| 1. |
- Fröjdh, Anna, 1986-, et al.
(författare)
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Processing and characterization of a MEDIPIX2-compatible silicon sensor with 220 mu m pixel size
- 2011
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 633:Suppl 1, s. S78-S80
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Tidskriftsartikel (refereegranskat)abstract
- Pixellated silicon detectors with a pixel size of 220 um have been fabricated at Mid Sweden University. The detectors will be bonded to the MEDIPIX2 [1] readout chip. The purpose is to investigate the performance of an energy sensitive X-ray imaging sensor with reduced charge sharing.The detectors were fabricated on high purity silicon with a wafer thickness of 500 um and a resistivity of more than 15 kohmcm. One reason for the choice of material was to get experience for future work with very thick detectors requiring ultra high resistivity in order to be depleted. During the initial work in this project some issued were found concerning inter pixel resistance and the efficiency of the guard rings. This led to a study of existing papers on the subject [2,3,4,5] and to extensive simulations of the electric field and the charge transport in different parts of the device.A modified process has been developed using alternating p+ and n+ guard rings and an outer n+ doping. The results of the simulations and the process will be described as well as an outline for a process for fabrication of very thick detectors with limited guard ring extension.References[1] - X. Llopart, M. Campbell, R. Dinapoli, D. San Segundo and E. Pernigotti, IEEE Trans. Nucl. Sci., vol. 49, 2279-2283, October 2002.[2] – L. Evensen, A. Hanneborg, B Sundby Avset, M. Mese, Nuclear Instruments and Methods in Physics Research A 337 (1993) 44 – 52[3] – T. Pavalainen, T. Tuuva, K. Leinonen, Nuclear Instruments and Methods in Physics Research A 573 (2007) 277 – 279[4] – Z. Li, W. Huang, L. J. Zhao, IEEE Trans. Nucl. Sci., vol. 47, No. 3. 729 – 735 , June 2000.[5] – D. Han, C. Wang, G. Wang, S. Du, L. Shen, X. Tian, X. Zhang, IEEE Transactions on Electron devices, Vol. 50, No. 2, 537 – 540, February 2003
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| 2. |
- Fröjdh, Erik, 1984-, et al.
(författare)
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Spectral response of a silicon detector with 220 mu m pixel size bonded to MEDIPIX2
- 2011
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 633:Supplement 1, s. S125-S127
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Tidskriftsartikel (refereegranskat)abstract
- The standard detector used with the MEDIPIX2 [1] readout chip suffers from severe charge sharing that reduces the spectral performance of the device. This problem is expected to be solved in the MEDIPIX3 [2] design. In order to significantly reduce the charge sharing and to make a detector which could be expected to have a similar response to MEDIPIX3 we have fabricated detectors with a pixel size of 220 um and bonded these detectors to the MEDIPIX2 chip using only a limited number of pixels on the readout chip. This makes the active area of the pixel comparable with the area covered by the charge summing in MEDIPIX3.The charge collection properties of the device have been tested by scanning a narrow beam over a pixel. The spectral response has been measured by taking a flood exposure at different tube voltages and comparing the result with the spectrum obtained from exposing the centre of the pixel with a narrow beam thus eliminating the charge sharing. This work represents an improved characterisation as compared to [3].Some initial images of different objects have been taken by placing the device in an X-ray microscope with a nanofocus X-ray tube imaging objects with magnification to simulate the original pixel size of 55 um.References[1] - X. Llopart, M. Campbell, R. Dinapoli, D. San Segundo and E. Pernigotti, IEEE Trans. Nucl. Sci., vol. 49, 2279-2283, October 2002.[2] - R. Ballabriga, M. Campbell, E. H. M. Heijne, X. Llopart, L. Tlustos, IEEE Trans. Nucl. Sci., Vol. 54, No. 5, October 2007.[3] – B. Norlin, C. Fröjdh, G. Thungström, D. Greiffenberg, NSS Conference record,19-25 Oct. 2008, Pages:3464 – 3469, Digital Object Identifier 10.1109/NSSMIC.2008.4775083
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| 3. |
- Norlin, Börje, 1967-, et al.
