ENHANCED COLUMNAR STRUCTURE IN CSI LAYER BY SUBSTRATE PATTERNING

Abstract

Columnar structure in evaporated CsI layers can be controlled by patterning substrates as well as varying evaporation conditions. Mesh-patterned substrates with various dimensions were created by spin-coating polyimide on glass or amorphous silicon substrates and defining patterns with standard photolithography technique. CsI(TI) layers 200-1000 mum were evaporated. Scintillation properties of these evaporated layers, such as light yield and speed, were equivalent to those of the source materials. Spatial resolution of X-ray detectors consisting of these layers and a linear array of Si photodiodes was evaluated by exposing them to a 25 mum narrow beam of X-ray. The results obtained with 200 mum thick CsI layers coupled to a linear photodiode array with 20 dots/mm resolution showed that the spatial resolution of CsI(TI) evaporated on patterned substrates was about 75 mum FWHM, whereas that of CsI(TI) on flat substrates was about 220 mum FWHM. Micrographs taken by SEM revealed that these layers retained the well-defined columnar struature originating from substrate patterns. Adhesion and light transmission of CsI(TI) were also improved by patterning the substrate.