JPH0262502B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a high-temperature glass-sealed thermistor element. More specifically, the present invention does not cause deterioration of each component during glass sealing in the manufacturing process of a glass-sealed thermistor element, and also has stable thermistor characteristics even when used at high temperatures of 500°C or higher. This invention relates to a glass-sealed thermistor element for high temperatures. Conventional technology Conventionally, thermistor elements have been widely used in many fields as temperature sensors for temperature measurement and temperature control by utilizing the temperature dependence of the electrical resistance of the temperature-sensitive resistor. As electronic control of equipment progresses, there is a growing demand for highly reliable equipment even when used under severe conditions. For example, thermistor elements used in automobile exhaust gas temperature detection sensors, oil and gas combustion control sensors, etc. are required to be able to withstand high temperatures. Thermistor elements include glass-sealed types and thin-film types. Among these, glass-sealed thermistor elements have a thermistor chip that has a pair of electrodes each connected to a lead wire, and is sealed in glass. It has a structure. Conventionally, lead glass has been used as the sealing glass used in such glass-sealed thermistor elements, but this glass has a low glass transition temperature of 400°C or less, so it is difficult to use this as the sealing glass. The thermistor elements used in the past were difficult to use at high temperatures, especially above 500°C, so they had to be limited in their use. By the way, glass has a glass transition temperature.Atoms and ions move easily around this glass transition temperature range, and the glass structure loosens, so the coefficient of thermal expansion of glass decreases rapidly above the glass transition temperature. It will increase to . For glass-sealed thermistors, the materials of the thermistor chip, sealing glass, lead wires, and other component parts are selected appropriately and their coefficients of thermal expansion are roughly matched to create a thermally stable thermistor element. It is important to. Considering the coefficient of thermal expansion in this way, the limit temperature for use of a glass-sealed thermistor element is limited by the glass transition temperature used for sealing. Therefore, in glass-sealed thermistor elements for high temperatures, borosilicate glass, which has a high transition temperature, is generally used as the sealing glass. However, although this borosilicate glass has a transition temperature of 500 to 600°C, which is considerably higher than lead glass, it is still insufficient, and the working temperature is usually over 1000°C, so it is difficult to manufacture thermistor elements. During the glass sealing process, the thermistor chip, electrodes, lead wires, etc. deteriorate due to heat and the electrical resistance changes, making it difficult to obtain a thermistor element with stable thermistor characteristics. Problems to be Solved by the Invention Under these circumstances, the present invention has been developed to provide a method that does not cause deterioration of constituent members during glass sealing in the manufacturing process of a glass-sealed thermistor element, and that can be used at high temperatures of 500°C or higher. The purpose of this invention is to provide a high-temperature glass-sealed thermistor element that has stable thermistor characteristics during use. Means for Solving the Problems As a result of intensive research to develop a high temperature glass-sealed thermistor element having the above-mentioned preferable properties, the present inventors have determined that a specific glass transition temperature (Tg) and working temperature (Tw), thermal expansion coefficient (α), and in some cases a predetermined electrical resistance value, it was found that the desired objective could be achieved, and based on this knowledge, the present invention was completed. That is, the present invention provides (a) 25 to 35% by weight of SiO ₂ and
In combination with B ₂ O ₃ 15-30% by weight, the total amount of both becomes
50 to 55% by weight, (b) Al ₂ O ₃ 2 to 15% by weight, (c) BaO alone or in combination with BaO and at least one oxide selected from SrO, CaO, MgO and ZnO. , BaO5% by weight or more, SrO20% by weight or less,
