DE10008929A1 - Laminated semiconductor ceramic element for overcurrent protection of circuits, includes internal electrodes which are laminated on semiconductor ceramic layer formed by sintering boron oxide - Google Patents

Abstract

The internal electrodes (7) are laminated on semiconductor ceramic layer (5) which is formed by sintering boron oxide having atomic ratio satisfying predetermined relation with barium titanate. The external electrode is formed on ceramic layer.

Description

The present invention relates to a monolithic made from a semiconductor ceramic electronic element and in particular a mono made of a semiconductor ceramic lithic electronic element (hereinafter referred to as a monolithic electronic element with a positive temperature coefficient of resistance.

Electronic semiconductor elements with a positive temperature coefficient of consistency (hereinafter referred to as PTC characteristic) - which means that the electrical resistance increased dramatically when the temperature exceeded the Curie temperature - became the Protection of a circuit against overcurrent or for controlling a demagnetizing mo duls of a color television set used. With regard to their advantageous PTC characteristics semiconductor ceramics predominantly comprising barium titanate have been commonly found in such electronic semiconductor elements used.

However, in order to make ceramics based on barium titanate semiconducting, the firing must mine done at a temperature of 1300 ° C or higher. Such treatment at high Temperature has the following disadvantages: a tendency to damage one to burn furnace used; high maintenance costs for the furnace; and high energy consumption. Therefore There was a demand for semiconductor ceramics containing barium titanate, which at can be burned at a lower temperature.

To overcome the above drawbacks, a modified technique is in "Semiconducting Barium Titanate Ceramics Prepared by Boron-Conducting Liquid-Phase Sinte ring "(In-Chyuan Ho, Communications of the American Ceramic Society, Volume 77, No. 3, pages  829-832, 1994). In short, the temperature at which the ceramics are semi-solid are reduced by adding boron nitride to barium titanate. The literature be judges that the ceramics based on boron nitride at a firing temperature of about 1100 ° C half can become a leader.

In the meantime, there has been a demand for semiconducting electronic keys in recent years Ceramic elements of the monolithic chip type, which have a low resistance and a achieve high breakdown voltage at bypass temperature and for a high density Pac suitable.

Generally, a monolithic chip type electronic semiconductor element is replaced by old ones kidney stacking of ceramic green sheets and inner electrode paste layers and burning the same made in a kiln. So a base metal, like nickel, used to manufacture internal electrodes by using such a base metal for one ohm contact with a ceramic material, even if the metal coexists the ceramic material is fired. When burning in air, such a base metal becomes oxi dated. This burns the stacked body above in a reducing atmosphere and then oxidized again at a temperature at which the internal electrodes did not oxidize to thereby combine a semiconductor ceramic material and an inner electrode material to burn men. However, a Reoxi performed at a relatively low temperature dation harmful to a PTC characteristic of the product so burned.

Japanese Patent Application Laid-Open (Kokai) No. 8-153605 describes a method to achieve a PTC characteristic even when reoxidation at a low temperature rature is carried out. The method uses a perovskite compound in the form of Microparticles as titanium salt, which serves as the predominant component. The use of the Perovskite connection allows sintering at a temperature of no more than 1000 ° C 1250 ° C and provides a PTC characteristic, even if the reoxidation at a tempera of no more than 500 ° C or higher.

However, a conventional monolithic electronic element must be reoxidized about 1000 ° C to obtain a satisfactory PTC characteristic, and the inner electrodes can be oxidized. So there was a demand for one  monolithic electronic element, which by firing at a low temperature can be produced to provide a satisfactory PTC characteristic by reoxidation a temperature below the conventionally used temperature hold.

In view of the foregoing, the present invention aims to provide a mo nolithic electronic element, which is produced by firing at 1000 ° C or less and shows a satisfactory PTC characteristic, even if that Element is made by reoxidation at low temperature.

Accordingly, the present invention provides a monolithic electronic element made of a semiconductor ceramic, the element comprising a sintered laminate formed from alternately stacked semiconductor ceramic layers and inner electrode layers, and outer electrodes formed on the sintered laminate, each semiconductor ceramic layer comprising semiconductive sintered barium titanate containing the following substances: boron oxide; a first oxide of at least one metal selected from barium, strontium, calcium, lead, yttrium and a rare earth element; and a second oxide of at least one metal selected from titanium, tin, zirconium, niobium, tungsten and antimony, the boron oxide being incorporated in an amount as reduced to atomic boron which satisfies the following relationships:

0.00 ≦ B / β ≦ 0.50 and
0.5 ≦ B / (α - β) ≦ 10.0

where α for the total number of atoms of barium, stron contained in the semiconductor ceramic tium, calcium, lead, yttrium and a rare earth element and β stands for the total number of in the atoms of titanium, tin, zirconium, niobium, tungsten and an contained in the semiconductor ceramic timon stands.

