Caliste 64, an Innovative CdTe Hard X-Ray Micro-Camera

A prototype 64 pixel miniature camera has been designed and tested for the Simbol-X hard X-ray observatory to be flown on the joint CNES-ASI space mission in 2014. This device is called Caliste 64. It is a high performance spectro-imager with event time-tagging capability, able to detect photons between 2 keV and 250 keV. Caliste 64 is the assembly of a 1 or 2 mm thick CdTe detector mounted on top of a readout module. CdTe detectors equipped with Aluminum Schottky barrier contacts are used because of their very low dark current and excellent spectroscopic performance. Front-end electronics is a stack of four IDeF-X V1.1 ASICs, arranged perpendicular to the detection plane, to read out each pixel independently. The whole camera fits in a 10$\,\times\,$10 $\,\times\,$20 ${\rm mm}^{3}$ volume and is juxtaposable on its four sides. This allows the device to be used as an elementary unit in a larger array of Caliste 64 cameras. Noise performance resulted in an ENC better than 60 electrons rms in average. The first prototype camera is tested at $-10^{\circ}{\rm C}$ with a bias of $-400~{\rm V}$. The spectrum summed across the 64 pixels results in a resolution of 697 eV FWHM at 13.9 keV and 808 eV FWHM at 59.54 keV.