WO2012036142A1

WO2012036142A1 - Positive characteristic thermistor and method for manufacturing positive characteristic thermistor

Info

Publication number: WO2012036142A1
Application number: PCT/JP2011/070789
Authority: WO
Inventors: 正人後藤; 直晃阿部; 岸本　敦司; 勝　勇人; 康訓並河
Original assignee: 株式会社村田製作所
Priority date: 2010-09-17
Filing date: 2011-09-13
Publication date: 2012-03-22
Also published as: DE112011103112T5

Abstract

A component element (1) is formed from a semiconductor ceramic in which the chief constituent is a BaTiO₃-based composition and some of the Ba is substituted with alkali metal and Bi, and the component element (1) is provided with: a high-resistance layer (4) having high room-temperature resistance and a high resistance/temperature coefficient; and low-resistance layers (3a, 3b) having low room-temperature resistance and a low resistance/temperature coefficient. The high-resistance layer (4) is formed on an outside surface section contacting external electrodes (2a, 2b), and also the low-resistance layers (3a, 3b) are formed in a middle section separated from the external electrodes (2a, 2b). The thickness (y) (μm) of the high-resistance layer (4) and the mol ratio (x) of the alkali metal in the chief constituent satisfy the relationship of 10≤y≤-3500x+525(0.010≤x≤0.147). Also, the component element (1) can be manufactured by a sheet processing method. In this way, a non-lead-based PTC thermistor can be implemented having good reliability in which deterioration over time of resistance can be suppressed without impairing PTC characteristics even when current is passed for a long period of time, and a method for manufacturing this PTC thermistor can also be implemented.

Description

Positive temperature coefficient thermistor and method for manufacturing positive temperature coefficient thermistor

The present invention relates to a positive temperature coefficient thermistor and a method of manufacturing a positive temperature coefficient thermistor, and more specifically, a positive temperature coefficient thermistor having a positive temperature coefficient of resistance (referred to as “PTC”) and used for heater applications or the like ( Hereinafter, it is referred to as “PTC thermistor”) and a method for manufacturing the PTC thermistor.

Barium titanate (BaTiO ₃ ) -based semiconductor ceramics have PTC characteristics that generate heat when a voltage is applied and the resistance value increases rapidly when the Curie point Tc at which phase transition from tetragonal to cubic is exceeded.

As described above, when the semiconductor ceramic having PTC characteristics exceeds the Curie point Tc due to heat generation by voltage application, the resistance value becomes large and the current does not easily flow, and the temperature decreases. And if temperature falls and resistance value becomes small, an electric current will flow easily again and temperature will rise. Semiconductor ceramics are widely used as a thermistor for a heater or a thermistor for starting a motor because it converges to a constant temperature or current by repeating the above-described process.

By the way, since the PTC thermistor used for a heater use is used at high temperature, it needs to have a high Curie point Tc. For this reason, conventionally, a part of Ba in BaTiO ₃ has been replaced with Pb to raise the Curie point Tc.

However, since Pb is an environmentally hazardous substance, it is required to realize a lead-free semiconductor ceramic that does not substantially contain Pb in consideration of the environment.

Therefore, for example, in Patent Document 1, in a structure of Ba _1-2X (BiNa) _x TiO ₃ (where 0 <x ≦ 0.15) in which a part of Ba of BaTiO ₃ is substituted with Bi—Na, Nb There has been proposed a method for producing a BaTiO ₃ -based semiconductor ceramic that is sintered in nitrogen after adding one or more of tantalum, Ta, and rare earth elements, and then heat-treated in an oxidizing atmosphere.

In Patent Document 1, a BaTiO ₃ semiconductor ceramic having a Curie point Tc as high as 140 to 255 ° C. and a resistance temperature coefficient of 16 to 20% / ° C. is obtained although it is lead-free.

Patent Document 2 discloses that the composition formula is [(Al _{0.5 A} 2 _0.5 ) _x (Ba _1-y Q _y ) _1-x ] TiO ₃ (where A1 is one or more of Na, K, and Li). , A2 represents Bi, Q represents one or more of La, Dy, Eu, and Gd), and the x and y satisfy 0 <x ≦ 0.2 and 0.002 ≦ y ≦ 0.01. Semiconductor porcelain compositions have been proposed.

Also in this Patent Document 2, a composition having a Curie point Tc of 130 ° C. or higher is obtained while being a lead-free semiconductor ceramic.

JP 56-169301 A JP 2005-255493 A

However, in PTC thermistors containing alkali metals and Bi as in Patent Document 1 and Patent Document 2, the resistance value may fluctuate significantly when energized for a long time, leading to characteristic deterioration.

That is, in the semiconductor ceramics of Patent Document 1 and Patent Document 2, alkali metals are likely to be present in the crystal grain boundaries, and these unstable alkali metal ions move to the external electrode side by voltage application. Corrosion may cause deterioration of characteristics.

As described above, in the conventional PTC thermistor containing alkali metal and Bi, the resistance value deteriorates with time even when energized for a long time, and sufficient reliability cannot be obtained.

The present invention has been made in view of such circumstances, and a highly reliable lead-free PTC thermistor capable of suppressing deterioration with time of resistance value without deteriorating PTC characteristics even when energized for a long time, and its An object is to provide a manufacturing method.

In order to achieve the above object, the present inventors conducted extensive research on {Ba, (M1, Bi)} TiO ₃ -based materials in which a part of Ba is substituted with alkali metals M1 and Bi. The outer surface part in contact is formed with a high resistance layer having a large room temperature resistance and a large resistance temperature coefficient, and the central part separated from the external electrode is formed with a low resistance layer having a small room temperature resistance and a small resistance temperature coefficient. By satisfying a certain relationship between the thickness and the molar ratio of the alkali metal M1 in the main component, the resistance change rate can be reduced even when a voltage is applied continuously for a long time, and thus PTC characteristics are not impaired. We obtained the knowledge that the reliability of the thermistor can be improved.

