Development of the monolithic "MALTA" CMOS sensor for the ATLAS ITK outer pixel layer
2019 May 21
2019 July 25
Depleted Monolithic Active Pixel Sensors (DMAPS) are an option for the outermost layer of the upgraded ATLAS ITk Pixel Detector at the CERN LHC. Two large size DMAPS named TJ MALTA and TJ Monopix were produced in the TowerJazz 180 nm CMOS imaging process in a small collection electrode design. The MALTA chip combines a low power front end with a novel matrix readout design to achieve a low power consumption of <80 mW/cm2. Threshold values of 250 e- with a dispersion of 30 e- and an ENC of < 10e- can be achieved before irradiation which is consistent with the results from TJ Monopix. Test beam measurements indicate an average efficiency of 96% before irradiation, with the inefficiency mainly due to problems with the slow control of the chip. After neutron irradiation to 1e15 neq/cm2 the efficiency in pixel centres is retained, but it is reduced in pixel corners. A proposal to improve charge collection in the corners is backed up by TCAD simulations and promises an improved performance with small modifications.