The semiconductor ceramic with such a composition can ge at 1000 ° C or lower be fired and shows an improved PTC characteristic, even if the ceramic one Is subjected to reoxidation at a low temperature. In this way, a base metal are used as the inner electrode, and it will have a satisfactory PTC Characteristic achieved.  

The monolithic electronic element made from a semiconductor ceramic preferably contains a donor element and an acceptor element, these elements being introduced in amounts which satisfy the following relationships:

0.0001 ≦ Md / β ≦ 0.005 and
0.00001 ≦ Ma / β ≦ 0.005

where Md is the total number of atoms of a donor element in the semiconductor ceramic layer ten stands for the total number of atoms of an acceptor element in the semiconductor ceramic layers and β stands for the total number of atoms contained in the semiconductor ceramic Titanium, tin, zirconium, niobium, tungsten and antimony.

The ceramic with such a composition provides a monolithic electronic Element that shows a very effective PTC characteristic.

Various other objects, features, and many of those associated with the present invention Benefits are readily apparent if they follow better with reference to those de detailed description of the preferred embodiments in connection with the beige added drawing, in which:

Fig. 1 is a schematic cross-sectional view of an example of a semiconductor ceramic according to the present invention-made monolithic electronic element.

The monolithic electronic element of the present invention comprises one of alternie rend stacked semiconductor ceramic layers made of barium titanate and inner electrode layers formed sintered laminate, which mainly comprise a base metal, and on a surface of the Sintered laminate formed outer electrodes where the inner electrodes are exposed.

The semiconductor ceramic used in the present invention includes Bari umtitanate as the predominant component and boron oxide as the secondary component.

Ba in the barium titanate above can be partially substituted by Sr, Ca, Pb, Y or a rare earth element can be substituted (these elements are referred to below as elements of the Ba position ), while Ti in the above barium titanate is partially replaced by each of Sn, Zr, Nb,  W and Sb can be substituted (these elements are referred to below as elements of the Ti Designated place).

In addition to the elements of the Ba site, Ba or another Ba-substitutable Ele ment, such as Sr, Ca, Pb, Y or a rare earth element, the above-mentioned semiconductor ceramic added so that the total amounts of Ba and Ba-substitutable elements, such as Sr, Ca, Pb, Y and rare earth element exceed the total amounts of Ti and Sn, Zr, Nb, W and Sb.

The aforementioned semiconductor ceramic can contain a donor element and an acceptor element. The term "donor element" herein refers to an element such as Y, Nb, Sb, W, Ta, Mo or a rare earth element which generally serves as a donor in BaTiO ₃ , while the term "acceptor element" herein refers to an element such as Mn, Fe, Co, Ni, Cr or an alkali metal, which generally serves as an acceptor in BaTiO ₃ .

The aforementioned inner electrodes can be made of a base metal such as Ni, Co, Fe or Mo be educated. These base metals can be used singly or in the form of an alloy become. Of these, Ni is preferred in view of its excellent oxidati resistance.

The above-mentioned outer electrodes are not particularly limited Material, and metals such as Ag, Pd and an Ag-Pd alloy can be used.

Examples

The present invention will next be described by way of examples, which are not as a limitation of the invention are to be understood.

example 1

A method for manufacturing the monolithic electronic element of the present invention is described. Fig. 1 is a schematic cross-sectional view of an example of the custom built from a semiconductor ceramic according to the present invention, mono lithic electronic element.

First, barium titanate was hydrothermally synthesized to obtain a ratio of Ba site elements to Ti site elements of 0.998. Then BaCO ₃ , Sm ₂ O ₃ , BN and MnCO _{3 were} weighed and added to the barium titanate to provide a mixture according to the following formula (I):

(Ba _0.998 TiO ₃ powder, hydrothermally synthesized) + 0.001 Sm ₂ O ₃ + xBaCO ₃ + yBN + 0.0002MnCO ₃ (I).

