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|High-Temperature Ceramic Capacitors for Power Inverters in Electric Drive Vehicles|
|Keywords: Ceramic Dielectric Films, High-Temperature Capacitors, Electric Drive Vehicles|
|Future availability of high-temperature power inverters will advance the market share for electric drive vehicles that are highly fuel efficient and environmentally friendly. DC buss capacitors are integral part of vehicle power inverters and they have a significant influence on inverter lifetime, reliability, cost, and temperature of operation. Advanced power inverters require capacitors that operate under high voltage conditions at under-hood conditions and yet have minimal footprint. This need can be realized by embedding high-permittivity dielectrics 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 films of lead lanthanum zirconium titanate (PLZT) on Ni foils by a chemical solution deposition technique. These prefabricated film-on-foil dielectric sheets can be embedded into PWBs for inverter applications. For PLZT films deposited on nickel foils, we measured a dielectric constant of ≈700 and dielectric loss of ≈0.07 at -50ºC, dielectric constant of ≈1300 and dielectric loss of ≈0.08 at 20ºC, and a dielectric constant of ≈2200 and dielectric loss of ≈0.06 at 150ºC. At room temperature, leakage current density of ≈7×10-9 A/cm2 and breakdown voltage of ≈2.5 MV/cm were measured. Under 300 V bias, we measured dielectric constant ≈110 and dielectric loss of ≈0.004 (0.4%) at room temperature on a ≈3-μm-thick PLZT film on Ni foil. Hysteresis loop analysis showed that energy densities of ≈15 J/cm3 and ≈85 J/cm3 can be stored in a ≈3-μm-thick PLZT film at 600 V and 1400 V, respectively. Recently, we stacked four 20-mm diameter PLZT films and measured a capacitance of ≈9 μF (capacitance density ≈4.8 μF/cm3). The fabrication procedures and dielectric properties of PLZT films deposited on Ni foils will be presented in this talk.|
|U. Balachandran, Senior Scietist, Section Leader
Argonne National Laboratory