thermistor

Abstract

The present application realizes a thermistor in which a complex including a plurality of particles composed of a metal oxide is used as a thermistor layer, and a high bonding strength is obtained between the thermistor layer and electrodes. A thermistor is a thermistor in which a structure including a thermistor layer and two electrodes is arranged on a base layer, the base layer includes a resin component, the thermistor layer includes a plurality of particles composed of a metal oxide including at least one first metal element, and a complex existing between the plurality of particles and including an amorphous phase of the same metal element as the first metal element, the first metal element including at least one of Mn and Ni, the two electrodes are composed of at least one second metal element selected from Cu, Al, Ag, and Ni, and a bonding layer in which the second metal element and the resin component are diffused in the complex exists between the two electrodes and the thermistor layer.

Description

Technical Field

[0001] The present invention relates to a thermistor, and more specifically to a thermistor having a structure comprising a thermistor layer and two electrodes disposed on a substrate layer. Background Technology

[0002] Previously, various thermistors, also known as thin-film thermistors, were known to have a structure containing a thermistor layer and two electrodes disposed on a substrate layer (substrate). (For example, see Patent Documents 1-4).

[0003] More specifically, Patent Document 1 discloses a thermistor comprising a metal substrate, a thermistor layer composed of a metal oxide formed on the metal substrate, and a pair of separate electrodes formed on the thermistor layer. Patent Documents 2-4 disclose a thermistor comprising a thermistor layer composed of a metal nitride and a pair of comb-shaped opposing electrodes formed sequentially or in reverse order on an insulating substrate serving as a resin film.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2011 / 024724

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-138798

[0008] Patent Document 3: Japanese Patent Application Publication No. 2019-96805

[0009] Patent Document 4: Japanese Patent Application Publication No. 2018-169248 Summary of the Invention

[0010] As a material for the thermistor layer, metal nitrides can be formed at room temperature by sputtering (see Patent Documents 2-4). However, the bonding strength between the sputtered thermistor layer (metal nitride) and the electrode is not necessarily sufficient. In contrast, in conventional forming methods, metal oxides need to be sintered at high temperatures above 900°C (see Patent Document 1). Due to the difference in thermal expansion coefficients between the thermistor layer (metal oxide) and the electrode, it is difficult to obtain high bonding strength between them.

[0011] The purpose of this invention is to realize a thermistor, which is a composite of multiple particles composed of metal oxides, wherein the metal element in the metal oxide includes at least one of Mn and Ni as the thermistor layer, and a high bonding strength is obtained between the thermistor layer and the electrode.

[0012] According to a first aspect of the present invention, a thermistor is provided, which is a thermistor having a structure comprising a thermistor layer and two electrodes disposed on a substrate layer.

[0013] The aforementioned matrix layer contains resin components.

[0014] The aforementioned thermistor layer comprises a plurality of particles consisting of a metal oxide containing at least one first metal element; and a composite of an amorphous phase existing between the plurality of particles and containing the same metal element as the first metal element, wherein the first metal element comprises at least one of Mn and Ni.

[0015] The two electrodes described above are composed of at least one second metallic element selected from Cu, Al, Ag, and Ni.

[0016] Between the two electrodes and the thermistor layer, there is a bonding layer in the composite where the second metal element and the resin component are diffused.

[0017] According to a second aspect of the present invention, a thermistor is provided, which is a thermistor having a structure comprising a thermistor layer and two electrodes disposed on a substrate layer.

[0018] The aforementioned matrix layer contains resin components.

[0019] The aforementioned thermistor layer comprises a plurality of particles consisting of a metal oxide containing at least one first metal element; and a composite of an amorphous phase existing between the plurality of particles and containing the same metal element as the first metal element, wherein the first metal element comprises at least one of Mn and Ni.

[0020] The two electrodes comprise a base material composed of at least one second metal element selected from Cu, Al, Ag and Ni; and a capping layer formed on the surface of the base material and composed of at least one third metal element selected from Ni, Au, Ag, Pt, Pd, Zn, Cr, W, Mo, Cu and Ti.

[0021] According to one aspect of the second aspect of the invention, a bonding layer in which the third metal element and the resin component diffuse into the composite exists between the two electrodes and the thermistor layer.

[0022] According to one aspect of the second aspect of the present invention, a bonding layer in which the second metal element, the third metal element, and the resin component diffuse into the composite is present between the two electrodes and the thermistor layer.

[0023] In the first and second aspects of the present invention, the structure may be two surfaces facing each other, the two surfaces having unevenness or flatness that is less than the thickness of the two electrodes.

[0024] In the first and second aspects of the present invention, the two electrodes can be disposed separately on the substrate layer, and the thermistor layer can be disposed on the two electrodes and the substrate layer.

[0025] In the first and second aspects of the present invention, the first metallic element may further include at least one selected from Fe, Al, Co and Cu.

[0026] In the first and second aspects of the present invention, the resin component may include at least one selected from polyethylene terephthalate, polyetherimide, polyamide imide, polyimide, polytetrafluoroethylene, epoxy resin and liquid crystal polymer.

[0027] According to the present invention, a thermistor is realized in which a composite comprising multiple particles of metal oxide (the metal element of the metal oxide includes at least one of Mn and Ni) is used as the thermistor layer, and a high bonding strength can be obtained between the thermistor layer and the electrode. Attached Figure Description

[0028] Figure 1 This is an explanatory diagram of a thermistor illustrating one embodiment of the present invention. (a) shows a simplified cross-sectional view of the thermistor, and (b) shows a simplified cross-sectional view obtained by enlarging the area Z enclosed by the dotted line in (a).

[0029] Figure 2 This is an explanatory diagram illustrating a thermistor according to one embodiment of the present invention, and is a partial schematic diagram showing the structure of the composite constituting the thermistor layer.

[0030] Figure 3 The figure illustrates an example of a thermistor according to one embodiment of the present invention. (a) shows a simplified cross-sectional view observed by X-rays in (b), and (b) shows a schematic top view.

[0031] Figure 4 This is an explanatory diagram illustrating another embodiment of the thermistor of the present invention. (a) shows a simplified cross-sectional view of the thermistor, and (b) shows a simplified cross-sectional view obtained by enlarging the region Z enclosed by the single-dotted line in (a).

[0032] Figure 5 These are explanatory diagrams illustrating the thermistor samples prepared in Examples 1-3 and Comparative Example 2. (a) is a top view illustrating a pair of electrodes and an extraction electrode, and (b) is a top view illustrating the thermistor layer (represented by diagonal lines in the figure).

[0033] Figure 6(a) is a field emission scanning electron microscope (FE-SEM) image of the cross section of the thermistor sample prepared in Example 1, and (b) is a field emission scanning electron microscope (FE-SEM) image of the cross section of the thermistor prepared in Comparative Example 2. Detailed Implementation

[0034] Regarding the thermistors of the two embodiments of the present invention, the following will refer to the accompanying drawings. Figure 1 The following explanations will be provided. In the diagrams, the same symbols are used for the same parts, and the same explanations will be used unless otherwise specified.

[0035] (Implementation Method 1)

[0036] This embodiment relates to a thermistor whose two electrodes are composed of a second metal element.

[0037] like Figure 1 As shown in (a) and (b), in the thermistor 30 of this embodiment, a structure 20 including a thermistor layer 11 and two electrodes 13a and 13b (collectively referred to as “13”) is disposed on a substrate layer 27.

[0038] The substrate layer 27 may simply contain a resin component. The resin component is not particularly limited, but may contain at least one selected from polyethylene terephthalate, polyetherimide, polyamide-imide, polyimide, polytetrafluoroethylene, epoxy resin, and liquid crystal polymer (LCP). From the viewpoint of heat resistance and adhesion, polyimide or polyamide-imide is preferred. The substrate layer 27 may, for example, be a resin substrate (resin film) composed of this resin component. In this embodiment, the substrate layer 27 is an insulating substrate.

[0039] like Figure 1 (b) and Figure 2 As shown, the thermistor layer 11 is a composite 10 (hereinafter also referred to as "a composite containing metal oxides"), the composite 10 comprising a plurality of particles (hereinafter simply referred to as "metal oxide particles") 1 composed of metal oxides containing at least one first metal element, and an amorphous phase (hereinafter also referred to as "first amorphous phase") 2 existing between the plurality of particles 1 and containing the same metal element as the first metal element.

