Radiation Hard Sensors Research Articles

Experimental study of different silicon sensor options for the upgrade of the CMS Outer Tracker

During the high-luminosity phase of the LHC (HL-LHC), planned to start in 2027, the accelerator is expected to deliver an instantaneous peak luminosity of up to 7.5×1034 cm−2 s−1. A total integrated luminosity of 0300 or even 0400 fb−1 is foreseen to be delivered to the general purpose detectors ATLAS and CMS over a decade, thereby increasing the discovery potential of the LHC experiments significantly. The CMS detector will undergo a major upgrade for the HL-LHC, with entirely new tracking detectors consisting of an Outer Tracker and Inner Tracker. However, the new tracking system will be exposed to a significantly higher radiation than the current tracker, requiring new radiation-hard sensors. CMS initiated an extensive irradiation and measurement campaign starting in 2009 to systematically compare the properties of different silicon materials and design choices for the Outer Tracker sensors. Several test structures and sensors were designed and implemented on 18 different combinations of wafer materials, thicknesses, and production technologies. The devices were electrically characterized before and after irradiation with neutrons, and with protons of different energies, with fluences corresponding to those expected at different radii of the CMS Outer Tracker after 0300 fb−1. The tests performed include studies with β sources, lasers, and beam scans. This paper compares the performance of different options for the HL-LHC silicon sensors with a focus on silicon bulk material and thickness.

Investigation of a direction sensitive sapphire detector stack at the 5 GeV electron beam at DESY-II

Extremely radiation hard sensors are needed in particle physics experiments to instrument the region near the beam pipe. Examples are beam halo and beam loss monitors at the Large Hadron Collider, FLASH or XFEL. Currently artificial diamond sensors are widely used. In this paper single crystal sapphire sensors are considered as a promising alternative. Industrially grown sapphire wafers are available in large sizes, are of low cost and, like diamond sensors, can be operated without cooling. Here we present results of an irradiation study done with sapphire sensors in a high intensity low energy electron beam. Then, a multichannel direction-sensitive sapphire detector stack is described. It comprises 8 sapphire plates of 1 cm2 size and 525 μ m thickness, metallized on both sides, and apposed to form a stack. Each second metal layer is supplied with a bias voltage, and the layers in between are connected to charge-sensitive preamplifiers. The performance of the detector was studied in a 5 GeV electron beam. The charge collection efficiency measured as a function of the bias voltage rises with the voltage, reaching about 10% at 095 V. The signal size obtained from electrons crossing the stack at this voltage is about 02200 e, where e is the unit charge.The signal size is measured as a function of the hit position, showing variations of up to 20% in the direction perpendicular to the beam and to the electric field. The measurement of the signal size as a function of the coordinate parallel to the electric field confirms the prediction that mainly electrons contribute to the signal. Also evidence for the presence of a polarisation field was observed.

The VELO Upgrade

A significant upgrade of the LHCb detector is scheduled to be installed in 2018–2019. Afterwards all sub-detectors will be read out at the LHC bunch crossing frequency of 40 MHz and the trigger will be fully implemented in software. The silicon strip vertex detector will be replaced by a hybrid pixel detector. In these proceedings the following items are discussed: frontend ASIC, data rates, data transmission, cooling, radiation hard sensors, module design and simulated performance.

Silicon sensors for trackers at high-luminosity environment

The planned upgrade of the LHC accelerator at CERN, namely the high luminosity (HL) phase of the LHC (HL-LHC foreseen for 2023), will result in a more intense radiation environment than the present tracking system that was designed for. The required upgrade of the all-silicon central trackers at the ALICE, ATLAS, CMS and LHCb experiments will include higher granularity and radiation hard sensors. The radiation hardness of the new sensors must be roughly an order of magnitude higher than in the current LHC detectors. To address this, a massive R&D program is underway within the CERN RD50 Collaboration “Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders” to develop silicon sensors with sufficient radiation tolerance. Research topics include the improvement of the intrinsic radiation tolerance of the sensor material and novel detector designs with benefits like reduced trapping probability (thinned and 3D sensors), maximized sensitive area (active edge sensors) and enhanced charge carrier generation (sensors with intrinsic gain). A review of the recent results from both measurements and TCAD simulations of several detector technologies and silicon materials at radiation levels expected for HL-LHC will be presented.

Radiation hard sensor materials for the CMS Tracker Phase II Upgrade - Charge collection of different bulk polarities

The upgrade of the LHC machine to deliver a significantly higher luminosity of about 5×1034cm−2s−1 is planned to be operational after 2022. This will simultaneously increase the radiation dose for the inner detector systems, requiring new radiation hard sensor materials for the CMS Tracker. To identify the appropriate materials which are able to withstand the radiation environment in the middle to outer layers of the CMS Tracker during the full lifetime of the high luminosity LHC, a large irradiation and measurement campaign has been conducted. Several test structures and sensors have been designed and manufactured on 18 different combinations of wafer materials, thicknesses and production technologies. The structures have been electrically characterised before and after irradiation with different fluences of neutrons and protons.This paper reports the final results on strip sensor performance considering the comparison of p-in-n technology with n-in-p type. Outcomes from signal and noise measurements before and after annealing depending on the radiation dose are discussed and the final recommendation of the CMS Tracker Collaboration for the strip sensor polarity for the Phase II Upgrade is presented.

