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VERTEX 2021 - 30th International Workshop on Vertex Detectors. September 27th–30th, 2021, Online from Oxford University, UK; International audience; Depleted Monolithic Active Pixel Sensors (DMAPS) are monolithic pixel detectors with high-resistivity substrates designed for use in high-rate and high-radiation environments. They are produced in commercial CMOS processes, resulting in relatively low production costs and short turnaround times, and offer a low material budget. LF-Monopix1 and TJ-Monopix1 are large DMAPS prototypes produced in 150 nm LFoundry and 180 nm TowerJazz technology, respectively, that follow two different design concepts regarding the charge collection electrode. Prototypes of both development lines have been extensively tested and characterized over the last years. The second-generation Monopix prototypes, Monopix2, were recently produced. They were designed to address the shortcomings of their predecessors, in particular related to radiation hardness and cross talk, and further improve upon their performance. The latest measurements with LF-Monopix1 and TJ-Monopix1 concerning hit efficiency, depletion, and radiation hardness as well as the initial test results of the new Monopix2 prototypes are presented

International audience; The monolithic CMOS pixel sensor for charged particle tracking has already become a mainstream technology in high energy particle physics (HEP) experiments. During the last decade, progressive improvements have been made for CMOS pixels to deal with the high-radiation and high-rate environments expected, for example, at the future High Luminosity LHC. One of the key ingredients of these improvements is to achieve a fully depleted sensitive layer, where the charge collection is guided by strong drift field lines. CMOS sensors incorporating such charge collection property, often referred to as DMAPS (Depleted Monolithic Active Pixel Sensor), have been recently demonstrated in several large-scale monolithic prototypes with integrated fast readout architectures. This contribution summarizes the recent progress made on the large-scale DMPAS development, focusing on two demonstrator chips designed in the LFoundry 150 nm and the TowerJazz 150 nm CMOS processes, namely LF-Monopix1 and TJ-Monopix1.

This paper outlines the results of investigations into the effects of radiation damage in the mini-MALTA depleted monolithic pixel sensor prototype. Measurements were carried out at Diamond Light Source using a micro-focus X-ray beam, which scanned across the surface of the device in 2 μ m steps. This allowed the in-pixel photon response to be measured directly with high statistics. Three pixel design variations were considered: one with the standard continuous n − layer layout and front-end, and extra deep p-well and n − gap designs with a modified front-end. Five chips were measured: one unirradiated, one neutron irradiated, and three proton irradiated. The standard design showed a decrease of 12% in pixel response after irradiation to 1e15 n eq ∕ cm 2 . For the two new designs the pixel response did not decrease significantly after irradiation. A decrease of pixel response at high biasing voltages was observed. The charge sharing in the chip was quantified and found to be in agreement with expectations.

Journal of Instrumentation 15(02), P02005 (2020). doi:10.1088/1748-0221/15/02/P02005, Depleted Monolithic Active Pixel Sensor (DMAPS) prototypes developed in the TowerJazz 180 nm CMOS imaging process have been designed in the context of the ATLAS upgrade Phase-II at the HL-LHC. The pixel sensors are characterized by a small collection electrode (3 μm) to minimize capacitance, a small pixel size (36.4× 36.4 μm$^2$), and are produced on high resistivity epitaxial p-type silicon. The design targets a radiation hardness of 1×10$^{15}$ 1 MeV n$_{eq}$/cm$^2$, compatible with the outermost layer of the ATLAS ITK Pixel detector. This paper presents the results from characterization in particle beam tests of the Mini-MALTA prototype that implements a mask change or an additional implant to address the inefficiencies on the pixel edges. Results show full efficiency after a dose of 1×10$^{15}$ 1 MeV n$_{eq}$/cm$^2$., Published by Inst. of Physics, London