25 to 40% by weight of divalent metal components including up to 15% by weight of CaO, up to 15% by weight of MgO, up to 5% by weight of ZnO, and optionally (d) up to 6% by weight of ZrO ₂ , up to 0.5% by weight of Li ₂ O, and up to 0.5% by weight of Li ₂ O. High-temperature glass-sealed type using borosilicate glass containing 1% by weight or less of O and 1% by weight or less of _K2 , and has a glass transition temperature (Tg) of 600℃ or higher and a working temperature (Tw) of 950℃ or lower. The present invention provides a thermistor element. The present invention will be explained in more detail below. As mentioned above, the sealing glass used in the thermistor element of the present invention is composed of a borosilicate component (a) consisting of SiO ₂ and B ₂ O ₃ as main components, an alumina component (b), and a predetermined divalent metal oxide. It has a composition consisting of component (c) and a predetermined optional component (d) that is added as desired. As for components (a) to (d), predetermined blending ratios are adopted for each of them, and this is due to the following reasons. That is, SiO ₂ in component (a) is the main component constituting the glass network, and is effective in stabilizing the glass and improving chemical durability. however,
If it is less than 25% by weight, the above effects will be small, and if it is more than 35% by weight, the viscosity of the glass will increase, leading to an increase in the working temperature (Tw). Like SiO ₂ , B ₂ O ₃ is a component of the glass network, and is effective in lowering the working temperature and increasing the glass transition temperature (Tg). However, if it is less than 15% by weight, the above effects will be small, and 30
When the amount exceeds % by weight, chemical durability deteriorates. Also, if the total amount of SiO ₂ and B ₂ O ₃ is less than 50% by weight, the stability of the glass will deteriorate, and if it exceeds 55% by weight, the working temperature (Tw) will increase, so it should be within the specified range. . Next, component (b) Al ₂ O ₃ is an effective component for improving chemical durability and increasing the glass transition temperature (Tg). However, if it is less than 2% by weight, the above effects cannot be obtained, and if it is more than 15% by weight, the working temperature (Tw) increases and the stability of the glass decreases. (iii) Ingredients BaO, SrO, CaO, MgO and ZnO are:
It is an effective component for lowering the working temperature (Tw) without adjusting the coefficient of thermal expansion or lowering the glass transition temperature (Tg). However, if BaO is less than 5% by weight, the above effects cannot be obtained, and if it is more than 40% by weight, the thermal expansion coefficient will exceed a predetermined range and the chemical durability will deteriorate. When SrO exceeds 20% by weight, CaO and
When MgO exceeds 15% by weight, it deteriorates the stability of the glass and increases its tendency to devitrify. ZnO is effective in lowering the working temperature (Tw), but if it exceeds 5% by weight, it increases the tendency to devitrify. And if the total amount of BaO, SrO, CaO, MgO and ZnO is less than 25% by weight, the above effect will be small,
If it exceeds 40% by weight, the stability and chemical durability of the glass will decrease. ZrO ₂ has a glass transition temperature (Tg) similar to Al ₂ O ₃
Although this component is effective in increasing the carbon content and improving chemical durability, if it exceeds 6% by weight, it promotes a tendency to devitrify. Li ₂ O, Na ₂ O and K ₂ O are effective ingredients for lowering the working temperature (Tw). But Li ₂ O is 0.5
When the weight percent of Na ₂ O and K ₂ O exceeds 1 weight percent, it is not preferable because it lowers the glass transition temperature and causes deterioration of electrical properties. Next, the composition (values are weight %), working temperature (Tw), transition temperature (Tg), coefficient of thermal expansion (α), and specific resistance at 500°C of the sealing glass according to the present invention are shown in the table.

【table】

[Table] Furthermore, the sealing glass used in the thermistor element of the present invention has a glass transition temperature of 600°C or higher, preferably in the range of 600 to 700°C, and a working temperature of 950°C or lower, preferably 800 to 950°C. It is necessary that the temperature be within the range of ℃. The glass transition temperature is 600℃
If the working temperature exceeds 950°C, it may not be possible to obtain a thermistor element with sufficiently stable thermistor characteristics in regular use at high temperatures of 500°C or higher, and if the working temperature exceeds 950°C, the glass seal during the manufacturing process of the thermistor element When the thermistor chip, electrodes, lead wires, etc. are deteriorated by heat, the electrical resistance value changes, making it difficult to obtain a thermistor element with stable thermistor characteristics. In some cases, the sealing glass preferably has a thermal expansion coefficient (α) of 50×10 ^-7 to 70×10 ^-7 deg ^-1 and a specific resistance of 1×10 ⁶ Ω·cm or more at 500°C. . Next, the method for manufacturing the high-temperature glass-sealed thermistor element of the present invention will be explained.
