In this paper we report on the timing resolution obtained in a beam test with pions of 180 GeV/c momentum at CERN for the first production of 45 μm thick Ultra-Fast Silicon Detectors (UFSD). UFSD are ...based on the Low- Gain Avalanche Detector (LGAD) design, employing n-on-p silicon sensors with internal charge multiplication due to the presence of a thin, low-resistivity diffusion layer below the junction. The UFSD used in this test had a pad area of 1.7 mm2. The gain was measured to vary between 5 and 70 depending on the sensor bias voltage. The experimental setup included three UFSD and a fast trigger consisting of a quartz bar readout by a SiPM. The timing resolution was determined by doing Gaussian fits to the time-of-flight of the particles between one or more UFSD and the trigger counter. For a single UFSD the resolution was measured to be 34 ps for a bias voltage of 200 V, and 27 ps for a bias voltage of 230 V. For the combination of 3 UFSD the timing resolution was 20 ps for a bias voltage of 200 V, and 16 ps for a bias voltage of 230 V.
The production of the strip sensors for the ATLAS Inner Tracker (ITk) will start in 2020. Nearly 22,000 large area sensors will be produced over a period of about five years by Hamamatsu Photonics ...K.K. (HPK). The institutes involved in the sensor development and production are committed to deliver and maintain the highest quality sensors for the experiment. A Quality Assurance (QA) strategy has been prepared to be carried out during the whole production period. Once the process has been characterized as providing the required pre-irradiation specifications and the proper radiation hardness, the onus is on the manufacturer to rigidly stick to that qualified process. Still, sample testing with specific device-element structures and irradiation of devices should be implemented by the ITk sensor collaboration.
A detailed irradiation and testing plan has been prepared by the ATLAS-ITk Collaboration, together with a newly designed test chip with specific structures to monitor different key technological and device parameters during the whole production. The tests and irradiations will be carried out on a sample basis. In order to have a practical methodology, samples from alternating batches will be sent for irradiations with protons, neutrons and gammas, and then tested in order to check that the characteristics remain within specifications. The detailed plan and the design and test methods for the structures in the test chip are presented here.
The ATLAS experiment is going to replace the current Inner Detector with an all new inner tracker (ITk) in the ATLAS detector for HL-LHC at CERN. Silicon strip detectors cover the outer layers of the ...barrel and the endcap sections. We have designed and fabricated a prototype single-sided n+-in-p AC-coupled silicon strip sensor for the outer barrel layer with long strips (LS), ATLAS17LS. It is of the maximum allowable size to fit in a 6-in. silicon wafer, with an outer dimension of 9.80(width)×9.76(length)cm2. The sensor features two rows of LS strip segments, 4.83 cm strip length per segment, a strip pitch of 75.5 μm, and a slim edge design. We have implemented technology for high voltage operation of up to 1000V, with a good signal collection after irradiation fluence of 5.6 × 1014neq∕cm2at the end of HL-LHC operation.
We had two objectives for the ATLAS17LS fabrication: qualification of the sensor design and fabrication quality, and providing an adequate number of the sensors for prototyping the building blocks of the strip detector. The sensors were fabricated in 3 batches by HPK with standard wafers from the foundry (320 μm physical thickness). Additional 10 sensors were fabricated with a thinner active thickness of 240 μm to investigate the influence of active thickness on charge collection. Another additional 5 sensors, with special passivation to investigate the influence of passivation on humidity sensitivity. The visual inspection of fabricated sensors revealed an inadequacy that the designed metal width of 10 μm was too narrow. The initial measurements by the vendor showed that the sensors fulfilled the specifications: onset voltages of Microdischarge VMD above the operation voltage VOP (700V for the 1st and 2nd batches; 500V for the 3rd batch, which has improved the yield), leakage currents of < 0.1μA/cm2 at VOP, full depletion voltages VFD< 330V, and rates of bad strips <<1%.
