Monolithic Active Pixel Sensors Research Articles

Optimizing Time Resolution Electronics for DMAPs

Depleted Monolithic Active Pixel Sensors (DMAPSs) are foreseen as an interesting choice for future high-energy physics experiments, mainly because of the reduced fabrication costs. However, they generally offer limited time resolution due to the stringent requirements of area and power consumption imposed by the targeted spatial resolution. This work describes a methodology to optimize the design of time-to-digital converter (TDC)-based timing electronics that takes advantage of the asymmetrical shape of the pulse at the output of the analog front-end (AFE). Following that methodology, a power and area efficient implementation fully compatible with the RD50-MPW3 solution is proposed. Simulation results show that the proposed solution offers a time resolution of 2.08 ns for a range of energies from 1000 e− to 20,000 e−, with minimum area and zero quiescent in-pixel power consumption.

Design of an SHA-Less Pipeline ADC With Op-Amp Sharing Techniques for MAPS

As the leading research platform of heavy-ion science in China, the heavy-ion physics and applications at the Heavy Ion Research Facility in Lanzhou (HIRFL) and the High-Intensity heavy-ion Accelerator Facility (HIAF) drive the development of new detector technology. A monolithic active pixel sensor (MAPS) has been designed in a 130-nm CMOS process for HIRLF and HIAF. This MAPS can measure the energy deposition and position of the particle hit. As the critical component of this MAPS, a regional 12-bit 40-Msps pipeline ADC has been designed to convert the analog signals from the pixels into digital data. Due to the strict limitation on power and area, this ADC adopts the SHA-less architecture and stepwise capacitance reduction. Also, the op-amp sharing technology is used in the 1.5-bit stages. This ADC has a power consumption of 60 mW and occupies <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$874\times 550\,\,\mu \text{m}$ </tex-math></inline-formula> . Simulation results indicate that it achieves an ENOB of 11.77 bits and a SINAD of 72.57 dB at the tt corner with an input frequency of 3.291 MHz. The figure of merits (FOM) value is 507 fJ/step.

Tolerance of the MIMOSIS-1 CMOS Monolithic Active Pixel Sensor to ionizing radiation

MIMOSIS is a CMOS Monolithic Active Pixel Sensor (CPS) developed to equip the Micro Vertex Detector (MVD) of the Compressed Baryonic Matter (CBM) experiment at FAIR/GSI. The sensor will combine a spatial resolution of -5 µm with a time resolution of 5 µs and provide a peak hit rate capability of ∼80 MHz/cm2. To fulfil its task, MIMOSIS will have to withstand ionising radiation doses of ∼5 MRad and fluences of ∼7 × 1013 neq/cm2 per year of operation.The paper summarises major requirements of the CBM-MVD and compares them to the detection performances of the first full scale prototype, called MIMOSIS-1, recently evaluated in the laboratory and with particle beams. The tolerance of the sensor to the expected ionising radiation load was evaluated; the paper describes the measurements performed and their outcome.

Study of MIPs effects on a MAPS for electron ion collider in China

The Monolithic Active Pixel Sensor (MAPS) is a good candidate for the inner tracking system of the Electron–Ion Collider in China (EicC). Hence, a MAPS with a pixel pitch of ∼30 µm is being designed. Two 130 nm CMOS processes have been proposed as candidates for this MAPS design. The first one is a commercial standard twin-well low-resistivity (<50 Ω cm−3) process, and the other one is a quadruple-well high-resistivity (>1 kΩ cm−3) process. A 3-dimensional TCAD model of the pixels has been established to evaluate the Minimum Ionizing Particles (MIPs) induced charge collection in these two processes. This paper will discuss the study of charge collection efficiency, charge collection time, and charge sharing among pixels.

Suitability of Athena Monolithic Active Pixel Sensor for upstream monitoring of 6 MV, 6 FFF and 10 MV treatments

We are developing a thin, real-time radiotherapy verification sensor based on the Athena, a large-scale MAPS. The goal in radiotherapy verification is to measure the multileaf collimator positions and beam intensity to ensure the accuracy and safety of treatment delivery. Previously, results on this have been published. In this paper, we present results that clearly demonstrate that the Athena does not saturate, even at the highest beam intensities in a 6 FFF 10 × 10 cm2 field and thus is suitable for clinical deployment.

