Thin wire type thermistor temperature sensing element

Abstract

To provide a thin wire temperature sensing element that can measure the temperature of a minute object with high responsiveness.SOLUTION: A thin wire thermistor temperature sensing element 10 includes: a linear base material 12 that has insulation properties and has a diameter of 200 μm or less; a first conductive layer 14 and a second conductive layer 16 provided with a gap 20 formed on the surface of the linear base material 12 and each of whose thickness is smaller than the diameter of the linear base material 12; and a thermistor film 18 that is provided to cover a part of the first conductive layer 14, the gap 20, and a part of the second conductive layer 16, has an electrical resistance value of 5 MΩ or less between the first conductive layer 14 and the second conductive layer 16, and has a thickness thinner than the diameter of the linear base material 12.SELECTED DRAWING: Figure 1

Description

[Technical Field] 【0001】 This application relates to a thermistor temperature sensing element with a thin wire shape and excellent responsiveness. [Background technology] 【0002】 In recent years, thermistor elements have seen increased demand for high sensitivity and fast response, as well as for applications in flexible devices such as wearable terminals. Achieving high sensitivity and fast response requires thinner thermistor films, leading to active development of thin-film thermistors. Furthermore, there is a growing need for thermistor elements capable of localized temperature measurement and possessing micro-shapes that do not affect the temperature of the object being measured. Such thermistor elements could, for example, enable monitoring of blood flow temperature within vascular catheters and measurement of temperature changes in microcellular cells in medical applications. 【0003】 Miniaturizing thermistor elements requires miniaturizing the substrate, which affects heat diffusion. Considering insertion into confined spaces, it is desirable that the substrate forming the thermistor thin film has a fine wire shape. Furthermore, for temperature measurement in confined spaces, the use of a highly sensitive and responsive thermistor element is suitable. In addition, to accommodate temperature measurement targets with various surface shapes, the substrate forming the thermistor thin film is preferably a flexible material with a degree of shape freedom. Substrates that satisfy these conditions are organic or metallic. However, since fabricating thermistor films, which are made of ceramic material, generally requires high-temperature processes exceeding 500°C, forming thermistor films on flexible substrates with low heat resistance is not easy. 【0004】 To address this problem, development has been underway on methods for forming thermistor films on flexible film substrates (Patent Document 1 and Non-Patent Document 1). Patent Document 1 discloses a method for forming a thermistor material on an organic substrate by crystallizing a precursor film formed by a coating method through light irradiation. Non-Patent Document 1 describes the formation of a ceramic thermistor film on a thin polyimide sheet with a thickness of 5 μm. Thus, improvements in low-temperature film formation technology have made it possible to form ceramic thermistor materials on sheet-like substrates. 【0005】 However, the thin-film thermistor elements described in Patent Document 1 and Non-Patent Document 1 are sheet-shaped. Even with a thickness of 5 μm, due to the thermal diffusion of the sheet-shaped substrate itself, the thin-film thermistor elements described in Patent Document 1 and Non-Patent Document 1 are unsuitable for high-speed measurements where extremely high reproducibility for local measurements is required. For example, even if the heating profile of the thermistor thin film can be responded to quickly by heating from directly above the thermistor thin film, there is a delay in the cooling profile when the heat source is removed. In other words, the thermal diffusion of the thermistor substrate itself is the cause of this delay in the cooling profile. 【0006】 For minute temperature-measuring objects measuring a few millimeters or less, further miniaturization of the substrate is necessary to measure true temperature changes. To minimize the thermal effects on the thermistor substrate, it is effective to make the substrate into a fine wire shape. As described in Patent Documents 2 and 3, currently available fine-wire type temperature sensing elements consist of existing chip thermistors mounted on metal wires. As a result, the size of the sensing element part is 0.5 mm or more. [Prior art documents] [Patent Documents] 【0007】 [Patent Document 1] Patent No. 6529023 [Patent Document 2] Japanese Patent Application Publication No. 1-53485 [Patent Document 3] Japanese Patent Application Laid-Open No. 63-46701 【Non-Patent Literature】 【0008】 【Non-Patent Literature 1】 ACS Appl. Mater. Interfaces 12 (2020) 36600. 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0009】 The present application has been made in view of such circumstances, and an object thereof is to provide a fine wire type temperature sensing element capable of measuring the temperature of a minute measurement object with high responsiveness. 