U.S. patent application number 10/679661 was filed with the patent office on 2004-04-15 for platinum temperature sensor.
This patent application is currently assigned to Sensotherm Temperatursensorik, GmbH. Invention is credited to Zitzmann, Heinrich.
Application Number | 20040070487 10/679661 |
Document ID | / |
Family ID | 7894235 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040070487 |
Kind Code |
A1 |
Zitzmann, Heinrich |
April 15, 2004 |
Platinum temperature sensor
Abstract
A Platinum temperature sensor comprises a ceramic substrate and
a platinum thin-film resistor applied to said ceramic substrate, a
ceramic cover layer and a connecting layer generated from a ceramic
green layer by pressure and temperature treatment. The ceramic
cover layer is connected with the ceramic substrate in such a way
via the connecting layer that the platinum thin-film resistor is
sealingly encapsulated with regard to the environment.
Inventors: |
Zitzmann, Heinrich; (Lauf an
der Pegnitz, DE) |
Correspondence
Address: |
DOUGHERTY, CLEMENTS & HOFER
1901 ROXBOROUGH ROAD
SUITE300
CHARLOTTE
NC
28211
US
|
Assignee: |
Sensotherm Temperatursensorik,
GmbH
Nuernberg
DE
|
Family ID: |
7894235 |
Appl. No.: |
10/679661 |
Filed: |
October 7, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10679661 |
Oct 7, 2003 |
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09889298 |
Aug 20, 2001 |
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6653926 |
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09889298 |
Aug 20, 2001 |
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PCT/EP00/00178 |
Jan 12, 2000 |
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Current U.S.
Class: |
338/25 ; 338/28;
374/E7.022 |
Current CPC
Class: |
H01C 17/02 20130101;
G01K 7/183 20130101; G01K 7/18 20130101; H01C 7/006 20130101 |
Class at
Publication: |
338/025 ;
338/028 |
International
Class: |
H01C 003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 14, 1999 |
DE |
19901184.2 |
Claims
What is claimed is:
1. Platinum temperature sensor comprising: a ceramic substrate; a
platinum thin-film resistor applied to the ceramic substrate; a
ceramic cover layer; and a connecting layer produced from a ceramic
green sheet by pressure and temperature treatment, by means of
which the ceramic cover layer is connected with the ceramic
substrate in such a way that the platinum thin-film resistor is
sealingly encapsulated with re-gard to the environment.
2. Platinum temperature sensor according to claim 1 wherein the
connecting layer is formed as a continuous face on the ceramic
substrate and the platinum thin-film resistor.
3. Platinum temperature sensor according to claim 1 wherein the
connecting layer is applied in a boarder area surrounding the
platinum thin-film resistor on the ceramic substrate.
4. Platinum temperature sensor according to claim 1 wherein the
connecting layer is generated from an Al.sub.20.sub.3
green-layer.
5. Platinum temperature sensor comprising: a ceramic substrate; a
platinum thin-film resistor applied to the ceramic substrate; a
ceramic cover layer; and a connecting layer made of a glaze that is
applied to the ceramic substrate in a boarder area surrounding the
platinum thin-film resistor by means of which the ceramic cover
layer is connected with the ceramic substrate in such way that the
platinum thin-film resistor is sealingly encapsulated with regard
to the environment.
6 Platinum temperature sensor according to claim 1 wherein the
ceramic substrate is made of Al.sub.20.sub.3.
7. Platinum temperature sensor according to claim 1 wherein the
ceramic cover layer is made of Al.sub.20.sub.3.
8. Platinum temperature sensor according to claim 1 wherein a
sealing cover is applied to the outer peripheral edges of the layer
structure consisting of ceramic substrate, connecting layer and
ceramic cover layer.
9. Platinum temperature sensor according to claim 8 wherein the
sealing layer is made of glass.
10. Method for producing a platinum temperature sensor comprising
the steps of: a) providing a fired ceramic substrate with a
platinum thin-film resistor applied to the main surface thereof; b)
applying a connecting layer made of a ceramic green layer to the
main surface of the ceramic substrate; and c) applying a fired
ceramic cover layer to the connecting layer in such a way that the
platinum thin-film resistor is sealingly encapsulated with regard
to the environment by subjecting the ceramic green layer to a
temperature treatment under application of pressure in such a way
that the ceramic substrate and the ceramic cover layer will be
connected.
11. Method according to claim 10 wherein the connecting layer is
applied as a continuous face in step b).
12. Method according to claim 10 wherein the connecting layer is
applied to the ceramic substrate in a border area surrounding the
platinum thin-film resistor in step b).
13. Method according to claim 10 wherein a sealing layer is applied
to outer peripheral edges of the layer structure consisting of
ceramic substrate, connecting layer and ceramic cover layer.
