Sensor assembly for a resistance temperature sensor element and a resistance temperature sensor element

Abstract

The present invention relates to a sensor assembly (1) for a resistance temperature sensor element (3) and a resistance temperature sensor element (3) comprising the sensor assembly (1). In order to reduce the risk of damage to the bond between a measuring structure (7) and a substrate (5), a sensor assembly (1) is provided, comprising a multilayer substrate (5) made of a plurality of layers (13, 17) and a measuring structure (7) arranged on the multilayer substrate (5), wherein the multilayer substrate (5) comprises at least one layer (13) mainly comprising a first material (15), the first material (15) being at least one of aluminum oxide and yttrium aluminum garnet, and at least one layer (17) mainly comprising a stable second material (19), the stable second material (19) being at least one of stable zirconium dioxide and stable hafnium dioxide, the stable second material (19) being stabilized by comprising an oxide of an element having a valence different from 4, the at least one layer (13) and the at least one layer (17) being arranged one above the other, and the thermal expansion coefficients (CTE) of the plurality of layers (13, 17) deviating from the thermal expansion coefficient of the measuring structure (7) by less than 5%.

Description

Technical Field

[0001] The present invention relates to a sensor assembly for a resistance temperature sensor element and a resistance temperature sensor element. Background Art

[0002] Sensor assemblies for resistive temperature sensor elements are known in the art. These sensor assemblies include a measuring structure, specifically a resistive element. This measuring structure is typically made of platinum. Changes in temperature cause a change in the resistance of the measuring structure. This resistance can be measured, and the corresponding temperature of the element can be calculated. The measuring structure is typically supported by a substrate.

[0003] The structural integrity of known sensor assemblies for resistance temperature sensor elements during their lifetime is critical. In particular, large temperature variations can degrade the structural integrity of the assembly and lead to failure of the assembly and the resistance thermometer. Summary of the Invention

[0004] It is therefore an object of the present invention to provide a sensor assembly for a resistive temperature sensor element that maintains its structural integrity over a large number of cycles of temperature changes.

[0005] For the sensor component according to the present invention, this object is achieved by a sensor component for a resistive temperature sensor element, the sensor component comprising a substrate and a measuring structure arranged on the substrate, wherein the substrate comprises at least one first material, the first material being at least one of aluminum oxide, spinel (magnesium aluminate) and yttrium aluminum garnet, at least one stable second material, the stable second material being at least one of stable zirconium dioxide and stable hafnium dioxide, the stable second material being stabilized by containing an oxide of an element with a valence different from four, wherein the deviation of the thermal expansion coefficient of the substrate from the thermal expansion coefficient of the measuring structure is less than 5%.

[0006] With the resistance temperature sensor element according to the invention, this object is achieved in that a resistance thermometer comprises at least one sensor component according to the invention.

[0007] Since the thermal expansion coefficients of the substrate and the measurement structure do not differ from each other by more than 5%, the thermal expansion coefficients are considered to be matched.

[0008] This matching is important because, in the case of a CTE mismatch, temperature changes can cause different volume changes in the substrate and the measurement structure. This leads to stress effects on the measurement structure. This can cause changes in resistance and the temperature coefficient of resistance. Furthermore, the measurement structure may undergo geometric changes. One effect can be hysteresis in resistance and the temperature coefficient of resistance with temperature cycling. Overall, the bond between the measurement structure and the substrate can be damaged. The measurement structure may even be destroyed.

[0009] Due to the stabilizing second material, the present invention allows a good matching of the thermal expansion coefficients even within a wide temperature range. This is explained below.

[0010] The measuring structure is typically made of platinum. However, it is not limited to platinum. The CTE of platinum is 9.5 ppm / K. It is known that the average CTE of zirconium dioxide is 10.5 ppm / K. The CTE of aluminum oxide is approximately 7.8 ppm / K, and it can be assumed that mixing these materials can achieve the CTE of platinum.

[0011] However, pure zirconium dioxide has a CTE of 10.3 ppm / K at room temperature only in certain directions of its crystal structure. The average CTE of pure zirconium dioxide at room temperature is only about 8.8 ppm / K.

[0012] Therefore, mixing pure zirconium dioxide with aluminum oxide may not produce a substrate with a CTE that matches platinum. The same problem exists for pure hafnium dioxide.

