DE19918003A1 - Multi-layer electrical temperature sensor - Google Patents

Abstract

An electrical temperature sensor has a platinum-containing resistance layer as a measuring resistor, which is applied to the electrically insulating surface of a ceramic substrate; To protect against contamination or damage, the resistance layer is provided on its side facing away from the ceramic substrate with an intermediate layer made of aluminum oxide or magnesium oxide as a diffusion barrier layer. DOLLAR A In a first embodiment, an additional platinum layer is applied to the intermediate layer, which protects the measuring resistor against stray silicon ions, which can escape, for example, from a passivation layer made of glass. DOLLAR A In a second embodiment, a cover layer as a passivation layer made of glass is applied to the intermediate layer. DOLLAR A The high temperature resistance of the temperature sensor has proven to be advantageous.

Description

The invention relates to an electrical temperature sensor with a platinum Wi the resistive layer as a measuring resistor provided with electrical connections on an elec trically insulating surface of a ceramic substrate, wherein the resistance layer to Protection against contamination or damage is provided with a multi-layer; represents Furthermore, the invention relates to an electrical temperature in a further embodiment ratur sensor, which also has an electrically insulating intermediate layer and an outer deck has layer.

According to EP 0 327 535 B1, column 2, lines 20-25, a multiple layer is one of several Layers of existing protective coating of a platinum thin-film resistance thermometer draws; such a multilayer can, for example according to lines 26-31, a dielectric cal layer as an electrically insulating intermediate layer and an outer cover layer exhibit.

EP 0 327 535 B1 describes a temperature sensor with a thin-film platinum resistor known; the temperature measuring resistor is made of platinum on a surface of an elec trically insulating substrate is formed, wherein the resistance element with a dielectric Protective layer is covered, which preferably consists of silicon dioxide and a thickness in Has a range of 2000-4000 angstroms. A diffusion barrier is also used as a cover layer layer provided by the precipitation of titanium in an oxygen atmosphere to form Titanium oxide is applied. This barrier layer has a thickness in the range of 6000-12000 Angstrom on. Even if the diffusion barrier layer prevents oxygen from entering the dielectric layer and thus an attack of released metal ions from the  Glass layer on the platinum layer largely prevented, it can be in extreme environmental conditions conditions nevertheless lead to an attack on the platinum layer, so that its physical Behavior as a temperature measuring element is disturbed.

Furthermore, there is an electrical measuring resistor for resistance thermometers and a method for producing such an electrical measuring resistor from US Pat. No. 4,050,052 or the corresponding DE 25 27 739 C3 known.

The object of the invention is to measure the resistance to external chemical or mechanical Protect attacks and, in particular, ensure that there is no contamination from the outer atmosphere into the measuring resistor.

The task is carried out for an electrical temperature sensor according to a first embodiment Form of the invention solved in that an intermediate layer as the Diffusion barrier layer is applied, with that facing away from the substrate surface An additional platinum layer is applied on the side of the resistance layer at a distance from it.

The long service life proves to be particularly advantageous, with a ratio at the same time moderately inexpensive manufacture is possible, so that the temperature sensor is also a mass product is suitable.

The thickness of the intermediate layer is preferably in the range from 0.2 μm to 20 μm. The Ge total height of the temperature sensor is in the range of 01 to 1 mm, while its base area surface a length in the range of 2 to 15 mm and a width in the range of 0.5 to 6 mm points. The temperature sensor carrier with a mounted chip element has the following geometric Dimensions: total height of the module in the range of 0.3 to 3 mm, the base area being Has a length of 4 to 80 mm and a width in the range of 2 to 12 mm.

In a preferred embodiment of the first embodiment, the additional platinum is layer covered by a passivation layer. It is preferably located between the additional platinum layer and the resistance layer at least part of the passive layer.

Such an arrangement has the advantage that the resistive layer through the passive layer is protected from the outside and electrically insulated, the intermediate layer being a Insulation layer between the resistance layer and platinum layer.  

In a further advantageous embodiment of the first embodiment, the additional Platinum layer on a spacing opposite the measuring resistor applied to the substrate; the additional platinum layer preferably covers one on the Carrier substrate applied lead to the measuring resistor; continues to be advantageous The additional platinum layer through an insulation layer from the feed line galvanically isolated; it proves to be advantageous that the platinum layer is electrically negative can be biased against the resistance layer or the supply line and except which is covered by additional coverage.

To protect against undesired bypass formation between the measuring resistor contacts, caused by the condensation of electrically conductive particles (soot), it has proven to be proven particularly advantageous, a gap between the measuring resistor and the opposite the carrier substrate on all sides with an electrically insulating material - preferably sealing glass - to seal.

