D Greiffenberg

Publications (15)12.78 Total impact

• Article: The AGIPD detector for the European XFEL

  D Greiffenberg
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  ABSTRACT: The Adaptive Gain Integrating Pixel Detector (AGIPD) is a hybrid pixel detector with bump-bonded silicon sensor, which is being developed for the European X-ray Free Electron Laser (XFEL). The XFEL provides photons in an energy range between 0.2 and 24.8 keV [1]. XFELs unique time structure comprises bunch trains at a repetition rate of 10 Hz, where each train consists of 2700 bunches with a temporal separation of 220 ns. Each bunch itself consists of ~ 1012 photons impinging in less than 100 fs. The challenges posed by this time structure will be addressed using a charge integrating device with dynamic gain switching and the possibility to store the analog signals on at least 200 storage cells. Up to now, three different prototype chips have been built, in order to investigate the different blocks of the final AGIPD chip. This paper will report on the results of the characterization of the first two prototype chips, namely AGIPD0.1 and AGIPD0.2. While the investigations on AGIPD0.1 focus on the readout chain (dynamic gain switching, linearity, etc.), the tests of AGIPD0.2 concentrate on the measurements involving the bump-bonded silicon sensor, such as the possibility of resolving single photons and pixel-to-pixel variations as well as the performance of the analog storage pipeline.
  Journal of Instrumentation 01/2012; 7(01):C01103. · 1.87 Impact Factor
• Source

  Available from: canterbury.ac.nz

  Article: Pixel sensitivity variations in a CdTe-Medipix2 detector using poly-energetic x-rays

  R Aamir, S P Lansley, R Zainon, M Fiederle, A Fauler, D Greiffenberg, P H Butler, A P H Butler
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  ABSTRACT: We have a 1-mm-thick cadmium telluride (CdTe) sensor bump-bonded to a Medipix2 readout chip. This detector has been characterized using a poly-energetic x-ray beam. Open beam images (i.e. without an attenuating specimen between the x-ray source and the detector) have been acquired at room temperature using the MARS-CT system. Profiles of various rows and columns were analyzed for one hundred, 35-ms exposures taken with a bias voltage of -300 V (operating in electron collection mode). A region of increased sensitivity is observed around the edges of the detector. A reasonably periodic, repeatable variation in pixel sensitivity is observed. Some small regions with very low sensitivity and others with zero signals are also observed. Surrounding these regions are circular rings of pixels with higher counts. At higher flux (higher tube current in the x-ray source) there is evidence of saturation of the detector assembly. In this paper we present our understanding of the origin of these features and demonstrate the improved image quality obtained after correcting for these variations.
  Journal of Instrumentation 01/2011; 6(01):C01059. · 1.87 Impact Factor
• Article: Characterization of the Medipix3 pixel readout chip

  R Ballabriga, G Blaj, M Campbell, M Fiederle, D Greiffenberg, E H M Heijne, X Llopart, R Plackett, S Procz, L Tlustos, D Turecek, W Wong
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  ABSTRACT: The Medipix3 chip is a hybrid pixel detector readout chip working in Single Photon Counting Mode. It has been developed with a new front-end architecture aimed at eliminating the spectral distortion produced by charge diffusion in highly segmented semiconductor detectors. In the new architecture charge deposited in overlapping clusters of four pixels is summed event-by-event and the incoming quantum is assigned as a single hit to the summing circuit with the biggest charge deposit (this mode of operation is called Charge Summing Mode (CSM)). In Single Pixel Mode (SPM) the charge reconstruction and the communication between neighbouring pixels is disabled. This is the operating mode in traditional detector systems. This paper presents the results of the characterization of the chip with electrical stimuli and radioactive sources.
  Journal of Instrumentation 01/2011; 6(01):C01052. · 1.87 Impact Factor
• Article: Energy resolution and transport properties of CdTe-Timepix-Assemblies

  D Greiffenberg, A Fauler, A Zwerger, M Fiederle
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  ABSTRACT: CdTe is a promising material for the detection of γ- and X-rays as 1 mm thick CdTe sensors offer an absorption efficiency that is higher than 50 {%} for photon energies up to 120 keV. Therefore 1mm thick CdTe from Acrorad has been flip-chipped as the sensor material on a Timepix readout-electronics ASIC at the Freiburg Materials Research Center (FMF). The transport properties of the CdTe material are investigated by determining the μτ-product of the charge carriers by illuminating the non-collecting electrode with alpha particles. The method commonly used to determine the μτ-product for non-pixelated devices was adapted for the Medipix pixelated readout-electronics. The position of the alpha particles on the pixel matrix provides spatial information, which was used to create a mapping of the μτ-product. The energy resolutions and the positions of the noise edge of two CdTe-Timepix assemblies, one with a pixel pitch of 110 x 110 μm2 and another one with a pixel pitch of 55 x 55 μm2 were investigated by performing a threshold scan of a 241Am source. A comparison of the energy spectra obtained with the two assemblies with different pixel pitches confirms the strong dependence of charge sharing on the energy spectra, as expected.
  Journal of Instrumentation 01/2011; 6(01):C01058. · 1.87 Impact Factor
• Article: Investigation of crystallographic and detection properties of CdTe at the ANKA synchrotron light source

