JP6929126B2 - Temperature sensor element - Google Patents

Description

The present invention relates to, for example, a temperature sensor element for high temperature used for measuring the temperature of exhaust gas and a catalyst passing through an exhaust pipe of an automobile, and in particular, a temperature sensor in which a resistance pattern containing platinum as a main component is formed on a ceramic substrate. Regarding the element.

A temperature sensor is attached to the exhaust pipe and catalyst of the automobile, and the temperature of the exhaust gas is sent to the engine control unit (ECU) as an electric signal. Combustion is controlled by the electric signal sent to the ECU, for example, to protect parts with strict heat resistance restrictions and to optimize the catalyst temperature, and to purify exhaust gas and improve fuel efficiency.

As an example of such an exhaust temperature sensor, as described in Patent Document 1, a resistance pattern made of a platinum film is formed on a rectangular alumina substrate, and a pair of electrodes connected to both ends of the resistance pattern are formed. There is known a flat plate type temperature sensor element formed, in which lead wires are bonded to each of these electrodes and led out to the outside, and the resistance pattern is covered with a protective film layer.

In the temperature sensor element described in Patent Document 1, since platinum, which is chemically extremely stable, is used as the temperature-sensitive film constituting the resistance pattern, the characteristics of the temperature-sensitive film are unlikely to fluctuate even at high temperatures. It is a sensor suitable for high temperature applications. However, in recent years, there has been a demand for a sensor that can be used even at a high operating temperature exceeding 900 ° C., and in such a high temperature range, there is a problem that the protective film layer covering the resistance pattern is electrochemically decomposed. Occurs.

Therefore, conventionally, as described in Patent Document 2, a resistance pattern made of a platinum film is formed on a ceramic substrate, and a ceramic layer deposited on the main surface of the ceramic substrate so as to cover the resistance pattern, and a ceramic. A temperature sensor element has been proposed in which a protective intermediate layer is formed by a ceramic paste layer provided on the layer, and a protective film layer is provided on the protective intermediate layer.

According to the temperature sensor element configured in this way, cracks occur under the ceramic paste layer which may cause cracks even when a continuous load is applied to the protective intermediate layer having a two-layer structure in a high temperature region. Since the ceramic layer is provided without fear, the protective film layer is always isolated from the platinum resistance pattern even if the protective film layer penetrates the ceramic paste layer, and the protective film layer is electrochemical. I try to prevent disassembly.

Japanese Unexamined Patent Publication No. 11-121207 Japanese Patent No. 3493343

Alumina substrates, which are widely used as ceramic substrates for temperature sensor elements, include SiO ₂ , CaO, BaO, MgO, ZnO, B ₂ O _{3 for the purpose of promoting sintering, preventing abnormal crystal growth, or improving characteristics.} Etc. are added to the sintering aid. However, platinum, which is a material of the resistance pattern formed on the alumina substrate, has high reactivity at high temperatures, and especially at high temperatures of 900 ° C. or higher, oxygen in the measurement atmosphere and the sintering aid contained in the alumina substrate. Impurities such as these diffuse into the resistance pattern, and the impurities react with the platinum in the resistance pattern or invade the grain boundaries of the platinum, which causes a problem of resistance drift and TCR change.

In the temperature sensor element described in Patent Document 2, the resistance pattern made of a platinum film is covered with a ceramic layer having a two-layer structure to separate the protective film layer from the resistance pattern and prevent electrochemical decomposition. However, since the ceramic layer formed by vapor deposition is in an amorphous state, the ceramic layer prevents impurities from diffusing into the resistance pattern, and suppresses the reaction of the resistance pattern with platinum and the penetration of platinum into the grain boundaries. It is not possible. Moreover, when an alumina substrate is used as the ceramic substrate, it is not possible to suppress the reaction of platinum in the resistance pattern with impurities such as sintering aids contained in the alumina substrate, so that this also causes resistance drift and TCR change. There is a problem of causing.

It is conceivable to use a single crystal sapphire substrate with less impurities instead of the alumina substrate as the ceramic substrate, but in that case, the linear expansion coefficients of the platinum and the sapphire substrate of the resistance pattern are significantly different, and the surface roughness is different. There is a problem that the platinum resistance pattern is peeled off from the sapphire substrate because the adhesion strength of the resistance pattern to the small sapphire substrate is lowered.

