The CMS detector at the CERN LHC features a silicon pixel detector as its innermost subdetector. The original CMS pixel detector has been replaced with an upgraded pixel system (CMS Phase-1 pixel detector) in the extended year-end technical stop of the LHC in 2016/2017. The upgraded CMS pixel detector is designed to cope with the higher instantaneous luminosities that have been achieved by the LHC after the upgrades to the accelerator during the first long shutdown in 2013–2014. Compared to the original pixel detector, the upgraded detector has a better tracking performance and lower mass with four barrel layers and three endcap disks on each side to provide hit coverage up to an absolute value of pseudorapidity of 2.5. This paper describes the design and construction of the CMS Phase-1 pixel detector as well as its performance from commissioning to early operation in collision data-taking.
This paper presents the design and characteristics of a front-end readout application-specific integrated circuit (ASIC) dedicated to a multichannel-plate photodetector coupled to LYSO scintillating crystals. In our configuration, the crystals are oriented in the axial direction readout on both sides by individual photodetector channels allowing the spatial resolution and the detection efficiency to be independent of each other. Both energy signals and timing triggers from the photodetectors are required to be read out by the front-end ASIC. A current-mode charge-sensitive amplifier is proposed for this application. This paper presents performance characteristics of a 10-channel prototype chip designed and fabricated in a 0.35-μm complementary metal-oxide semiconductor process. The main results of simulations and measurements are presented and discussed. The gain of the chip is 13.1 mV/pC while the peak time of a CR-RC pulse shaper is 280 ns. The signal-to-noise ratio is 39 dB and the rms noise is 300 μV/√(Hz). The nonlinearity is less than 3% and the crosstalk is about 0.2%. The power dissipation is less than 15 mW/channel. This prototype will be extended to a 64-channel circuit with integrated time-to-digital converter and analog-to-digital converter together for a high-sensitive small-animal positron emission tomography imaging system.
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.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.