Development of PLZT Film-on-Foil Capacitors with High Dielectric Strength
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1199-F03-01
Development of PLZT Film-on-Foil Capacitors with High Dielectric Strength Beihai Ma, Manoj Narayanan, and U. (Balu) Balachandran Energy Systems Division, Argonne National Laboratory, Argonne, Illinois 60439, U.S.A.
ABSTRACT Ferroelectric film-on-foil capacitors hold special promise to replace discrete passive components in the development of electronic devices that require greater performance and smaller size. We have grown ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films on nickel substrates by chemical solution deposition. The dielectric properties were determined for samples of ≈1.15-µm-thick PLZT film grown on LaNiO3-buffered nickel substrates. Measurements on these samples yielded a dielectric constant of ≈1300, dielectric loss (tan δ) of ≈0.05, and leakage current density of ≈7 × 10-9 A/cm2. An energy density of ≈74 J/cm3 was measured at room temperature with 250-µm-diameter capacitors. Highly accelerated lifetime tests were conducted at 100ºC to determine the reliability of the ≈1.15-µm-thick film-on-foil capacitors under field stress conditions (with applied electric field from 8.7 × 105 V/cm to 1.3 × 106 V/cm). The breakdown behavior of the PLZT film-on-foil capacitors was evaluated by Weibull analysis. A voltage acceleration factor of ≈-6.3 was obtained. From the test results, a mean time to failure of >3000 hr was projected for capacitors operated at 100ºC with ≈2.6 × 105 V/cm dc electric field. INTRODUCTION Increased interest has been focused on development of ferroelectric (FE) thin films in recent years because of their anticipated applications for decoupling capacitors, micro-actuators, electro-optical components, and digital memories [1-6]. Applications are also feasible in advanced power electronics, which require capacitors that are capable of operating under high voltage and yet have minimal footprint. This requirement can be fulfilled by stacking or embedding high-permittivity ceramic film capacitors into a printed circuit board (PCB). Technology development in this area would free up surface space, reduce the number of solder joints on the PCB, and therefore, lead to increased device reliability and minimization of electromagnetic interference and inductance loss. Although the technology has primarily received attention for decoupling capacitors in microelectronic applications, it can potentially be extended to high-power energy storage applications, such as plug-in hybrid electric vehicles. The maximum energy storage capability of a capacitor is proportional to the dielectric constant times the square of the breakdown strength. Therefore, ferroelectric materials with high dielectric constant and breakdown strength provide significant advantages of reducing the volume and weight of an energy storage device. However, at present, integration of high-permittivity ceramic dielectric films into PCBs is challenging because of the incompatibility in the processing conditions for the different materials involved. Polymer layers in a PCB cannot withstand the high temperatures (600-700°
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