The upgrade of the tracking detectors for the High Luminosity-LHC (HL-LHC) requires the development of novel radiation hard silicon sensors. The development of Depleted Monolithic Active Pixel Sensors targets the replacement of hybrid pixel detectors with radiation hard monolithic CMOS sensors. We designed, manufactured and tested radiation hard monolithic CMOS sensors in the TowerJazz 180 nm CMOS imaging technology with small electrodes pixel designs. These designs can achieve pixel pitches well below current hybrid pixel sensors (typically 50 × 50 μ m ) for improved spatial resolution. Monolithic sensors in our design allow to reduce multiple scattering by thinning to a total silicon thickness of only 50 μ m . Furthermore monolithic CMOS sensors can substantially reduce detector costs. These well-known advantages of CMOS sensor for performance and costs can only be exploited in pp-collisions at HL-LHC if the DMAPS sensors are designed to be radiation hard, capable of high hit rates and have a fast signal response to satisfy the 25 ns bunch crossing structure of LHC. Through the development of the MALTA and Mini-MALTA sensors we show the necessary steps to achieve radiation hardness at 1 0 15 n e q /cm2 for DMAPS with small electrode designs. The sensors combine high granularity (pitch 36.4x 36 . 4 μ m 2), low detector capacitance ( 5fF/pixel) of the charge collection electrode ( 3 μ m ), low noise (ENC ≈ 10 e − ) and low power operation (1 μ W/pixel) with a fast signal response (25 ns bunch crossing). The sensors feature arrays of 512 × 512 (MALTA) and 16 × 64 (Mini-MALTA) pixels. To cope with high hit rates expected at HL-LHC ( > 200 MHz/cm2) we have implemented a novel high-speed asynchronous readout architecture. The paper summarises the optimisation of the pixel design to achieve radiation hard pixel designs with full efficiency after irradiation at > 98% after 1 0 15 n e q /cm2).

The MALTA monolithic silicon pixel sensors have been used to study dicing and thinning of monolithic silicon pixel detectors for large area and low mass modules. Dicing as close as possible to the active circuitry will allow to build modules with very narrow inactive regions between the sensors. Inactive edge regions of less than 5 μ m to the electronic circuitry could be achieved for 100 μ m thick sensors. The MALTA chip (Cardella et al., 2019) also offers the possibility to transfer data and power directly from chip to chip. Tests have been carried out connecting two MALTA chips directly using ultrasonic wedge wire bonding. Results from lab tests show that the data accumulated in one chip can be transferred via the second chip to the readout system, without the need of a flexible circuit to route the signals. The concept of chip to chip data and power transfer to achieve low mass modules has also been studied on prototype wafers using Cu-stud interconnection bridges. First results are presented, outlining technical challenges and possible future steps to achieve a low mass large area monolithic pixel sensor module.

The ATLAS collaboration is currently investigating CMOS monolithic pixel sensors for the outermost layer of the upgrade of its Inner Tracker (ITk). For this application, two large scale prototypes featuring small collection electrode have been produced in a radiation-hard process modification of a standard 0.18 μm CMOS imaging technology: the MALTA, with a novel asynchronous readout, and the TJ MONOPIX, based on the well established "column-drain" architecture. The MALTA chip is the first full-scale prototype suitable for the development of a monolithic module for the ITk. It features a fast and low-power front-end, an architecture designed to cope with an hit-rate up to 2 MHz/mm2 without clock distribution over the matrix, hence reducing total power consumption, and LVDS drivers. Laboratory tests confirmed the performance of the asynchronous architecture expected from simulations. Extensive testbeam measurements have proved an average detection efficiency of 96% before irradiation at a threshold of ~230 e− with dispersion of ~36 e− and ENC lower than 10 e−. A non fully functional pixel masking scheme, forces operation at relatively high thresholds, causing inefficiency. A severe degradation of efficiency has been measured after neutron irradiation at a fluence 1 × 1015 1 MeV neq/cm2. Consistent results have been produced with the TJ MONOPIX. A correlation with inefficiency plots and pixel layout has triggered TCAD simulations, ending up to two possible solutions, implemented in a new prototype, the MiniMALTA.

The ATLAS experiment is planning a major upgrade of its tracking detectors, both strip and pixel, to take full advantage of the High Luminosity LHC. A novel Monolithic Active Pixel Sensor based on 180 nm TowerJazz CMOS imaging technology, dubbed MALTA, has been designed to meet the radiation hardness requirements (1.5x10$^{15}$ 1 MeV $n_{eq}$/cm$^{2}$) of the outer barrel layers of the ITk Pixel detector. MALTA combines low noise (ENC

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., Comment: Proceedings of the PIXEL 2018 Workshop

This contribution outlines the results of investigations into the effects of radiation damage in the mini-MALTA depleted monolithic pixel sensor prototype using a micro-focus X-ray beam at Diamond Light Source. The in-pixel photon response was measured for three different pixel design variations: one with the standard continuous $\mathrm{n^-}$ layer layout and standard front-end, and extra deep p-well and $\mathrm{n^-}$ gap designs with a modified front-end. The standard design showed a decrease of 12\% in pixel response after irradiation to 1e15 $\mathrm{n_{eq}/cm^2}$. The two new designs did not show a significant decrease in pixel response after irradiation.

