Anna Macchiolo

Planar pixel sensors for the ATLAS upgrade: beam tests results

The performance of planar silicon pixel sensors, in development for the ATLAS Insertable B-Layer and High Luminosity LHC (HL-LHC) upgrades, has been examined in a series of beam tests at the CERN SPS facilities since 2009. Salient results are reported on the key parameters, including the spatial resolution, the charge collection and the charge sharing between adjacent cells, for different bulk materials and sensor geometries. Measurements are presented for n+-in-n pixel sensors irradiated with a range of fluences and for p-type silicon sensors with various layouts from different vendors. All tested sensors were connected via bump-bonding to the ATLAS Pixel read-out chip. The tests reveal that both n-type and p-type planar sensors are able to collect significant charge even after the lifetime fluence expected at the HL-LHC.

Thin n-in-p pixel sensors and the SLID-ICV vertical integration technology for the ATLAS upgrade at the HL-LHC

Abstract This R&D activity is focused on the development of new modules for the upgrade of the ATLAS pixel system at the High Luminosity LHC (HL-LHC). The performance after irradiation of n-in-p pixel sensors of different active thicknesses is studied, together with an investigation of a novel interconnection technique offered by the Fraunhofer Institute EMFT in Munich, the Solid–Liquid-InterDiffusion (SLID), which is an alternative to the standard solder bump-bonding. The pixel modules are based on thin n-in-p sensors, with an active thickness of 75 μ m or 150 μ m , produced at the MPI Semiconductor Laboratory (MPI HLL) and on 100 μ m thick sensors with active edges, fabricated at VTT, Finland. Hit efficiencies are derived from beam test data for thin devices irradiated up to a fluence of 4 × 10 15 n eq / cm 2 . For the active edge devices, the charge collection properties of the edge pixels before irradiation are discussed in detail, with respect to the inner ones, using measurements with radioactive sources. Beyond the active edge sensors, an additional ingredient needed to design four side buttable modules is the possibility of moving the wire bonding area from the chip surface facing the sensor to the backside, avoiding the implementation of the cantilever extruding beyond the sensor area. The feasibility of this process is under investigation with the FE-I3 SLID modules, where Inter Chip Vias are etched, employing an EMFT technology, with a cross section of 3 μ m × 10 μ m , at the positions of the original wire bonding pads.

Performance of novel silicon n-in-p planar pixel sensors

The performance of novel n-in-p planar pixel detectors designed for future upgrades of the ATLAS Pixel system is presented. The n-in-p silicon sensors technology is a promising candidate for the pixel upgrade thanks to its radiation hardness and cost effectiveness that allow for enlarging the area instrumented with pixel detectors. The n-in-p modules presented here are composed of pixel sensors produced by CiS connected by bump-bonding to the ATLAS read-out chip FE-I3. The characterization of these devices has been performed before and after irradiation up to a fluence of 5×1015 1 MeV neqcm−2. Charge collection measurements carried out with radioactive sources have proven the functioning of this technology up to these particle fluences. First results from beam test data with a 120 GeV/c pion beam at the CERN-SPS are also discussed, demonstrating a high tracking efficiency of (98.6±0.3)% and a high collected charge of about 10 ke for a device irradiated at the maximum fluence and biased at 1 kV.

Heavily irradiated N-in-p thin planar pixel sensors with and without active edges

We present the results of the characterization of silicon pixel modules employing n-in-p planar sensors with an active thickness of 150 μm, produced at MPP/HLL, and 100–200 μm thin active edge sensor devices, produced at VTT in Finland. These thin sensors are designed as candidates for the ATLAS pixel detector upgrade to be operated at the HL-LHC, as they ensure radiation hardness at high fluences. They are interconnected to the ATLAS FE-I3 and FE-I4 read-out chips. Moreover, the n-in-p technology only requires a single side processing and thereby it is a cost-effective alternative to the n-in-n pixel technology presently employed in the LHC experiments. High precision beam test measurements of the hit efficiency have been performed on these devices both at the CERN SpS and at DESY, Hamburg. We studied the behavior of these sensors at different bias voltages and different beam incident angles up to the maximum one expected for the new Insertable B-Layer of ATLAS and for HL-LHC detectors. Results obtained with 150 μm thin sensors, assembled with the new ATLAS FE-I4 chip and irradiated up to a fluence of 4 × 1015 neq/cm2, show that they are excellent candidates for larger radii of the silicon pixel tracker in the upgrade of the ATLAS detector at HL-LHC. In addition, the active edge technology of the VTT devices maximizes the active area of the sensor and reduces the material budget to suit the requirements for the innermost layers. The edge pixel performance of VTT modules has been investigated at beam test experiments and the analysis after irradiation up to a fluence of 5 × 1015 neq/cm2 has been performed using radioactive sources in the laboratory.