[0040] The metal oxide constituting the metal oxide particle 1 may include at least one of Mn and Ni as the first metal element, and further include at least one selected from Fe, Al, Co, and Cu. Mn and / or Ni are essential metal elements of the metal oxide. Additionally, at least one selected from Fe, Al, Co, and Cu is an optional additive metal element of the metal oxide. The optional additive metal element is preferably at least one selected from Fe, Al, and Co. The metal oxide may be a metal oxide semiconductor, particularly having a spinel-type structure, but is not limited thereto.

[0041] The proportion of metal elements in the overall metal oxide comprising multiple metal oxide particles 1 is not particularly limited and can be appropriately selected according to desired electrical properties, etc. Regarding essential metal elements, in the presence of both Mn and Ni, the Mn:Ni ratio (atomic ratio) can be, for example, 1 to 100:1. In the presence of any added metal elements, the total amount of any added metal elements (if multiple are present) is sufficient as long as it is less than the essential metal elements (if both Mn and Ni are present), but the ratio (atomic ratio) of essential metal elements to any added metal elements can still be, for example, 1 to 100:1.

[0042] The average particle size of the metal oxide particles 1 can be, for example, 0.01 μm to 100 μm, particularly 0.02 μm to 1 μm. By making the average particle size of the metal oxide particles 1 within the range of 0.01 μm to 100 μm or less, in the manufacturing method described later in this embodiment, the metal oxide particles can be easily transported between other metal oxide particles through a liquid medium and / or fluid (preferably a solvent) from metal acetylacetone, thereby enabling more efficient high-density composite formation. In this specification, the average particle size refers to the particle size (D50) at the point where the cumulative value is 50% in a cumulative curve with the total volume as 100%, based on the particle size distribution determined by volume. This average particle size can be measured using a laser diffraction-scattering particle size and particle size distribution measuring device or an electron scanning microscope.

[0043] The metal oxide particles 1 can be a mixture of two or more metal oxide particles with different metal oxide compositions and / or average particle sizes.

[0044] The first amorphous phase 2 exists between the metal oxide particles 1, allowing the metal oxide particles 1 to adhere to each other. Therefore, the composite 10 itself has high strength. Although not limited to this embodiment, it is possible to form a structure in which a plurality of metal oxide particles 1 are dispersed in a continuous phase of the first amorphous phase 2. In addition, the composite 10 can contain metal oxide particles 1 at a high density through the first amorphous phase 2 (it is possible to form a conductive path based on the highly dispersed metal oxide particles 1). Furthermore, the first amorphous phase 2 can exhibit electrical properties that approximate those of metal oxide (semiconductor) particles 1 having a crystalline structure. Thus, the same electrical properties as those of sintered bodies formed by sintering metal oxide particles at high temperatures using conventional methods can be obtained.

[0045] The first amorphous phase 2 contains the same metal element as the first metal element contained in the metal oxide particles 1. Therefore, even if interdiffusion occurs between the metal oxide particles 1 and the first amorphous phase 2, the deterioration of the electrical properties of the composite 10 can be effectively prevented.

[0046] In this specification, an amorphous phase refers to a phase that does not actually have crystallinity or has a low degree of crystallinity, which can be distinguished from particles with a crystalline structure based on electron X-ray diffraction patterns obtained by methods known to those skilled in the art.

[0047] In this embodiment, the presence of the first amorphous phase 2 between the metal oxide particles 1 means that the first amorphous phase 2 can fill the space between multiple metal oxide particles 1. Therefore, voids that may be contained in the composite 10 can be eliminated by filling the space with the first amorphous phase 2, thus reducing the change in resistance value before and after placement in a high-temperature and high-humidity environment, which is considered to be due to voids. Considering any two adjacent metal oxide particles 1, these two metal oxide particles 1 may have the first amorphous phase 2 between them, or they may be in contact (preferably bonded) without the first amorphous phase 2 actually present between them. In the former case, the first amorphous phase 2 can exist with a thickness of 100 μm or less. The smaller the thickness of the first amorphous phase 2, the better, considering electrical properties and / or strength. In the latter case, the portion without the first amorphous phase 2 actually present can exist in the composite 10.

[0048] It should be noted that composite 10 (especially the first amorphous phase 2) does not actually contain silicon oxides such as SiO2 glass. Silicon oxides are undesirable because they cause a significant reduction in electrical properties. The content of silicon oxides in composite 10 (relative to the total mass of metal oxide particles) is, for example, 0.1% by mass or less, preferably 0.01% by mass or less, and practically more preferably zero% by mass.

[0049] The composite 10 is obtained by heating (also called firing, or "sintering" in the case of metal oxide particles) a mixture of raw materials (containing metal oxide particles 1 and metal acetylacetone) as the precursor under pressure at a temperature below 600°C, as described below. In other words, the composite 10 can be manufactured by low-temperature firing.

[0050] The two electrodes 13a and 13b are composed of at least one second metal element selected from Cu, Al, Ag, and Ni. When electrode 13 is composed of two or more second metal elements, it can be an alloy. The second metal element is preferably any one or more of Ni, Cu, and Ag. This second metal element is cheaper than Ag-Pd (an alloy formed by mixing and sintering Ag particles and Pd particles) described in Patent Document 1 and is readily available. According to this embodiment, expensive and resource-scarce metals can be avoided. For example, when performing heat treatment at 600°C or below (co-sintering with the thermistor layer, and in this case, annealing), Ag, Ni, etc., can be used; when performing heat treatment at 500°C or below, Cu, Al, Ag, Ni, etc., can be used. It should be noted that in this specification, the term "co-sintering" refers to a heat treatment (firing) simultaneously applied to the precursor (raw material mixture) for sintering the thermistor layer. In this embodiment, the substrate layer and the electrode are co-sintered with the thermistor layer.

[0051] In this embodiment, such as Figure 1 As shown in (a) and (b), bonding layers 15a and 15b (collectively referred to as "15") exist between the two electrodes 13a and 13b and the thermistor layer 11 (composite 10). Bonding layer 15 is formed by diffusing a second metal element and a resin component into the composite 10. In practice, the boundary between the composite 10 and bonding layer 15 may be unclear (in the figures, a dashed line indicates an imaginary boundary). In this case, the composite 10 and bonding layer 15 can be collectively understood as either a composite layer containing metal oxides or a thermistor layer. The composite 10 located between the electrodes 13a and 13b can function together with the bonding layers 15a and 15b as a thermistor layer whose resistance changes according to temperature (more specifically, having a negative temperature coefficient).

[0052] More specifically, the bonding layer 15 is formed by the diffusion of a second metal element from the electrode 13 and a resin component from the substrate layer 27 into the composite 10 (comprising metal oxide particles 1 and a first amorphous phase 2). The second metal element can be formed by diffusion from the electrode 13 to the composite 10 via heat and dissolution (more specifically, by dissolution of the metal element into the metal acetylacetone that can occur during the application and heat treatment of the raw material mixture (comprising a mixture of metal oxide particles and metal acetylacetone). The resin component can be formed by diffusion from the substrate layer 27 to the composite 10 via heat and dissolution (more specifically, by dissolution of the resin component into the metal acetylacetone that can occur during the application and heat treatment of the raw material mixture). The second metal element and the resin component can diffuse into either the metal oxide particles 1 or the first amorphous phase 2, but in most cases, they can diffuse more extensively into the first amorphous phase 2. As described above, since the first amorphous phase 2 contains the same metal element as the first metal element, it can also be understood that in the bonding layer 15, the second amorphous phase 12 contains the same metal element as the first metal element, the same metal element as the second metal element, and an element identical to the resin composition (carbon element if the resin composition contains carbon). The bonding layer 15 can be understood as a region containing both the same metal element as the second metal element and elements identical to the resin composition (representatively carbon element). It should be noted that the elements (especially metal elements and carbon elements) contained in the thermistor layer and the bonding layer can be confirmed using scanning electron microscopy (STEM) and / or energy dispersive X-ray analysis (EDX).

[0053] According to the thermistor 30 of this embodiment, since the composite 10, which can be manufactured by low-temperature sintering, is used in the thermistor layer 11, by heating the raw material mixture used to obtain the composite 10 together with the substrate layer 27 and the electrodes 13a, 13b, it is possible to co-sinter the composite 10 with the substrate layer 27, the electrodes 13a, 13b, and the thermistor layer 11. As a result, bonding layers 15a, 15b, formed by the diffusion of a second metal element and resin components in the composite, are formed between the electrodes 13a, 13b and the thermistor layer 11. Through these bonding layers 15a, 15b, a high bonding strength can be obtained between the thermistor layer 11 (composite 10) and the electrodes 13a, 13b.