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 a 180nm CMOS imaging process in a small col- lection electrode design. The TJ MALTA chip combines a low power front end with a novel matrix readout design to achieve a low power consumption of < 80mW/cm2. Threshold values of ≈ 250 e− with a dispersion of ≈ 30 e− and an ENC of < 10 e− can be achieved before irradia- tion 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 a non fully func- tional masking scheme, forcing operation at relatively high thresholds. 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.

LF-Monopix1 and TJ-Monopix1 are depleted monolithic active pixel sensors (DMAPS) in 150 nm LFoundry and 180 nm TowerJazz CMOS technologies respectively. They are designed for usage in high-rate and high-radiation environments such as the ATLAS Inner Tracker at the High-Luminosity Large Hadron Collider (HL-LHC). Both chips are read out using a column-drain readout architecture. LF-Monopix1 follows a design with large charge collection electrode where readout electronics are placed inside. Generally, this offers a homogeneous electrical field in the sensor and short drift distances. TJ-Monopix1 employs a small charge collection electrode with readout electronics separated from the electrode and an additional n-type implant to achieve full depletion of the sensitive volume. This approach offers a low sensor capacitance and therefore low noise and is typically implemented with small pixel size. Both detectors have been characterized before and after irradiation using lab tests and particle beams., 7 pages, 8 figures. Proceedings of the 12th International "Hiroshima" Symposium on the Development and Application of Semiconductor Tracking Detectors

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 Hadron Collider (HL-LHC). 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 ($

Radiation hard silicon sensors are required for the upgrade of the ATLAS tracking detector for the High- Luminosity Large Hadron Collider (HL-LHC) at CERN. A process modification in a standard 0.18 μm CMOS imaging technology combines small, low-capacitance electrodes (∼2 fF for the sensor) with a fully depleted active sensor volume. This results in a radiation hardness promising to meet the requirements of the ATLAS ITk outer pixel layers (1.5 × 1015 neq /cm2 ), and allows to achieve a high signal-to-noise ratio and fast signal response, as required by the HL-LHC 25 ns bunch crossing structure. The radiation hardness of the charge collection to Non-Ionizing Energy Loss (NIEL) has been previously characterised on pro- totypes for different pixel sensor cell designs. The encouraging results enabled the design of full-size monolithic CMOS sensors for the ATLAS ITk outermost pixel layer, which comprises ∼1.8 m2 of pixel sensor active area. In the MALTA sensor, we implement a fast, low-power analogue front-end together with a novel high-speed matrix readout architecture capable of meeting the challenging hit- rate requirements of up to 2 MHz/mm2 in the outer layers of the ITk pixel tracker. The front- end was optimized for the low sensor capacitance to achieve low noise (ENC < 20 e-) and low power operation (< 1 μW/pixel), with timing that meets the 25 ns requirement. The small size (∼2 μm) of the collection electrode also allows better shielding to prevent crosstalk from the full swing digital signals in the 36.4×36.4 μm2 pixel. MALTA features a 512×512 pixel matrix with a fully asynchronous readout architecture, without clock distribution over the matrix. This approach combines low digital power consumption with fast signal response and high hit-rate capability. This paper describes the implementation of this novel depleted monolithic sensor based on a low-capacitance analogue design with asynchronous readout, together with first test results from lab tests, radioactive source tests and X-ray measurements.

