Ceramic sensor with metallized layer

Abstract

The present invention relates to a sensor comprising a ceramic substrate (1) and two metallization layers (2) applied on opposite surfaces of the ceramic substrate (1), each having an adhesion layer (2A) applied directly onto the ceramic substrate (1) and a gold layer (2B) applied on each adhesion layer (2A). Furthermore, the present invention relates to a method for manufacturing the sensor.

Description

[Technical Field]

[0001] The present invention relates to a sensor having a ceramic substrate and a metallization layer applied thereon, and a method for manufacturing the sensor. [Background technology]

[0002] The demands on temperature sensors are constantly increasing, with regard to higher operating temperatures and at the same time particularly high reliability and low manufacturing costs, which requires the use of tailored and innovative material combinations and manufacturing techniques.

[0003] Previously available sensors have limitations on their operating temperatures, typically only up to 300°C.

[0004] At the current state of the art, temperature measurement for monitoring and control purposes is primarily performed using ceramic thermistor elements in a wide variety of applications.

[0005] Electrical contact with ceramics requires the application of metal electrodes. In the prior art, thick-film metallization is mainly used. For example, silver paste is applied by a screen printing process and then sintered. This silver metallization is mainly used for soldering connections to connecting wires.

[0006] However, the operating temperature of solder joints is limited by the melting point of the solder. High-lead solders have a melting point of approximately 300°C, and most lead-free solders melt at temperatures below 230°C. Solder joints cannot be sufficiently reliable under frequent temperature changes. Many solder materials are prone to migration in humid or wet environments.

[0007] Welding a wire onto a ceramic electrode is not a suitable alternative because it will damage the electrode or the ceramic. Wires that are significantly thicker than the thickness of the electrode layer require a very high energy input to melt the connection. This can result in the electrode layer being completely detached from the ceramic, and the resulting thermal shock can cause the ceramic to crack or deteriorate its electrical properties. Summary of the Invention

[0008] SUMMARY OF THE INVENTION It is an object of the present invention to describe an improved sensor and a method for manufacturing the sensor.

[0009] The present invention relates to a sensor comprising a ceramic substrate, on two opposing surfaces of which a metallization layer is applied or deposited. Opposite surfaces here particularly refer to surfaces of the substrate facing in opposite directions or at least approximately in opposite directions. Preferably, the two opposing surfaces are the two outer surfaces of the ceramic substrate, which are spaced a minimum distance apart from each other. The two opposing surfaces can be, for example, the lower and upper surfaces of the ceramic substrate, or the front and rear surfaces of the ceramic substrate.

[0010] Each of the two metallization layers includes an adhesive layer applied directly onto the ceramic substrate and a gold layer applied onto the respective adhesive layer. In one embodiment, both metallization layers or one of the metallization layers consists of a respective gold layer and a respective adhesive layer. In this case, each metallization layer does not include layers other than the gold layer and the adhesive layer.

[0011] By the adhesive layer being applied directly to the ceramic substrate, it is meant that the adhesive layer is in direct contact with the substrate and there are no other layers between the adhesive layer and the ceramic substrate.

[0012] The metallization layer can cover part or all of the two opposing surfaces. Preferably, the adhesive layer has at least the area of ​​the gold layer, so that the gold layer is applied entirely onto the adhesive layer and not directly onto the ceramic substrate.

[0013] The gold layer is preferably applied directly onto the adhesive layer.

[0014] In one embodiment, the metallization layer is formed in a circular shape. In another embodiment, the metallization layer is formed as finger electrodes. In one embodiment, the metallization layer covers the entire surface of each of the ceramic substrates, and therefore conforms to the shape of the ceramic substrate. Additionally, other suitable geometric shapes are possible.

[0015] The adhesive layer acts as a glue between the gold layer and the ceramic layer. This adhesive layer improves the adhesion of the gold layer to the ceramic substrate. It creates a stable bond with high tensile strength between the ceramic substrate and the metallization layer. Therefore, with the adhesive layer, the sensor is more stable against mechanical stress than without it. Furthermore, premature delamination of the gold layer from the ceramic substrate is avoided, thereby extending the sensor's service life compared to sensors without an adhesive layer.

