High Granularity Timing Detector Research Articles

Performance of LGAD sensors with carbon enriched gain layer produced by USTC

The Low Gain Avalanche Detector (LGAD) technology is proposed for the ATLAS High Granularity Timing Detector (HGTD) and the CMS Endcap Timing Layer (ETL) towards the High-Luminosity Large Hadron Collider (HL-LHC), for which radiation hardness is one of the key requirements. In this paper we report results from the measurements on LGAD sensors designed by the University of Science and Technology of China (USTC) and fabricated by the Institute of Microelectronics of the Chinese Academy of Science (IME, CAS). These sensors have been irradiated with irradiation fluences of 8×1014, 1.5×1015, 2.5×1015 and 6×1015 cm−2 1 MeV neutron equivalent. Both un-irradiated and irradiated sensors were measured with a 90Sr-based beta scope at −30∘C to extract the collected charge and time resolution. The results show that sensors with carbon implantation can provide collected charge of more than 4 fC and time resolution better than 70 ps at appropriate bias voltage even for the equivalent fluence of 2.5×1015 cm−2. Both the collected charge and the time resolution meet the design specification of HGTD.

Design and testing results of a long flexible printed circuit for the ATLAS high granularity timing detector

The high granularity timing detector for the ATLAS upgrade is under construction to meet the challenges of the HL-LHC. The silicon detectors along with the electronics are installed in two double-sided disks per end-cap and consist of basic units (called modules) connected to the peripheral electronics by flexible printed circuit cables. The complexity of the system impacts on the requirements of having high number of interconnections for the power delivery network, the data-links for the high-speed readout as well as the inputs for the system control. This and other constraints on the topology, the reduced space between disks and mechanical robustness led to the development of a flexible printed circuit cable. We present the design and test of a two-layer flexible cable of a maximum connection distance for the module.

Effects of Shallow Carbon and Deep N++ Layer on the Radiation Hardness of IHEP-IME LGAD Sensors

Low-gain avalanche diode (LGAD) is the chosen technology for the ATLAS high-granularity timing detector (HGTD). According to previous studies, the acceptor removal effect due to the radiation and the single-event burnout (SEB) at high bias voltages are still a challenge for the LGAD. The Institute of High Energy Physics (IHEP), Beijing, China, cooperated with the Institute of Microelectronics (IME), Beijing, China, for the design and fabrication of the IHEP-IME LGAD sensors with shallow carbon and deep N++ layer to improve the radiation hardness of LGAD. After neutron irradiation up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.5 \times 10^{15}\,\,{\mathrm{ n}}_{\mathrm{ eq}}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the leakage current, the collected charge, and timing resolution of the three IHEP-IME sensors measured with a beta telescope setup meet the HGTD requirements ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; 125~\mu \text{A}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , >4 fC, and <70 ps). The LGAD sensor with shallow carbon had the lowest operation voltage after irradiation and is very promising to avoid the SEB effect. A sensor with a deep N++ layer increased the breakdown voltage of the LGAD with a high dopant concentration, which could alleviate the problem of the early breakdown of radiation-hard LGAD before irradiation.

A High Granularity Timing Detector for the ATLAS Detector Phase-II Upgrade

To boost the performance of the Large Hadron Collider (LHC) and increase the potential of discoveries after 2027, the High-Luminosity LHC (HL-LHC) project has been announced, with the aim of increasing the luminosity by a factor of 10 above the design value of the LHC. This will lead to an increase of the pile-up interactions and will negatively impact the reconstruction of objects in the ATLAS detector, as well as its triggering performance. In particular, at the forward region, where the inner detector has a lower momentum resolution and the electromagnetic calorimeter has a coarser granularity. Therefore, a high granularity timing detector (HGTD) has been proposed to mitigate the pile-up effect; complementing the inner tracker (ITk) and providing a luminosity measurement, it will be located in front of the LAr end-cap calorimeter. The HGTD will cover the pseudo-rapidity region between 2.4 and 4.0, with two layers of double-sided silicon sensors that will provide a time resolution of 30 ps per track. Each readout cell has a cross Section of 1.3 mm <inline-formula> <tex-math notation="LaTeX">$\times1.3$ </tex-math></inline-formula> mm, ensuring a high granular detector with 3.7 million channels. To achieve the required high signal-to-noise ratio and provide sufficient gain, Low Gain Avalanche Detector (LGAD) technology was chosen. The general specifications and requirements of LGAD will be outlined, as well as the technical design and status of the project. The ongoing research and development effort to study the sensors, readout ASIC, and other components, supported by laboratory and test beam results, will also be presented, in addition to some physics and performance results.

