Seamless tiling of amorphous silicon photodiode-TFT arrays for very large area X-ray image sensors

We propose a method for producing a truly seamless tiled image sensor from four identical subarrays, such that the resulting tiled image sensor has no missing pixels, Four standard amorphous silicon photodiode-TFT (thin film transistor) arrays are cut parallel to the bus-bars, in the space between t he bus-bar and the preceding pixel electrode. The cut is done in such a way that it is adjacent to the pixel electrode on the active plate. The four s ubarrays are then rotated by 90 degrees, with respect to their neighbors, a nd butted together. In this way, the seam between each tile has no adjacent bus-bar, and it is possible to reproduce the pixel pitch between neighbori ng tiles, with an acceptable alignment tolerance of the tiles. We have demo nstrated the feasibility of the method, with the aid of a small prototype, based on a 192 x 192 pixel array, with a 200-mu m pitch. Some image process ing is necessary to rotate the images back for display on a conventional di splay monitor. This can cause artefacts, in some fast moving scenes, in whi ch case an alternative scheme, which uses two mirror image arrays, each rot ated by 180 degrees, can be used. However. for static X-ray images and most images in dynamic medical X-ray applications this is not necessary and we can obtain good quality seamless images, free from any significant artefact s.