Temperature sensor element

Abstract

A resistance pattern that contains platinum as a main component is formed into a meander shape and on a main surface of a ceramic substrate. A protective film layer that covers the resistance pattern has a two-layer structure including a trap layer as an inner layer and an overcoat layer as an outer layer. The trap layer contains alumina as a main component and 2 to 30 vol % of platinum. The overcoat layer contains alumina as a main component. With such a configuration, even when reactivity of the platinum resistance pattern becomes higher under high temperature use, platinum contained in the trap layer reacts with oxygen or impurities etc. contained in the ceramic substrate. Thus, reaction of the platinum resistance pattern can be suppressed.

Claims

1. A temperature sensor element comprising: a ceramic substrate; a resistance pattern that contains platinum as a main component, and that is formed on a main surface of the ceramic substrate; and a protective film layer that covers the resistance pattern; wherein: the protective film layer includes: a trap layer that contains alumina as a main component, and that is formed on the main surface of the ceramic substrate so as to cover the resistance pattern; and an overcoat layer that contains alumina as a main component, and that is formed on the trap layer; and the trap layer contains 2 to 30 vol % of platinum, and the overcoat layer does not contain platinum.

2. A temperature sensor element comprising: a ceramic substrate; a surface smoothening layer that contains alumina as a main component, and that is formed on a main surface of the ceramic substrate; a resistance pattern that contains platinum as a main component, and that is formed on the surface smoothening layer; and a protective film layer that contains alumina as a main component, and that covers the resistance pattern; wherein: the protective film layer includes: a trap layer that is formed on the surface smoothening layer so as to cover the resistance pattern; and an overcoat layer that is formed on the trap layer; and both the surface smoothening layer and the trap layer contain 2 to 30 vol % of platinum, and the overcoat layer does not contain platinum.

3. A temperature sensor element according to claim 1, wherein: the trap layer has a two-layer structure including a lower layer and an upper layer; the lower layer is smaller in content of platinum than the upper layer and contains 0 to 10 vol % of platinum; and the upper layer contains 2 to 30 vol % of platinum.

4. A temperature sensor element according to claim 2, wherein: the trap layer has a two-layer structure including a lower layer and an upper layer; the lower layer is smaller in content of platinum than the upper layer and contains 0 to 10 vol % of platinum; and the upper layer contains 2 to 30 vol % of platinum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a plan view of a temperature sensor element according to a first embodiment of the invention;

(2) FIG. 2 is a sectional view taken along a line II-II of FIG. 1;

(3) FIG. 3 is a sectional view taken along a line III-III of FIG. 1;

(4) FIG. 4 is a sectional view of a temperature sensor element according to a second embodiment of the invention;

(5) FIG. 5 is a sectional view of a temperature sensor element according to a third embodiment of the invention;

(6) FIG. 6 is a sectional view of a temperature sensor element according to a fourth embodiment of the invention;

(7) FIG. 7 is a plan view of a temperature sensor element according to a fifth embodiment of the invention;

(8) FIG. 8 is a sectional view taken along a line II-II of FIG. 7;

(9) FIG. 9 is a sectional view taken along a line III-III of FIG. 8;

(10) FIG. 10 is a plan view of a temperature sensor element according to a sixth embodiment of the invention; and

(11) FIG. 11 is a sectional view taken along a line V-V of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

(12) Embodiments of the invention will be described with reference to the drawings. Incidentally, in the following description, portions the same or regarded as the same in each of the embodiments will be referred to by the same signs correspondingly and respectively, and duplicated description thereof will be omitted appropriately. As shown in FIGS. 1 to 3, a temperature sensor element 1 according to a first embodiment of the invention is configured to include a ceramic substrate 2, a resistance pattern 3, a pair of electrodes 4, a protective film layer 5, and not-shown lead wires. The ceramic substrate 2 is shaped like a rectangular parallelepiped. The resistance pattern 3 having a meander shape is formed on a main surface (front surface) 2a of the ceramic substrate 2. The pair of electrodes 4 are formed on the main surface 2a of the ceramic substrate 2 so as to be connected to opposite end portions of the resistance pattern 3. The protective film layer 5 covers the resistance pattern 3. The lead wires are bonded on the pair of electrodes 4 and then protrude outward from the ceramic substrate 2.