【Means for Solving the Problems】 【0010】 The inventor of the present application provided a pair of metal electrodes on a resin fine wire, applied a thermistor precursor dispersion liquid in which oxide nanoparticles with an appropriate particle diameter were dispersed between these electrodes, and formed a thermistor film, and found that the obtained element functions as a fine wire type temperature sensing element. 【0011】 A fine wire type thermistor temperature sensing element according to an aspect of the present application includes an insulating linear base material having a diameter of 200 μm or less, a first conductive layer and a second conductive layer provided with a gap formed on the surface of the linear base material, each having a thickness smaller than the diameter of the linear base material, and a thermistor film provided so as to cover a part of the first conductive layer, the gap, and a part of the second conductive layer, having an electrical resistance value between the first conductive layer and the second conductive layer of 5 MΩ or less, and a thickness smaller than the diameter of the linear base material. 【0012】 Another embodiment of the present invention provides a thin wire type thermistor temperature sensing element comprising a linear substrate having a conductor on its surface and a diameter of 200 μm or less; a thermistor film covering one end of the linear substrate so as to be electrically connected to the conductor and having a thickness less than the diameter of the linear substrate; a conductive layer further covering the portion of the thermistor film covering the end and having a thickness less than the diameter of the linear substrate; and an insulating layer electrically insulating the conductor and the conductive layer and having a thickness less than the diameter of the linear substrate, wherein the electrical resistance of the thermistor film between the conductor and the conductive layer is 5 MΩ or less. [Effects of the Invention] 【0013】 The thin-wire type thermistor temperature sensing element of this invention suppresses minute temperature changes in the object being measured, enabling high-precision temperature measurement with a fast response. [Brief explanation of the drawing] 【0014】 [Figure 1] A central cross-sectional view along the longitudinal direction of the thin wire type thermistor temperature sensing element of the first embodiment. [Figure 2] End view of three cross-sections perpendicular to the longitudinal direction of the thin wire type thermistor temperature sensing element of the first embodiment. [Figure 3] A central cross-sectional view along the longitudinal direction of the thin wire type thermistor temperature sensing element of the second embodiment. [Figure 4] End view of three cross-sections perpendicular to the longitudinal direction of the thin-wire type thermistor temperature sensing element of the second embodiment. [Figure 5] Particle size distribution diagram of oxide nanoparticles contained in the thermistor precursor dispersion of Example 1. (a) represents the number of particles, and (b) represents the volume fraction, showing the particle size distribution of oxide nanoparticles. [Figure 6] External view image of the thin-wire type thermistor temperature sensing element of Example 1. [Figure 7] A graph showing the temperature dependence of the electrical resistance value of the thermistor film in the nanowire type thermistor temperature sensing element of Example 1. [Figure 8] A graph showing the temperature change during measurement of the thermal time constant of the thermistor film of the nanowire type thermistor temperature sensing element of Example 1. [Modes for carrying out the invention] 【0015】 The thin-wire type thermistor temperature sensing element of this application will be described below with reference to the drawings, based on each embodiment and example. Note that the thin-wire type thermistor temperature sensing element, its components, and surrounding components shown in the drawings are schematic representations of the structure and do not necessarily correspond to the actual dimensions and dimensional ratios. Also, the same reference numeral may be assigned to the same component. Furthermore, in the description of the thin-wire type thermistor temperature sensing element of the second embodiment, explanations that overlap with those of the thin-wire type thermistor temperature sensing element of the first embodiment will be omitted as appropriate. 【0016】 (First Embodiment) Figure 1 schematically shows the central cross-section along the longitudinal direction of the nanowire type thermistor temperature sensing element 10 of the first embodiment of the present application. Figure 2 schematically shows three cross-sections perpendicular to the longitudinal direction of the nanowire type thermistor temperature sensing element 10. Specifically, Figure 2(a) shows the end face of the section cut along line AA in Figure 1, Figure 2(b) shows the end face of the section cut along line BB in Figure 1, and Figure 2(c) shows the end face of the section cut along line CC in Figure 1. The nanowire type thermistor temperature sensing element 10 comprises a linear substrate 12, a first conductive layer 14, a second conductive layer 16, and a thermistor film 18. The linear substrate 12 is insulating. "Insulating" means an resistivity that is sufficiently high so as not to affect the resistivity measurement of the thermistor film 18 between the first conductive layer 14 and the second conductive layer 16. Such a resistivity is, for example, 10 12 Examples include those with an Omega-cm or larger. 