Evaluating direct detection detectors for short-range order characterization of amorphous materials by electron scattering

The introduction of direct electron detectors (DEDs) to transmission electron microscopy has set off the ‘resolution revolution’, especially for cryoTEM low-dose imaging of soft matter.In comparison to traditional indirect electron detectors such as Charged-Coupled Devices (CCD), DEDs show an improved modulation transfer function (MTF) and detective quantum efficiency (DQE) across all spatial frequencies, as well as faster frame rates which enable single electron counting.The benefits of such characteristics for imaging, spectroscopy and electron holography have been demonstrated previously. However, studies are lacking on the application of DEDs for localized characterization of short- to medium- range-order (SRO, MRO) in amorphous materials using electron scattering.Therefore, we evaluate the performance of a Monolithic Active Pixel Sensor DED for the characterization of SRO and MRO in nanoscale volumes of amorphous materials, using SiO2 and Ta2O5 thin films as test cases. The performance of the detector is compared systematically to electron scattering measurements recorded on an indirect detector (CCD) using 200 keV electrons and electron doses starting at approximately 500e−Å2 . In addition, the effects of sample cooling and energy-filtering on the measured SRO of the oxides were investigated.We demonstrate that the performance of the DED resulted in improved SRO characterization in comparison to that obtained from the CCD measurements. The DED enabled to achieve a larger measured maximal scattering vector, ∼16.51Å compared to ∼151Å, for the CCD. Furthermore, an improved signal-to-noise ratio of approximately two-fold was observed across all spatial frequencies for both 200 keV and 80 keV electrons. These improvements are shown to result from the superior DQE of the DED. Consequently, the DED measurements enabled to determine the coordination numbers of atomic bonds more accurately.We expect that further benefits of the DED for S/MRO characterization will be highlighted for ultra- sensitive materials that cannot withstand electron doses above several e−Å2 .

Results from single event effect tests with MIMOSIS-1

Being installed as close as 5.5 mm to the beam axis, the Micro Vertex Detector (mvd) of the cbm experiment will be exposed to a sizable flow of heavy beam ions and nuclear fragments. The cmos Monolithic Active Pixel Sensor for the mvd, mimosis, must resist the related heavy ion impacts without permanent damage or frequent interrupt of operation as caused by single event effects (see). We motivate the requirements on the sensor and introduce our concept for protecting the device against sees. Moreover, we report the results of a related test campaign carried out with the first full size sensor prototype, mimosis-1, and different heavy ion beams at gsi.

MAPS-based tracking and vertexing for the Electron–Ion Collider

Experiments at the future Electron–Ion Collider (EIC) pose stringent requirements on the tracking system for the measurement of the scattered electron and charged particles produced in the collision, as well as the position of the collision point and any decay vertices of hadrons containing heavy quarks. Monolithic Active Pixel Sensors (MAPS) offer the possibility of high granularity in combination with low power consumption and low mass, making them ideally suited for the inner tracker of the EIC detector(s). In this contribution, we will discuss the configuration optimized for the ATHENA detector, selected physics performance metrics, and associated R&D towards a well-integrated, large-acceptance, precision tracking and vertexing solution for the EIC based on a new generation of MAPS sensors in 65 nm CMOS imaging technology.

Performance of a Full-Scale Upstream MAPS-Based Verification Device for Radiotherapy.

Intensity-modulated radiotherapy is a widely used technique for accurately targeting cancerous tumours in difficult locations using dynamically shaped beams. This is ideally accompanied by real-time independent verification. Monolithic active pixel sensors are a viable candidate for providing upstream beam monitoring during treatment. We have already demonstrated that a Monolithic Active Pixel Sensor (MAPS)-based system can fulfill all clinical requirements except for the minimum required size. Here, we report the performance of a large-scale demonstrator system consisting of a matrix of 2 × 2 sensors, which is large enough to cover almost all radiotherapy treatment fields when affixed to the shadow tray of the LINAC head. When building a matrix structure, a small dead area is inevitable. Here, we report that with a newly developed position algorithm, leaf positions can be reconstructed over the entire range with a position resolution of below ∼200 μm in the centre of the sensor, which worsens to just below 300 μm in the middle of the gap between two sensors. A leaf position resolution below 300 μm results in a dose error below 2%, which is good enough for clinical deployment.