The upgrade of the ATLAS tracking detector (ITk) for the High-Luminosity Large Hadron Collider at CERN requires the development of novel radiation hard silicon sensor technologies. Latest developments in CMOS sensor processing offer the possibility of combining high-resistivity substrates with on-chip high-voltage biasing to achieve a large depleted active sensor volume. We have characterised depleted monolithic active pixel sensors (DMAPS), which were produced in a novel modified imaging process implemented in the TowerJazz 180 nm CMOS process in the framework of the monolithic sensor development for the ALICE experiment. Sensors fabricated in this modified process feature full depletion of the sensitive layer, a sensor capacitance of only a few fF and radiation tolerance up to $10^{15} n_{\mathrm{eq}}/ \mathrm{cm}^2$. This paper summarises the measurements of charge collection properties in beam tests and in the laboratory using radioactive sources and edge TCT. The results of these measurements show significantly improved radiation hardness obtained for sensors manufactured using the modified process. This has opened the way to the design of two large scale demonstrators for the ATLAS ITk. To achieve a design compatible with the requirements of the outer pixel layers of the tracker, a charge sensitive front-end taking 500 nA from a 1.8 V supply is combined with a fast digital readout architecture. The low-power front-end with a 25 ns time resolution exploits the low sensor capacitance to reduce noise and analogue power, while the implemented readout architectures minimise power by reducing the digital activity.

Depleted monolithic active pixel sensors (DMAPS), which exploit high voltage and/or high resistivity add-ons of modern CMOS technologies to achieve substantial depletion in the sensing volume, have proven to have high radiation tolerance towards the requirements of ATLAS in the high-luminosity LHC era. Depleted fully monolithic CMOS pixels with fast readout architectures are currently being developed as promising candidates for the outer pixel layers of the future ATLAS Inner Tracker, which will be installed during the phase II upgrade of ATLAS around year 2025. In this work, two DMAPS prototype designs, named LF-MonoPix and TJ-MonoPix, are presented. LF-MonoPix was designed and fabricated in the LFoundry 150~nm CMOS technology, and TJ-MonoPix has been designed in the TowerJazz 180~nm CMOS technology. Both chips employ the same readout architecture, i.e. the column drain architecture, whereas different sensor implementation concepts are pursued. The design of the two prototypes will be described. First measurement results for LF-MonoPix will also be shown., International Workshop on Radiation Imaging Detectors 2017

International audience; The upgrade of the ATLAS tracking detector for the High-Luminosity Large Hadron Collider at CERN requires the development of novel radiation hard silicon sensor technologies.The MALTA Monolithic Active Pixel Sensor prototypes have been developed with the 180 nm TowerJazz CMOS imaging technology. This combines the engineering of high-resistivity sub- strates with on-chip high-voltage biasing to achieve a large depleted active sensor volumes, to meet the radiation hardness requirements of the outer barrel layers of the ATLAS ITK Pixel de- tector (1.5× 10$^{15}$ 1 MeV n$_{eq}$/cm$^{2}$ and 80 MRad TID). MALTA combines low noise (ENC < 20 e$^{-}$) and low power operation (1 uW / pixel) with a fast signal response (25 ns bunch crossing) in small pixel size (36.4 $\times$ 36.4 $\mu m^{2}$), and a small collection electrode (3$\mu$m), with a novel high- speed asynchronous read out architecture to cope with the high hit rates expected at HL-LHC. The latest developments, embedded in so-called Mini-MALTA chip, address the issues observed in previous designs to meet the desired radiation hardness requirements. This contribution will summarize the design and recent improvements of this technology, together with the measure- ments of analog and digital performance, as obtained in test beams and lab and radioactive source tests.

A pseudo-LVDS driver has been designed in a 180 nm technology for operation up to 5 Gb/s. It contains parallel main driver units based on an H-bridge circuit steering a current on an external load. The number of active units is adjustable, to reduce switching capacitance and static current, and hence power consumption, if a smaller current swing can be tolerated. Pre-emphasis is applied with a capacitively coupled charge-injection circuit. In the nominal condition with a steering current of 4 mA over a 100 $\Omega$ termination resistor, it consumes 30 mW from a 1.8 V supply.

MALTA is a full scale monolithic pixel detector implemented in TowerJazz 180 nm CMOS technology. The small pixel electrode allowed for the implementation of a fast, low noise and low power front-end, which is sensitive to the charge released by ionizing radiation in a 20–25 μ m deep depleted region. The novel asynchronous matrix architecture is designed to ensure low power consumption and high rate capability. Such features make MALTA a possible candidate for the outer layer of ATLAS Inner Tracker (ITk) upgrade. Unirradiated and irradiated MALTA sensors have been extensively tested in laboratory and with high energy particle beams. Results of this measurements campaign are shown, and the further improvements that are being implemented in the next versions of the chip are discussed.