The present invention has been made based on such knowledge, and the PTC thermistor according to the present invention uses a lead-free semiconductor ceramic that does not substantially contain lead as a component body, and both end portions of the component body. The semiconductor ceramic is mainly composed of a BaTiO ₃ -based composition, a part of Ba is replaced with an alkali metal and Bi, and the component body is A high resistance layer having a large room temperature resistance and a large resistance temperature coefficient, and a low resistance layer having a small room temperature resistance and a small resistance temperature coefficient. The high resistance layer is formed at least on an outer surface portion in contact with the external electrode. In addition, the low resistance layer is formed in a central portion separated from the external electrode, and the thickness y (μm) of the high resistance layer is 10 to the molar ratio x of the alkali metal in the main component. ≦ y ≦ −35 0x + 525 (here, x is, 0.010 ≦ x ≦ 0.147) is characterized in that it satisfies the relationship.

In addition, in the above description, “substantially free of lead” means that Pb is not intentionally added, and such a composition system in which Pb is not intentionally added is referred to as a non-lead type in the present invention.

In the PTC thermistor of the present invention, it is also preferable that the high resistance layer is formed around the low resistance layer so as to cover the low resistance layer.

In the PTC thermistor of the present invention, it is preferable that the high resistance layer contains Mn in the semiconductor ceramic.

Further, in the PTC thermistor of the present invention, it is preferable that a part of the Ba is substituted with a rare earth element in the semiconductor ceramic.

In the PTC thermistor of the present invention, it is preferable that the alkali metal contains at least one of Na, K, and Li.

The PTC thermistor uses a so-called sheet method, and appropriately laminates a ceramic green sheet for a low resistance layer and a ceramic green sheet for a high resistance layer, and fires the obtained laminate, thereby efficiently. Can be manufactured.

That is, the manufacturing method of the PTC thermistor according to the present invention is a first ceramic green sheet manufacturing method for manufacturing a first ceramic green sheet from a ceramic raw material containing a Ba compound, a Ti compound, a Na compound, a Bi compound, and a rare earth compound. A second ceramic green sheet producing step for producing a second ceramic green sheet in which a high resistance material is added to the ceramic raw material, and the second ceramic green sheet producing step on both main surfaces of the first ceramic green sheet. It is characterized by including a laminate manufacturing step of arranging a ceramic green sheet and preparing a laminate, and a firing step of firing the laminate to form a component body.

Further, in the method for producing a PTC thermistor according to the present invention, it is preferable that the high resistance substance includes Mn.

Also, the method for manufacturing a PTC thermistor according to the present invention includes a ceramic paste manufacturing step of manufacturing a ceramic paste in which the high resistance substance is added to the ceramic raw material, and the ceramic paste is applied to the side surface of the laminate. It is also preferable to include a coating process.

According to the PTC thermistor of the present invention, a BaTiO ₃ composition is a main component, a part of Ba is substituted with an alkali metal and Bi, and the component body has a large room temperature resistance and a large resistance temperature coefficient. A high resistance layer and a low resistance layer having a low room temperature resistance and a small resistance temperature coefficient, and the high resistance layer is formed at least on an outer surface portion in contact with the external electrode, and the low resistance layer includes the The thickness y of the high-resistance layer formed in the central portion separated from the external electrode satisfies the above-described fixed relationship with the molar ratio x mole of the alkali metal in the main component. The resistance change rate can be suppressed even when a voltage is applied continuously for a time. That is, even when a voltage is applied, it is difficult for the internal low resistance layer to be loaded with a voltage, so the absolute amount of the alkali metal that moves to the external electrode side is reduced. Therefore, the absolute amount of alkali metal moving to the external electrode side is reduced as compared with the case where the entire region of the component body has a high resistance, and electrode corrosion due to the alkali metal is suppressed. As a result, even if a voltage is applied continuously for a long time, it is possible to avoid an increase in the rate of resistance change, and it is possible to improve reliability. In addition, since the high resistance layer is formed on the outer surface portion in contact with the external electrode, PTC characteristics can be ensured, and both PTC characteristics and reliability can be achieved.

In addition, even when the high resistance layer is formed around the low resistance layer so as to cover the low resistance layer, the absolute amount of the alkali metal that moves to the external electrode side can be reduced. The same operational effects can be achieved.

In addition, according to the method for producing a PTC thermistor of the present invention, a laminate is produced using the first ceramic green sheet for the low resistance layer and the second ceramic green sheet for the high resistance layer, and fired. Therefore, a PTC thermistor having both PTC characteristics and reliability can be efficiently manufactured.

In addition, by including a ceramic paste preparation step of preparing a ceramic paste in which a high resistance material is added to a ceramic raw material, and a coating step of applying the ceramic paste to the side surface of the laminate, A PTC thermistor having a high resistance layer formed in the periphery can be easily manufactured.

1 is a perspective view showing an embodiment (first embodiment) of a PTC thermistor according to the present invention. FIG. 2 is a cross-sectional view taken along the line AA in FIG. It is a figure which shows the resistance-temperature characteristic in a high resistance layer and a low resistance layer. It is a figure which shows the relationship between the thickness y (micrometer) of a high resistance layer, and the molar ratio x of an alkali metal. It is sectional drawing which shows 2nd Embodiment of the PTC thermistor which concerns on this invention. FIG. 5 is a diagram in which the measurement points of each sample of Example 1 and Examples 4 to 6 are plotted together with the relationship diagram of FIG.

Next, an embodiment of the present invention will be described in detail.

FIG. 1 is a perspective view schematically showing an embodiment (first embodiment) of a PTC thermistor according to the present invention, and FIG. 2 is a cross-sectional view taken along line AA of FIG.

That is, this PTC thermistor includes a component body 1 and a pair of

external electrodes

2 a and 2 b formed on both ends (surfaces) of the component body 1. The

external electrodes

2a and 2b are formed in a single layer structure or a multilayer structure made of a conductive material such as Cu, Ni, Al, Cr, Ag, Ni—Cr alloy, Ni—Cu or the like.

