H. Moilanen

University of Helsinki, Helsinki, Uusimaa, Finland

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Publications (12)14.31 Total impact

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    ABSTRACT: The planned luminosity upgrade of the CERN LHC to the super LHC (sLHC) requires investigation of new radia-tion hard tracking detectors. Compared to the LHC, tracking detectors must withstand a 5-10 times higher radiation fluence. Promising radiation hard options are planar silicon detectors with n-side readout and silicon detectors in 3D technology, where columnar electrodes are etched into the silicon substrate. This article presents beam test measurements performed with planar and 3D n-in-p silicon strip detectors. The detectors were irradi-ated to different fluences, where the maximum fluence was 3 × 10 15 1 MeV neutron equivalent particles per square centimetre (neq/cm 2) for the planar detectors and 2 × 10 15 neq/cm 2 for the 3D detectors. In addition to signal measurements, charge sharing and resolution of both detector technologies are com-pared. An increased signal from the irradiated 3D detectors at high bias voltages compared to the signal from the unirradiated detector indicates that charge multiplication effects occur in the 3D detectors. At a bias voltage of 260 V, the 3D detector irradiated to 2 × 10 15 neq/cm 2 yields a signal almost twice as high as the signal of the unirradiated detector. Only 30 % of the signal of an unirradiated detector could be measured with the planar detector irradiated to 3 × 10 15 neq/cm 2 at a bias voltage of 600 V, which was the highest bias voltage applied to this sensor.
    IEEE Transactions on Nuclear Science 06/2011; 58(3). DOI:10.1109/TNS.2011.2126598 · 1.46 Impact Factor
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    ABSTRACT: For the unprecedentedly high radiation level at the sLHC, the luminosity upgrade of the LHC, new tracking detectors are investigated. Among different approaches, silicon detectors in 3D technology constitute a promising option. Columnar electrodes are etched into the substrate, therefore the distance for charge collection and depletion is decoupled from the detector thickness. Thus, two of the detrimental effects caused by radiation in silicon (increased depletion voltage and charge carrier trapping) can be reduced. Results of measurements with irradiated 3D silicon strip detectors produced by IMB-CNM are presented.
    Nuclear Physics B - Proceedings Supplements 06/2011; 215(1):247-249. DOI:10.1016/j.nuclphysbps.2011.04.021 · 0.88 Impact Factor
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    ABSTRACT: High resistivity and high oxygen concentration of silicon wafers can be beneficial for the radiation hardness of silicon detectors. Wafers of Magnetic Czochralski silicon (MCz-Si) can be grown with a resistivity of a few and with well-controlled, high oxygen concentration. According to the beam test results presented in this paper, n-type MCz-Si bulk, p-strip readout detectors with can be operated with acceptable signal-to-noise ratio up to the irradiation fluence of 1×1015 cm−2 1-MeV neutron equivalent. The improved radiation hardness compared to that of traditional p-in-n Float Zone silicon (p-in-n FZ-Si) detectors can be explained by better electric field distribution inside MCz-Si detectors. The difference between the distributions is clearly shown by Transient Current Technique (TCT) measurements, presented in this paper. Thus, strip detectors made on n-type MCz-Si are a feasible option for the outer tracker layers of the potential upgrade of the Large Hadron Collider (LHC), the Super-LHC. This corresponds approximately 95% of the total area of silicon detectors in the Super-LHC.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/2011; 636(1). DOI:10.1016/j.nima.2010.04.089 · 1.32 Impact Factor
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    ABSTRACT: For the planned luminosity upgrade of the CERN LHC to the sLHC new radiation hard technologies for the tracking detectors are investigated. Corresponding to the luminosity increase, the radiation dose will be approximately a factor of ten higher than for the detectors currently installed in the LHC experiments. One option for radiation tolerant detectors are 3D silicon detectors with columnar electrodes penetrating into the silicon bulk. This article reports results of beam test measurements performed with 3D-DDTC (Double-Sided, Double Type Column) silicon strip detectors, where the columns do not pass through the detector completely. The devices were produced by IMB-CNM (Barcelona, Spain) and by FBK-irst (Trento, Italy). Important properties like space-resolved charge collection and efficiency are investigated.
    IEEE Transactions on Nuclear Science 11/2010; 57(5-57):2987 - 2994. DOI:10.1109/TNS.2010.2058863 · 1.46 Impact Factor
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    ABSTRACT: With an expected ten-fold increase in luminosity in S-LHC, the radiation environment in the tracker volumes will be considerably harsher for silicon-based detectors than the already harsh LHC environment. Since 2006, a group of CMS institutes, using a modified CMS DAQ system, has been exploring the use of Magnetic Czochralski silicon as a detector element for the strip tracker layers in S-LHC experiments. Both p+/n-/n+ and n+/p-/p+ sensors have been characterized, irradiated with proton and neutron sources, assembled into modules, and tested in a CERN beamline. There have been three beam studies to date and results from these suggest that both p+/n-/n+ and n+/p-/p+ Magnetic Czochralski silicon are sufficiently radiation hard for the $R>25$ cm regions of S-LHC tracker volumes. The group has also explored the use of forward biasing for heavily irradiated detectors, and although this mode requires sensor temperatures less than -50\,$^\circ$C, the charge collection efficiency appears to be promising.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2010; 628(1). DOI:10.1016/j.nima.2010.06.327 · 1.32 Impact Factor