  A Cecilia, E Hamann, C Haas, D Greiffenberg, A Danilewsky, D Haenscke, A Fauler, A Zwerger, G Buth, P Vagovivc, T Baumbach, M Fiederle
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  ABSTRACT: The crystallographic properties of a semiconducting CdTe pixelated sensor were investigated at the ANKA synchrotron facility (KIT, Karlsruhe) by means of back reflection white beam topography and high resolution X-ray diffraction. From the results, several orientation contrast features were identified that could be assigned to small angle grain boundaries of 0.01. Those structures are disseminated in the whole area of the investigated crystal and form a mosaic structure network of tiled and twisted blocks. The topographic mapping of the sensor was correlated with its X-ray response map. The comparison demonstrates the presence of similar features, proving that the structural quality of the sensor material influences the charge carrier transport and consequently the detector performances.
  Journal of Instrumentation. 01/2011; 6(10):P10016.
• Conference Proceeding: Investigations of the high flux behavior of CdTe-Medipix2 assemblies at the synchrotron ANKA

  D Greiffenberg, A Cecilia, A Zwerger, A Fauler, P Vagovic, J Butzer, E Hamann, T Santos Rolo, T Baumbach, M Fiederle
  Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 11/2010
• Article: Investigation of Growth Conditions of CdTe Thick Films on Properties and Demands for X-Ray Detector Applications

  R. Sorgenfrei, D. Greiffenberg, M. Fiederle
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  ABSTRACT: CdTe thick films were prepared by vacuum deposition on amorphous substrates using MBE technique. The growth was performed at different temperatures to investigate the development of the growth rate, surface morphology, structure and optical properties. Properties of films deposited with a single CdTe source are compared with films grown with an additional Cd source. The growth experiments are discussed with regard to demands for X-ray detector applications.
  IEEE Transactions on Nuclear Science 09/2009; · 1.45 Impact Factor
• Conference Proceeding: Characterization of Medipix2 assemblies with CdTe sensor using synchrotron radiation

  D. Greiffenberg, A. Cecilia, A. Zwerger, A. Fauler, T. dos Santos Rolo, D. Pelliccia, P. Vagovic, Rolf Simon, T. Baumbach, M. Fiederle
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  ABSTRACT: Medipix2 assemblies with CdTe sensors have been characterized using synchrotron radiation. Processing of the assemblies has been done at the Freiburg material research center (FMF), the characterization has been performed at the ANKA at the Forschungszentrum Karlsruhe. The following paper reports the first results of the research of efficient pixelarray detectors for application in a synchrotron providing high energetic photons. Examinations on the homogeneity of the sensor, charge sharing and an energy scan will be shown.
  Nuclear Science Symposium Conference Record, 2008. NSS '08. IEEE; 11/2008
• Conference Proceeding: Evaluation of the ATLAS-MPX devices for neutron field spectral composition measurement in the ATLAS experiment

  Z. Vykydal, J. Bouchami, M. Campbell, Z. Dolezal, M. Fiederle, D. Greiffenberg, A. Gutierrez, E. Heijne, T. Holy, J. Idarraga, [......], M. Platkevic, S. Pospisil, V. Sochor, J. Solc, M. Suk, L. Tlustos, P. Vichoudis, J. Visschers, I. Wilhelm, J. Zemlicka
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  ABSTRACT: A network of 15 Medipix2-based devices (ATLAS-MPX devices) has been installed at various positions in the ATLAS detector within the framework of the ATLAS-MPX collaboration. The aim of the network is to perform real-time measurement of spectral characteristics and composition of the main radiation types in the experiment including slow and fast neutrons, especially during the initial low luminosity LHC operation. This contribution describes the network structure and focuses on the neutron efficiency calibration process of the ATLAS-MPX devices and its simulation in order to predict the behavior of the device in complex neutron fields.
  Nuclear Science Symposium Conference Record, 2008. NSS '08. IEEE; 11/2008
• Article: Characterization of Medipix2 assemblies with CdTe sensor using synchrotron radiation