[0016] In one embodiment, the gold layer contains at least 80% by weight of gold. Additionally, the gold layer can contain additional metals or metal oxides, such as nickel, aluminum, vanadium, chromium, manganese, and oxides of these metals. In further embodiments, the gold layer can contain at least 90% by weight of gold or consist of gold.

[0017] The adhesive layer may preferably be a copper layer. In one embodiment, the copper layer comprises at least 80% by weight of copper. Furthermore, the adhesive layer may comprise additional metals or metal oxides, such as nickel, aluminum, vanadium, chromium, or manganese, and oxides of the above metals. In a further embodiment, the copper layer may contain at least 90% by weight of copper or consist of copper.

[0018] Gold metallization is more stable to chemical reactions than silver metallization. Gold oxidation and ionization are relatively rare, and the selected gold metallization is particularly stable at high temperatures against migration effects that occur when using silver metallization, for example, thus avoiding short circuits between the two metallization layers.

[0019] Furthermore, the described metallization layer allows for consistent adjustment of the electrical behavior of the sensor: the electrical parameters of the sensor, for example the electrical resistance at different temperatures, show very little variation even with repeated measurements.

[0020] In particular, the metallization layer functions as an electrical contact layer and acts as an external electrode for the ceramic substrate, which can be contacted to the metallization layer via electrical contact elements such as electrical leads.

[0021] In one embodiment, the ceramic substrate is rectangular shaped. Here, it particularly refers to a rectangular parallelepiped having a rectangular base and sides.

[0022] In this embodiment, the two metallization layers are applied to opposite surfaces of a rectangular parallelepiped-shaped ceramic substrate. The rectangular parallelepiped shape allows for easy, e.g., modular, integration of the ceramic substrate into the sensor. The rectangular parallelepiped shape also makes it simpler and therefore less expensive to manufacture.

[0023] In one embodiment, the ceramic substrate comprises a thermistor ceramic, which can be a positive temperature coefficient (PTC) thermistor, i.e., a cold conductor, or a negative temperature coefficient (NTC) thermistor, i.e., a hot conductor. Alternatively, the ceramic substrate can comprise, for example, a varistor.

[0024] Preferably, the thermistor ceramic is an NTC ceramic.

[0025] The use of thermistor ceramics, in particular NTC ceramics, makes it possible to electrically measure the ambient temperature via the sensor.

[0026] The use of NTC ceramics in particular is well suited to allow the sensor to capture high temperatures and convert them into a corresponding electrical signal.

[0027] A sensor comprising an NTC ceramic as ceramic substrate and a metallization layer as defined above, including an adhesion layer of, for example, a copper layer and a gold layer, is suitable for use in high temperature environments and has no limitations in its functionality even at high temperatures.

[0028] In one embodiment, the ceramic substrate comprises a ceramic having a perovskite structure.

[0029] Ceramics with a perovskite structure are suitable for adjusting the thermal conductivity properties of ceramic substrates.

[0030] Ceramics having a perovskite structure have high heat resistance, allowing the ceramic substrate to be used at high temperatures.

[0031] In alternative embodiments, the ceramic of the ceramic substrate may have other structures, such as a spinel structure, which may also be used to provide a ceramic substrate with particularly good thermal conductivity.

[0032] In one embodiment, the metallization layer is formed by sputtering. In particular, the adhesion layer and the gold layer are each formed by sputtering. Thus, during the manufacture of the sensor, the adhesion layer is preferably sputtered in a first step, and the gold layer is sputtered onto the adhesion layer in a second step.

[0033] Sputtered layers can be made significantly thinner than layers applied by (screen) printing, for example. This saves material and reduces the manufacturing costs of the sensor. Furthermore, sensor manufacturing is resource-efficient and environmentally friendly.

[0034] The sputtered layer also has an improved surface wetting property compared to layers applied, for example, by screen printing, i.e. the sputtered metallization layer completely or almost completely covers the surface of the ceramic substrate and there are no holes in the layer where the ceramic substrate is not covered by the metallization layer.

