major
surface thereof, with a concave first central area which, as
the concave first central area extends towards a first
cylindrical surface, merges into a convex surface having a
first vertex line, said convex first surface being formed as
a first planar ring surface proximate to the first vertex
line; depositing a first electrode on the first central area
and providing an electrical connection from the first
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electrode through the first substrate to a second major
surface of the substrate opposite the first major surface
providing a second ceramic substrate, at a first major
surface thereof, with a concave second central area which,
as the concave second central area extends towards the
second cylindrical surface of the second substrate, merges
into a convex second surface having a second vertex line,
said convex second surface being formed as a second planar
ring surface proximate to the second vertex line; depositing
a second electrode on the second central area and providing
an electrical connection from the second electrode through
the second substrate to a second major surface of the second
substrate opposite the first major surface; providing a
ceramic diaphragm congruent with the first major surface of
the first substrate, on a planar first surface thereof, with
a third electrode dimensioned so that, after the diaphragm
has been placed on the first ring surface of the first
substrate, said third electrode extends up to said first
ring surface: providing a planar second surface of the
diaphragm opposite the first surface with a fourth electrode
dimensioned so that, after the diaphragm has been placed on
the second ring surface of the second substrate, said fourth
electrode extends up to said second ring surface: applying
respective quantities of active brazing solder sufficient to
braze the first and second diaphragms to the substrate to
portions of the convex first surface of the substrate
located between the first ring surface and the cylindrical
surface and to portions of the convex second surface of the
substrate located between the second ring surface and the
cylindrical surface; placing the first surface of the
diaphragm, provided with the third electrode, on the first
ring surface of the substrate; placing the second surface of
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the diaphragm, provided with the fourth electrode, on the
second ring surface of the substrate; and heating the
substrate and diaphragm in a vacuum or inert-gas atmosphere
until the active brazing solder has melted, and then
allowing them to cool down.
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In respective preferred embodiments of the first to third
variants of the invention, the substrate or substrates and
the diaphragm or diaphragms are made of alumina ceramic,
and the active brazing solder is a Zr-Fe-Ti-Be alloy or a
Zr-Ni-Ti alloy.
In respective further preferred embodiments of the first to
third variants of the invention, at least the electrode of
the diaphragm or the electrodes of the diaphragms are
covered, at least in a respective edge region, with a sol-
der resist layer.
In preferred embodiments of the fourth and fifth variants
of the invention, at least the electrode of the diaphragm
or the electrodes of the diaphragms are covered, at least
in a respective edge region, with a solder resist layer.
The basic idea of the invention is, instead of holding the
diaphragm and the substrate at a distance from each other
at a joint by a quantity of active brazing solder as has
been done so far, to braze the diaphragm and the substrate
outside the area where they rest on each,other by means of
such a quantity of active brazing solder that long-term
stability and high-vacuum tightness are ensured.
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One advantage of the invention is that in contrast to the
prior art, the volume of the sensing chamber does not
depend on the thickness of the ring of active brazing sol-
der and on manufacturing tolerances resulting after the
brazing.
Another advantage of the invention is that an expensive
formed part of active brazing solder is no longer neces-
sary. Such formed parts have to be produced by the complex
and costly melt-spinning process.
The invention is particularly suited for automated applica-
tion of a active brazing solder paste by means of a dis-
penser. The special shape and arrangement of the joint
between diaphragm and substrate ensures that solvents
commonly contained in an active brazing solder paste will
escape from the region of the joint residue-free.
A further advantage of the invention is that the special
shape of the substrate or substrates in the region of the
joint or joints ensures that no active brazing solder will
penetrate into the sensing chamber or sensing chambers.
BRIEF DESCRIPTION QF THE DRAWINGS
The invention will become more apparent from the following
description of embodiments when taken in conjunction with
the accompanying drawings. Like parts are designated by
like reference characters throughout the figures: to sim-
plify the illustration, reference characters that have
already been used are not repeated in subsequent figures.