The component body 1 is formed of a semiconductor ceramic, and has high resistance layers 3a and 3b having a large room temperature resistance and a large resistance temperature coefficient, and a low resistance layer 4 having a small room temperature resistance and a small resistance temperature coefficient. The high resistance layers 3a and 3b are formed on the outer surface portion in contact with the

external electrodes

2a and 2b, and the low resistance layer 4 is formed at the center portion separated from the

external electrodes

2a and 2b.

The semiconductor ceramic forming the low resistance layer 4 has a perovskite structure whose main component is represented by the general formula (A).

_{_{{Ba 1-uv-w M1}} u Bi v Ln w} m TiO 3 ... (A)
Here, M1 represents an alkali metal typified by Li, Na, and K, and Ln represents a rare earth element. The rare earth element Ln is not particularly limited as long as it acts as a semiconducting agent. For example, at least one selected from the group of Y, Sm, Nd, Dy, and Gd is used. Can do.

Also, the total molar ratio (u + v) of the alkali metals M1 and Bi is preferably 0.02 to 0.20. The Curie point Tc can be increased by substituting a part of Ba with alkali metals M1 and Bi. However, if the total molar ratio (u + v) is less than 0.02, the Curie point Tc may be sufficiently increased. Can not. On the other hand, since the alkali metals M1 and Bi are easily volatilized as described above, when the total molar ratio (u + v) exceeds 0.20, a composition deviation from the theoretical composition of the sintered body tends to occur.

Further, the molar ratio w of the rare earth element Ln is preferably 0.0005 to 0.015. The rare earth element Ln is added as a semiconducting agent, but if the molar ratio w is less than 0.0005 or exceeds 0.015, it becomes difficult to make it a semiconductor.

The molar ratio m of the Ba site and the Ti site is 1.000 in the stoichiometric composition, but is not limited to this and is appropriately selected within the range of 0.992 to 1.004 as required. be able to.

Also, the semiconductor ceramic forming the high resistance layers 3a and 3b has the high resistance material M2 added to the main component as represented by the general formula (B).

(Ba _1-u-v-w M1 _u Bi _v Ln _w ) _m TiO ₃ + nM2 (B)
The addition amount of the high-resistance material M2 is preferably 0.0001 to 0.0020 mol part with respect to 1 mol part of the main component from the viewpoint of obtaining a desired high resistance and a large resistance temperature coefficient.

Further, the high resistance material M2 is not particularly limited as long as it has the intended effect, but Mn is preferably used for the following reasons.

That is, the capability of the PTC thermistor can be evaluated by the number of PTC digits ΔR defined by Equation (1).

ΔR = log (ρmax / ρmin) (1)
Here, ρmax is a maximum value of specific resistance, and ρmin is defined by a minimum value of specific resistance.

And since Mn has an action as an acceptor, it forms an acceptor level at the grain boundary, thereby contributing to an increase in the temperature coefficient of resistance and increasing the number of PTC digits ΔR. Therefore, Mn is particularly suitable as the high resistance material M2.

In addition, when adding Mn, it does not specifically limit as an addition form, Arbitrary manganese compounds, such as manganese oxide sol and powder, or a manganese nitrate aqueous solution, can be used.

The thickness y (μm) of the high resistance layers 3a and 3b is adjusted so as to satisfy Expression (2) with the molar ratio x of the alkali metal M1 in the main component.

10 ≦ y ≦ −3500x + 525 (2)
Here, the molar ratio x of the alkali metal M1 is limited to the range shown in Formula (3).

0.010 ≦ x ≦ 0.147 (3)
That is, when the molar ratio x is less than 0.010, the Curie point Tc is lowered and it is not suitable for high temperature use such as heater use. On the other hand, if the molar ratio x exceeds 0.147, the absolute amount of the alkali metal M1 increases, and electrode corrosion is likely to occur, and sufficient reliability cannot be improved.

FIG. 3 is a graph showing the relationship between the thickness y (μm) of the high resistance layers 3a and 3b and the molar ratio x of the alkali metal M1, and is a graph of the formulas (2) and (3). The horizontal axis represents the molar ratio x of the alkali metal M1, and the vertical axis represents the thickness y of the high resistance layers 3a and 3b.

The shaded area shown in FIG. 3 is the scope of the present invention. Reliability cannot be improved in the region above the hatched portion, and the number of PTC digits ΔR decreases in the region below the shaded portion, and sufficient PTC characteristics cannot be obtained.

FIG. 4 shows the resistance-temperature characteristics of the high resistance layers 3a and 3b and the low resistance layer 4 of the PTC thermistor, where the horizontal axis is the temperature T (° C.) and the vertical axis is the resistance logR (Ω). In the figure, (a) shows the resistance-temperature characteristics of the high resistance layer, (b) shows the resistance-temperature characteristics of the low resistance layer, and Tc shows the Curie point.

As shown in (a), the high resistance layers 3a and 3b have a room temperature resistance larger than that of the low resistance layer 4 and a PTC digit number ΔR, and PTC characteristics can be secured in the high resistance layer portion.

On the other hand, as shown in (b), the low resistance layer 4 has a room temperature resistance smaller than that of the high resistance layers 3a and 3b and a smaller number of PTC digits ΔR. For this reason, the movement of the alkali metal ions present in the low resistance layer 4 to the

external electrodes

2a, 2b side is suppressed. That is, the alkali metal ions present in the high resistance layers 3a and 3b move to the

external electrodes

2a and 2b, but the absolute amount of the alkali metal M1 is smaller than that in the case where the entire region of the component element body 1 is increased in resistance. Decrease. For this reason, the absolute amount of the alkali metal M1 moving to the

external electrodes

2a and 2b side is also reduced, and the electrode corrosion of the

external electrodes

2a and 2b is suppressed. As a result, the rate of change in resistance can be suppressed even when a voltage is applied continuously for a long time, thereby improving the reliability.

Thus, according to the present embodiment, the component body 1 has the high resistance layers 3a and 3b having a large room temperature resistance and a large resistance temperature coefficient, and the low resistance layer 4 having a small room temperature resistance and a small resistance temperature coefficient. The high resistance layers 3a and 3b are formed on the outer surface portion in contact with the

external electrodes

2a and 2b. The thickness y of 3b satisfies the above-described mathematical formulas (3) and (4) with the molar ratio x of the alkali metal M1 in the main component, so the PTC characteristics are secured by the high resistance layers 3a and 3b. However, reliability can be improved.

