HEXID: A finely pixelated readout ASIC for future hard X-ray space missions

This work presents the Hyper-Spectral X-ray Imaging Device (HEXID) readout integrated circuit for future Hard X-ray space telescopes missions. Following the success of the NuSTAR (Nuclear Spectroscopic Telescope Array) mission (launched in 2012), follow-up missions, such as the proposed: HEX-P, BEST, and FORCE, could perform a deeper black hole census providing a more refined measurements thanks to recent hard X-ray mirror technologies, where mirrors, made of monolithic silicon segments or shells, demonstrated the feasibility of making hard X-ray mirrors with angular resolutions of 5-10 arc-seconds Half Power Diameter (HPD) compared to the NuSTAR’s 1 arcminute HPD. Such a high angular resolution requires matched detectors (higher degree of segmentation) to fully benefit from the achievable improved spatial resolution. In this framework, a first prototype of the HEXID ASIC family, named HEXID65P1, has been developed and characterized. This prototype features a novel pixelated front-end tailored to reading out a finely segmented CZT sensor with a 150 um pixel pitch in a hexagonal arrangement. The prototype implements an array of 8 by 8 pixels and it employs the Event-based readout EDWARD. This readout ASIC is capable of processing the photon-generated charge over a large dynamic range (from 2 keV up to 180 keV), while keeping a low input noise (ENC < 20 e-) up to 18 keV. This work presents the characterization results of the spectroscopic performances of the ASIC in terms of noise, linear response over the defined energy range and its sparsified readout. Moreover, the plan for its future expansion into a larger detection area will be detailed.