ULTRAVIOLET-ABSORPTION AND PHOTOCONDUCTION SPECTRA OF POLYIMIDE FILMS FABRICATED AT VARIOUS CURING TEMPERATURES

The absorption and photoconduction spectra in the ultraviolet region for PMDA-ODA polyimide films fabricated under various curing temperatures have been measured. There are four absorption peaks located at 3.65, 4.35, 5.65, and 6.40 eV in the fully cured polyimide films. The peak at 6.40 eV is practically independent of the curing temperature, but the other three peaks increase with increasing curing temperature. These four peaks are due to intra- and intermolecular optical transitions. In the photoconduction quantum efficiency spectra, there are also four peaks in the fully cured polyimide films but they are located at 3.55, 4.05, 4.90, and 5.80 eV. Analysis of the photoconduction quantum efficiency spectra yields values of 4.17 and 4.37 eV as the potential barrier heights for photoemission from Au and Ag electrodes to polyimide, respectively. The quantum efficiency increases with increasing applied electric field, following closely the Onsager theory with a thermalization separation 30 angstrom in the uv region. The primary yield increases with increasing curing temperature. All experimental results are briefly discussed.