After fabricating a wafer of about 3 inches in diameter and 0.5 mm thick made of a sintered body with a coefficient of thermal expansion of about 30 x 10 ^-7 to 90 x 10 ^-7 deg ^-1 , an electrode layer is placed on both sides of the wafer. Then, the wafer with the electrode layer formed thereon is cut into square pieces with sides of about 0.75 mm using a dicing saw or the like to form chips. There are no particular restrictions on the sintered body used at this time, and materials that are conventionally used as thermistor materials, such as
MnO ₂ −NiO system, Al ₂ O ₃ −NiO system, ZrO ₂ system,
Al ₂ O ₃ -CrO ₃ type, Fe ₂ O ₃ type, spinel type, SiC type, etc. can be used, but in particular, it contains at least one selected from carbides, nitrides, borides, and silicides. A sintered body that has the following properties is preferably used. Among such thermistor materials, those having a thermal expansion coefficient of 30×10 ^-7 to 90×10 ^-7 deg ^-1 , preferably 50
A range of ×10 ⁻⁷ to 70×10 ⁻⁷ deg ⁻¹ is suitable. If this coefficient of thermal expansion deviates from the above range,
This is undesirable because it becomes difficult to select materials for lead wires and sealing glass suitable for the high-temperature thermistor element. Examples of the carbide include SiC, B ₄ C, TiC,
ZrC, Mo ₂ , NbC, CrO ₃ C ₂ etc., nitrides such as BN, TiN, NbN, Cr ₂ N etc., borides such as CrB, ZrB, MoB, WB etc., silicides such as _MoSi2 , _CrSi2 ,
Examples include TiSi ₂ and WSi ₂ . A sintered body containing at least one selected from these carbides, nitrides, borides, and silicides is effective in stabilizing the B constant in a high temperature range and in high-temperature sealing in an inert gas. It is advantageous. Examples of such materials include Al ₂ O ₃ −SiC
system, Al ₂ O ₃ −B ₄ C system, Al ₂ O ₃ −SiC−B ₄ C system,
Al ₂ O ₃ −B ₄ C−BN system, Al ₂ O ₃ − (TiN, NbN)
Examples include those containing Al _{2 O 3 such as Al 2 O 3} -TiSi ₂ type and Al ₂ O 3 -TiSi 2 type. Among these materials, it is preferable that the content of Al ₂ O ₃ is in the range of 50 to 95% by weight. When containing SiC, the content is preferably 50% by weight or less, and if it exceeds 50% by weight, there is a risk that a large amount of foaming will occur during glass sealing. On the other hand, there are no particular restrictions on the electrode layer, and any electrode layer can be selected from among electrodes made of conductive materials or electrodes containing conductive materials that have been conventionally used in thermistor elements. As the conductive material, known conductive substances,
For example, Au, Ag, Pt, Pd, W, Cu, Ni, Mo,
Ml, Fe, Ti, Mn, etc., or Pt−Au, Pd−
Au, Pt-Pd-Au, Pd-Ag, Pt-Pd-Ag, Fe
Alloys such as -Ni-Co, Fe-Ni, Mo-Mn, etc. can be used. These conductive materials may be formed into an electrode layer by vapor phase plating, liquid phase plating, thermal spraying, or brazing in a foil. In addition, these conductive materials are mixed with a binder and a solvent, and more preferably with an appropriate oxide, to prepare a conductive paste, and this conductive paste is applied to a thermistor chip and fired to form an electrode. It may also be formed by a so-called thick film method. Note that it is preferable to use a glass fritless paste that does not contain glass. If an electrode layer containing glass frit is used, foaming is likely to occur during connection, which may impair connectivity and adhesion.The thickness of such an electrode layer is usually selected in the range of 5 to 200 μm. Next, the diameter of the chip thus obtained is
After connecting a lead wire with a diameter of 0.2 to 0.5 mm and a length of 20 to 100 mm, this is usually connected to a wire with a diameter of 1.5 to 2.5 mm and a length of 5 mm.
It is inserted into a glass tube made of sealing glass with a diameter of about 1.2 mm and sealed at a temperature of about 750 to 900 °C in an inert atmosphere such as an argon gas atmosphere. A glass-sealed thermistor element can be obtained by aging at a temperature of about 10 to 100 hours. There are no particular restrictions on the lead wire used at this time, and the lead wire that is conventionally used as a heat-resistant lead wire in thermistor elements, for example, 29% by weight.
Kovar alloy has a composition of Ni - 17% by weight, Co - residual Fe, and a composition of 41 to 43% by weight Ni - residual Fe.
42 alloy or Fe-Cr alloy can be used, but among these, Kovar alloy is preferred from the viewpoint of thermal expansion coefficient and adhesion to the sealing glass. Such lead wires may have their surfaces plated in advance with a heat-resistant metal such as platinum. The lead wire usually has a diameter of 0.2 to 0.5
mm, length in the range of 20 to 100 mm is used,
Further, as a method for connecting this lead wire to the electrode layer, any method may be used, such as a method of electrically contacting and connecting using a conductive paste such as gold paste, a method using welding, a method using an ultrasonic bonder, etc. A method can be used. The structure of the glass-sealed thermistor element produced in this way will be explained according to the attached drawings.
