High Temperature Capacitors for Power Converters

In this SBIR program, TRS Technologies and its subsidiary, Centre Capacitor, will develop a new family of high volumetric efficiency, high temperature capacitors based on high Curie temperature relaxor-ferroelectric ceramics that operate at temperatures far beyond conventional X7R and X8R dielectric formulations (125C to 150C). These new higher temperature (>300oC) materials will be suited for advanced power electronics based on emerging solid state switching technologies such as IGBT?s and SiC. Capacitors used in these circuits must operate at high frequency (10?s to 100 kHz) with voltages ranging from 200 to 600V. They must be able to handle high AC ripple currents implying low dielectric loss, low equivalent series resistance (ESR), and high insulation resistance. For applications on spacecraft, electric automobiles, supersonic aircraft, and ships the capacitors must have a high volumetric efficiency to minimize volume and weight. This implies a high dielectric constant and/or very low dielectric layer thickness. In the Phase I program TRS? approach to this problem was to develop a unique high temperature relaxor ferroelectric with a dielectric constant >10,000 @ 300?C and dielectric loss 109 W-cm at 300oC. Our strategy was to develop a high dielectric constant material so that the layer thickness in a multilayer capacitor could be kept relatively thick (100?s of microns) to ensure capacitor reliability. Capacitor lifetime has been shown to degrade significantly as dielectric layer thickness decreases and temperature increases.