ATLAS ITk Research Articles

Design production and testing of ATLAS ITk strip bus tapes

This paper reviews the bus tapes used for the barrel and end cap detectors for the ATLAS ITk strip detector. The long copper/polyimide tapes with narrow track and gap are very challenging to produce with an acceptable yield. Two different technologies for these tapes are compared. After several iterations, barrel and end cap tapes are in production at two different manufacturers. Results from the electrical and dimensional QC show that both approaches meet the tight specifications. Tests of the radiation tolerance are also discussed.

Outer Barrel services chain characterisation for the ATLAS ITk Pixel detector

For the high-luminosity upgrade of the ATLAS Inner Tracking detector of the ATLAS experiment, a new pixel detector will be installed to allow for a bigger bandwidth and cope with the increased radiation among other challenges. This contribution will present the evaluation of the Outer Barrel Pixel layer services chains. A full data transmission study covering data merging will be presented from the pixel module all the way to the FELIX data acquisition system, using most of the components foreseen for the detector. Challenges and results of the services chain of the Outer Barrel will be highlighted.

How the discovery of Cold Noise delayed the production of ATLAS ITk strip tracker modules by a year

The construction of the ATLAS strip tracker barrel will require the assembly of 12,000 barrel detector modules over the course of 3.5 years. In 2022, during the module pre-production phase, modules were found to display clusters of noisy channels outside required specifications when tested at operating temperatures (-35°C), called “Cold Noise”. Extensive investigations into the cause and mechanism of Cold Noise interrupted pre-production and occupied most barrel module assembly sites. This contribution presents an overview of the year-long investigations into Cold Noise, the final identification of the underlying mechanism and necessary changes for the transition to production.

MALTA-Cz: a radiation hard full-size monolithic CMOS sensor with small electrodes on high-resistivity Czochralski substrate

Depleted Monolithic Active Pixel Sensor (DMAPS) sensors developed in the Tower Semiconductor 180 nm CMOS imaging process have been designed in the context of the ATLAS ITk upgrade Phase-II at the HL-LHC and for future collider experiments. The “MALTA-Czochralski (MALTA-Cz)” full size DMAPS sensor has been developed with the goal to demonstrate a radiation hard, thin CMOS sensor with high granularity, high hit-rate capability, fast response time and superior radiation tolerance. The design targets radiation hardness of > 1015 (1 MeV) neq/cm2 and 100 Mrad TID. The sensor shall operate as tracking sensor with a spatial resolution of ≈ 10 μm and be able to cope with hit rates in excess of 100 MHz/cm2 at the LHC bunch crossing frequency of 40 MHz. The 512 × 512 pixel sensor uses small collection electrodes (3.5 μm) to minimize capacitance. The small pixel size (36.4 × 36.4 μm2) provides high spatial resolution. Its asynchronous readout architecture is designed for high hit-rates and fast time response in triggered and trigger-less detector applications. The readout architecture is designed to stream all hit data to the multi-channel output which allows an off-sensor trigger formation and the use of hit-time information for event tagging.The sensor manufacturing has been optimised through process adaptation and special implant designs to allow the manufacturing of small electrode DMAPS on thick high-resistivity p-type Czochralski substrate. The special processing ensures excellent charge collection and charge particle detection efficiency even after a high level of radiation. Furthermore the special implant design and use of a Czochralski substrate improves the sensor's time resolution. This paper presents a summary of sensor design optimisation through process and implant choices and TCAD simulation to model the signal response. Beam and laboratory test results on unirradiated and irradiated sensors have shown excellent detection efficiency after a dose of 2 × 1015 1 MeV neq/cm2. The time resolution of the sensor is measured to be σ = 2 ns.

Second generation Monitoring of Pixel System (MOPS) chip for the Detector Control System (DCS) of the ATLAS ITk Pixel detector

The MOPSv2 chip is an Application Specific Integrated Circuit (ASIC) to provide the temperature and the voltage monitoring data of individual front-end detector modules to the DCS of the ATLAS ITk Pixel detector. The chip implements CANopen in a hardwired logic, provides the possibility of remote reset without a power cycle and automated on-chip frequency trimming using CAN messages. The chip has proven to be radiation hard during testing up to an ionizing dose of 500 Mrad, immune to Single Event Upsets (SEUs) and works reliably under irradiation at high operating temperatures of up to 40 °C. In this paper, the functionality and performance of the second version of the chip will be discussed, and also results from the irradiation campaigns will be presented.

Radiation tolerance studies of the HV-mux GaNFETs for the HL-LHC ATLAS ITk Strip detector

For the High-Luminosity upgrade of the LHC, the current ATLAS inner detector will be replaced with a new silicon charged-particle tracker, the ITk, which consists of the ITk Pixel and the ITk Strip subdetector. The high voltage multiplexing (HV-Mux) GaNFETs are radiation-tolerant transistors that permit switching off high voltage to malfunctioning sensors on the ITk Strip modules. To ensure the reliability of the GaNFETs in the high radiation environment expected at the HL-LHC, a sample of the production batch was exposed to gamma radiation. The GaNFETs were characterized pre-irradiation and post-irradiation, and monitored during irradiation.

