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Hybrid pixel detectors: Characterization and optimization
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University , 2015. , 209 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 228
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-26794Local ID: STCISBN: 978-91-88025-37-1 (print)OAI: oai:DiVA.org:miun-26794DiVA: diva2:890476
Public defence
2015-09-08, 13:00
Supervisors
Available from: 2016-01-04 Created: 2016-01-04 Last updated: 2016-12-23Bibliographically approved
List of papers
1. Count rate linearity and spectral response of the Medipix3RX chip coupled to a 300μm silicon sensor under high flux conditions
Open this publication in new window or tab >>Count rate linearity and spectral response of the Medipix3RX chip coupled to a 300μm silicon sensor under high flux conditions
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2014 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 9, no 4, Art. no. C04028- p.Article in journal (Refereed) Published
Abstract [en]

For clinical X-ray imaging, the detector performance under high flux conditions is very important, with typical flux rates for modern CT systems reaching 109 photons s-1 mm-2 in the direct beam. In addition, for spectral imaging a good energy resolution under these conditions is needed. This poses difficulties, since pulse pileup in the pixel electronics does not only affect the count rate, leading to a deviation from the otherwise linear behavior, but also degrades the spectral response of the detector, making k-edge subtraction and other contrast enhancement techniques less efficient. In this paper, we investigate the count rate capabilities and the energy response of the Medipix3RX chip under high flux conditions using 10 keV monochromatic photons. © CERN 2014.

Keyword
Hybrid detectors, X-ray detectors
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-22044 (URN)10.1088/1748-0221/9/04/C04028 (DOI)000336123800028 ()2-s2.0-84899579747 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Note

Language of Original Document: English

Available from: 2014-06-02 Created: 2014-05-30 Last updated: 2017-03-06Bibliographically approved
2. Timepix3: first measurements and characterization of a hybrid-pixel detector working in event driven mode
Open this publication in new window or tab >>Timepix3: first measurements and characterization of a hybrid-pixel detector working in event driven mode
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2015 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 10, C01039Article in journal (Refereed) Published
Abstract [en]

Timepix3 is a hybrid pixel detector readout chip. It features a data driven readout mode where the chip sends out a data packet containing pixel coordinate, time over threshold and time of arrival immediately after the hit is processed by the pixel. The maximum hit rate is 40 Mhits/cm(2)/s with a minimum time step in the arrival time measurement of 1.56 ns. The pixel matrix consist of 256 x 256 square pixels at a 55 m m pitch and the pixel front end noise is 61 e(-) RMS. In this paper we present the first radiation measurements with Timepix3 bump bonded to a 300 m m thick silicon sensor. The chip is calibrated per pixel, using internal test pulses and the calibration is verified using X-ray fluorescence. The energy resolution, threshold dispersion and gain dispersion is measured. The energy resolution in time over threshold mode under normal operation conditions is 4.07 keV FWHM at 59.5 keV. At 10.5 keV an energy resolution of 0.72 keV FWHM was achieved in photon counting mode and in time over threshold mode, by optimizing the energy response, we achieved a 1.38 keV FWHM. We also investigate the time walk and present first results on using the time information for track reconstruction.

Keyword
Solid state detectors, X-ray detectors, Hybrid detectors
National Category
Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-26550 (URN)10.1088/1748-0221/10/01/C01039 (DOI)000362261900026 ()2-s2.0-84943415877 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2015-12-16 Created: 2015-12-16 Last updated: 2016-12-19Bibliographically approved
3. X-ray absorption and charge transport in a pixellated CdTe detector with single photon processing readout
Open this publication in new window or tab >>X-ray absorption and charge transport in a pixellated CdTe detector with single photon processing readout
2011 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 6, no 2, Art. no. P02012- p.Article in journal (Refereed) Published
Abstract [en]

The image forming process in a CdTe detector is both a function of the X-ray interaction in the material, including scattering and fluorescence, and the charge transport in the material [2-4]. The response to individual photons has been investigated using a CdTe detector with a pixel size of 110 m m, bonded to a TIMEPIX [5] readout chip operating in time over threshold mode. The device has been illuminated with mono-energetic photons generated by fluorescence in different metals and by gamma emission from Am-241 and Cs-137. Each interaction will result in charge distributed in a cluster of pixels where the total charge in the cluster should sum up to the initial photon energy. By looking at the individual clusters the response from shared photons as well as fluorescence photons can be identified and separated. By using energies below and above the K-edges of Cd and Te the contribution from fluorescence can be further isolated. The response is analyzed to investigate the effects of both charge diffusion and fluorescence on the spectral response in the detector.