The present invention has been made in view of such an actual situation of the prior art, and an object of the present invention is to provide a temperature sensor element in which resistance value drift and TCR change are unlikely to occur even under high temperature use.

As one means for achieving the above object, the temperature sensor element of the present invention has a ceramic substrate, a meander-shaped resistance pattern containing platinum as a main component formed on the main surface of the ceramic substrate, and the resistance pattern. In a temperature sensor element provided with a protective film layer covering the ceramic substrate, the protective film layer is a trap layer made of an alumina material containing platinum and a thick film is formed on the main surface of the ceramic substrate so as to cover the resistance pattern. The trap layer is composed of an overcoat layer containing alumina as a main component formed on the trap layer, and the trap layer is characterized by containing 2 to 30% by volume of platinum as a main component of alumina.

In the temperature sensor element configured in this way, the protective film layer covering the platinum resistance pattern on the ceramic substrate contains an inner trap layer containing 2 to 30% by volume of platinum as the main component of alumina and an alumina as the main component. Even when the reactivity of the platinum resistance pattern becomes high under high temperature use, the platinum dispersed in the alumina material of the trap layer reacts with oxygen and impurities contained in the ceramic substrate. By doing so , the reaction of the platinum resistance pattern is suppressed, so that a highly reliable sensor capable of suppressing resistance value drift and TCR change can be realized.

Further, as another means for achieving the above object, the temperature sensor element of the present invention comprises a ceramic substrate, a surface smoothing layer containing alumina as a main component formed on the main surface of the ceramic substrate, and the surface smoothing. A resistance pattern containing platinum as a main component formed on the layer and a protective film layer containing alumina as a main component covering the resistance pattern are provided, and the surface smoothing is provided so that the protective film layer covers the resistance pattern. It is composed of a trap layer formed on the layer and an overcoat layer formed on the trap layer, and the surface smoothing layer and the trap layer are both characterized by containing 2 to 30% by volume of platinum. There is.

In the temperature sensor element configured in this way, a surface smoothing layer containing 2 to 30% by volume of platinum as a main component of alumina is formed on the main surface of the ceramic substrate, and is formed on the surface smoothing layer. The protective film layer covering the platinum resistance pattern is composed of a trap layer of an inner layer containing 2 to 30% by volume of platinum as a main component of alumina and an overcoat layer of an outer layer containing 2 to 30% by volume of platinum as a main component of alumina. Even when the reactivity of the resistance pattern becomes high, the reaction of the platinum resistance pattern is suppressed by reacting the platinum contained in both the surface smoothing layer and the trap layer with oxygen and impurities contained in the ceramic substrate, and in particular, Since the surface smoothing layer suppresses the reaction between the impurities contained in the ceramic substrate and the platinum resistance pattern, it is possible to realize a highly reliable sensor capable of further suppressing the resistance value drift and the TCR change.

Further, in the temperature sensor element having the above configuration, the ceramic substrate is an alumina substrate having an alumina purity of 96% or more, and the trap is larger than the total of the impurities contained in the alumina substrate and the impurities other than alumina and platinum in the protective film layer. The layer preferably contains a large amount of platinum.

According to the temperature sensor element of the present invention, it is possible to prevent the resistance value drift and the TCR change due to the reaction of the platinum resistance pattern and the invasion of impurities into the grain boundaries even under high temperature use.

It is a top view of the temperature sensor element which concerns on 1st Embodiment of this invention. It is sectional drawing which follows the line II-II of FIG. It is sectional drawing which follows the line III-III of FIG. It is sectional drawing of the temperature sensor element which concerns on 2nd Embodiment of this invention. It is sectional drawing of the temperature sensor element which concerns on 3rd Embodiment of this invention. It is sectional drawing of the temperature sensor element which concerns on 4th Embodiment of this invention.

Explaining the embodiment of the present invention with reference to the drawings, as shown in FIGS. 1 to 3, the temperature sensor element 1 according to the first embodiment of the present invention includes a rectangular ceramic substrate 2 and a ceramic substrate. A meander-shaped resistance pattern 3 formed on the main surface (surface) 2a of 2 and a pair of electrodes 4 formed on the main surface 2a of the ceramic substrate 2 so as to be connected to both ends of the resistance pattern 3 and a resistance pattern. It is configured to include a protective film layer 5 that covers 3 and a lead wire (not shown) that is joined onto a pair of electrodes 4 and projects to the outside of the ceramic substrate 2.