A High-Granularity Timing Detector for the ATLAS Phase-II upgrade

The increase of the particle flux at the HL-LHC with instantaneous luminosities up to L=7.5 × 10 34 cm −2 s −1 will have a severe impact on the ATLAS detector reconstruction and trigger performance. The end-cap and forward region where the liquid Argon calorimeter has coarser granularity and the inner tracker has poorer momentum resolution will be particularly affected. A High Granularity Timing Detector will be installed in front of the liquid Argon end-cap calorimeters to help in charged-particle reconstruction and luminosity measurement. This low angle detector is introduced to augment the new all-silicon Inner Tracker in the pseudo-rapidity range from 2.4 to 4.0. Two silicon-sensor double-sided per end-cap will provide precision timing information for minimum-ionizing particles with a resolution as good as 30 ps per track in order to assign each particle to the correct vertex. Readout cells have a size of 1.3 mm × 1.3 mm, leading to a highly granular detector with 3.7 million channels. The Low Gain Avalanche Detectors technology has been chosen as sensor as it provides excellent timing performance. The requirements and overall specifications of the High Granularity Timing Detector are presented as well as the technical design and the project status. The on-going R&D effort carried out to study the sensors, the readout ASIC, and the other components, supported by laboratory and test beam results, are also presented.

Radiation hardness characterization of low gain avalanche detector prototypes for the high granularity timing detector

The high granularity timing detector (HGTD) is a crucial component of the ATLAS phase II upgrade to cope with the extremely high pile-up (the average number of interactions per bunch crossing can be as high as 200). With the precise timing information (&lt;i&gt;σ&lt;sub&gt;t&lt;/sub&gt;&lt;/i&gt;～30 ps) of the tracks, the track-to-vertex association can be performed in the “4-D” space. The Low Gain Avalanche Detector (LGAD) technology is chosen for the sensors, which can provide the required timing resolution and good signal-to-noise ratio. Hamamatsu Photonics K.K. (HPK) has produced the LGAD with thicknesses of 35 μm and 50 μm. The University of Science and Technology of China(USTC) has also developed and produced 50 μm LGADs prototypes with the Institute of Microelectronics (IME) of Chinese Academy of Sciences. To evaluate the irradiation hardness, the sensors are irradiated with the neutron at the JSI reactor facility and tested at USTC. The irradiation effects on both the gain layer and the bulk are characterized by &lt;i&gt;I&lt;/i&gt;-&lt;i&gt;V&lt;/i&gt; and &lt;i&gt;C&lt;/i&gt;-&lt;i&gt;V&lt;/i&gt; measurements at room temperature (20 ℃) or −30 ℃. The breakdown voltages and depletion voltages are extracted and presented as a function of the fluences. The final fitting of the acceptor removal model yielded the &lt;i&gt;c&lt;/i&gt;-factor of 3.06×10&lt;sup&gt;−16&lt;/sup&gt; cm&lt;sup&gt;−2&lt;/sup&gt;, 3.89×10&lt;sup&gt;−16&lt;/sup&gt; cm&lt;sup&gt;−2&lt;/sup&gt; and 4.12×10&lt;sup&gt;−16&lt;/sup&gt; cm&lt;sup&gt;−2&lt;/sup&gt; for the HPK-1.2, HPK-3.2 and USTC-1.1-W8, respectively, showing that the HPK-1.2 sensors have the most irradiation resistant gain layer. A novel analysis method is used to further exploit the data to get the relationship between the &lt;i&gt;c&lt;/i&gt;-factor and initial doping density.

