Selection of the silicon sensor thickness for the Phase-2 upgrade of the CMS Outer Tracker

Abstract During the operation of the CMS experiment at the High-Luminosity LHC the silicon sensors of the Phase-2 Outer Tracker will be exposed to radiation levels that could potentially deteriorate their performance. Previous studies had determined that planar float zone silicon with n-doped strips on a p-doped substrate was preferred over p-doped strips on an n-doped substrate. The last step in evaluating the optimal design for the mass production of about 200 m2 of silicon sensors was to compare sensors of baseline thickness (about 300 μm) to thinned sensors (about 240 μm), which promised several benefits at high radiation levels because of the higher electric fields at the same bias voltage. This study provides a direct comparison of these two thicknesses in terms of sensor characteristics as well as charge collection and hit efficiency for fluences up to 1.5 × 1015 neq/cm2. The measurement results demonstrate that sensors with about 300 μm thickness will ensure excellent tracking performance even at the highest considered fluence levels expected for the Phase-2 Outer Tracker.</jats:p

Comparative evaluation of analogue front-end designs for the CMS Inner Tracker at the High Luminosity LHC

Abstract The CMS Inner Tracker, made of silicon pixel modules, will be entirely replaced prior to the start of the High Luminosity LHC period. One of the crucial components of the new Inner Tracker system is the readout chip, being developed by the RD53 Collaboration, and in particular its analogue front-end, which receives the signal from the sensor and digitizes it. Three different analogue front-ends (Synchronous, Linear, and Differential) were designed and implemented in the RD53A demonstrator chip. A dedicated evaluation program was carried out to select the most suitable design to build a radiation tolerant pixel detector able to sustain high particle rates with high efficiency and a small fraction of spurious pixel hits. The test results showed that all three analogue front-ends presented strong points, but also limitations. The Differential front-end demonstrated very low noise, but the threshold tuning became problematic after irradiation. Moreover, a saturation in the preamplifier feedback loop affected the return of the signal to baseline and thus increased the dead time. The Synchronous front-end showed very good timing performance, but also higher noise. For the Linear front-end all of the parameters were within specification, although this design had the largest time walk. This limitation was addressed and mitigated in an improved design. The analysis of the advantages and disadvantages of the three front-ends in the context of the CMS Inner Tracker operation requirements led to the selection of the improved design Linear front-end for integration in the final CMS readout chip.</jats:p

Beam test performance of a prototype module with Short Strip ASICs for the CMS HL-LHC tracker upgrade

International audienceThe Short Strip ASIC (SSA) is one of the four front-endchips designed for the upgrade of the CMS Outer Tracker for the HighLuminosity LHC. Together with the Macro-Pixel ASIC (MPA) it willinstrument modules containing a strip and a macro-pixel sensorstacked on top of each other. The SSA provides both full readout ofthe strip hit information when triggered, and, together with theMPA, correlated clusters called stubs from the two sensors for useby the CMS Level-1 (L1) trigger system. Results from the firstprototype module consisting of a sensor and two SSA chips arepresented. The prototype module has been characterized at theFermilab Test Beam Facility using a 120 GeV proton beam

Evaluation of HPK n+n^+-pp planar pixel sensors for the CMS Phase-2 upgrade

International audienceTo cope with the challenging environment of the planned high luminosity upgrade of the Large Hadron Collider (HL-LHC), sched-uled to start operation in 2029, CMS will replace its entire tracking system. The requirements for the tracker are largely determinedby the long operation time of 10 years with an instantaneous peak luminosity of up to 7.5 × 1034 cm−2 s−1 in the ultimate perfor-mance scenario. Depending on the radial distance from the interaction point, the silicon sensors will receive a particle fluencecorresponding to a non-ionizing energy loss of up to Φeq = 3.5 × 1016 cm−2. This paper focuses on planar pixel sensor design andqualification up to a fluence of Φeq = 1.4 × 1016 cm−2.For the development of appropriate planar pixel sensors an R&D program was initiated, which includes n+-p sensors on 150 mm(6”) wafers with an active thickness of 150 μm with pixel sizes of 100 × 25 μm2 and 50 × 50 μm2 manufactured by Hamamatsu.Single chip modules with ROC4Sens and RD53A readout chips were made. Irradiation with protons and neutrons, as well was anextensive test beam campaign at DESY were carried out. This paper presents the investigation of various assemblies mainly withROC4Sens readout chips. It demonstrates that multiple designs fulfill the requirements in terms of breakdown voltage, leakagecurrent and efficiency. The single point resolution for 50 × 50 μm2 pixels is measured as 4.0 μm for non-irradiated samples, and6.3 μm after irradiation to Φeq = 7.2 × 1015 cm−2

