Monolithic Active Pixel Sensors Research Articles

Quad-module characterization with the MALTA monolithic pixel chip

The MALTA silicon pixel detector combines a depleted monolithic active pixel sensor (DMAPS) with a fully asynchronous front-end and readout. It features a high granularity pixel matrix with a 36.4 μm symmetric pixel pitch, low power consumption of <1 μW/pixel and low material budget with detector thicknesses as little as 50 μm. It achieves a radiation hardness to 100MRad TID and more than 1 × 10E15 1 MeV neq/cm2 with a time resolution of <2 ns (Pernegger et al., 2023).In order to cover large sensitive areas efficiently with a minimum of power and data connections the development of modules, comprising of up to 4 MALTA detectors, is studied.This contribution presents the beam test performance of parallel and serial powered MALTA 4-chip modules in an effort to characterize the sensor’s chip-to-chip data and power transmission and prepare the production of a first prototype of an ultra-light weight 4-chip module on a flexible circuit with next generation MALTA2 sensors.

Characterization of IMIC, an implantable needle-shaped positron sensitive monolithic active pixel sensor for preclinical molecular neuroimaging

The correlation of molecular neuroimaging and behavior studies in preclinical PET imaging is of major interest to unlock progress in the understanding of brain processes and assess the validity of preclinical studies in drug development. However, fully achieving this ambition requires performing molecular images of awake and freely moving animals, whereas most of the preclinical imaging procedures are currently performed under anesthesia. To overcome this issue, the MAPSSIC project aims to develop a pixelated intracerebral probe to be implanted into awake and freely moving rats. The aforementioned probe relies on IMIC (Imageur Moléculaire Intra Cérébral), a Monolithic Active Pixel Sensor (MAPS) prototype set to directly detect positrons. The IMIC sensors were produced in 5 different configurations. Measurements using a 204Tl source showed that the sensor parameters can be optimized to boost its performance allowing to increase the sensitivity and reduce the average cluster size. In addition, comparisons between sensor configurations show a clear gain provided by the introduction of CMOS process modifications. Finally, the choice of the optimal sensor configuration will depend on the expected in vivo conditions.

LURAD: Design study of a comprehensive radiation monitor package for the gateway and the lunar surface

Moon is an auspicious environment for the study of Galactic cosmic rays (GCR) and Solar Particle Events (SEP) due to the absence of magnetic field and atmosphere. The same characteristics raise the radiation risk for human presence in orbit around it or at the lunar surface. The secondary (albedo) radiation resulting from the interaction of the primary radiation with the lunar soil adds an extra risk factor, because neutrons are produced, but also it can be exploited to study the soil composition. In this paper, the design of a comprehensive radiation monitor package tailored to the lunar environment is presented. The detector, named LURAD, will perform spectroscopic measurements of protons, electrons, heavy ions, as well as gamma-rays, and neutrons. A microdosimetry monitor subsystem is foreseen which can provide measurements of LET(Si) spectra in a wide dynamic range of LET(Si) and flux for SPE and GCR, detection of neutrons and biological dose for radiation protection of astronauts. The LURAD design leverages on the following key enabling technologies: (a) Fully depleted Si monolithic active pixel sensors; (b) Scintillators read by silicon photomultipliers (SiPM); (c) Silicon on Insulator (SOI) microdosimetry sensors; These technologies promise miniaturization and mass reduction with state-of-the-art performance. The instrument’s design is presented, and the Monte Carlo study of the feasibility of particle identification and kinetic energy determination is discussed.

Electrical/piezoresistive effects in bent Alpide MAPS

The ITS3 upgrade baseline design employs MAPS (Monolithic Active Pixel Sensor) in bent state. Bending experiments with the existing ITS2 MAPS (=Alpide chip) show it remains functional but with relative large analog supply current changes. It is shown that by the piezoresistive effect, rotation of current mirror FETs can be responsible which was confirmed after validating the layout. Measured Gauge Factor has proper sign but is 3 times lower than typical values derived from literature. The magnitude of the measured strain induced PMOS V th shift is as expected but the sign differs for compressive strain with some of the literature.