(författare)
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Energy Resolved X-ray Imaging as a Tool for Characterization of Paper Coating Quality
- 2009
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Ingår i: IEEE Nuclear Science Symposium Conference Record 2009. - : IEEE conference proceedings. - 9781424439621 ; , s. 1703-1706
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Konferensbidrag (refereegranskat)abstract
- Energy resolved X-ray imaging can be used as a tool to analyze the variation in the chemical content of an object. In this work we have used energy resolved X-ray imaging to measure the variation in the chemical content of paper and paper coating. This is an important quality parameter for the paper industry. In order to separate the variation in coating thickness from the variation in paper thickness, energy resolution is used to separate the response of the coating from the response of the paper. The MEDIPIX2 single photon processing X-ray imaging system [1] has been used in the measurements. The measurement results are compared to simulations with MCNP. The influence of charge sharing is discussed and the effects have been studied by comparing results from detectors with 220x220 µm2 pixels and detectors with 55x55 µm2 pixels. There is a trade-off between good spatial resolution obtained with detectors with small pixels and good energy resolution obtained with detectors with large pixels. The requirements on image quality, to achieve the resolution of coating distribution relevant for the application, are discussed.
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| 4. |
- Abdalla, Munir A, et al.
(författare)
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A CMOS APS for dental X-ray imaging using scintillating sensors
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 460:1, s. 197-203
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present an integrating CMOS Active Pixel Sensor (APS) circuit to be used with scintillator type X-ray sensors for intra oral dental X-ray imaging systems. Different pixel architectures were constructed to explore their performance characteristics and to study the feasibility of the development of such systems using the CMOS technology. A prototype 64 x 80 pixel array has been implemented in a CMOS 0.8 mum double poly n-well process with a pixel pitch of 50 mum. A spectral sensitivity measurement for the different pixels topologies, as well as measured X-ray direct absorption in the different APSs are presented. A measurement of the output signal showed a good linearity over a wide dynamic range. This chip showed that the very low sensitivity of the CMOS APSs to direct X-ray exposure adds a great advantage to the various CMOS advantages over CCD-based imaging systems,
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| 5. |
- Abdalla, Munir A, et al.
(författare)
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A new biasing method for CMOS preamplifier-shapers
- 2000
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Ingår i: ICECS 2000: 7TH IEEE INTERNATIONAL CONFERENCE ON ELECTRONICS, CIRCUITS & SYSTEMS, VOLS I AND II. ; , s. 15-18
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Konferensbidrag (refereegranskat)
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| 6. |
- Abdalla, Munir A, et al.
(författare)
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An integrating CMOS APS for X-ray imaging with an in-pixel preamplifier
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 466:1, s. 232-236
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Tidskriftsartikel (refereegranskat)abstract
- We present in this paper an integrating CMOS Active Pixel Sensor (APS) circuit coated with scintillator type sensors for intra-oral dental X-ray imaging systems. The photosensing element in the pixel is formed by the p-diffusion on the n-well diode. The advantage of this photosensor is its very low direct absorption of X-rays compared to the other available photosensing elements in the CMOS pixel. The pixel features an integrating capacitor in the feedback loop of a preamplifier of a finite gain in order to increase the optical sensitivity. To verify the effectiveness of this in-pixel preamplification, a prototype 32 x 80 element CMOS active pixel array was implemented in a 0.8 mum CMOS double poly, n-well process with a pixel pitch of 50 mum. Measured results confirmed the improved optical sensitivity performance of the APS. Various measurements on device performance are presented.
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| 7. |
- Aboelfotoh, M. O., et al.
