Single Photon Counting Integrated Circuit Operating with CdTe Pixel Detector

P. Maj, P. Gryboś, P. Kmon, R. Szczygieł (AGH Univ. of Science and Techn., Poland)

CdTe detectors are very good candidate for medical X-ray imaging applications, because of their relatively high atomic number and significant progress in their fabrication process during the last decade. For this reason we built a hybrid pixel detector based on CdTe sensor and the UFXC32k integrated circuit designed in CMOS 130 nm process and operating in a single photon counting mode. The core of the IC is the matrix of 128 x 256 square shaped pixels of 75 µm pitch. Each pixel contains a charge sensitive amplifier, a shaper, a discriminator, correction circuits and two 14-bit counters. The UFXC32k chip was bump-bonded to a pixel CdTe sensor and characterized using X-ray radiation. The measured equivalent noise charge is equal to 125 e- rms for the gain of 33 uV/e-. Thanks to a good quality of bump-bonding process we also managed to obtain a satisfactory X-ray radiograms.