A basic component for ISGRI, the CdTe gamma camera on board the INTEGRAL satellite

A basic component, called Polycell, has been developed for the ISGRI (INTEGRAL Soft Gamma Ray Imager) CdTe camera on board the INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) satellite. Operating at room temperature, it covers the 20 keV -1 MeV energy range. It features a sub-ensemble of 16 CdTe detectors and their associated front end electronics. This electronics is based on 4-channel analog-digital ASICs. Their analog part features a low noise preamplifier, allowing a threshold below 20 keV and a pulse rise-time measurement which permits a charge loss correction. The digital part ensures the internal acquisition timing sequence as well as the dialogue with external electronics. Two versions of the ISGRI ASIC have been developed in a collaboration of two CEA microelectronics teams from CEA/DTA/LETI/DSYS and CEA/DSM/DAPNIA/SEI, respectively on a standard CMOS AMS process hardened against radiation by lay-out, and on a Silicon On Insulator process (DMILL MHS), the latter being latch-up free. This paper presents the ASIC and polycell architecture as well as experimental results obtained with polycells equipped with AMS ASICs.