Specifically, to obtain a PTC thermistor having good reliability with a resistance change rate Δρ / ρ ₀ of less than 30% with respect to a specific resistance ρ ₀ at room temperature while securing a PTC characteristic having a PTC digit number ΔR of 3 or more. Can do.

Next, a method for manufacturing the PTC thermistor will be described.

First, a Ba compound, a Ti compound, an M1 compound containing an alkali metal M1, a Bi compound, and an Ln compound containing a predetermined rare earth element Ln are prepared as ceramic raw materials. Then, these ceramic raw materials are weighed and mixed to obtain a mixed powder so that the component composition of the semiconductor ceramic becomes a predetermined ratio.

Next, an organic solvent and a polymeric dispersant are added to the mixed powder, and the mixture is thoroughly mixed and pulverized in a ball mill together with a pulverizing medium such as PSZ (partially stabilized zirconia) balls, and then the organic solvent is dried. Then, sizing using a mesh with a predetermined opening. Subsequently, heat treatment is performed in the range of 800 to 1000 ° C. for 2 hours to obtain a calcined powder.

To the calcined powder, an organic binder such as vinyl acetate or polyvinyl alcohol, a dispersant, and pure water are added, and the mixture is pulverized and sufficiently mixed with a pulverizing medium again to obtain a first ceramic slurry. Next, the first ceramic slurry is formed into a sheet using a forming method such as a doctor blade method, and dried to produce a first ceramic green sheet.

Further, the M2 compound containing the high resistance material M2, the organic binder, the dispersant, and pure water are added to the calcined powder, and the mixture is sufficiently mixed and pulverized with a pulverization medium to obtain a second ceramic slurry. Next, the second ceramic slurry is formed into a sheet using a forming method such as a doctor blade method, and dried to produce a second ceramic green sheet.

Next, the second ceramic green sheet to be the high resistance layer is disposed on both main surfaces of the first ceramic green sheet to be the low resistance layer 4 and laminated, and bonded to produce a laminate block having a predetermined thickness. To do. Here, a predetermined number of the first ceramic green sheets and the second ceramic green sheets are appropriately laminated so as to have a predetermined thickness after firing in consideration of the above formulas (3) and (4).

Then, the laminated body block is punched into a disk shape to obtain a laminated molded body. Next, the laminated molded body is heated at 500 to 600 ° C. in a predetermined atmosphere (for example, in an air atmosphere, a nitrogen atmosphere, or a mixed gas stream) to perform a binder removal treatment, and then in a predetermined atmosphere. Baking is performed for a predetermined time at a temperature at which a semiconductor is formed (for example, in a nitrogen atmosphere or a mixed air stream in a reducing atmosphere), for example, a maximum temperature of 1250 to 1450 ° C., to obtain a component body 1 that is a sintered body.

Thereafter, the

external electrodes

2a and 2b are formed on both ends of the component body 1 by a plating method, a sputtering method, a coating baking method, or the like, thereby producing a PTC thermistor.

Thus, the present PTC thermistor can be easily manufactured by using the sheet method.

FIG. 5 is a cross-sectional view showing a second embodiment of the PTC thermistor according to the present invention. In this second embodiment, the component body 5 includes a high resistance layer 6 and a low resistance layer 4. It is formed in the periphery of the low resistance layer 4 so as to cover it.

Also in the second embodiment, the low resistance layer 4 having a low room temperature resistance and a small resistance temperature coefficient is formed inside the component element body 1, and the high resistance layer 6 is formed around the low resistance layer 4. Therefore, as in the first embodiment, the absolute amount of the alkali metal M1 that moves to the

external electrodes

2a and 2b can be reduced, and thus the high resistance layer 6 can ensure the PTC characteristics and improve the reliability. Can be made.

The second embodiment can be easily manufactured as follows.

That is, as in the first embodiment, the first ceramic green sheet to be the low resistance layer 4 and the second ceramic green sheet to be the high resistance layer 6 are produced.

Also, the above-mentioned calcined powder, M2 compound, and organic binder are dispersed in an organic solvent to produce a ceramic paste.

Next, the second ceramic green sheet is disposed on both main surfaces of the first ceramic green sheet, laminated, and pressure-bonded to produce a laminated body block having a predetermined thickness. Make it. Then, a ceramic paste is applied to the side surface of the multilayer molded body, and the multilayer molded body coated with the ceramic paste is in a predetermined atmosphere (for example, in an air atmosphere, in a nitrogen atmosphere, or in a mixed gas stream), The binder is removed by heating at 500 to 600 ° C. Thereafter, firing is performed for a predetermined time at a maximum temperature of 1250 to 1450 ° C. in a predetermined atmosphere (for example, in a nitrogen atmosphere or a mixed air stream in a reducing atmosphere), thereby obtaining a component body 5 which is a sintered body.

Thereafter, as in the first embodiment,

external electrodes

2a and 2b are formed on both main surfaces (both ends) of the component element body 5 by plating, sputtering, coating and baking, etc. The PTC thermistor of the embodiment can be produced.

The present invention is not limited to the above embodiment. For example, in the above-described semiconductor ceramic, it is only necessary that BaTiO ₃ is a main component and a part of Ba is replaced with at least an alkali metal and Bi, and a part of Ba is replaced with Ca or Sr according to required PTC characteristics. It is also preferable.

In addition, even if inevitable impurities are mixed in the semiconductor ceramic, the characteristics are not affected. For example, the PSZ balls used for the grinding medium during wet mixing and grinding may be mixed by about 0.2 to 0.3% by weight as a whole, but this does not affect the characteristics. Similarly, trace amounts of Fe, Si, and Cu of about 10 ppm by weight may be mixed in the ceramic raw material, but this does not affect the characteristics.

Further, the semiconductor ceramic of the present invention is lead-free, but as described in the section of [Means for Solving the Problems], it should be substantially free of Pb and does not affect the characteristics. However, it does not exclude even Pb that is inevitably mixed in the range of 10 ppm by weight or less.