NAPA-p1: monolithic nanosecond timing pixel for large area sensors, designed for future e + e - colliders

NAPA-p1 is a prototype Monolithic Active Pixel Sensor 'MAPS' developed as a first iteration towards meeting the detectors general requirements for future e + e - colliders. Long-term objective is to develop a wafer-scale sensor in MAPS with an area ∼ 10 cm × 10 cm. This article presents the motivations for the design choices of NAPA-p1, translating the physics requirement into circuit specifications. Simulations show a pixel jitter of < 400 ps-rms and an equivalent noise charge of 13 e -rms with an average power consumption of 1.15 mW/cm2 assuming a 1% duty cycle, meeting the target specifications. The prototype is designed in 65 nm CMOS imaging technology, with dimensions of 1.5 mm × 1.5 mm and a pixel pitch of 25 μm. The prototype chip has been fabricated and characterization results will be available soon.

4 Gbps serializer circuits in a 180 nm technology for monolithic pixel sensor prototypes developed for the CEPC vertex detector

Monolithic Active Pixel Sensor is one of the promising candidates for the Circular Electron Positron Collider Vertex detector, due to its good performance and trade-off of granularity, readout speed, material budgets and power consumption. A full-scale TaichuPix chip, including a matrix of 512 × 1024 pixels with a size of 25 × 25 μm2 is developed to provide a spatial resolution better than 5 μm. It requires a raw data rate up to 3.84 Gbps and power consumption less than 100 mA for the serializer circuit. Based on one of the small-scale prototypes, the highest serial data rate is tested to be 3.36 Gbps with a peak-to-peak jitter of about 150 ps and large current consumption. Moreover, the 32-bit parallel data width of the serializer isn't suitable for the 8B10B encoder. Therefore, two 4 Gbps serializers have been designed and optimized to meet these requirements based on the same process node of 180 nm as the TaichuPix, considering the funding and time costs. The serializer consists of a phase locked loop (PLL), several 5:1 sub-multiplexers based on a shift-register chain, a 4:1 or 8:1 sub-multiplexer based on the binary-tree structure, a clock distributor and a high-speed driver. Both ring-oscillating PLL and LC-tank PLL were integrated for performance evaluation. The preliminary tests showed low-jitter characteristics of the two PLLs despite this version's biasing problem, and both serializer circuits functioned correctly. A revision corrected the error and was submitted in October 2023.

Radiation hardness of MALTA2 monolithic CMOS imaging sensors on Czochralski substrates

MALTA2 is the latest full-scale prototype of the MALTA family of Depleted Monolithic Active Pixel Sensors (DMAPS) produced in Tower Semiconductor 180 nm CMOS sensor imaging technology. In order to comply with the requirements of high energy physics (HEP) experiments, various process modifications and front-end changes have been implemented to achieve low power consumption, reduce random telegraph signal (RTS) noise, and optimise the charge collection geometry. Compared to its predecessors, MALTA2 targets the use of a high-resistivity, thick Czochralski (Cz) substrates in order to demonstrate radiation hardness in terms of detection efficiency and timing resolution up to 3 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes $$\\end{document} 1015\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{15}$$\\end{document} 1 MeV neq/cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {n_{eq}/{cm}^2}$$\\end{document} with backside metallisation to achieve good propagation of the bias voltage. This manuscript shows the results that were obtained with non-irradiated and irradiated MALTA2 samples on Cz substrates from the CERN SPS test beam campaign from 2021 to 2023 using the MALTA telescope.