  D. Greiffenberg, A. Cecilia, A. Zwerger, A. Fauler, T. dos Santos Rolo, D. Pelliccia, P. Vagovic, R. Simon, T. Baumbach, M. Fiederle
  Nuclear Symposium Conference Record, NSS'08.IEEE. 01/2008; 08:287-290.
• Article: Growth of Thick Films CdTe From the Vapor Phase

  D.. Greiffenberg, R.. Sorgenfrei, K.H. Bachem, M.. Fiederle
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  ABSTRACT: 100 thick films of CdTe were grown on semi-insulating (100) GaAs substrates by physical vapor transport (PVT) in a modified molecular beam epitaxy facility. The grown layers were highly oriented as revealed from X-ray pole figure measurements. Temperature- and intensity-dependent photoluminescence measurements were taken before and after the chemical removal of the substrate to determine the effect of the GaAs substrate and to estimate the crystallographic quality of the layers. Current-voltage characteristics were performed to obtain the resistitivity of the layers with .
  IEEE Transactions on Nuclear Science 09/2007; · 1.45 Impact Factor
• Article: Preliminary characterisation of CdTe M–π–n diode structures

  D. Greiffenberg, A. Fauler, A. Zwerger, T. Baumbach, M. Fiederle
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  ABSTRACT: Due to the high Z, 1 mm CdTe (Z=52, 48) offers a high absorption probability for photons with energies up to 100 keV [1] (Zwerger and Fiederle, 2007). In order to further reduce the dark current flowing through the sensor when applying high voltage, CdTe diode structures (M–π–n) have been processed at the Freiburg Materials Research Center (FMF). As comparison, CdTe sensors with ohmic contacts, working as photoresistors have also been produced. The different sensor structures have been flip-chip bonded on Medipix2 readout electronics [5] (Llopart and Campbell, 2002). This work reports on the I–V characteristics of the different sensor structures, confirming the improved leakage current flowing through the diode structure. Furthermore, the imaging capabilities of the diode structures with respect to their spatial resolution are presented.
  Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 633. · 1.21 Impact Factor
• Article: Energy calibration measurements of MediPix2

  M. Fiederle, D. Greiffenberg, J. Idárraga, J. Jakůbek, V. Král, C. Lebel, C. Leroy, G. Lord, S. Pospíšil, V. Sochor, M. Suk
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  ABSTRACT: Real-time measurement of the composition and spectroscopic characteristics of the radiation field inside the ATLAS detector and cavern will be carried out with MediPix2 devices. In view of this application, a calibration of the low energy threshold was performed by illuminating the devices with low energy photons, using 241Am sources and X-rays. A procedure was thereafter established for the calibration of all MediPix2 devices to be used in ATLAS. Using X-ray tubes with filters at the Czech Metrology Institute, photons of energies between 8 and 250 keV were obtained and the detection efficiency of the MediPix devices to these radiations was determined. An exponential decrease of the photon intensity as a function of detector depth was observed, illuminating the detector with the beam almost parallel to the surface. The properties of the decrease of intensity were used to determine the exact incident angle of the beam.
  Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 591(1):75-79. · 1.21 Impact Factor
• Article: Detection efficiency of ATLAS-MPX detectors with respect to neutrons

  D Greiffenberg, M Fiederle, Z. Vykydal, V. Kral, J. Jakubek, T. Holy, S. Pospisil, D Maneuski, V O'Shea, M. Suk, M Kralik, C. Lebel, C Leroy
• Article: The Medipix2-based network for measurement of spectral characteristics and composition of radiation in ATLAS detector

  Z. Vykydal, J. Bouchami, M Campbell, Z. Dolezal, M Fiederle, D Greiffenberg, A Gutierrez, E. Heijne, T. Holy, J. Idarraga, [......], M. Nessi, V O'Shea, M Platkevic, S. Pospisil, M. Suk, L. Tlustos, P Vichoudis, J Visschers, I Wilhelm, J Zemlicka
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  ABSTRACT: The ATLAS detector is now installed at the CERN LHC and a precise evaluation of the radiation environment within and around the detector is required to understand the performance of the various detector systems, and to predict their useful lifetime. Furthermore, validation of earlier Monte Carlo predictions about the radiation field in ATLAS is necessary. In particular, it is important to perform these measurements in the early phases of the LHC operation. Many other radiation measuring devices lack sensitivity to low doses, and usually do not provide information on the composition of the radiation during this low intensity period. A network of 15 ATLAS-MPX devices has been installed at various positions in the ATLAS detector. These devices are capable of providing quantitative real-time information on the fluxes and flux distributions of the main radiation types in the experiment, including slow and fast neutrons. The technical description of the ATLAS-MPX detector network as well as the principles of the data analysis is presented.