Rafael Ballabriga

CERN | CERN · Physics Department (PH)

The CERN EP R&D WP 1.2 aims to develop state-of-art monolithic pixel detectors using modern CMOS processes. The TPSCo 65 nm process is a suitable candidate and its radiation tolerance and sensor performance are therefore being studied. The impact of the back bias on the transistor behavior has also been measured to provide the designers with accura...

A Scalable Low Voltage Signaling (SLVS) transmitter and receiver have been developed as IP blocks in a 28 nm standard CMOS technology for the future upgrades for the high luminosity LHC. At the target data rate of 1.28 Gbps, the transmitter consumes 6 mW and the receiver consumes 2 mW. The transmitter’s output is powered with 1.2 V to provide compa...

Eye lens dosimetry has been an important field of research in the last decade. Dose measurements with a prototype of an active personal eye lens dosemeter based on the Dosepix detector are presented. The personal dose equivalent at 3 mm depth of soft tissue, $\boldsymbol {H}_{\textbf {p}}\boldsymbol {(3)}$ , was measured in the center front of a...

First investigations regarding dosimetric properties of the hybrid, pixelated, photon-counting Dosepix detector in the direct beam of a pulsed photon field (RQR8) for the personal dose equivalent H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> (10) are presented. The influence quantities su...

This manuscript describes the optimization of the front-end readout electronics for high granularity hybrid pixel detectors. The theoretical study aims at minimizing the noise and jitter. The model presented here is validated with both circuit post layout simulations and measurements on the Timepix4 Application Specific Integrated Circuit (ASIC). T...

Small collection-electrode monolithic CMOS sensors profit from a high signal-to-noise ratio and a small power consumption, but have a limited active sensor volume due to the fabrication process based on thin high-resistivity epitaxial layers. In this paper, the active sensor depth is investigated in the monolithic small collection-electrode technol...

A characterisation of the Timepix4 pixel front-end with a strong focus on timing performance is presented. Externally generated test pulses were used to probe the per-pixel time-to-digital converter (TDC) and measure the time-bin sizes by precisely controlling the test-pulse arrival time in steps of 10 ps. The results indicate that the TDC can achi...

This work presents the 8-channel FastIC ASIC developed in CMOS 65 nm technology suitable for the readout of positive and negative polarity sensors in high energy physics experiments, Cherenkov detectors and time-of-flight systems. The front-end can be configured to perform analog summation of up to 4 single-ended channels before discrimination in v...

Small collection-electrode monolithic CMOS sensors profit from a high signal-to-noise ratio and a small power consumption, but have a limited active sensor volume due to the fabrication process based on thin high-resistivity epitaxial layers. In this paper, the active sensor depth is investigated in the monolithic small collection-electrode technol...

A characterisation of the Timepix4 pixel front-end with a strong focus on timing performance is presented. Externally generated test pulses were used to probe the per-pixel time-to-digital converter (TDC) and measure the time-bin sizes by precisely controlling the test-pulse arrival time in steps of 10 ps. The results indicate that the TDC can achi...

This paper presents the case for how students can be helped to increase their scientific vocation by experimental work and the introduction of particle physics into pre-university studies. These two ideas are the two main lines of work of the ADMIRA initiative, which has been created by individuals belonging to different and complementary education...

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 enab...

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 enab...

Timepix4 is a 24.7 × 30.0 mm ² hybrid pixel detector readout ASIC which has been designed to permit detector tiling on 4 sides. It consists of 448 × 512 pixels which can be bump bonded to a sensor with square pixels at a pitch of 55 µm. Like its predecessor, Timepix3, it can operate in data driven mode sending out information (Time of Arrival, ToA...

Over the 50 years since its inception, the history of computed tomography (CT) technology development consists of a few quantum leaps (revolutions), which changed the dimensionality of clinical CT data ( Fig. 1 ).

This work presents the 8-channel FastIC ASIC developed in CMOS 65 nm technology suitable for the readout of positive and negative polarity sensors with intrinsic amplifi- cation in High Energy Physics experiments, Positron Emission Tomography and other Time-of-Flight systems. The front-end can be configured to readout each input channel individuall...

First investigations regarding dosimetric properties of the hybrid, pixelated, photon-counting Dosepix detector in a pulsed photon field (RQR8) for the personal dose equivalent $H\mathrm{_p(10)}$ are presented. The influence quantities such as pulse duration and dose rate were varied, and their responses were compared to the legal limits provided i...