In the drawings:
Fig. la is a schematic perspective view of a substrate of a
pressure sensor cell of a first variant of the
invention;
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Fig. 1b is a schematic perspective view of a diaphragm of
the pressure sensor cell of Fig. 1a:
Fig. 2 is a schematic vertical section of the first
5 variant of the invention;
Fig. 3a shows an enlarged view of a section III of the
pressure sensor cell of Fig. 2 before the dia-
phragm is joined to the substrate;
Fig. 3b shows the section III of the pressure sensor cell
of Fig. 3a after the diaphragm has been joined to
the substrate;
Fig. 4 is a schematic vertical section of a second variant
of the invention; and
Fig. 5 is a schematic vertical section of a third variant
of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Fig. 1a, there is shown a perspective view of
a ceramic substrate 1 of a capacitive pressure sensor cell
which has a cylindrical surface 11 and, at a first major
surface 12, a concave central area 121 provided with a
first electrode 122. In the direction of and up to cylind-
rical surface 11, central area 121 merges into a convex
area 124, which has a vertex line 125 and forms a planar
ring surface 126 in the area of vertex line 125 (see
Fig. 2).
Fig. lb is a perspective view of a ceramic diaphragm 5
whose planar inner surface 51, which will face the sub-
strate 1 of Fig. la after it has been fixed to the latter,
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is provided with an electrode 52, which is a second elec-
trode 52 the pressure sensor cell.
Fig. 2 shows a vertical section through a pressure sensor
cell according to the first variant of the invention. The
ceramic diaphragm 5 depicted in Fig. ib rests on ring sur-
face 126 of substrate 1. Diaphragm 5 and the portion of
convex surface 124 extending between ring surface 126 and
cylindrical surface 11 form a circumferential wedge zone
91. By means of active brazing solder 10 in wedge zone 91,
diaphragm 5 is joined to substrate 1 to form a high-vacuum-
tight sensing chamber 9.
Contact is made to electrode 52 on diaphragm 5 through
wedge zone 91. An electrical connection 123 is provided
from electrode 122 through substrate 1 to a second major
surface 13 of substrate 1. Electrode 122 and electrode 52
together form a capacitor which provides a signal cor-
responding to the pressure acting on diaphragm 5.
Fig. 2 clearly shows how central area 121 merges into
convex surface 124 in the direction of and up to cylind-
rical surface 11. In the area of vertex line 125 bounded in
Fig. 2 by dashed lines 1261 and 1262, convex surface 124
forms a planar ring surface 126. A central line CL illus-
trates that the pressure sensor cell is preferably rota-
tionally symmetrical.
Fig. 3a shows an enlarged view of section III of the pres-
sure sensor cell of Fig.. 2 prior to the joining of dia-
phragm 5 to substrate 1. It shows clearly how central area
121 merges into convex surface 124 in the direction of and
up to cylindrical surface 11. In the area of vertex line
125 bounded by dashed lines 1261 and 1262 (see Fig. 2,
too), convex surface 124 forms a planar ring surface 126.
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Electrode 52 of diaphragm 5 extends up to the portion of
inner surface 51 of diaphragm 5 which will subsequently
rest on substrate 1. By contrast, electrode 122 is confined
to concave central area 121 of substrate 1 and does not
extend up to convex surface 124.
Before diaphragm 5 is placed on substrate 1, active brazing
solder 10 is applied to the portion of convex surface 12
of substrate 1 which extends between cylindrical surface 11
and ring surface 126. Preferably, use is made of an active
brazing solder paste which is applied by means of a suit-
able dispenser and in a quantity sufficient to join dia-
phragm 5 and substrate 1. However, other processes by which
active brazing solder 10 can be applied to substrate 1 are
also conceivable.
After diaphragm 5 has been joined to substrate 1, the
solidified active brazing solder 10 fills the wedge zone 91
formed between diaphragm 5 and substrate 1, as shown in
Fig. 3b. Although diaphragm 5 rests firmly on planar ring
surface 126, because of the ceramic material used for the
substrate and diaphragm microscopically small pores with
diameters of the order of their grain sizes are formed
between the substrate and diaphragm.