Evaluation of HPK n+n^+-pp planar pixel sensors for the CMS Phase-2 upgrade

To cope with the challenging environment of the planned high luminosity upgrade of the Large Hadron Collider (HL-LHC), scheduled to start operation in 2029, CMS will replace its entire tracking system. The requirements for the tracker are largely determined by the long operation time of 10~years with an instantaneous peak luminosity of up to $7.5\times 10^{34}$~cm$^{-2}$s$^{-1}$ in the ultimate performance scenario. Depending on the radial distance from the interaction point, the silicon sensors will receive a particle fluence corresponding to a non-ionizing energy loss of up to $\Phi_{\text{eq}} = 3.5\times 10^{16}$~cm$^{-2}$. This paper focuses on planar pixel sensor design and qualification up to a fluence of $\Phi_{\text{eq}} = 1.4\times 10^{16}$~cm$^{-2}$. For the development of appropriate planar pixel sensors an R\&D program was initiated, which includes $n^+$-$p$ sensors on 150 mm (6'') wafers with an active thickness of 150~$\mu$m with pixel sizes of $100\times 25$~$\mu$m$^2$ and $50\times 50$~$\mu$m$^2$ manufactured by Hamamatsu Photonics K.K.\ (HPK). Single chip modules with ROC4Sens and RD53A readout chips were made. Irradiation with protons and neutrons, as well was an extensive test beam campaign at DESY were carried out. This paper presents the investigation of various assemblies mainly with ROC4Sens readout chips. It demonstrates that multiple designs fulfill the requirements in terms of breakdown voltage, leakage current and efficiency. The single point resolution for $50\times 50$~$\mu$m$^2$ pixels is measured as 4.0~$\mu$m for non-irradiated samples, and 6.3~$\mu$m after irradiation to $\Phi_{\text{eq}} = 7.2\times 10^{15}$~cm$^{-2}$.To cope with the challenging environment of the planned high luminosity upgrade of the Large Hadron Collider (HL-LHC), sched- uled to start operation in 2029, CMS will replace its entire tracking system. The requirements for the tracker are largely determined by the long operation time of 10 years with an instantaneous peak luminosity of up to 7.5 × 1034 cm−2 s−1 in the ultimate perfor- mance scenario. Depending on the radial distance from the interaction point, the silicon sensors will receive a particle fluence corresponding to a non-ionizing energy loss of up to Φeq = 3.5 × 1016 cm−2. This paper focuses on planar pixel sensor design and qualification up to a fluence of Φeq = 1.4 × 1016 cm−2. For the development of appropriate planar pixel sensors an R&D program was initiated, which includes n+-p sensors on 150 mm (6”) wafers with an active thickness of 150 μm with pixel sizes of 100 × 25 μm2 and 50 × 50 μm2 manufactured by Hamamatsu. Single chip modules with ROC4Sens and RD53A readout chips were made. Irradiation with protons and neutrons, as well was an extensive test beam campaign at DESY were carried out. This paper presents the investigation of various assemblies mainly with ROC4Sens readout chips. It demonstrates that multiple designs fulfill the requirements in terms of breakdown voltage, leakage current and efficiency. The single point resolution for 50 × 50 μm2 pixels is measured as 4.0 μm for non-irradiated samples, and 6.3 μm after irradiation to Φeq = 7.2 × 1015 cm−2.To cope with the challenging environment of the planned high luminosity upgrade of the Large Hadron Collider (HL-LHC), scheduled to start operation in 2029, CMS will replace its entire tracking system. The requirements for the tracker are largely determined by the long operation time of 10 years with an instantaneous peak luminosity of up to 7.5 × 1034cm−2s−1 in the ultimate performance scenario. Depending on the radial distance from the interaction point, the silicon sensors will receive a particle fluence corresponding to a non-ionising energy loss of up to Φeq= 3.5 × 1016cm−2. This paper focuses on planar pixel sensor design and qualification up to a fluence of Φeq = 1.4 × 1016cm−2. For the development of appropriate planar pixel sensors an R&D program was initiated, which includes n+-p sensors on 150mm (6”) wafers with an active thickness of 150µm with pixel sizes of 100×25 µm2 and 50×50 µm2 manufactured by Hamamatsu Photonics K.K. (HPK). Single chip modules with ROC4Sens and RD53A readout chips were made. Irradiation with protons and neutrons, as well was an extensive test beam campaign at DESY were carried out. This paper presents the investigation of various assemblies mainly with ROC4Sens readout chips. It demonstrates that multiple designs fulfil the requirements in terms of breakdown voltage, leakage current and efficiency. The single point resolution for 50×50 µm2 pixels is measured as 4.0µm for non-irradiated samples, and 6.3µm after irradiation to Φeq = 7.2 × 1015cm−2

Beam test performance of a prototype module with Short Strip ASICs for the CMS HL-LHC tracker upgrade

Abstract The Short Strip ASIC (SSA) is one of the four front-end chips designed for the upgrade of the CMS Outer Tracker for the High Luminosity LHC. Together with the Macro-Pixel ASIC (MPA) it will instrument modules containing a strip and a macro-pixel sensor stacked on top of each other. The SSA provides both full readout of the strip hit information when triggered, and, together with the MPA, correlated clusters called stubs from the two sensors for use by the CMS Level-1 (L1) trigger system. Results from the first prototype module consisting of a sensor and two SSA chips are presented. The prototype module has been characterized at the Fermilab Test Beam Facility using a 120 GeV proton beam.</jats:p