JPS6159525B2 - - Google Patents

Abstract

A semiconductive ceramic capacitor composition has a main component consisting of 14-21 mol% CaO, 29-36 mol% of SrO and 49.5-51 mol% of Ti2O2 which contains 0.05-1 mol part of at least one of Ta2O5 and Nb2O5, 0.5-6 parts of SiO2 and 0.5-6 parts of Bi2O3 per 100 mol parts of the main component.

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a CaTiO ₃ --SrTiO ₃ based semiconductor ceramic capacitor body which has a high dielectric constant, a very small temperature change rate, and a small dielectric loss (tan δ) at 10 KHz and 100 KHz. Conventionally, a trimmer porcelain capacitor has been used in the oscillation circuit of a quartz wristwatch, and by adjusting its capacitance, the lag or advance of the clock has been adjusted. With the miniaturization of such watches, there has been a demand for trimmer capacitors to be miniaturized. For this purpose, porcelain materials with high dielectric constants are becoming necessary, but conventional porcelain materials have dielectric constants of about 100 to 300.
Although BaTiO ₃ porcelain has a high dielectric constant of about 2000, since it is a ferroelectric material, the temperature hysteresis of the capacitance and tan δ are large, so it cannot be said to be a material suitable for the above-mentioned uses. Conventional semiconductor capacitors include those based on BaTiO ₃ or SrTiO ₃ , and their apparent dielectric constants are on the order of tens of thousands. Such an apparent permittivity is too large for a trimmer capacitor, and the capacitance changes due to processing of the trimmer capacitor or its rotor rotation angle are too large, making it difficult to adjust the capacitance. Such porcelain could not be used for trimmer capacitors. Also, the temperature change rate of these capacitances is 20
-25° to +85°C based on capacity at °C
BaTiO ₃ was large at ±15 to 40%, and SrTiO ₃ was large at ±10 to 15%. The present invention provides three
properties, i.e. dielectric constant 1000-3500, tanδ
(10KHz) and tanδ (100KHz) are 1% or less,
This satisfies the requirement that the temperature change rate of capacitance is within ±8%. The porcelain material has a SrTiO ₂ −CaTiO ₃ solid solution as a matrix, and as an element to convert it into a semiconductor.
Add _{Nb2O5 or Ta2O5} and further as _an additive
It is made by adding both SiO ₂ and Bi ₂ O ₃ , and this composition is mixed, calcined, shaped, and fired in N ₂ or N ₂ - H ₂ mixed gas, and B ₂ O is added to the surface of this porcelain. After coating _{No. 3} , heat treatment is performed to convert only the grain boundaries into insulators. That is, one or more of Ta ₂ O ₅ and Nb ₂ O ₅ is added to 100 mol parts of the main components consisting of 14 to 21 mol% of CaO, 29 to 36 mol% of SrO, and 49.5 to ₅₁ mol% of TiO 2 .
A mixed powder prepared to form porcelain containing 0.5 to 1.0 mole parts and 0.5 to 6.0 mole parts each of SiO ₂ and Bi ₂ O ₃ is calcined at 900° to 1200°C, pulverized, molded, and then neutralized. From 1270℃ in atmosphere or reducing atmosphere
Porcelain obtained by firing at an ambient temperature of 1380℃
Add 0.3 to 6 mg of B ₂ O ₃ to 1 g, respectively.
After heat treatment at 1000° to 1200°C and 950° to 1200°C, electrodes are applied to both sides of the porcelain.
The reason for these limited compositions and manufacturing methods will be explained with reference to examples. [Experiment 1] Industrial raw materials SrCO ₃ , CaCO ₃ , TiO ₂ ,
Nb ₂ O ₅ , Ta ₂ O ₅ , SiO ₂ and Bi ₂ O ₃ were blended in the composition ratio shown in Table 1, wet mixed, preformed at a pressure of 300 Kg/cm ² and then heated at 1100°C for 2 hours. After calcining and wet grinding, it was molded to a diameter of 12 mm and a thickness of 0.6 mm under a pressure of 1000 Kg/cm ² . Each molded body was fired at 1320° C. for 4 hours in a 90% N ₂ -10% H ₂ mixed gas. Apply 1.5 mg of Cu ₂ O per 1 g to the surface of this porcelain,
A heat treatment was performed at 1080° C. for 2 hours to coat both sides of the porcelain with silver paste, and the porcelain was baked at 800° C. for 15 minutes. Table 2 shows the temperature change in dielectric constant tan δ capacitance of this element.