[0054] In the thermistor 30 of this embodiment, the bonding layer 15 (more specifically, the second amorphous phase 12) contains the same metal element as the first metal element and the second metal element. The bonding layer 15 can exhibit electrical properties similar to those of metal oxide (semiconductor) particles 1 having a crystalline structure. In addition, by making the bonding layer 15 contain the same metal element as the first metal element and the second metal element, the resistance between the composite 10, the bonding layer 15 and the electrode 13 (briefly speaking, the Schottky barrier between the metal oxide (semiconductor) particles 1 and the electrode 13; more specifically, the interfacial resistance between the metal oxide particles 1 and the second amorphous phase 12 and between the second amorphous phase 12 and the electrode 13) can be reduced, thereby improving the electrical properties of the thermistor 30.

[0055] In the thermistor 30 of this embodiment, since the composite 10 contains metal oxide particles 1 at a high density through the first amorphous phase 2, and the first amorphous phase 2 and the second amorphous phase 12 exhibit electrical properties similar to those of metal oxide (semiconductor) particles 1, it is possible to obtain the same electrical properties as a sintered body formed by sintering metal oxide particles at high temperature using conventional methods, thus achieving the desired electrical properties (e.g., thermistor characteristics, more specifically, room temperature resistivity, B constant, etc.). Furthermore, in the thermistor 30 of this embodiment, the composite 10 is securely bonded to the electrodes 13a and 13b via bonding layers 15a and 15b, achieving high bonding strength. High bonding strength also results in small deviations in the resistance value of the thermistor 30, achieving high reliability. This primarily stabilizes the initial characteristics of the thermistor 30 and ensures the reliability of the thermistor 30 in response to environmental changes.

[0056] On the other hand, in conventionally known thermistors (for example, see Patent Document 1), metal elements can diffuse from the electrode through simple heat treatment. However, in this case, oxidation of the electrode can occur, reducing the thermistor characteristics. In addition, due to the difference in thermal expansion coefficients between the electrode and the thermistor layer, it is difficult to obtain high bonding strength. In contrast, the thermistor 30 of this embodiment does not impair the thermistor characteristics and can obtain high bonding strength.

[0057] In the thermistor 30 of this embodiment, the thickness of the structure 20 (including the thermistor layer 11 and electrodes 13a, 13b) disposed on the substrate layer 27 can be, for example, 100 μm or less, and more specifically, 1 μm to 30 μm. This thermistor 30 is also referred to as a thin-film thermistor. The thickness of the substrate layer 27 is not particularly limited, but in the case of a thin-film thermistor, it can be, for example, 1 to 50 μm.

[0058] By thinning the thermistor 30 as described above, it can be easily installed in confined spaces. Furthermore, it reduces physical damage to both the thermistor 30 and the object on which it is mounted, caused by pressure during installation and operation. Additionally, the thermistor 30 exhibits high temperature responsiveness due to its small heat capacity. Moreover, because the composite 10 (and bonding layers 15a, 15b) is thin and flexible, it is not easily damaged even with deformation. In particular, when a flexible substrate (e.g., a resin film) is used as the base layer 27, a flexible thermistor 30 can be obtained as a whole.

[0059] In this embodiment, the structure 20 has two opposing surfaces A and B (these surfaces may also be opposite to the main surface of the substrate layer 27). These two surfaces A and B have unevenness that is smaller than the thickness of the two electrodes 13a and 13b, but are preferably flat. Figure 1 (a) indicates the case where surfaces A and B are flat. Compared to the substrate layer 27 containing resin components, the thermistor layer 11, which is a composite containing metal oxides, and the structure 20, which contains the electrode 13 as a metal, have significant differences in material properties such as height and stress deformation, resulting in higher hardness. Because surfaces A and B of the structure 20 have small irregularities, and more preferably flatness, when sandwiched between two objects with flat opposing surfaces and pressure F is applied in the thickness direction of the thermistor 30, pressure is evenly applied to the structure 20 and the substrate layer 27, and the thermistor characteristics are not damaged. Furthermore, when the thermistor 30 is used as a temperature sensor, it is less likely to damage the object being measured (which can be either of the two objects mentioned above), resulting in high pressure resistance. Either surface A or B of the structure 20 is in contact with the object being measured, but has small irregularities, or more preferably flatness, thus providing a large contact area and excellent thermal responsiveness. Only structure 20 can achieve both high pressure resistance and thermal responsiveness (in the case of unevenness that is larger than the thickness of the electrode, a resin layer is not formed in order to reduce unevenness).

[0060] The thickness of electrodes 13a and 13b is preferably greater than 1 μm to effectively avoid electrode breakage. While the aforementioned effect can be minimized even with the smallest electrode thickness, for example, when the thermistor layer is approximately 1 to 10 μm thick, sufficient effects on pressure resistance and thermal responsiveness can be achieved by keeping the unevenness present on the two surfaces A and B to less than 1 μm.

[0061] On the other hand, conventionally known thermistors (see, for example, Patent Documents 1, 3, and 4) have relatively large unevenness on the surface of the structure composed of electrodes and a thermistor layer. If the thermistor is sandwiched between two objects with flat opposing surfaces and pressure F is applied in the thickness direction, the load concentrates on the electrodes and / or thermistor layer, which have high hardness and low elastic deformation, potentially damaging the thermistor's characteristics. Furthermore, when the thermistor is used as a temperature sensor, it may damage the object being measured. Additionally, when there is relatively large unevenness on the surface of the structure, an air layer forms, reducing the contact area with the object being measured and worsening the thermal responsiveness. While it is thought that a countermeasure could be made by embedding the relatively large unevenness in resin, resin generally has thermal resistance, leading to impaired thermal responsiveness. In contrast, the thermistor 30 of this embodiment achieves high voltage resistance and thermal responsiveness.

[0062] In this embodiment of the thermistor 30, the arrangement of the thermistor layer 11 and the two electrodes 13a and 13b is not particularly limited, such as Figure 1 As shown in (a), the two electrodes 13a and 13b can be disposed separately on the substrate layer 27, and the thermistor layer 11 can be disposed on the two electrodes 13a and 13b and the substrate layer 27. It should be noted that the electrodes are not limited to these two; depending on the situation, there may be three or more.

[0063] In one example of the thermistor 30 in this embodiment, electrodes 13a and 13b are as follows: Figure 3 The image shows a comb-shaped counter electrode formed on the substrate layer 27. It should be noted that... Figure 3 In (b), electrodes 13a and 13b located below the thermistor layer 11 are shown in a perspective view, omitting bonding layers 15a and 15b. This allows for control of the electrical characteristics of the thermistor 30 (e.g., further reducing resistance deviation), achieving high temperature resolution. In this example of the thermistor 30, the two electrodes 13a and 13b can be electrically connected to two external electrodes 14a and 14b, respectively. In this example, by forming comb-shaped opposing electrodes on the substrate layer 27, which serves as an insulating substrate, gaps can be formed in the planar direction (parallel to the main surface of the substrate layer 27) between these electrodes. It should be noted that... Figure 3 In the example shown, external electrodes 14a and 14b are provided on the two outer sides of the pair of opposing electrodes 13a and 13b in the comb-like shape (on the two outer sides of the length direction L1 of the teeth), but an extraction electrode extending along the width direction L2 of the teeth can be formed on the two outer sides of the pair of opposing electrodes 13a and 13b in the comb-like shape.

[0064] The thermistor 30 of this embodiment described above can be manufactured using any suitable method, but for example, it can be manufactured using the method described below.

[0065] First, electrodes 13a and 13b, composed of a second metal element, are formed on the substrate layer 27. The electrodes 13a and 13b can be patterned by any suitable method such as photolithography, electroplating, vapor deposition, or sputtering. Alternatively, a paste containing particles of the second metal element can be used to form the precursors of the electrodes 13a and 13b, which can then be fired simultaneously with the precursor of the thermistor layer 11.

