Thermistor element and its manufacturing method

Abstract

To provide a thermistor element in which an excellent electrical connection between a sealing electrode and a thermistor chip can be obtained even in a type sealed on an insulating tube such as a glass tube and a manufacturing method for the same.SOLUTION: The thermistor element includes a chip or plate-shaped thermistor chip 2, a pair of sealing electrodes 3 arranged to oppose each other on the top and bottom surfaces of the thermistor chip, and an insulating tube 4 to which the pair of sealing electrodes is bonded at both ends and that also seals the thermistor chip to the inside. The thermistor chip includes a chip or plate-shaped thermistor element body 2a, a pair of electrode film 2b formed on the top and bottom surfaces of the thermistor element body, and an insulating protective film 2c formed on the outer surface of the thermistor element body and on the pair of electrodes. At least a portion of the protective film on the surface of the electrode film inside a ridge line of the thermistor element body is removed, exposing the electrode film, and an exposed portion 2d of the electrode film is in contact with the sealing electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermistor element suitable for use in temperature sensors and protection circuits for electronic devices, and a method for manufacturing the same. [Background technology]

[0002] Thermistors have a resistance that changes with temperature, and because this change is very sensitive to temperature, they are widely used in applications such as temperature sensors and protection circuits for electronic devices. The transition metals that make up such thermistors, such as NTC thermistors, can take on a wide variety of valence states, making the thermistor material susceptible to the effects of the outside air. In particular, in the case of glass diode-type thermistor elements sealed in glass tubes, oxygen defects occur in the thermistor material in an inert atmosphere during sealing, and in the case of flake-type thermistors, etc., in a reducing atmosphere during solder reflow, which can cause problems such as changes in the thermistor's properties.

[0003] To address this issue, surface-mounted thermistors, also known as chip thermistors, are coated with glass on the sides (outer surfaces) to prevent oxygen defects from forming, but it has been difficult to apply a protective coating only to the sides of flake-type thermistors. Patent Document 1 describes a method in which a glass paste is applied to the electrode surface and baked to form a glass layer, and regions on the ridges of the thermistor element are exposed to make contact with the electrode film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6098208 Summary of the Invention [Problem to be solved by the invention]

[0005] The above conventional techniques still have the following problems. In conventional thermistor elements, as shown in FIG. 6, a glass diode type thermistor element has a thermistor chip 102 mechanically sandwiched between a pair of sealed electrodes 3 within a glass tube (not shown). Because the glass layer 102c formed on the thermistor body 2a is thick, it can be difficult to bring the electrode film 102b on the ridge portion of the thermistor body 2a (within the two-dot chain circle in FIG. 6) into contact with the sealed electrode 3, such as a lead wire, and further improvements in electrical connection have been desired.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a thermistor element and a manufacturing method thereof that can obtain good electrical connection between the sealed electrode and the thermistor chip, even in the case of a type that is sealed in an insulating tube such as a glass tube. [Means for solving the problem]

[0007] The present invention employs the following configuration to solve the above problems: That is, a thermistor element of a first invention comprises a chip-shaped or plate-shaped thermistor chip, a pair of sealed electrodes arranged opposite each other on the upper and lower surfaces of the thermistor chip, and an insulating tube to which the pair of sealed electrodes are joined at both ends and which seals the thermistor chip inside, the thermistor chip comprising a chip-shaped or plate-shaped thermistor body, a pair of electrode films formed on the upper and lower surfaces of the thermistor body, and an insulating protective film formed on the outer peripheral surface of the thermistor body and on the pair of electrode films, at least a part of the protective film inside a ridge line of the thermistor body within the plane of the electrode film is removed to expose the electrode film to form an electrode film exposed portion, and the electrode film exposed portion is in contact with the sealed electrode.

[0008] In this thermistor element, at least a portion of the protective film on the surface of the electrode film that is inside the ridge of the thermistor body is removed to expose the electrode film, forming an electrode film exposed portion, and since the electrode film exposed portion is in contact with the sealed electrode, the thermistor chip and a pair of sealed electrodes can be electrically connected while the protective film covering the outer peripheral surface ensures reduction resistance and prevents oxygen defects.