(13) The ceramic substrate 2 is an alumina substrate whose alumina purity is 96% or higher. In the ceramic substrate (alumina substrate) 2, a sintering aid of SiO.sub.2, MgO, or the like is added to alumina (Al.sub.2O.sub.3) that is a main component.

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

(15) The pair of electrodes 4 are obtained by screen-printing, drying and sintering an electrode paste containing platinum as a main component. In the case of the embodiment, the pair of electrodes 4 are both disposed on portions of an illustrated left short side of the ceramic substrate 2. However, the pair of electrodes 4 may be distributed and disposed on longitudinally opposite end portions of the ceramic substrate 2.

(16) The protective film layer 5 has a two-layer structure including a trap layer 6 and an overcoat layer 7. The trap layer 6 is formed on the main surface 2a of the ceramic substrate 2 so as to cover the resistance pattern 3. The overcoat layer 7 is formed on the trap layer 6. The trap layer 6 is obtained by screen-printing, drying and sintering an alumina paste containing platinum. The content of platinum relative to alumina that is amain component is 2 to 30 vol %. The overcoat layer 7 is obtained by screen-printing, drying and sintering an alumina paste. Platinum is not contained in the overcoat layer 7.

(17) Incidentally, a pair of the not-shown lead wires are, for example, nickel-core platinum-clad wires. These lead wires are bonded on the corresponding electrodes 4 by welding.

(18) Next, manufacturing steps of the temperature sensor element 1 configured thus will be described. First, a large-sized substrate (e.g. alumina purity of 99%) from which a large number of ceramic substrates 2 can be obtained is prepared. Primary division grooves and secondary division grooves are provided in the large-sized substrate to forma grid pattern in advance. Each of grids defined by the two division grooves is a chip region corresponding to one temperature sensor element 1.

(19) After a film of platinum (Pt) is sputter-deposited on a front surface of the large-sized substrate, the Pt film is patterned by photolithography. Thus, a meander-shaped resistance pattern 3 is formed in each chip region on the large-sized substrate.

(20) Next, an electrode paste containing platinum is screen-printed on the front surface of the large-sized substrate, dried and then sintered at a high temperature of about 1,400° C. Thus, electrodes 4 connected to opposite end portions of the resistance pattern 3 are formed.

(21) Next, an alumina paste containing 2 to 30 vol % of platinum (e.g. 90 vol % of alumina and 10 vol % of platinum) is screen-printed on the front surface of the large-sized substrate, dried and then sintered at a high temperature equal to or higher than 1,400° C. Thus, a trap layer 6 covering the resistance pattern 3 is formed in each chip region on the large-sized substrate. The trap layer 6 makes tight contact with the front surface of the large-sized substrate exposed surrounding the resistance pattern 3. Places at each of which the resistance pattern 3 and the electrode 4 are connected to each other are also covered with the trap layer 6.

(22) Next, an alumina paste is screen-printed from above the trap layer 6, dried and then sintered at a high temperature equal to or higher than 1,400° C. Thus, an overcoat layer 7 covering the trap layer 6 is formed. As a result, a protective film layer 5 having a two-layer structure including the trap layer 6 as an inner layer and the overcoat layer 7 as an outer layer is formed. The trap layer 6 contains alumina as a main component and 2 to 30 vol % of platinum. The overcoat layer 7 contains alumina as a main component but does not contain platinum.

(23) The respective steps described so far are carried out by batch processing on the large-sized substrate from which the large number of the ceramic substrates 2 can be obtained. However, in a next step, the large-sized substrate is divided along the primary division grooves and the secondary division grooves and separated into individual chips. Thus, each of the single chips equivalent in size to the ceramic substrate 2 is obtained. Then, lead wires are welded to the electrodes 4 of the individually separated single chip, and places where the lead wires are welded are covered with a reinforced film of potting glass etc. Thus, a temperature sensor element 1 shown in FIGS. 1 to 3 is obtained.

