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|High-Dielectric-Constant Capacitors for High-Temperature Power Inverters in Hybrid Electric Vehicles|
|Keywords: capacitors, power inverters, under-hood operation|
|Future availability of high-temperature (¡Ö140¡ãC) power inverters will advance the market share for hybrid vehicles that are highly fuel efficient and environmentally friendly. Capacitors have a significant influence on inverter lifetime, reliability, cost, and temperature of operation. They account for ¡Ö40% volume, ¡Ö23% weight, and ¡Ö23% cost of inverters. Development of inverters with higher performance, improved reliability, and smaller size and weight requires the capacitors to be embedded within a printed wire board (PWB). The ¡°film-on-foil¡± approach, where the dielectric is deposited on base-metal foil, is a promising method for embedding the capacitors within a PWB. We have deposited high-permittivity ceramic films of lead lanthanum zirconium titanate (PLZT) on base metal foils by chemical solution deposition. These prefabricated film-on-foil dielectric sheets can be embedded into PWBs for inverter applications. Among the many challenges in fabricating these sheets is avoiding a reduction in capacitance density from the formation of a parasitic low-permittivity interfacial layer of base metal oxide during thermal processing of the PLZT. We followed two approaches (presented in this talk) to overcome this problem. Subsequently, we grew high-quality PLZT films on Ni and Cu foils. For the PLZT films deposited on Ni foils, we measured a dielectric constant of 1300 (at 25¡ãC) and 1800 (at 150¡ãC), leakage current density of 6.6 x 10-9 A/cm2 (at 25¡ãC) and 1.4 x 10-8 A/cm2 (at 150¡ãC), and breakdown field strength of 1.2 MV/cm. Initial results were encouraging with samples of PLZT on Cu foils, which gave a dielectric constant ¡Ö670 (at 25¡ãC). The temperature coefficient of capacitance (between 25 and 150¡ãC) was ¡Ö12%. The fabrication and dielectric properties of film-on-foil PLZT samples will be discussed. Work supported by the U.S. Department of Energy, Office of Vehicles Technology Program, under Contract DE-AC02-06CH11357.|
|U. Balachandran, Manager, Ceramics Section
Argonne National Laboratory