Radiation hardness of thin Low Gain Avalanche Detectors Kramberger, G.; Carulla, M.; Cavallaro, E. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2018, Letnik:
891
Journal Article
Recenzirano
Low Gain Avalanche Detectors (LGAD) are based on a n++-p+-p-p++ structure where an appropriate doping of the multiplication layer (p+) leads to high enough electric fields for impact ionization. Gain ...factors of few tens in charge significantly improve the resolution of timing measurements, particularly for thin detectors, where the timing performance was shown to be limited by Landau fluctuations. The main obstacle for their operation is the decrease of gain with irradiation, attributed to effective acceptor removal in the gain layer. Sets of thin sensors were produced by two different producers on different substrates, with different gain layer doping profiles and thicknesses (45, 50 and 80 μm). Their performance in terms of gain/collected charge and leakage current was compared before and after irradiation with neutrons and pions up to the equivalent fluences of 5⋅1015 cm−2. Transient Current Technique and charge collection measurements with LHC speed electronics were employed to characterize the detectors. The thin LGAD sensors were shown to perform much better than sensors of standard thickness (∼300 μm) and offer larger charge collection with respect to detectors without gain layer for fluences <2⋅1015 cm−2. Larger initial gain prolongs the beneficial performance of LGADs. Pions were found to be more damaging than neutrons at the same equivalent fluence, while no significant difference was found between different producers. At very high fluences and bias voltages the gain appears due to deep acceptors in the bulk, hence also in thin standard detectors.
We present a new compilation of Type Ia supernovae (SNe Ia), a new data set of low-redshift nearby-Hubble-flow SNe, and new analysis procedures to work with these heterogeneous compilations. This ...'Union' compilation of 414 SNe Ia, which reduces to 307 SNe after selection cuts, includes the recent large samples of SNe Ia from the Supernova Legacy Survey and ESSENCE Survey, the older data sets, as well as the recently extended data set of distant supernovae observed with the Hubble Space Telescope (HST). A single, consistent, and blind analysis procedure is used for all the various SN Ia subsamples, and a new procedure is implemented that consistently weights the heterogeneous data sets and rejects outliers. We present the latest results from this Union compilation and discuss the cosmological constraints from this new compilation and its combination with other cosmological measurements (CMB and BAO). The constraint we obtain from supernovae on the dark energy density is image, for a flat, Lambda CDM universe. Assuming a constant equation of state parameter, w, the combined constraints from SNe, BAO, and CMB give image. While our results are consistent with a cosmological constant, we obtain only relatively weak constraints on a w that varies with redshift. In particular, the current SN data do not yet significantly constrain w at image. With the addition of our new nearby Hubble-flow SNe Ia, these resulting cosmological constraints are currently the tightest available.
The ATLAS community is facing the last stages prior to the production of the upgraded silicon strip Inner Tracker for the High-Luminosity Large Hadron Collider. An extensive Market Survey was carried ...out in order to evaluate the capability of different foundries to fabricate large area silicon strip sensors, satisfying the ATLAS specifications. The semiconductor manufacturing company, Infineon Technologies AG, was one of the two foundries, along with Hamamatsu Photonics K.K., that reached the last stage of the evaluation for the production of the new devices. The full prototype wafer layout for the participation of Infineon, called ATLAS17LS-IFX, was designed using a newly developed Python-based Automatic Layout Generation Tool, able to rapidly design sensors with different characteristics and dimensions based on a few geometrical and technological input parameters. This work presents the layout design process and the results obtained from the evaluation of the new Infineon large area sensors before and after proton and neutron irradiations, up to fluences expected in the inner layers of the future ATLAS detector.
The Quality Control (QC) of pre-production strip sensors for the Inner Tracker (ITk) of the ATLAS Inner Detector upgrade has finished, and the collaboration has embarked on the QC test programme for ...production sensors. This programme will last more than 3 years and comprises the evaluation of approximately 22000 sensors. 8 Types of sensors, 2 barrel and 6 endcap, will be measured at many different collaborating institutes. The sustained throughput requirement of the combined QC processes is around 500 sensors per month in total. Measurement protocols have been established and acceptance criteria have been defined in accordance with the terms agreed with the supplier. For effective monitoring of test results, common data file formats have been agreed upon across the collaboration. To enable evaluation of test results produced by many different test setups at the various collaboration institutes, common algorithms have been developed to collate, evaluate, plot and upload measurement data. This allows for objective application of pass/fail criteria and compilation of corresponding yield data. These scripts have been used to process the data of more than 3000 sensors so far, and have been instrumental for identification of faulty sensors and monitoring of QC testing progress.
This paper reports the latest technological development on the Low Gain Avalanche Detector (LGAD) and introduces a new architecture of these detectors called inverse-LGAD (iLGAD). Both approaches are ...based on the standard Avalanche Photo Diodes (APD) concept, commonly used in optical and X-ray detection applications, including an internal multiplication of the charge generated by radiation. The multiplication is inherent to the basic n++–p+–p structure, where the doping profile of the p+ layer is optimized to achieve high field and high impact ionization at the junction.
The LGAD structures are optimized for applications such as tracking or timing detectors for high energy physics experiments or medical applications where time resolution lower than 30ps is required. Detailed TCAD device simulations together with the electrical and charge collection measurements are presented through this work.
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