[0009] The thermistor element of the second invention is the thermistor element of the first invention, characterized in that a plurality of protrusions are formed on the surface of the electrode film, and the exposed electrode film portions are at least some of the protrusions. That is, in this thermistor element, the exposed portion of the electrode film is at least a part of the convex portion, so that the exposed convex portion and the sealing electrode can easily and reliably come into contact with each other, thereby obtaining good electrical contact.

[0010] The thermistor element of the third invention is characterized in that, in the first or second invention, the protective film is formed from a material whose adhesion strength to the electrode film is weaker than that to the thermistor body. In other words, in this thermistor element, the protective film is formed from a material that has a lower adhesion strength to the electrode film than to the thermistor body, so that the protective film adheres firmly to the outer surface of the thermistor body and the protective film on the electrode film can be easily peeled off, making it easy to form partial exposed portions of the electrode film.

[0011] A fourth aspect of the present invention is the thermistor element of the third aspect, characterized in that the electrode film is made of a noble metal, and the protective film is an oxide film or a nitride film. That is, in this thermistor element, the electrode film is formed of a precious metal and the protective film is an oxide film or a nitride film, so that the oxide film or nitride film, which has strong adhesion to the oxide material (e.g., perovskite-based material or spinel-based material) that constitutes the thermistor of the thermistor element but weak adhesion to the precious metal, can be easily formed by a gas phase method such as sputtering or CVD, or a liquid phase deposition method.

[0012] A thermistor element of a fifth invention is the thermistor element of any one of the first to fourth inventions, characterized in that the thickness of the protective film is 10 nm or more and 1000 nm or less. That is, the reason why the thickness of the protective film in this thermistor element is set to 10 nm or more and 1000 nm or less is that if it is less than 10 nm, the reduction resistance is insufficient and the effect of suppressing oxygen defects is reduced, and if it exceeds 1000 nm, it becomes too thick and becomes difficult to peel off, and there is a possibility that the contact between the sealing electrode and the electrode film will be insufficient.

[0013] The thermistor element of the sixth invention is characterized in that, in any of the first to fifth inventions, the coverage rate of the protective film on the outer peripheral surface of the thermistor body is greater than the coverage rate of the protective film on the surface of the electrode film.

[0014] A seventh aspect of the present invention is a thermistor element according to any one of the first to sixth aspects of the present invention, characterized in that the coverage of the protective film within the surface of the electrode film is 99.99% or less. In other words, the reason why the coverage rate of the protective film on the surface of the electrode film in this thermistor element is set to 99.99% or less is that if it exceeds 99.99%, the contact area between the electrode film and the sealing electrode becomes too small and sufficient electrical connection may not be obtained.

[0015] A manufacturing method for a thermistor element of the eighth invention is a method for manufacturing the thermistor element of any of the first to seventh inventions, and includes a thermistor chip forming process including an electrode film forming process for forming a pair of electrode films on the upper and lower surfaces of a chip-shaped or plate-shaped thermistor body and a protective film forming process for forming an insulating protective film on the outer peripheral surface of the thermistor body and on the pair of electrode films; a protective film peeling process for peeling off at least a part of the protective film within the surface of the electrode film on the thermistor chip that is inside the ridge line of the thermistor body to form the exposed electrode film portion; and a sealing process for joining the pair of sealed electrodes to both ends of an insulating tube with the pair of sealed electrodes arranged opposite each other on the upper and lower surfaces of the thermistor chip and sealing the thermistor chip inside, wherein in the sealing process, the exposed electrode film portion and the sealed electrodes come into contact when the thermistor chip is sandwiched between the pair of sealed electrodes.

[0016] That is, this thermistor element manufacturing method includes a protective film peeling step in which at least a portion of the protective film on the surface of the electrode film that is inside the ridge line of the thermistor body is peeled off to form an exposed electrode film portion, which makes it easy to bring the exposed electrode film portion into contact with the sealing electrode in the sealing step. In particular, even with a thin, plate-shaped (flake-shaped) thermistor body, a protective film is first formed on the outer peripheral surface of the thermistor body and on the pair of electrode films, i.e., on the entire surface, and then the protective film is peeled off in the sealing step, so that the protective film can be formed on the outer peripheral surface (side surface) and the electrode film can be exposed.