The ceramic substrate 2 is an alumina substrate having an alumina purity of 96% or more, and in this ceramic substrate (alumina substrate) 2, a _{sintering aid such as SiO 2} or MgO is added to _{alumina (Al 2} O ₃ ) which is the main component. Has been done.

The resistance pattern 3 is a thin film resistance film containing platinum (Pt) as a main component, and the resistance pattern 3 is formed in a meander shape on the main surface 2a of the ceramic substrate 2 by sputtering and patterning Pt. ..

The pair of electrodes 4 are made by screen-printing an electrode paste containing platinum as a main component, drying and firing. In the case of this embodiment, both of the pair of electrodes 4 are the short sides on the left side of the ceramic substrate 2 in the drawing. Although it is arranged in the portion, the pair of electrodes 4 may be distributed and arranged at both ends in the longitudinal direction of the ceramic substrate 2.

The protective film layer 5 has a two-layer structure consisting of a trap layer 6 formed on the main surface 2a of the ceramic substrate 2 so as to cover the resistance pattern 3 and an overcoat layer 7 formed on the trap layer 6. .. The trap layer 6 is obtained by screen-printing an alumina paste containing platinum, drying and firing it, and the content of platinum with respect to alumina as the main component is 2 to 30% by volume. The overcoat layer 7 is obtained by screen-printing an alumina paste, drying and firing, and the overcoat layer 7 does not contain platinum.

The pair of lead wires (not shown) are, for example, platinum-coated wires of nickel core wires, and these lead wires are joined to the corresponding electrodes 4 by welding.

Next, the manufacturing process of the temperature sensor element 1 configured in this way will be described. First, a large-format substrate (for example, alumina purity 99%) on which a large number of ceramic substrates 2 are taken is prepared. The large-format substrate is provided with a primary dividing groove and a secondary dividing groove in a grid pattern in advance, and each of the squares divided by both dividing grooves serves as a chip area for one piece.

Then, platinum (Pt) is sputter-deposited on the surface of the large-format substrate to form a film, and then the Pt film is patterned by photolithography to form a meander-shaped resistance pattern 3 in each chip region on the large-format substrate. ..

Next, an electrode paste containing platinum is screen-printed on the surface of a large-format substrate, dried and fired at a high temperature of about 1400 ° C. to form electrodes 4 connected to both ends of the resistance pattern 3.

Next, an alumina paste containing 2 to 30% by volume of platinum (for example, 90 vol% of alumina and 10 vol% of platinum) is screen-printed on the surface of a large-format substrate, dried and fired at a high temperature of 1400 ° C. or higher. A trap layer 6 covering the resistance pattern 3 is formed in each chip region on the large-format substrate. The trap layer 6 is in close contact with the surface of the large-format substrate exposed around the resistance pattern 3, and the connection portion between the resistance pattern 3 and the electrode 4 is also covered by the trap layer 6.

Next, the alumina paste is screen-printed on the trap layer 6, dried and fired at a high temperature of 1400 ° C. or higher to form the overcoat layer 7 covering the trap layer 6. As a result, the protective film layer 5 having a two-layer structure composed of a trap layer 6 of an inner layer containing 2 to 30% by volume of platinum as a main component of alumina and an overcoat layer 7 of an outer layer containing 2 to 30% by volume of platinum as a main component of alumina and containing no platinum as a main component. Is formed.

Each step up to this point is a batch process for a large-format substrate for taking a large number of pieces, but in the next step, the ceramic substrate 2 is divided into individual pieces along the primary dividing groove and the secondary dividing groove. Obtain a single chip of the same size as. After that, the lead wire is welded to the electrode 4 of each of the individual chips, and the welded portion is covered with a reinforcing film such as potting glass, whereby the temperature sensor element 1 as shown in FIGS. 1 to 3 is formed. can get.

As described above, in the temperature sensor element 1 according to the first embodiment, the protective film layer 5 covering the resistance pattern 3 made of a platinum film has a two-layer structure of a trap layer 6 and an overcoat layer 7, and is an outer layer. The overcoat layer 7 is made of alumina that does not contain platinum, and the trap layer 6 of the inner layer that covers the resistance pattern 3 and adheres to the main surface 2a of the ceramic substrate 2 contains 2 to 30% by volume of platinum as the main component of alumina. Therefore, for example, even under high temperature use of 1000 ° C. or higher, the platinum contained in the trap layer 6 reacts with oxygen in the measurement atmosphere, impurities contained in the ceramic substrate 2, and the like, so that the platinum resistance pattern 3 is formed. The reaction with oxygen in the measurement atmosphere, impurities in the ceramic substrate 2, and the like is alleviated, and the resistance value drift and TCR change caused by the reaction of the platinum resistance pattern 3 can be suppressed.