Characterization of Irradiated Boron, Carbon-Enriched and Gallium Si-on-Si Wafer Low Gain Avalanche Detectors

Low Gain Avalanche Detectors (LGADs) are n-on-p silicon sensors with an extra doped p-layer below the n-p junction which provides signal amplification. The moderate gain of these sensors, together with the relatively thin active region, provides excellent timing performance for Minimum Ionizing Particles (MIPs). To mitigate the effect of pile-up during the High-Luminosity Large Hadron Collider (HL-LHC) era, both ATLAS and CMS experiments will install new detectors, the High-Granularity Timing Detector (HGTD) and the End-Cap Timing Layer (ETL), that rely on the LGAD technology. A full characterization of LGAD sensors fabricated by Centro Nacional de Microelectrónica (CNM), before and after neutron irradiation up to 1015 neq/cm2, is presented. Sensors produced in 100 mm Si-on-Si wafers and doped with boron and gallium, and also enriched with carbon, are studied. The results include their electrical characterization (I-V, C-V), bias voltage stability and performance studies with the Transient Current Technique (TCT) and a Sr-90 radioactive source setup.

The performance of IHEP-NDL LGAD sensors after neutron irradiation

The performances of Low Gain Avalanche Diode (LGAD) sensors from a neutron irradiation campaign with fluences of 0.8 × 1015, 1.5 × 1015 and 2.5 × 1015 n eq/cm2 are reported in this article. These LGAD sensors are developed by the Institute of High Energy Physics, Chinese Academy of Sciences and the Novel Device Laboratory for the High Granularity Timing Detector of the High Luminosity Large Hadron Collider.The timing resolution and collected charge of the LGAD sensors were measured with electrons from a beta source.After irradiation with a fluence of 2.5 × 1015 n eq/cm2, the collected charge decreases from 40 fC to 7 fC, the signal-to-noise ratio deteriorates from 48 to 12, and the timing resolution increases from 29 ps to 39 ps.

Digital switch boards for IV and CV measurements of large-array Low Gain Avalanche Detectors

The High-Granularity Timing Detector (HGTD), with a time resolution of approximately 30 ps, is proposed for the ATLAS Phase II upgrade to address the challenge of greatly increased pile-up interactions. The HGTD is based on the technology of Low Gain Avalanche Detectors (LGADs). The current–voltage (IV) and capacitance–voltage (CV) measurements are important methods to study the main characteristics that can be exploited for quality controlling LGADs during production. A single probe can be controlled via computer to switch channels when using an automatic probe station, but this leaves the remaining, adjacent channels floating and results in inaccurate measurements due to the punch-through effect. We designed the digital switch boards for the IV and CV measurements of 5 × 5 and 15 × 15 LGADs arrays. With the digital switch board and probe cards, channels on a large-array LGADs can be scanned automatically during the measurement, which greatly improves the measurement efficiency. The results show that the leakage currents and noise of all channels induced by the two digital switch boards are lower than 10 pA. We show the IV and CV curves of all channels on two LGADs from Hamamatsu Photonics K. K. (HPK) with our digital switch boards. Compared with the results measured by HPK with an automatic probe station, the IV and CV curves that we measured have better uniformity and accuracy, demonstrating that the quality control of the large-array LGADs can be conducted well with our digital switch board.

A High-Granularity Timing Detector for the Phase-II upgrade of the ATLAS Calorimeter system: detector concept, description and R&amp;D and beam test results

The particle flux increase (pile-up) at the HL-LHC with luminosities of L = 7.5 × 1034 cm−2 s−1 will have a significant impact on the reconstruction of the ATLAS detector and on the performance of the trigger. The forward region and the end-cap where the internal tracker has poorer longitudinal track impact parameter resolution, and where the liquid argon calorimeter has coarser granularity, will be significantly affected. A High Granularity Time Detector (HGTD) is proposed to be installed in front of the LAr end-cap calorimeter for the mitigation of the pileup effect, as well as measurement of luminosity. It will have coverage of 2.4 to 4.0 from the pseudo-rapidity range. Two dual-sided silicon sensor layers will provide accurate timing information for minimum-ionizing particles with a resolution better than 30 ps per track (before irradiation), for assigning each particle to the correct vertex. The readout cells are about 1.3 mm × 1.3 mm in size, which leads to a high granular detector with 3 million channels. The technology of low-gain avalanche detectors (LGAD) with sufficient gain was chosen to achieve the required high signal-to-noise ratio. A dedicated ASIC is under development with some prototypes already submitted and evaluated. The requirements and general specifications of the HGTD will be maintained and discussed. R&amp;D campaigns on the LGAD are carried out to study the sensors, the related ASICs and the radiation hardness. Both laboratory and test beam results will be presented.