Response of the MIMOSIS-1 CMOS Monolithic Active Pixel Sensor to particle beams with different dE/dx

The ultra-thin and highly granular CMOS Monolithic Active Pixel Sensors (MAPS) are typically optimized for high rate high precision tracking, which implies the use of a very thin active medium and digital readout. Both features hamper using the devices for identifying low momentum particles by means of dE/dx. Still, MAPS feature charge sharing and typically clusters of more than one fired pixel per impinging particles are formed. It was previously shown that the number of fired pixels per cluster scales with the dE/dx, which allowed identifying highly ionizing nuclear fragments [1]. Assuming a sufficiently strong response to different dE/dx, this approach could also be considered for distinguishing minimum ionizing particles (MIP) from light fragments like alpha particles in tracking detectors. In this work, we study this response with particle beams with a dE/dx of up to four times the ones of MIPs, for non-irradiated and irradiated chips, with different sensing nodes as implemented in the MIMOSIS-1 prototype used for the vertex detector of the CBM experiment.

A monolithic active pixel sensor with node-based, data-driven, parallel readout for the high energy physics experiment vertex detector

We present the design of a prototype MAPS sensor MIC6_V1 based on a 55 nm Quad-well CMOS Image Sensor process for the CEPC vertex detector. A new node-based, data-driven, parallel readout architecture is implemented to achieve high spatial resolution, fast readout, and low power consumption. The size of MIC6_V1 is 2.8 mm × 2.8 mm, which contains a pixel matrix of 64 rows by 64 columns, and the pixel size is 23.6 μ m × 20 μ m. The integration time is 5 μs, and the hit arrival time measurement accuracy is 10 ns.

Simulation and first characterization of MAPS test structures with gain for timing applications

Thanks to their advantages in terms of easiness of manufacturing and reduced production costs, Monolithic Active Pixel Sensors (MAPS) represent an appealing solution for radiation imaging applications, which require to cover large areas with pixelated detectors. In the next upgrade of the ALICE detector, that will have to deal with the higher event rate resulting from the planned increase in the LHC luminosity, it is foreseen to include two additional sensor layers to perform Time of Flight (ToF) measurements. Trying to reach the challenging timing resolution required by the ALICE ToF layers, an internal gain layer has been included in the test structures of the third engineering run of the ARCADIA project to improve the timing performance of this MAPS technology. In the paper we will present an overview of the main results obtained from the electrical and the dynamic characterization of the fabricated devices, which have been compared with the behavior expected from the preliminary TCAD simulations carried out in the design phase. The experimental results confirmed the feasibility of embedding a gain layer in the ARCADIA 110 nm CMOS technology to develop monolithic LGADs.

Prototype design of a Monolithic Active Pixel Sensor for the Electron-ion collider in China

The Nupix-R1 is a prototype Monolithic Active Pixel Sensor designed for the Electron-ion collider in China. It consists of 128 rows × 128 columns of square pixels with a pitch of 26.3 µm. Since it is implemented in a 130 nm commercial triple-well process, the in-pixel circuit contains only NMOS transistors. The Nupix-R1 can simultaneously measure the energy, arrival time and position of particle hits. In addition, it can also record only the hit positions with a novel zero-compression scheme to increase the readout speed and reduce the data volume. This paper will discuss the design of the Nupix-R1 sensor.

The DMAPS upgrade of the Belle II vertex detector

Abstract The SuperKEKB collider will undergo a major upgrade to reach the target luminosity of 6 × 1035 cm-2 s-1 during the long shutdown (LS2) foreseen to start around year 2027. We are developing a new vertex detector (VTX) to replace the current one (VXD). This new pixel silicon tracker aims to be both more robust against the higher level of machine background and more performant in terms of precision on the decay vertices and standalone track finding efficiency. The baseline layout consists of two layers composing the inner part (iVTX) and three outer layers (oVTX), all arranged in a barrel-shaped geometry, with minimal material budget. All layers will be equipped with dedicated depleted monolithic active CMOS pixel sensors (DMAPS) named OBELIX, designed in the TowerJazz 180 nm technology. This paper will review all the aspects of the project: the detector specifications and the baseline design, the expected improved performance, the OBELIX features and its design status, including the tests of the forerunner chip TJ-Monopix2, and the fabrication and tests for the iVTX and oVTX ladder prototypes.