[0035] The advantageous structure of the sputtered layer further reduces the variation in the electrical properties of the sensor, for example the electrical resistance of the metallization layer changes very little at different temperatures or with repeated measurements.

[0036] In particular, for example, the resistance R 25 , resistance R at 100°C 100 , and the B value B are almost constant. In particular, the resistance R 25 or resistor R 100 The coefficient of variation for is at most 1.0, preferably at most 0.9.

[0037] The coefficient of variation for the B value is preferably at most 0.1.

[0038] The coefficient of variation is defined as the ratio of the standard deviation to the mean of a series of measurements.

[0039] The B value of a thermistor is defined as: B=1483.4·ln(R 25 / R 100 )

[0040] In one embodiment, the adhesion layer has a thickness of at most 200 nm. Preferably, the thickness is at most 100 nm. Such thin thicknesses can be achieved in particular by sputtering.

[0041] The adhesive layer is preferably formed as a thin film.

[0042] The above layer thicknesses are sufficient to provide good adhesion of the metallization layer to the ceramic substrate.

[0043] The above-mentioned layer thicknesses are also sufficient to achieve complete surface wetting at the surface of the ceramic substrate, i.e. wetting without holes in the metallization layer.

[0044] Applying thin layers can save materials.

[0045] According to one embodiment, the gold layer has a thickness of up to 1000 nm.

[0046] Preferably, the layer thickness is at most 500 nm. Such small layer thicknesses can be achieved in particular by sputtering.

[0047] The gold layer is preferably formed as a thin film.

[0048] The layer thicknesses mentioned above are sufficient for the metallization layer to provide functionality as an electrical contact layer, i.e. as an external electrode of the sensor.

[0049] The layer thicknesses mentioned above are sufficient to achieve complete surface wetting, i.e. wetting without holes in the metallization layer.

[0050] Applying thin layers can save materials.

[0051] In one embodiment, the sensor is a temperature sensor, which is the case in embodiments where the ceramic substrate comprises or consists of a thermistor ceramic, in particular an NTC ceramic.

[0052] In one embodiment, the sensor has unlimited functionality at temperatures up to 600° C. In particular, at these temperatures the sensor has unlimited electrical functionality, i.e., the functionality of the sensor is not affected by high temperatures.

[0053] This requires, among other things, the proper selection of materials for the ceramic substrate and the metallization layer, as well as the proper construction of the ceramic material and the metallization layer, and in particular the proper method of application of the metallization layer, as described above.

[0054] If a ceramic substrate with a spinel structure is selected instead of a ceramic substrate with a perovskite structure, the sensor will have stable functionality in a temperature range up to at least 300°C.

[0055] In one embodiment, the sensor further comprises an electrical contact element, e.g., a conductor wire. The electrical contact element, e.g., the conductor wire, is applied directly onto the metallization layer for electrical contact. In particular, the electrical contact element or conductor wire is directly connected to the surface of the metallization layer, in particular the surface of the gold layer. The metallization layer contacts or at least partially surrounds the conductor wire.

[0056] In one embodiment, the electrical contact elements or conductors are sintered together with the metallization layer, i.e., a metallization paste surrounding the metallization layer and the ends of the conductors is sintered in a common step, thereby establishing a closed connection between the conductors and the metallization layer.

[0057] For example, for this purpose, the wires are dipped in a gold paste containing gold metal (Goldmetall). The periphery of the wires wetted with the paste is then pressed into a metallization layer. The sensor with the pressed wires is placed in a furnace and subjected to a thermal profile, which sinters the metallization layer together with the wires.

[0058] The wire may be a nickel alloy wire that is particularly resistant to high temperatures, for example a nickel chromium alloy wire, particularly an Inconel wire, which is particularly resistant to temperatures and allows the sensor to be used in high temperature environments.

[0059] Alternatively, the conductors may be made of other suitable materials, such as copper or nickel.