Sensor R&D for the CMS outer tracker upgrade for the HL-LHC

At an instantaneous luminosity of 5 × 1034 cm−2s−1, the high-luminosity phase of the Large Hadron Collider (HL-LHC) is expected to deliver a total of 3000 fb−1 of collisions, hereby increasing the discovery potential of the LHC experiments significantly. However, the radiation environment of the tracking system will be severe, requiring new radiation hard sensors for the CMS tracker. The CMS tracker collaboration has almost completed a large material investigation and irradiation campaign to identify the silicon material and design that fulfills all requirements of a new tracking detector at HL-LHC. Focusing on the upgrade of the outer tracker region, pad diodes as well as fully functional strip sensors have been implemented on silicon wafers with different material properties and thicknesses. The samples were irradiated with a mixture of neutrons and protons corresponding to fluences as expected for various positions in the future tracker. The measurements performed on the structures include electrical sensor characterization, measurements of the collected charge and bulk defect characterization. In this paper, the performance and limitations of the different materials are presented.

Characterisation of micro-strip and pixel silicon detectors before and after hadron irradiation

The use of segmented silicon detectors for tracking and vertexing in particle physics has grown substantially since their introduction in 1980. It is now anticipated that roughly 50,000 six inch wafers of high resistivity silicon will need to be processed into sensors to be deployed in the upgraded experiments in the future high luminosity LHC (HL-LHC) at CERN. These detectors will also face an extremely severe radiation environment, varying with distance from the interaction point. The volume of required sensors is large and their delivery is required during a relatively short time, demanding a high throughput from the chosen suppliers. The current situation internationally, in this highly specialist market, means that security of supply for large orders can therefore be an issue and bringing additional potential vendors into the field can only be an advantage. Semiconductor companies that could include planar sensors suitable for particle physics in their product lines will, however, need to prove their products meet all the stringent technical requirements. A semiconductor company with very widespread experience of producing science grade CCDs (including deep depletion devices) has adapted their CCD process to fabricate for the first time several wafers of pixel and micro-strip radiation hard sensors, suitable for future high energy physics experiments. The results of the pre-irradiation characterization of devices fabricated with different processing parameters and the measurements of charge collection properties after different hadron irradiation doses up to those anticipated for the (larger area) outer pixel layers at the high-luminosity LHC (HL-LHC) are presented and compared with results from more established particle physics suppliers.

Charge Collection Studies and Electrical Measurements of Heavily Irradiated 3D Double-Sided Sensors and Comparison to Planar Strip Detectors

Three-dimensional (3D) silicon detectors offer advantages over standard planar devices as more radiation hard sensors. These detectors and their applications in the upgrades of the LHC experiments are discussed. 3D detectors with a double-sided geometry have been fabricated as very short strip detectors with similar inter-column spacing as proposed for the ATLAS pixel detector and LHCb vertex locator upgrades. The detectors have been irradiated up to a fluence of 2 × 1016 cm-2 1 MeV equivalent neutrons, which is twice the expected dose of the inner pixel layer of the ATLAS detector and of the upgraded LHCb vertex locator for LHC high luminosity upgrade (HL-LHC) operation. Electrical measurements show a lateral depletion voltage of only 4 V for the device before irradiation which increases to 200 V after an irradiation to a fluence of 1 × 1016 cm-2 1 MeV equivalent neutrons. The strip isolation of the p-type detectors was robust to the maximum fluence. Charge collection studies have been performed with analogue readout with 25 ns shaping time, as required for LHC experiments. The response of the detectors to high energy electrons from a 90Sr source and a collimated pulsed laser light source are shown and compared with planar devices. The 3D detector, operated at no more than 350 V, is shown to have superior charge collection characteristics to planar devices for all the fluence range expected at HL-LHC even when compared to planar devices operating at 1000 V. When operated at a bias voltage of 350 V the 3D detector collects 2.8 times more charge than a p-type planar device operated at 1000 V after a fluence of 1016 cm-2 1 MeV equivalent neutrons. Charge multiplication in 3D detectors is also reported, in both 90Sr and laser tests, which leads to further enhancement in the charge collection and signal-to-noise ratio of the detector. The effect is demonstrated, through laser tests, to occur close to the junction electrode.