First measurements with monolithic active pixel test structures produced in a 65 nm CMOS process

The Inner Tracking System (ITS) of the ALICE experiment at CERN will undergo an upgrade during the LHC long shutdown 3, in which the three innermost tracking layers will be replaced. This upgrade, named the Inner Tracking System 3 (ITS3), employs stitched wafer-scale Monolithic Active Pixel Sensors fabricated in a 65 nm CMOS process. The sensors are 260 mm in length and thinned to less than 50 μm then bent to form truly half-cylindrical half-barrels. The feasibility of this process for the ITS3 was explored with the first test production run (MLR1) in 2021, whose goal was to evaluate the charged particle detection efficiency and the sensor performance under non-ionising and ionising radiation up to the expected levels for ALICE ITS3 of 1013 1 MeV neq cm-2 (NIEL) and 10 kGy (TID). Three sensor flavours were produced to investigate this process: Analog Pixel Test Structure (APTS), Circuit Exploratoire 65 (CE65) and Digital Pixel Test Structure (DPTS).This contribution gives an overview of the MLR1 submission and test results, describing the different sensor flavours and presenting the results of the performance measurements done with particle beams for various chip variants and irradiation levels.

First results of the upgraded ALICE Inner Tracking System in LHC Run 3

Major upgrades of the ALICE experiment at CERN were completed during the LHC Long Shutdown 2 (2019–2021). The ALICE detector is currently taking data and has been doing so from the start of the third period of operation of the LHC (Run 3) on July 5th, 2022. One key part of these upgrades is the new Inner Tracking System (ITS2), a full silicon-pixel vertexing and tracking detector constructed entirely with CMOS monolithic active pixel sensors (ALPIDE). The ITS2 consists of three inner layers (50 μm thick sensors) and four outer layers (100 μm thick sensors) covering 10 m2 and containing 12.5 billion pixels with a pixel pitch of 27 μ m × 29 μm. It offers a significant improvement in impact-parameter resolution and tracking efficiency, thanks to the increased granularity, the very low material budget (0.35% X0 /layer in the inner barrel) as well as a smaller beam pipe radius.The ITS2 was successfully installed in the ALICE experiment in May 2021, followed by a period of comprehensive on-site commissioning, before starting data taking in July 2022. In this paper, the detector construction and commissioning will be introduced briefly. The performance results from the first phase of proton-proton collisions recorded to date in LHC Run 3 will be discussed in detail, which include detector calibration, long-term evolution of the ALPIDE sensor threshold and noise, and the first measurement of the impact parameter.

ALICE ITS3: a bent stitched MAPS-based vertex detector

The ALICE ITS3 is a novel vertex detector replacing the innermost layers of ITS2 during LS3. Composed of three truly cylindrical layers of wafer-sized 65 nm stitched Monolithic Active Pixel Sensors, ITS3 provides high-resolution tracking of charged particles generated in heavy-ion collisions. This contribution presents an overview of the ITS3 detector, highlighting its design features, integration and cooling, and the ongoing development towards the final sensor. Furthermore, the paper introduces the off-detector service electronics, which play an essential role in the readout, control, and power supply of the detector.

Detector development for particle physics

In high-energy physics experiments, tracking and vertexing is nowadays mostly done using semiconductor detectors. Among the employed detectors are hybrid pixel sensors, passive sensors and recently also depleted monolithic active pixel sensors (DMAPS), which integrate the particle sensor with front-end electronics. Currently, the dominant material for the production of such sensors is silicon. However, the use of silicon carbide is currently being investigated. In this work we report on our progress on the development of silicon-based DMAPS. Further, we present two approaches for reading out passive silicon carbide detectors at particle rates from the kHz to the GHz range.

