High Temperature Capacitors for Power Electronics

The development of passive components for power generation and distribution has not kept pace with the rapid advances in wide band gap semiconductors. As a result, a large portion of the size and weight of power electronics systems is due to passivedevices such as capacitors. The most commonly used high-efficiency capacitors are based on high dielectric constant barium titanate doped to yield and X7R temperature dependence, but above their maximum use temperature their capacitance drops off veryquickly leading to low volumetric efficiency and high temperature dependence at power inverter/converter operating temperatures. NPO capacitors have a much flatter temperature response than X7Rs, and their use can be relatively easily extended to hightemperature, but the dielectrics in these capacitors have inherently low dielectric constants, which again reduces volumetric efficiency. The solution proposed in this STTR program is to develop a dielectric with a high dielectric constant over a widetemperature range, so that high volumetric efficiency capacitors can be made. A composite approach will be used to engineer an X7R-like temperature dependence from room temperature to >300C. The high insulation resistance of this dielectric material willfurther insure capacitor reliability and ripple current capability through low ESR. There is an immediate need for high efficiency capacitors with decreased volume, weight, and extended temperature range for power electronics in both the military andcivilian markets. This is particularly true from power inverter/converter circuits used on electric vehicles. Though an emerging technology, its success is expected to be highly dependent on miniaturization of the passive components. These systems willbe a major focus of the military over the next decade leading into a very large civilian market as commercial automotive manufacturers introduce electric vehicles. Also, as the processing speeds of microprocessors increase, there will be anever-increasing demand for decoupling capacitors that are capable of operating at temperatures exceeding the 125-140¿C limit for X7R/X8R materials. High power capacitors developed on this program would also be well suited for use as high-temperaturedecoupling capacitors, opening another large consumer market for these devices. Additional, existing markets include