【0017】 The linear substrate 12 is an elongated linear member with a substantially circular cross-section perpendicular to its length, and is made of, for example, resin. The linear substrate 12 can be made of a linear substrate that has a heat resistance temperature, i.e., a softening point, of 200°C or less and is flexible. Examples of flexible linear substrates include resin wires such as aramid and pulp wires. Furthermore, from the viewpoint of realizing a high-speed response of the thin-wire type thermistor temperature sensing element 10, the diameter of the linear substrate 12 is 200 μm or less. It is more preferable that the diameter of the linear substrate 12 is 20 μm or less. The diameter of the linear substrate refers to the diameter of the smallest circle that can accommodate the entire cross-section perpendicular to the length of the linear substrate. 【0018】 The "fast response" of a thin-wire thermistor temperature sensing element means that the thermal time constants when the surface of the thermistor film heats up from 40°C to 45°C and when it cools down from 45°C to 40°C are both 500 ms (milliseconds) or less. It is more preferable that these thermal time constants be 200 ms or less. To achieve a fast response in the thin-wire thermistor temperature sensing element 10, the thermistor film is made thinner or its electrical resistance is reduced. 【0019】 The thermal time constant during heating is the time it takes for the temperature of the black thermistor film 18 of the thin-wire type thermistor temperature sensing element 10 to rise by 63.2% of the change in temperature from the initial value to the stable value, calculated from the resistance value of the thermistor film 18, when the surface of the thermistor film 18 is irradiated with an ultraviolet LED at an intensity that raises the temperature to 40°C to 45°C at room temperature. The thermal time constant during cooling is the time it takes for the temperature to drop by 63.2% of the change in temperature from the temperature at the time of stopping the ultraviolet LED irradiation when the surface of the thermistor film 18 is 40°C to 45°C, to room temperature. 【0020】 The resistivity of the thermistor film 18 is calculated by measuring the voltage using a digital multimeter or oscilloscope while a constant current is applied. The light intensity of the ultraviolet LED must reach its maximum intensity in a time sufficiently shorter than the thermal time constant of the thermistor film, for example, 1 μs or less. In the embodiment described later, the time it takes for the ultraviolet LED to reach its maximum intensity satisfies this condition. 【0021】 The high-speed response of the thin wire type thermistor temperature sensing element 10 also depends on the thermal conductivity characteristics of the linear substrate 12, such as its thermal conductivity and heat capacity. For example, in a thin wire type thermistor temperature sensing element 10 in which a linear substrate 12 made of an aromatic polyamide resin such as aramid and having a diameter of 15 μm is used, and the thermistor film 18 has a thickness of several μm, a high-speed response of approximately 110 ms is possible for both the heating and cooling thermal time constants. From the viewpoint of realizing a high-speed response of the thin wire type thermistor temperature sensing element 10 with a linear substrate 12 of 200 μm or less in diameter, the heat capacity of the linear substrate 12 is preferably 25 μJ / K or less, and more preferably 20 μJ / K or less. 【0022】 As shown in Figure 1, the first conductive layer 14 and the second conductive layer 16 are provided on the surface of the linear substrate 12 with a gap 20 formed between them. More specifically, the cylindrical first conductive layer 14 and the second conductive layer 16 cover the surface of the linear substrate 12 with a gap 20 between them. The first conductive layer 14 and the second conductive layer 16 are obtained, for example, by forming a pair of metal films on half of the surface of the linear substrate 12, divided along the length direction, using a mask so that a gap 20 is formed, and similarly forming a pair of metal films on the opposite half of the surface. The first conductive layer 14 and the second conductive layer 16 are made of conductive material, typically metal, and function as a pair of electrodes for the thin wire type thermistor temperature sensing element 10. "Conductive" means 10 -3 This refers to resistivity of Ω·cm or less. 【0023】 The thickness t1 of the first conductive layer 14 and the second conductive layer 16 is smaller than the diameter d of the linear substrate 12. Therefore, the thin wire type thermistor temperature sensing element 10 can be made thin, and a thin wire type thermistor temperature sensing element 10 with a high-speed response can be obtained. For example, if the linear substrate 12 is an aramid resin fiber with a diameter of 15 μm, the first conductive layer 14 and the second conductive layer 16 can be formed by creating a thin metal film using a conductive ink such as Ag nanoparticle ink. If this metal film is too thin and the electrical resistance value does not decrease sufficiently, applying Ni plating with a thickness of 10 μm or less to this metal film will sufficiently lower the electrical resistance values ​​of the first conductive layer 14 and the second conductive layer 16. 