The task is carried out for an electrical temperature sensor according to a second embodiment form of the invention with a multiple layer, which additionally an electrically insulating intermediate layer and has an outer cover layer, solved in that the intermediate layer is formed as a diffusion barrier layer, the aluminum oxide, magnesium oxide or tantalum oxide or has a mixture of two materials of these oxides or a multilayer system, wherein the cover layer is formed as a passivation layer made of glass.

The simple and inexpensive construction proves to be particularly advantageous, so that it temperature sensor according to the invention can also be produced as a mass product.

In an advantageous embodiment of the second embodiment, the cover layer consists of a mixture of silicon oxide, barium oxide and aluminum oxide, the weight ratio of the three oxides is in the range of 35:50:15. The actual ceramic substrate exists preferably made of aluminum oxide.

The thickness of the intermediate layer is in the range of 0.2 µm to 20 µm, while the outer Top layer has a thickness in the range of 10 to 30 microns; the thickness of the entire load Layering (as a multiple layer) is in the range of 10.5 to 50 µm.

The total height of a temperature sensor according to the second embodiment lies in the loading range from 0.1 to 1 mm. Its base has a length in the range of 2 to 15 mm and  a width in the range of 0.5 to 6 mm. The geometry of the second embodiment The temperature sensor on the carrier (module) is built in the same areas for height, length and width as already described for the first embodiment has been.

The miniaturized construction also proves to be advantageous, so that the temperature Sensor can also be used directly in the exhaust gas for automotive applications up to 1100 ° C, whereby due to the miniaturization, a redundancy circuit of several temperature sensors is possible, so that the reliability of the measuring or control system is significantly improved; moreover, the thermal behavior is improved.

Furthermore, in a preferred embodiment of the second embodiment of the invention on the side of the resistance layer facing away from the substrate surface outside the intermediate layer an additional platinum layer is applied, with the difference between the additional Platinum layer and the resistance layer at least a part of the passivation layer det; the additional platinum layer is preferably between the passivation layer and the intermediate layer. In a preferred embodiment, the additional platinum layer can be encased by the passivation layer.

Furthermore, it is also possible to remove the additional platinum layer from that of the resistance layer to arrange the opposite side of the passivation layer. It is an advantage that the additional platinum layer the resistance layer in the sense of a "sacrificial electrode" against atmo protects spherical poisoning.

In a further embodiment, the additional platinum layer is electrically connected conclude; it is possible to coat the platinum layer with at least one bias the measuring resistor electrically negative. It proves to be advantageous in that the platinum poisons present as positive ions in extreme environmental conditions (Si and metal ions) are drawn to the negative platinum layer.

In a preferred embodiment according to both the first and the second embodiment of the invention, the ceramic substrate consists of Al ₂ O ₃ . Furthermore, according to both embodiments, the intermediate layer also preferably consists of Al ₂ O ₃ , MgO or a mixture of both materials, the weight fraction of Al ₂ O _{3 being} in the range from 20% to 70%; it is also possible to build up the intermediate layer from a layer system with a layer sequence of at least two layers, each of which is formed from at least one oxide from the group Al ₂ O ₃ , MgO, Ta ₂ O ₅ ; at least one layer can be formed from two of the oxides mentioned, a physical mixture of oxides preferably being used; however, it is also possible to use mixed oxides.

In a further embodiment of the invention, the group of oxides consisting of Al ₂ O ₃ , MgO, Ta ₂ O ₅ can be expanded to include hafnium oxide.

The intermediate layer preferably consists of a single-layer system according to Table 1 with the materials specified in items 1 to 6 or of a multi-layer system according to Table 2, which has at least two layers 1 and 2 , with layer 2 each having a further layer or more Can connect layers. The different layer materials are designated in the individual positions or lines with numbers 7 to 30 .

Table 1

Single-layer system

Table 2

Multilayer system

The use of these materials proves to be particularly advantageous since these metal oxides are stable even at high temperatures. The intermediate layer is preferably produced by means of PVD, IAD, IBAD, PAD or magnetron sputtering processes, where PVD means: Physi cal Vapor Deposition,
IAD: Ion Assisted Deposition,
IBAD: Ion Beam Assisted Deposition,
PAD: Plasma Assisted Deposition.

Furthermore, the passivation layer according to both embodiments has a mixture of SiO ₂ , BaO and Al ₂ O ₃ , the weight fraction of SiO _{2 being} in the range from 20% to 50%.

It proves to be advantageous that this mixture has a high insulation resistance having.