The resulting mixture was mixed with a binder, and the resulting mixture was wet mixed with zirconia beads for 10 hours to thereby form a ceramic slurry. The slurry was shaped by a doctor blade method and dried to thereby form green ceramic sheets. Ni paste was applied to each of the green sheets by printing to form an inner electrode layer on the sheet, and the sheets thus formed were stacked to thereby form a laminate. After removing the binder at 300 ° C in air, the laminate was baked at 950 ° C in a reducing hydrogen / nitrogen atmosphere for two hours to thereby form a sinter laminate. The composition of each ceramic layer in the sintered laminate is given by the following formula:

Ba _0.998 Sm _0.002 TiO ₃ + xBaO + 1 / 2yB ₂ O ₃ + 0.0002MnO ₂ .

Next, as shown in FIG. 1, a paste for forming an Ag electrode was applied to surfaces of a sintered laminate 3 comprising the ceramic semiconductor layers 5 and the inner electrode layers 7, the inner electrodes being exposed to the surfaces. The obtained part was baked at 800 ° C in air for two hours, thereby forming the outer electrodes 9 by baking and thereby performing reoxidation. In this way, a monolithic electronic element 1 according to the present invention was manufactured.

The electrical resistance at room temperature and the change ratio of the resistance, indicated by log (R250 / R25), wherein R250 stands for the resistance at 250 ° C and R25 stands for the resistance at 25 ° C, have been used for a variety of in a similar manner measured on manufactured electronic elements, the elements being produced by modifying the amount of BaCO ₃ (X) added and the amount of BN (Y) added to form the corresponding ceramic. The results are shown in Table 1. The symbol * in Table 1 refers to samples that are outside the scope of the present invention. In Example 1, the following relationships are satisfied: B / β = B / Ti and B / (α - β) = B / (Ba + Sm - Ti).

Table 1

• 1. Sample No.
• 2. Additives
• 3. Amount of elemental Ba (mole)
• 4. Amount of elemental B (mole)
• 5. Characteristics
• 6.Resistance at room temperature (Ω)
• 7. Change ratio of the resistance log (R250 / R25)
• 8. at least 1,000,000
• 9. not measurable
• 10. Sinterability
• 11. The symbol * refers to samples outside the scope of the invention lie.

As is clear from Table 1, samples show parameters that fall into the ranges 0.001 ≦ B / β ≦ 0.50 and 0.5 ≦ B / (α - β) ≦ 10.0 fall, a low resistance at room temperature rature and a change ratio of the resistance, indicated by log (R250 / R25) of at least 2.

Samples Nos. 1 to 5, which have a B / β of less than 0.001, show a very high one Resistance at room temperature and a low change ratio of resistance, whereas Sample Nos. 31 to 35, which have a B / β greater than 0.50, are high Resistance at room temperature and a low change ratio of the resistance demonstrate. Samples Nos. 1, 6, 11, 16, 21, 26 and 31, which have a B / (α - β) of less than 0.5 sen, show a high resistance at room temperature and a low change behavior ratio of resistance, whereas samples Nos. 5, 10, 15, 20, 25, 30 and 35, which have a B / (α -  b) have greater than 10.0, a high resistance at room temperature and a low show the change ratio of the resistance.

Example 2

The procedure of Example 1 was repeated except that the amount of BaCO ₃ (X) added and the amount of BN (Y) added were set to 0.02 mol and 0.06 mol, respectively, and the amount of Sm added ₂ O ₃ (Md) serving as a source of a donor and the amount of MnCO ₃ (Ma) added serving as a source for an acceptor element were modified to thereby produce monolithic electronic elements. In a similar manner, the electrical resistance at room temperature and the change ratio of the resistance indicated by log (R250 / R25) were measured. The results are shown in Table 2. The symbol * refers to samples that are outside the scope of the present invention.

Table 2

• 1. Sample No.
• 2.Resistance at room temperature (Ω)
• 3. Change ratio of the resistance log (R250 / R25)
• 4. The symbol * refers to samples outside the scope of the present Invention lie.

As is clear from Table 2, samples show parameters that fall into the ranges 0.0001 ≦ Md / β ≦ 0.005 and 0.00001 ≦ Ma / β ≦ 0.005 fall, with a low resistance Room temperature and a large increase in the change ratio of resistance, indicated by log (R250 / R25).

Sample No. 49, which has an Md / β of less than 0.0001, shows a very high resistance stood at room temperature and a low change ratio of resistance wherever against Sample No. 54, which has an Md / β greater than 0.005, a low change ration ratio of the resistance shows.  

Sample No. 41, which has a Ma / β of less than 0.00001, shows a low change ratio of resistance, whereas Sample No. 48, which has a Ma / β greater than 0.005 has a high resistance at room temperature and a low change ver ratio of resistance shows.