(24) In the temperature sensor element 1 according to the first embodiment, as described above, the protective film layer 5 covering the resistance pattern 3 made of the platinum film has the two-layer structure including the trap layer 6 and the overcoat layer 7. The overcoat layer 7 as the outer layer is formed out of alumina not containing platinum. In addition, the trap layer 6 as the inner layer covering the resistance pattern 3 and making tight contact with the main surface 2a of the ceramic substrate 2 contains alumina as the main component and 2 to 30 vol % of platinum. Accordingly, platinum contained in the trap layer 6 reacts with oxygen in a measurement atmosphere or impurities etc. contained in the ceramic substrate 2, for example, even under use at a high temperature equal to or higher than 1,000° C. Thus, reaction of the platinum resistance pattern 3 with the oxygen in the measurement atmosphere or the impurities etc. of the ceramic substrate 2 is relaxed. As a result, drift of a resistance value or change of a TCR caused by the reaction of the platinum resistance pattern 3 can be suppressed.

(25) When the content of platinum in the trap layer 6 is less than 2 vol % here, the trap layer 6 can hardly function to suppress reaction of the platinum resistance pattern 3. On the contrary, when the content of platinum in the trap layer 6 exceeds 30 vol %, the resistance value of the platinum resistance pattern 3 decreases largely due to platinum contained in the trap layer 6. Therefore, the content of platinum added into the trap layer 6 containing alumina as the main component is 2 to 30 vol % in the temperature sensor element 1 according to the first embodiment.

Second Embodiment

(26) FIG. 4 is a sectional view of a temperature sensor element 10 according to a second embodiment of the invention. In FIG. 4, portions corresponding to those in FIG. 2 will be referred to by the same signs respectively.

(27) The temperature sensor element 10 according to the second embodiment is basically the same in configuration as the temperature sensor element 1 according to the first embodiment except that a platinum resistance pattern 3 is not formed on a main surface 2a of a ceramic substrate 2 but a surface smoothening layer 8 containing alumina as a main component and 2 to 30 vol % of platinum is sandwiched between the platinum resistance pattern 3 and the main surface 2a of the ceramic substrate 2.

(28) That is, in the temperature sensor element 10 shown in FIG. 4, the surface smoothening layer 8 containing alumina as the main component and platinum (whose content is 2 to 30 vol %) is formed on the main surface 2a of the ceramic substrate 2, and the resistance pattern 3 made of a platinum film is formed on the surface smoothening layer 8. In addition, a protective film layer 5 having a two-layer structure is formed by a trap layer 6 as an inner layer and an overcoat layer 7 as an outer layer. The trap layer 6 covers the resistance pattern 3. The overcoat layer 7 covers the trap layer 6. As a result, the structure is formed in such a manner that the resistance pattern 3 is sandwiched between the surface smoothening layer 8 containing platinum and the trap layer 6, and a peripheral edge portion of the overcoat layer 7 makes tight contact with the main surface 2a of the ceramic substrate 2 exposed surrounding the surface smoothening layer 8.

(29) In the temperature sensor element 10 configured thus according to the second embodiment, the surface smoothening layer 8 containing alumina as the main component and 2 to 30 vol % of platinum is formed on the main surface 2a of the ceramic substrate 2, and the protective film layer 5 covering the platinum resistance pattern 3 formed on the surface smoothening layer 8 includes the trap layer 6 as the inner layer containing alumina as a main component and 2 to 30 vol % of platinum, and the overcoat layer 7 as the outer layer containing alumina as a main component. Accordingly, even when reactivity of the platinum resistance pattern 3 becomes higher under high temperature use, platinum contained in both the surface smoothening layer 8 and the trap layer 6 reacts with oxygen or impurities contained in the ceramic substrate due to the structure in which the platinum resistance pattern 3 is entirely covered with the surface smoothening layer 8 and the trap layer 6 both of which contain alumina as the main component and 2 to 30 vol % of platinum. As a result, reaction of the platinum resistance pattern 3 is suppressed so that drift of a resistance value or change of a TCR can be prevented.

Third Embodiment

(30) FIG. 5 is a sectional view of a temperature sensor element 20 according to a third embodiment of the invention. In FIG. 5, portions corresponding to those in FIG. 2 will be referred to by the same signs respectively.

(31) The temperature sensor element 20 according to the third embodiment is basically the same in configuration as the temperature sensor element 1 according to the first embodiment except that, of an overcoat layer 7 and a trap layer 6 constituting a protective film layer 5, the trap layer 6 is formed into a two-layer structure including a lower layer 6a and an upper layer 6b. Here, alumina is used as a main component in both the lower layer 6a and the upper layer 6b. The lower layer 6a making contact with the platinum resistance pattern 3 is smaller in content of platinum than the upper layer 6b and contains 0 to 10 vol % of platinum. The upper layer 6b contains 2 to 30 vol % of platinum. That is, when, for example, the content of platinum in the lower layer 6a is 5 vol %, it will go well if the content of platinum in the upper layer 6b is 5 to 30 vol %. When the lower layer 6a does not contain platinum at all, it will go well if the content of platinum in the upper layer 6b is 2 to 30 vol %.