ARCADIA MAPS process qualification through the electrical characterization of passive pixel arrays

The development of novel Monolithic Active Pixel Sensor (MAPS) technologies has been pursued by several collaborations in the last two decades. The ARCADIA project aims to design fully depleted MAPS for medical, space, HEP and X-ray detection applications, that can be produced with a commercial 110 nm CMOS production process. Among the test structures of the first two engineering runs of the project, passive pixel arrays with different pitches and layouts were included. The main characteristics of the produced devices in terms of dark current, depletion voltage, punch through current and pixel capacitance have been evaluated from IV and CV characteristics of the pixel arrays. Groups of four samples have been extracted from as many different positions within each wafer and electrically characterized to obtain information on the variability in the pixel operating voltage range and in the pixel dark current, reflecting variations related to the employed production process. The experimental data demonstrated a good uniformity in the considered parameters for different sample positions within the produced wafers, as well as for samples extracted from different wafers with the same substrate type.

Towards a new generation of Monolithic Active Pixel Sensors

A new generation of Monolithic Active Pixel Sensors (MAPS), produced in a 65 nm CMOS imaging process, promises higher densities of on-chip circuits and, for a given pixel size, more sophisticated in-pixel logic compared to larger feature size processes. MAPS are a cost-effective alternative to hybrid pixel sensors since flip-chip bonding is not required. In addition, they allow for significant reductions of the material budget of detector systems, due to the smaller physical thicknesses of the active sensor and the absence of a separate readout chip. The TANGERINE project develops a sensor suitable for future Higgs factories as well as for a beam telescope to be used at beam-test facilities. The sensors will have small collection electrodes (order of $\mu$m) to maximize the signal-to-noise ratio, which makes it possible to minimize power dissipation in the circuitry. The first batch of test chips, featuring full front-end amplifiers with Krummenacher feedback, was produced and tested at the Mainzer Mikrotron (MAMI) at the end of 2021. MAMI provides an electron beam with currents up to 100 $\mu$A and an energy of 855 MeV. The analog output signal of the test chips was recorded with a high bandwidth oscilloscope and used to study the charge-sensitive amplifier of the chips in terms of waveform analysis. A beam telescope was used as a reference system to allow for track-based analysis of the recorded data.

Design and readout architecture of a monolithic binary active pixel sensor in TPSCo 65 nm CMOS imaging technology

The Digital Pixel Test Structure (DPTS) is a monolithic active pixel sensor prototype chip designed to explore the TPSCo 65 nm ISC process in the framework of the CERN-EP R&D on monolithic sensors and the ALICE ITS3 upgrade. It features a 32 × 32 binary pixel matrix at 15 μm pitch with event-driven readout, with GHz range time-encoded digital signals including Time-Over-Threshold. The chip proved fully functional and efficient in testbeam allowing early verification of the complete sensor to readout chain. This paper focuses on the design, in particular the digital readout and its perspectives with some supporting results.

Bandgap reference, temperature sensor and low drop-out regulator circuits monolithic sensors in TPSCo 65 nm ISC technology

With Inner Tracking System v3 (ITS3), the ALICE experiment is pursuing a wafer-scale Monolithic Active Pixel Sensor (MAPS). The chip is being developed in TPSCo 65 nm ISC technology which is under study in the framework of CERN EP R&D on monolithic sensors for High Energy Physics (HEP) applications. This contribution presents designs and measurement results of building blocks needed for this chip, in particular bandgap references and temperature sensors. In addition, simulation results of the design of Low Drop-out Regulator (LDO) to be submitted for the next prototyping run will be discussed.