[0013] At temperatures above 1200°C, the average CTE of pure zirconium dioxide is 10.5 ppm / K, as the material generally has a tetragonal crystal structure. Above 2400°C, the crystal structure becomes cubic. However, this is not useful for measurements below 1200°C.

[0014] The solution of the present invention overcomes this problem by using stabilized zirconium dioxide or stabilized hafnium dioxide.

[0015] To obtain a stabilizing material, pure zirconium dioxide or pure hafnium dioxide is mixed with a stabilizing material. The stabilizing material is preferably an oxide of an element whose valence differs from that of zirconium. The valence of zirconium is 4.

[0016] Therefore, elements with a valence of 3 or 5 are preferred for stabilizing the material. Mixing pure zirconium dioxide with such oxides results in a stable material with a stable cubic and / or tetragonal crystal structure even at room temperature. This structure allows the stabilized material to have a uniform CTE. The same applies to hafnium dioxide.

[0017] In summary, the sensor assembly according to the present invention allows a fine-tuned matching of the thermal expansion coefficients of the measurement structure and the substrate, thereby achieving a reliable sensor assembly.

[0018] The above adjustments can even exist over a wide applicable temperature range, for example from -200°C to temperatures above 1200°C.

[0019] In the following, further developments of the invention are described. The additional developments can be combined independently of one another, depending on whether the particular advantages of a particular development are required in a particular application.

[0020] According to a first advantageous refinement, the second material can be stabilized by a stabilizing material that is an oxide of at least one of the following elements: yttrium, cerium, tantalum, and niobium. However, other elements can also be used. The use of materials other than oxides as stabilizing materials is not excluded.

[0021] The stable second material preferably has a substantially tetragonal or cubic crystal structure. Thus, a stable and uniform CTE can be obtained even over a wide temperature range.

[0022] According to another advantageous improvement, the substrate may further include an insulating layer between the measurement structure and the remaining substrate. Due to the stable material in the second material, the substrate can be at least partially conductive. In particular, the material may have non-negligible ionic conductivity. This ionic conductivity may be caused by valence differences that produce voids or excess oxygen. However, an insulating layer between the measurement structure and the remaining substrate can overcome this problem. The insulating layer may preferably mainly contain at least one of aluminum oxide, spinel (magnesium aluminate) and magnesium titanate. However, the insulating layer can also be made of other materials.

[0023] The measuring structure is preferably made essentially of platinum, in particular of pure platinum. A measuring structure made of platinum provides reliable temperature-dependent resistance measurement. Alternatively, the measuring structure can be made of, for example, a platinum alloy, nickel, a nickel alloy, iridium or an iridium alloy.

[0024] According to a further advantageous refinement, the substrate is a multilayer substrate made of a plurality of layers, at least one layer predominantly comprising the first material and at least one layer predominantly comprising the stable second material, wherein the at least one layer predominantly comprising the first material and the at least one layer predominantly comprising the stable second material are arranged one above the other, and wherein the thermal expansion coefficients of the plurality of layers deviate from the thermal expansion coefficient of the measuring structure by less than 5%.

[0025] Preferably, the CTE of the layer comprising primarily the first material is different from the CTE of the layer comprising primarily the stable second material, wherein the CTE of the plurality of layers is adjusted by the number and / or thickness of the layers comprising the first and stable second materials, respectively.

[0026] In order to obtain a homogeneous substrate, the layers comprising the first material and the stabilizing second material are preferably arranged on top of each other in an alternating manner.The total number of layers may be between 5 and 25 layers.

[0027] In order to improve the matching accuracy between the CTE of the substrate and the measurement structure made of platinum, the sum of the thicknesses of the layers comprising the stabilizing second material is preferably approximately 150% of the sum of the thicknesses of the layers comprising the first material.

[0028] The thickness of each layer is preferably between 10 and 100 μm, more preferably between 20 and 70 μm.

[0029] The first material may comprise alumina, spinel, yttrium aluminum garnet, or a mixture of two or three of these materials. The term alumina refers to a material described by the general molecular formula Al2O3. The term spinel refers to a material described by the general molecular formula MgAl2O4. The term yttrium aluminum garnet (referred to as "YAG") refers to the material Y3Al2[AlO4]3, which is described by the general molecular formula Y3Al5O 12 describe.