(32) In the temperature sensor element 20 configured thus according to the third embodiment, the lower layer 6a smaller in content of platinum than the upper layer 6b is sandwiched between the upper layer 6b of the trap layer 6 and the platinum resistance pattern 3. Accordingly, while change of a resistance value caused by platinum contained in the trap layer 6 is suppressed due to the lower layer 6a, the amount of platinum contained in the upper layer 6b is increased so that reaction of the platinum resistance pattern 3 can be suppressed more effectively.

Fourth Embodiment

(33) FIG. 6 is a sectional view of a temperature sensor element 30 according to a fourth embodiment of the invention. In FIG. 6, portions corresponding to those in FIG. 5 will be referred to by the same signs respectively.

(34) The temperature sensor element 30 according to the fourth embodiment is basically the same in configuration as the temperature sensor element 20 according to the third embodiment except that a platinum resistance pattern 3 is not formed on a main surface 2a of a ceramic substrate 2 but a surface smoothening layer 8 containing alumina as a main component and 2 to 30 vol % of platinum is sandwiched between the platinum resistance pattern 3 and the main surface 2a of the ceramic substrate 2.

(35) That is, in the temperature sensor element 30 shown in FIG. 6, the surface smoothening layer 8 containing alumina as the main component and platinum (whose content is 2 to 30 vol %) is formed on the main surface 2a of the ceramic substrate 2, and the resistance pattern 3 made of a platinum film is formed on the surface smoothening layer 8. In addition, of a protective film layer 5 including a trap layer 6 covering the resistance pattern 3 and an overcoat layer 7, the trap layer 6 is formed into a two-layer structure including a lower layer 6a and an upper layer 6b. As a result, the structure is formed in such a manner that the lower layer 6a smaller in content of platinum than the upper layer 6b of the trap layer 6 is sandwiched between the upper layer 6b and the platinum resistance pattern 3, and the platinum resistance pattern 3 is sandwiched between the lower layer 6a and the surface smoothening layer 8 containing platinum.

(36) In the temperature sensor element 30 configured thus according to the fourth embodiment, even when reactivity of the platinum resistance pattern 3 becomes higher under high temperature use, platinum contained in both the surface smoothening layer 8 and the trap layer 6 reacts with oxygen or impurities etc. contained in the ceramic substrate 2. Thus, reaction of the platinum resistance pattern 3 is suppressed so that drift of a resistance value or change of a TCR can be prevented. Moreover, the trap layer 6 has the two-layer structure including the lower layer 6a and the upper layer 6b both containing alumina as a main component, and the lower layer 6a smaller in content of platinum than the upper layer 6b is sandwiched between the upper layer 6b and the platinum resistance pattern 3. Accordingly, while change of the resistance value caused by platinum contained in the trap layer 6 is suppressed due to the lower layer 6a, the amount of platinum contained in the upper layer 6b is increased so that reaction of the platinum resistance pattern 3 can be suppressed more effectively.

Fifth Embodiment

(37) As shown in FIGS. 7 to 9, a temperature sensor element 40 according to a fifth embodiment of the invention is provided with a ceramic substrate 2, a resistance pattern 3, a pair of electrodes 4, a trap layer 6, an overcoat layer 7, and not-shown lead wires. The ceramic substrate 2 is shaped like a rectangular parallelepiped. The resistance pattern 3 having a meander shape is formed on a main surface (front surface) 2a of the ceramic substrate 2. The pair of electrodes 4 are formed on the main surface 2a of the ceramic substrate 2 so as to be connected to opposite end portions of the resistance pattern 3. The trap layer 6 covers the resistance pattern 3. The overcoat layer 7 covers the trap layer 6. The lead wires are bonded on the pair of electrodes 4 and then protrude outward from the ceramic substrate 2. A protective film layer 5 is constituted by the trap layer 6 and the overcoat layer 7. Incidentally, in the fifth embodiment, portions corresponding to those in the first embodiment will be referred to by the same signs respectively.