[0066] Next, as described above, in the designated area of ​​the substrate layer 27 where the electrodes 13a, 13b (or the precursor) are formed (the area where the composite 10 and the bonding layers 15a, 15b, i.e., the area where the composite layer containing metal oxides is formed), a mixture containing metal oxide particles 1 and metal acetylacetone (hereinafter also referred to as "raw material mixture" in this specification) is applied and heated under pressure at a temperature above the melting point of the aforementioned metal acetylacetone and below 600°C, thereby forming the composite 10 and the bonding layers 15a, 15b (and, in the case of co-firing, the electrodes 13a, 13b) simultaneously and integrally in the form of a sintered body containing metal oxide particles 1.

[0067] The raw material mixture can be applied to a specified area (e.g., coating, printing (screen printing, etc.)) using methods known to those skilled in the art. The substrate layer to which the raw material mixture has been applied is then subjected to drying treatments such as heating or natural drying as needed. Subsequently, it can be heated under pressure at a temperature above the melting point of metallic acetylacetone and below 600°C using means known to those skilled in the art, such as a stamping press.

[0068] In this specification, metal acetylacetone refers to the metal acetylacetone salt, and more specifically, the acetylacetone ion ((CH3COCHCOCH3) with bidentate ligands). － This can also be abbreviated as (acac). － The metal acetylacetone contains a chelating ligand of the central metal. The metal element contained in the metal acetylacetone is selected from any one or more of the first metal elements mentioned above, preferably the same metal element as the first metal element contained in the metal oxide particle 1, but is not limited thereto.

[0069] Metallic acetylacetones can be used with one type of metallic acetylacetone or in combination with two or more types. When the metal oxide particle 1 contains two or more of the first metallic element, the combination of two or more metallic acetylacetones can be used, depending on the ratio of these metallic elements present; this is not a limitation.

[0070] A raw material mixture is obtained by mixing metal oxide particles and metal acetylacetone. The mixing of metal oxide particles and metal acetylacetone can be carried out in an atmosphere at normal temperature and humidity and atmospheric pressure. The metal acetylacetone relative to the total mass of the metal oxide particles can be mixed in a ratio of, for example, 0.1% to 50% by mass, preferably 1% to 30% by mass, and more preferably 2% to 10% by mass.

[0071] The mixed metal acetylacetone can be used in any state. For example, the raw material mixture can be obtained by mixing metal oxide particles with dry, powdered solid metal acetylacetone. In this case, the raw material mixture is obtained by mixing the metal oxide particles with the powdered metal acetylacetone, for example, at atmospheric pressure in one or more solvents selected from water, acetylacetone, alcohols containing methanol and / or ethanol, or in one or more gases selected from air, nitrogen, etc.

[0072] Alternatively, the raw material mixture can be obtained by mixing metal oxide particles, metal acetylacetone, and a solvent. Any suitable solvent can be used, for example, it can be one or a mixture of two or more selected from water, acetylacetone, alcohols containing methanol and / or ethanol. The solvent should not be excessive, only sufficient to allow for heating the raw material mixture under pressure; there is no particular limitation, but relative to the total mass of the metal oxide particles, it can be mixed in a ratio of, for example, 50% by mass or less, preferably 30% by mass or less. During mixing, the metal acetylacetone and the solvent can be used separately, or a liquid in which the metal acetylacetone is dispersed or dissolved in the solvent can be used. In the latter case, a liquid containing synthesized metal acetylacetone can be used, and the metal acetylacetone will not separate from the liquid. More specifically, metal acetylacetone can be synthesized by mixing liquid acetylacetone with a metal compound (e.g., a metal hydroxide or chloride), and the synthesized liquid can be used in this state or with the addition of solvent as needed.

[0073] It should be noted that the raw material mixture may contain any suitable materials other than the metal oxide particles and metal acetylacetone, to the extent that it does not negatively affect the desired electrical properties. More specifically, the raw material mixture may further include additives such as pH adjusters, sintering aids, and pressure easing agents. These additives may be mixed in a ratio of, for example, 0.01% to 10% by mass relative to the total mass of the metal oxide particles, preferably in a ratio of 0.01% to less than 1% by mass, and more preferably in a ratio of 0.01% to 0.1% by mass.

[0074] By heating the raw material mixture obtained as described above under pressure at a temperature above the melting point of metallic acetylacetone and below 600°C, a relatively high-density sintered body can be formed. During this heating process, the metallic acetylacetone liquefies and functions as a liquid medium. Heating is preferably performed in the presence of a fluid. In this specification, the fluid is, for example, a liquid, preferably a liquid that can be used as a solvent, and more preferably water. For example, when water is present during the heating and pressurization of the raw material mixture, water is present at the interface of the metal oxide particles contained in the raw material mixture. Therefore, the raw material mixture can be sintered at a lower temperature, and the strength of the sintered body can be effectively improved.

[0075] In this specification, "the mixture is in a state where water is present" can also mean that water is not actively added to the mixture, but is only slightly present at the interface of the metal oxide particles. It can also refer to the degree to which the metal oxide particles absorb moisture at room temperature. Active addition of water can be carried out by inclusion (mixing) into the raw material mixture, or by heating and pressurizing the raw material mixture under a steam atmosphere. Particularly when water is present in the raw material mixture, it is possible for water to effectively propagate through the interfaces of the particles. When water is mixed into the raw material mixture, the amount is not particularly limited, but relative to the total mass of the metal oxide particles, it can be, for example, 20% by mass or less, preferably 15% by mass or less, and representatively 10% by mass. By keeping the water mixed in the raw material mixture at 20% by mass or less, water can be incorporated into the raw material mixture, and the reduction in the formability of the raw material mixture can be more effectively prevented. To effectively improve the strength of the sintered body, it is preferable to use as much water as possible within the above range, specifically 10% to 20% by mass. In addition, in order to facilitate molding, it is preferable to use less water within the above range, specifically more than 0% by mass and less than 10% by mass.

[0076] The pressure applied to the raw material mixture can be, for example, 1 MPa to 5000 MPa, preferably 5 MPa to 1000 MPa, and more preferably 10 MPa to 500 MPa. In this specification, pressurizing the raw material mixture refers to applying pressure (or physical / mechanical pressure) to the raw material mixture (more specifically, the solid components contained in the raw material mixture) using, for example, a pressure molding machine. Therefore, even when the raw material mixture is pressurized, it should be noted that the liquid components contained in the raw material mixture are exposed to the pressure of the ambient atmosphere (typically atmospheric pressure).

[0077] The heating temperature of the raw material mixture (hereinafter referred to as "heating temperature" in this specification) refers to the firing temperature, which can be a temperature above and below 600°C of the melting point of the metallic acetylacetone contained in the raw material mixture. In this specification, melting point refers to the temperature measured at room temperature and atmospheric pressure using a method defined by JIS standards. It should be noted that melting points vary depending on various conditions such as the pressure during pressurization. The melting points of various metallic acetylacetones are shown in Table 1 below. When using two or more metallic acetylacetones, "melting point of metallic acetylacetone" refers to the highest melting point among all metallic acetylacetones. The heating temperature of the raw material mixture is determined according to the type of metal oxide used, etc., and can be a temperature 5°C or higher than the melting point of the metallic acetylacetone but below 600°C, for example, 100°C to 600°C, preferably 100°C to 400°C, and more preferably 100°C to 300°C.

[0078] [Table 1]

[0079] Metallic acetylacetone Melting point (°C) Manganese acetylacetone 161 Nickel acetylacetone 230 Iron acetylacetone 185 Aluminum acetylacetone 193 Zirconium acetylacetone 198 Copper acetylacetone 284

[0080] By heating the raw material mixture under pressure at a temperature above the melting point of metallic acetylacetone, a relatively high-density sintered body can be formed at a low temperature, as described above. In this specification, "relatively high density" refers to a density ratio relative to the theoretical density of the sintered body obtained therefrom that is higher than the density ratio relative to the theoretical density of the sintered body obtained when the metal oxide particles contained in the raw material mixture are heated and pressurized individually (without metallic acetylacetone) under the same temperature and pressure conditions. The sintered body obtained according to this embodiment can have a relatively high density, and the density ratio relative to the theoretical density is determined according to the composition of the metal oxide particles used, for example, it can be 70% or more, preferably 80% or more. It is conceivable that the metal oxides contained in the obtained sintered body are essentially the same as the metal oxide particles contained in the raw material mixture. The heating and pressurization time of the raw material mixture can be appropriately selected, but is preferably 1 second or more and 120 minutes or less.