[0030] The term zirconium dioxide is the main component of the stabilizing second material and refers to ZrO2. The term hafnium dioxide refers to HfO2.

[0031] In an alternative to a multi-layer substrate, the substrate may have a grain structure formed by a mixture of grains made of a first material and grains made of a stable second material.

[0032] The grain ratio of the two materials can be adjusted to define the CTE of the substrate.

[0033] The substrate can preferably be produced by tape casting. The material is brought onto a carrier, and a cutting tool is moved along the material, shaping it for the substrate. If the substrate is made of a granular structure, a material containing a mixture of granules of two materials is used and formed into a single layer. If a multilayer substrate is desired, a first material and a second, stable material are tape cast one on top of the other in repeated cycles.

[0034] The resistance temperature sensor element according to the invention can be part of a resistance thermometer.

[0035] Hereinafter, the present invention and its improvements are described in more detail using exemplary embodiments and with reference to the accompanying drawings. As mentioned above, the various features shown in the embodiments can be used independently of each other in specific applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In the following drawings, elements having the same function and / or the same structure will be denoted by the same reference numerals.

[0037] In the attached figure:

[0038] Figure 1 A preferred embodiment of a sensor assembly according to the present invention is shown in cross-section;

[0039] Figure 2 Similar to Figure 1 : a view showing a resistive temperature sensor element comprising a sensor assembly according to the present invention; and

[0040] Figure 3 A second preferred embodiment of a sensor assembly according to the invention is shown in cross-section. DETAILED DESCRIPTION

[0041] The sensor assembly 1 according to the preferred embodiment is Figure 1 The sensor assembly 1 can be used with a resistance temperature sensor element 3, which is Figure 2 Shown in.

[0042] The sensor assembly 1 comprises a substrate 4 and a measurement structure 7 arranged on the substrate 4 .

[0043] The substrate 4 of the first embodiment is a multilayer substrate 5 composed of a plurality of layers.

[0044] The resistance temperature sensor element 3 may further include additional elements, Figure 2 In addition to the assembly 1 , the resistance temperature sensor element 3 can be provided with leads 9 which are electrically connected to the measuring structure 7 .

[0045] Furthermore, the resistance temperature sensor element 3 may comprise a covering layer 11, which covers at least the measuring structure 7. The covering layer 11 may also cover at least parts of the leads 9. The covering layer 11 may be made of one or more glass materials.

[0046] Hereinafter, the multilayer substrate 5 is described. The multilayer substrate 5 includes at least one layer 13 mainly made of a first material 15. The first material 15 is at least one of aluminum oxide and yttrium aluminum garnet. Therefore, the first material 15 may also be a mixture of the two materials.

[0047] The multi-layer substrate 5 further comprises at least one layer 17, which is mainly made of a stable second material 19. The stable second material 19 may include at least one of zirconium dioxide and hafnium dioxide.

[0048] To form the stabilized second material 19, at least one stabilizing material 21 is added to the original second material 18. The original second material 18 is preferably at least one of zirconium dioxide and hafnium dioxide. As a result of the addition of the stabilizing material 21 to the second material 18, the stabilized second material 19 is formed.

[0049] The stable second material 19 may have a stable crystal structure, particularly within a desired temperature range. Figure 1 These circles will only show that the stabilizing material 21 is dissolved in the original second material 18, but do not represent any structure.

[0050] The stabilizing material 21 is preferably an oxide of an element having a valence different from 4, in particular 3 or 5. For the original second material 18 , the valence is four.

[0051] The layers 13 and 17 are arranged one above the other, preferably in an alternating manner.

[0052] The stabilizing material 21 is preferably an oxide of yttrium, cerium or niobium.

[0053] The stabilizing material 21 preferably stabilizes the tetragonal and / or cubic crystal structure in the second material 19. In particular, the stabilizing material 21 stabilizes the tetragonal and / or cubic crystal structure of zirconium dioxide and / or hafnium dioxide.

[0054] The total number of layers 13 and 17 is preferably between 5 and 25. Of course, the multilayer substrate 5 may also contain fewer than 5 layers or more than 25 layers.