[0060] The electrical leads connect the sensor to electronic circuitry that can be used to drive and control the sensor and / or process and evaluate the sensor's electrical signals.

[0061] In one embodiment, the sensor further comprises a glass encapsulant.

[0062] In one embodiment, the ceramic substrate and metallization are enclosed in a glass encapsulant.

[0063] Preferably, the ceramic substrate and the metallization layer are completely surrounded or covered by a glass seal, and likewise, the electrical contact elements that are in contact with the metallization layer, such as the ends of the conductors, are also surrounded or covered by a glass seal.

[0064] The glass encapsulation protects the sensor from environmental influences, for example, preventing corrosion from altering the surface of the ceramic substrate, metallization, or lead ends.

[0065] Additionally, the glass encapsulant provides electrical insulation between the sensor and the surrounding environment.

[0066] Furthermore, the glass seal is stable at temperatures up to 600°C.

[0067] The glass encapsulation can be provided, for example, by placing a preformed glass body, i.e., a pre-shaped glass body, for example, a glass cylinder, on the remaining sensor and deforming it, or by immersing the remaining sensor in a glass paste. The remaining sensor can include, in particular, the ceramic substrate, the metallization layer, and the ends of the electrical leads.

[0068] The glass sleeve thus formed can be subjected to a subsequent temperature treatment in order to achieve a gas-tight seal.

[0069] Furthermore, the present invention relates to a method for manufacturing a sensor, which can be configured in particular as described above. The above features and embodiments are also applicable to the method.

[0070] In this method, in a first step, an adhesive layer, for example a copper layer, is applied to each of two opposing surfaces of a ceramic substrate.

[0071] In the second step, two gold layers are applied onto each adhesive layer, one gold layer on each adhesive layer.

[0072] The different metal layers, i.e., the adhesion layer and the gold layer, are applied in different steps to ensure the layer order described above, so the second step is preferably performed after the first step is completed.

[0073] The gold layer is not in direct contact with the ceramic substrate, but rather the adhesion of the gold layer to the ceramic substrate is enhanced via an adhesive layer disposed therebetween as an adhesive.

[0074] Both layers can be applied in the same production unit, for example using the same sputtering equipment.

[0075] In one embodiment of the method, the layer is applied by sputtering.

[0076] The present invention will now be described in detail with reference to embodiments and related drawings, but the present invention is not limited to the embodiments shown in the drawings. [Brief explanation of the drawings]

[0077] [Figure 1] FIG. 1 shows a cross section of a first embodiment of a sensor. [Figure 2] 2 shows an embodiment of the sensor further comprising electrical leads for electrical contact and a glass encapsulant, which is shown transparent for purposes of illustration. [Figure 3] 3 shows a further embodiment of the sensor with electrical contact wires during the manufacturing process, with a glass cylinder surrounding the remaining components of the sensor. DETAILED DESCRIPTION OF THE INVENTION

[0078] Similar or apparently identical elements in the drawings are provided with the same reference numerals. The figures in the drawings and the dimensional ratios therein are not necessarily to scale.

[0079] 1 shows a first embodiment of the sensor, which in particular comprises a ceramic substrate 1.

[0080] The ceramic substrate 1 preferably comprises a thermistor ceramic, for example an NTC ceramic with a negative temperature coefficient, i.e. a thermally conductive ceramic (Heissleiter-Keramik).

[0081] The ceramic substrate 1 preferably comprises a ceramic having a perovskite structure.

[0082] The ceramic substrate 1 comprises, for example, a drift-stable perovskite ceramic. In particular, the ceramic substrate 1 comprises a perovskite ceramic having the general formula [SE 1-x M II x][Cr 1-y-z R y L z ]O3, where SE represents one or more rare earth metals, and M II represents one or more metals in oxidation state +II, L represents Al and / or Ga, R represents one or more metals selected from Fe, Zn, Ge, Sn, preferably satisfying the following conditions: <x<1;0<y<1;0.5<z<1;y+z<1;0.1<1-y-z<0.2。

[0083] In this embodiment, the ceramic substrate 1 is formed in a rectangular parallelepiped shape. This rectangular parallelepiped ceramic substrate has six outer surfaces, each of which is rectangular.