[0017] The ninth invention is a method for manufacturing a thermistor element according to the eighth invention, characterized in that in the protective film forming process, the protective film is formed from a material whose adhesion strength to the electrode film is weaker than that to the thermistor body. In other words, in this method of manufacturing a thermistor element, the protective film is formed from a material that has a weaker adhesion strength to the electrode film than to the thermistor body, so the electrode film, which has weak adhesion to the electrode film, can be easily peeled off and exposed, allowing electrical connection to the sealed electrode. Furthermore, since the protective film has strong adhesion to the thermistor body, the protective film that has weak adhesion to the electrode film can be easily peeled off, leaving the protective film on the outer periphery of the thermistor body, and exposing the electrode film.

[0018] The tenth invention is a method for manufacturing a thermistor element according to the eighth or ninth invention, characterized in that in the sealing process, the pressure applied when the thermistor chip is sandwiched between the pair of sealing electrodes peels off at least a portion of the protective film within the surface of the electrode film, thereby forming the exposed electrode film portion. That is, in this manufacturing method of the thermistor element, in the sealing process, the pressure applied when the thermistor chip is sandwiched between a pair of sealing electrodes peels off at least a portion of the protective film on the surface of the electrode film, forming an exposed portion of the electrode film. Therefore, without adding a separate process of peeling off the protective film within the surface of the electrode film, the electrode film, which has weak adhesion to the electrode film, can be easily mechanically peeled off and exposed by pressing the sealing electrode, and electrical connection with the sealing electrode can be made. [Effects of the Invention]

[0019] According to the present invention, the following effects are achieved. In other words, according to the thermistor element and manufacturing method thereof of the present invention, the protective film is formed by excluding at least a portion of the protective film inside the ridge of the thermistor body within the plane of the electrode film, and the exposed portion of the electrode film and the sealed electrode are in contact within the plane of the electrode film, so that the protective film covering the outer peripheral surface ensures reduction resistance and prevents oxygen defects, and the thermistor chip and a pair of sealed electrodes can be electrically connected. Therefore, the thermistor element and the manufacturing method thereof of the present invention make it possible to obtain a glass diode type thermistor element or the like that is less likely to have oxygen defects and has stable characteristics. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view of a thermistor element illustrating one embodiment of a thermistor element and a method for manufacturing the same according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a thermistor chip according to the embodiment. [Figure 3] 1 is an electron microscope image of the top surface of a thermistor chip in an embodiment of the thermistor element and the manufacturing method thereof according to the present invention. [Figure 4] This is a binarized image of the image in Figure 3 into black and white. [Figure 5] 10 is an electron microscope image of the top surface of a thermistor chip in a comparative example of the thermistor element and manufacturing method thereof according to the present invention. [Figure 6] 1 is a cross-sectional view showing a pair of sealing electrodes and a thermistor chip in a conventional thermistor element and a method for manufacturing the same according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] An embodiment of a thermistor element and a method for manufacturing the same according to the present invention will be described below with reference to Figures 1 and 2. Note that the scale of each drawing used in the following description has been appropriately changed so that each component can be recognized or easily recognized.

[0022] As shown in Figures 1 and 2, the thermistor element 1 of this embodiment comprises a chip-shaped or plate-shaped (flake-shaped) thermistor chip 2, a pair of sealing electrodes 3 arranged opposite each other on the upper and lower surfaces of the thermistor chip 2, and an insulating tube 4 to which the pair of sealing electrodes 3 are joined at both ends and which seals and encloses the thermistor chip 2 inside. The insulating tube 4 is, for example, a glass tube. The thermistor chip 2 comprises a chip-shaped or plate-shaped thermistor body 2a, a pair of electrode films 2b formed on the upper and lower surfaces of the thermistor body 2a, and an insulating protective film 2c formed on the outer peripheral surface of the thermistor body 2a and the pair of electrode films 2b.