Keyword
Solid state detectors; X-ray detectors; Hybrid detectors
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-13471 (URN)10.1088/1748-0221/6/02/P02012 (DOI)000287860600018 ()2-s2.0-79952635522 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2011-04-06 Created: 2011-04-06 Last updated: 2016-10-14Bibliographically approved
4. Imaging and spectroscopic performance studies of pixellated CdTe Timepix detector
Open this publication in new window or tab >>Imaging and spectroscopic performance studies of pixellated CdTe Timepix detector
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2012 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, no 1, Art. no. C01038- p.Article in journal (Refereed) Published
Abstract [en]

In this work the results on imaging and spectroscopic performances of 14 × 14 × 1 mm CdTe detectors with 55 × 55Όm and 110 × 110Όm pixel pitch bump-bonded to a Timepix chip are presented. The performance of the 110 × 110Όm pixel detector was evaluated at the extreme conditions beam line I15 of the Diamond Light Source. The energy of X-rays was set between 25 and 77 keV. The beam was collimated through the edge slits to 20Όm FWHM incident in the middle of the pixel. The detector was operated in the time-over-threshold mode, allowing direct energy measurement. Energy in the neighbouring pixels was summed for spectra reconstruction. Energy resolution at 77 keV was found to be ΔE/E = 3.9%. Comparative imaging and energy resolution studies were carried out between two pixel size detectors with a fluorescence target X-ray tube and radioactive sources. The 110 × 110Όm pixel detector exhibited systematically better energy resolution in comparison to 55 × 55Όm. An imaging performance of 55 × 55Όm pixellated CdTe detector was assessed using the Modulation Transfer Function (MTF) technique and compared to the larger pixel. A considerable degradation in MTF was observed for bias voltages below -300 V. Significant room for improvement of the detector performance was identified both for imaging and spectroscopy and is discussed. © 2012 IOP Publishing Ltd and SISSA.

Keyword
Gamma detectors (scintillators, CZT, HPG, HgI etc); Hybrid detectors; Instrumentation for synchrotron radiation accelerators
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-16747 (URN)10.1088/1748-0221/7/01/C01038 (DOI)000303806200038 ()2-s2.0-84857025847 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2012-08-20 Created: 2012-08-17 Last updated: 2016-10-20Bibliographically approved
5. Depth of interaction and bias voltage dependence of the spectral response in a pixellated CdTe detector operating in time-over-threshold mode subjected to monochromatic X-rays
Open this publication in new window or tab >>Depth of interaction and bias voltage dependence of the spectral response in a pixellated CdTe detector operating in time-over-threshold mode subjected to monochromatic X-rays
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2012 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, no 3, Art. no. C03002- p.Article in journal (Refereed) Published
Abstract [en]

High stopping power is one of the most important figures of merit for X-ray detectors. CdTe is a promising material but suffers from: material defects, non-ideal charge transport and long range X-ray fluorescence. Those factors reduce the image quality and deteriorate spectral information. In this project we used a monochromatic pencil beam collimated through a 20Όm pinhole to measure the detector spectral response in dependance on the depth of interaction. The sensor was a 1mm thick CdTe detector with a pixel pitch of 110Όm, bump bonded to a Timepix readout chip operating in Time-Over-Threshold mode. The measurements were carried out at the Extreme Conditions beamline I15 of the Diamond Light Source. The beam was entering the sensor at an angle of ∌20 degrees to the surface and then passed through ∌25 pixels before leaving through the bottom of the sensor. The photon energy was tuned to 77keV giving a variation in the beam intensity of about three orders of magnitude along the beam path. Spectra in Time-over-Threshold (ToT) mode were recorded showing each individual interaction. The bias voltage was varied between -30V and -300V to investigate how the electric field affected the spectral information. For this setup it is worth noticing the large impact of fluorescence. At -300V the photo peak and escape peak are of similar height. For high bias voltages the spectra remains clear throughout the whole depth but for lower voltages as -50V, only the bottom part of the sensor carries spectral information. This is an effect of the low hole mobility and the longer range the electrons have to travel in a low field. © 2012 IOP Publishing Ltd and Sissa Medialab srl.