Beam test results of NDL Low Gain Avalanche Detectors (LGAD)

A High-Granularity Timing Detector (HGTD) is proposed based on the Low-Gain Avalanche Detector (LGAD) for the ATLAS experiment to satisfy the time resolution requirement for the up-coming High Luminosity at LHC (HL-LHC). We report on beam test results for two proto-types LGADs (BV60 and BV170) developed for the HGTD. Such modules were manufactured by the Institute of High Energy Physics (IHEP) of Chinese Academy of Sciences (CAS) collaborated with Novel Device Laboratory (NDL) of the Beijing Normal University. The beam tests were performed with 5 GeV electron beam at DESY. The timing performance of the LGADs was compared to a trigger counter consisting of a quartz bar coupled to a SiPM readout while extracting reference SiPM by fitting with a Gaussian function. The time resolution was obtained as 41 ps and 63 ps for the BV60 and the BV170, respectively.

A High-Granularity Timing Detector for the Phase-II upgrade of the ATLAS Calorimeter system: detector concept, description, R&D and beam test results

The increase of the number of interactions at the High Luminosity LHC will have a severe impact on the ATLAS detector reconstruction and trigger performance. The end-cap and forward regions, where the Liquid Argon calorimeter has coarser granularity and the inner tracker has poorer momentum resolution, will be particularly affected. A High Granularity Timing Detector (HGTD) is proposed in front of the Liquid Argon end-cap calorimeters for pile-up mitigation and for luminosity measurement. It will cover the pseudo-rapidity range 2.4 < |η| < 4.0. Two silicon sensors double-sided layers on each end-cap will provide precision timing information for minimum ionising particles in order to assign each particle to the correct vertex. Readout cells have a size of 1.3 × 1.3 mm, leading to a highly granular detector with over 3.6 million channels. The Low Gain Avalanche Detectors (LGAD) technology has been chosen for the HGTD detector as it provides a compact sensor with large signal over noise ratio leading to excellent timing performance. The requirements and overall specifications of the HGTD will be presented. LGAD R&D campaigns were carried out to study the sensors and their radiation hardness. Latest laboratory and test beam results will be presented.

Layout and performance of HPK prototype LGAD sensors for the High-Granularity Timing Detector

The High-Granularity Timing Detector is a detector proposed for the ATLAS Phase II upgrade. The detector, based on the Low-Gain Avalanche Detector (LGAD) technology, will cover the pseudo-rapidity region of 2.4<|η|<4.0 with two end caps on each side and a total area of 6.4 m2. The timing performance can be improved by implanting an internal gain layer that can produce signals with a fast rising edge. It significantly improves the signal-to-noise ratio. The required average timing resolution per track for a minimum ionizing particle is 30 ps at the start and 50 ps at the end of the HL-LHC operation. This is achieved with several layers of LGAD. The innermost region of the detector would accumulate a 1MeV neutron-equivalent fluence up to 2.5× 1015 neq/cm2 including a safety factor of 1.5 before being replaced during the scheduled shutdowns. The addition of this new detector is expected to play an important role in the mitigation of high pile-ups at the HL-LHC. The layout and performance of the various versions of LGAD prototypes produced by Hamamatsu (HPK) have been studied by the ATLAS Collaboration. The breakdown voltages, depletion voltages, inter-pad gaps, collected charge as well as the time resolution have been measured and the production yield of large size sensors has been evaluated.

Radiation campaign of HPK prototype LGAD sensors for the High-Granularity Timing Detector (HGTD)

We report on the results of a radiation campaign with neutrons and protons of Low Gain Avalanche Detectors (LGAD) produced by Hamamatsu (HPK) as prototypes for the High-Granularity Timing Detector (HGTD) in ATLAS. Sensors with an active thickness of 50μm were irradiated in steps of roughly 2× up to a fluence of 3×1015neqcm−2. As a function of the fluence, the collected charge and time resolution of the irradiated sensors will be reported for operation at −30 °C.