Testing of the HCC and AMAC functionality and radiation tolerance for the HL-LHC ATLAS ITk strip detector

For the high-luminosity phase of the LHC, which begins operation in 2029, the current ATLAS inner detector will be replaced by a new tracker, the ITk. The ITk consists of two subdetectors, one using pixels and the second using silicon-strips, the ITk Strip detector. The HCC and AMAC chip are radiation-tolerant ASICs that contribute to the front-end readout, monitoring and control of the ITk Strip subsystem. Low temperature startups and low internal regulated voltage tests have been performed on HCC and AMAC to guarantee their reliability at edge operation conditions. In addition, to ensure the operation of the HCC and AMAC under a radiation heavy environment, gamma and x-ray irradiation campaigns were conducted. HCC and AMAC successfully operated at harsher conditions than the ones expected during the HL-LHC.

Quality control testing of the HCC ASIC for the HL-LHC ATLAS ITk strip detector

The high-luminosity upgrade to the LHC requires a new silicon-strip charged-particle tracking detector for ATLAS. The HCC (Hybrid Controller Chip) is one of three new radiation-tolerant ASICs for this silicon-strip detector. As the interface to multiple binary readout ASICs, the HCC is responsible for buffering and forwarding control signals and readout requests to them as well as serializing their readout data into a 640 Mbps output. All HCCs undergo a suite of tests to verify their analog and digital functionality. The yield for the HCC exceeds the 90% target for production.

Irradiation testing of ASICs for the HL-LHC ATLAS ITk Strip Detector

For the high-luminosity upgrade to the LHC, the ATLAS Inner Detector will be replaced by an all-silicon tracker (ITk) consisting of two systems: pixels and strips. HCC and AMAC are ITk Strip ASICs vital for performing the system readout, monitoring, and control. To ensure these ASICs will successfully operate in the high-radiation environment of the HL-LHC, they need to be tested for radiation tolerance, and tests have been performed using both heavy ions and protons. The ASIC designs were shown to protect against single event effects due to radiation.

Development of the radiation and magnetic field tolerant DC/DC converter system for the ATLAS ITk Strip Detector

The radiation and magnetic field tolerant step-down DC/DC converter system is developed to supply low-voltage power for the ATLAS ITk Strip Detector. The system is modular and consists of custom designed crates with embedded cooling plates, backplane, and DC/DC converter modules. Each converter module comprises two or four power channels. Each channel comprises a 48-to-11 V DC/DC converter, hardware overcurrent and overvoltage protection circuits, correction circuitry to compensate for voltage drops along the cables, and control and monitoring functionality based on the AMACStar chip. We present the design and performance of such a DC/DC converter system, including evaluation of its radiation tolerance.

Electrical performances of pre-production staves for the ATLAS ITk Strip Detector Upgrade

The ATLAS experiment is currently preparing for an upgrade of the inner tracking detector for the High-Luminosity LHC. The new tracker, ITk, employs an all-silicon detector with outer strip layers. The building block of the ITk strip barrel is the stave which consists of a low-mass support structure hosting the common electrical, optical and cooling services as well as 28 silicon modules. In this contribution, we outline the challenging aspects of the stave pre-production testing phase at Brookhaven National Laboratory. The electrical characterization of these staves, hosting the final design of all ASICs, will be discussed in detail.

Production and testing of the powerboard for ATLAS ITk Strip barrel modules

The upgrade of the ATLAS ITk strips detector for HL-LHC will employ a custom PCB (powerboard) for on-module DC-DC conversion, HV switching, and monitoring. Production of about 14100 of such PCBs with high reliability is a big challenge. This paper will present the production procedure and quality control (QC) testing system for the powerboards to be installed on ITk Strip barrel modules. During production, about 150 powerboards will be produced every week. Each powerboard will need to pass QC tests before they are assembled to module. The QC tests include thermal cycling between −35 °C and 40 °C, soak test (continuous running of DC-DC converter at high load at 20 °C), and basic functionality and characterization electrical tests of the low voltage (LV), high voltage (HV), and monitoring functions of the powerboard. A custom QC test system is described, which is based on a reusable PCB (active board) with all testing circuits, a one-time powerboard carrier card, and a Z-turn SoC board which hosts and runs the testing program. The production procedure and QC test system has been tested with 400 powerboards during pre-production, and the system has been proven ready for production with the desired testing program, speed, safety, and cost. Performance and typical failures of powerboards observed during the QC test of pre-production powerboards is also presented.