The subject matter of the invention is explained in more detail below with reference to FIGS. 1 to 5.

Fig. 1 shows a measuring resistor with a resistance layer on a ceramic substrate, the resistance layer being covered by a diffusion barrier layer and a passivation layer;

Fig. 2 shows a similar embodiment as Figure 1, wherein an additional platinum layer is provided on the diffusion barrier layer at a distance from the resistance layer. both fi gures are shown in cross section;

Fig. 3 shows a similar embodiment as Fig. 1, wherein an additional platinum layer is applied to the passivation layer at a distance from the resistance layer.

FIG. 4a shows a prepared for application of the sensor (with additional platinum layer) carrier substrate;

FIG. 4b shows a top view of a fully assembled temperature sensor module of FIG. 2;

Fig. 5 shows a cross section along the line AA of Fig. 4b.

Referring to FIG. 1 there is serving as the measuring resistor resistive layer 1 on a planar surface of a ceramic substrate 2 which is made of alumina. The resistance layer 1 is in the form of a meander with terminal contact surfaces, as is known for example from DE 40 26 061 C1. The resistance layer 1 is seen on its side facing away from the substrate with a diffusion barrier layer as an intermediate layer 10 , which in turn is covered with a passivation layer 3 made of glass. Due to the glass passivation layer, the sensitive structure of the platinum measuring resistor 1 is effectively protected against atmospheric poisoning of the environment. The configuration of a multilayer structure holds the platinum very harmful for the resistance layer 1 Siliziu mionen back which platinum contaminate very rapidly at high temperatures due to physical diffusion and thus dramatically affect the temperature / resistance function of the platinum alloy resulting, so that the high temperature stability of the Resistance layer 1 for temperature measurements is no longer given. Due to the first thermodynamically stable and pure aluminum oxide layer as the intermediate layer 10 or diffusion barrier, the access of silicon ions and other substances or ions poisoning the platinum is prevented, and thus the meandering resistance layer is protected from poisoning. The application of the intermediate layer 10 can be achieved by physical vapor deposition. The aluminum oxide layer is applied stoichiometrically in such a way that a very stable layer of pure aluminum oxide (Al ₂ O ₃ ) covers the platinum structure of the resistance layer 1 . The passivation layer 3 made of glass, which has silicon ions, thus receives no contact whatsoever with the active platinum resistance layer, and a sealing of the resistance layer 1 as mechanical protection against external contaminating elements is thus ensured.

According to FIG. 2, the resistance layer 1 made of platinum serving as measuring resistor is located on a flat surface of a substrate 2 made of aluminum oxide ceramic (Al ₂ O ₃ ). It is preferably formed in the form of a meander with connection contact fields, as is known for example from DE 40 26 061 C1 already mentioned. The resistance layer 1 is surrounded on the side facing away from the substrate 2 by a diffusion barrier layer as an intermediate layer 10 , which in turn is covered by an outer cover layer as a passivation layer 3 made of glass; between the passivation layer 3 and the diffusion barrier layer as an intermediate layer 10 , an additional platinum layer 4 is applied in a parallel plane to the substrate level at a distance from the resistance layer 1 , which from the passivation layer 3 of glass keep any silicon ions escaping from the measuring resistance layer 1 of platinum by absorbing the silicon ions. It is therefore possible to provide protection against stray silicon ions from dissolving silicon oxide compounds of the passivation layer, even in an aggressive high-temperature environment, the otherwise occurring change in the resistance temperature curve of the measuring resistor being prevented by the additional platinum layer 4 in front of it. In this way, the high temperature resistance of the resistance layer 1 made of platinum and thus the entire temperature sensor is maintained for a long measurement period.

FIG. 3 shows a structure similar to FIG. 1, but with an additional platinum layer 4 being provided on the outside on the outer surface of the passivation layer 3 ; This platinum layer 4 is arranged at an equal distance from the actual resistance layer 1 electrically insulating on the outside of the passivation layer. 3 The additional platinum layer 4 protects the resistance layer 1 made of platinum in the sense of a "sacrificial electrode" against atmospheric poisoning. The additional platinum layer 4 is negatively biased with respect to the resistance layer 1 , so that poisoning substances or ions are sucked in and the resistance layer 1 is protected.

According to Fig. 4a, 4b and 5, it is also possible to use the additional platinum layer 4 as the electrode terminal-contact field and they ge by means of an external terminal negative bias genüber the platinum-measuring resistor or resistance layer 1. Such a negatively biased platinum layer 4 has the essential advantage that the resistance layer 1 poisoning ions are sucked out beforehand.

