The production of strip sensors within the framework of the ATLAS Inner Tracker (ITk) development is a process which requires continuous evaluation during the full production period (about 4 years). Such an evaluation is divided into two different parts: Quality Control (QC), which focuses on the final product (the actual sensors) and tries to identify possible defects once the fabrication is completed, and Quality Assurance (QA), which aims to prevent deviations in the manufacturing process and uses specifically-designed test structures. The initial sensor pre-production consists of 5% (1041 sensors) of the total number of sensors expected during production. As part of pre-production, the collaboration has measured key parameters from miniature strip sensors (minis), monitor diodes (MD8), and the ATLAS Testchip, before and after irradiation. In this contribution we focus on the analysis of the results of the MD8 and the Testchip. All parameters have been obtained from the test structures (MD8, bias resistors, interdigitated structures, field oxide capacitors, coupling capacitors, punch-through protection structures and cross-bridge resistors) measured at the different test sites (KEK/Tsukuba, Birmingham, Toronto, Ljubljana, Valencia, Carleton, Prague, CNM-Barcelona). The results are compared to predefined pre- and post-irradiation specifications for each tested parameter.
The successful pre-production delivery of strip sensors for the new Inner Tracker (ITk)
for the upgraded ATLAS detector at the High Luminosity LHC (HL-LHC) at CERN was completed and
based on their performance full production has commenced. The overall delivery period is
anticipated to last 4 years to complete the approximately 22000 sensors required for the ITk. For
Quality Assurance (QA), a number of test structures designed by the collaboration, along with a
large area diode and miniature version of the main sensor, are produced in every wafer by the
foundry Hamamatsu Photonics K.K (HPK). As well as Quality Control (QC) checks on every main
sensor, samples of the QA pieces from each delivery batch are tested both before and after
irradiation with results after exposure to neutrons, gammas or protons to fluences and doses
corresponding to those anticipated after operation at the HL-LHC to roughly 1.5 times the ultimate
integrated luminosity of 4000 fb-1. In this paper the procedures are presented and the
studies carried out to establish that the seven ITk QA Strip Sensor irradiation and test sites
meet all the requirements to support this very extensive programme throughout the strip sensor
production phase for the ITk project.
During the prototyping phase of the new ATLAS Inner-Tracker
(ITk) strip sensors, a degradation of the device breakdown voltage
at high humidity was observed. Although the degradation was
temporary, showing a fast recovery in dry conditions, the study of
the influence of humidity on the sensor performance was critical to
establish counter-measures and handling protocols during production
testing in order to ensure the proper performance of the upgraded
detector.
The work presented here has the objective to study for the first
time the breakdown voltage deterioration in presence of ambient
humidity of ATLAS ITk production-layout strip sensors with different
surface properties, before and after proton, neutron and gamma
irradiations. A study of the humidity sensitivity of miniature ATLAS
ITk strip sensors, before and after proton irradiations, is also
presented to compare the sensitivity of devices with different
sizes.
The sensors were also exposed for several days to high humidity with
the aim to recreate and evaluate the influence of the detector
integration environment expected during the Large Hadron Collider
(LHC) Long Shutdown 3 (LS3) in 2026, where the sensors will be
exposed to ambient humidity for prolonged times.
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