Single photon counting integrated circuit operating with CdTe pixel detector

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 × 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 μV/e-. Thanks to a good quality of bump-bonding process we also managed to obtain a satisfactory X-ray radiograms.