【0024】 As shown in Figure 1, the thermistor film 18 is provided so as to cover a portion of the gap 20 side of the first conductive layer 14, the gap 20, and a portion of the gap 20 side of the second conductive layer 16. More specifically, the thermistor film 18 is provided in a cylindrical shape so as to slightly protrude from both ends of the gap 20 and cover a portion of the first conductive layer 14 and the second conductive layer 16. The thickness t2 of the thermistor film 18 is smaller than the diameter d of the linear substrate 12. As a result, the thin wire type thermistor temperature sensing element 10 can be made thin, and a thin wire type thermistor temperature sensing element 10 with a high-speed response can be obtained. 【0025】 From the viewpoint of achieving a high-speed response for the thin-wire type thermistor temperature sensing element 10, the electrical resistance value r of the thermistor film 18 between the first conductive layer 14 and the second conductive layer 16 is 5 MΩ or less. More preferably, the electrical resistance value r is 3 MΩ or less. The electrical resistance value r can be calculated using the following formula, which uses the distance L between the first conductive layer 14 and the second conductive layer 16 and the electrical resistivity ρ of the thermistor film 18 material. This calculated value is in close agreement with the measurement value obtained by a digital multimeter (the same applies to the second embodiment). r = ρL / [π{(t² + d / 2) 2 -(d / 2) 2}] 【0026】 The thermistor film 18 is obtained by applying a dispersion containing oxide nanoparticles, which are precursors to the thermistor film 18 (hereinafter sometimes referred to as "thermistor precursor dispersion"), to the film-forming area including the gap 20 to form a thermistor precursor film, and then drying this thermistor precursor film at an appropriate temperature. When the linear substrate 12 is made of resin, it is preferable to dry the thermistor precursor film at a temperature of 200°C to 250°C. In addition, in the fine-wire type thermistor temperature sensing element 10, a ceramic thin film or the like having a protective film or anti-reflective film function may be formed on the surface of the linear substrate 12 or the thermistor film 18 separately from the thermistor film 18. 【0027】 The thermistor precursor dispersion is obtained by the wet grinding method of oxide materials. More specifically, the bulk ceramics of the oxide obtained by the solid-phase reaction method are put into an organic solvent such as alcohol, toluene, or xylene, or water, and the thermistor precursor dispersion is prepared by a grinding method such as a bead mill. In addition, a sol-gel or metal organic acid salt solution corresponding to the composition of the thermistor film 18 may be added before or after the grinding of the bulk ceramics of the oxide. 【0028】 For the oxide nanoparticles in the thermistor precursor dispersion, a substance that can lower the electrical resistance value when it becomes the thermistor film 18 can be adopted. Examples of such oxides include oxides containing Ni, Cu, Co, Mn, or Fe. Specifically, oxides of spinel structure represented by the chemical formula Mn 3-(a+b+c+d) Co a Ni b Cu c Fe d O4 (0 ≤ a + b + c + d < 3, 0 ≤ d < 0.90), and oxide nanoparticles of perovskite structure represented by the chemical formula R j Ba k La m Sr n Ca p Mn 2-q Ni q O 5+r (R is one or more selected from La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Y, j + k + m + n + p = 1, 0 ≤ q ≤ 1, 0 ≤ r ≤ 1). 【0029】 There are no particular restrictions on the method of applying the thermistor precursor dispersion; methods such as jet dispenser, inkjet, and mechanical dispenser can be used. To prevent cracking of the thermistor film 18, it is preferable to make the thickness of the thermistor precursor film between 1 μm and 3 μm. Furthermore, depending on the particle size of the oxide nanoparticles in the thermistor precursor dispersion or the reactivity of the thermistor precursor dispersion, the electrical resistance of the thermistor film 18 may be high with only temperature drying. In this case, the electrical resistance of the thermistor film 18 can be reduced by mixing a metal-organic compound solution with the thermistor precursor dispersion or by irradiating the dried thermistor film with a pulsed laser. 【0030】 In other words, if the electrical resistance of the thermistor film 18 does not decrease sufficiently after drying at the appropriate temperature, the electrical resistance of the thermistor film 18 can be further reduced by promoting crystallization of the thermistor film 18 by irradiation with a pulsed ultraviolet laser with a wavelength of 400 nm or less. The fluence of the laser irradiation at this time is 10 mJ / cm, depending on the thickness of the thermistor film 18. 2 ~70 mJ / cm² 2 It is preferable that the first irradiation step is 10-45 mJ / cm². 2 The light is irradiated, and as a second irradiation step, 70 mJ / cm² is applied. 2 Irradiating the thermistor film 18 with light up to this point may contribute to improving its density. 