The ATLAS ITk Strip Detector for the Phase-II LHC Upgrade

The inner detector of the present ATLAS experiment has been designed and developed to function in the environment of the present Large Hadron Collider (LHC). At the ATLAS Phase-II Upgrade, the particle densities and radiation levels will exceed current levels by a factor of ten. The instantaneous luminosity is expected to reach unprecedented values, resulting in up to 200 proton-proton interactions in a typical bunch crossing. The new detectors must be faster and they need to be more highly segmented. The sensors used also need to be far more resistant to radiation, and they require much greater power delivery to the front-end systems. At the same time, they cannot introduce excess material which could undermine tracking performance. For those reasons, the inner tracker of the ATLAS detector was redesigned and will be rebuilt completely. The ATLAS Upgrade Inner Tracker (ITk) consists of several layers of silicon particle detectors. The innermost layers will be composed of silicon pixel sensors, and the outer layers will consist of silicon microstrip sensors. This contribution focuses on the strip region of the ITk. The central part of the strip tracker (barrel) will be composed of rectangular short (~ 2.5 cm) and long (~5 cm) strip sensors. The forward regions of the strip tracker (end-caps) consist of six disks per side, with trapezoidal shaped sensors of various lengths and strip pitches. After the completion of final design reviews in key areas, such as Sensors, Modules, Front-End electronics, and ASICs, a large scale prototyping program has been completed in all areas successfully. We present an overview of the Strip System and highlight the final design choices of sensors, module designs and ASICs. We will summarise results achieved during prototyping and the current status of pre-production and production on various detector components, with an emphasis on QA and QC procedures

Design of Bus Tapes for the ATLAS Strip End-Cap at the HL-LHC

The ATLAS Phase-II Upgrade will replace the Inner detector with a new all-silicon Inner Tracker (ITk) to accommodate the radiation damage and track density expected at the High-Luminosity LHC (HL-LHC). The all-silicon ITk for the HL-LHC consists of a pixel detector with 5 barrel layers and multiple forward disks at a small radius, and a strip tracking detector at the outermost part with 4 barrel layers and 6-end-cap disks on each side. This contribution presents the design of the flexible circuit (bus tape) for the local support structures of the end-cap region of the strip detector, called petals. The bus tapes provide the electrical interface to common services for all the on-board subsystems including power, control and data interfaces. Connections to external services outside of the petals are carried out through the End-of-Structure (EoS) card using optical fibres and copper wires. The bus tapes are manufactured as a 2-layer printed circuit board using polyimide and adhesive Kapton films, with a total thickness of 185 $\mu$m and a total length of 60 cm. The layout design has been focused on achieving good signal and power integrity while keeping low mass and low thermal resistance. A total of 768 end-cap bus tapes will be produced between 2021 and 2022 for the assembly of 384 petals with 6,912 modules, where each end-cap disk will consist of 32 petals

Experimental Study and Empirical Modelling of Long Term Annealing of the ATLAS18 Sensors

In order to continue the program of the LHC, the accelerator will be upgraded to the HL-LHC, which will have a design luminosity 10e3 cm^2 s^-1, an order of magnitude greater than the present machine. In order to meet the occupancy and radiation hardness requirements resulting from this increase in luminosity, the present ATLAS tracking detector must be replaced. The ATLAS Collaboration is constructing a new central tracking system based completely on silicon sensors. The system comprises an inner pixel detector, a barrel strip detector and an endcap strip detector. In order to satisfy the radiation hardness requirements we have developed a new n-in-p sensor design. Extensive studies have shown that it results in detectors which comfortably reach the required end-of-life performance. The latest sensor layouts prepared for preproduction, known as ATLAS18, implement this design. However, as well as knowing the performance after a given irradiation fluence, operational considerations require an understanding of the time development of the annealing, and resulting variation of the collected charge, of irradiated detectors at different temperatures. This requirement results from the fact that there are various proposed temperature profiles for the operation of the detector over the expected lifetime of 14 years. Here we describe the measurement of charge collection performance as a function of irradiated fluence and long term annealing time. We also describe a semi-empirical model based on these measurements which allows us to predict the end-of-life charge collection as a function of the temperature profile during operation of the detector. The use of the model to study the effect of annealing on the strip detector at a radius of 40 cm and an integrated irradiation fluence of 16e14 MeV neutron equiv. is presented. This methodology can be applied to other regions of the detector, such as the pixels

Analysis of the Quality Assurance results from the initial part of production of the ATLAS18 ITk strip sensors

