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Thin polymer lm was deposited on various substrates by using a novel physical vapour deposition method, the Modi ed Ionized Cluster Beam (MICB) deposition method. For example, to fabricate polyimide lms by the MICB method, PMDA and ODA monomer clusters formed from specially designed sources were deposited to form polyamic-acid (PAA). Then, the PAA lms were transformed to polyimide by a low-temperature curing process. The residual gas analyzer (RGA) results show that during the curing process the water molecules were released as a result of the imidization process. The onset temperature and the properties of the lm varied with deposition conditions, such as acceleration voltage, ionizer energy and beam current. In this study, PI thin lms with various thicknesses and packing densities were used as bu er layers between ITO and MEH-PPV in a polymer EL device. Precise measurements of the hole-drift velocities in the actual devices with a bu er layer were carried out by using the time-of- ight method and the transient EL method. By controlling the charge-carrier injection ratio and the carrier- drift velocity with the thickness of inserted PI bu er layers, balanced recombination of charge carriers can be accomplished and, therefore, the quantum eciency of devices can be increased within a certain range of thickness.