Because of its wetting properties, the active brazing
solder 10 migrates in the pores between diaphragm 5 and
ring surface 126 of substrate 1 from wedge zone 91 to an
inner edge of ring surface 126, and thus to electrode 52.
The latter is wetted by active brazing solder 10, so that
an electrical connection is provided between wedge zone 91
and electrode 52.
Fig. 4 shows a schematic vertical section of a capacitive
differential pressure sensor cell according to a second
variant of the invention which comprises a ceramic sub-
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strate 2 having a cylindrical surface 21 and, at a first
major surface 22, a concave first central area 221 which is
provided with a first electrode 222. A first electrical
connection 223 is provided from first electrode 222 through
substrate 2 to cylindrical surface 21.
In the direction of and up to cylindrical surface 21, cent-
ral area 21 merges into a convex first surface 224, which
has a first vertex line 225 and which forms a first planar
ring surface 226 in the area of vertex line 225.
At a second major surface 23 opposite major surface 22,
substrate 2 has a concave second central area 231, which is
provided with a second electrode 232. A second electrical
connection 233 is provided from second electrode 232
through substrate 2 to cylindrical surface 21.
In the direction of and up to cylindrical surface 21, the
second central area 231 merges into a convex second surface
234, which has a second vertex line 235 and which forms
asecond planar ring surface 236 in the area of vertex line
235. The first and second central areas 221, 231 are con-
nected with one another through a connecting channel 239.
A first ceramic diaphragm 6 rests on ring surface 226 of
substrate 2. This diaphragm 6 and the portion of convex
surface 224 which extends between ring surface 226 and
cylindrical surface 21 form a first circumferential wedge
zone 92. By means of active brazing solder 10 in wedge zone
92, diaphragm 6 is joined to substrate 2 to form a first
high-vacuum-tight sensing chamber M1.
On a planar first inner surface 61 of diaphragm 6 facing
substrate 2, a third electrode 62 is provided, to which
contact is made through first wedge zone 92. Third elec-
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trode 62 and electrode 222 on substrate 2 form a first
capacitor.
A second ceramic diaphragm 7 rests on ring surface 236 of
substrate 2. This diaphragm 7 and the portion of convex
surface 234 which extends between ring surface 236 and
cylindrical surface 21 form a second circumferential wedge
zone 93. By means of active brazing solder 10 in wedge zone
93, diaphragm 7 is joined to substrate 2 to form a second
high-vacuum-tight sensing chamber M2.
On a planar inner surface 71 of diaphragm 7 facing the
substrate 2, a fourth electrode 72 is provided, to which
contact is made through the second wedge zone 93. Electrode
72 and electrode 232 together form a second capacitor.
Fig. 5 shows a vertical section of a capacitive differen-
tial pressure sensor cell according-to a third variant of
the invention. This differential pressure sensor cell
comprises a first ceramic substrate 3, which has a first
cylindrical surface 31 and, at a first major surface 32, a
concave first central area 321. The latter is provided with
a first electrode 322, and a first electrical connection
323 is provided from electrode 322 through substrate 3 to a
second major surface 33 opposite first major surface 32. In
the direction of and up to cylindrical surface 31, central
area 321 merges into a convex first surface 324, which has
a first vertex line 325 and which forms a first planar ring
surface 326 in the area of vertex line 325.
The differential pressure sensor cell further comprises a
second ceramic substrate 4, which has a second cylindrical
surface 41 and, at a first major surface 42, a concave sec-
ond central area 421. The latter is provided with a second
electrode 422, and a second electrical connection 423 is
provided from electrode 422 through substrate 4 to a second
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major surface 43 opposite first major surface 42. In the
direction of and up to cylindrical surface 41, central area
421 merges into a convex second surface 424, which has a
second vertex line 425. In the area of the second vertex
5 line 425, convex surface 424 forms a second planar ring
surface 426.
A ceramic diaphragm 8 rests with a first planar inner sur
face 81 on ring surface 326 of first substrate 3. diaphragm
10 8 and the portion of convex surface 324 which extends
between ring surface 326 and cylindrical surface 31 of
substrate 3 form a first circumferential wedge zone 95. By
means of active brazing solder 10 in wedge zone 95, the
diaphragm 8 is joined to substrate 3 to form a first high-
15 vacuum-tight sensing chamber M1'.
