Electrical properties of polyimide Langmuir-Blodgett films deposited on noble metal electrodes

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Abstract
The authors have examined the electrical properties of ultrathin insulating layers of polyimide (PI) deposited on a base of Au electrodes by using tunnel junctions with structures of Au/PI/(Pb-Bi) and Au/PI/Au. For Au/PI/Au junctions, ultrathin PI Langmuir-Blodgett films having good electrical insulating properties were obtained when the number of deposited layers was greater than about 30. It was found that the I-V characteristic of electrically insulating Au/PI/Au junctions was explained by a model on Simmons' tunnelling theory (1963), assuming that application of the top Au electrode resulted in a reduction of the PI layer thickness. For Au/Pi/(Pb-Bi) junctions, typical I-V characteristics of tunnel junctions were obtained at a temperature below the critical temperature of a superconducting Pb-Bi alloy, when the number of deposited layers was 27. It was concluded that the I-V characteristic was governed by the tunnelling conduction mechanism based on the Bardeen-Cooper-Schrieffer (BCS) theory.