The ATLAS Inner Detector will be replaced by an all-silicon system, the
Inner Tracker (ITk) and its innermost part will consist of a pixel detector.
Different silicon sensor
technologies will be employed in its five barrel and endcap layers. Components for structures with multiple modules based
on FE-I4 front-end chips were produced and are in assembly and evaluation.With the arrival of the
first readout chip prototype, the RD53A chip, the development of hybrid detector modules is
starting to address numerous production issues, understanding of which will be crucial for
the layout and production of the final ITk pixel detector modules
For the high luminosity era of the Large Hadron Collider (HL-LHC) it is foreseen to replace the
current inner tracker of the ATLAS experiment with a new, all-silicon detector to cope with
the occurring increase in occupancy, bandwidth and radiation damage. It will consist of an
inner pixel and outer strip detector aiming to provide tracking coverage up to |η|=4. The
layout of the pixel detector is foreseen to have five layers of pixel silicon sensor modules in
the central region and several ring-shaped layers in the forward region. This results in up to
14 m. of silicon depending on the selected layout.
Detector requirements in terms of radiation hardness and occupancy, as well as thermal
performance depend strongly on the distance from the interaction region. Therefore, the
innermost layer will feature 3D silicon sensors, due to their inherent radiation hardness and
low power consumption, while the remaining layers will employ planar silicon sensors with
thickness ranging from 100μm to 150μm. All hybrid detector modules will be read out by
novel ASICs, implemented in 65nm CMOS technology and thinned to 150μm, which will be
connected to the silicon sensors using bump bonding. With about 4 104 pixels per cm. the
bump bond density is a much higher than in previous hybrid detectors.
With the recent availability of the first prototype readout chip, the RD53A, module
development for the ITk Pixel Detector is entering a new phase. Numerous modules will be
assembled to test the performance of bump bonding of objects of realistic area, very small
thickness and high bump bond density, as well as to finalize studies of the module
performance with pixel pitches of 50x50μm. and 25x100μm. on the sensors. Flex circuits are glued on top of thenmodules for connection and routing of services which have to be qualified too. Moreover, tests of the new serial powering scheme for low voltage supply of the modules will be done
as part of the prototyping program. The quality assurance criteria for the production of the
final detector modules are verified, including mechanical properties like module flatness as
well as electrical tests of the functionality of the modules and the bump bond quality.
In addition, a large prototyping programme on system test level is ongoing within the ITk
pixel detector community. Components for larger structures with multiple modules based on
the FE-I4 front-end chips were produced and are in assembly and evaluation. By this the
system integration and design is prototyped and validated.
The paper will present the latest results from the assembly and characterization of the
prototype modules. Important qualification steps of the module design will be discussed.
Moreover, latest evaluation and results of thermo-mechanical prototypes and fully electrical
prototypes are presented and the system-relevant aspects highlighted.