Fast neutron irradiation of high- Tc superconducting materials engineered for magnetic field and THz photon detection

Radiation-hard sensors are at present time highly requested for applications in environments with potential radiation hazard such as space, accelerators and fusion machines. We developed device prototypes for magnetic field and THz photon detection, both based on YBa 2Cu 3O 7− x (YBCO) superconducting films locally nanostructured by means of 0.25 GeV Au-ion lithography. This micro-collimated implantation of high-density columnar defects in YBCO films allows localizing external electromagnetic excitations by means of dissipative signals only induced into the nanostructured regions. The radiation hardness of detector prototypes was checked under fast neutron radiation. It turns out that, up to a neutron fluence comparable with those expected for 10 years long permanence in the space, no significant change was detected in superconductor characteristics such as zero-field resistance-temperature or magneto-resistance, whose variations could dramatically affect device figures of merit as responsivity or noise equivalent power. Fluences and energy spectrum of the neutrons impinging on the sensor prototypes were determined by a Monte-Carlo code implemented “ad hoc”.

Solid state detectors

Solid state detectors play a fundamental role in particle physics providing precision vertex detection, identification of heavy quarks and leptons, and momentum measurement. The status of the LHC experiments will be reviewed including their performance and the lesson that we have learned from their construction. The development of extremely radiation hard sensors, for the LHC luminosity upgrade will also be discussed. Progress in hybrid, monolithic or semi-monolithic pixel detectors will be presented including the application of monolithic active pixels (MAPS) and DEPFET pixels for RHIC and SuperBelle upgrades.

The forward region of the future ILC detector

In the very forward region of the future detector at the International Linear Collider (ILC) the following subsystems will be considered: a luminosity detector (LumiCal) for precise measurement of the Bhabha event rate; a beam calorimeter (BeamCal) and a beamstrahlung photon monitor (GamCal) for providing a fast feed-back in tuning the luminosity. BeamCal and GamCal will support also the determination of beam parameters. Both LumiCal and BeamCal will extend the angular coverage of the electromagnetic calorimeter at small polar angles. Detailed simulations are currently done to optimize the design of these detectors. Both LumiCal and BeamCal are planned as compact and highly segmented sandwich calorimeters. Tungsten disks of one X0 thickness are interspersed with sensor planes. For LumiCal, silicon pad sensors will be used. BeamCal will work in an extreme radiation environment, hence radiation hard sensors will be used. The sensors have to withstand a dose of up to several MGy per year. Several options for possible sensor materials have been investigated: polycrystalline and single crystal CVD diamond, as well as GaAs. Since the occupancy of LumiCal is relatively large and BeamCal must be readout after each bunch crossing, a fast readout electronics is necessary. The uncertainty of the luminosity measurement must be smaller than 10 − 3 for the running at high energy and about 10 − 4 in the GigaZ program focused to precision measurements of the Z boson. Systematic effects originating from hardware design as the accuracy of the sensor position, the calorimeter position and the dynamic range of the readout electronics, but also from physics processes have been studied. This work presents the current status of the research carried out to instrument this difficult region of the future ILC detector.

Diamond thin film detectors for beam monitoring devices

AbstractDiamonds offer radiation hard sensors, which can be used directly in primary beams. Here we report on the use of a polycrystalline CVD diamond strip sensor as beam monitor of heavy ion beams with up to ∼109 lead ions per bunch. The strips allow for a determination of the transverse beam profile to a fraction of the pitch of the strips, while the timing information yields the longitudinal bunch length with a resolution of the order of a few mm. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Development of radiation hard sensors for very high luminosity colliders—CERN-RD50 project

The requirements at the Large Hadron Collider (LHC) at CERN have pushed today's silicon tracking detectors to the very edge of the current technology. Future very high luminosity colliders or a possible upgrade of the LHC to a 10 times increased luminosity of 10 35 cm −2 s −1 will require semiconductor detectors with substantially improved properties. Considering the expected total fluences of fast hadrons above 10 16 cm −2 and a possible reduced bunch-crossing interval of ≈10 ns, the detector must be ultra radiation hard, provide a fast and efficient charge collection and be as thin as possible. The newly formed CERN-RD50 project is aiming to provide detector technologies, which are able to operate safely and efficiently in such an environment. This article describes the approaches and first results of RD50 to develop ultra radiation hard sensors by optimizing existing methods and evaluating new ways to engineer the silicon bulk material, the detector structure and the detector operational conditions as well as investigating the possibility to use semiconductor materials other than silicon.

Radiation tolerant sensors for the ATLAS pixel detector

The pixel detector in the ATLAS experiment at the LHC, Geneva, is an important detector component for high resolution tracking and vertex identification. For this demanding task the hybrid pixel detector with silicon sensors has to work in a very harsh radiation environment with up to 3.5×10 14 n eq/cm 2 per year. On the basis of the known radiation effects a dual-track strategy was followed for the development of radiation tolerant silicon pixel sensors. The ATLAS pixel collaboration successfully developed the radiation hard sensor design which meets the challenging requirements for the ATLAS pixel detector. In parallel, the hardening of the silicon itself was followed within the ROSE collaboration, which developed the radiation tolerant DOFZ-silicon with oxygen enrichment by diffusion. Taking all the results together the radiation tolerant silicon sensors have been designed, produced and showed excellent performance before and after irradiation.