Also, the external shape of the PTC thermistor is not limited, and any shape can be used.

Next, specific examples of the present invention will be described.

BaCO ₃ , Na ₂ CO ₃ , Bi ₂ O ₃ , TiO ₂ , and Y ₂ O ₃ are prepared as ceramic raw materials, and the composition after sintering is Ba _0.898 Bi _0.05 Na _0.05 Y _0.002 TiO ₃ . These ceramic raw materials were weighed and mixed to obtain a mixed powder.

Next, ethanol as an organic solvent and a polymer-type dispersant (maleic anhydride and ethylene oxide / propylene oxide derivative) are added to the mixed powder, and mixed and pulverized in a ball mill for 24 hours together with PSZ balls, Thereafter, ethanol was dried, and sized with a mesh having an opening of 300 μm. Subsequently, heat treatment was performed for 2 hours in a temperature range of 800 to 1000 ° C. to obtain a calcined powder.

Next, a vinyl acetate-based organic binder, the above-mentioned dispersant, and pure water were added to the calcined powder, and the mixture was again mixed and pulverized with a PSZ ball in a ball mill for 16 hours to prepare a first ceramic slurry. Next, the first ceramic slurry was formed into a sheet using a doctor blade method to produce a first ceramic green sheet to be a low resistance layer having a thickness of 6 to 50 μm.

In addition, Mn ₃ O ₄ sol, vinyl acetate organic binder, the above dispersant, and pure water are added to the calcined powder described above, and the mixture is pulverized with a PSZ ball in a ball mill for 16 hours in a wet manner, and then the second ceramic slurry. Was made. Next, this second ceramic slurry was formed into a sheet using a doctor blade method, and a second ceramic green sheet to be a high resistance layer having a thickness of 6 to 50 μm was produced. The Mn ₃ O ₄ sol was weighed so as to be 0.00025 mol part in terms of Mn with respect to 1 mol part of the main component and added to the calcined powder.

Next, a predetermined number of first ceramic green sheets are laminated, and a predetermined number of second ceramic green sheets are arranged on both main surfaces of the first ceramic green sheet so that the thickness after firing is 0 to 500 μm. Then, the laminate block was produced by pressure bonding. And the laminated body block was punched out and the disk-shaped laminated molded object was obtained.

Next, this laminated molded body was subjected to a binder removal treatment in an air atmosphere at a temperature of 600 ° C. for 2 hours and fired at a maximum temperature of 1400 ° C. for 2 hours in a nitrogen atmosphere having an oxygen concentration of 10,000 ppm by volume. I got the body.

Next, this component body is lapped and then dry-plated to form an external electrode having a three-layer structure of NiCr / NiCu / Ag, thereby forming a diameter of 12 mm, a thickness of 2.0 mm, and a high resistance layer. Samples Nos. 1 to 9 having y of 0 to 500 μm were prepared.

Next, the specific resistance ρ ₀ , the PTC digit number ΔR, and the Curie point Tc at a temperature of 25 ° C. (room temperature) were determined for each of the samples Nos. 1 to 9.

Here, the specific resistance ρ ₀ was measured by applying a voltage of 1 V at a temperature of 25 ° C. using a DC four-terminal method.

The PTC digit number ΔR was obtained from the maximum value and the minimum value by measuring the characteristic between the temperature T and the specific resistance ρ (hereinafter referred to as “ρ-T characteristic”).

The Curie point Tc was a temperature at which the specific resistance ρ ₀ at a temperature of 25 ° C. was doubled, and the Curie point Tc was obtained from the ρ-T characteristic.

In addition, an energization test was performed to evaluate reliability. That is, a DC voltage of 13 V was applied to each sample and left for 1000 hours. Then, the resistance change rate ρ ₀ before the test and the resistance change rate ρ ₁ after the test are measured at a temperature of 25 ° C., the difference Δρ (= ρ ₁ −ρ ₀ ) is obtained, and the resistance change rate Δρ / ρ ₀ is obtained. Calculated. In this way, ten current samples were conducted for each sample, the average value of the resistance change rate Δρ / ρ ₀ was calculated, and the reliability was evaluated.

Table 1 shows the thickness y of the high resistance layer of each sample Nos. 1 to 9, the amount of Na in the high resistance layer, the specific resistance ρ ₀ at 25 ° C. (room temperature), the PTC digit number ΔR, the resistance change rate Δρ / ρ ₀ is shown.

The Curie point Tc was determined to be a non-defective product having a temperature of 120 ° C. or more, a PTC digit number ΔR of 3 or more, and a resistance change rate Δρ / ρ ₀ of 30% or less.

Sample No. 1 has a good resistance change rate Δρ / ρ ₀ of 2%, but does not have a high resistance layer, so the number of PTC digits ΔR is as low as 1.5, and the desired PTC characteristics cannot be obtained. It was. That is, Sample No. 1 is formed of only a low resistance layer, so that even when an energization test is performed, the amount of Na moving to the external electrode side is small, and the resistance change rate Δρ / ρ ₀ is small, but the PTC characteristics are improved. I found it inferior.

In sample number 2, the thickness y of the high resistance layer is 5 μm, and the thickness y of the high resistance layer is smaller than the molar ratio x of Na of 0.05. For this reason, although the resistance change rate Δρ / ρ ₀ was as small as 4%, the PTC digit number ΔR was as small as 2.3, indicating that the PTC characteristics were inferior.

On the other hand, Sample No. 9 has a high resistance layer thickness y of 500 μm, a high resistance layer thickness y is larger than Na molar ratio x: 0.05, and the Na content of the high resistance layer is also Sample Nos. 1-8. More than. For this reason, it was found that the amount of Na moving to the external electrode side in the energization test increased, and the resistance change rate Δρ / ρ ₀ increased to 189%, impairing reliability.

In contrast, Sample Nos. 3 to 8 have a high resistance layer thickness y of 10 to 350 μm and an appropriate thickness with respect to a molar ratio x of Na of 0.05: PTC digit number ΔR is 3.2 to 4.3, 3 or more can be secured, and the resistance change rate Δρ / ρ ₀ is 5 to 26%, which can be improved to 30% or less, and the reliability is improved.

