Dielectric characteristics of Poly(chloro-p-Xylene) thin films for high energy density pulsed power capacitors
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0949-C04-11
Dielectric Characteristics of Poly(Chloro-p-Xylene) Thin Films for High Energy Density Pulsed Power Capacitors Pratyush Tewari, Eugene Furman, and Michael T. Lanagan Pennsylvania State University, Materials Research Laboratory, University park, PA, 16802
ABSTRACT Poly(chloro-p- Xylene) or Parylene –C thin films are particularly attractive for dielectric as well as biomedical applications. In the current work the dielectric properties of Parylene-C thin films are investigated to form laminar composites with oxide thin films for high energy density pulsed power capacitors. Parylene-C thin films were synthesized by pyrolytic vapor decomposition polymerization of dichloro-di(p-Xylene) monomer. Annealing of films at 225°C has shown to enhance crystallinity of film. Conduction in Parylene-C thin films appears to be bulk-controlled with the hopping charges contributing to leakage current. The barrier height of 0.89eV and hopping distance of 2 - 2.5nm are physically plausible and similar to previously reported values in polymer literature. INTRODUCTION The energy density of a dielectric is directly proportional to its dielectric constant and breakdown strength. Hence a combination of phases with high breakdown strength and high dielectric constant is an interesting avenue to pursue, especially with nano composite oxides.[1] Based on connectivities of the oxide and polymer phases, diphasic composites can be broadly classified into 0-3, 2-2, and 1-3 systems.[2] The energy stored in a diphasic composite dielectric is the summation of stored energies in the constituent phases and in the interfacial volume between these two phases. Laminar (2-2) composite is proposed as a model system to understand the interfacial electrical characteristics of 13 and 0-3 composites. Nature of migration and trapping of charge carriers across an interface is believed to provide the signature of energy and density of interfacial states. Hence conduction analysis in oxide, polymer, and composite dielectrics is essential to deduce interfacial characteristics. This work represents the first step in the process of understanding transport in composites: characterization of individual constituent parylene-C. Parylene-C was chosen as an organic layer due to its high reported breakdown strength (~200MV/m), low dielectric losses, and ease of deposition.[3] In order to understand the conduction mechanism, AC and DC electrical characterizations are carried out on one micron thick Parylene-C films. Impedance spectroscopy was carried out to investigate the relaxation mechanism. Impedance spectroscopy results were compared with ideal Maxwell-Wagner space charge model and complex capacitance Cole-Cole diagram.[4] Leakage current –voltage characteristics analysis was done in the nonlinear conduction region to investigate the high field conduction mechanism in Parylene-C thin films.
EXPERIMENTAL PROCEDURE Sample preparation Parylene-C thin films were deposited by pyrolytic vapor decomposition polymerization process on PDS 2010 Parylene labcoater sys
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