(38) The ceramic substrate 2, the resistance pattern 3, the pair of electrodes 4, the overcoat layer 7 and the lead wires are the same in configuration as those in the first embodiment. In addition, the overcoat layer 7 covers the whole of an upper layer 6b, and a peripheral edge portion of the overcoat layer 7 makes tight contact with the main surface 2a of the ceramic substrate 2.

(39) The trap layer 6 is formed into a two-layer structure including a lower layer 6a and the upper layer 6b. The lower layer 6a covers the resistance pattern 3 and makes tight contact with the main surface 2a of the ceramic substrate 2. The upper layer 6b covers the lower layer 6a. A peripheral edge portion of the upper layer 6b makes tight contact with the main surface 2a of the ceramic substrate 2. The lower layer 6a and the upper layer 6b are obtained by screen-printing, drying and sintering an alumina paste containing alumina as amain component. The content of platinum relative to alumina that is the main component varies between the lower layer 6a and the upper layer 6b. The relation about the content of platinum between the lower layer 6a and the upper layer 6b is similar to or the same as that in the aforementioned third embodiment.

(40) Next, manufacturing steps of the temperature sensor element 40 configured thus will be described. First, a large-sized substrate (e.g. alumina purity of 99%) from which a large number of ceramic substrates 2 can be obtained is prepared. Primary division grooves and secondary division grooves are provided in the large-sized substrate to forma grid pattern in advance. Each of grids defined by the two division grooves is a chip region corresponding to one temperature sensor element 1.

(41) After a film of platinum (Pt) is sputter-deposited on a front surface of the large-sized substrate, the Pt film is patterned by photolithography. Thus, a meander-shaped resistance pattern 3 is formed in each chip region on the large-sized substrate.

(42) Next, an electrode paste containing platinum is screen-printed on the front surface of the large-sized substrate, dried and then sintered at a high temperature of about 1,400° C. Thus, electrodes 4 connected to opposite end portions of the resistance pattern 3 are formed.

(43) Next, an alumina paste containing 0 to 10 vol % of platinum (e.g. 98 vol % of alumina and 2 vol % of platinum) is screen-printed on the front surface of the large-sized substrate, dried and then sintered at a high temperature equal to or higher than 1,400° C. Thus, a lower layer 6a covering the resistance pattern 3 is formed in each chip region on the large-sized substrate. The lower layer 6a makes tight contact with the front surface of the large-sized substrate exposed surrounding the resistance pattern 3. Places at each of which the resistance pattern 3 and the electrode 4 are connected to each other are also covered with the lower layer 6a.

(44) Next, an alumina paste containing 2 to 30 vol % of platinum (e.g. 90 vol % of alumina and 10 vol % of platinum) is screen-printed from above the lower layer 6a, dried and then sintered at a high temperature equal to or higher than 1,400° C. Thus, an upper layer 6b covering the whole of the lower layer 6a is formed. The upper layer 6b makes tight contact with the front surface of the large-sized substrate exposed outside the lower layer 6a. A trap layer 6 is formed by the lower layer 6a and the upper layer 6b.

(45) Next, an alumina paste is screen-printed from above the upper layer 6b, dried and then sintered at a high temperature equal to or higher than 1,400° C. Thus, an overcoat layer 7 covering the trap layer 6 is formed. As a result, a protective film layer 5 having a lamination structure including the trap layer 6 as an inner layer and the overcoat layer 7 as an outer layer is formed. The trap layer 6 (the lower layer 6a and the upper layer 6b) contains alumina as a main component and 2 to 30 vol % of platinum. The overcoat layer 7 contains alumina as a main component but does not contain platinum.

(46) The respective steps described so far are carried out by batch processing on the large-sized substrate from which the large number of the ceramic substrates 2 can be obtained. However, in a next step, the large-sized substrate is divided along the primary division grooves and the secondary division grooves and separated into individual chips. Thus, each of the single chips equivalent in size to the ceramic substrate 2 is obtained. Then, lead wires are welded to the electrodes 4 of the individually separated single chip, and places where the lead wires are welded are covered with a reinforced film of potting glass etc. Thus, a temperature sensor element 40 shown in FIGS. 7 to 9 is obtained.

