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CMOS Active Pixel Sensors

Various activities can be subsumed under the term ‘CMOS Active Pixel Sensors’. Known since the 90ties are monolithic active pixels sensors (MAPS) which are very promising candidates for experiments with moderate timing and radiation hardness requirement. On the other hand, there are hybrid pixel detectors, successful in operation at the large scale LHC experiments (ATLAS, CMS etc.) and other applications like counting X-ray imagers.

Both detector concepts, hybrid pixel detectors and MAPS, have the potential to be improved by making use of advancements in current (commercial) CMOS technology:

Pure monolithic pixels detectors could benefit from the fast charge collection by drift when using high resistivity silicon bulk material instead using of a thin, non-depleted epi-layer, providing better timing resolution and radiation hardness. These fully depleted monolithic active pixels sensors are therefore called DMAPS. In a DFG project by the same name we evaluate the technology offers from different CMOS vendors and the performance of test chips manufactured in various processes.

For hybrid pixel detectors, the planar, passive silicon sensor can be replaced by a CMOS active pixel sensor, which would have the first analog signal processing stages already implemented on the sensor layer. This concept (‘smart’ hybrid pixel detector) has the potential to allow for higher integration density which enables smaller pixel geometries by the separation of analog and digital signal processing on two silicon layers. Also the radiation hardness – a stringent requirement for the high luminosity LHC (HL-LHC) upgrades – can possibility improved over standard planar sensors. This effort is largely driven by the HL-LHC upgrade of the ATLAS pixel detector and active CMOS sensors of various types (HV-/HR-CMOS for ATLAS pixels) and produced in different CMOS technologies a currently being developed and characterized in a hybrid pixel detector configuration bonded to FE-I4 read-out chips.

cmos_pixel

Illustration of the CMOS technology advancements in order to develop advanced pixel modules by exploiting new technologies. In the ‘hybrid’ pixel concept sensor and readout chip are separated (left). The monolithic approach (top right) unifies all functions into one chip. A ‘smart hybrid’ concept (bottom right) includes analog electronics into a ‘smart sensor’ chip, which is bonded to the R/O chip.

 

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