Characterization of a prototype pixel array detector (PAD) for use in microsecond framing time-resolved x-ray diffraction studies

A 4 by 4 pixel array device has been designed and built as a prototype for a high-speed two-dimensional x-ray imaging detector. This detector is a two-tier device, with an x-ray sensitive photo-diode array bump-bonded to a 1.2 micrometer CMOS analog integrated circuit. Each 150 micrometer square pixel of the detective layer is matched to a corresponding section of the electronics. Each pixel of the electronics is capable of integrating the signal from the diode for the desired framing time, storing the result in one of eight storage capacitors, and sequentially outputting the stored value to an on-chip buffering op-amp. Tests of the electronics have demonstrated a full-well (per pixel, per frame) of over 10,500 12 keV x-rays with an electronics noise level corresponding to less than 2.8 12keV x-rays. Speed tests indicate the ability to integrate to the full-well within 2 microseconds (an average pixel 'count-rate' of 5.2 GHz). We present detailed characterizations of the performance of this initial device, including an analysis of noise, stability, linearity and point-spread. In addition, we will discuss plans for large-scale integration towards the goal of a 1024 by 1024 pixel detector.