Capacitors for high power and elevated temperatures based on glass ceramics

Summary

Power electronic sees a trend towards increasing power densities, increasing voltages and current densities. Following from this the thermal load on all components is also increasing and often the passive components, namely the capacitors, are the limiting components for a further increase in operating temperature. Bulk glass ceramics obtained from a true glassy phase form an entirely new class of materials as a dielectric in high power capacitors. The _green_ glasses of these glass ceramics are produced via a molten liquid in a production quality which is comparable to a production of optical glasses. In a second and independent step crystalline phases are grown in a controlled way by applying a well de_ned time-temperature pro_le. By controlling the latter process crystalline phases with para- or ferroelectric phases, which dominate the dielectric properties of the glass ceramic, are grown and the size of the crystallites can be controlled from a few nanometer to several micrometer in diameter. Due to such a production process the resulting materials are free of pores and show very high dielectric breakdown strengths in comparison to usual ceramic materials. In the current paper we present a material with a dielectric constant of _ = 34, a close to NP0 temperature characteristic and good dielectric properties for temperatures up to 300 oC. This glass ceramic further has very high dielectric breakdown strength of the order of 44 kV/mm measured on 1.2mm thick samples. The application of this new material class for high power capacitors is discussed. The dielectric is currently commercialized under the SCHOTT brand name Poweramic®.

Additional informations

Authors

Huang Jianwen, Zhou Yuanxiang, Huang Meng, Liu Xinqu, Jahangiri Tohid, Bak Claus Leth