JPS6250968B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dielectric ceramic composition useful as a grain-boundary insulated semiconductor capacitor.
δ) and provides a semiconductor capacitor with excellent insulation properties. In recent years, capacitive elements have been manufactured by imparting semiconductivity to polycrystalline sintered bodies and selectively insulating the grain boundaries of the crystals, thereby creating a dielectric layer on the surface of the semiconducting crystal. It is generally known that a very large dielectric constant can be obtained compared to a ceramic capacitor. This is called a grain boundary insulated semiconductor capacitor.
Some use barium titanate and strontium titanate as the main ingredients. Capacitors whose main component is barium titanate solid solution in which strontium titanate, barium stannate, etc. are dissolved in barium titanate are called barium titanate-based grain boundary insulated semiconductor capacitors, and this type of capacitor has a relative dielectric constant. but
Very large capacitors of 30,000 to 70,000 can be obtained, providing small capacitive elements. This barium titanate grain boundary insulated semiconductor capacitor is approximately 50 to 100μ
CuO on the surface of semiconducting porcelain with a grain size of
It is generally well known that oxides such as Cr ₂ O ₃ , Bi ₂ O ₃ , MnO, etc. are applied and thermally diffused to diffuse these oxides into the grain boundaries to insulate the grain boundaries. Considering the grain boundaries of barium titanate-based porcelain based on domestic and foreign literature, etc., it is found that they act as diffusion pipes that cause rapid diffusion.In other words, they form a highly disordered state of grain boundaries and are quite thick. It has become a thing. Therefore, the tan δ of barium titanate-based grain boundary insulated semiconductor capacitors is 3 to 3.
5%, and has drawbacks such as poor bias voltage dependence of capacitance due to its ferroelectric properties, limiting its practical usefulness as a capacitor. On the other hand, in a grain boundary insulated semiconductor capacitor mainly composed of strontium titanate, the grain boundaries of strontium titanate do not function as a diffusion pipe as prominently as compared to barium titanate. That is, the grain boundaries are not very disordered and their thickness is probably extremely thin. Therefore, even though the dielectric constant of strontium titanate is an order of magnitude lower than that of barium titanate, when viewed as the dielectric constant of a grain boundary insulated semiconductor capacitor, it is possible to obtain a dielectric constant of 10,000 or more. This may be due to this difference. Conventionally known grain boundary insulated semiconductor capacitors mainly composed of strontium titanate have a dielectric loss tangent (tan δ) of around 1%, and the temperature characteristics and DC bias dependence of capacitance are lower than that of barium titanate grain boundary insulated capacitors. It is superior to both semiconductor capacitors and general high dielectric constant ceramic capacitors. However, the dielectric constant is still insufficient to provide miniaturized capacitive elements industrially, and the insulation resistance is still insufficient.
It also has poor DC voltage dependence and withstand voltage, which limits its usage. However, strontium titanate-based grain boundary insulated semiconductor capacitors have extremely superior temperature characteristics and DC bias characteristics of dissipation tangent capacitance compared to conventionally known high dielectric constant ceramic capacitors and semiconductor capacitors, and have a large relative dielectric constant. In addition, the appearance of ceramic dielectric compositions with high withstand voltage greatly contributes to the miniaturization and stabilization of low-voltage electronic circuits. The present invention is a semiconducting porcelain obtained by firing and reducing a composition whose main component is SrTiO ₃ in which some of the Sr ²⁺ ions have been replaced with Bi ³⁺ ions, to which a small amount of ZnO is added. This is a dielectric ceramic composition for grain boundary insulated semiconductor capacitors that is characterized by selectively insulating the grain boundaries of strontium titanate based grain boundary insulated semiconductor capacitors. It is characterized by maintaining temperature characteristics and DC bias characteristics and having a high withstand voltage despite an extremely large dielectric constant. Examples thereof are shown below. Examples (1) The present invention has a composition represented by (S _r1-x Bix)TiO ₃ (where x indicates the atomic ratio, 0.0003 to 0.007) as the main component, and ZnO is added to this main component as y. weight%
(y is 0.03 to 3.0) Table 1 shows the composition ratios of x and y when added. Accurately weigh _TiO3 to have the composition (S _r1-x Bix) shown in Table 1, perform wet mixing, and pre-calcine in air at 1100°C for 2 hours to decompose the raw material powder and undergo solid phase reaction. Wake me up,
Y% by weight of ZnO was added to the obtained reaction product powder, which was ground and mixed in a ball mill to obtain a prepared raw material. Approximately 3.0% by weight of an organic binder of PVA is added and mixed to the obtained prepared raw material as a binder, granulated into granules, pressure molded into a disk shape at a pressure of 1000 kg/ ^cm2 , and heated in air at 1400 kg/cm2. It was baked at 1450°C for 2 hours. Furthermore, the sintered porcelain was reduced for 2 hours at 1450°C in a nitrogen reducing atmosphere containing 10% hydrogen.
A disk-shaped semiconducting porcelain with mmφ and thickness of about 0.40 mm was obtained. 3 to 10 mg of a diffusion paste containing Bi ₂ O ₃ and CuO was applied to this semiconducting porcelain, and heat treatment was performed at 1100 to 1150°C for 2 hours to selectively insulate the grain boundaries. Silver paste was applied to plate-shaped dielectric ceramic using a conventional method and baked at 800°C for 30 minutes to form electrodes, thereby obtaining a grain-boundary insulated semiconductor capacitor element. Table 1 shows the measurement results for each sample of the capacitor thus prepared. The capacitance tan δ was measured at a frequency of 1 kHz and 1 Vrms, the capacitance was converted to a dielectric constant, and the tan δ was the actual measured value. Insulation resistance is the value obtained by converting the resistance value after applying 25VDC for 30 seconds to resistivity. The breakdown voltage is determined by DC voltage step-up breakdown method.
The breakdown voltage is converted into electric field strength and shown.