Here, if the platinum content in the trap layer 6 is less than 2%, the trap layer 6 hardly exerts the function of suppressing the reaction of the platinum resistance pattern 3, and conversely, the platinum content in the trap layer 6 is high. If it exceeds 30%, the resistance value of the platinum resistance pattern 3 is greatly lowered by the platinum contained in the trap layer 6. Therefore, in the temperature sensor element 1 according to the first embodiment, the trap containing alumina as the main component is used. The content of platinum added to layer 6 is set to 2 to 30%.

FIG. 4 is a cross-sectional view of the temperature sensor element 10 according to the second embodiment of the present invention, and the parts corresponding to FIG. 2 are designated by the same reference numerals.

The difference between the temperature sensor element 10 according to the second embodiment and the temperature sensor element 1 according to the first embodiment is that the platinum resistance pattern 3 is not formed on the main surface 2a of the ceramic substrate 2, and platinum. A surface smoothing layer 8 containing 2 to 30% by volume of platinum as a main component of alumina is interposed between the resistance pattern 3 and the main surface 2a of the ceramic substrate 2, and other configurations are basic. Is the same.

That is, in the temperature sensor element 10 shown in FIG. 4, a surface smoothing layer 8 containing alumina as a main component and containing platinum (content rate 2 to 30%) is formed on the main surface 2a of the ceramic substrate 2, and the surface smoothing layer 8 is formed. A resistance pattern 3 made of a platinum film is formed on the 8 and a protective film layer 5 having a two-layer structure is formed by an inner trap layer 6 covering the resistance pattern 3 and an outer overcoat layer 7 covering the trap layer 6. Is formed. As a result, the resistance pattern 3 is sandwiched between the platinum-containing surface smoothing layer 8 and the trap layer 6, and the peripheral portion of the overcoat layer 7 is formed on the main surface 2a of the ceramic substrate 2 exposed around the surface smoothing layer 8. Has a structure that is in close contact with each other.

In the temperature sensor element 10 according to the second embodiment configured in this way, a surface smoothing layer 8 containing 2 to 30% by volume of platinum as a main component of alumina is formed on the main surface 2a of the ceramic substrate 2. At the same time, the protective film layer 5 covering the platinum resistance pattern 3 formed on the surface smoothing layer 8 contains an inner trap layer 6 containing 2 to 30% by volume of platinum as a main component of alumina and an alumina as a main component. Since it is composed of the overcoat layer 7 of the outer layer, even when the reactivity of the platinum resistance pattern 3 becomes high under high temperature use, the circumference of the platinum resistance pattern 3 is entirely composed of alumina and 2 to 30 volumes of platinum. The structure is covered with the surface smoothing layer 8 and the trap layer 6 containing%, and the platinum contained in both the surface smoothing layer 8 and the trap layer 6 reacts with oxygen and impurities contained in the ceramic substrate to resist platinum. It is possible to suppress the reaction of pattern 3 and prevent resistance value drift and TCR change.

FIG. 5 is a cross-sectional view of the temperature sensor element 20 according to the third embodiment of the present invention, and the parts corresponding to FIG. 2 are designated by the same reference numerals.

The difference between the temperature sensor element 20 according to the third embodiment and the temperature sensor element 1 according to the first embodiment is that the trap layer 6 is among the overcoat layer 7 and the trap layer 6 constituting the protective film layer 5. Is a two-layer structure of a lower layer 6a and an upper layer 6b, and the other configurations are basically the same. Here, both the lower layer 6a and the upper layer 6b contain alumina as a main component, but the lower layer 6a in contact with the platinum resistance pattern 3 has a lower platinum content than the upper layer 6b, and the lower layer 6a has a lower platinum content. The upper layer 6b contains 2 to 30% by volume of platinum and contains 0 to 10% by volume of platinum. That is, when the platinum content in the lower layer 6a is, for example, 5% by volume, the platinum content in the upper layer 6b is 5 to 30% by volume, and when the lower layer 6a does not contain platinum at all, the upper layer The platinum content in 6b may be 2 to 30% by volume.