[0084] Two metallization layers 2 are formed on two opposing surfaces of the ceramic substrate 1, for example the front and back surfaces or the bottom and top surfaces.

[0085] For example, one metallization layer 2 is formed on the bottom surface of the substrate 1 and one metallization layer 2 is formed on the top surface.

[0086] For example, each metallization layer 2 covers the entire surface of the ceramic substrate 1 to which it is applied, or the metallization layer 2 is formed, for example, in a circular shape.

[0087] The metallization layer 2 may alternatively only partially cover the corresponding surface of the ceramic substrate 1 .

[0088] Both metallization layers 2 each comprise an adhesion layer 2A, in particular a copper layer, and a gold layer 2B.

[0089] The adhesive layer 2A is applied directly onto the surface of the ceramic substrate 1. Preferably, the adhesive layer 2A, e.g. a copper layer, is applied by sputtering. No further layers are provided between the adhesive layer 2A and the ceramic substrate 1. The adhesive layer exhibits high adhesion to the ceramic substrate 1.

[0090] A gold layer 2B is applied to each of the adhesive layers 2A on the surface facing away from the ceramic substrate 1. The gold layer 2B is preferably applied directly onto the adhesive layer 2A, preferably by sputtering.

[0091] The adhesive layer 2A as adhesive ensures sufficient adhesion of the gold layer 2B to the ceramic substrate 1, ensuring stable functionality and a long service life of the sensor.

[0092] Both layers 2A and 2B are preferably applied by sputtering.

[0093] Applying layer 2 by sputtering allows layer 2 to be made thinner and to require less material.

[0094] For example, the adhesive layer 2A has a thickness of 200 nanometers or less, preferably 100 nanometers or less. The gold layer 2B has a thickness of, for example, up to 1000 nanometers, preferably 500 nanometers or less.

[0095] These specified layer thicknesses ensure that the metallization layer 2 completely wets the ceramic substrate 1. Complete wetting means in particular that there are no corresponding metal-free holes in the adhesion layer 2A or the gold layer 2B, respectively.

[0096] The metallization layer 2, and in particular the gold layer 2B, serves as an external electrode, i.e. as an electrical contact layer, by means of which the ceramic substrate 1 can be electrically contacted from the outside. For this purpose, electrical contact elements, for example conductors 3, are arranged in contact with the metallization layer 2.

[0097] FIG. 2 shows an embodiment of the sensor with leads 3 and a glass seal 4 for electrical contact.

[0098] The sensor is otherwise configured similarly to, for example, the first embodiment. The conductive wire 3 is sintered together with the gold layer 2B on the surface of the gold layer 2B.

[0099] For this purpose, a contact paste is prepared that contains gold and other paste components. Other paste components include, for example, organic additives that adjust the plasticity of the paste.

[0100] The contact portions, e.g., end portions, of the conductors 3 are immersed in the contact paste, so that they are wetted with the contact paste. At this time, it is preferable that the entire surface of the corresponding conductor portion is wetted with the paste. However, the edge length of the circumferential surface along the extension direction of the conductor that is wetted with the paste must be shorter than the dimension of the gold layer 2B in the corresponding direction.

[0101] The conductor 3, with its contacts wetted, is then pressed against the sensor with a suitable mechanical device under mechanical stress and then heat treated: for this purpose, the device together with the sensor is placed in a furnace and subjected to a thermal heating profile, which causes the conductor 3 to be sintered onto the surface of the gold layer 2B.

[0102] The sensor is then covered with a glass encapsulant 4, as also shown in FIG.

[0103] The glass encapsulation 4 can be produced, for example, according to the first method, by dipping the remaining sensor together with the ends of the sintered conductors 3 into a container with glass paste. The remaining sensor comprises, in particular, the ceramic substrate 1, the metallization layer 2 and the ends of the conductors 3. The sensor is dipped at a defined speed until the sensor and the ends of the conductors are completely enveloped in the glass paste.

