Test-beam and simulation studies for the CLICTD technology demonstrator -- a monolithic CMOS pixel sensor with a small collection diode

The CLIC Tracker Detector (CLICTD) is a monolithic pixel sensor featuring pixels of 30um x 37.5um and a small collection diode. The sensor is fabricated in a 180 nm CMOS imaging process, using two different pixel flavours: the first with a continuous n-type implant for full lateral depletion, and the second with a segmentation in the n-type implant for accelerated charge collection. Moreover, CLICTD features an innovative sub-pixel segmentation scheme that allows the digital footprint to be reduced while maintaining a small sub-pixel pitch. In this contribution, test-beam measurements for the pixel flavour with the segmented n-implant are presented. The performance is evaluated in terms of time and spatial resolution as well as efficiency. Furthermore, the test-beam data is compared to simulation studies using a combination of 3D TCAD and Monte Carlo simulation tools

Combining TCAD and Monte Carlo Methods to Simulate CMOS Pixel Sensors with a Small Collection Electrode using the Allpix Squared Framework

Combining electrostatic field simulations with Monte Carlo methods enables realistic modeling of the detector response for novel monolithic silicon detectors with strongly non-linear electric fields. Both the precise field description and the inclusion of Landau fluctuations and production of secondary particles in the sensor are crucial ingredients for the understanding and reproduction of detector characteristics. In this paper, a CMOS pixel sensor with small collection electrode design, implemented in a high-resistivity epitaxial layer, is simulated by integrating a detailed electric field model from finite element TCAD into a Monte Carlo based simulation with the Allpix$^2$ framework. The simulation results are compared to data recorded in test-beam measurements and very good agreement is found for various quantities such as cluster size, spatial resolution and efficiency. Furthermore, the observables are studied as a function of the intra-pixel incidence position to enable a detailed comparison with the detector behavior observed in data. The validation of such simulations is fundamental for modeling the detector response and for predicting the performance of future prototype designs. Moreover, visualization plots extracted from the charge carrier drift model of the framework can aid in understanding the charge propagation behavior in different regions of the sensor.Comment: 15 pages, 18 figure

Test-beam Performance Results of the FASTPIX Sub-Nanosecond CMOS Pixel Sensor Demonstrator

Within the ATTRACT FASTPIX project, a monolithic pixel sensor demonstrator chip has been developed in a modified 180 nm CMOS imaging process technology, targeting sub-nanosecond timing precision for single ionising particles. It features a small collection electrode design on a 25 micrometers-thick epitaxial layer and contains 32 mini matrices of 68 hexagonal pixels each, with pixel pitches ranging from 8.66 to 20 micrometers. Four pixels are transmitting an analog output signal and 64 are transmitting binary hit information. Various design variations are explored, aiming at accelerating the charge collection and making the timing of the charge collection more uniform over the pixel area. Signal treatment of the analog waveforms, as well as reconstruction of digital position, time and charge information, is carried out off-chip. This contribution introduces the design of the sensor and readout system and presents performance results for various pixel designs achieved in recent test beam measurements with external tracking and timing reference detectors. A time resolution below 150 ps is obtained at full efficiency for all pixel pitches.Comment: 14 pages, 15 figures, submitted to NIMA (special issue for ULITIMA 2023 conference

Transient Monte Carlo Simulations for the Optimisation and Characterisation of Monolithic Silicon Sensors

An ever-increasing demand for high-performance silicon sensors requires complex sensor designs that are challenging to simulate and model. The combination of electrostatic finite element simulations with a transient Monte Carlo approach provides simultaneous access to precise sensor modelling and high statistics. The high simulation statistics enable the inclusion of Landau fluctuations and production of secondary particles, which offers a realistic simulation scenario. The transient simulation approach is an important tool to achieve an accurate time-resolved description of the sensor, which is crucial in the face of novel detector prototypes with increasingly precise timing capabilities. The simulated time resolution as a function of operating parameters as well as the full transient pulse can be monitored and assessed, which offers a new perspective on the optimisation and characterisation of silicon sensors. In this paper, a combination of electrostatic finite-element simulations using 3D TCAD and transient Monte Carlo simulations with the Allpix Squared framework are presented for a monolithic CMOS pixel sensor with a small collection diode, that is characterised by a highly inhomogeneous, complex electric field. The results are compared to transient 3D TCAD simulations that offer a precise simulation of the transient behaviour but long computation times. Additionally, the simulations are benchmarked against test-beam data and good agreement is found for the performance parameters over a wide range of different operation conditions

