Fabrication of Gd2O2S:Tb based phosphor films coupled with photodetectors for x-ray imaging applications

The Gd2O2S:Tb based phosphor coupled with photodetectors has been widely used in digital x-ray imaging applications. The key issues associated with phosphor film are x-ray absorption and conversion efficiency, spatial resolution. deposition uniformity, and integration with the imaging array. In this article we report on experimental studies of the phosphor film synthesis, deposition, and characterization. A composite material, consisting of Gd2O2S:Tb, polyvinyl alcohol, and water coupled with a small amount of additives, is synthesized as a phosphor paste. The parameters controlling film quality include individual component concentrations, grain sizes of phosphor, and viscosity of the solution. A sedimentation technique is used to deposit the phosphor directly on the imaging array. A number of phosphor films have been synthesized with the particle sizes ranging from 2.5 to 25 mum and film thickness ranging from 85 to 1100 mum. and measurement results of x-ray conversion efficiency and spatial resolution in terms of modulation transfer function are presented. A new technology for phosphor patterning is proposed to seamlessly integrate the phosphor with the photodetectors by using negative photoresist SU-8 and preliminary results are presented. (C) 2002 American Vacuum Society.