In the figure, a pair of electrode layers 4 are provided on both sides of a thermistor chip 1, a lead wire 3 is connected to each of the electrode layers 4, and the entire lead wire except for a part is sealed with a sealant 2. It shows the structure that was created. Examples Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way. Note that the heat resistance of the thermistor element is determined by
After holding at 500℃ for 5000 hours, the change in resistance value due to high temperature storage is ΔR, and the resistance value before high temperature storage is R ₀ , and the resistance change rate is calculated according to the formula: Resistance change rate (%) = ΔR/R ₀ × 100 was determined and evaluated. Example 1 A composite sintered body with a diameter of 3 inches and a thickness of 0.5 mm consisting of 86% by weight of Al ₂ O ₃ and 14% by weight of B ₄ C was fired at
After hot-press sintering at 1650℃ and press pressure of 200Kg/ ^cm2 , a 0.5μm thick Ni electrode layer was formed on both sides of the composite sintered body by vapor deposition, and on top of this, A platinum electrode layer with a thickness of 1.0 μm was formed by plating to prepare a wafer. Next, the wafer thus obtained is sliced on one side with a diamond blade using a peripheral slicing machine.
The thermistor chip was obtained by cutting into a 0.75 mm square. Next, add a diameter of 0.3 mm and a length of 65 mm to this chip.
The Kovar alloy lead wires were connected by parallel gap welding under the conditions shown below. (Parallel gap welding conditions) AC voltage: 0.06 to 0.83V Time: 30 to 40msec Gap length: 0.20mm Applied pressure: 2.8Kg Next, the material obtained in this way was No. 1 with a glass transition temperature of 650℃ and a working temperature of 942℃. The tube was inserted into a 2.5 mm diameter and 4 mm length tube made of glass (composition, No. 1 in the table), sealed at 800°C in an argon gas atmosphere, and then aged. A glass-sealed thermistor element was fabricated. When this material was examined for heat resistance, the rate of change in resistance was 1.0% or less. Example 2 As the sealing glass in Example 1, instead of No. 1 glass, a glass transition temperature of 623°C and a working temperature of 879°C was used.
A glass-sealed thermistor element was prepared in exactly the same manner as in Example 1, except that No. 2 glass (composition, No. 2 in the table) of ℃ was used, and its heat resistance was examined. As a result, the resistance change rate was 1.0% or less. Comparative Example Instead of the No. 1 glass in Example 1, Corning 7052 borosilicate glass (SiO ₂ 5% by weight, B ₂ O ₃ 18
Glass _sealing was _carried out in exactly the same _manner as in Example 1, except that ₇ wt _. A type thermistor element was manufactured and its heat resistance was investigated. As a result, the resistance change rate was 10.0%. Effects of the Invention The high temperature glass-sealed thermistor element of the present invention has a glass transition temperature (Tg) of 600°C or more and a working temperature (Tw) of less than 1000°C, particularly 950°C or less.
Thermal expansion coefficient (α) is 50×10 ^-7 ×10 ^-7 deg ^-1 and
By using sealing glass with a specific resistance of 1 x 10 ⁶ Ω・cm or more at 500°C, there is no deterioration of the constituent members during glass sealing in the manufacturing process of glass-sealed thermistor elements, and Stable thermistor characteristics can be provided even when used at high temperatures of ℃ or higher. This glass-sealed thermistor element is suitable as a high-temperature sensor such as an automobile exhaust gas temperature detection sensor or an oil/gas combustion control sensor.

[Brief explanation of drawings]

The figure shows one of the glass-sealed thermistor elements of the present invention.
This is a cross-sectional view of an example, in which reference numeral 1 is a thermistor chip, 2 is a sealing glass, 3 is a lead wire, and 4 is an electrode layer.

Claims (1)

[Claims] 1 (a) 25 to 35% by weight of SiO ₂ and 15 to 30% by weight of B ₂ O ₃
(b) Al ₂ O _{3 2} to 15% by weight, (c) BaO alone or BaO and SrO, CaO, MgO and
A divalent metal component containing 5% by weight or more of BaO, 20% by weight or less of SrO, 15% by weight or less of CaO, 15% by weight or less of MgO, and 5% by weight or less of ZnO in combination with at least one oxide selected from ZnO.
40% by weight and as desired (d) ZrO ₂ 6% by weight or less, Li ₂ O 0.5% by weight or less,
Contains 1% by weight or less of Na ₂ O, 1% by weight or less of K ₂ O, and has a glass transition temperature (Tg)
A high-temperature glass-sealed thermistor element using borosilicate glass with a working temperature (Tw) of 600℃ or higher and a working temperature (Tw) of 950℃ or lower. 2 The borosilicate glass has a coefficient of thermal expansion (α)
2. The high-temperature glass-sealed thermistor element according to claim 1, having a specific resistance of 1×10 ⁶ Ω·cm or more at 50×10 ⁻⁷ to 70×10 ⁻⁷ deg ⁻¹ and 500° C. 3. The high-temperature glass-sealed thermistor element according to claim 1, wherein the thermistor element is a sintered body containing one or more of carbides, nitrides, borides, and silicides.