The basic component of the ISGRI CdTe γ-ray camera for space telescope IBIS on board the INTEGRAL satellite

The gamma-ray imager telescope IBIS, on board the INTEGRAL satellite, features a coded mask aperture and two detector arrays. The first detector array (ISGRI) is an assembly of 16 384 CdTe detectors (4 x 4 mm(2) large, 2 mm thick) operating at room temperature under 100 V bias. ISGRI covers the lower part (20 keV-1 MeV) of the IBIS energy range (20 keV-10 MeV). The polycell is the basic component of the ISGRI detector array. It is made of 16 CdTe pixels and their front-end electronics. In order to improve the response of the instrument, a charge loss correction based on the charge-drift time is necessary. Therefore, the front-end electronics performs the rise-time measurement in addition to the standard pulse height measure. On the other hand, the necessarily tight packaging and the limited available power requires the use of ASICs. These 4-channel analog-digital ASICs should be radiation resistant either through the use of a latch up free technology or by applying an appropriate layout design. The optimal operating temperature (around 0 degrees C)is ensured under vacuum conditions by radiative cooling. This paper describes the ISGRI design with particular emphasis bn the ASICs and polycells, and reports preliminary performance measurements. (C) 1999 Elsevier Science B.V. All rights reserved.