[Table] In Table 1, sample numbers 1, 11, 12, 16, and 17 are outside the scope of the present invention, and sample numbers 2 to 10 and 13 to 15 are related to the present invention. The composition of sample number 6 has an extremely large dielectric constant of 50,600, and an excellent tan δ of 0.6%. When this sample was used to make a 0.1 μF grain boundary insulated semiconductor capacitor, the following characteristics were obtained.

[Table] In grain boundary insulated semiconductor capacitors, improving the dielectric constant generally tends to worsen the insulation resistance withstand voltage, but the ceramic composition according to the present invention has a good dielectric constant of 50,000. Despite its characteristics, its major feature is that it has an extremely high breakdown voltage of 400V. The diffusion paste used to achieve the properties shown in Table 1 was made by thoroughly mixing Bi ₂ O ₃ and CuO at a molar ratio of 3:1, reacting at 650°C for 2 hours, and mixing this with ethyl cellulose resin. 3 to 10 mg of the dielectric material is applied to both surfaces of semiconductive porcelain, and the diffusing agent is thermally diffused to the grain boundaries by heat treatment to selectively insulate the grain boundaries, resulting in dielectric porcelain. In the (S _r1-x Bix)TiO ₃ +yZnO composition of the present invention, the Bi ³⁺ content x is limited to 0.0003 to 0.007 (atomic ratio) and y (added amount of ZnO) is limited to 0.03 to 3.0% by weight. The reason for this is as follows. When the amounts of Bi ₂ O ₃ and ZnO added are 0, the dielectric constant is low as is clear from sample numbers 1, 12, and 17 in Table 1. This is because grains do not grow even when fired at 1450°C. If the amount of Bi ₂ O ₃ added is approximately 0.0003 in terms of atomic ratio, grain growth will be clearly observed and the dielectric constant will also improve. Therefore, it is set as the lower limit of the claim of x. When ZnO is added in an amount of about 0.03% by weight, grain growth becomes remarkable, and the effect is remarkable. Therefore, the lower limit of the scope of the claims of y is set. When the amount of ZnO added exceeds 3.0% by weight, grain growth is promoted, but porcelain fusion occurs and crystal grains grow too much, resulting in a decrease in insulation resistance and breakdown voltage.
If the amount of Bi ₂ O ₃ added exceeds 0.7% by weight, tan δ increases and the dielectric constant decreases, which is not preferable. In the examples of the present invention, Bi ₂ O ₃ and ZnO were used, but equivalent characteristics can be expected even if salts such as carbonates and nitrates of Bi or Zn are used. As is clear from Table 1, the optimum amounts of Bi ₂ O ₃ and ZnO to be added are when x is 0.003 and y is 0.2% by weight. At this time, the dielectric constant was extremely good at 50,600, and the characteristics of the semiconductor capacitor using this dielectric ceramic are shown in Table 2. As mentioned above, the dielectric ceramic composition of the present invention has an extremely high dielectric constant, and has excellent properties in terms of insulation resistance and breakdown voltage. This is a very useful grain boundary insulated semiconductor capacitor with voltage.

Claims (1)

[Claims] 1 SrTiO ₃ whose main component is 0.03 to 0.7 atomic % of Sr ²⁺ ions replaced with Bi ³⁺ ions,
A dielectric porcelain composition in which a composition in which 0.03 to 3.0% by weight of ZnO is added to this main component is made into semiconducting porcelain by firing and reduction, and the crystal grain boundaries are insulated.