【table】

【table】

【table】

[Experiment 2]

Samples adjusted to have the same composition as samples 18, 24, 28, and 29 in Experiment 1 (hereinafter composition numbers 18, 24,
28, 29), the relationship between firing temperature and properties was investigated. The firing temperatures are as shown in Table 3, and firing was performed at each temperature for 4 hours. Other manufacturing conditions were the same as those in Experiment 1. In addition, samples 117 to 120 were in the N ₂ range, and samples 101 to 116 were in 90% N ₂ -10% H ₂
Each was fired in an atmosphere.

[Table] In the above sample 108, the element bodies were fused and adhered to each other during firing, and its properties could not be investigated. In a composition in which 1 mol part each of SiO ₂ and Bi ₂ O ₃ is added, the temperature is 1270° to 1380°C in a reducing atmosphere.
By firing it, the desired properties can be obtained.
In a composition in which both SiO ₂ and Bi ₂ O ₃ are added in large amounts of 6 mol parts, the upper limit of the firing temperature tends to be slightly lower, and good characteristics can be obtained at 1270 to 1360°C. When the firing temperature is 1250°C or less, the firing is insufficient and the solid solution of the semiconductor element is insufficient, so that it is reoxidized in the grain boundary diffusion process of Cu ₂ O. If fired at 1400℃ or higher, it will be overfired.
Dense porcelain cannot be obtained and tanδ becomes large. Firing in an N ₂ atmosphere raises the optimum firing temperature compared to a reducing atmosphere and tends to lower the characteristics slightly, but the characteristics for trimmer capacitors are met. Example 1 As a reference example, samples 18, 24, 28, and
A porcelain body with the same composition as 29 was made under the same conditions, and
Apply Cu ₂ O at the ratio shown in Table 4 and heat it at 1080℃ for 2 hours.
Heat treated for hours. Furthermore, as an example, samples 221 to 225 having the same composition as sample 18 were coated with different amounts of B ₂ O ₃ and heat treated. Its characteristics are summarized in Table 4.

[Table] Each sample has good dielectric constant and temperature characteristics, and regarding tan δ, Cu ₂ O is 0.1 to 2.5 mg per 1 g of porcelain body, and B ₂ O ₃ is 0.3 to 6 mg, which is 1%.
The following is true. Example 2 A molded body adjusted to have the same composition as Sample 18 of Experiment 1 was placed in a 90% N ₂ -10% H ₂ atmosphere.
It was baked at 1320°C for 4 hours. Then 1g of porcelain body
2 mg of B ₂ O ₃ or as a reference example 15 mg of
Cu ₂ O was applied respectively, and 2
Heat treated for hours. Its characteristics are summarized in Table 5. Cu ₂ O for samples 301-307 and 308-
As for 313, B ₂ O ₃ was applied respectively.

[Table] As is clear from the results in the table above, Cu ₂ O and B ₂ O ₃
The diffusion temperature range of is slightly different, and for the former
1000° to 1200°C, and 950 to 1200°C for the latter. As is clear from the above description, according to the method of the present invention, a ceramic body suitable for a small capacitor with good temperature characteristics can be manufactured.

Claims (1)

[Claims] 1. Ta ₂ O 5 and Nb ₂ O ₅ based on 100 mol parts of the main components consisting of 14 to 21 mol % of CaO, 29 to 36 mol % of SrO, and 49.5 to ₅₁ mol _% of TiO 2 . at least 1
A composition prepared to contain 0.05 to 1.0 mol parts of seeds, 0.5 to 6 mol parts of SiO ₂ , and 0.5 to 6 mol parts of Si ₂ O ₃ is fired in a neutral or reducing atmosphere. to make semiconductor porcelain, then add B ₂ O ₃ to the semiconductor porcelain at a rate of 0.3 to 6 mg per 1 g, and then heat it in air to convert only the grain boundary layer of the semiconductor porcelain into an insulator. A method for manufacturing a semiconductor ceramic capacitor body, characterized by: 2. The method for producing an element body for a semiconductor ceramic capacitor according to claim 1, wherein the heating temperature for converting the crystal grain boundary layer of the semiconductor ceramic into an insulator is 950° to 1200°C.