A niobium alloy for capacitors containing at least one element selected from groups 2 to 16 of the periodic table as an alloying component and containing 0.1 to 70 mass % niobium monitride crystals with average particle size of 0.05 to 5μm and BET specific surface area of 0.5 to 40m2/g, Sintered bodies of niobium granular products with average particle size of 10 to 500μm, niobium alloy powder or sintered bodies thereof, are capacitors of sintered bodies and methods of manufacture thereof. The niobium capacitor using niobium alloy powder or its granular product has high capacity and low leakage current, and has excellent high temperature and heat resistance characteristics.
Capacitors used in electronic devices such as mobile phones and personal computers need to be small in size and large in capacitance. Among these capacitors, tantalum capacitors are preferred because of their large capacitance and good performance in the same size. In this kind of tantalum capacitor, the sintered body of tantalum powder is usually used for the anode part. In order to improve the capacitance of tantalum capacitors, it is necessary to increase the mass of sintered bodies or use sintered bodies that increase the surface area by crushing tantalum powder.
The method of increasing the mass of sintered body will inevitably increase the appearance of capacitor, which can not meet the requirements of miniaturization. On the other hand, in the crushing of tantalum powder to increase the specific surface area, the pore size of the tantalum sintered body will decrease or the closed pores will increase in the sintering stage. As a result, the impregnation of the cathode reagent in the subsequent steps will become difficult. One study aimed at solving these problems is the manufacture of capacitors using sintered bodies of material powders that provide a greater dielectric constant than tantalum. Niobium and titanium are known as materials that provide greater permittivity.
The stability of niobium sintered material is worse than that of tantalum sintered material in oxide dielectric film. At high temperatures, the difference becomes even more pronounced. Many reasons have been considered for this, but one is the assumption that thermal deformation at high temperatures accelerates the deterioration of the oxide dielectric film due to the difference between the composition of the oxide dielectric film and the composition of the niobium sintered bulk electrode.
Similarly, capacitors using niobium sintered bodies must be subjected to reduced reliability grades at room temperature, and their service life is sometimes judged to be defective. Therefore, its use is limited in practice.