[0055] The layers 13 and 17 may have different thicknesses. Preferably, the thickness 23 of the layer 13 is less than the thickness 25 of the layer 17.

[0056] Preferably, all layers 13 comprising the first material 15 each have the same thickness 23, and the layers 17 comprising the stabilizing second material 19 each have the same thickness 25. However, this is not mandatory.

[0057] Not all layers 13 comprising the first material 15 necessarily have the same thickness 23. Likewise, not all layers 17 comprising the stabilizing second material 19 necessarily have the same thickness 25.

[0058] In a preferred embodiment, thicknesses 23 and 25 are between 30 and 80 μm.

[0059] The measurement structure 7 has a coefficient of thermal expansion (CTE) 27. The multilayer substrate 5 has a CTE 29. The coefficients of thermal expansion (CTE) 27 and 29 are matched such that they differ from each other by less than 5%.

[0060] The measuring structure 7 is preferably made of platinum. The CTE of platinum is 9.5 ppm / K. Therefore, the CTE 29 of the substrate 4 (here the multilayer substrate 5 ) preferably deviates from the CTE of platinum by no more than 5% and is preferably between 9.025 and 9.975 ppm / K.

[0061] More preferably, the CTE of the substrate 4 / multilayer substrate 5 deviates from the CTE of the measurement structure 7 by less than 2.5%.

[0062] The CTE 29 of the substrate 4 / multilayer substrate 5 is adjusted by the number and thickness 23 and 25 of the layers 13 and 17. The materials 15 and 19 forming the layers 13 and 17 each have a different CTE.

[0063] Preferably, the CTE 28 of the first material 15 is approximately 7.8 ppm / K, and the CTE 30 of the stabilizing second material 19 is approximately 10.5 ppm / K.

[0064] Depending on the number of layers 13 and 17 and the thicknesses 23 and 25, an overall CTE of approximately platinum, ie 9.5 ppm / K, can be obtained.

[0065] This good match is due to the stabilizing material 21 in the stabilizing second material 19 stabilizing the crystal structure of the material, such that the CTE of the stabilizing second material 19 is approximately 10.5 ppm / K in all crystal directions and within the desired temperature range.

[0066] By way of example only, the sum of thicknesses 25 of layers 17 may be approximately 150% of the sum of thicknesses 23 of layers 13 .

[0067] Since the stabilizing material 21 in the stabilizing second material 19 may result in an electrically conductive multilayer substrate 5 , an additional insulating layer 31 may be present between the measurement structure 7 and the remaining layers 13 and 17 of the multilayer substrate 5 .

[0068] The insulating layer 31 electrically insulates the measurement structure 7 from the conductive layers of the remaining substrate 4 / multilayer substrate 5. The insulating layer 31 preferably comprises aluminum oxide (Al2O3), spinel (MgAl2O4), or magnesium titanate (MgTiO3), or a mixture of two or three of these materials. The material of the insulating layer 31 is not limited to the above examples.

[0069] Figure 3 Another preferred embodiment of the present invention is shown. For the sake of brevity, only the differences from the first embodiment are described in detail.

[0070] Here, the substrate 4 is not a multilayer substrate 5, but comprises a grain structure 33. The grain structure 33 comprises grains 35 made mainly of the first material 15 and grains 37 made mainly of the stabilizing second material 19. However, it is not excluded that the substrate 4 comprises additional materials.

[0071] exist Figure 3 In the figure, for explanation reasons, only some of the grains 35 and 37 are shown schematically. The grains shown do not represent any size or shape or number distribution.

[0072] The CTE 29 of the substrate 4 can be defined by adjusting the ratio of the grains 35 to the grains 37 .

[0073] As in the assembly of the first embodiment, an additional insulating layer 31 is present between the substrate 4 and the measurement structure 7 .

