# The Monopix chips: Depleted monolithic active pixel sensors with a column-drain read-out architecture for the ATLAS Inner Tracker upgrade

## TL;DR

This paper presents two prototypes of depleted monolithic CMOS active pixel sensors with column-drain read-out for the ATLAS Inner Tracker upgrade, demonstrating their performance and radiation tolerance for high-energy physics applications.

## Contribution

Introduces and compares two DMAPS prototypes with different CMOS processes and designs, advancing sensor technology for HL-LHC upgrades.

## Key findings

- Both chips are operational after thinning and back-side processing.
- Measurements show acceptable noise, threshold dispersion, and efficiency.
- Prototypes withstand neutron irradiation up to 1×10^{15} n_{eq}/cm^{2}."

## Abstract

Two different depleted monolithic CMOS active pixel sensor (DMAPS) prototypes with a fully synchronous column-drain read-out architecture were designed and tested: LF-Monopix and TJ-Monopix. These chips are part of a R&D effort towards a suitable implementation of a CMOS DMAPS for the HL-LHC ATLAS Inner Tracker. LF-Monopix was developed using a 150nm CMOS process on a highly resistive substrate (>2 k$\Omega\,$cm), while TJ-Monopix was fabricated using a modified 180 nm CMOS process with a 1 k$\Omega\,$cm epi-layer for depletion. The chips differ in their front-end design, biasing scheme, pixel pitch, dimensions of the collecting electrode relative to the pixel size (large and small electrode design, respectively) and the placement of read-out electronics within such electrode. Both chips were operational after thinning down to 100 $\mathrm{\mu}$m and additional back-side processing in LF-Monopix for total bulk depletion. The results in this work include measurements of their leakage current, noise, threshold dispersion, response to minimum ionizing particles and efficiency in test beam campaigns. In addition, the outcome from measurements after irradiation with neutrons up to a dose of $1\times10^{15}\,\mathrm{n_{eq} / cm}^{2}$ and its implications for future designs are discussed.