The CLIC Tracker Detector (CLICTD) is a monolithic pixel sensor. It is fabricated in a 180 nm CMOS imaging process, modified with an additional deep low-dose n-type implant to obtain full lateral depletion. The sensor features a small collection diode, which is essential for achieving a low input capacitance. The CLICTD sensor was designed as a tec...

First measurements characterizing dosimetric properties of a dosimetry system designed for the purpose of active personal dosimetry for photons with mean energies from 12.4 keV to 1250 keV according to PTB requirements are presented. The system consists of three Dosepix detectors, which is a hybrid, pixelated, photon-counting X-ray detector. The en...

The Silicon Photomultiplier (SiPM) sensor is replacing the extensive use of the Photomultiplier Tube (PMT) in fast timing applications. These photo-sensors can be applied in different fields such as medical imaging systems like Positron Emission Tomography (PET), LIDAR technologies or High Energy Physics (HEP) experiments. More specific, Time-of-Fl...

The CLIC Tracker Detector (CLICTD) is a monolithic pixel sensor. It is fabricated in a 180 nm CMOS imaging process, modified with an additional deep low-dose n-type implant to obtain full lateral depletion. The sensor features a small collection diode, which is essential for achieving a low input capacitance. The CLICTD sensor was designed as a tec...

The time resolution of active pixel sensors whose timestamp mechanism is based on Time-to-Digital Converters is critically linked to the accuracy in the distribution of the master clock signal that latches the timestamp values across the detector. The Clock Distribution Network that delivers the master clock signal must compensate process-voltage-t...

A novel monolithic pixelated sensor and readout chip, the CLIC Tracker Detector (CLICTD) chip, is presented. The CLICTD chip was designed targeting the requirements of the silicon tracker development for the experiment at the Compact Linear Collider (CLIC), and has been fabricated in a modified 180 nm CMOS imaging process with charge collection on...

The Medipix4 chip is the latest member of the family of Medipix pixel detector readout chips aimed at high rate spectroscopic X-ray imaging. Unlike its predecessors, it will be possible to tile the chip on all 4 sides permitting seamless large area coverage. This paper focuses on the development of the new Medipix4 front-end architecture capable of...

X-ray imaging is a widely used imaging modality in the medical diagnostic field due to its availability, low cost, high spatial resolution and fast image acquisition. X-ray photons in standard X-ray sources are polychromatic. Detectors that allow to extract the “colour” information of the individual X-rays can lead to contrast enhancement, improved...

The CLIC Tracker Detector (CLICTD) is a monolithic pixelated sensor chip produced in a $180$ nm imaging CMOS process built on a high-resistivity epitaxial layer. The chip, designed in the context of the CLIC tracking detector study, comprises a matrix of ${16\times128}$ elongated pixels, each measuring ${300\times30}$ $\mu$m$^2$. To ensure prompt c...

The first Medipix chip which aimed at permitting single photon counting on a sizable matrix of pixels was developed in the mid-1990’s. In the following 20 years two families of chips have evolved from that initial effort. The Medipix photon counting family of chips comprises Medipix, Medipix2 and Medipix3. A 4th generation chip, Medipix4, is under...

The Timepix2 ASIC (application-specific integrated circuit) is the upgraded successor to the Timepix [1] hybrid pixel detector readout chip. Like the original, Timepix2 contains a matrix of 65k square pixels of 55 μm pitch that can be coupled to a similarly segmented semiconductor sensor, or integrated in an ionising gas detector. The pixels are pr...

Detector developments are currently enabling new capabilities in the field of transmission electron microscopy (TEM). We have investigated the limits of a hybrid pixel detector, Medipix3, to record dynamic, time varying, electron signals. Operating with an energy of 60 keV, we have utilised electrostatic deflection to oscillate electron beam positi...

Single quantum imaging can be achieved for visible wavelengths by using very small capacitance attopixels, so that even one electron charge produces a good signal. In different e.m. frequency domains, X-rays or gamma quanta, or quanta with mass, generate a signal of many e-h pairs in an extended semiconductor sensor volume. Imagers incorporating so...

Detector developments are currently enabling new capabilities in the field of Transmission Electron Microscopy (TEM). We have investigated the limits of a hybrid pixel detector, Medipix3, to record dynamic, time varying, electron signals. Operating with an energy of 60keV, we have utilised electrostatic deflection to oscillate electron beam positio...

