X-ray tests of a Pixel Array Detector for coherent x-ray imaging at the Linac Coherent Light Source

Abstract

Test results are presented of a pixel array detector (PAD)developed for x-ray imaging at the Stanford Linear Coherent LightSource (LCLS). The basic module of the PAD consists of twobump-bonded chips: a reverse-biased silicon diode chip of 185 × 194 pixels, each of which is coupled by bump-bonds to acharge integrating CMOS ASIC with digitization in each pixel. TheLCLS experiment requires a high signal-to-noise ratio for detectionof single 8 keV x-rays, a pixel full-well exceeding1,000 8 keV x-rays, a frame-rate of 120 Hz, and the ability to handle the arrival of thousands ofx-rays per pixel in tens of femtoseconds. Measurements haveverified a pixel full-well value of 2,700 8 keVx-rays. Single 8 keV photon detection has been shownwith a signal-to-noise ratio of >6. Line-spread responsemeasurements confirmed charge spreading to be limited to nearestneighbor pixels. Modules still functioned after dosages up to 75 Mrad(Si) at the detector face. Work is proceeding toincorporate an array of modules into a large-area detector.