Samples Nos. 11 to 19 were prepared in the same manner and procedure as in [Example 1] except that the diameter of the component body was 20 mm.

Next, with respect to each of the samples Nos. 11 to 19, the specific resistance ρ ₀ , PTC digit number ΔR, Curie point Tc, and resistance change at a temperature of 25 ° C. (room temperature) by the same method and procedure as in [Example 1] The rate Δρ / ρ ₀ was determined.

Table 2 shows the thickness y of the high resistance layer of each sample Nos. 11 to 19, the amount of Na in the high resistance layer, the specific resistance ρ ₀ at 25 ° C. (room temperature), the PTC digit number ΔR, the resistance change rate Δρ / ρ ₀ is shown.

As in [Example 1], a Curie point Tc of 120 ° C. or more, a PTC digit number ΔR of 3 or more, and a resistance change rate Δρ / ρ ₀ of 30% or less were judged as non-defective products.

Sample No. 11 has a good resistance change rate Δρ / ρ ₀ of 2%. However, like Sample No. 1 (Table 1), since it does not have a high resistance layer, the number of PTC digits ΔR is 1.3. It was low.

In Sample No. 12, the thickness y of the high resistance layer is 5 μm, and the thickness y of the high resistance layer is smaller than the molar ratio x of Na of 0.05. For this reason, the resistance change rate Δρ / ρ ₀ was as small as 3% as in Sample No. 2 (Table 2), but the PTC digit number ΔR was as small as 2.2, indicating that the PTC characteristics were inferior.

On the other hand, Sample No. 19 has a high resistance layer thickness y of 500 μm, a high resistance layer thickness y larger than a Na molar ratio x: 0.05, and the Na amount of the high resistance layer is also Sample Nos. 11-18. More than. For this reason, the amount of Na moving to the external electrode side in the energization test increased, and it was found that the resistance change rate Δρ / ρ ₀ increased to 189% and the reliability was impaired, as in the case of Sample No. 9 (Table 1). .

On the other hand, samples Nos. 13 to 18 have a high resistance layer thickness y of 10 to 350 μm and an appropriate thickness with respect to the Na molar ratio x: 0.05, so that the PTC digit number ΔR is 3.3. It was found that the _{value of} ˜4.4 was 3 or more and the resistance change rate Δρ / ρ ₀ was 5 to 28%, which was improved to 30% or less, and the reliability was improved.

Samples Nos. 21 to 29 were prepared in the same manner and procedure as in [Example 1] except that the thickness of the component body was set to 3.0 mm.

Next, with respect to each of the samples Nos. 21 to 29, the specific resistance ρ ₀ , PTC digit number ΔR, Curie point Tc, and resistance change at a temperature of 25 ° C. (room temperature) in the same manner and procedure as in [Example 1] The rate Δρ / ρ ₀ was determined.

Table 3 shows the thickness y of the high resistance layer of each sample Nos. 21 to 29, the amount of Na in the high resistance layer, the specific resistance ρ ₀ at 25 ° C. (room temperature), the PTC digit number ΔR, the resistance change rate Δρ / ρ ₀ is shown.

Sample No. 21 has a good resistance change rate Δρ / ρ ₀ of 3%, but, like Sample No. 1 (Table 1), it does not have a high resistance layer, so the PTC digit number ΔR is 1.1. It was low.

In sample number 22, the thickness y of the high resistance layer is 5 μm, which is smaller than the molar ratio x of Na of 0.05. For this reason, the resistance change rate Δρ / ρ ₀ was as small as 3% as in the case of the sample number 2 (Table 1), but the PTC digit number ΔR was as small as 1.9, indicating that the PTC characteristics were inferior.

On the other hand, in sample number 29, the thickness y of the high resistance layer was 500 μm, which was larger than the molar ratio x: 0.05 of Na, and the amount of Na in the high resistance layer was also larger than in sample numbers 21 to 28. For this reason, it was found that the amount of Na moving to the external electrode side in the energization test increased, and the resistance change rate Δρ / ρ ₀ increased to 153%, and the reliability was impaired as in the case of Sample No. 9 (Table 1). .

On the other hand, in Sample Nos. 23 to 28, the thickness y of the high resistance layer is 10 to 350 μm and the molar ratio x of Na is 0.05, which is an appropriate thickness. Therefore, the PTC digit number ΔR is 3.2 to 4 It was found that the resistance change rate Δρ / ρ ₀ was 4 to 27% and could be improved to 30% or less, and the reliability was improved.

As is apparent from [Example 1] to [Example 3], the thickness y of the high resistance layer is 10 to 350 μm with respect to the molar ratio x: 0.05 of Na irrespective of the external dimensions of the component body. It was confirmed that both the PTC characteristics and the reliability can be achieved within the above range.

Samples Nos. 31 to 39 were prepared in the same manner and procedure as in [Example 1] except that the molar ratio x of Na and Bi in the main component was 0.01.

Next, for each of the samples Nos. 31 to 39, the specific resistance ρ ₀ , PTC digit number ΔR, Curie point Tc, and resistance change at a temperature of 25 ° C. (room temperature) in the same manner and procedure as in Example 1. The rate Δρ / ρ ₀ was determined.

Table 4 shows the thickness y of the high resistance layer of each sample Nos. 31 to 39, the amount of Na in the high resistance layer, the specific resistance ρ ₀ at 25 ° C. (room temperature), the PTC digit number ΔR, the resistance change rate Δρ / ρ ₀ is shown.

Sample No. 31 has a good rate of resistance change Δρ / ρ ₀ of 3%. However, like Sample No. 1 (Table 1), since it does not have a high resistance layer, the PTC digit number ΔR is 1.3. It was low.

In sample number 32, the thickness y of the high resistance layer is 5 μm, and the thickness y of the high resistance layer is smaller than the molar ratio x of Na of 0.01. For this reason, although the resistance change rate Δρ / ρ ₀ was as small as 3%, the PTC digit number ΔR was as small as 2.1, indicating that the PTC characteristics were inferior.