Referring to FIG. 4b, and 5 is the additional platinum layer 4 of the temperature sensor as a counter electrode (or polarizing electrode) with its outer surface on a Trä gersubstrat 12, fixed to the mechanical support and electrical connection of the temperature sensor is used; in addition to quick responsiveness, there is also some practical protection against mechanical damage to the temperature sensor; according to Fig. 4a, the external terminal contact pads 21, 22 over platinum conductor 23, 24 with low resistance on the surface of the carrier substrate 12 with terminal contact pads 25, 26 for contacting the terminal contacts of the resistive layer 1 (Fig. 5) connected. Connection contact 26 is connected to the designated point 15 of the feed line 24 with connection contact 25, wherein the non-visible part is shown in broken lines 15 °.

Furthermore, connection 22 is connected to supply line 27 for contacting the additional platinum layer 4 visible in cross section according to FIG. 5, supply line 27 being guided separately from connection contact 22 ; Terminal contact 22 is connected to the negative pole of a power supply, while terminal 21 is switched positive. The connection contact fields 25 , 26 for connecting the resistance layer 1 ( Fig. 4a, Fig. 5) are applied by means of sintered platinum conductive paste. Based on Fig. 5 it can be seen that the symbolic is applied in Fig. 4a to supply line 24 illustrated terminal connection pad 26 on the carrier substrate 12, which part is the feed line 24 provided with reference number 15. Can also be seen in cross-section, in that supply line 15 (or 24) surrounded by an insulation layer 14, the tung Zulei 15 relative to the electrically insulated in cross-section according to Fig. 5 visible additional platinum layer 4. The additional platinum layer 4 is surrounded on the side facing away from the carrier substrate 12 by a passivation layer 3 , which preferably consists of glass. The passivation layer 3 is mechanically firmly connected to the intermediate layer 10 as a diffusion barrier layer, in which the resistance layer 1 designed as a meander is also embedded, corresponding to FIG. 3. As can be seen from FIG. 5, the resistance measuring layer 1 arranged between the ceramic substrates 2 and 12 is well protected against external mechanical damage.

A gap occurring between measuring resistor 1 and carrier substrate 12 is sealed according to FIGS . 4b and 5 by means of sealing material 28 - preferably sealing glass - in order to prevent the already mentioned bypass formation between the measuring resistor contacts; since the connection contact fields are sealed with.

A temperature sensor according to FIG. 2 is produced in the following process steps:

• 1. Application of a platinum resistance layer on ceramic substrate 2 by means of PVD (Physical Vapor Deposition), IAD (Ion Assisted Deposition), magnetron sputtering or resinate printing.
• 2. Applying a photoresist mask (coating in the spin coating, lacquer drying, UV exposure, Develop and harden).
• 3. Transfer the resist mask to the platinum resistance layer using ion etching areas not covered by the photoresist mask.
• 4. Remove the photoresist mask with NaOH or plasma strips.
• 5. Application of the Al ₂ O ₃ barrier layer using magnetron sputtering or plasma spraying. The coating of the contact surfaces is prevented by using shading masks.
• 6. Application of the additional platinum layer and the contact pads by means of screen printing or PVD or sputtering using shading masks.
• 7. Setting the resistance value of the resistance layer by means of laser trimming.
• 8. Application of the passivation layer by means of screen printing.
• 9. Separate the substrate benefit to individual resistance sensors by sawing.
• 10. Application of the temperature sensor to the carrier substrate with the screen-printed structure structures made of platinum conductive paste by sintering.

Claims (25)