Verification of simulated ASIC functionality and radiation tolerance for the HL-LHC ATLAS ITk Strip Detector

The verification of ASICs through simulation is critical to ensure their successful operation in particle physics detectors and to minimize the number of long and expensive production cycles required. Three radiation-tolerant ASICs (HCC, AMAC, and ABC) will perform the front-end readout, monitoring, and control of the ITk Strip charged-particle tracker for the ATLAS detector at the HL-LHC. The Python-based cocotb verification framework is used to design sophisticated tests with contributions from ASIC verification non-experts and students. The verification program includes interactions between multiple ASICs, realistic data flows, operational stress tests, and a focus on mitigation of disruptive Single Event Effects due to radiation.

An environmental monitoring and control system for the ATLAS ITk Outer Barrel quality control and integration

This paper describes the development of a system based on Programmable Logic Controllers (PLC) for safety interlocking and environmental monitoring during ATLAS ITk Outer Barrel (OB) loaded local support quality control (QC) and later integration. The system has been developed at CERN with a focus on scalability, maintainability and reliability, and is expected to be deployed at the different ITk OB loading and integration sites.

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. Radiation hard n+-in-p micro-strip silicon sensors were developed by the ATLAS Inner Tracker strip collaboration and are produced by Hamamatsu Photonics K.K. Production of the total amount of 22000 strip sensors has started in 2020 and will continue until 2025. The ATLAS 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 procedures were developed to check whether the delivered large-format sensors adhere to the ATLAS specifications. The institutes performing the Quality Control testing of the pre-production and production ATLAS ITk strip sensors had to initially be qualified for multiple high-throughput tests by successfully completing the Site Qualification process. The Quality Control procedures and the qualification process are described in this paper.

Effect of irradiation and annealing performed with bias voltage applied across the coupling capacitors on the interstrip resistance of ATLAS ITk silicon strip sensors

The powering configuration of the silicon strip modules developed for the new Inner Tracker of the ATLAS experiment includes a voltage of up to 0.5 V across the coupling capacitor of each individual strip. However, this voltage is usually not applied in the sensor irradiation studies due to the significant technical and logistical complications. To study the effect of an irradiation and a subsequent beneficial annealing on the strip sensors in real experimental conditions, four prototype ATLAS17LS miniature sensors were irradiated by 60Co source and annealed, both with and without the bias voltage of 0.5 V applied across the coupling capacitors. The values of interstrip resistance measured on irradiated samples before and after annealing indicate that increase of radiation damage caused by the applied voltage can be compensated by the presence of this voltage during annealing.

Monitoring System of the ATLAS ITk Laboratory

The ATLAS ITk Upgrade project, culminating in the installation into the experiment in 2026, enters this year its production period. Cooperating laboratories dealing with the strip part of the project needs to meet various conditions in clean rooms and testing environments to ensure safety for production components during assembly and measurement procedures. One of the ITk laboratories, located in Prague, prepared for modules’ production is presented as a model case. For this purpose, dedicated DAQ software called ITSDAQ is used together with the slow control monitoring system based on RS232/GPIB standards, MySQL database entry and Grafana visualization platform. Data are stored in the local database storage, a subset of them and the test results are also sent into the ITk Production Database. Such an integrated tool offers real-time plotting of crucial parameters and the possibility of receiving an immediate notification in case of exceeding any threshold.

Cold temperature characterization of ring triplets based on RD53A readout chip

This paper reports the Trento test setup and the cold test procedure for three triplets (ID: R4, R5, and R6) assembled with RD53A readout cheap and planar sensors. The trim and tuning of Front Ends (FE), as well as sensor I-V measurements, were made for a cold temperature (−25 °C) for an applied voltage (−30 V for R4, −10 V for R5 and R6). As a part of QC, initially, several test scans: analog, digital, threshold, ToT, noise, etc., were performed to evaluate the module response at −25 °C before applying a necessary tuning script to find a spatially uniform threshold distribution over the pixel matrix. Later, the crosstalk-based disconnected-bump and X-ray scans were made to check modules’ bump bonding quality and hits per pixel. Results reported here show a good agreement to a qualified triplet module, assuring the Trento cold test setup capacity for the ATLAS ITk QA/QC process.

Performance Studies of the ATLASpix HV-MAPS Prototype for Different Substrate Resistivities

The ATLASpix high-voltage monolithic active pixel sensor (HV-MAPS) was designed as a technology demonstrator for the ATLAS ITk Upgrade and the CLIC tracking detector. In this contribution new results from laboratory-based energy calibration measurements using fluorescence X-rays are presented for the ATLASpix_Simple matrix. These findings are complemented by new results from test-beam studies with inclined tracks, in which the active charge collection depth is determined.

The ATLAS ITk detector system for the Phase-II LHC upgrade

The ATLAS experiment is planning a complete replacement of its inner detector with a new all-silicon inner tracker for the high luminosity phase of the LHC. The new detector is designed to cope with the increased pile-up, data rates and radiation levels of the HL-LHC, while maintaining or improving the current ATLAS tracking performance. The ITk design and technology R&D have been completed and pre-production of the detector modules is starting. This paper presents the ITk layout, performance and the ongoing transition into production phase.