On the other hand, in the

sample numbers

38 and 39, the thickness y of the high resistance layer is 700 μm and 900 μm, respectively, and the thickness y of the high resistance layer is large with respect to the molar ratio x: 0.01 of Na. More than sample numbers 31-37. For this reason, the amount of Na moving to the external electrode side in the energization test increased, and the resistance change rate Δρ / ρ ₀ became 30% or more, which proved that the reliability was impaired.

On the other hand, Sample Nos. 33 to 37 have a high resistance layer thickness y of 10 to 490 μm and an appropriate thickness for the Na molar ratio x: 0.01, so that the PTC digit number ΔR is 3.3 to 4.3, 3 or more can be secured, and the resistance change rate Δρ / ρ ₀ is 4-25%, which can be improved to 30% or less, and the reliability is improved.

Samples Nos. 41 to 49 were prepared in the same manner and procedure as in [Example 1] except that the molar ratio x of Na and Bi in the main component was 0.10.

Next, for each of the samples Nos. 41 to 49, the specific resistance ρ ₀ at the temperature of 25 ° C. (room temperature), the PTC digit number ΔR, the Curie point Tc, and the resistance change are performed in the same manner and procedure as in [Example 1]. The rate Δρ / ρ ₀ was determined.

Table 5 shows the thickness y of the high resistance layer of each sample Nos. 41 to 49, the amount of Na in the high resistance layer, the specific resistance ρ ₀ at 25 ° C. (room temperature), the PTC digit number ΔR, the resistance change rate Δρ / ρ ₀ is shown.

Sample No. 41 has a good resistance change rate Δρ / ρ ₀ of 5%. However, like Sample No. 1 (Table 1), since it does not have a high resistance layer, the PTC digit number ΔR is 1.2. It was low.

In sample number 42, the thickness y of the high resistance layer is 5 μm, and the thickness y of the high resistance layer is smaller than the molar ratio x: 0.10 of Na. For this reason, although the resistance change rate Δρ / ρ ₀ is as small as 4%, the PTC digit number ΔR is as small as 1.9, and a desired PTC characteristic could not be obtained.

On the other hand, in the

sample numbers

48 and 49, the thickness y of the high resistance layer is 200 μm and 350 μm, respectively, and the thickness y of the high resistance layer is large with respect to the molar ratio x: 0.10 of Na. More than sample numbers 41-47. For this reason, the amount of Na moving to the external electrode side in the energization test increased, and the resistance change rate Δρ / ρ ₀ became 30% or more, which proved that the reliability was impaired.

On the other hand, in the sample numbers 43 to 47, the thickness y of the high resistance layer is 10 to 175 μm, and the thickness is appropriate for the molar ratio x: 0.10 of Na. Therefore, the PTC digit number ΔR is 3.3 to 4.2, 3 or more can be secured, and the resistance change rate Δρ / ρ ₀ is 7-28%, which can be improved to 30% or less, and it has been found that the reliability is improved.

Samples Nos. 51 to 54 were prepared in the same manner and procedure as in [Example 1] except that the molar ratio x of Na and Bi in the main component was 0.147.

Next, for each of the samples 51 to 54, the specific resistance ρ ₀ at the temperature of 25 ° C. (room temperature), the PTC digit number ΔR, the Curie point Tc, and the resistance change are performed in the same manner and procedure as in [Example 1]. The rate Δρ / ρ ₀ was determined.

Table 6 shows the thickness y of the high resistance layer of each sample Nos. 51 to 54, the amount of Na in the high resistance layer, the specific resistance ρ ₀ at 25 ° C. (room temperature), the PTC digit number ΔR, the resistance change rate Δρ / ρ ₀ is shown.

Sample No. 51 has a good resistance change rate Δρ / ρ ₀ of 12%. However, like Sample No. 1 (Table 1), since it does not have a high resistance layer, the number of PTC digits ΔR is 1.3. It was low.

In sample number 52, the thickness y of the high resistance layer is 5 μm, and the thickness y of the high resistance layer is smaller than the molar ratio x: 0.147 of Na. Therefore, although the resistance change rate Δρ / ρ ₀ was as small as 21%, the PTC digit number ΔR was as small as 1.8, indicating that the PTC characteristics were inferior.

On the other hand, in sample number 54, the thickness y of the high resistance layer is 25 μm, the thickness y of the high resistance layer is larger than the molar ratio x: 0.147 of Na, and the amount of Na in the high resistance layer is also sample numbers 51 to 53. More than. For this reason, the amount of Na moving to the external electrode side in the energization test was increased, and the resistance change rate Δρ / ρ ₀ was also 56% or more, and it was found that the reliability was impaired.

On the other hand, in sample number 53, the thickness y of the high resistance layer is 10 μm, and is an appropriate thickness with respect to the molar ratio x: 0.147 of Na. Therefore, the PTC digit number ΔR is 3.2, which is 3 or more. It was found that the resistance change rate Δρ / ρ ₀ was 25% and could be improved to 30% or less, and the reliability was improved.

As apparent from [Example 1] and [Example 4] to [Example 6], from the viewpoint of achieving both PTC characteristics and reliability, increasing the molar ratio x of Na increases the thickness of the high resistance layer. It was necessary to reduce y, and it was found that a certain correlation exists between the molar ratio x of Na and the thickness y of the high resistance layer.

FIG. 6 is a diagram in which the measurement points of each sample of [Example 1] and [Example 4] to [Example 6] are plotted. The horizontal axis is the molar ratio x of Na, and the vertical axis is the high resistance layer. The thickness y (μm) is shown. The shaded area is within the scope of the present invention.

That is, both the PTC characteristics and the reliability can be satisfied within the range where the thickness y (μm) of the high resistance layer and the molar ratio x of Na satisfy 10 ≦ y ≦ −3500x + 525 and 0.01 ≦ x ≦ 0.147. I understood.

First and second ceramic green sheets were produced by the same method and procedure as in [Example 1].