Power consumption is always a concern in the design of readout chips for hybrid pixel detectors. The Timepix3 chip is capable of dealing with up to 80 Mhits/cm²/sec and tagging each hit within a time bin of 1.56 ns. At full speed the Timepix3 chip will consume 1.3 W. We consider how to reduce power consumption if hit rate and/or time stamp precisio...

Hybrid pixel detectors were developed to meet the requirements for tracking in the inner layers at the LHC experiments. With low input capacitance per channel (10-100 fF) it is relatively straightforward to design pulse processing readout electronics with input referred noise of ∼100 e-rms and pulse shaping times consistent with tagging of events t...

The concept of capacitive coupling between sensors and readout chips is under study for the vertex detector at the proposed high-energy CLIC electron positron collider. The CLICpix Capacitively Coupled Pixel Detector (C3PD) is an active High-Voltage CMOS sensor, designed to be capacitively coupled to the CLICpix2 readout chip. The chip is implement...

In this paper we report quantitative measurements of the imaging performance for the current generation of hybrid pixel detector, Medipix3, used as a direct electron detector. We have measured the modulation transfer function and detective quantum efficiency at beam energies of 60 & 80 keV. In single pixel mode, energy threshold values can be chose...

VeloPix, a 130 nm CMOS technology chip with data driven and zero suppressed readout, will be used as a readout chip for the hybrid pixel system of the LHCb Vertex Locator (VELO) upgrade. The upgrade, scheduled for LHC Run-3, will enable the experiment to be read out at 40 MHz in trigger-less mode, with event selection being performed in the CPU far...

In our article we report first quantitative measurements of imaging performance for the current generation of hybrid pixel detector, Medipix3, as direct electron detector. Utilising beam energies of 60 & 80 keV, measurements of modulation transfer function (MTF) and detective quantum efficiency (DQE) have revealed that, in single pixel mode (SPM),...

Semiconductor detector readout chips with pulse processing electronics have made possible spectroscopic X-ray imaging, bringing an improvement in the overall image quality and, in the case of medical imaging, a reduction in the X-ray dose delivered to the patient. In this contributionwe reviewthe state of the art in semiconductor-detector readout A...

The Medipix3 Collaboration has broken new ground in spectroscopic X-ray imaging and in single particle detection and tracking. This paper will review briefly the performance and limitations of the present generation of pixel detector readout chips developed by the Collaboration. Through Silicon Via technology has the potential to provide a signific...

Spectroscopic micro-computed tomography (CT) using photon counting detectors is a technology that promises to deliver material-specific images in pre-clinical research while suppressing noise related to dark current. Inherent to such applications is the need for a high spatial resolution, which can only be achieved with small focal spot sizes in th...

The Medipix3RX is the latest version of the Medipix3 photon counting ASICs, which implements two new operational modes, with respect to the Medipix2 ASIC, aimed at eliminating charge shared events (referred to as Charge Summing Mode (CSM)) and at providing spectroscopic information (referred to as Colour Mode (CM)). The Medipix3RX is a redesign of...

Part of 16th International Workshop on Radiation Imaging Detectors The Dosepix detector is a hybrid photon-counting pixel detector based on ideas of the Medipix and Timepix detector family. 1 mm thick cadmium telluride and 300 μm thick silicon were used as sensor material. The pixel matrix of the Dosepix consists of 16 x 16 square pixels with 12 r...

Spectroscopic micro-computed tomography using photon counting detectors is a technology that promises to deliver material-specific images in pre-clinical research. Inherent to such applications is the need for a high spatial resolution, which can only be achieved with small focal spot sizes in the micrometer range. This limits the achievable x-ray...

The LHCb Vertex Detector (VELO) will be upgraded in 2018 along with the other subsystems of LHCb in order to enable full readout at 40 MHz, with the data fed directly to the software triggering algorithms. The upgraded VELO is a lightweight hybrid pixel detector operating in vacuum in close proximity to the LHC beams. The readout will be provided b...

Spectroscopic x-ray imaging based on pixellated semiconductor detectors can be sensitive to charge sharing and K-fluorescence, depending on the sensor material used, its thickness and the pixel pitch employed. As a consequence, spectroscopic resolution is partially lost. In this paper, we study a new detector ASIC, the Medipix3RX, that offers a nov...