[0081] The sintered body formed by contacting electrodes 13 (13a, 13b) using a raw material mixture containing metal oxide particles and metal acetylacetone, as described above, is an example. Figure 1 (b) and Figure 2As shown schematically, this corresponds to a composite 10 containing metal oxide particles 1 and a first amorphous phase 2, and a bonding layer 15 (15a, 15b) containing a second amorphous phase 12. The first amorphous phase 2 contains a metal element from metal acetylacetone (the same metal element as the first metal element). The bonding layer 15 (second amorphous phase 12) contains, in addition to the metal element from metal acetylacetone (the same metal element as the first metal element), a second metal element from the electrode 13 and a resin component from the substrate layer 27.

[0082] To effectively form the bonding layer 15, the heat treatment is preferably carried out under conditions where the resin component of the substrate layer 27 is slightly molten. For example, when a polyimide film is used as the substrate layer 27, a heated press is used to heat at 270°C for 30 minutes under a pressure of 100 MPa, and then, in order to remove any residual unwanted organic matter, annealing at 250°C for 10 hours is preferably carried out.

[0083] Therefore, the thermistor 30 of this embodiment can be manufactured.

[0084] (Implementation Method 2)

[0085] This embodiment relates to a thermistor comprising a base material with two electrodes made of a second metal element, and a cover layer formed on the surface of the base material and made of a third metal element.

[0086] like Figure 4 As shown in (a) and (b), in the thermistor 30' of this embodiment, a structure 20' including a thermistor layer 11 and two electrodes 13a' and 13b' (collectively referred to as "13'") is disposed on a substrate layer 27.

[0087] The two electrodes 13a' and 13b' comprise a base material 3a and 3b (collectively referred to as "3") composed of at least one second metal element selected from Cu, Al, Ag, and Ni, and a capping layer 5a and 5b (collectively referred to as "5") formed on the surface of the base material and composed of at least one third metal element selected from Ni, Au, Ag, Pt, Pd, Zn, Cr, W, Mo, Cu, and Ti. When the base material 3 is composed of two or more second metal elements, it can be an alloy. The second metal element is preferably any one or more of Ni, Cu, and Ag. When the capping layer 5 is composed of two or more third metal elements, it can be an alloy or a laminate. The third metal element is a metal element different from the second metal element, preferably one with a low resistance value (e.g., similar to Cu and Ag), low surface condition, low diffusion amount compared to the metal element in the base material 3, and capable of preventing the diffusion of the metal element in the base material 3 to some extent. The third metallic element is preferably any one or more of Ni, Au, Ag, Pt, Pd, Zn, Cr, W, Mo, Cu, and Ti, with Au being more preferred. This second and third metallic element is much cheaper and readily available compared to the Ag-Pd alloy (an alloy obtained by sintering a mixture of Ag and Pd particles) described in Patent Document 1. According to this embodiment, expensive and resource-scarce metals can be avoided. The thickness of the capping layer 5 can be appropriately selected, for example, from 0.1 to 1.0 μm.

[0088] According to the thermistor 30' of this embodiment, a high bonding strength can be obtained between the thermistor layer 11 (composite 10) and the electrodes 13a' and 13b'. In particular, when Au is used as the third metal element, compared with the thermistor 30 of Embodiment 1, the initial electrical characteristics (resistance value and B constant) are improved, and the deterioration of electrical characteristics (increase in resistance value and change in B constant) under high temperature and high humidity environments can be reduced.

[0089] While not limiting to this implementation method, however... Figure 4As shown in (a) and (b), bonding layers 15a' and 15b' (collectively referred to as "15'") may exist between the two electrodes 13a' and 13b' and the thermistor layer 11 (composite 10). A third metal element and resin component, and, depending on the case, a second metal element, may diffuse into the composite 10 in the bonding layer 15'. In practice, the boundary between the composite 10 and the bonding layer 15' is not necessarily clear (in the figures, the imaginary boundary is shown by a dashed line). Depending on the case, the composite 10 and the bonding layer 15 can also be understood as a composite layer containing metal oxides or a thermistor layer. The composite 10 located between the electrodes 13a' and 13b' can function together with the bonding layers 15a' and 15b' as a temperature-dependent resistance (more specifically, having a negative temperature coefficient) thermistor layer.

[0090] More specifically, the bonding layer 15' is formed by the diffusion of a third metal element from the capping layer 5 and a resin component from the substrate layer 27 (and, where applicable, a second metal element from the parent material 3) into the composite 10 (comprising metal oxide particles 1 and a first amorphous phase 2). The third metal element (and, where present, a second metal element) can be formed by the diffusion of the metal element into the composite 10 through heat and dissolution (more specifically, the dissolution of the metal element into the metal acetylacetone that occurs during the application and heat treatment of the raw material mixture (comprising a mixture of metal oxide particles and metal acetylacetone). The resin component can be formed by the diffusion of the resin component into the composite 10 through heat and dissolution (more specifically, the dissolution of the resin component into the metal acetylacetone that can occur during the application and heat treatment of the raw material mixture). The third metal element (and, where present, a second metal element) and the resin component can diffuse into either the metal oxide particles 1 or the first amorphous phase 2, but in most cases, they can diffuse more extensively into the first amorphous phase 2. As described above, since the first amorphous phase 2 contains the same metal element as the first metal element, the second amorphous phase 12' in the bonding layer 15' can also be understood as containing the same metal element as the first metal element, the same metal element as the third metal element (and, if present, the same metal element as the second metal element), and an element identical to the resin component (carbon element if the resin component contains carbon). The bonding layer 15' can be understood as a region containing the same metal element as the third metal element and an element identical to the resin component (represented by carbon element).

[0091] Based on the bonding layers 15a' and 15b', it is believed that a high bonding strength can be obtained between the thermistor layer 11 (composite 10) and the electrodes 13a' and 13b'. In particular, when Au is used as the third metal element, the presence of the third metal element from the capping layer 5 in the bonding layers 15a' and 15b' is believed to ensure conduction stability, improve the initial electrical characteristics (resistance value and B constant), and reduce the deterioration of electrical characteristics (increase in resistance value and change in B constant) under high temperature and high humidity environments.

[0092] In the thermistor 30 of this embodiment, the bonding layer 15' (more specifically, the second amorphous phase 12') contains the same metal element as the first metal element and the third metal element (and, if present, the second metal element). The bonding layer 15' can exhibit electrical properties that approximate the metal oxide (semiconductor) particles 1 having a crystalline structure. In addition, by including the same metal element as the first metal element and the third metal element (and, if present, the second metal element) in the bonding layer 15', the resistance between the composite 10, the bonding layer 15', and the electrode 13' (briefly, the Schottky barrier between the metal oxide (semiconductor) particles 1 and the electrode 13', and more specifically, the interfacial resistance between the metal oxide particles 1 and the second amorphous phase 12' and between the second amorphous phase 12' and the electrode 13') can be reduced, thereby improving the electrical properties of the thermistor 30'.

[0093] For the others, the same description as in Implementation 1 can also be used in this implementation.

[0094] The thermistor 30' of this embodiment described above can be manufactured by any suitable method, for example, by the method described below.

[0095] First, base materials 3a and 3b, composed of a second metallic element, are formed on the substrate layer 27. Patterns can be formed on the base materials 3a and 3b using any suitable method such as photolithography, electroplating, or vapor deposition sputtering. Furthermore, capping layers 5a and 5b, composed of a third metallic element, are formed on the surfaces of the base materials 3 and 3b. The capping layers 5a and 5b can be formed using any suitable method such as electroplating. Thus, electrodes 13a' and 13b' are formed.

[0096] Then, the same sequence as described in Embodiment 1 can be implemented. It should be noted that in this embodiment, the bonding layer 15' is not necessary, but the bonding layer 15' (second amorphous phase 12') contains, in addition to the metal element from metal acetylacetone (the same metal element as the first metal element), a third metal element from the electrode 13' (and, if present, a second metal element) and a resin component from the substrate layer 27.

[0097] Therefore, the thermistor 30' of this embodiment can be manufactured.

[0098] Alternatively, this embodiment is not limited, but if the thickness of the thermistor layer 11 is thin, the bonding layers 15a', 15b' and the thermistor layer 11 cannot be distinguished. In this case, the thermistor layer 11 may be formed by diffusing a third metal element, a resin component, and, depending on the situation, a second metal element into the composite 10.

