Electrical conduction of parylene composite thin films

Parylene (poly-p-xylene) is a famous heat-resisting polymer and its melting point is ~400°C. Especially Parylene is often used as a flexible sheet and encapsulation film of organic transistors and light-emitting diodes. However, Parylen has an interesting electrical behavior, the same negative temperature dependence of current as metals. In this report, the electronic states (HOMO and LUMO) of Parylene N are showed and the strange current behavior of the Parylene C/N and N/C bilayer films. The negative temperature dependence of current for the Parylene C/N (Parylene C on Parylene N) is 2-order stronger than that for a single Parylene N. On the other hand, the temperature dependence for the Parylene N/C (Parylene N on Parylene C) is positive but it shows smaller positive dependence than that for a single Parylene C. The current of Palylene thin film relates to electroluminescence (EL). It is reported that the EL is caused by the electronic avalanche, that is, an intrinsic EL. The EL of the Parylne bilayer films also depend on the amount of current. The top layer will control the carrier injection into the bottom layer and the divided voltage of the bottom layer.