Dosepix is a hybrid pixel detector based on the technology of the Medipix and Timepix detectors. The Dosepix detector has a matrix of 16 × 16 square pixels, with the sensor segmented into rows of small (55 μm) and big (220 μm) pixels. In addition to photon counting, the Dosepix detector has a time over threshold mode which permits energy resolved m...

For clinical X-ray imaging, the detector performance under high flux conditions is very important, with typical flux rates for modern CT systems reaching 109 photons s−1 mm−2 in the direct beam. In addition, for spectral imaging a good energy resolution under these conditions is needed. This poses difficulties, since pulse pileup in the pixel elect...

Photon-counting detectors in medical x-ray imaging provide a higher dose efficiency than integrating detectors. Even further possibilities for imaging applications arise, if the energy of each photon counted is measured, as for example K-edge-imaging or optimizing image quality by applying energy weighting factors. In this contribution, we show res...

With energy-resolving photon-counting detectors in grating-based x-ray phase-contrast imaging it is possible to reduce the dose needed and optimize the imaging chain towards better performance. The advantage of photon- counting detector’s linear energy response and absence of electronic noise in attenuation based imaging is known. The access to the...

A prototype hybrid pixel detector ASIC specifically designed to the requirements of the vertex detector for CLIC is described and first electrical measurements are presented. The chip has been designed using a commercial 65 nm CMOS technology and comprises a matrix of 64 × 64 square pixels with 25 μm pitch. The main features include simultaneous 4-...

This paper describes a front-end for hybrid pixel readout chips, which was developed for the Timepix3 and Smallpix ASICs. The front-end contains a single-ended preamplifier with a structure for leakage current compensation which can handle both signal polarities, and a single-threshold discriminator with compensation for pixel-to-pixel mismatch. Pr...

We have carried out grating-based x-ray differential phase-contrast measurements with a hybrid pixel detector in 16 energy channels simultaneously. A method for combining the energy resolved phase-contrast images based on energy weighting is presented. An improvement in contrast-to-noise ratio by 58.2% with respect to an emulated integrating detect...

The Medipix3 chips have been designed to permit spectroscopic imaging in highly segmented hybrid pixel detectors. Spectral degradation due to charge sharing in the sensor has been addressed by means of an architecture in which adjacent pixels communicate in the analog and digital domains on an event-by-event basis to reconstruct the deposited charg...

The Medipix family of chips use on-pixel pulse processing front-ends, digitization and counters to produce images of radiation. The devices have been derived from developments for the Large Hadron Collider (LHC) physics experiments at CERN. With the miniaturization of the associated readout system a new method of dosimetry becomes accessible, where...

Innovative detector systems for non-destructive material analysis and for medical diagnosis are an important development to improve the performance and the quality of examination methods. For a number of years now photon-counting X-ray detectors are being developed to process incoming X-ray photons as single events. These detectors facilitate a hig...

The radiation characteristics with respect to Total Ionizing Dose (TID) and Single-Event Upsets (SEUs) of a 65 nm CMOS technology have been investigated. Single transistor structures of a variety of dimensions and several basic circuits were designed and fabricated. The circuits include a 64-kbit shift-register, a 56-kbit SRAM and a ring-oscillator...

We present the first electrical measurements of an application-specific integrated circuit (ASIC) to be used in a hybrid pixel detector intended for dosimetry and radiation detection. The dosimeter has three programmable modes of operation: photon counting mode, energy integration mode, and dosimetry mode. The ASIC comprises a matrix of 16 by 16 (2...

Pixelated photon counting semiconductor X-ray detectors like the Medipix feature adjustable energy thresholds allowing selective counting of photons of a specified energy. This development permits for energy selective X-ray imaging with advanced material information. Furthermore the photon counting function principle of these detectors allows X-ray...

In this work we present the design of a chip which provides the readout of a highly segmented diode array, in which signals induced by individual X-ray photons are processed discretely. There are several benefits to this approach, including the ability to achieve a high signal to noise ratio due to the inherently low sensor capacitance, and the sup...

The Medipix3 (MP3) detector is the most recent addition to the family of Medipix spectral x-ray detectors. It offers many advantages to the previous version of the Medipix detector, such as charge summing mode, dual counters, improved radiation hardening and the ability to operate in continuous read/write mode. Although these added features provide...