Development of Film-on-Foil Ceramic Dielectrics for Embedded Capacitors for Power Inverters in Electric Drive Vehicles Uthamalingam (Balu) Balachandran  , Manoj Narayanan, Shanshan Liu, and Beihai Ma Energy Systems Division, Argonne National Laboratory, Argonne, IL 60439, U.S.A. E-mail: balu@anl.gov Received October 20, 2012; revised December 19, 2012; accepted December 25, 2012; published online May 20, 2013 Advanced power inverters for electric drive vehicles require capacitors that operate under high voltage at under-hood temperatures and have minimal footprint. This need can be realized by embedding ceramics with high dielectric constant within a printed wire board (PWB). The ‘‘film-on- foil’’ approach, where the high-dielectric-constant ceramic is first deposited on base-metal foil, is a promising method for embedding the capacitors within a PWB. We have deposited lead lanthanum zirconium titanate (PLZT) on nickel foils and characterized the samples in the temperature range between 50 and 250  C. The measured dielectric constants varied with temperature: from 700 at 50  C to 2200 at 250  C. The dielectric loss remained fairly constant at 0:05{0:08. At 300 V bias, a dielectric constant of 110 and dielectric loss of 0:004 were measured. Hysteresis loop analysis showed an energy density of 85 J/cm 3 . The fabrication procedures and dielectric properties of the PLZT film-on-foils will be described in this paper. # 2013 The Japan Society of Applied Physics 1. Introduction Future availability of high-temperature power inverters will advance the market share for hybrid vehicles that are highly fuel efficient and environmentally friendly. An integral part of vehicle power inverters is the DC buss capacitors, which have a significant influence on inverter lifetime, reliability, cost, and temperature of operation. The drive train and backup systems in electric vehicles utilize AC power drawn from a battery via a power inverter. Large ripple currents can be produced due to imperfect inversion and would reduce the battery performance, lifetime, and charge/discharge efficiencies. However, capacitors are used in the power inverters to block the ripple currents from reaching the battery. To limit the ripple current in power electronic inverters, the capacitor energy should be as high as possible. At present, polymer-based capacitors are used in electric- drive power inverters. Due to the low dielectric constant (k  3) of polymer films, the currently used capacitors are very bulky; they occupy about 35% of the inverter volume. Current polymer film capacitors have temperature limita- tions for under-hood operation; they are limited to 85  C. Therefore, in present-day hybrid vehicles two separate cooling systems are used, the standard radiator cooling at 105  C and a secondary system at 70  C to cool the power electronics. Because the two separate cooling systems add weight and cost to hybrid vehicles, there is a need for a high performance capacitor that can operate at the temperature of the existing radiator cooling system, thereby eliminating the need for the secondary cooling system. This new capacitor would reduce the overall cost for hybrid vehicles compared to vehicles with conventional internal combustion engines and enhance the wide-spread adaptation of electric drive vehicles. Advanced power inverters require capacitors that operate at high voltage and under-hood conditions and yet have minimal footprint. This need can be realized by embedding high-k dielectrics within the layers of a printed wire board (PWB). Embedding the dielectrics into PWB to replace discrete surface-mounted capacitors is advantageous in electronics miniaturization, device reliability, and manufac- turing cost reduction. Embedded capacitors can be located directly underneath the active devices, greatly reducing component footprint and dramatically shortening intercon- nect lengths. These factors reduce parasitic inductive losses and electromagnetic interference and enable higher fre- quency operation. Photolithographic methods combined with etching and metallization steps can be used to fabricate the necessary capacitive elements and interconnections rapidly and in large quantities. 1) Although the embedding technology has primarily received attention for decoupling capacitors in microelectronic applications, 1,2) it can also be extended to high voltage and high power applications, such as for use in power inverters in hybrid electric vehicles. However, the integration of high-k ceramics into PWBs is challenging because of the incompatibility of the different processing conditions involved. Polymer layers in a PWB cannot withstand the high temperatures (>800  C) required for processing the ceramic dielectric films to obtain the desired crystalline structures. Development of these crystal- line structures becomes extremely difficult, if not impos- sible, at reduced processing temperatures. Recently, great success has been achieved with a film-on-foil approach by which a thin metal foil is first coated by a chemical solution of the dielectric’s components, and then the dielectric is crystallized at high temperatures. 3–7) These coated foils, film-on-foil capacitors, can then be embedded into PWBs. Funded by the U.S. Department of Energy’s Vehicle Technologies Program, Argonne is developing capacitors fabricated from lead lanthanum zirconium titanate (PLZT)- based ferroelectric films on nickel foils. Because the maximum energy storage capability of a capacitor is proportional to the dielectric constant times the square of the breakdown strength, ferroelectric materials with high dielectric constant and breakdown strength provide the significant advantages of reducing the volume of the capacitor. PLZT possess high dielectric constant (k  100 at 300 V bias field) compared to the currently used polymer film capacitor that has k  3. Since PLZT has a Curie temperature around 200  C, 8,9) they can handle large ripple currents at under-hood conditions. Integration of nickel as a bottom electrode provides significant cost advantage over the use of noble metal electrodes. To produce film-on-foil capacitors with high quality, we have found it necessary to Japanese Journal of Applied Physics 52 (2013) 05DA10 05DA10-1 # 2013 The Japan Society of Applied Physics REGULAR PAPER http://dx.doi.org/10.7567/JJAP.52.05DA10