14. Platinum temperature sensor according to claim 5 wherein the
ceramic substrate is made of Al.sub.20.sub.3.
15. Platinum temperature sensor according to claim 5 wherein the
ceramic cover layer is made of Al.sub.2O.sub.3.
16. Platinum temperature sensor according to claim 5 wherein a
sealing cover is applied to the outer peripheral edges of the layer
structure consisting of ceramic substrate, connecting layer and
ceramic cover layer.
17. Platinum temperature sensor according to claim 16 wherein the
sealing layer is made of glass.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a platinum temperature
sensor and a method for producing the same, and in particular to a
platinum temperature sensor in the case of which a platinum
thin-film resistor, which is applied to a ceramic substrate, is
used for temperature detection.
[0003] 2. Description of Prior Art
[0004] A known platinum temperature sensor is shown in FIG. 3. In
this known platinum temperature sensor, a platinum thin-film
resistor 2 is applied to a ceramic substrate 4 which normally
consists of aluminum oxide Al.sub.2O.sub.3. In the area in which
the platinum thin-film resistor 2 is formed, a protective glaze 6
is provided on the surface of the ceramic substrate 4. The platinum
layer, in which the platinum thin-film resistor 2 is normally
formed in a meandering shape, is additionally patterned so as to
include connecting areas 8 having lead wires 10 connected thereto
in an electrically conductive manner for taking the sensor signal.
For fixing the lead wires 10, a glaze 12 is provided.
[0005] The field of use of the platinum temperature sensor, which
is shown in FIG. 3 and which is implemented in thin-film
technology, is normally limited to 600.degree. C. In the last few
years, there has, however, been an increasing demand for an
embodiment that can be used for higher operating temperatures,
which may exceed 1,000.degree. C. In the field of high-temperature
sensors considerable efforts have therefore been made to provide
platinum temperature sensors which are suitable to be used in such
high temperature ranges. By purposefully selecting the composition
of the protective glaze 6, it has already been possible to find
satisfactory solutions for some cases of use, whereas in very
particular fields of application, e.g. in special cases of use in
the field of automotive engineering, the results do not satisfy all
requirements. For example, the long-term stability of temperature
sensors of the type described hereinbefore, especially when they
have applied thereto a certain measurement current, which may e.g.
be 5 mA, is not sufficiently guaranteed at the high temperatures
occurring, viz. temperatures in the range of 800.degree. C. and
1,000.degree. C., since the protective glazes used may be
decomposed electrochemically by the necessary measurement current
at these high temperatures. The resultant material migration has a
negative influence on the properties of the platinum so that the
sta-bility of the sensors and, consequently, the measuring accuracy
are impaired.
[0006] By purposefully selecting the composition of the protective
glazes, improvements could be achieved to a certain extent, but it
was impossible to find protective glazes that withstand the
electrochemical decomposition by the measurement current in the
case of continuous loads in a temperature range of 1,000.degree. C.
or more than 1,000.degree. C.
[0007] From the article "Fuigen von Technischen Keramiken mit
Keramik-Grunfolien" by M. Neuhuser et al., sfi/Ber. DKG 72 (1995)
Nr. 1-2, methods for joining technical ceramics are known wherein
ceramics green foils are used to connect two ceramic layers. A
prerequisite for the joining method described there is that the
sintering temperature of the ce-ramic green foil is below the
sintering temperature of the ceramic to be jointed.
[0008] A temperature sensor having a platinum resistance layer,
which is applied to a ceramic substrate and encapsulated by a
glaze, is disclosed in DE 7629727 U1.
[0009] From De 37 33 192 C1 a PTC-temperature sensor is known
wherein a platinum resistor formed by means of a platinum
thick-film technique is arranged between two ceramic green foils
and an interlaminar binder layer, whereupon the two foils are
laminated together by use of a pressure and a risen temperature and
are sintered after that.
[0010] In DE 4445243 A1 a temperature sensor is described wherein
three unprocessed ceramic substrates are laminated together,
pressed and fired at 1.600.degree. C. in order to form a uniform
piece. Before laminating a platinum resistor is arranged between
two of the ceramic substrates.
SUMMARY OF THE INVENTION
[0011] It is the object of the present invention to provide a
platinum temperature sensor which supplies reliable measurement
results even in the case of continuous loads in a high temperature
range, and a method for producing such a platinum temperature
sensor.
[0012] According to a first aspect of the invention this object is
achieved by a platinum temperature sensor comprising:
[0013] a ceramic substrate;
[0014] a platinum thin-film resistor applied to the ceramic
substrate;
[0015] a ceramic cover layer; and
[0016] a connecting layer produced from a ceramic green sheet by
pressure and temperature treatment, by means of which the ceramic
cover layer is connected with the ceramic substrate in such a way
that the platinum thin-film resistor is sealingly encapsulated with
regard to the environment.