Keyword
Detector design and construction technologies and materials; X-ray detectors
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-16738 (URN)10.1088/1748-0221/7/03/C03002 (DOI)000304015300002 ()2-s2.0-84858777567 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2012-08-21 Created: 2012-08-17 Last updated: 2016-10-20Bibliographically approved
6. Probing Defects in a Small Pixellated CdTe Sensor Using an Inclined Mono Energetic X-Ray Micro Beam
Open this publication in new window or tab >>Probing Defects in a Small Pixellated CdTe Sensor Using an Inclined Mono Energetic X-Ray Micro Beam
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2012 (English)In: 2012 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE RECORD (NSS/MIC), IEEE conference proceedings, 2012, 4233-4236 p., 6551965Conference paper, Published paper (Other academic)
Abstract [en]

High quantum efficiency is important in X-ray imaging applications. This means using high-Z sensor materials. Unfortunately many of these materials suffer from defects that cause non-ideal charge transport. In order to increase the understanding of these defects, we have mapped the 3D response of a number of defects in two 1 mm thick CdTe sensors with different pixel sizes (55 mu m and 110 mu m) using a monoenergetic microbeam at 79 keV. The sensors were bump bonded to Timepix read out chips. Data was collected in photon counting as well as time-over-threshold mode. The time-over-threshold mode is a very powerful tool to investigate charge transport properties and fluorescence in pixellated detectors since the signal from the charge that each photon deposits in each pixel can be analyzed. Results show distorted electrical field around the defects and indications of excess leakage current and large differences in behavior between electron collection and hole collection mode. The experiments were carried out in the Extreme Conditions Beamline I15 at Diamond Light Source.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2012
Series
IEEE Nuclear Science Symposium Conference Record, ISSN 1082-3654
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-17568 (URN)000326814204069 ()2-s2.0-84881576398 (Scopus ID)STC (Local ID)978-1-4673-2030-6 (ISBN)978-1-4673-2028-3 (ISBN)STC (Archive number)STC (OAI)
Conference
IEEE Nuclear Science Symposium / Medical Imaging Conference Record (NSS/MIC) / 19th Room-Temperature Semiconductor X-ray and Gamma-ray Detector Workshop
Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2016-10-20Bibliographically approved
7. A Geant4 based framework for pixel detector simulation
Open this publication in new window or tab >>A Geant4 based framework for pixel detector simulation
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2014 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 9, no 12, C12018Article in journal (Refereed) Published
Abstract [en]

The output from a hybrid pixel detector depends on the interaction of the radiation with the sensor material, the transport of the resulting charge in the sensor, the pulse processing in the readout circuit and processing of the resulting signal. In order to understand the full behaviour of the device and to predict the performance of future devices it is important to have a framework that can simulate the entire process in the detector system.Geant4 is a Monte Carlo based toolkit for simulation of particle interaction with matter which is developed and actively used for CERN experiments and detector development [1]. By extending the Monte Carlo code in Geant4 with a charge carrier transport model of the sensor material and basic amplifier functionality as well as read out logic, a simulation of the complete detector system is possible.The MEDIPIX is a state of the art hybrid pixel detector that allows bonding of a wide range of sensor materials [2,3]. Simulation models have been developed and tested for different chips from the MEDIPIX family. The simulation is defined using configuration files to set the geometry, sensor material properties, number of pixels, pixel pitch and chip properties. Source properties as well as filters and objects in the beam can be added for different experimental set-ups. The interaction of radiation with the sensor is taken into account in the transport of the charge carriers in the sensor material and a current induced in the pixel electrode that triggers an amplifier response. Simulation results have been verified with X-ray fluorescence and radioactive sources using MEDIPIX family chips. In this paper we present the developed simulation framework and first results.

Keyword
Performance of high energy physics detectors, Simulation methods and programs, Software architectures (event data models, frameworks and databases)
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:miun:diva-23708 (URN)10.1088/1748-0221/9/12/C12018 (DOI)000351342900002 ()2-s2.0-84918823479 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Conference
16th International Workshop on Radiation Imaging Detectors
Available from: 2014-12-12 Created: 2014-12-12 Last updated: 2017-03-06Bibliographically approved
8. Spectral response of the energy-binning Dosepix ASIC coupled to a 300 mu m silicon sensor under high fluxes of synchrotron radiation
Open this publication in new window or tab >>Spectral response of the energy-binning Dosepix ASIC coupled to a 300 mu m silicon sensor under high fluxes of synchrotron radiation
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2015 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 804, 43-49 p.Article in journal (Refereed) Published
Abstract [en]