Next, a Mn ₃ O ₄ sol and an organic binder were dispersed in an organic solvent in the calcined powder produced in [Example 1] to produce a ceramic paste. The amount of Mn ₃ O ₄ added was adjusted to 0.00025 mol part in terms of Mn with respect to 1 mol part of the main component after firing.

Next, a predetermined number of first ceramic green sheets are laminated, and a predetermined number of second ceramic green sheets are arranged on both main surfaces of the laminated first ceramic green sheets, and the laminated body block is bonded by pressure bonding. Then, it was punched into a square plate shape to obtain a laminated molded body.

Next, after applying a ceramic paste to the side surface of this laminated molded body, it was subjected to binder removal treatment in the atmosphere at a temperature of 600 ° C. for 2 hours, and further in a nitrogen atmosphere having an oxygen concentration of 10,000 ppm by volume at a maximum temperature of 1400 ° C. for 2 hours. Firing was performed to obtain component bodies of sample numbers 61 to 69.

Next, this component body is lapped and then dry-plated to form an external electrode having a three-layer structure of NiCr / NiCu / Ag, thereby 10 mm long, 10 mm wide, 2.0 mm thick, and high Samples Nos. 61 to 69 having a resistance layer thickness y of 0 to 500 μm were prepared.

Next, with respect to each of the samples 61 to 69, the specific resistance ρ ₀ , PTC digit number ΔR, Curie point Tc, and resistance change at a temperature of 25 ° C. (room temperature) in the same manner and procedure as in [Example 1] The rate Δρ / ρ ₀ was determined.

Table 7 shows the thickness y of the high-resistance layer of each sample Nos. 61 to 69, the amount of Na in the high-resistance layer, the specific resistance ρ ₀ at 25 ° C. (room temperature), the PTC digit number ΔR, the resistance change rate Δρ / ρ ₀ is shown.

Sample No. 61 has a good resistance change rate Δρ / ρ ₀ of 1%. However, like Sample No. 1 (Table 1), since it does not have a high resistance layer, the number of PTC digits ΔR is 1.2. It was low.

In sample number 62, the thickness y of the high resistance layer is 5 μm, and the thickness y of the high resistance layer is smaller than the molar ratio x of Na of 0.05. For this reason, although the resistance change rate Δρ / ρ ₀ is as small as 3%, the PTC digit number ΔR is as small as 2.3, and a desired PTC characteristic could not be obtained.

On the other hand, in sample number 69, the thickness y of the high resistance layer is 500 μm, and the thickness y of the high resistance layer is too large with respect to the molar ratio x: 0.05 of Na. More than 68. For this reason, the amount of Na moving to the external electrode side in the energization test increased, and the resistance change rate Δρ / ρ ₀ became 135% or more, and it was found that reliability was impaired.

On the other hand, samples Nos. 63 to 68 have a high resistance layer thickness y of 10 to 350 μm and an appropriate thickness with respect to a Na molar ratio x: 0.05, so that the PTC digit number ΔR is 3.1 to As a result, it was confirmed that the resistance change rate Δρ / ρ ₀ was 3 to 28% and could be improved to 30% or less.

That is, as is clear from Example 7, even when the central portion is a low resistance layer and the periphery of the low resistance layer is covered with a high resistance layer, the molar ratio x of Na is the same as in [Example 1]. It was confirmed that both the PTC characteristics and the reliability can be achieved when the thickness y of the high resistance layer is in the range of 10 to 350 μm with respect to 0 and 05.

In a Ba (Na, Bi) TiO ₃ PTC thermistor, the reliability can be improved without impairing the PTC characteristics. It is particularly useful for high temperature applications such as in-vehicle heaters.

1

Component Element

2a,

2b External Electrode

3a, 3b High Resistance Layer 4 Low Resistance Layer 5 Component Element 6 High Resistance Layer

Claims

A positive temperature coefficient thermistor in which lead-free semiconductor ceramic that does not substantially contain lead is used as a component body, and external electrodes are formed at both ends of the component body,
The semiconductor ceramic is mainly composed of a BaTiO 3 composition, and a part of Ba is replaced with an alkali metal and Bi,
The component body includes a high resistance layer having a large room temperature resistance and a large resistance temperature coefficient, and a low resistance layer having a small room temperature resistance and a small resistance temperature coefficient.
The high resistance layer is formed at least on an outer surface portion in contact with the external electrode, and the low resistance layer is formed in a central portion separated from the external electrode,
And the thickness y (μm) of the high resistance layer is between the molar ratio x of the alkali metal in the main component,
10 ≦ y ≦ -3500x + 525
(Where x is 0.010 ≦ x ≦ 0.147)
A positive temperature coefficient thermistor characterized by satisfying this relationship.
2. The positive temperature coefficient thermistor according to claim 1, wherein the high resistance layer is formed in a peripheral portion of the low resistance layer so as to cover the low resistance layer.
3. The positive temperature coefficient thermistor according to claim 1, wherein the high resistance layer contains Mn in the semiconductor ceramic.
4. The positive temperature coefficient thermistor according to claim 1, wherein a part of the Ba is substituted with a rare earth element in the semiconductor ceramic.
The positive temperature coefficient thermistor according to any one of claims 1 to 4, wherein the alkali metal contains at least one of Na, K, and Li.
A first ceramic green sheet production step of producing a first ceramic green sheet from a ceramic raw material containing a Ba compound, a Ti compound, an Na compound, a Bi compound, and a rare earth compound;
A second ceramic green sheet production step of producing a second ceramic green sheet in which the high resistance material is added to the ceramic raw material;
A laminated body producing step of arranging the second ceramic green sheet on both main surfaces of the first ceramic green sheet and producing a laminated body;
A method for producing a positive temperature coefficient thermistor comprising a firing step of firing the laminate to form a component body.
The method of manufacturing a positive temperature coefficient thermistor according to claim 6, wherein the high resistance material includes Mn.
A ceramic paste production step of producing a ceramic paste in which the high resistance material is added to the ceramic raw material;
The method for producing a positive temperature coefficient thermistor according to claim 6, further comprising a coating step of coating the ceramic paste on a side surface of the laminate.