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    ABSTRACT: Strip detectors with an area of 16cm2 were processed on high resistivity n-type magnetic Czochralski silicon. In addition, detectors were processed on high resistivity Float Zone wafers with the same mask set for comparison. The detectors were irradiated to several different fluences up to the fluence of 3×10151MeVneq/cm2 with protons or with mixed protons and neutrons. The detectors were fully characterized with CV- and IV-measurements prior to and after the irradiation. The beam test was carried out at the CERN H2 beam line using a silicon beam telescope that determines the tracks of the incoming particles and hence provides a reference measurement for the detector characterization. The n-type MCz-Si strip detectors have an acceptable S/N at least up to the fluence of 1×1015neq/cm2 and thus, they are a feasible option for the strip detector layers in the SLHC tracking systems.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2010; DOI:10.1016/j.nima.2009.08.017 · 1.32 Impact Factor
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    ABSTRACT: A heavily irradiated (3×1015 1 MeV neq/cm2) Current Injected Detector (CID) was tested with 225 GeV muon beam at CERN H2 beam line. In the CID concept the current is limited by the space charge. The injected carriers will be trapped by the deep levels and this induces a stable electric field through the entire bulk regardless of the irradiation fluence the detector has been exposed to. The steady-state density of the trapped charge is defined by the balance between the trapping and the emission rates of charge carriers (detrapping). Thus, the amount of charge injection needed for the electric field stabilization depends on the temperature. AC-coupled 16 cm2 detector was processed on high resistivity n-type magnetic Czochralski silicon, and it had 768 strips, 50 μm pitch, 10 μm strip width and 3.9 cm strip length. The beam test was carried out using a silicon beam telescope that is based on the CMS detector readout prototype components, APV25 readout chips, and eight strip sensors made by Hamamatsu having 60 μm pitch and intermediate strips. The tested CID detector was bonded to the APV25 readout, and it was operated at temperatures ranging from −40 to −53 °C. The CID detector irradiated at 3×1015 1 MeV neq/cm2 fluence shows about 40% relative Charge Collection Efficiency with respect to the non-irradiated reference plane sensors.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2010; DOI:10.1016/j.nima.2009.08.006 · 1.32 Impact Factor
  • T. Mäenpää · H. Moilanen · D. Ungaro
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    ABSTRACT: The Finnish Cosmic Rack (FinnCRack) is a position-sensitive telescope measuring the tracks of cosmic particles. The FinnCRack is based on silicon strip detectors and CERN CMS tracker data acquisition electronics. We present the FinnCRack as a reference tracker suitable for the characterization of novel detectors. The FinnCRack is unencumbered by accelerator beam time availability but suffers from a low tracking rate. The resolution of the reference tracks is .
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/2009; DOI:10.1016/j.nima.2009.01.068 · 1.32 Impact Factor
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    ABSTRACT: Pad and strip detectors processed on high resistivity n-type magnetic Czochralski silicon (MCz-Si) were irradiated to several different fluences with protons. The pad detectors were characterized with the transient current technique (TCT) and the full-size strip detectors with a reference beam telescope and a 225 GeV muon beam. The TCT measurements indicate a double junction structure and space charge sign inversion in MCz-Si detectors after 6×1014 1 MeV neq/cm2 fluence. In the beam test a signal-to-noise (S/N) ratio of 50 was measured for a non-irradiated MCz-Si sensor, and a S/N ratio of 20 for the sensors irradiated to the fluences of 1×1014 1 and 5×1014 1 MeV neq/cm2.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/2009; 604:254-257. DOI:10.1016/j.nima.2009.01.071 · 1.32 Impact Factor
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    ABSTRACT: The Silicon Beam Telescope (SiBT07) at the CERN H2 beam is a position-sensitive beam telescope targeted for LHC upgrade tests. The telescope consists of eight consecutive silicon microstrip detectors and slots for two test detectors. This article describes the reconstruction of reference tracks with the CMS data analysis software CMSSW. The related data analysis and calibration procedures, including pedestal corrections, common-mode corrections, and track-based alignment, are also described.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/2009; 602(2):600-606. DOI:10.1016/j.nima.2009.01.189 · 1.32 Impact Factor
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    ABSTRACT: The increase of the radiation dose at the luminosity upgrade of the LHC (sLHC) necessitates the development of novel tracking detectors. Among these, 3D silicon detectors constitute a promis-ing option. By etching columnar electrodes of both doping types into the sensor, the distance for depletion and charge collection is decoupled from the sensor thickness and can be considerably smaller than in standard planar sensors. Two of the main effects of radiation damage in silicon detectors (increasing depletion voltage and trapping) can be significantly reduced. Silicon strip detectors in 3D-DDTC (double-sided, double type column) design produced by FBK-IRST (Trento, Italy) and CNM-IMB (Barcelona, Spain) have been measured in a test beam at the CERN SPS. Important properties like spatially resolved charge collection and detection efficiency were investigated.
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    ABSTRACT: A beam telescope based on the CMS Tracker data acquisition prototype cards has been developed in order to test sensor candidates for S-LHC tracking systems. The telescope consists of up to eight reference silicon microstrip modules and slots for a couple of test modules. Beam tracks, as measured by the reference modules, provide a means of determining the position resolution and efficiency of the test modules. The impact point precision of reference tracks at the location of the test modules is about . This note presents a detailed description of the silicon beam telescope (SiBT) along with some results from its initial operation in summer 2007 in the CERN H2 beamline.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2008; 593(3-593):523-529. DOI:10.1016/j.nima.2008.05.012 · 1.32 Impact Factor