ATLAS Pixels

Sebastián Grinstein

The Pixel group develops new silicon detector technologies for high energy physics experiments and other applications. After making key contributions to the ATLAS IBL and AFP sub-systems the group is qualifying for the production of 3D sensor modules for the ITk pixel detector and has produced the first full size module prototypes for HGTD. In parallel the group is exploring monolithic devices (DMAPS) for HEP and other applications.

3D Pixel Sensors for the HL-LHC

After IFAE demonstrated the radiation hardness capabilities of 3D sensors (which surpass any other sensing technology), ATLAS selected these sensors for the innermost layer of the pixel tracker for the high-luminosity era. IFAE is now qualifying its assembly line to produce 3D modules for the first barrel layer of the ITk pixel detector. The first qualifying step was completed with the fabrication of dummy modules. The second step, the fabrication of RD53A modules, is well underway. The production of 3D sensors at CNM is delayed due to the upgrade of the CNM clean rooms. IFAE is also working towards the qualification of its bump-bonding process. Three publications were produced in 2020 around the 3D sensor activities.
Figure 1: RD53A module
Figure 2: Testing of the RD53A modules.


IFAE continued to play a leading role in the HGTD activities, leading the sensor, module assembly and test-beam groups, and with S. Grinstein acting as the sub-Project Leader. IFAE is also playing a critical role in the digital design of the final HGTD readout chip. The first full size prototype chip was fabricated in 2021 and IFAE was the first institute to bump-bond the chip to LGAD sensors. The hybridization process, which includes UBM of the ASIC and sensor at CNM, and the ball deposition and flip-chip at IFAE, is well established: five full size prototypes have been produced and the bump-bonding yield so far is 100%. Furthermore, IFAE developed the firmware and software for a redout system called Alvin, that is currently one of the two systems used by HGTD and was used to test the first devices and verify, with a radioactive source, that all the channels were working, a critical milestone for the HGTD project.
Figure 3: First ALTIROC2 modules fully fabricated at IFAE.
Figure 4: First ALTIROC2 module being tested at IFAE.
Figure 5: Source scan of an ALTIROC2 device, demonstrating that all the pixels are working (pixel 0,0 is not operational on these ASICs).


The CMOS effort during 2021 concentrated on the tests of the TaichuPix1&2 ASIC, an early prototype for the CEPC vertex detector. The TaichuPix1 was partially designed by IFAE and has been characterized in our laboratory. Furthermore, the group continues to explore the usage of HV-CMOS sensors beyond high energy physics, developing CMOS SPADs in the context of a BIST funded project with ICFO. Finally, together with ICN2, IFAE explored the usage of 2D materials for MIP detection, also in the framework of a BIST Ignite project.