[0099] Example

[0100] (Example 1)

[0101] Example 1, in the manner described in Embodiment 1, relates to a thermistor provided with a pair of opposing electrodes in a comb-like shape made of Cu.

[0102] A raw material mixture with an average particle size of approximately 0.2 μm, comprising Mn:Ni:Co in an atomic ratio of 3:1:2, was mixed with manganese acetylacetone at a ratio of 10% by mass (relative to the total mass of the metal oxide particles) and ethanol as a solvent for 16 hours to obtain a slurry-like raw material mixture. A 10 μm thick Cu layer was patterned on a 10 μm thick polyimide film substrate by photolithography, and a pair of comb-shaped opposing electrodes were fabricated together with an extraction electrode. Viewed from above, the overall area of ​​the pair of comb-shaped opposing electrodes is 1.5 mm (length of the teeth) × 3.0 mm (width of the teeth). The extraction electrode is formed on both sides of the pair of comb-shaped opposing electrodes with dimensions of 0.5 mm (length of the teeth) × 4.5 mm (width of the teeth) respectively (see reference). Figure 5 (a)). On the exposed surfaces of these electrodes and substrate layers, the raw material mixture obtained above is supplied in the form of a sheet with a thickness of 15 μm by a scraping method to obtain a precursor laminate ( Figure 5 (b) Reference). The precursor laminate was dried at 100°C for 10 hours, then heated at 270°C for 30 minutes under pressure of 100 MPa using a heated press. Then, to remove residual unwanted organic matter, it was annealed at 250°C for 10 hours to obtain the laminate (therefore, it is considered that the composite containing the metal oxide is formed together with the bonding layer). The obtained laminate was cut using a cutting saw, as shown... Figure 5 The thermistor sample, with a total thickness of 30 μm, was obtained by observing the dimensions from top view as shown in (a) to (b), which are 3.0 mm × 4.5 mm.

[0103] Therefore, the thermistor sample of Example 1 was embedded in resin, cut into two parts along the width direction of the comb-shaped electrode, and the cross-section was observed using field emission scanning electron microscopy (FE-SEM). The results are shown below. Figure 6 (a). According to Figure 6 (a) confirms that the bottom layer is a polyimide matrix layer with two Cu electrodes on the left and right sides thereon. On the polyimide matrix layer and the two Cu electrodes, a thermistor layer containing a metal oxide composite is formed (the layer on the thermistor layer is a resin used for embedding the sample).

[0104] (Comparative Example 1)

[0105] Comparative Example 1 is an example of co-sintering a precursor for a thermistor layer disposed on a substrate layer (metal substrate) made of Cu or Ni, relating to a thermistor manufactured by forming discrete electrodes thereon. It should be noted that in the thermistor of Patent Document 1, a gap is formed in the vertical direction (the direction perpendicular to the main surface of the substrate) between the metal substrate and the comb-shaped counter electrode.

[0106] An organic binder is added at a mass ratio of 10% (relative to the total mass of the metal oxide particles) to metal oxide particles containing Mn:Ni:Co in an atomic ratio of 3:1:2, with an average particle size of approximately 0.2 μm. Ethanol is added as a solvent, and the mixture is stirred for 16 hours to obtain a raw material mixture in slurry form. The raw material mixture obtained above is then applied to a substrate layer of Cu or Ni foil with a thickness of 20 μm in the form of a sheet with a thickness of 15 μm using a doctor blade method to obtain a precursor laminate. This precursor laminate is placed in a zirconia box and heated at 300°C for 100 hours in a nitrogen atmosphere to remove the organic binder. Then, it is sintered in the box at 800–1300°C for 60 minutes in a reducing atmosphere to obtain a sintered body.

[0107] However, in Comparative Example 1, at the moment the sintered body was obtained, the Cu or Ni of the Cu foil or Ni foil (substrate layer) was oxidized / melted and peeled off, so no separation electrode was formed on the sintered body (thermostat layer), and the thermistor sample was discontinued.

[0108] (Comparative Example 2)

[0109] Comparative Example 2 relates to a thermistor, which, after forming a composite containing metal oxides that can function as a thermistor layer, forms a matrix layer containing resin components, and then provides a pair of counter electrodes in a comb-like shape made of Cu.

[0110] In a mixture of metal oxide particles containing Mn:Ni:Co in an atomic ratio of 3:1:2 with an average particle size of approximately 0.2 μm, manganese acetylacetone was added at a mass ratio of 20% (relative to the total mass of the metal oxide particles), with ethanol added as a solvent. The mixture was stirred for 16 hours to obtain a raw material mixture in slurry form. This raw material mixture was then fed onto a 10 μm thick Cu foil in the form of a 15 μm thick sheet using a doctor blade method to obtain a precursor laminate. After drying the precursor laminate at 100°C for 10 hours, it was heated at 270°C for 30 minutes under a pressure of 100 MPa using a heated press. Then, to remove any remaining unwanted organic matter, it was annealed at 250°C for 10 hours to obtain the laminate (thus forming a composite containing metal oxides). Then, a polyamide-imide precursor solution was coated to a thickness of 15 μm onto the film (a metal oxide-containing composite that can function as a thermistor layer) from the aforementioned sheet in the obtained laminate. The film was then heated at 250°C for 1 hour to thermally cure the polyamide-imide and form a resin substrate. Next, a Cu foil (more specifically, a copper foil coated with photoresist, exposed according to a predetermined pattern, developed, etched to remove a predetermined portion of the Cu foil, and the remaining photoresist) was patterned using photolithography. A pair of comb-shaped opposing electrodes were used as extraction electrodes, arranged in the same manner as in Example 1. The laminate was cut using a cutting saw to obtain a thermistor sample with dimensions of 3.0 mm × 4.5 mm and a total thickness of 30 μm when viewed from top, similar to Example 1.

[0111] Therefore, the cross-section of the thermistor sample obtained in Comparative Example 2 was observed using field emission scanning electron microscopy (FE-SEM) in the same manner as in Example 1. The results are shown below. Figure 6 (b) According to Figure 6 (b) confirms that the bottom layer is a polyamide-imide matrix layer, on which a thermistor layer containing a metal oxide composite is formed, and two Cu electrodes are formed on the left and right sides of the thermistor layer (the two Cu electrodes and the layer on the thermistor layer are resins used for embedding the sample).

[0112] (Example 2)

[0113] Example 2: In the above-described manner of embodiment 2, a thermistor is provided, which has a base material made of Cu covered by a capping layer made of Ni, and has a pair of counter electrodes in the shape of comb teeth.

[0114] In a mixture of metal oxide particles containing Mn:Ni:Co in an atomic ratio of 3:1:2 and with an average particle size of approximately 0.2 μm, manganese acetylacetone was added at a mass percentage (relative to the total mass of the metal oxide particles), and ethanol was added as a solvent. The mixture was stirred for 16 hours to obtain a raw material mixture in slurry form. A 10 μm thick Cu layer was patterned by photolithography on a substrate layer consisting of a 10 μm thick polyimide film to obtain a master material. A 1–5 μm thick Ni layer was then formed on the surface of this master material by electroplating. A pair of comb-shaped opposing electrodes and an extraction electrode were fabricated together at the same dimensions as in Example 1. The raw material mixture obtained above was then fed to the exposed surfaces of the electrodes and substrate layer in the form of a 15 μm thick sheet using a doctor blade method to obtain a precursor laminate. After drying the precursor laminate at 100°C for 10 hours, it was heated at 270°C for 30 minutes under pressure of 100 MPa using a heated press. Then, to remove any remaining unwanted organic matter, it was annealed at 250°C for 10 hours to obtain the laminate (therefore, it is considered that the composite containing metal oxides is preferably formed together with the bonding layer). The obtained laminate was cut using a cutting saw to obtain a thermistor sample with the same dimensions and total thickness as in Example 1 when viewed from top view.

[0115] (Example 3)

[0116] Example 3 is a variation of Example 2, and relates to a thermistor in which a base material made of Cu is covered by a capping layer made of Au, and a pair of opposing electrodes in the shape of comb teeth are provided.

