ABSTRACT
X-rays interact inelastically with matter in three ways: photoelectric, Compton, and pair production. These energy-loss mechanisms all eventually produce thermalized electron–hole pairs in the conduction and valence bands of the semiconductors. Cadmium telluride (CdTe) and cadmium zinc telluride (CZT) are currently the most favored crystals for this application. Area-array detectors built with CdTe or CZT use typically 1–10 mm thick material, depending on the energy of the incident photons and the efficiency required. Detectors with small pixels are required due to their imaging resolution, but also because the small-pixel effect allows single carrier-type readout due to the high weighting field around the pixels. Clearly, for large-area imaging detectors with many imaging pixels a high level of segmented multichannel readout is needed. Pixel detectors require a direct connection from the pads on the sensor material to the bond pads on the Application-Specific Integrated Circuit (ASIC). Bump bonding is used to connect the detector pixels to the ASICs.
