Evaluation of a structured cesium iodide film for radiation imaging purposes

The authors describe the properties of evaporated layers of Cesium Iodide (Thallium activated) deposited on substrates that enable easy coupling to amorphous silicon pixel arrays. The CsI(Tl) layers range in thickness from 65 to 220 μm. The authors used the two-boat evaporator system to deposit CsI(Tl) layers. This system ensures the formation of the scintillator film with homogenous Tl concentration which is essential for optimizing the scintillation light emission efficiency. The Tl concentration was kept to 0.1-0.2 mole % for the highest light output. Temperature annealing can affect the microstructure as well as light output of the CsI(Tl) film. 200-300°C annealing can increase the light output by a factor of two. The amorphous silicon pixel arrays are p-i-n diodes approximately 1 μm thick with transparent electrodes to enable them to detect the scintillation light produced by X-rays incident on the CsI(Tl). Digital radiography requires a good spatial resolution. This is accomplished by making the detector pixel size less then 50 μm. The light emission from the CsI(Tl) is collimated by techniques involving the deposition process on patterned substrates. The authors have measured MTFs of greater than 12 line pairs per mm at the 10% level