Diaphragm 8.rests with a second planar inner surface 85 on
ring surface 426 of second substrate 4. The diaphragm 8 and
the portion of convex surface 424 which extends between
20 ring surface 426 and cylindrical surface 41 form a second
circumferential wedge zone 96. By means of active brazing
solder 10 in wedge zone 96, diaphragm 8 is joined to sub-
strate 4 to form a second high-vacuum-tight sensing chamber
M2'.
The inner surface 81 of diaphragm 8 is provided with a
third electrode 82, to which contact is made through wedge
zone 95. The inner surface 85 of dia-phragm 8 is provided
with a fourth electrode 86, to which contact is made
through wedge zone 96. The first electrode 322 on substrate
3 and the third electrode 82 form a first capacitor, and
the second electrode 422 on substrate 4 and the fourth
electrode 86 form a second capacitor.
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All of the substrates and diaphragms mentioned above and
shown in Figs. 1 to 5, i.e., substrates 1, 2, 3, 4 and
diaphragms 5, 6, 7, 8, are preferably of alumina ceramic,
particularly of a 96 % alumina ceramic. In all cases, an
active brazing solder 10 of a Zr-Fe-Ti-Be alloy (cf. EP-A
835 716) or a Zr-Ni-Ti alloy (cf. U.S. Patent 5,334,344)
has proved particularly advantageous since such an active
brazing solder has an excellent wetting ability, high
strength, and a coefficient of thermal expansion corres-
ponding to that of the ceramic material of diaphragm 5 and
sub-strate 1. For the electrodes, tantalum can be used
(cf. U.S. Patent 5,050,034).
To make sure that no active brazing solder paste can pen-
etrate into the sensing chambers M, M1, M2, M1', and M2',
it has proved advantageous to cover electrode 52 on dia-
phragm 5, electrodes 82 and 86 on diaphragm 8, and elec-
trodes 62 and 72 on diaphragms 6 and 7, respectively, with
a solder resist layer. If tantalum is used for electrodes
52, 62, 72, 82, 86, such a solder resist cover can be im-
plemented in a particularly simple manner with a tantalum-
oxide layer.
The electrical connections through the substrates can be
produced as described in U.S. Patent 5,154,697 or U.S.
Patent 5,050,035, for example.
The pressure sensor cell of Fig. 2 is manufactured as fol-
lows. The ceramic substrate 1 is provided, at its first
najor surface 12, with the concave central area 121, which
is shaped so as to merge into the convex surface 124 in the
direction of and up to the cylindrical surface il. The con-
vex surface 124 is flattened in the area of its vertex line
125 to form the planar ring surface 126. This is achieved
by grinding the substrate 1 in a suitable manner.
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Electrode 122 is deposited on central area 121, and an
electrical connection is made from this electrode through
substrate 1 to the second major surface 13 of the substrate
in the usual manner.
On a planar inner surface 51, ceramic diaphragm 5 is pro-
vided with the second electrode 52, which is so dimensioned
that, after diaphragm 5 has been placed on ring surface 126
of substrate 1, this electrode extends only up to ring sur-
face 126.
A sufficient quantity of active brazing solder 10 is ap-
plied to the portions of convex surface 124 between ring
surface 126 and cylindrical surface 11. Preferably, use is
made of an active brazing solder paste which is applied to
substrate 1 by means of a suitable dispenser.
Next, the inner surface 51 of diaphragm 5, provided with
the second electrode 52, is placed on ring surface 126 of
substrate 1, and substrate 1 and diaphragm 5 are heated in
a vacuum or inert-gas atmosphere until the active brazing
solder 10 has melted. After substrate 1 and diaphragm 5
have cooled down, the pressure sensor cell shown in Fig. 2
is complete.