[0023] At least a portion of the protective film 2c inside the ridge line of the thermistor body 2a within the surface of the electrode film 2b is removed to expose the electrode film 2b, forming an electrode film exposed portion 2d, and the electrode film exposed portion 2d is in contact with the sealing electrode 3. That is, at least a part of the protective film 2c inside the ridge line of the thermistor body 2a within the surface of the electrode film 2b has peeled off.

[0024] In this embodiment, there is a portion (electrode film exposed portion 2d) where the protective film 2c is peeled off inside the ridge line of the thermistor body 2a within the surface of the electrode film 2b. In particular, there is a portion (electrode film exposed portion 2d) where the protective film 2c is peeled off at least in the center within the surface of the electrode film 2b. The central portion refers to a region in the center of the electrode film 2b that has a similar shape and an area that is 1 / 4 of that of the electrode film 2b. For example, if the electrode film 2b is rectangular, the central portion refers to a region that is inward from the outer periphery by 1 / 4 of the length of one side of the electrode film 2b.

[0025] Furthermore, the electrode film exposed portion 2d is in contact with the opposing sealing electrode 3 within the surface of the electrode film 2b. In particular, a plurality of protrusions 2e are formed on the surface of the electrode film 2b, and the electrode film exposed portions 2d are at least some of the protrusions 2e. That is, the electrode film exposed portion 2d is flush with or protrudes from the surface of the protective film 2c. For example, if an Au paste is printed and baked on the upper and lower surfaces of the thermistor body 2a to form the Au electrode film 2b, many irregularities including a plurality of protrusions 2e are formed on the surface of the electrode film 2b.

[0026] The protective film 2c is made of a material that has a lower adhesive strength to the electrode film 2b than to the thermistor body 2a. That is, the electrode film 2b is made of a noble metal, and the protective film 2c is an oxide film or a nitride film. For example, the electrode film 2b is a metal film containing at least one of Pt, Au, and Ag, and the protective film 2c is an oxide film such as SiO2, Al2O3, ZrO2, or HfO2, or a nitride film such as AlN or Si3N4.

[0027] Furthermore, the protective film 2c is a thin film having a thickness set to 10 nm or more and 1000 nm or less. Also, the coverage rate of the protective film 2c in the plane of the electrode film 2b is preferably 99.99% or less. That is, the rate occupied by the electrode film exposed portion 2d in the plane of the electrode film 2b is preferably 0.01% or more. Note that there is no particular limitation on the lower limit of the coverage rate of the protective film 2c in the plane of the electrode film 2b, and it may even be 0%. Depending on the method of peeling the protective film 2c in the plane of the electrode film 2b, the protective film on the outer peripheral surface may also be peeled off at the same time. In that case, the coverage rate of the protective film 2c in the plane of the electrode film 2b is preferably 10% or more, and more preferably 50% or more.

[0028] The thermistor element 2a is an NTC thermistor containing a transition metal, and a perovskite-based material or a spinel-based material is adopted. For example, the thermistor element 2a is a metal oxide sintered body containing a perovskite-type oxide, and for example, the general formula: La 1-y Ca y (Cr 1-x Mn x )O3 (0.0 ≦ x ≦ 1.0, 0.0 < y ≦ 0.7). The sintered body may further contain, as an insulator material, for example, Y2O3, ZrO2, MgO, Al2O3, CeO2.

[0029] The above sealing electrode 3 is a so-called Dumet wire with a lead wire 3a connected to the outer surface, contains metal elements such as Fe, Ni, Cu as constituent components, and has a cuprous oxide film formed on the surface.

[0030] Next, a method for manufacturing the thermistor element of the present embodiment will be described. The method for manufacturing the thermistor element of this embodiment includes a thermistor chip formation process including an electrode film formation process for forming a pair of electrode films 2b on the upper and lower surfaces of a chip-shaped or plate-shaped thermistor body 2a and a protective film formation process for forming an insulating protective film 2c on the outer peripheral surface of the thermistor body 2a and on the pair of electrode films 2b; a protective film peeling process for peeling off at least a portion of the protective film 2c on the surface of the electrode film 2b on the thermistor chip 2 that is inside the ridge line (corner) of the thermistor body 2a to form an exposed electrode film portion 2d; and a sealing process for joining the pair of sealed electrodes 3 to both ends of an insulating tube 4 with the pair of sealed electrodes 3 arranged opposite each other on the upper and lower surfaces of the thermistor chip 2 and sealing the thermistor chip 2 inside.

