3DX: A Micromachined Silicon Crystallographic Detector

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DESCRIPTION (provided by applicant): We propose to continue development of the "3DX" silicon pixel array detector, in which diffracted X rays are captured directly in thick, high-resistivity silicon, micromachined by inductively-coupled plasma etching. Each pixel is 150x150mu m with one n- and one p-type electrode, and it is bonded with a conducting (indium) bump to a corresponding pixel of a CMOS readout chip, located behind the sensor. Each silicon sensor is an array of 64x64 pixels (total size: 9.6mmx9.6mm). In our design the sensor wafer is active to the very edge. Overlapping arrays of these sensors therefore have no dead gaps. We have now fabricated many hundreds of sensors, tested many of them, and they work. We have now also learned the art of bump- bonding, and have succeeded in bonding our sensor to our readout chip without bonding defects. We have designed, fabricated, debugged, tested, and characterized the CMOS readout chip, which is protected from X rays behind the sensor on three sides. The readout chip works, but we need to correct minor bugs in the design, and expand it to full size, during the next project period. Our detector discriminates individual X rays yet responds linearly to radiation levels approaching 400,000/s/pixel. Its point response lies within a single pixel. It reads out continuously with a 64mu s period. During the next stage of the project we will fabricate many full-scale sensor/ASIC module sandwiches, design and make a field-programmable gate array (FPGA) to control the module and interface it to a host computer, and design and implement an integrated system that includes controls software. In year 3 we will make our first practical system: a small array designed specifically for high-speed time-resolved small-angle X-ray diffraction of biological samples. In years 4-5 we will make a large detector system for protein crystallography that will incorporate between 900 -1,000 modules and cover an area of 30cm x 30cm.