【0031】 Furthermore, from the viewpoint of reducing the interparticle pores of the thermistor precursor film and lowering the electrical resistance of the thermistor film 18 after drying, and from the viewpoint of suppressing excessive heating during pulsed laser irradiation and producing a uniform thermistor film 18, it is preferable that the particle size of the oxide nanoparticles in the thermistor precursor dispersion is 1 μm or less. "Particle size" refers to the maximum value of the volume fraction relative to the particle diameter, and can be obtained by dropping the dispersion onto an arbitrary substrate, drying it, and performing image analysis on an electron microscope image at 50,000x magnification. For example, analysis software such as ImageJ can be used. 【0032】 The thin wire type thermistor temperature sensing element 10 reads the electrical resistance value of the thermistor film 18 between the first conductive layer 14 and the second conductive layer 16, i.e., along the length direction of the linear substrate 12, and calculates the surface temperature of the thermistor film 18 corresponding to that electrical resistance value. The thin wire type thermistor temperature sensing element 10 can be inserted, for example, into a typical vascular catheter with a diameter of about 1 mm, to more accurately grasp changes in blood flow temperature than before. The width of the gap 20 can be appropriately changed according to the electrical resistance value of the thermistor film 18 material. For example, when the diameter of the linear substrate 12 is 20 μm or less and the electrical resistance value of the thermistor film 18 is high, it is preferable to set the width of the gap 20 to 100 μm or less. 【0033】 By miniaturizing the diameter of the thin wire-type thermistor temperature sensing element 10 to approximately 10 μm, it can be implemented in next-generation microvascular catheters capable of detecting capillary-level blood vessels, enabling precise biological monitoring. Furthermore, the thin wire-type thermistor temperature sensing element 10 is expected to be used as a novel thermistor-type temperature prober, such as for measuring the temperature of cell surfaces measuring 10 μm to 20 μm in size. Moreover, because lightweight, compact, and inexpensive organic materials can be used for the linear substrate 12, the thin wire-type thermistor temperature sensing element 10 can be used in a variety of devices. 【0034】 (Second embodiment) Figure 3 schematically shows the central cross-section along the longitudinal direction of the thin wire type thermistor temperature sensing element 30 of the second embodiment of the present application. Figure 4 schematically shows three cross-sections perpendicular to the longitudinal direction of the thin wire type thermistor temperature sensing element 30. Specifically, Figure 4(a) shows the end face of the cut portion of line AA in Figure 3, Figure 4(b) shows the end face of the cut portion of line BB in Figure 3, and Figure 4(c) shows the end face of the cut portion of line CC in Figure 3. The thin wire type thermistor temperature sensing element 30 comprises a linear substrate 32, a thermistor film 38, an insulating layer 40, and a conductive layer 42. 【0035】 The thin wire type thermistor temperature sensing element 30 can be obtained, for example, by forming a thermistor film 38 on one end 32c of a linear substrate 32, forming an insulating layer 40 on the surface of the conductive film 32b, which is the conductive part of the linear substrate 32, so as to cover a portion of the thermistor film 38 on the opposite side of the end 32c, and forming a conductive layer 42 so as to cover a portion of the insulating layer 40 on the end 32c side and the thermistor film 38. To improve durability, the thin wire type thermistor temperature sensing element 30 may have a thin insulating protective film on its surface. 【0036】 The linear substrate 32 is an elongated linear member with a substantially circular cross-section perpendicular to its length. The diameter of the linear substrate 32 is 200 μm or less. More preferably, the diameter of the linear substrate 32 is 20 μm or less. The linear substrate 32 has a conductor on its surface. The conductor is a material that possesses electrical conductivity. Note that the entire surface of the linear substrate 32 is not conductor; only a part of the surface is conductor. Examples of linear substrates 32 whose entire surface is conductor include substrates composed of conductors, such as metal fine wires of titanium, gold, or copper, and substrates in which the entire surface of an insulating wire is coated with a conductor. 【0037】 In this embodiment, the linear substrate 32 comprises an insulating wire 32a and a conductive film 32b, which is a conductor, formed on a part of the surface of the wire 32a. Examples of the wire 32a include flexible linear materials with a heat resistance temperature, i.e., a softening point, of 200°C or less, such as resin wires such as aramid and pulp wires. The linear substrate 32 is obtained by forming the conductive film 32b on the surface of the wire 32a in the same manner as in the first embodiment, in which the first conductive layer 14 or the second conductive layer 16 was formed on the surface of the linear substrate 12. 