[0031] In the sealing step, when the thermistor chip 2 is sandwiched between a pair of sealing electrodes 3, the electrode film exposed portion 2d and the sealing electrodes 3 are brought into contact with each other. In particular, in the protective film forming process, the protective film 2c is formed from the above-mentioned material whose adhesion strength with the electrode film 2b is weaker than that with the thermistor body 2a, and in the sealing process, at least a portion of the protective film 2c on the surface of the electrode film 2b is peeled off by the pressure applied when the thermistor chip 2 is sandwiched between a pair of sealing electrodes 3, thereby forming an exposed portion of the electrode film 2d.

[0032] In the protective film forming step, a vapor phase method such as sputtering or CVD can be used as a film forming method (coating method) for the protective film 2c, and a liquid phase deposition method can be used as a wet method. In the vapor phase method, film formation is performed in a vacuum, and oxygen defects may be formed in the thermistor material depending on the conditions. Therefore, a liquid phase deposition method using an alkoxide is preferred.

[0033] In this way, in the thermistor element 1 of this embodiment, at least a portion of the protective film 2c inside the ridge of the thermistor body 2a within the surface of the electrode film 2b is removed, exposing the electrode film 2b, and the exposed portion 2d of the electrode film is in contact with the sealed electrode 3. Therefore, the thermistor chip 2 and the pair of sealed electrodes 3 can be electrically connected while the protective film 2c covering the outer peripheral surface ensures resistance to reduction and prevents oxygen defects. Furthermore, since the electrode film exposed portion 2d is at least a part of the convex portion 2e, the exposed convex portion 2e and the sealing electrode 3 can easily and reliably come into contact with each other, thereby achieving good electrical contact. Even if the electrode film 2b does not have the protrusions 2e, the thermistor chip 2 and the pair of sealed electrodes 3 may be connected by peeling off the protective film 2c using the protrusions on the surface of the sealed electrode 3.

[0034] Furthermore, since the protective film 2c is formed from a material whose adhesion strength to the electrode film 2b is weaker than that to the thermistor body 2a, the protective film 2c adheres firmly to the outer peripheral surface of the thermistor body 2a, and the protective film 2c on the electrode film 2b can be easily peeled off, making it easy to form partial exposed portions 2d of the electrode film. In particular, since the electrode film 2b is formed of a precious metal and the protective film 2c is an oxide film or a nitride film, the protective film 2c of an oxide film or a nitride film that has strong adhesion to the thermistor material of the thermistor body 2a but weak adhesion to the precious metal can be easily obtained by a gas phase method such as sputtering or CVD, or a liquid phase deposition method.

[0035] Furthermore, in electrode films 2b formed by baking precious metal paste, voids often form in parts of the electrode film 2b, exposing the thermistor body 2a. However, in the thermistor element 1 of this embodiment, the thermistor body 2a exposed by the voids in the electrode film 2b is coated with a protective film 2c that has high adhesion to the thermistor material, and only the protective film 2c on the electrode film 2b made of precious metal, which has weak adhesion, is peeled off, which is more effective in suppressing the formation of oxygen defects than when only the outer surface (side surface) is coated with a protective film.

[0036] Furthermore, the manufacturing method for the thermistor element 1 of this embodiment includes a protective film peeling step in which at least a portion of the protective film 2c within the plane of the electrode film 2b that is located inside the ridge line of the thermistor body 2a is peeled off to form an exposed electrode film portion 2d, which makes it easy to bring the exposed electrode film portion 2d into contact with the sealing electrode 3 in the sealing step. In particular, even with a thin, plate-like (flake-like) thermistor body 2a, the protective film 2c is first formed on the outer peripheral surface of the thermistor body 2a and on the pair of electrode films 2b, i.e., on the entire surface, and then the protective film 2c is peeled off in the sealing step, so that the protective film 2c can be formed on the outer peripheral surface (side surface) and the electrode film 2b can be exposed.

