X-ray imaging using a 320 x 240 hybrid GaAs pixel detector

We present room temperature measurements on 200 mu m thick GaAs pixel detec tors, which were hybridized to silicon readout circuits. The whole detector array contains 320 x 240 square shaped pixel with a pitch of 38 mu m and i s based on semi-insulating liquid-encapsulated Czochralski (LEC) GaAs mater ial. After fabricating and dicing, the detector chips were indium bump flip chip bonded to CMOS readout circuits based on charge integration and final ly evaluated. This readout chip was originally designed for the readout of flip chip bonded infrared detectors, but appears to be suitable for X-ray a pplications as well. A bias voltage between 50 V and 100 V was sufficient t o operate the detector at room temperature. The detector array did respond to x-ray radiation by an increase in current due to production of electron hole pairs by the ionization processes. Images of various objects and slit patterns were acquired by using a standard X-ray source for dental imaging. The new X-ray hybrid detector was analyzed with respect to its imaging pro perties. Due to the high absorption coefficient for X-rays in GaAs and the small pixel size, the sensor shows a high modulation transfer function up t o the Nyquist frequency.