[0017] According to a second aspect of the invention this object is
achieved by a platinum temperature sensor comprising:
[0018] a ceramic substrate;
[0019] a platinum thin-film resistor applied to the ceramic
substrate;
[0020] a ceramic cover layer; and
[0021] a connecting layer made of a glaze that is applied to the
ceramic substrate in a boarder area surrounding the platinum
thin-film resistor by means of which the ceramic cover layer is
connected with the ceramic substrate in such way that the platinum
thin-film resistor is sealingly encapsulated with regard to the
environment.
[0022] According to a third aspect of the invention, this object is
achieved by a method for producing a platinum temperature sensor
comprising the steps of:
[0023] providing a fired ceramic substrate with a platinum
thin-film resistor applied to the main surface thereof;
[0024] applying a connecting layer made of a ceramic green layer to
the main surface of the ceramic substrate; and
[0025] applying a fired ceramic cover layer to the connecting layer
in such a way that the platinum thin-film resistor is sealingly
encapsulated with regard to the environment by subjecting the
ceramic green layer to a temperature treat-ment under application
of pressure in such a way that the ceramic substrate and the
ceramic cover layer will be con-nected.
[0026] The present invention is based on the knowledge that ceramic
materials, especially aluminum oxide Al.sub.20.sub.3 are
in-sensitive to the above-described current induced decomposition,
and thus this material that in addition is used in thin-film
platinum temperature sensors as substrate material for the platinum
film can advantageously also be used as protective material for
capsulation of the platinum film layer. Thus, the problems of
electrochemical decomposition and the connected deterioration of
properties of the platinum temperature sensors are prevented, even
when the protective cover is realized from a ceramic material.
[0027] On the one hand, the structured platinum film in the
inventive platinum temperature sensor is therefore sufficiently
protected against mechanical and chemical environmental influences.
On the other hand the inventive platinum temperature sensor
supplies reliable measurement results even in the case of
continuous loads in a high temperature range of for example
1000.degree. C. or more than 1000.degree. C., since the
above-described disadvantageous decomposition phenomenons do not
occur in the case of the inventive platinum film temperature
sensor.
[0028] In the inventive platinum temperature sensor the connecting
layer is either applied to the whole area of the ceramic substrate
provided with the platinum thin-film resistor or alternatively only
on a border area of the same, so that the platinum thin-film
resistor is surrounded by the connecting layer. If the connecting
layer is only provided on the border area it is preferable to
provide a sealing layer that can be made of glass, for example, on
the side edges of the resulting layer structure. However, such a
layer can also be provided when the connecting layer is applied to
the whole area.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Preferred embodiments of the present invention will be
explained below in detail referring to the enclosed drawings. They
show:
[0030] FIG. 1: a schematic cross-sectional view of a platinum
temperature sensor according to the present invention;
[0031] FIG. 2: a schematic top view of a platinum temperature
sensor according to the present invention; and
[0032] FIG. 3: a schematic cross sectional view of a known platinum
temperature sensor.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0033] First, referring to FIG. 1, a first embodiment of a platinum
temperature sensor according to the present invention is described
in detail. The platinum temperature sensor comprises a ceramic
substrate that consists of Al.sub.2O.sub.3 in preferred embodiments
on which a structured platinum layer is applied defining a platinum
resistor trace 2 and connecting areas A lead wire 10 can be
electrically conductive connected with the connecting areas 8. A
ceramic cover layer 16 which is also made from Al.sub.2O.sub.3 in
the preferred embodiments of the present invention is applied on
the surface of the ceramic substrate 4 on which the platinum
resistor trace is provided via a connecting layer 14, which
consists also of Al.sub.2O.sub.3 in the preferred embodiments of
the present invention. Further, in FIG. 1 a glass ceramic 18 is
illustrated that serves for fixing the lead wire.
[0034] It is preferable to use the same material for the cover
layer 16 that is used for the ceramic substrate 4. However, a
similar material can be used. The cover layer 16 can have the same
thickness as the ceramic layer or a smaller thick-ness, for example
10 to 20% thinner, as long as the thickness of the cover layer can
obtain a sufficient protective effect against adverse environmental
influences. The connecting layer can have a small thickness since
the protective effect for the platinum film with regard to the
outer atmosphere is achieved by the thicker cover layer 16.
