Electrical conduction in double-layer P-SiO/sub 2//polymer dielectric structures

The dc electrical conduction in MI/sub 1/M and MI/sub 1/I/sub 2/M composite specimens has been studied, where I/sub 1/ is polyimide (PI) or polyester (PET), and I/sub 2/ is a thin plasma deposited silicon compound film (oxide, P-SiO/sub 2/, or nitride, P-SiN). The current-electric field (j(E,T)) characteristics have been measured over a wide range of E values (O/spl les/E/spl les/2/spl times/10/sup 5/ V cm/sup -1/) and temperatures (20/spl les/T/spl les/170/spl deg/C). The observed transport characteristics are in broad agreement with data reported in the literature, except for PI based MI/sub 1/I/sub 2/M specimens, for which polarity dependent transport behavior occurs for T>60/spl deg/C and E>2/spl times/10/sup 3/ V cm/sup -1/. The observed behavior of all specimen types can be explained in terms of protonic hopping conduction; the charge carriers are created by thermal dissociation and ionization of carboxylic acid (-COOH) groups, present in PI as several percent of unimidized polyamic acid, and in PET at chain ends. When the polarity is +MI/sub 1/I/sub 2/M-, the relatively abundant free protons in PI flow to the I/sub 1//I/sub 2/ interface, where they can accumulate and give rise to a space charge-induced potential barrier of /spl sim/0.2 eV. By modifying Lewis' molecular dipole model so as to include this potential barrier, we derive expressions for j(E,T) which describe the experimentally observed polarity dependence in PI rather well. The effect is not observed in PET based MI/sub 1/I/sub 2/M specimens on account of the much lower concentration of free protons in this polymer.<
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