【0038】 As shown in Figure 3, the thermistor film 38 covers one end 32c of the linear substrate 32 so as to be electrically connected to the conductive film 32b. The thickness T1 of the thermistor film 38 is smaller than the diameter D of the linear substrate 12. In this embodiment, the thickness of the thermistor film 38 is the maximum thickness at each location formed near the side surface and near the end surface 32c of the linear substrate 32. The thermistor film 38 can be formed in the same manner as in the first embodiment. Note that if the linear substrate 32 is a metal wire, the drying temperature of the thermistor precursor film can be set to about 500°C. 【0039】 The insulating layer 40 has insulating properties. The insulating layer 40 electrically insulates the conductor 32b from the conductive layer 42. The thickness T3 of the insulating layer 40 is smaller than the diameter D of the linear substrate 12. Preferably, the insulating layer 40 is formed on a part of the surface of the conductor 32b and the thermistor film 38 by electrodeposition using a polyimide resin coating. In this case, if the portion of the thermistor film 38a covering the end 32c is coated with an acrylic resin to insulate it before electrodeposition, a part of the surface of the conductor 32b and the thermistor film 38 will be covered with the insulating layer 40. After that, the acrylic resin is dissolved and removed with an organic solvent such as acetone. 【0040】 The conductive layer 42 further covers the thermistor film 38a in the portion covering the end 32c. The thickness T2 of the conductive layer 42 is smaller than the diameter D of the linear substrate 12. In this embodiment, the thickness of the conductive layer 42 is the maximum thickness at each location formed near the side surface and near the end surface 32c of the linear substrate 32. The conductive layer 42 is obtained in the same manner as in the first embodiment in which the first conductive layer 14 or the second conductive layer 16 was formed on the surface of the linear substrate 12. The thin wire type thermistor temperature sensing element 30 reads the electrical resistance value of the thermistor film 38 between the conductor 32b and the conductive layer 42, and calculates the surface temperature of the thermistor film 38 corresponding to that electrical resistance value. This surface temperature of the thermistor film 38 is approximately the same as the temperature directly above the conductive layer 42 covering the thermistor film 38. 【0041】 The electrical resistance R of the thermistor film 38 between the conductor 32b and the conductive layer 42 is 5 MΩ or less. This electrical resistance R is the minimum value of the electrical resistance of the thermistor film 38 between any point on the conductor 32b and any point on the conductive layer 42. It is more preferable that this electrical resistance R is 3 MΩ or less. This electrical resistance R can be calculated in advance using the following formula, which uses the thickness T4 of the conductive film 32b, the length L of the thermistor film 38 protruding from the insulating layer 40 towards the end 32c, and the electrical resistivity ρ of the thermistor film 38 material. This calculated value is in close agreement with the measured value. R = ρT1 / {π(T4 + D / 2)} 2 L} [Examples] 【0042】 The present invention will be described in more detail below with reference to examples and comparative examples. The present invention is not limited to these examples. 【0043】 (Example 1) First, Ag nanoparticles (Harima Chemical Industries' NPS-J) were coated onto half of the surface of a 15 μm diameter aramid resin nanowire (Teijin Technola, hereinafter the same) so that there was a 25 μm gap between them. The nanowires were then dried and sintered at 200°C to form a pair of Ag thin films. Next, Ni plating was applied to these Ag thin films at 1.5 V in an aqueous nickel sulfate solution to create a first conductive layer and a second conductive layer. The thickness of the first and second conductive layers was several μm, clearly less than 15 μm. 【0044】 Next, MnCO3, CoO, NiO, and CuO are mixed so that the molar ratio of Mn:Co:Ni:Cu is 1.4:0.9:0.5:0.2, and then the calcined Mn is produced by a solid-phase reaction method that involves calcination in two stages at 950°C and 1150°C. 1.4 Co 0.9 Ni 0.5 Cu 0.2O4 was synthesized. The calcined body was then dry-milled to obtain a powder. Next, this powder was added to a toluene solution containing organic salts of Mn, Co, Ni, and Cu, with a molar ratio of Mn:Co:Ni:Cu of 1.4:0.9:0.5:0.2. The mixture was then mixed and pulverized in a bead mill to obtain oxide nanoparticles of Mn. 1.4 Co 0.9 Ni 0.5 Cu 0.2 A thermistor precursor dispersion containing O4 was obtained. 【0045】 Figure 5 shows the particle size distribution of oxide nanoparticles contained in this thermistor precursor dispersion. The particle sizes were distributed in the range of 20 nm to 250 nm. As shown in Figure 5(a), the number of particles was maximum at a particle size of 39 nm. Also, as shown in Figure 5(b), the volume fraction was maximum at a particle size of 96 nm, confirming that a thermistor precursor dispersion mainly containing particles with a particle size of approximately 100 nm or less was obtained. 【0046】 The thermistor precursor dispersion was applied to the gaps using a jet dispenser and dried at 200°C. Next, at room temperature, 30 mJ / cm³ was added to the oxide nanoparticle dispersion. 2 The KrF excimer laser light was irradiated with 100 pulses at this fluence, and then 45 mJ / cm² was added. 