CMOS Monolithic Pixel Sensors based on the Column-Drain Architecture for the HL-LHC Upgrade

TL;DR

This paper presents two CMOS monolithic pixel sensor prototypes, LF-Monopix and TJ-Monopix, designed for the HL-LHC upgrade, demonstrating high radiation tolerance, low noise, and efficient performance in a compact, low-power architecture.

Contribution

Introduction of two novel DMAPS prototypes with column-drain architecture, optimized for high radiation tolerance and low power for HL-LHC upgrades.

Findings

LF-Monopix achieves 99% detection efficiency after irradiation.

TJ-Monopix demonstrates low noise and power consumption with full depletion.

Both prototypes meet the timing and performance requirements for HL-LHC.

Abstract

Depleted Monolithic Active Pixel Sensors (DMAPS) constitute a promising low cost alternative for the outer layers of the ATLAS experiment Inner Tracker (ITk). Realizations in modern, high resistivity CMOS technologies enhance their radiation tolerance by achieving substantial depletion of the sensing volume. Two DMAPS prototypes that use the same "column-drain" readout architecture and are based on different sensor implementation concepts named LF-Monopix and TJ-Monopix have been developed for the High Luminosity upgrade of the Large Hardon Collider (HL-LHC). LF-Monopix was fabricated in the LFoundry 150 nm technology and features pixel size of $50x250~\mu m^{2}$ and large collection electrode opted for high radiation tolerance. Detection efficiency up to 99\% has been measured after irradiation to $1\cdot10^{15}~n_{eq}/cm^{2}$. TJ-Monopix is a large scale $(1x2~cm^{2})$ prototype featuring pixels of $36x40~\mu m^{2}$ size. It was fabricated in a novel TowerJazz 180 nm modified process that enables full depletion of the sensitive layer, while employing a small collection electrode that is less sensitive to crosstalk. The resulting small sensor capacitance ($<=3~fF$) is exploited by a compact, low power front end optimized to meet the 25ns timing requirement. Measurement results demonstrate the sensor performance in terms of Equivalent Noise Charge (ENC) $\approx11e^{-}$, threshold $\approx300~e^-$, threshold dispersion $\approx30~e^-$ and total power consumption lower than $120~mW/cm^2$.