Characterization of the DECAL sensor - a CMOS MAPS prototype for digital electromagnetic calorimetry and tracking

The DECAL sensor is a fully depleted monolithic active pixel sensor (DMAPS) prototype for digital electromagnetic calorimetry and tracking. Its 64×64 pixels with a pitch of 55 μm are fabricated in the modified TowerJazz 180nm CMOS imaging process using a 25 μm epitaxial silicon layer. The sensor readout at 40MHz is configurable in counting the sum of particles passing through the pixels grouped in either strips or pads. Sensor tests with sources of americium-241 and strontium-90 as well as with an X-ray tube are presented. The uniformity of the pixels is shown, allowing the summation of counts across all pixels. A characterization of the sensor is obtained through X-rays in the energy range of 4 to 60 keV. Two stand-alone energy calibration methods are developed and agree with each other. The signal height per photon energy is obtained to be a = 5.54 ± 0.37mV/keV which corresponds to a conversion gain of c_g = 19.95 ± 1.32 μV/e−. The relative energy resolution for photon absorption yields σ_E/E = 12.2 ± 3.5%. The absolute counts observed with the DECAL sensor agree with expectations and substantiate the assumption of a fully depleted epitax. Building upon the sensor characterization described in this thesis, further tests are proposed that could pave the way for the design of a multi-layered digital calorimeter prototype.