Developing a Monolithic Silicon Sensor in a 65 nm CMOS Imaging Technology for Future Lepton Collider Vertex Detectors

Monolithic CMOS sensors in a 65 nm imaging technology are being investigated by the CERN EP Strategic R&D Programme on Technologies for Future Experiments for an application in particle physics. The appeal of monolithic detectors lies in the fact that both sensor volume and readout electronics are integrated in the same silicon wafer, providing a reduction in production effort, costs and scattering material. The Tangerine Project WP1 at DESY participates in the Strategic R&D Programme and is focused on the development of a monolithic active pixel sensor with a time and spatial resolution compatible with the requirements for a future lepton collider vertex detector. By fulfilling these requirements, the Tangerine detector is suitable as well to be used as telescope planes for the DESY-II Test Beam facility. The project comprises all aspects of sensor development, from the electronics engineering and the sensor design using simulations, to laboratory and test beam investigations of prototypes. Generic TCAD Device and Monte-Carlo simulations are used to establish an understanding of the technology and provide important insight into performance parameters of the sensor. Testing prototypes in laboratory and test beam facilities allows for the characterization of their response to different conditions. By combining results from all these studies it is possible to optimize the sensor layout. This contribution presents results from generic TCAD and Monte-Carlo simulations, and measurements performed with test chips of the first sensor submission.Comment: 7 pages, 8 figures, submitted to IEEE Xplore as conference record for 2022 IEEE NSS/MIC/RTS

The CLICTD Monolithic CMOS Sensor

CLICTD is a monolithic silicon pixel sensor fabricated in a modified 180 nm CMOS imaging process with a small collection electrode design and a high-resistivity epitaxial layer. It features an innovative sub-pixel segmentation scheme and is optimised for fast charge collection and high spatial resolution. The sensor was developed to target the requirements for the tracking detector of the proposed future Compact Linear Collider (CLIC). Most notably, a temporal resolution of a few nanoseconds and a spatial resolution below 7 μm are demanded. In this contribution, the sensor performance measured in beam tests is presented with emphasis on recent studies using assemblies with different thicknesses (down to 50 μm to minimize the material budget) and inclined particle tracks.CLICTD is a monolithic silicon pixel sensor fabricated in a modified 180 nm CMOS imaging process with a small collection electrode design and a high-resistivity epitaxial layer. It features an innovative sub-pixel segmentation scheme and is optimised for fast charge collection and high spatial resolution. The sensor was developed to target the requirements for the tracking detector of the proposed future Compact Linear Collider (CLIC). Most notably, a temporal resolution of a few nanoseconds and a spatial resolution below 7 µm are demanded. In this contribution, the sensor performance measured in beam tests is presented with emphasis on recent studies using assemblies with different thicknesses (down to 50 µm to minimize the material budget) and inclined particle tracks.CLICTD is a monolithic silicon pixel sensor fabricated in a modified 180 nm CMOS imaging process with a small collection electrode design and a high-resistivity epitaxial layer. It features an innovative sub-pixel segmentation scheme and is optimised for fast charge collection and high spatial resolution. The sensor was developed to target the requirements for the tracking detector of the proposed future Compact Linear Collider (CLIC). Most notably, a temporal resolution of a few nanoseconds and a spatial resolution below 7 microns are demanded. In this contribution, the sensor performance measured in beam tests is presented with emphasis on recent studies using assemblies with different thicknesses (down to 50 microns to minimize the material budget) and inclined particle tracks