The differential pressure sensor cell of Fig. 4 is nanufac-
tured as follows. The first major surface 22 of the ceramic
substrate 2 is provided with the concave central area 221,
which merges into the convex surface 224 in the direction
of and up to the cylindrical surface 21. In the area of the
vertex line 225 of the convex area 224, the latter is
formed into the planar ring surface 226. Electrode 222 is
deposited on central area 221, and an electrical connection
is provided from electrode 222 through substrate 2 to the
cylindrical surface 21 of the substrate.
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At its second major surface 23, substrate 2 is provided
with the concave central area 231, which merges into the
convex area 234 in the direction of and up to the cylind-
rical surface 21 of substrate 2. Convex area 234 is also
flattened in the area of its vertex line 235 to form the
planar ring surface 236. Electrode 232 is deposited on
central area 231, and an electrical connection is provided
from electrode 232 through substrate 2 to cylindrical sur-
f ace 21.
The planar inner surface 61 of diaphragm 6 is provided with
electrode 62, which is dimensioned so as to extend up to,
and only up to, ring surface 226 after diaphragm 6 has been
placed on the ring surface 226. The planar inner surface 71
of diaphragm 7 is provided with electrode 72, which is
dimensioned so as to extend up to ring surface 236 after
diaphragm 7 has been placed on the ring surface 236.
Next, quantities of active brazing solder 10 sufficient to
braze diaphragms 6 and 7 to substrate 2 are applied to
those portions of the convex surfaces 224, 234 of substrate
2 which are located between the respective ring surfaces
226, 236 and the cylindrical surface 21. For this, too, an
active brazing solder paste is preferably used, which is
applied by means of a suitable dispenser.
After that, diaphragm 6, provided with electrode 62 on its
inner surface 61, is placed on ring surface 226 of sub-
strate 2, and diaphragm 7, provided with electrode 72 on
its inner surface 71, is placed on ring surface 236. Then,
substrate 2 and diaphragms 6, 7 are heated in a vacuum or
inert-gas atmosphere until the active brazing solder 10 has
melted, and subsequently allowed to cool down.
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The differential pressure sensor cell of Fig. 5 is made as
follows. The major surface 32 of the ceramic substrate 3 is
provided with the concave central area 321, which merges
into convex surface 324 in the direction of and up to
cylindrical surface 31 of substrate 3. In the area of its
vertex line 325, convex surface 324 is formed as a planar
ring surface 326. Electrode 322 is deposited on central
area 321, and an electrical connection is made from elec-
trode 322 through substrate 3 to surface 33 of substrate 3.
The major surface 42 of substrate 4 is provided with the
concave central area 421, which merges into the convex sur-
face 424 in the direction of and up to cylindrical surface
41. In the area of its vertex line 425, the convex surface
424 is formed as a planar ring surface 426. Electrode 422
is deposited on central area 421, and an electrical connec-
tion is made from electrode 422 through substrate 4 to sur-
face 43 of substrate 4.
The planar inner surface 81 of the ceramic diaphragm 8 is
provided with the electrode 82, which is dimensioned so as
to extend up to the ring surface 326 of the first substrate
3 after diaphragm 8 has been placed on the ring surface
326. On its other planar inner surface 85, diaphragm 8 is
provided with electrode 86, which is dimensioned so as to
extend up to ring surface 426 of substrate 4 after dia-
phragm 8 has been placed on the ring surface 426.
Quantities of active brazing solder 10 sufficient to braze
diaphragm 8 to substrates 3 and 4 are applied to the por-
tion of convex surface 324 of substrate 3 located between
ring surface 326 and cylindrical surface 31 and to the
portion of convex surface 424 of substrate 4 located
between ring surface 426 and cylindrical surface 41. In
this case, too, an active brazing solder paste is prefer-
CA 02298815 2000-02-16
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ably used, which is applied by means of a suitable dis-
penser.
Next, the inner surface 81 of diaphragm 8, provided with
electrode 82, is placed on ring surface 326 of substrate 3,
and the inner surface 85 of diaphragm 8, provided with
electrode 86, is placed on ring surface 426 of substrate 4.
Thereafter, substrates 3, 4 and diaphragm 8 are heated in a
vacuum or inert-gas atmosphere until the active brazing
solder 10 has melted, and allowed to cool down.
