Avalanche detector with field emitter readout

We are investigating a new concept of flat-panel x-ray imaging detector with avalanche gain which is called scintillator avalanche photo-conductor with high resolution emitter readout (SAPHIRE). It is made by optically coupling a needle structured scintillator (Csl) to a thin uniform layer (0.5-25 mum) of amorphous selenium (a-Se) photoconductor. The final image is read out by a 2D field emitter array (FEA). Avalanche gain can boost the performance for low dose application and the FEA can potentially be made with small pixel size (e.g. 50 mum). The spatial resolution was investigated and it was found that the lateral spread of electron beams emitted from the FE tips is the dominant source of image blur. To reduce the spread, three different electron-optics designs were simulated including mesh electrode (ME), magnetic focus (B focus) and electrostatic focus (E focus) designs. Both B and E focus methods provide better spatial resolution compared with ME, however the blur with B focus is signal-dependent, which is not desirable. Hence E focus is ideal for producing high resolution images with good spatial uniformity.