The production of strip sensors for the ATLAS Inner Tracker (ITk) started in 2021. Since then, a Quality Assurance (QA) program has been carried out continuously, by using specific test structures, in parallel to the Quality Control (QC) inspection of the sensors. The QA program consists of monitoring sensor-specific characteristics and the technological process variability, before and after the irradiation with gammas, neutrons, and protons. After two years, half of the full production volume has been reached and we present an analysis of the parameters measured as part of the QA process. The main devices used for QA purposes are miniature strip sensors, monitor diodes, and the ATLAS test chip, which contains several test structures. Such devices are tested by several sites across the collaboration depending on the type of samples (non-irradiated components or irradiated with protons, neutrons, or gammas). The parameters extracted from the tests are then uploaded to a database and analyzed by Python scripts. These parameters are mainly examined through histograms and time-evolution plots to obtain parameter distributions, production trends, and meaningful parameter-to-parameter correlations. The purpose of this analysis is to identify possible deviations in the fabrication or the sensor quality, changes in the behavior of the test equipment at different test sites, or possible variability in the irradiation processes. The conclusions extracted from the QA program have allowed test optimization, establishment of control limits for the parameters, and a better understanding of device properties and fabrication trends. In addition, any abnormal results prompt immediate feedback to the vendor

Characterization of the Polysilicon Resistor in Silicon Strip Sensors for ATLAS Inner Tracker as a Function of Temperature, Pre- And Post-Irradiation

The high luminosity upgrade of the Large Hadron Collider, foreseen for $2029$, requires the replacement of the ATLAS Inner Detector with a new all-silicon Inner Tracker (ITk). The expected ultimate total integrated luminosity of $4000\, \mathrm{fb}^{-1}$ means that the strip part of the ITk detector will be exposed to the total particle fluences and ionizing doses reaching the values of $1.6 \cdot 10^{15}$ $1\, \mathrm{MeV}$ $\mathrm{n_{eq}/cm^2}$ and $0.66\, \mathrm{MGy}$, respectively, including a safety factor of $1.5$. Radiation hard n${}^+$-in-p micro-strip sensors were developed by the ATLAS ITk strip collaboration and are produced by Hamamatsu Photonics K.K. The active area of each ITk strip sensor is delimited by the n-implant bias ring, which is connected to each individual n${}^+$ implant strip by a polysilicon bias resistor. The total resistance of the polysilicon bias resistor should be within a specified range to keep all the strips at the same potential, prevent the signal discharge through the grounded bias ring and avoid the readout noise increase. While the polysilicon is a ubiquitous semiconductor material, the fluence and temperature dependence of its resistance is not easily predictable, especially for the tracking detector with the operational temperature significantly below the values typical for commercial microelectronics. Dependence of the resistance of polysilicon bias resistor on the temperature, as well as on the total delivered fluence and ionizing dose, was studied on the specially-designed test structures called ATLAS Testchips, both before and after their irradiation by protons, neutrons, and gammas to the maximal expected fluence and ionizing dose. The resistance has an atypical negative temperature dependence. It is different from silicon, which shows that the grain boundary has a significant contribution to the resistance. We will discuss the contributions by parameterizing the activation energy of the polysilicon resistance as a function of the temperature for unirradiated and irradiated ATLAS Testchips

Test and extraction methods for the QC parameters of silicon strip sensors for ATLAS upgrade tracker

The Quality Control (QC) of pre-production strip sensors for the Inner Tracker (ITk) of the ATLAS Inner Detector upgrade has finished, and the collaboration has embarked on the QC test programme for production sensors. This programme will last more than 3 years and comprises the evaluation of approximately 22000 sensors. 8 Types of sensors, 2 barrel and 6 endcap, will be measured at many different collaborating institutes. The sustained throughput requirement of the combined QC processes is around 500 sensors per month in total. Measurement protocols have been established and acceptance criteria have been defined in accordance with the terms agreed with the supplier. For effective monitoring of test results, common data file formats have been agreed upon across the collaboration. To enable evaluation of test results produced by many different test setups at the various collaboration institutes, common algorithms have been developed to collate, evaluate, plot and upload measurement data. This allows for objective application of pass/fail criteria and compilation of corresponding yield data. These scripts have been used to process the data of more than 3000 sensors so far, and have been instrumental for identification of faulty sensors and monitoring of QC testing progress

Test and extraction methods for the QC parameters of silicon strip sensors for ATLAS upgrade tracker

The Quality Control (QC) of pre-production strip sensors for the Inner Tracker (ITk) of the ATLAS Inner Detector upgrade has finished, and the collaboration has embarked on the QC test programme for production sensors. This programme will last more than 3 years and comprises the evaluation of approximately 22000 sensors. 8 Types of sensors, 2 barrel and 6 endcap, will be measured at many different collaborating institutes. The sustained throughput requirement of the combined QC processes is around 500 sensors per month in total. Measurement protocols have been established and acceptance criteria have been defined in accordance with the terms agreed with the supplier. For effective monitoring of test results, common data file formats have been agreed upon across the collaboration. To enable evaluation of test results produced by many different test setups at the various collaboration institutes, common algorithms have been developed to collate, evaluate, plot and upload measurement data. This allows for objective application of pass/fail criteria and compilation of corresponding yield data. These scripts have been used to process the data of more than 2500 sensors so far, and have been instrumental for identification of faulty sensors and monitoring of QC testing progress. The analysis algorithms and criteria were also used in a dedicated study of strip tests on gamma-irradiated full-size sensors