(47) In the temperature sensor element 40 according to the fifth embodiment, as described above, the trap layer 6 covered with the overcoat layer 7 has the two-layer structure including the lower layer 6a and the upper layer 6b. The lower layer 6a covers the resistance pattern 3 and makes tight contact with the main surface 2a of the ceramic substrate 2. The upper layer 6b covers the lower layer 6a and makes tight contact with the main surface 2a of the ceramic substrate 2. The upper layer 6b is formed out of a material containing alumina as the main component and 2 to 30 vol % of platinum, and the lower layer 6a is formed out of a material containing alumina as the main component and 0 to 10 vol % of platinum. Accordingly, even when reactivity of the platinum resistance pattern 3 becomes higher under high temperature use, platinum contained in the lower layer 6a or the upper layer 6b reacts with oxygen or impurities etc. of the ceramic substrate so that reaction of the platinum resistance pattern 3 can be suppressed. As a result, it is possible to realize a highly reliable sensor in which drift of a resistance value or change of a TCR can be prevented.

(48) When the content of platinum in the whole of the trap layer 6 including the lower layer 6a and the upper layer 6b is less than 2 vol % here, the trap layer 6 can hardly function to suppress reaction of the platinum resistance pattern 3. On the contrary, when the content of platinum in the trap layer 6 is large, the resistance value of the platinum resistance pattern 3 decreases due to platinum contained in the trap layer 6. When the content of platinum in the trap layer 6 exceeds 30 vol %, electric continuity is established due to platinum contained in the trap layer 6 so that the resistance value decreases largely. In the configuration of the temperature sensor element 40 according to the fifth embodiment, the lower layer 6a smaller in content of platinum than the upper layer 6b is sandwiched between the upper layer 6b and the platinum resistance pattern 3. Accordingly, in the state in which the decrease of the resistance value of the platinum resistance pattern 3 has been suppressed due to the lower layer 6a, the amount of platinum contained in the upper layer 6b is increased so that reaction of the platinum resistance pattern 3 can be suppressed more effectively.

Sixth Embodiment

(49) FIG. 10 is a plan view of a temperature sensor element 50 according to a sixth embodiment of the invention. FIG. 11 is a sectional view taken along a line V-V of FIG. 10. In FIGS. 10 and 11, portions corresponding to those in FIGS. 7 to 9 will be referred to by the same signs respectively.

(50) The temperature sensor element 50 according to the sixth embodiment is basically the same in configuration as the temperature sensor element 40 according to the fifth embodiment except that a lower layer 6a has notch portions 6c each positioned between adjacent ones of meandering conductor portions of a meander-shaped resistance pattern 3, and an upper layer 6b passes the notch portions 6c and makes tight contact with a main surface 2a of a ceramic substrate 2.

(51) That is, in the temperature sensor element 50 shown in FIGS. 10 and 11, the resistance pattern 3 is formed into a meander shape having three meandering conductor portions 3a. The lower layer 6a covering the resistance pattern 3 is formed into a comb shape (the shape of an alphabet “E”) having two notch portions 6c each going into adjacent ones of the meandering conductor portions 3a. In addition, the upper layer 6b that is shaped like a rectangle in plan view and that covers the lower layer 6a makes tight contact with the main surface 2a of the ceramic substrate 2 not only at a peripheral edge portion but also inside the notch portions 6c.

(52) Also in the temperature sensor element 50 configured thus according to the sixth embodiment, the lower layer 6a smaller in content of platinum than the upper layer 6b of a trap layer 6 is sandwiched between the upper layer 6b and the platinum resistance pattern 3. Accordingly, in the state in which a decrease of a resistance value of the platinum resistance pattern 3 has been suppressed due to the lower layer 6a, the amount of platinum contained in the upper layer 6b is increased so that reaction of the platinum resistance pattern 3 can be suppressed more effectively. Moreover, the lower layer 6a has the notch portions 6c each positioned between adjacent ones of the meandering conductor portions 3a of the resistance pattern 3, and the upper layer 6b passes the notch portions 6c and makes tight contact with the main surface 2a of the ceramic substrate 2. Therefore, a contact area between the upper layer 6b large in the content of platinum and the ceramic substrate 2 can increase accordingly. Thus, reaction of the platinum resistance pattern 3 with impurities of the ceramic substrate 2 can be suppressed more greatly.