CMOS MAPS upgrade for the Belle II Vertex Detector

The success of the Belle II experiment in Japan relies on the very high instantaneous luminosity, close to 6×1035 cm−2 s−1, expected from the SuperKEKB collider. The corresponding beam conditions at such luminosity levels generate large rates of background particles and creates stringent constraints on the vertex detector, adding to the physics requirements. Current prospects for the occupancy rates in the present vertex detector (VXD) at full luminosity fall close to the acceptable limits and bear large uncertainties. In this context, the Belle II collaboration is considering the possibility to install an upgraded VXD system around 2027 to provide a sufficient safety margin with respect to the expected background rate and possibly enhance tracking and vertexing performance.The VTX collaboration has started the design of a fully pixelated VXD, called VTX, based on fast and highly granular Depleted Monolithic Active Pixel Sensors (DMAPS) integrated on light support structures.The two main technical features of the VTX proposal are the usage of a single sensor type over all the layers of the system and the overall material budget below 2% of radiation length, compared to the current VXD which has two different sensor technologies and about 3% of radiation length. A dedicated sensor (OBELIX), taylored to the specific needs of Belle II, is under development, evolving from the existing TJ-Monopix2 sensor. The time-stamping precision below 100 ns will allow all VTX layers to take part in the track finding strategy contrary to the current situation. The first two detection layers are designed according to a self-supported all-silicon ladder concept, where 4 contiguous sensors are diced out of a wafer, thinned and interconnected with post-processed redistribution layers. The outermost detection layers follow a more conventional approach with a cold plate and carbon fibre support structure, and light flex cables interconnecting the sensors.This document will review the context, technical details and development status of the proposed Belle II VTX.

Study of imaging system in proton computed tomography with data acquisition from a monolithic active pixel sensor

The first proton therapy system in Thailand has been installed at King Chulalongkorn Memorial Hospital (KCMH) since 2019. Apart from its clinical usage, Suranaree University of Technology (SUT) has initiated the collaborative research work with KCMH to explore a possibility of developing a proton computed tomography (pCT) prototype. Due to the proton’s depth-dose properties, this technique is more effective than photon treatment. Prior to proton therapy, pCT could help with the treatment planning. This technique simplifies proton treatment calculations since both processes involve the same particle interaction with matter. We simulated the experiment setup using G4beamline with the proton beam using a monolithic active pixel sensor (MAPS) as a proton tracker. The sensor’s output revealed that the ratio of data from protons interacting on the sensor was low, so we pre-processed the data with MATLAB by applying a mean filter to replace any empty pixels with the average of their nearby pixels. A 3D reconstruction was performed by stacking all the axial images reconstructed by the back projection method. The result shows that the material densities of reconstructed samples can be identified, however, it is still in the preliminary stage and not yet suitable for clinical trials. It is, however, possible to improve the quality of images and obtain a better 3D reconstruction for the pCT prototype by using a back-projection method.

First characterization results of ARCADIA FD-MAPS after X-ray irradiation

The ARCADIA collaboration is developing fully-depleted (FD) Monolithic Active Pixel Sensors (MAPS) in a 110 nm CMOS process in collaboration with LFoundry. The sensor design incorporates an n+ collection node within a n-type epi-layer on top of a high-resistivity n-type substrate and p+ backside. Thus, the pn-junction sits on the backside and through an applied backside bias, the full substrate gets depleted. The targeted applications of this technology range from future high energy physics experiments to space applications, and medical and industrial scanners. Together, these applications set the minimum requirements on the detector: data collection at hit rates of (10–100) MHz/cm2, full signal processing within (1–10) μs, maximum power consumption (5–20) mW/cm2 and radiation tolerances of up to 3.4 Mrad or 6.2 × 1012 1 MeV neutron equivalent fluence. In order to proof the performance of the technology, a demonstrator chip of 512 × 512 pixels with 25 μm pitch was designed and fabricated in a first engineering run in 2021, together with additional test structures of pixel and strip arrays with different pitches and sensor geometries. The production run has produced functional passive and active pixel matrices. Earlier studies have shown that positive oxide charges and traps at the Si-SiO2 interface, introduced by ionising radiation, affect the depletion region around the collection electrode, increasing the pixel capacitance. By varying the gap size between collection node and pwells, the geometry can be optimised to keep the capacitance low also after irradiation. To study the performance after irradiation, of the optimised diode designs, the passive pixel matrices were irradiated with doses up to 10 Mrad (SiO2) using a X-ray tube with a Tungsten anode. The measurements are complemented by TCAD simulations. The maximum capacitance increase after irradiation was found to reach 6 and 12 fF/pixel for pixel pitches of 25 and 50 μm, respectively. The relative capacitance increase after irradiation has hereby been found to reach up to 250% after a dose of 10 Mrad.

