One common approach with digital X-ray imaging using amorphous silicon is to integrate a uniform phosphor layer for conversion of X-ray to visible photons onto an array of image sensor pixels. Each pixel in the array consists of an a-Si:H photodiode (PD) and an a-Si:H thin film transistor (TFT)  (Fig. 1). The X-ray conversion efficiency of phosphor layer, which increases with thickness, is limited because of crosstalk among adjacent pixels. This paper presents a design incorporating a new SU-8 microstructure that alleviates the crosstalk issue.
Hydrogenated amorphous silicon is known for its large area imaging applications because of its high photoconductivity and high absorption coefficient in the visible light range. This material can be also applied to X-ray imaging when coupled with a uniform scintillation (e.g. Gd2O2S phosphor) film integrated on top of a 2-D detection array. A thick phosphor layer is the prerequisite for high X-ray conversion efficiency. In reality, however, there may be significant crosstalk between adjacent pixels thus undermining spatial resolution. This paper introduces a high aspect ratio microstructure with the new photoresist SU-8 epoxy, which limits the phosphor to regions above the photodiodes. The differences between the above scheme and that of a continuous phosphor layer are compared in terms of the absorption efficiency, the conversion efficiency, and the modulation transfer function (MTF). The measurements are carried out in a medical testing environment with X-ray source voltages of 40-120kVp. The results show a great improvement in the spatial resolution.