1. Electrical temperature sensor with a platinum resistance layer ( 1 ) as a measuring resistor provided with electrical connections on an electrically insulating surface of a ceramic substrate ( 2 ), the resistance layer ( 1 ) for protection against contamination or damage with a multiple layer is provided, as characterized by, that an intermediate layer (10) is applied as a diffusion barrier layer on the resistive layer (1), wherein on the substrate surface side facing away from the opposing resistive layer (1) at a distance therefrom, an additional platinum layer ( 4 ) is applied. 2. Temperature sensor according to claim 1, characterized in that the thickness of the inter mediate layer ( 10 ) is in the range of 0.2 microns to 20 microns. 3. Temperature sensor according to claim 1 or 2, characterized in that the additional platinum layer ( 4 ) is covered by a passivation layer ( 3 ). 4. Temperature sensor according to claim 3, characterized in that there is at least part of the passivation layer ( 3 ) between the additional platinum layer ( 4 ) and the resistance layer ( 1 ). 5. Temperature sensor according to one of claims 1 to 4, characterized in that the additional platinum layer ( 4 ) on a at a distance from the measuring resistor ( 1 ) opposite carrier substrate ( 12 ) is applied. 6. Temperature sensor according to claim 5, characterized in that the additional platinum layer ( 4 ) on the carrier substrate ( 12 ) applied supply line ( 15 ) to Meßwi resistance ( 1 ) covers. 7. Temperature sensor according to claim 6, characterized in that the additional platinum layer ( 4 ) is electrically isolated from the supply line ( 15 ) by an insulation layer ( 14 ). 8. Electrical temperature sensor with a platinum resistance layer ( 1 ) as a measuring resistor provided with electrical connections on an electrically insulating surface of a ceramic substrate ( 2 ), the resistance layer ( 1 ) for protection against contamination or damage with a multiple layer is provided, the egg ne electrically insulating intermediate layer ( 10 ) and an outer cover layer, characterized in that the intermediate layer ( 10 ) is formed as a diffusion barrier layer, the aluminum oxide, magnesium oxide or tantalum oxide or a mixture of two materials of these oxides or a multilayer system has, wherein the cover layer is formed as a passivation layer ( 3 ) made of glass. 9. Temperature sensor according to claim 8, characterized in that the thickness of the inter mediate layer ( 10 ) is in the range from 0.2 µm to 20 µm, the thickness of the entire multilayer being a maximum of 50 µm. 10. Temperature sensor according to one of claims 1 to 4, 8, 9, characterized in that an additional platinum layer ( 4 ) is applied on the side of the resistance layer ( 1 ) facing away from the substrate surface, wherein there is at least a part of the passivation layer ( 3 ) between the additional platinum layer ( 4 ) and the resistance layer ( 1 ). 11. Temperature sensor according to one of claims 1 to 4, 8 to 10, characterized in that the additional platinum layer ( 4 ) between the passivation layer ( 3 ) and the intermediate layer ( 10 ) is arranged. 12. Temperature sensor according to claim 11, characterized in that the additional platinum layer ( 4 ) is encased by the passivation layer ( 3 ). 13. Temperature sensor according to claim 1 or 8, characterized in that the additional platinum layer ( 4 ) on the resistance layer ( 1 ) facing away from the passivation layer ( 3 ) is arranged. 14. Temperature sensor according to one of claims 1 to 13, characterized in that the additional platinum layer ( 4 ) is provided with an external electrical connection. 15. Temperature sensor according to one of claims 1 to 14, characterized in that the platinum layer ( 4 ) with respect to at least one connection ( 7 , 8 ) of the measuring resistor ( 1 ) is electrically negatively biased. 16. Temperature sensor according to claim 1 or 8, characterized in that the ceramic substrate ( 2 ) consists of Al ₂ O ₃ . 17. Temperature sensor according to claim 1 or 8, characterized in that the intermediate layer ( 10 ) consists of Al ₂ O ₃ . 18. Temperature sensor according to claim 1 or 8, characterized in that the intermediate layer ( 10 ) consists of MgO. 19. Temperature sensor according to claim 1 or 8, characterized in that the intermediate layer ( 10 ) consists of tantalum oxide. 20. Temperature sensor according to claim 1 or 8, characterized in that the intermediate layer ( 10 ) has a mixture of Al ₂ O ₃ and MgO, the weight fraction of Al ₂ O _{3 being} in the range from 20% to 70%. 21. Temperature sensor according to claim 1 or 8, characterized in that the intermediate layer ( 10 ) consists of a layer system with a layer sequence of at least two layers, each of at least one oxide from the group Al ₂ O ₃ , MgO, Ta ₂ O _{5 are} formed. 22. Temperature sensor according to claim 21, characterized in that at least one Layer is formed from two oxides. 23. Temperature sensor according to claim 1 or 8, characterized in that the intermediate layer ( 10 ) by means of PVD (Physical Vapor Deposition), IAD (Ion Assisted Deposition), IEAD (Ion Beam Assisted Deposition), PAD ( Plasma Assisted Deposition) or magnetic tron sputtering process. 24. Temperature sensor according to one of claims 3, 4, 8 to 13, characterized in that the passivation layer ( 3 ) has a mixture of SiO ₂ , BaO and Al ₂ O ₃ , the weight fraction of SiO ₂ in the range from 20% to 50%. 25. Temperature sensor according to claim 5, characterized in that a gap between the measuring resistor ( 1 ) and the opposite carrier substrate ( 12 ) is sealed on all sides with a sealing glass ( 28 ) and the glass is a mixture of SiO ₂ , Al ₂ O ₃ and BaO, the weight fraction of SiO _{2 being} in the range from 20% to 50%.