[0037] Furthermore, since the protective film 2c is formed of a material whose adhesion strength to the electrode film 2b is weaker than that to the thermistor body 2a, the electrode film 2b, which has weak adhesion to the electrode film 2b, can be easily peeled off and exposed, allowing electrical connection to the sealed electrode 3. In particular, during the sealing process, the pressure applied when the thermistor chip 2 is sandwiched between a pair of sealing electrodes 3 peels off at least a portion of the protective film 2c on the surface of the electrode film 2b, forming an exposed portion 2d of the electrode film.Therefore, without adding a separate process of peeling off the protective film 2c within the surface of the electrode film 2b, the electrode film 2b, which has weak adhesion to the electrode film 2b, can be easily mechanically peeled off and exposed by pressing the sealing electrode 3, and electrical connection with the sealing electrode 3 can be made. Furthermore, since the protective film 2c has strong adhesion to the thermistor body 2a, the protective film 2c that has weak adhesion to the electrode film 2b can be easily peeled off while leaving the protective film 2c on the outer surface of the thermistor body 2a, thereby exposing the electrode film 2b. [Example]

[0038] Next, the rate of change in resistance value was measured for examples in which the thermistor element 1 of the above embodiment was actually produced by the above production method. The specific manufacturing method of the embodiment of the present invention was to first print and bake Au paste on a 0.2 mm thick thermistor wafer to form an Au electrode film, and then cut it into 0.5 mm squares to produce flake-shaped chips.

[0039] Next, as the protective film formation process, 100 g of a water-ethanol mixed solvent and the above-mentioned flake chips were placed in a beaker, and while stirring so that the flake chips were floating in the liquid, 5.2 g of ethyl orthosilicate and 16.6 g of an aqueous NaOH solution (0.2 mol / L) were added to form a protective film made of silicon oxide as a protective coating film on the entire surface of the flake chips, thereby producing a thermistor chip. The protective film has a thickness of 400 nm. Furthermore, the thermistor chip was sandwiched between a pair of sealing electrodes made of dumet wires in an Ar atmosphere and sealed in an insulating glass tube to prepare a glass diode type thermistor element.

[0040] For the examples of the present invention prepared in this manner, the rate of change in resistance value before and after sealing with an insulating tube, and the rate of change in resistance value before and after conducting a heat resistance test at 300°C for 1000 hours after sealing were measured and evaluated. As a comparative example of the present invention, a glass diode type thermistor element was also produced using a thermistor chip in which the outer peripheral surface of the flake-shaped chip was exposed without forming the protective film, and similar measurements and evaluations were carried out.

[0041] As a result, in the comparative example in which no protective film was formed, the rate of change in resistance value before and after sealing with the insulating tube was 27%, whereas in the example of the present invention, the rate of change in resistance value before and after sealing with the insulating tube was very small at 0.9%. In addition, in the comparative example, the rate of change in resistance value before and after the heat resistance test was 3.5%, whereas in the example of the present invention, the rate of change in resistance value before and after the heat resistance test was small at 0.9%. In the embodiment of the present invention, good electrical connection is obtained between the pair of sealed electrodes and the thermistor chip.

[0042] Next, in an example of the present invention, a thermistor chip was sandwiched between a pair of sealing electrodes and sealed in an insulating tube, and then the thermistor chip was removed and its surface was photographed with an electron microscope. Figure 3 shows an image of the surface, where the white dots in the image indicate exposed portions of the electrode film where the protective film has peeled off. This image was then binarized to black and white to more clearly show the exposed electrode film area, as shown in Figure 4. As can be seen from this image, there are areas within the surface of the electrode film where the protective film has peeled off, inside the ridge of the thermistor body. Furthermore, the coverage rate of the protective film excluding the exposed portion of the electrode film from this image, that is, the coverage rate of the protective film within the surface of the electrode film, was analyzed, and the coverage rate was found to be 99.53%. Furthermore, the coverage of the protective film on the outer peripheral surface of the thermistor body was confirmed to be nearly 100%, meaning that the coverage of the outer peripheral surface by the protective film was greater than the coverage of the electrode film within the surface.