ATLAS ITk Strip Sensor Quality Control and Review of ATLAS18 Pre-Production Sensor Results

With the upgrade of the LHC to the High-Luminosity LHC (HL-LHC), the Inner Detector will be replaced with the new all-silicon ATLAS Inner Tracker (ITk) to maintain tracking performance in a high-occupancy environment and to cope with the increase in the integrated radiation dose. Comprising an active area of $165\,\mathrm{m^2}$, the outer four layers in the barrel and six disks in the endcap region will host strip modules, built with single-sided micro-strip sensors and glued-on hybrids carrying the front-end electronics necessary for readout. The strip sensors are manufactured as n$^+$-in-p devices from high-resistivity silicon in 8 different shapes, from square in the barrel staves to a stereo annulus wedge-shape in the endcap discs, developed to withstand a total fluence of $1.6 \times 10^{15}\,\mathrm{n_{eq}/cm^2}$ and a total ionising dose of $66\,\mathrm{MRad}$. In 2020 the ITk Strip Sensors project has transitioned into the pre-production phase, where 5% of the production volume, a total of 1101 ATLAS18 wafers, was produced by Hamamatsu Photonics. Before being shipped out for module building, the ATLAS18 main sensors were tested at different institutes in the collaboration for mechanical and electrical compliance with technical specifications, the quality control (QC), while fabrication parameters were verified using test structures from the same wafers, the quality assurance (QA). The sensor QC evaluation program, test results and statistics, as well as experience gained from pre-production will be summarised in this contribution

ATLAS ITk strip sensor quality control procedures and testing site qualification

The high-luminosity upgrade of the Large Hadron Collider, scheduled to become operational in 2029, requires the replacement of the ATLAS Inner Detector with a new all-silicon Inner Tracker (ITk). Radiation hard n+-in-p micro-strip silicon sensors were developed by the ATLAS ITk strip collaboration and are produced by Hamamatsu Photonics K.K. Production of the total amount of 22 000 ITk strip sensors has started in 2020 and will continue until 2025. The ATLAS ITk strip sensor collaboration has the responsibility to monitor the quality of the fabricated devices by performing detailed measurements of individual sensor characteristics and by comparing the obtained results with the tests done by the manufacturer. Dedicated Quality Control (QC) procedures were developed to check whether the delivered large-format sensors adhere to the ATLAS specifications. The institutes performing the QC testing of the pre-production and production ATLAS ITk strip sensors (QC sites) had to initially be qualified for multiple high-throughput tests by successfully completing Site Qualification process. The QC procedures and the qualification process are described in this paper

Specifications and Pre-Production of n+-in-p Large-format Strip Sensors fabricated in 6-inch Silicon Wafers, ATLAS18, for Inner Tracker of ATLAS Detector for High-Luminosity Large Hadron Collider

The full volume of the inner tracker of the ATLAS experiment will be replaced with new all-Silicon detectors for HL-LHC. The strip detectors, in the radial extent of 40 to 100 cm, are made of four layers of cylindrical-structures in the barrel and six layers of disk-structures in the endcap section with 2 layers of strip sensors for stereo-viewing in each layer-structure. The corresponding area of strip sensors, at 165 m^2, will be covered with 10976 barrel and 6912 endcap sensors. A new approach is adopted to use p-type material to be more radiation-tolerant, making the readout in n-strips, so-called n+-in-p sensors, to cope with the fluence of 9.7×10^14　(1.6×10^15) 1-MeV neutron-equivalent (neq)/cm^2 and ionizing dose of 44 (66) Mrad at the maximum in the barrel (endcap in the parenthesis) section, for its lifetime including a safety factor of 1.5. The readout is AC-coupled and the strips are biased via Polysilicon resistors for all sensors. In the barrel sensors, the geometry is square, 9.8×9.8 cm^2, to have the largest area of sensor possible from a 6-inch wafer. The strips are laid out in parallel with a strip pitch of 75.5 µm and 4 or 2 rows of strip segments in two types of sensors, "short strips (SS)" for the inner 2 layers and "long strips (LS)" for the outer 2, respectively. In the endcap, we have designed roughly trapezoidal sensors with built-in stereo angle, curved edges along the circumference, and in 6 unique shapes in each radial extent, R0 to R5. The strips are in fan geometry, with a mean pitch of approximately 75 µm and 4 or 2 rows of strip segments. The sensors of this specification are labelled as "ATLAS18xx" where xx stands for SS, LS, Rx (x=0 to 5). With the specifications of mechanical features and electrical performance, CAD files for processing were laid out by following successful designs of ATLAS07, ATLAS12 and ATLAS17LS of the barrel sensors, and ATLAS12EC/R0 of the R0 endcap sensors, together with a number of optimizations. "Pre-Production" amount of 1041 wafers were fabricated and delivered with the tests carried out by vendor. The quality of the sensors was reviewed through the data as provided by the vendor. These sensors were used for establishing and exercising acceptance procedures, and subsequently to be used for pre-production of strip modules and layer structures