[0117] In a 3:1:2 (atomic ratio) mixture of Mn:Ni:Co metal oxide particles with an average particle size of approximately 0.2 μm, manganese acetylacetone was added at a ratio of 10% by mass (relative to the total mass of the metal oxide particles), with ethanol added as a solvent. The mixture was stirred for 16 hours to obtain a raw material mixture in slurry form. A 10 μm thick Cu layer was patterned by photolithography on a 10 μm thick polyimide film substrate to form a master material. Further, an Au layer with a thickness of 0.1–0.5 μm was formed on the surface of this master material by electroplating. A pair of comb-shaped opposing electrodes, along with an extraction electrode, were fabricated with the same dimensions as in Example 1. The raw material mixture obtained above was fed to the exposed surfaces of these electrodes and the substrate layer in the form of a 15 μm thick sheet using a doctor blade method to obtain a precursor laminate. After drying the precursor laminate at 100°C for 10 hours, it was heated at 270°C for 30 minutes under pressure of 100 MPa using a heated press. Then, to remove any remaining unwanted organic matter, it was annealed at 250°C for 10 hours to obtain the laminate (therefore, the composite containing metal oxides is preferably formed together with the bonding layer). The obtained laminate was cut using a cutting saw to obtain a thermistor sample with the same dimensions and total thickness as in Example 1 when viewed from top view.

[0118] (evaluate)

[0119] The thermistor samples prepared in Examples 1-3 and Comparative Example 2 are evaluated as follows.

[0120] • Bond strength (adhesion)

[0121] For Examples 1-3 and Comparative Example 2, two thermistor specimens were prepared for each, and the bonding strength (adhesion) was evaluated. This evaluation was based on the cross-section method defined in JIS K5600-5-6. The evaluation results are classified as follows.

[0122] 0: The edges of the cut are completely smooth, and there is no detachment in any mesh.

[0123] 1. Minor peeling of the coating at the intersection of the cuts. No more than 5% of the coating at the intersection of the cuts is affected.

[0124] 2: The coating peels off along the edges of the cut and / or at the intersections. The affected area at the intersections is significantly more than 5%, but no more than 15%.

[0125] 3: Large peeling occurred, partially or completely, along the edge of the cut, and / or partially or completely peeled off various parts of the mesh. At the cross-cutting areas, the affected area clearly exceeded 15% but did not exceed 35%.

[0126] 4. Large-scale peeling occurred, partially or completely, along the edges of the cuts, and / or partial or complete peeling occurred on several areas of the mesh. At the intersecting cuts, more than 65% of the area was significantly affected.

[0127] 5: A type of peeling that cannot be classified by category 4.

[0128] The bonding strength (adhesion) evaluation results of the thermistor samples in Examples 1-3 were all classified as category 0. Specifically, no peeling was observed between the two electrodes and the composite layer containing metal oxides. On the other hand, Comparative Example 2 was classified as category 1. Specifically, only slight peeling was observed between the two electrodes and the composite layer containing metal oxides.

[0129] In the thermistor samples of Examples 1-3, the precursor (raw material mixture) of the thermistor layer, together with the polyimide matrix layer and the Cu electrode, was heated to 270°C and subsequently annealed at 250°C (co-sintering). Therefore, the resin component of the matrix layer (detected as C element) diffuses into the metal oxide-containing composite through heat and dissolution (dissolution into metal acetylacetone), and the Cu of the electrode diffuses into the metal oxide-containing composite through heat and dissolution (dissolution into metal acetylacetone). Thus, in the bonding layer formed between the electrode and the thermistor layer, the resin component from the matrix layer and the Cu from the electrode diffuse into the metal oxide-containing composite. It should be noted that the C element detected in the thermistor samples of Examples 1-3 is conveniently considered to originate from the resin component. Since the annealing at 250°C is above the decomposition temperature of metal acetylacetone, C element from metal acetylacetone is practically absent, or present only in trace amounts, in order to remove any remaining unwanted organic matter. Furthermore, the carbon element detected in the thermistor samples of Examples 1-3 was abundantly distributed in the bonding layer, which approximates the substrate layer, suggesting a resin component originating from the substrate layer. This is because the carbon element from metallic acetylacetone is evenly distributed in the thermistor layer. On the other hand, in the thermistor sample of Comparative Example 2, the precursor (raw material mixture) of the thermistor layer and the Cu foil (which ultimately becomes the Cu electrode) were subjected to heating at 270°C and subsequent annealing (co-sintering) at 250°C. Therefore, the Cu in the Cu foil diffused into the metal oxide-containing composite through heat and dissolution (dissolution into metallic acetylacetone), thus indicating that Cu diffused into the metal oxide-containing composite in the bonding layer formed between the electrode and the thermistor layer. However, since the substrate layer was subsequently formed by thermal curing, the resin component of the substrate layer could not dissolve (dissolution into metallic acetylacetone), and the bonding layer that may exist between the thermistor layer and the Cu electrode did not contain the resin component of the substrate layer. Due to this difference, the thermistor samples of Examples 1-3 can achieve higher bonding strength (adhesion) compared to the thermistor sample of Comparative Example 2.

[0130] The diffusion of metal elements and resin components in the thermistor sample is confirmed as follows.

[0131] The thermistor samples of Examples 1-3 and Comparative Example 2 were cut into two parts along the width of the teeth of a comb-shaped electrode. The cross-sections were removed using a focused ion beam (FIB) and observed using a scanning transmission electron microscope (STEM, JEOL JEM-F200). Energy dispersive X-ray analysis (EDX, Noran system 7) was used to identify the elements present at the observation locations based on the intensity at each applied voltage. For example, C was identified based on the peak near 0.2 eV, and Cu was identified based on the peak near 1.0 eV, confirming the diffusion of each element.

[0132] • Strength test (pressure resistance)

[0133] A strength test (pressure resistance) was performed on the thermistor samples compared to those of Example 1 and Comparative Example 2. More specifically, the thermistor sample was clamped between two disc-shaped iron clamps with a diameter of 50 mm and a thickness of 25 mm, and a pressure of 0.5 tons was applied repeatedly five times to confirm the change in the measured resistance value. During the resistance value measurement, a pressure-sensitive membrane (Prescale medium pressure type, detection sensitivity 10 MPa) of Fujifilm was clamped between the surface opposite to the substrate of the thermistor sample and the iron clamps, and the load (pressure) was measured to investigate the load distribution.

[0134] In the thermistor sample of Example 1, the rate of change of resistance value under pressure (with the resistance value at the same temperature without pressure as a reference) is less than 3%. Even under pressure, the error as a temperature sensor is within 1°C. Between resistance value measurements, load (pressure) measurements based on the pressure-sensitive diaphragm confirmed that a load was applied not only to the area where the electrodes are located, but also to the entire surface of the thermistor sample. Considering that the area where the electrodes are located accounts for approximately 30% of the total area of ​​the sample, the load is uniformly distributed across the entire area, thereby reducing the load applied to the electrodes to approximately 1 / 3. Therefore, it is considered that the rate of change of resistance value can be reduced.

[0135] In Comparative Example 2, the resistance value of the thermistor sample showed a change rate of over 5% in the first resistance measurement under pressure. Subsequently, the rate of change increased with each subsequent measurement. Furthermore, load (pressure) measurements based on the pressure-sensitive diaphragm confirmed that the load was concentrated only in the area where the electrodes of the thermistor sample were located, particularly showing a deviation in the load at the corners of the electrodes. Additionally, observation of the thermistor sample after the measurement revealed that the electrodes were embedded in the thermistor layer, and cracks had been introduced into the thermistor layer.

[0136] • Initial electrical characteristics (resistance value and B constant)

[0137] For Examples 1-3, 10 thermistor samples were prepared respectively, and the initial electrical characteristics (resistance value and B constant) were evaluated. More specifically, for the resistance value, for each thermistor sample, the average of the resistance value (Ω) measured twice at 25°C was used as the resistance value of that thermistor sample. For each example, the average, standard deviation, maximum, and minimum values ​​of the resistance values ​​(Ω) of the 10 thermistor samples were calculated. The results are shown in Table 2. For the B constant, for a single thermistor sample, the B constant (-) was calculated using the resistance values ​​(Ω) measured at 25°C and 35°C. For each example, the average, standard deviation, maximum, and minimum values ​​of the B constant of the 10 thermistor samples were calculated. The results are shown in Table 3.

[0138] [Table 2]

[0139]

[0140] [Table 3]

[0141]

[0142] As shown in Table 2, compared with Examples 1 and 2, the resistance value (average value) and deviation (standard deviation) are smaller in Example 3. As shown in Table 3, compared with Examples 1 and 2, Example 3 yields a B constant (average value) that is approximately the same as that of the powder (referring to the B constant of a sintered body (monomer) of metal oxide particles with the same metal ratio as in the examples, sintered at a temperature above 1000°C; specifically, 3700, and the same applies below), and the deviation (standard deviation) is also smaller.