Development of n-in-p pixel modules for the ATLAS Upgrade at HL-LHC

Thin planar pixel modules are promising candidates to instrument the inner layers of the new ATLAS pixel detector for HLLHC, thanks to the reduced contribution to the material budget and their high charge collection e ciency after irradiation. 100-200 m thick sensors, interconnected to FE-I4 read-out chips, have been characterized with radioactive sources and beam tests at the CERN-SPS and DESY. The results of these measurements are reported for devices before and after irradiation up to a fluence of 14 10 15 neq=cm 2 . The charge collection and tracking e ciency of the di erent sensor thicknesses are compared. The outlook for future planar pixel sensor production is discussed, with a focus on sensor design with the pixel pitches (50x50 and 25x100 m 2 ) foreseen for the RD53 Collaboration read-out chip in 65 nm CMOS technology. An optimization of the biasing structures in the pixel cells is required to avoid the hit e ciency loss presently observed in the punch-through region after irradiation. For this purpose the performance of di erent layouts have been compared in FE-I4 compatible sensors at various fluence levels by using beam test data. Highly segmented sensors will represent a challenge for the tracking in the forward region of the pixel system at HL-LHC. In order to reproduce the performance of 50x50 m 2 pixels at high pseudo-rapidity values, FE-I4 compatible planar pixel sensors have been studied before and after irradiation in beam tests at high incidence angle (80 ) with respect to the short pixel direction. Results on cluster shapes, charge collection and hit e ciency will be shown.

Thin n-in-p planar pixel sensors and active edge sensors for the ATLAS upgrade at HL-LHC

Silicon pixel modules employing n-in-p planar sensors with an active thickness of 200 μm, produced at CiS, and 100-200 μm thin active/slim edge sensor devices, produced at VTT in Finland have been interconnected to ATLAS FE-I3 and FE-I4 read-out chips. The thin sensors are designed for high energy physics collider experiments to ensure radiation hardness at high fluences. Moreover, the active edge technology of the VTT production maximizes the sensitive region of the assembly, allowing for a reduced overlap of the modules in the pixel layer close to the beam pipe. The CiS production includes also four chip sensors according to the module geometry planned for the outer layers of the upgraded ATLAS pixel detector to be operated at the HL-LHC. The modules have been characterized using radioactive sources in the laboratory and with high precision measurements at beam tests to investigate the hit efficiency and charge collection properties at different bias voltages and particle incidence angles. The performance of the different sensor thicknesses and edge designs are compared before and after irradiation up to a fluence of 1.4 × 1016 neq/cm2.

Characterization of thin pixel sensor modules interconnected with SLID technology irradiated to a fluence of 2⋅1015 neq/cm2.

A new module concept for future ATLAS pixel detector upgrades is presented, where thin n-in-p silicon sensors are connected to the front-end chip exploiting the novel Solid Liquid Interdiffusion technique (SLID) and the signals are read out via Inter Chip Vias (ICV) etched through the front-end. This should serve as a proof of principle for future four-side buttable pixel assemblies for the ATLAS upgrades, without the cantilever presently needed in the chip for the wire bonding. The SLID interconnection, developed by the Fraunhofer EMFT, is a possible alternative to the standard bump-bonding. It is characterized by a very thin eutectic Cu-Sn alloy and allows for stacking of different layers of chips on top of the first one, without destroying the pre-existing bonds. This paves the way for vertical integration technologies. Results of the characterization of the first pixel modules interconnected through SLID as well as of one sample irradiated to

Investigation of thin n-in-p planar pixel modules for the ATLAS upgrade

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A module concept for the upgrades of the ATLAS pixel system using the novel SLID-ICV vertical integration technology

\,\neqcm{} are discussed. Additionally, the etching of ICV into the front-end wafers was started. ICVs will be used to route the signals vertically through the front-end chip, to newly created pads on the backside. In the EMFT approach the chip wafer is thinned to (50--60)\,

Novel silicon n-in-p pixel sensors for the future ATLAS upgrades

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