The Dosepix hybrid pixel detector was designed for dosimetry and radiation monitoring applications. It has three programmable modes of operation: photon counting mode, energy integration mode, and dosimetry mode. The dosimetry mode measures the energy of individual X-ray photons and automatically sorts events into pre-defined energy bins. The output is a histogram representing the measured X-ray energy spectrum, permitting a dose reconstruction that accounts for the attenuation of photons at each energy bin. This presents a potential radiation protection and dosimetry instrument in medical radiodiagnostic practices, including high flux systems such as computed tomography (CT). In this paper, we characterise the Dosepix chip by investigating the energy response and count rate capabilities when coupled to a 300 pm silicon sensor under high fluxes of monochromatic synchrotron radiation. Under nominal settings, the Dosepix detector can detect photons down to 3.5 keV, with an energy resolution of 16.5% FWHM for 8.5 keV photons and 8% FWHM for 40 keV photons. The chip can count up to 1.67 Mcps/mm(2) of 40 keV photons whilst maintaining linear counting behaviour. This count rate range can be further increased by changing the programmable operating settings of the detector, making it suitable for a range of photon dosimetry applications.

Keyword
Hybrid pixel detector, Time over threshold, Energy binning, X-ray dosimetry
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-26519 (URN)10.1016/j.nima.2015.09.018 (DOI)000364133700005 ()2-s2.0-84943514621 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2015-12-16 Created: 2015-12-16 Last updated: 2016-12-19Bibliographically approved
9. The Medipix3RX: a high resolution, zero dead-time pixel detector readout chip allowing spectroscopic imaging
Open this publication in new window or tab >>The Medipix3RX: a high resolution, zero dead-time pixel detector readout chip allowing spectroscopic imaging
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2013 (English)In: Journal of Instrumentation, ISSN 1748-0221, Vol. 8, no 2, C02016- p.Article in journal (Refereed) Published
Abstract [en]

The Medipix3 chips have been designed to permit spectroscopic imaging in highly segmented hybrid pixel detectors. Spectral degradation due to charge sharing in the sensor has been addressed by means of an architecture in which adjacent pixels communicate in the analog and digital domains on an event-by-event basis to reconstruct the deposited charge in a neighbourhood prior to the assignation of the hit to a single pixel. The Medipix3RX chip architecture is presented. The first results for the characterization of the chip with 300 μm thick Si sensors are given. ~ 72e− r.m.s. noise and ~ 40e− r.m.s. of threshold dispersion after chip equalization have been measured in Single Pixel Mode of operation. The homogeneity of the image in Charge Summing mode is comparable to the Single Pixel Mode image. This demonstrates both modes are suitable for X-ray imaging applications.

Keyword
Electronic detector readout concepts (solid-state) Analogue electronic circuits Digital electronic circuits
National Category
Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-21130 (URN)10.1088/1748-0221/8/02/C02016 (DOI)
Available from: 2014-01-23 Created: 2014-01-23 Last updated: 2016-01-04Bibliographically approved
10. Measurement of an accelerator based mixed field with a Timepix detector
Open this publication in new window or tab >>Measurement of an accelerator based mixed field with a Timepix detector
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2015 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 10, P03005Article in journal (Refereed) Published
Abstract [en]

We present an analysis of a high energy mixed field taken with a Timepix chip at the CERF facility at CERN. The Timepix is an active array of 65K energy measuring pixels which allows visualization and energy measurement of the tracks created by individual particles. This allows characteristics of interest such as the LET and angular distributions of the incoming tracks to be calculated, as well as broad morphological track categories based on pattern recognition techniques. We compute and compare LET-like and angular information for different morphological track categories. Morphological track categories are found to possess overlapping LET and energy spectra, however the approaches are found to be complementary with morphological clustering yielding information which is indistinguishable on the basis of LET alone. The use of the Timepix as an indirect monitoring device outside of the primary beam at CERF is briefly discussed.

Keyword
Dosimetry concepts and apparatus, Particle tracking detectors (Solid-state detectors), Pattern recognition, cluster finding, calibration and fitting methods
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Physical Sciences
Identifiers
urn:nbn:se:miun:diva-25654 (URN)10.1088/1748-0221/10/03/P03005 (DOI)000357944500055 ()2-s2.0-84924264777 (Scopus ID)
Available from: 2015-08-28 Created: 2015-08-18 Last updated: 2016-01-04Bibliographically approved

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