3DX: an X-ray pixel array detector with active edges

We are developing a prototype X-ray detection system that should be ideal for many types of synchrotron science. X-rays are captured directly in thick, high-resistivity, single-crystal, silicon pixel sensors. Unlike other X-ray detectors, which have a substantial dead area around their borders, these have "active edges"-edges formed from electrodes in the third dimension, perpendicular to the top and bottom surfaces, with full sensitivity to within a micron of the physical border. Each sensor is 0.96 mm×0.96 mm, having a 64×64 two-dimensional array of 150 μm pixels. Behind each sensor, a custom CMOS readout chip is bump-bonded to the sensor. It provides high-speed (64μs/full-array) readout of each pixel, with a dead time for each row, during pixel reset, of 1 μs. On three edges, it lies completely hidden behind the sensor. A 3 mm wide region on the remaining edge of each CMOS chip contains readout circuits and connections. Here it protrudes beyond the sensor edge, but is covered by the active region of a neighboring sensor module in an array similar to that of shingles on a roof. Sensor units can be easily arrayed to cover large areas. The readout chip has 128 ADCs and, for each pixel, a charge amplifier. To save fabrication costs, the prototype readout has just 8×64 pixels. Using pulse heights, we should be able to combine signals when X-rays share charge between adjacent pixels. We have already made accurate quantum-counts of 0 to 7 X-ray events/pixel during each 64 μs readout cycle.