G4beamline simulation for rotating telescope at SLRI BTF

A plan to upgrade the ALICE Inner Tracking System has been proposed, and the Monolithic Active Pixel Sensor, a novel silicon sensor technology, will be employed. The silicon sensor is planned to be investigated with a rotating telescope at the Synchrotron Light Research Institute Beam Test Facility using a 1.2 GeV electron beam. A part of this work is to investigate the pixel sensor telescope when the angle of the Device Under Test (DUT) plane changes. Simulation has been performed with the G4beamline software. Once a G4beamline simulation is completed, a ROOT file is produced. Beam profiles and correlation plots are then analyzed. This data was used to calculate the scattering angle, which was found to be between 0.171 and 0.178 mrad when the DUT plane is perpendicular to the test beam. Furthermore, the simulation result has been compared and agrees with the theoretical calculation within 4.8% error.

SpacePix2: SOI MAPS detector for space radiation monitoring

The SpacePix2 monolithic active pixel sensor (MAPS) is a novel ASIC for space radiation monitoring designed in a 180 nm SOI CMOS technology. The active sensor area is 3.84 × 3.84 mm2, pixel matrix is arranged as a 64 × 64 array with 60 µm pitch. The pixel front-end amplifier signal range is 2–80 ke−, extended up to 30 Me− using a backside channel. Diodes integrated in the handle wafer in each pixel are biased at −150 V. Impinging particle generates a charge pulse converted to voltage pulse by charge sensitive amplifier (CSA). Maximum voltage memorized by the peak detector hold (PDH) circuit is digitized using on-chip 10-bit asynchronous column SAR ADCs. Two readout interfaces are available, 400 MHz LVDS and 50 MHz SPI. Total power consumption is 43 mA from a 1.8 V power supply. The ASIC has been tested in space in low Earth orbit (LEO) and sample data are shown.

Design of an analog monolithic pixel sensor prototype in TPSCo 65 nm CMOS imaging technology

A series of monolithic active pixel sensor prototypes (APTS chips) were manufactured in the TPSCo 65 nm CMOS imaging process in the framework of the CERN-EP R&D on monolithic sensors and the ALICE ITS3 upgrade project. Each APTS chip contains a 4 × 4 pixel matrix with fast analog outputs buffered to individual pads. To explore the process and sensor characteristics, various pixel pitches (10 µm–25 µm), geometries and reverse biasing schemes were included. Prototypes are fully functional with detailed sensor characterization ongoing. The design will be presented with some experimental results also correlating to some transistor measurements.

ARCADIA FD-MAPS: Simulation, characterization and perspectives for high resolution timing applications

Monolithic Active Pixel Sensors (MAPS) are a promising technology that provides large sensitive areas at potentially low power consumption and low material budget. The ARCADIA project is developing Fully Depleted MAPS (FD-MAPS) with an innovative sensor design, that uses a backside bias to improve charge collection efficiency and timing over a wide range of operational and environmental conditions. The ARCADIA collaboration has produced a large set of prototypes in the first two engineering runs, with the main design consisting of a 512 × 512 pixel matrix with 25μm pixel pitch and other smaller active sensor arrays. Test structures of pixel matrices with pixel pitches ranging from 10 to 50μm and total thicknesses of 50 to 200μm have also been included, to ease the characterization of the sensors independently from integrated electronics. We give an overview of the status of the project and then focus on the characterization of the passive pixel matrices which include Capacitance–Voltage (CV) and Current–Voltage (IV), as well as Transient Current Technique (TCT) measurements with a red and an infrared laser. We could confirm a single pixel capacitance below 5fF for pixels with 25μm pitch, and a 90% charge collection of MIP-like charge depositions within 12ns in 100μm active thickness. These results are complemented and supported by Technology Computer Aided Design (TCAD) simulations.