[0035] First, for producing the platinum temperature sensor
according to the invention the fired ceramic substrate 4 that is a
Al.sub.2O.sub.3-substrate in the preferred embodiments of the
present invention is supplied with the platinum resistor trace 2
provided thereon. Subsequently, a very thin ceramic green layer
with a thickness of for example 0.1 to 0.2 mm is supplied at least
in the area of the platinum resistor trace 2. This connecting layer
is preferably an Al.sub.2O.sub.3 green layer. Subsequently the
fired cover layer 16, preferably also a Al.sub.2O.sub.3 layer, is
applied to the green layer. This total layer construction will then
be fired with very high temperatures under an additional outer
pressure that can for example be generated by an additional ceramic
plate. By this firing procedure the two ceramic plates, i.e. the
ceramic substrate 14 and the cover layer 16 are tightly connected
via the foil 14. Thus, the platinum thin-film resistor 2 is tightly
closed against the outer atmosphere.
[0036] Thus, the present invention provides a platinum temperature
sensor that ensures a secure protection of the platinum thin-film
resistor against penetration of foreign material from the
environment even in high temperature ranges, wherein no chemical
decomposition influences by the measurement current necessary for
operating the temperature sensor need to be feared.
[0037] It is not possible to apply the ceramic cover layer directly
to the ceramic substrate by means of screen-printing, like it is
done when using glazes as protective layer, for example. If
Al.sub.2O.sub.3 is used as a cover layer this procedure cannot be
applied since the melting point for Al.sub.2O.sub.3 is much to
high, namely above the melting of the platinum and would further
also melt the carrier substrate.
[0038] Even when the whole cover layer is applied as a green layer,
wherein green layer means a ceramic with binding agents
volatilizing in the firing procedure, problems arise since this
green layer is subject to a certain shrinkage, wherein the cover
layer would not have the required impermeability due to shrinkage
cracks. The above-mentioned shrinkage becomes even more apparent
the thicker the foil is. On the other hand, a certain thickness in
the range of 0.3 to 0.5 mm is necessary in order to achieve a
sufficient protective effect against adverse environmental
influences with the mentioned high temperatures of 800.degree. C.
to 1000.degree. C. or more.
[0039] In FIG. 2 a schematic top-view of an alternative embodiment
of a platinum temperature sensor according to the invention is
illustrated. In FIG. 2 again the ceramic substrate 4 servicing as a
carrier and the platinum layer structural thereon that defines a
platinum thin-film resistor 2 and connecting areas 8 shown. Further
two lead wires 10 each connected with one of the connecting areas 8
are illustrated. However, in the embodiment shown in FIG. 2 the
connecting layer 10 is not applied to the whole area of the surface
of the ceramic substrate 4 and the platinum thin-film resistor 2
but only in a border area surrounding the platinum thin-film
resistor 2. In this embodiment the platinum thin-film resistor is
not covered by the connecting layer. By means of this connecting
layer 20 surrounding the platinum thin-film resistor 2 a cover
layer (not shown in FIG. 2) ill now be connected with the ceramic
substrate 4, so that again the platinum thin-film resistor 2 is
sealingly encapsulated with regard to the environment. In this
embodiment it is preferred to provide an additional sealing layer
made of glass, for example, on the perpendicular outer edges formed
by the layer structure.
[0040] In the embodiment shown in FIG. 2 either also a
Al.sub.2O.sub.3-foil can be used as a connecting layer 20, while
alternatively a protective glaze for sealing connection, i.e.
fusion of the carrier substrate with the cover foil, can be used a
connecting layer instead of the foil. Even when the protective
glaze is used a connecting layer 20 the current carrying platinum
resistor trace 2 has no contact to the glaze layer 20, so that the
above-described decomposition phenomenons do not occur in this
case. Using a glaze for the connecting layer 20 can offer
advantages for the production and can be used for up to
1000.degree. C. if a high melting glaze with a melting temperature
of more than 1,300.degree. C. is used.
[0041] The connecting layers 14 in FIG. 1 and 20 in FIG. 2 used
according to the invention can alternatively be replaced by a
ceramic paste printed on by a screen-printing method. In this case
a ceramic paste is printed onto the structured ceramic substrate
coated with the structured platinum film by screen-printing and
covered with the ceramic cover plate after pre-drying. Subsequently
under application of pressure a firing is performed in order to
connect ceramic substrate and ceramic cover layer. The ceramic
paste can consist of a pasted mixture of several ceramic powders
and quartz powders, for example Al.sub.2O.sub.3, MGO,
SiO.sub.2.
[0042] Thus, the present invention provides a platinum temperature
sensor, which on the one hand provides a secure protection of the
platinum film resistor against outer influences and on the other
hand exhibits no deterioration of precision even in the case of
continuous loads in a high temperature range.
[0043] The platinum temperature sensor according to the invention
can preferably be produced by wafer processing, with the exception
of mounting the lead wires and fixing them in such a way that a
plurality of platinum temperature sensors can be produced from one
ceramic wafer. After dicing-up the individual platinum temperature
sensors the above-mentioned sealing layer can be applied to the
respective perpendicular cutting edges.
* * * * *