2 A KrF excimer laser beam was irradiated with 200 pulses at the specified fluence. The same treatment was applied to the remaining half of the surface of the fine wire substrate to obtain a fine wire type thermistor temperature sensing element of Example 1, which corresponds to the first embodiment. The thickness of the thermistor film was several μm, clearly less than 15 μm. 【0047】 Figure 6 shows the appearance of this thin-wire thermistor temperature sensing element. Note that "MCNC" in Figure 6 stands for Mn 1.4 Co 0.9 Ni 0.5 Cu 0.2The material is O4. The electrical resistance of the thermistor film of the thin-wire type thermistor temperature sensing element in Example 1 was 2.48 MΩ. Figure 7 shows the electrical characteristics of the thermistor film of the thin-wire type thermistor temperature sensing element in Example 1. As shown in Figure 7, the thermistor constant (B constant) of this thermistor film was 2722 K. 【0048】 Figure 8 shows the responsiveness of the nanowire type thermistor temperature sensing element of Example 1. The thermal time constant of the thermistor film of the nanowire type thermistor temperature sensing element of Example 1 was 10¹ ms during heating and 10⁹ ms during cooling. This indicates that the thermistor film has an extremely small thermal time constant. Furthermore, there was high symmetry between the thermal time constants of the thermistor film during heating and cooling. This is because the miniaturization of the substrate reduced the heat capacity and improved thermal diffusion, resulting in a small thermal time constant even during cooling. 【0049】 In conventional thermistor temperature sensing elements using a sheet-like substrate with a thickness of approximately 50 μm, the thermal time constant of the thermistor film was approximately 1 s to 2 s. In contrast, the thin-wire type thermistor temperature sensing element of Example 1 achieved extremely fast response. If the thickness of the thermistor film is 1 μm to 3 μm, the response of the thermistor temperature sensing element depends on the heat capacity of the substrate. According to thermal diffusion simulations (Ansys Mechanical, Ansys), if the thickness of the thermistor film is 3 μm or less and the diameter of the linear substrate 32 is 200 μm or less, it is estimated that the thermal time constant of the thermistor film will be within 1 s. 【0050】 (Example 2) A nanowire type thermistor temperature sensing element of Example 2 was obtained in the same manner as in Example 1, except that the drying temperature of the thermistor precursor film was set to 250°C and subsequent laser irradiation was not performed. Electrical conductivity of the thermistor film was also obtained in the nanowire type thermistor temperature sensing element of Example 2, and its operation as a thermistor temperature sensing element was confirmed. 【0051】 (Example 3) Ag nanoparticles were coated onto the surface of a 15 μm diameter aramid resin nanowire, dried at 220°C, and sintered to obtain an Ag thin film. This Ag thin film was plated with Ni at 1.5 V in an aqueous nickel sulfate solution to obtain a nanowire substrate with a conductive surface. Next, using a jet dispenser, the same thermistor precursor dispersion as in Example 1 was coated onto one end of the nanowire substrate and dried at 220°C. This coating and drying at 220°C was repeated five times to form a thermistor film. The thickness of this thermistor film was several μm, clearly less than 15 μm. 【0052】 Next, molten acrylic resin was applied to the end face where the thermistor film was formed, and to the thermistor film in a region approximately 1.0 mm wide extending from this end face toward the other end, thereby insulating the surface of the thermistor film. Then, a modified polyimide amide resin (INSULEED, manufactured by Nippon Paint) was coated onto a portion of the thermistor film surface and the conductive material on the surface of the fine wire substrate by electrodeposition. Next, the acrylic resin attached to the ends was dissolved and removed with acetone. 【0053】 Next, Ag nanoparticles were applied to the acrylic resin removal area, dried at 220°C, and sintered to obtain an Ag thin film. Then, Ni plating was performed on this Ag thin film in an aqueous nickel sulfate solution at 1.5V to form a conductive layer, thereby obtaining the nanowire type thermistor temperature sensing element of Example 3, which corresponds to the second embodiment. Electrical conductivity of the thermistor film was also obtained in the nanowire type thermistor temperature sensing element of Example 3, and its operation as a thermistor temperature sensing element was confirmed. 【0054】 (Comparative Example 1) A nanowire type thermistor temperature sensing element of Comparative Example 1 was fabricated in the same manner as in Example 1, except that a powder was obtained by mixing MnCO3, CoO, and Fe3O4 so that the molar ratio of Mn:Co:Fe was 0.80:1.30:0.90, and a thermistor precursor dispersion was obtained using organic salts of Mn, Co, and Fe in the same molar ratio. The thermistor film of the nanowire type thermistor temperature sensing element of Comparative Example 1 had an electrical resistance value of 1 GΩ or more. In other words, the nanowire type thermistor temperature sensing element of Comparative Example 1 was not suitable for temperature measurement near room temperature as a thermistor temperature sensing element. 