As described hereinabove, the monolithic electronic element made of a semiconductor ceramic according to the present invention comprises a sintered laminate formed of alternately stacked semiconductor ceramic layers and inner electrode layers, and outer electrodes formed on the sintered laminate, each semiconductor ceramic layer comprising a semiconducting sintered barium titanate containing the following substances: boron oxide; a first oxide of at least one metal selected from barium, strontium, calcium, lead, yttrium and a rare earth element; and a second oxide of at least one metal selected from titanium, tin, zirconium, niobium, tungsten and antimony, the boron oxide being incorporated in an amount as reduced to atomic boron (B) which satisfies the following relationships:

0.001 ≦ B / β ≦ 0.50 and
0.5 ≦ B / (α - β) ≦ 10.0

where α for the total number of atoms of barium, stron contained in the semiconductor ceramic tium, calcium, lead, yttrium and a rare earth element and β stands for the total number of in the atoms of titanium, tin, zirconium, niobium, tungsten and an contained in the semiconductor ceramic timon stands. Thus, the monolithic electronic element can be fired at 1000 ° C or lower and shows a satisfactory PTC characteristic, even if it is made by reoxidation at low temperature.

The monolithic electronic element made from a semiconductor ceramic preferably contains a donor element and an acceptor element, these elements being introduced in amounts which satisfy the following relationships:

0.0001 ≦ Md / β ≦ 0.005 and
0.00001 ≦ Ma / β ≦ 0.005

where Md is the total number of atoms of a donor element in the semiconductor ceramic layer ten stands for the total number of atoms of an acceptor element in the semiconductor ceramic layers and β stands for the total number of atoms contained in the semiconductor ceramic Titanium, tin, zirconium, niobium, tungsten and antimony. The element thus shows satisfaction PTC characteristic.

Table 1

Table 2

Claims (4)

1. A monolithic electronic element made of a semiconductor ceramic, the element comprising a sintered laminate formed from alternately stacked semiconductor ceramic layers and inner electrode layers, and outer electrodes formed on the sintered laminate, each semiconductor ceramic layer comprising semiconducting sintered barium titanate containing the following substances: boron oxide ; a first oxide of at least one metal selected from barium, strontium, calcium, lead, yttrium and a rare earth element; and a second oxide of at least one metal selected from titanium, tin, zirconium, niobium, tungsten and antimony, the boron oxide being incorporated in an amount as reduced to atomic boron which satisfies the following relationships:
0.001 ≦ B / β ≦ 0.50 and
0.5 ≦ B / (α - β) ≦ 10.0
where α stands for the total number of atoms of barium, strontium, calcium, lead, yttrium and a rare earth element contained in the semiconductor ceramic and β stands for the total number of atoms of titanium, tin, zirconium, niobium, tungsten and antimony contained in the semiconductor ceramic . 2. Monolithic electronic element made of a semiconductor ceramic according to claim 1, wherein the element contains a donor element and an acceptor element, these elements being incorporated in amounts that satisfy the following relationships:
0.0001 ≦ Md / β ≦ 0.005 and
0.00001 ≦ Ma / β ≦ 0.005
where Md stands for the total number of atoms of a donor element in the semiconductor ceramic layers, Ma stands for the total number of atoms of an acceptor element in the semiconductor ceramic layers and β stands for the total number of atoms of titanium, tin, zirconium, niobium, tungsten and Antimony stands. 3. A semiconductor ceramic comprising: boron oxide; a first oxide of at least one metal selected from barium, strontium, calcium, lead, yttrium and a rare earth element; and a second oxide of at least one metal selected from titanium, tin, zirconium, niobium, tungsten and antimony, the boron oxide being incorporated in an amount as reduced to atomic boron which satisfies the following relationships:
0.001 ≦ B / β ≦ 0.50 and
0.5 ≦ B / (α - β) ≦ 10.0
where α stands for the total number of atoms of barium, strontium, calcium, lead, yttrium and a rare earth element contained in the semiconductor ceramic and β stands for the total number of atoms of titanium, tin, zirconium, niobium, tungsten and antimony contained in the semiconductor ceramic . 4. The semiconductor ceramic according to claim 3, further comprising: a donor element and an acceptor element, these elements being introduced in amounts that satisfy the following relationships:
0.0001 ≦ Md / β ≦ 0.005 and
0.00001 ≦ Ma / β ≦ 0.005
where Md stands for the total number of atoms of a donor element in the semiconductor ceramic layers, Ma stands for the total number of atoms of an acceptor element in the semiconductor ceramic layers and β stands for the total number of atoms of titanium, tin, zirconium, niobium, tungsten and Antimony stands.