[0104] To ensure a bubble-free coating, the sensor undergoes a defined lateral movement in the glass paste. The sensor is then withdrawn from the glass paste at a defined speed. The defined speed is selected in the range of 0.1 mm / min (millimeters per minute) to 5 mm / min, for example 1 mm / min.

[0105] The glass paste-coated sensor is subjected to a defined multi-stage temperature profile for drying and vitrification.

[0106] The drying process must also be carried out carefully enough to ensure a bubble- and defect-free glass seal and to allow the necessary additives for the production of the glass paste to escape.

[0107] After drying, a vitrification process is carried out, during which the glass sleeve is heated using a defined temperature profile to a temperature above the glass softening point and melted. In the glass sealing process, a gas-tight glass seal is formed.

[0108] FIG. 3 further illustrates an alternative approach to manufacturing a glass encapsulant.

[0109] According to the embodiment of Figure 3, a pre-formed glass cylinder 4A is placed around the ceramic substrate 1, the metallization layer 2 and the rest of the sensor including the end of the wire 3 sintered thereto.

[0110] The sensor is then placed in a furnace together with the surrounding glass cylinder 4A, and the glass cylinder 4A is melted in the furnace.

[0111] If unsintered glass cylinders are used, the temperature profile in the furnace can include several stages in order to evaporate any organic additives that may be contained in the glass cylinders.

[0112] The molten glass is finally formed into the desired shape in a glass encapsulation process, after which it is cooled and hardened.

[0113] The last-mentioned method has the particular advantage of being low cost, simple and quick to implement. [Explanation of symbols]

[0114] 1. Ceramic substrate 2 Metallisierungsschicht 2A Adhesive layer (Haftschicht) 2B Gold layer (Goldschicht) 3 Conductor 4 Glass sealing body 4A Glass Cylinder

Claims

1. A sensor comprising a ceramic substrate (1) and two metallization layers (2) applied on opposite surfaces of said ceramic substrate (1), The two metallization layers (2) each have an adhesive layer (2A) applied directly onto the ceramic substrate (1) and further each have a gold layer (2B) applied onto the respective adhesive layer (2A). Sensor.

2. The adhesive layer (2A) is a copper layer (2A), The sensor of claim 1.

3. The ceramic substrate (1) comprises a thermistor ceramic, in particular an NTC ceramic; 3. The sensor according to claim 1 or 2.

4. The ceramic substrate (1) comprises a ceramic having a perovskite structure. The sensor according to any one of claims 1 to 3.

5. The metallization layer (2) is a sputtering layer. A sensor according to any one of claims 1 to 4.

6. The adhesive layer (2A) has a layer thickness of at most 200 nm, preferably at most 100 nm; A sensor according to any one of claims 1 to 5.

7. The gold layer (2B) has a thickness of at most 1000 nm, preferably at most 500 nm; A sensor according to any one of claims 1 to 6.

8. the sensor is a temperature sensor; A sensor according to any one of claims 1 to 7.

9. The sensor has unlimited functionality at temperatures up to 600°C. A sensor according to any one of claims 1 to 8.

10. A conducting wire (3) is sintered to make direct electrical contact with the gold layer (2B). A sensor according to any one of claims 1 to 9.

11. The ceramic substrate (1) and the metallization layer (2) are surrounded by a glass seal (4). A sensor according to any one of claims 1 to 10.

12. 1. A method of manufacturing a sensor, comprising: In a first step, adhesive layers (2A) are applied to two opposing surfaces of a ceramic substrate (1), respectively; In a second step, two gold layers (2B) are applied onto each of the adhesive layers (2A), method.

13. The adhesion layer (2A) and the gold layer (2B) are applied by sputtering.

13. The method of claim 12.

14. The second step is performed after the first step.

14. The method according to claim 12 or 13.

15. In a third step, a conducting wire is sintered to make direct electrical contact with the gold layer (2B).

15. The method of any one of claims 12 to 14.

16. In a further step, a glass seal (4) is formed around the remaining sensor.

16. The method of any one of claims 12 to 15.

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