Performance of a Front End prototype ASIC for picosecond precision time measurements with LGAD sensors

For the High-Luminosity phase of LHC, the ATLAS experiment is proposing the addition of a High Granularity Timing Detector (HGTD) in the forward region, to mitigate the effects of the increased pile-up. The chosen detection technology is Low Gain Avalanche Detector (LGAD) silicon sensors that can provide an excellent timing resolution below 50 ps. The front-end read-out ASIC must exploit the large signal derivative and small noise provided by the sensor, while keeping low power consumption. This paper presents the results on the first prototype of a front-end ASIC, named ALTIROC0, which contains the analog stages (preamplifier and discriminator) of the read-out chip. The ASIC was characterised both alone and as part of a module with a 2×2 LGAD array of 1.1×1.1 mm2 pads bump-bonded to it. The various contributions of the electronics to the time resolution were investigated in test-bench measurements with a calibration setup. Both when the ASIC is alone or with a bump-bonded sensor, the jitter of the ASIC is better than 20 ps for an injected charge of 10 fC . The time walk effect, which arises from the different preamplifier response for various injected charges, can be corrected up to 10 ps using a Time Over Threshold measurement. The combined performance of the ASIC and the LGAD sensor, which was measured during a beam test campaign in October 2018 with pions of 120 GeV energy at the CERN SPS, is around 40 ps for all measured modules. All tested modules show good efficiency and time resolution uniformity.

Design and fabrication of Low Gain Avalanche Detectors (LGAD): a TCAD simulation study

Low Gain Avalanche Detectors (LGAD) are silicon sensors with a time resolution better than 20 ps. The ATLAS and CMS experiments are designing LGAD detectors to address the pile-up challenge at the High Luminosity-Large Hadron Collider (HL-LHC) . The Institute of High Energy Physics (IHEP) High-Granularity Timing Detector group has recently developed its first version of LGAD sensors. The LGAD structure was designed using Technology Computer-Aided Design (TCAD) simulations and optimized to obtain a high breakdown voltage and ideal gain. The n-type Junction Termination Extension (N-JTE) zone is a critical structure to guarantee a high breakdown voltage. The gain layer is optimized for an ideal gain factor and hence good time resolution. The optimized LGAD sensor has a gain higher than six and a breakdown voltage higher than 400 V.

A High-Granularity Timing Detector (HGTD) for the Phase-II upgrade of the ATLAS detector

The expected increase of the particle flux at the high-luminosity phase of the LHC (HL-LHC) with instantaneous luminosities up to L = 7.5× 1034 cm−1s−1 will have a severe impact on the ATLAS detector performance. The pile-up is expected to increase on average to 200 interactions per bunch crossing. The reconstruction and trigger performance for electrons, photons as well as jets and transverse missing energy will be severely degraded in the end-cap and forward region, where the liquid Argon based electromagnetic calorimeter has coarser granularity and the inner tracker has poorer momentum resolution compared to the central region. A High Granularity Timing Detector (HGTD) is proposed in front of the liquid Argon end-cap calorimeters for pile-up mitigation and for bunch per bunch luminosity measurements. This device should cover the pseudo-rapidity range of 2.4 to about 4.0. Two Silicon sensors double-sided layers are foreseen to provide a precision timing information for minimum ionizing particle with a time resolution better than 50 pico-seconds per hit (i.e. 30 pico-seconds per track) in order to assign the particle to the correct vertex. Each readout cell has a transverse size of 1.3 mm×1.3 mm leading to a highly granular detector with about 3 millions of readout electronics channels. Low-Gain Avalanche Detector (LGAD) technology has been chosen as it provides an internal gain good enough to reach large signal over noise ratio needed for excellent time resolution. Extensive LGAD research and development (R&D) campaigns are carried out to investigate the suitability of this new technology as timing sensors for HGTD. The related readout ASIC is also being studied extensively.

