Monolithic pixel sensor development in a novel 180nm CMOS process for the ATLAS inner tracker upgrade

The high luminosity LHC upgrade sets unprecedented constraints in terms of radiation tolerance and particle hit rate. To comply with these challenging requirements, a new full scale depleted monolithic active pixel sensor chip with pixel pitch equal to 36 $\times$ 40 $\mu$m${}^2$, called TJ-Monopix, has been developed for the outer layers of the ATLAS inner tracking detector. While inheriting the advantages of monolithic implementations, it combines high analog performance with high radiation tolerance. The key to its realization is a novel modification of the TowerJazz 180nm CMOS process, that enables full depletion of the sensitive volume, yielding charge collection efficiency above 95% even after a dose of 10${}^{15}$ n${}_{eq}$/cm${}^2$ (NIEL). Below 3fF sensor capacitance is made possible by employing a small size collection electrode. A compact, low power analog front end, optimized for fast timing and linearity is used. The simulated time walk is less than 25 ns and the equivalent noise charge is lower than 15e${}^{-}$, while the analog power consumption is only 70 mW/cm${}^2$. Hit timing and analog ToT information is read out by a synchronous column-drain architecture. First measurement results are expected during the first quarter of 2018.