In the temperature sensor element 20 according to the third embodiment configured in this way, the lower layer having a lower platinum content than the upper layer 6b between the upper layer 6b of the trap layer 6 and the platinum resistance pattern 3 Since 6a is interposed, the lower layer 6a suppresses the change in resistance value due to the platinum contained in the trap layer 6, and the amount of platinum contained in the upper layer 6b is increased to make the reaction of the platinum resistance pattern 3 more effective. It can be suppressed.

FIG. 6 is a cross-sectional view of the temperature sensor element 30 according to the fourth embodiment of the present invention, and the parts corresponding to FIG. 5 are designated by the same reference numerals.

The difference between the temperature sensor element 30 according to the fourth embodiment and the temperature sensor element 20 according to the third embodiment is that the platinum resistance pattern 3 is not formed on the main surface 2a of the ceramic substrate 2, and platinum. A surface smoothing layer 8 containing 2 to 30% by volume of platinum as a main component of alumina is interposed between the resistance pattern 3 and the main surface 2a of the ceramic substrate 2, and other configurations are basic. Is the same.

That is, in the temperature sensor element 30 shown in FIG. 6, a surface smoothing layer 8 containing alumina as a main component and platinum (content rate 2 to 30% by volume) is formed on the main surface 2a of the ceramic substrate 2. A resistance pattern 3 made of a platinum film is formed on the surface smoothing layer 8, and of the protective film layer 5 composed of a trap layer 6 and an overcoat layer 7 covering the resistance pattern 3, the trap layer 6 is the lower layer 6a. It has a two-layer structure of the upper layer 6b and the upper layer 6b. As a result, the lower layer 6a having a lower platinum content than the upper layer 6b is interposed between the upper layer 6b of the trap layer 6 and the platinum resistance pattern 3, and the lower layer 6a and the surface smoothness containing platinum are smoothed. The platinum resistance pattern 3 is sandwiched between the layer 8 and the layer 8.

In the temperature sensor element 30 according to the fourth embodiment configured in this way, even when the reactivity of the platinum resistance pattern 3 becomes high under high temperature use, it is contained in both the surface smoothing layer 8 and the trap layer 6. By reacting the platinum with oxygen or impurities contained in the ceramic substrate, the reaction of the platinum resistance pattern 3 can be suppressed and the resistance value drift and the TCR change can be prevented. Moreover, the trap layer 6 has a two-layer structure of a lower layer 6a and an upper layer 6b containing alumina as a main component, and the platinum content between the upper layer 6b and the platinum resistance pattern 3 is lower than that of the upper layer 6b. Since the lower layer 6a intervenes, the lower layer 6a suppresses the change in resistance value due to the platinum contained in the trap layer 6, and the amount of platinum contained in the upper layer 6b is increased to make the reaction of the platinum resistance pattern 3 more effective. Can be suppressed.

1,10,20,30 Temperature sensor element 2 Ceramic substrate 2a Main surface 3 Resistance pattern 4 Electrode 5 Protective film layer 6 Trap layer 6a Lower layer 6b Upper layer 7 Overcoat layer

Claims (3)

In a temperature sensor element provided with a ceramic substrate, a platinum-based meander-shaped resistance pattern formed on the main surface of the ceramic substrate, and a protective film layer covering the resistance pattern.
The protective film layer is composed of a trap layer made of a platinum-containing alumina material in which a thick film is formed on the main surface of the ceramic substrate so as to cover the resistance pattern, and an alumina formed on the trap layer as a main component. A temperature sensor element comprising an overcoat layer, wherein the trap layer contains alumina as a main component and platinum in an amount of 2 to 30% by volume. A ceramic substrate, a surface smoothing layer containing alumina as a main component formed on the main surface of the ceramic substrate, a resistance pattern containing platinum as a main component formed on the surface smoothing layer, and alumina covering the resistance pattern. With a protective film layer whose main component is
The protective film layer is composed of a trap layer formed on the surface smoothing layer so as to cover the resistance pattern, and an overcoat layer formed on the trap layer.
The temperature sensor element, wherein both the surface smoothing layer and the trap layer contain 2 to 30% by volume of platinum. In the description of claim 1 or 2, the ceramic substrate is an alumina substrate having an alumina purity of 96% or more, and the sum of impurities contained in the alumina substrate and impurities other than alumina and platinum in the protective film layer is larger than the total. The temperature sensor element, wherein the trap layer contains a large amount of platinum.

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