Upgrade of the ATLAS detectors and trigger for the High Luminosity LHC: Tracking and timing for pile-up suppression

The High Luminosity-Large Hadron Collider is expected to start data-taking in 2026 and to provide an integrated luminosity of 3000 fb −1 , giving a factor 10 more data than that will be collected by 2023. This high statistics will make it possible to perform precise measurements in the Higgs sector and improve searches of new physics at the TeV scale. The peak luminosity is expected to be 7.5 × 10 34 cm −2 s −1 , corresponding to about 200 proton–proton interactions per event (pile-up), which will increase the rates at each level of the trigger and degrade the reconstruction performance. To cope with such a harsh environment many sub-detectors of the ATLAS experiment will be upgraded and some completely substituted. The Trigger-DAQ system will be upgraded. In this talk an overview of two new sub-detectors enabling powerful pile-up suppression, a new Inner Tracker and a High Granularity Timing Detector, will be given, describing the two technologies, their performance, and their interplay. Emphasis will also be given to the possibility of using tracking and timing information at the earliest, hardware based, ATLAS trigger stage. • Pileup suppression techniques for jets reconstruction at HL-LHC. • Tracking and Timing detectors of ATLAS detector at HL-LHC. • Tracking for Trigger at HL-LHC.

Formula omitted] thin Low Gain Avalanche Detectors (LGAD) for timing applications

LGAD detectors on 300μm thick high resistivity p-type substrates were proposed for the first time by IMB-CNM-CSIC. They are customized Avalanche Photodiodes (APD) to obtain a high electric field region confined close to the reversed junction. Therefore, only electrons generated by an incident particle passing through the detector and drifting to the n+ contact, start the impact ionization process. Thus, the collected charge is multiplied. The basic difference between APDs and LGADs is the gain. LGADs have a moderate gain in order to avoid the inherent problems due to high multiplication: cross talk and high noise. In that way, the detector signal can be kept high without increasing the noise.These devices have been successfully fabricated and extensively characterized, before and after irradiation. Unfortunately, neutron and proton radiation cause the degradation of the gain and the creation of bulk traps, degrading the timing resolution. One way to reduce the radiation induced degradation is to minimize the substrate thickness, thus improving the timing resolution of LGAD detectors.Two technology approaches have been contemplated: the use of SOI (Silicon on insulator) substrates and Silicon to Silicon bonding substrates, both with a very thin active silicon layer of 50μm. As a consequence, drifting distances of generated electrons and holes are significantly reduced, resulting in a decrease in the number of electrons and holes trapped by radiation induced bulk defects.A new family of thin detectors, produced in 2×2 arrays prototypes, for the ATLAS experiment High Granularity Timing Detector (HGTD) is proposed. These detectors are suitable for timing applications with time resolution in the range of 30 ps at 20 °C. Optimization of the LGAD structures for the HGTD experiment and the detector experimental performances are presented and discussed.

Beam test measurements of Low Gain Avalanche Detector single pads and arrays for the ATLAS High Granularity Timing Detector

For the high luminosity upgrade of the LHC at CERN, ATLAS is considering the addition of a High Granularity Timing Detector (HGTD) in front of the end cap and forward calorimeters at |z|= 3.5 m and covering the region 2.4 <|η|< 4 to help reducing the effect of pile-up. The chosen sensors are arrays of 50 μm thin Low Gain Avalanche Detectors (LGAD). This paper presents results on single LGAD sensors with a surface area of 1.3×1.3 mm2 and arrays with 2×2 pads with a surface area of 2×2 mm2 or 3×3 mm2 each and different implant doses of the p+ multiplication layer. They are obtained from data collected during a beam test campaign in autumn 2016 with a pion beam of 120 GeV energy at the CERN SPS. In addition to several quantities measured inclusively for each pad, the gain, efficiency and time resolution have been estimated as a function of the position of the incident particle inside the pad by using a beam telescope with a position resolution of few μm. Different methods to measure the time resolution are compared, yielding consistent results. The sensors with a surface area of 1.3×1.3 mm2 have a time resolution of about 40 ps for a gain of 20 and of about 27 ps for a gain of 50 and fulfil the HGTD requirements. Larger sensors have, as expected, a degraded time resolution. All sensors show very good efficiency and time resolution uniformity.