[0074] Reference Signs List

[0075] 1 Sensor assembly

[0076] 3 Resistance temperature sensor elements

[0077] 4 substrate

[0078] 5 Multilayer substrate

[0079] 7 Measurement structure

[0080] 9 leads

[0081] 11 Covering

[0082] 13 Layer comprising a first material

[0083] 15 First Material

[0084] 17 Layer comprising a stabilizing second material

[0085] 18 Original Second Material

[0086] 19 Stabilize the second material

[0087] 21 Stabilizing Materials

[0088] 23 Thickness of the layer comprising the first material

[0089] 25 Thickness of the layer comprising the stabilizing second material

[0090] 27 Measuring the thermal expansion coefficient of a structure

[0091] 28 Coefficient of thermal expansion of the layer comprising the first material

[0092] 29 Thermal expansion coefficient of substrate

[0093] 30 Coefficient of thermal expansion of the layer comprising the stabilizing second material

[0094] 31 Insulation layer

[0095] 33 Grain structure

[0096] 35. Grains containing a first material

[0097] 37 Grains containing a stabilizing second material

Claims

1. A sensor assembly (1) for a resistance temperature sensor element (3), the sensor assembly (1) comprising a substrate (4) and a measuring structure (7) arranged on the substrate (4), wherein the substrate (4) comprises: - at least one first material (15), the first material (15) being at least one of aluminum oxide, magnesium aluminate and yttrium aluminum garnet, at least one stable second material (19), the stable second material (19) being at least one of stable zirconium dioxide and stable hafnium dioxide, the stable second material (19) being stabilized by the inclusion of an oxide of at least cerium having a valence different from four, The deviation between the thermal expansion coefficient (29) of the substrate (4) and the thermal expansion coefficient (27) of the measuring structure (7) is less than 5%.

2. The sensor assembly (1) according to claim 1, wherein The stabilizing second material (19) is stabilized by comprising an oxide of a trivalent or pentavalent element.

3. The sensor assembly (1) according to claim 2, wherein The stabilizing second material (19) is further stabilized by comprising an oxide of at least one of the following elements: yttrium, niobium, and tantalum.

4. The sensor assembly (1) according to claim 1, wherein The stable second material (19) has a tetragonal or cubic crystal structure.

5. The sensor assembly (1) according to claim 4, wherein The substrate (4) further comprises an insulating layer (31) located between the measurement structure (7) and the rest of the substrate (4).

6. The sensor assembly (1) according to claim 5, wherein The insulating layer (31) comprises at least one of aluminum oxide, magnesium aluminate or magnesium titanate.

7. The sensor assembly (1) according to claim 6, wherein The measuring structure (7) is made of at least one of platinum, platinum alloy, nickel, nickel alloy, iridium, and iridium alloy.

8. The sensor assembly (1) according to claim 7, wherein The substrate (4) has a grain structure formed by a mixture of grains (35) made of a first material (15) and grains (37) made of a stable second material (19).

9. The sensor assembly (1) according to claim 7, wherein The substrate (4) is a multilayer substrate (5) made of a plurality of layers (13, 17), at least one layer (13) comprising a first material (15) and at least one layer (17) comprising a stable second material (19), wherein the at least one layer (13) comprising the first material (15) and the at least one layer (17) comprising the stable second material (19) are arranged one above the other, and wherein the thermal expansion coefficients (29) of the plurality of layers (13, 17) deviate from the thermal expansion coefficient (27) of the measurement structure (7) by less than 5%.

10. The sensor assembly (1) according to claim 9, wherein The thermal expansion coefficient (28) of the layer (13) comprising the first material (15) is different from the thermal expansion coefficient (30) of the layer (17) comprising the stabilizing second material (19), and the thermal expansion coefficient (29) of the plurality of layers (13, 17) is adjusted by the number and thickness (23, 25) of the layers (13, 17).

11. The sensor assembly (1) according to claim 10, wherein The layers (13) comprising the first material (15) and the layers (17) comprising the stabilizing second material (19) are arranged in an alternating manner.

12. The sensor assembly (1) according to claim 11, wherein The total number of layers (13) comprising the first material (15) and layers (17) comprising the stabilizing second material (19) is between 5 and 25 layers.

13. The sensor assembly (1) according to claim 12, wherein The sum of the thicknesses (25) of the layers (17) comprising the stabilizing second material (19) is 150% of the sum of the thicknesses (23) of the layers (13) comprising the first material (15).

14. The sensor assembly (1) according to claim 13, wherein The thickness (23, 25) of each layer (13) comprising the first material (15) and each layer (17) comprising the stabilizing second material (19) is between 10 μm and 100 μm.

15. A resistance temperature sensor element (3) comprising a sensor assembly (1) according to claim 14.

Images