[0043] The technical scope of the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment and example, the protective film is peeled off by pressing the sealing electrode, but the protective film within the electrode film surface may be intentionally peeled off in advance by ultrasonic cleaning or barrel polishing. [Explanation of symbols]

[0044] 1... thermistor element, 2, 102... thermistor chip, 2a... thermistor element body, 2b, 102b... electrode film, 2c... protective film, 2d... exposed electrode film portion, 2e... convex portion, 3... sealed electrode, 4... insulating tube

Claims

1. a chip-shaped or plate-shaped thermistor chip; a pair of sealing electrodes disposed opposite to each other on the upper and lower surfaces of the thermistor chip; an insulating tube to which the pair of sealed electrodes are joined at both ends and which seals the thermistor chip therein; The thermistor chip comprises a chip-shaped or plate-shaped thermistor element; a pair of electrode films formed on the upper and lower surfaces of the thermistor body; an insulating protective film formed on the outer peripheral surface of the thermistor body and on the pair of electrode films; a part of the protective film on the inner side of the ridge line of the thermistor body within the surface of the electrode film is removed to form an electrode film exposed portion, the exposed portion of the electrode film is in contact with the sealing electrode, the electrode film is formed of a noble metal, the protective film is an oxide film or a nitride film, pores are formed in a part of the electrode film, the electrode film exposed portions are scattered in a plurality of locations within a surface of the electrode film, The thermistor element is characterized in that the protective film covers the electrode film except for the scattered exposed electrode film portions, and also covers the thermistor element body exposed by the holes.

2. 2. The thermistor element according to claim 1, a plurality of protrusions formed on the surface of the electrode film; A thermistor element, wherein the exposed electrode film portion is at least a part of the convex portion.

3. 3. The thermistor element according to claim 1, A thermistor element characterized in that the protective film is formed of a material having a lower adhesive strength with the electrode film than with the thermistor element body.

4. The thermistor element according to any one of claims 1 to 3, A thermistor element characterized in that the thickness of the protective film is 10 nm or more and 1000 nm or less.

5. The thermistor element according to any one of claims 1 to 4, A thermistor element characterized in that the coverage of the protective film on the outer peripheral surface of the thermistor body is greater than the coverage of the electrode film within the surface of the electrode film.

6. The thermistor element according to any one of claims 1 to 5, A thermistor element characterized in that the coverage of the protective film within the surface of the electrode film is 99.99% or less.

7. A method for manufacturing the thermistor element according to any one of claims 1 to 6, comprising the steps of: a thermistor chip forming process including an electrode film forming process for forming a pair of electrode films, some of which have voids, on the upper and lower surfaces of a chip-shaped or plate-shaped thermistor element by baking a noble metal paste; and a protective film forming process for forming an insulating protective film on the outer peripheral surface of the thermistor element and on the pair of electrode films; a protective film peeling step of peeling off a part of the protective film on the inner side of the ridge line of the thermistor body within the surface of the electrode film of the thermistor chip to form the exposed electrode film portion; a sealing step of joining a pair of sealing electrodes to both ends of an insulating tube in a state where the pair of sealing electrodes are arranged opposite each other on the upper and lower surfaces of the thermistor chip, and sealing the thermistor chip therein; In the protective film forming step, the thermistor body exposed by the holes is also covered with the protective film; a thermistor element manufacturing method, characterized in that in the sealing step, the exposed portion of the electrode film is brought into contact with the sealing electrodes when the thermistor chip is sandwiched between the pair of sealing electrodes;

8. 8. The method for manufacturing a thermistor element according to claim 7, A method for manufacturing a thermistor element, wherein in the protective film forming step, the protective film is formed from a material whose adhesive strength with the electrode film is smaller than that with the thermistor element body.

9. 9. The method for manufacturing a thermistor element according to claim 7 or 8, A method for manufacturing a thermistor element, characterized in that in the sealing process, a portion of the protective film within the surface of the electrode film is peeled off by the pressure applied when the thermistor chip is sandwiched between the pair of sealing electrodes, thereby forming the exposed portion of the electrode film.

Images