Silicon vertex and tracking detector R&D for CLIC

The physics aims at the proposed future high-energy linear e+e- collider CLIC pose challenging demands on the performance of the detector system. In particular, the vertex and tracking detectors have to combine a spatial resolution of a few micrometres and a low material budget with a time-stamping accuracy of a few nanoseconds. For the vertex detector, fine-pitch sensors, dedicated 65nm readout ASICs, fine-pitch bonding techniques using solder bumps or anisotropic conductive films as well as monolithic devices based on Silicon-On-Insulator technology are explored. Fully monolithic CMOS sensors with large and small collection electrodes are under investigation for the large surface CLIC tracker. This contribution gives an overview of the CLIC vertex and tracking detector R&D, focusing on recent results from test-beam campaigns and simulation-based sensor optimisation studies

Simulation Studies and Characterisation of Monolithic Silicon Pixel-Detector Prototypes for Future Collider Detectors & Unsupervised Anomaly Detection in Belle II Pixel-Detector Data

Present and future high-energy physics experiments pose challenging demands on the detector systems and analysis methods. This dissertation addresses both aspects by focusing on the optimisation and characterisation of a novel technology demonstrator for a monolithic silicon sensor design and the development of model-agnostic analysis techniques for the pixel detector at the Belle II experiment. In the first part, the requirements of vertex and tracking detectors for future Higgs factories such as the Compact Linear e+e- Collider (CLIC) or the Future Circular e+e- Collider (FCCee) are addressed. The experimental conditions at these colliders require high-precision sensors with a low material content. The CLIC Tracker Detector (CLICTD) is a technology demonstrator for a monolithic pixel sensor fabricated in a modified 180 nm CMOS imaging process that targets the requirements of the CLIC tracker. The performance of the sensor is assessed for different operation conditions, pixel designs and wafer materials. A spatial resolution down to (3.9 ± 0.2) μm, time resolution down to (4.8 ± 0.1) ns as well as a hit detection efficiency >99.7 % over a wide range of detection thresholds is observed and the CLIC tracker requirements are found to be fulfilled. Modern silicon sensors such as CLICTD incorporate complex sensor designs that are challenging to simulate and model. This dissertation presents a combination of elec- trostatic finite-element and transient Monte Carlo simulations to provide simultaneous access to precise sensor modelling and high-statistics simulation samples. The advanced simulation approach is validated against data and excellent agreement is found over a wide range of different operation conditions. In the second part, patterns of minimally-processed pixel hits recorded by the Belle II pixel detector are investigated. In particular, a focus on model-agnostic approaches is placed that enable an unbiased exploration of data, while filtering out anomalous detector signatures that could hint at new physics scenarios. The identification of hypothetical magnetic monopoles against Belle II beam background is presented using Self-Organizing Kohonen Maps and Autoencoders. The two unsupervised algorithms are compared to a convolutional Multilayer Perceptron and a superior signal efficiency at high background- rejection levels is found for the unsupervised techniques

Combining TCAD and Monte Carlo Methods to Simulate High-Resistivity CMOS Pixel Detectors using the Allpix2 Framework

For the research and development (R&D) of new silicon sensor technology, simulations of silicon detectors are a vital tool for determining their characteristics and performance. Simulations furthermore complement and help to understand experiments conducted on silicon sensors. In this project electrostatic field simulations with TCAD are combined with a Monte Carlo method with the Allpix2 in order to determine the properties of an High-Resistivity CMOS silicon sensor. The simulation is validated against test beam data and the performance of the silicon detector is assessed

Search for Highly Ionizing Particles with the Pixel Detector at Belle II

The Belle II experiment, located at the SuperKEKB collider at the high-energy research facility KEK in Tsukuba, Japan, started operation in 2018. Compared to the predecessor experiment Belle, Belle II plans to increase the peak luminosity by a factor of about 40, by employing nano-beam technology in the interaction region. In particular the new, innermost sub-detector of Belle II the Pixel Vertex Detector (PXD) - is in close proximity to the interaction point. This allows for the detection of particles, which do not leave a signal in the outer sub-detectors. Among these, Highly Ionizing Particles (HIPs) encounter a characteristically high energy loss, limiting their penetration depth into the detector. Anti-deuterons and magnetic monopoles as possible HIPs are considered. Without a signal in the outer sub-detectors, no track trigger is issued, resulting in possible information loss. The possibility of identifying HIPs solely with information provided by the PXD is presented, by using neural network algorithms operating in a multidimensional parameter space of PXD cluster data