【0055】 (Comparative Example 2) With a linear substrate 32 having a diameter of 300 μm, the thermal time constant of the thermistor film of the thin wire type thermistor temperature sensing element of Comparative Example 2 was calculated by the thermal diffusion simulation performed in Example 1. This thermal time constant exceeded 1.7 s. It became clear that the thin wire type thermistor temperature sensing element of Comparative Example 2 is unsuitable for use as a thermistor temperature sensing element for high-speed response applications. 【0056】 (Comparative Example 3) Firing body Mn 1.4 Co 0.9 Ni 0.5 Cu 0.2 In Comparative Example 3, a nanowire type thermistor temperature sensing element with a high electrical resistance value of the thermistor film was fabricated in the same manner as in Example 1, except that a toluene solution containing organic salts of Mn, Co, Ni, and Cu with a molar ratio of Mn:Co:Ni:Cu of 1.4:0.9:0.5:0.2 was used as the thermistor film precursor solution. The electrical resistance value of the thermistor film of the nanowire type thermistor temperature sensing element of Comparative Example 3 was high, exceeding the measurement limit, and the change in electrical resistance could not be measured. In other words, the nanowire type thermistor temperature sensing element of Comparative Example 3 did not function as a thermistor temperature sensing element. 【0057】 (Comparative Example 4) Firing body Mn 1.4 Co 0.9 Ni 0.5 Cu0.2 In Comparative Example 4, a nanowire type thermistor temperature sensing element with a high electrical resistance value of the thermistor film was fabricated in the same manner as in Example 3, except that a toluene solution containing organic salts of Mn, Co, Ni, and Cu with a molar ratio of Mn:Co:Ni:Cu of 1.4:0.9:0.5:0.2 was used as the thermistor film precursor solution. The electrical resistance value of the thermistor film of the nanowire type thermistor temperature sensing element of Comparative Example 4 was high, exceeding the measurement limit, and the change in electrical resistance could not be measured. In other words, the nanowire type thermistor temperature sensing element of Comparative Example 4 did not function as a thermistor temperature sensing element. [Industrial applicability] 【0058】 The thin-wire thermistor temperature sensing element of this invention offers a high degree of freedom in terms of the shape and size of the location of use, making it applicable to tiny, thin devices and wearable devices, as well as to electronic substrates, localized areas on biological surfaces, narrow areas inside complexly shaped structures, and confined spaces. Furthermore, the thin-wire thermistor temperature sensing element of this invention is expected to be used as a thermistor-type temperature prober that enables unprecedentedly precise biological monitoring, such as by being implemented in next-generation microvascular catheters capable of responding to blood vessels at the capillary level. [Explanation of Symbols] 【0059】 10. Thin-wire type thermistor temperature sensing element 12 Linear base material 14 First conductive layer 16 Second conductive layer 18 Thermistor film 20 gaps 30 Thin-wire thermistor temperature sensing element 32 Linear base material 32a wire rod 32b Conductive film 32c end 38 Thermistor film 38a Thermistor film covering the end of the linear substrate 40 Insulating layer 42 Conductive layer

Claims

[Claim 1] A linear substrate with insulating properties and a diameter of 200 μm or less, A first conductive layer and a second conductive layer are provided on the surface of the linear substrate with a gap formed between them, and each has a thickness smaller than the diameter of the linear substrate. A thermistor film is provided so as to cover a part of the first conductive layer, the gap, and a part of the second conductive layer, wherein the electrical resistance between the first conductive layer and the second conductive layer is 5 MΩ or less, and the thickness is smaller than the diameter of the linear substrate, A thin wire type thermistor temperature sensing element having the following characteristics. [Claim 2] A linear substrate with a conductive surface and a diameter of 200 μm or less, A thermistor film covering one end of the linear substrate so as to be electrically connected to the conductor, with a thickness less than the diameter of the linear substrate, A conductive layer is provided that further covers the thermistor film in the portion covering the end, and whose thickness is smaller than the diameter of the linear substrate. An insulating layer is provided which the conductor and the conductive layer are electrically insulated, and whose thickness is smaller than the diameter of the linear substrate. It has, A thin-wire type thermistor temperature sensing element in which the electrical resistance of the thermistor film between the conductor and the conductive layer is 5 MΩ or less. [Claim 3] In claim 1 or 2, A thin wire type thermistor temperature sensing element in which the thermistor film thickness is 1 μm or more and 3 μm or less. [Claim 4] In claim 3, A thin wire type thermistor temperature sensing element in which the thermal time constants of the thermistor film during heating and cooling are both 200 ms or less. [Claim 5] In claim 3, A thin wire type thermistor temperature sensing element wherein the heat capacity of the linear substrate is 25 μJ / K or less.

Images