[0143] In Example 1, during heating and pressurization, Cu from the Cu electrode diffused into the composite containing metal oxides. It is presumed that this was due to the formation of a bonding layer, and the initial resistance value was not as low as in Example 3. In Example 2, during heating and pressurization, Cu and Ni from the Cu substrate and Ni from the capping layer diffused into the composite containing metal oxides. Because a bonding layer was formed, it is presumed that the initial resistance value was not as low as in Example 3. In contrast, in Example 3, the Au capping layer had a sufficiently low resistance value, its surface state was not easily altered during heating and pressurization, and it could, to some extent, prevent Cu from the Cu substrate from diffusing into the composite containing metal oxides. Therefore, a sufficiently low resistance value was obtained, and it is presumed that the B constant (average value) is approximately the same as that of the powder (3700).

[0144] • Changes in electrical properties under high temperature and high humidity conditions (rate of change of resistance and rate of change of B constant)

[0145] Ten thermistor samples were prepared according to Examples 1-3, and high-temperature and high-humidity environmental tests were conducted to investigate the rate of change of electrical characteristics (resistance value and B constant). More specifically, after placing all thermistor samples in a high-temperature and high-humidity environment of 60°C and 95% humidity for 24 hours using a small environmental testing machine, the resistance value (Ω) and B constant (−) were calculated using the same method as described above. For each thermistor sample, the rate of change of resistance value (%) was calculated based on the initial resistance value (Ω). According to each example, the average, standard deviation, maximum, and minimum values ​​of the rate of change of resistance value for the ten thermistor samples were calculated. The results are shown in Table 4. In addition, for each thermistor sample, the rate of change of B constant (%) was calculated based on the initial B constant (−). For each example, the average, standard deviation, maximum, and minimum values ​​of the rate of change of B constant for the ten thermistor samples were calculated. The results are shown in Table 5.

[0146] [Table 4]

[0147]

[0148] [Table 5]

[0149]

[0150] Referring to Table 4, the resistance value increased in all thermistor samples after the high-temperature and high-humidity environment test (the minimum value was positive). Referring to Table 5, the B constant increased in some cases and decreased in others after the high-temperature and high-humidity environment test (the minimum value was negative). Compared with Examples 1 and 2, the rate of change of resistance value and the rate of change of B constant (average value) in Example 3 were smaller, and these deviations (standard deviations) were also smaller. That is, Example 3 yielded a thermistor with minimal changes in electrical characteristics even when exposed to high-temperature and high-humidity environments.

[0151] In Example 1, during heating and pressurization, Cu from the Cu electrode diffuses into the composite containing metal oxides. Due to the formation of a bonding layer, the rate of change of resistance and B constant under high temperature and high humidity conditions is presumably greater than in Example 3. In Example 2, during heating and pressurization, Cu, Ni from the Cu substrate, and Ni from the capping layer diffuse into the composite containing metal oxides. Due to the formation of a bonding layer, the rate of change of resistance and B constant under high temperature and high humidity conditions is presumably greater than in Example 3. In contrast, in Example 3, the Au capping layer has a sufficiently low resistance value, its surface state is less prone to change during heating and pressurization, and it can, to some extent, prevent Cu from the Cu substrate from diffusing into the composite containing metal oxides. Therefore, it is presumably able to significantly reduce the rate of change of resistance and B constant under high temperature and high humidity conditions.

[0152] Industrial availability

[0153] The thermistor of the present invention can be used in a wide variety of applications, such as temperature sensors. For example, when the thermistor of the present invention is configured as a flexible whole, it can be used as a flexible temperature sensor for applications such as fire detection at high temperatures, degradation of automotive batteries, temperature measurement for temperature management of smart batteries, and body temperature measurement in the medical and healthcare fields. However, the thermistor of the present invention is not limited to the above applications.

[0154] This application claims priority based on Japanese Patent Application No. 2020-110348 filed in Japan on June 26, 2020, the entire contents of which are incorporated herein by reference.

[0155] Symbol Explanation

[0156] 1 particle (metal oxide particle)

[0157] 2. Amorphous phase (first amorphous phase)

[0158] 3, 3a, 3b parent materials

[0159] 5, 5a, 5b Covering layers

[0160] 10. Complexes (complexes containing metal oxides)

[0161] 11. Thermistor layer

[0162] 12,12' Amorphous phase (second amorphous phase)

[0163] Electrodes 13, 13a, 13b, 13', 13a', 13b'

[0164] 14a, 14b External electrodes

[0165] 15, 15a, 15b, 15', 15a', 15b' bonding layers

[0166] 20, 20' structure

[0167] 27. Matrix layer (resin substrate)

[0168] 30, 30' thermistor

Claims

1. A thermistor, wherein a structure comprising a thermistor layer and two electrodes is disposed on a substrate layer. The matrix layer contains a resin component. The thermistor layer is a composite material comprising: a plurality of particles composed of a metal oxide containing at least one first metal element; and an amorphous phase containing the same metal element as the first metal element, existing between the plurality of particles; and the first metal element comprising at least one of Mn and Ni. The two electrodes comprise: a base material composed of at least one second metallic element selected from Cu, Al, Ag, and Ni; and a capping layer formed on the surface of the base material and composed of at least one third metallic element selected from Ni, Au, Ag, Pt, Pd, Zn, W, Mo, Cu, and Ti. The third metal element is a different metal element from the second metal element, and in the cross-sectional view of the two electrodes, the base material is formed on the substrate layer. The cover layer is formed on the upper surface and side surface of the base material, thereby separating the base material from the thermistor layer by the cover layer. The third metal element is less likely to diffuse into the complex compared to the second metal element.

2. A thermistor, wherein a structure comprising a thermistor layer and two electrodes is disposed on a substrate layer. The matrix layer contains a resin component. The thermistor layer is a composite material comprising: a plurality of particles composed of a metal oxide containing at least one first metal element; and an amorphous phase containing the same metal element as the first metal element, existing between the plurality of particles; and the first metal element comprising at least one of Mn and Ni. In the cross-sectional view, the two electrodes comprise: a base material formed on the substrate layer and composed of at least one second metal element selected from Cu, Al, Ag, and Ni; and a capping layer formed on the upper surface and side surface of the base material and composed of at least one third metal element selected from Ni, Au, Ag, Pt, Pd, Zn, Cr, W, Mo, Cu, and Ti. The third metal element is a different metal element from the second metal element.

3. A thermistor, wherein a structure comprising a thermistor layer and two electrodes is disposed on a substrate layer. The matrix layer contains a resin component. The thermistor layer is a composite material comprising: a plurality of particles composed of a metal oxide containing at least one first metal element; and an amorphous phase containing the same metal element as the first metal element, existing between the plurality of particles; and the first metal element comprising at least one of Mn and Ni. The two electrodes comprise: a base material composed of at least one second metal element selected from Cu, Al, Ag, and Ni; and a capping layer formed on the surface of the base material and composed of at least one third metal element selected from Ni, Au, Ag, Pt, Pd, Zn, Cr, W, Mo, Cu, and Ti. The base material and the thermistor layer are separated by the capping layer. The third metal element is a different metal element from the second metal element, and is less likely to diffuse into the complex compared to the second metal element.

4. The thermistor according to any one of claims 1 to 3, wherein Between the two electrodes and the thermistor layer, there exists a bonding layer in the composite where the third metal element and the resin component diffuse into the composite.

5. The thermistor according to any one of claims 1 to 3, wherein, The structure has two opposing surfaces, which are either uneven or flat, with a thickness less than that of the two electrodes.

6. The thermistor according to any one of claims 1 to 3, wherein, The two electrodes are separated from each other and disposed on the substrate layer, and the thermistor layer is disposed on the two electrodes and the substrate layer.

7. The thermistor according to any one of claims 1 to 3, wherein, The first metallic element further comprises at least one selected from Fe, Al, Co, and Cu.

8. The thermistor according to any one of claims 1 to 3, wherein, The resin component comprises at least one selected from polyethylene terephthalate, polyetherimide, polyamide imide, polyimide, polytetrafluoroethylene, epoxy resin, and liquid crystal polymer.

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