Study of MAPS silicon detector prototypes for the ALICE Inner Tracking System upgrade

The ALICE experiment, which is located at the Large Hadron Collider (LHC) at CERN, has planned an upgrade of the Inner Tracking System (ITS), called ITS3, which will be installed during the LHC Long Shutdown 3, in 2026–2028. The cornerstone of the upgrade is a new 65 nm CMOS pixel chip, produced using Monolithic Active Pixel Sensor (MAPS) technology and the stitching technology to extend the chip length to 26 cm. The produced chips will be bent and they will replace the three innermost layers of the existing detector with new ultra-light, truly cylindrical layers. The ITS3 will improve tracking performance, especially at low transverse momentum, thanks to better track impact-parameter resolution, improved by a factor two with respect to the present ITS in LHC Run 3. In addition, the detector will be closer to the interaction point and will have a much lower material budget, of 0.05% X0/layer. This proceedings paper presents the final configuration and structure of the ITS3, the challenges related to its design and construction, and the results of the current R&D program on the sensor design and characterization. Finally, it also reports the results of beam tests preformed at CERN, where an analog pixel test chip (APTS Source Follower) was investigated in terms of detection efficiency.

Deep Learning Approach for High-accuracy Electron Counting of Monolithic Active Pixel Sensor-type Direct Electron Detectors at Increased Electron Dose.

Electron counting can be performed algorithmically for monolithic active pixel sensor direct electron detectors to eliminate readout noise and Landau noise arising from the variability in the amount of deposited energy for each electron. Errors in existing counting algorithms include mistakenly counting a multielectron strike as a single electron event, and inaccurately locating the incident position of the electron due to lateral spread of deposited energy and dark noise. Here, we report a supervised deep learning (DL) approach based on Faster region-based convolutional neural network (R-CNN) to recognize single electron events at varying electron doses and voltages. The DL approach shows high accuracy according to the near-ideal modulation transfer function (MTF) and detector quantum efficiency for sparse images. It predicts, on average, 0.47 pixel deviation from the incident positions for 200 kV electrons versus 0.59 pixel using the conventional counting method. The DL approach also shows better robustness against coincidence loss as the electron dose increases, maintaining the MTF at half Nyquist frequency above 0.83 as the electron density increases to 0.06 e-/pixel. Thus, the DL model extends the advantages of counting analysis to higher dose rates than conventional methods.

Commissioning of Pixel Sensor Telescope for Monolithic Active Pixel Sensor Characterization

The Monolithic Active Pixel Sensors (MAPS) have been promisingly demonstrated as a core part of tracking detectors used in many experiments. In order to obtain decent particle tracks generated after high-energy particle collision, it is especially important that the detector must consist of high-performance MAPS. A pixel sensor telescope is a tool employed to investigate the properties of MAPS using high-energy particle test beams. At the Synchrotron Light Research Institute (SLRI), the pixel sensor telescope assembled with five layers of 50-µm thick pixel sensors has been commissioned and tested both in the laboratory with a radioactive source and by a high-energy electron test beam produced at the SLRI Beam Test Facility. With sensor signal threshold ranging from 9.73 to 10.15 DAC and noises between 0.62 and 0.87 DAC, each plane of the pixel sensor telescope can detect particles decaying from the radioactive source. Moreover, the test beam profiles have been measured to be 4.00 - 4.56 mm and 1.15 - 2.29 mm in horizontal and vertical axes, respectively. Correlations between each plane have been observed and confirm the proper operation of the pixel sensor telescope. Consequently, the pixel sensor telescope can be used to characterize the pixel sensor prototype.

Beam test of a 180 nm CMOS Pixel Sensor for the CEPC vertex detector

The proposed Circular Electron Positron Collider (CEPC) imposes new challenges for the vertex detector in terms of pixel size and material budget. A Monolithic Active Pixel Sensor (MAPS) prototype called TaichuPix, based on a column drain readout architecture, has been developed to address the need for high spatial resolution. In order to evaluate the performance of the TaichuPix-3 chips, a beam test was carried out at DESY II TB21 in December 2022. Meanwhile, the Data Acquisition (DAQ) for a multi-plane configuration was tested during the beam test. This work presents the characterization of the TaichuPix-3 chips with two different processes, including cluster size, spatial resolution, and detection efficiency. The analysis results indicate the spatial resolution better than 5µm and the detection efficiency exceeding 99.5% for TaichuPix-3 chips with the two different processes.