(författare)
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Schottky-barrier behavior of metals on n- and p-type 6H-SiC
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:7, s. 075312-
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Tidskriftsartikel (refereegranskat)abstract
- The Schottky-barrier height of a number of metals (Ti, Ni, Cu, and Au) on n- and p-type Si-terminated 6H-SiC has been measured in the temperature range 150-500 K. It is found that the barrier height to n-type 6H-SiC does not exhibit a temperature dependence, while for p-type 6H-SiC the change in the barrier height with temperature follows very closely the change in the indirect energy gap in 6H-SiC. These results are inconsistent with models of Schottky-barrier formation based on the concept of a charge neutrality level. Furthermore, the present results cannot be reconciled with a defect pinning mechanism, contrary to the conclusions of earlier studies on III-V compound semiconductors. We suggest that chemical bonding at the metal-semiconductor interface plays an important role in determining the Schottky-barrier height.
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| 8. |
- An, Siwen, et al.
(författare)
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Signal-to-Noise Ratio Optimization in X-ray Fluorescence Spectrometry for Chromium Contamination Analysis
- 2021
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Ingår i: Talanta. - : Elsevier BV. - 0039-9140 .- 1873-3573. ; 230
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Tidskriftsartikel (refereegranskat)abstract
- In most cases, direct X-ray fluorescence (XRF) analysis of solutions entails technical difficulties due to a high X-ray scattering background resulting in a spectrum with a poor signal-to-noise ratio (SNR). Key factors that determine the sensitivity of the method are the energy resolution of the detector and the amount of scattered radiation in the energy range of interest. Limiting the width of the primary spectrum by the use of secondary targets, or filters, can greatly improve the sensitivity for specific portions of the spectrum. This paper demonstrates a potential method for SNR optimization in direct XRF analysis of chromium (Cr) contamination. The suggested method requires minimal sample preparation and achieves higher sensitivity compared to existing direct XRF analysis. Two states of samples, fly ash and leachate from municipal solid waste incineration, were investigated. The effects of filter material, its absorption edge and filter thickness were analyzed using the combination of Monte Carlo N-Particle (MCNP) code and energy-dispersive XRF spectrometry. The applied filter removes primary photons with energies interfering with fluorescence photons from the element of interest, thus results in lower background scattering in the spectrum. The SNR of Cr peak increases with filter thickness and reaches a saturation value when further increased thickness only increases the measurement time. Measurements and simulations show that a Cu filter with a thickness between 100 μm and 140 μm is optimal for detecting Cr by taking into account both the SNR and the exposure time. With direct XRF analysis for solutions, the limit of quantitation (LOQ) of the achieved system was 0.32 mg/L for Cr, which is well below the allowed standard limitation for landfills in Sweden. This work shows that XRF can gain enough sensitivity for direct monitoring to certify that the Cr content in leachate is below environmental limits.
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| 9. |
- Badel, Xavier, et al.
(författare)
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Improvement of an X-ray imaging detector based on a scintillating guides screen
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 487:1-2, s. 129-135
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Tidskriftsartikel (refereegranskat)abstract
- An X-ray imaging detector has been developed for dental applications. The principle of this detector is based on application of a silicon charge coupled device covered by a scintillating wave-guide screen. Previous studies of such a detector showed promising results concerning the spatial resolution but low performance in terms of signal to noise ratio (SNR) and sensitivity. Recent results confirm the wave-guiding properties of the matrix and show improvement of the detector in terms of response uniformity, sensitivity and SNR. The present study is focussed on the fabrication of the scintillating screen where the principal idea is to fill a matrix of Si pores with a CsI scintillator. The photoluminescence technique was used to prove the wave-guiding property of the matrix and to inspect the filling uniformity of the pores. The final detector was characterized by X-ray evaluation in terms of spatial resolution, light output and SNR. A sensor with a spatial resolution of 9 LP/mm and a SNR over 50 has been achieved using a standard dental X-ray source and doses in the order of those used at the moment by dentists (around 25 mR).
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| 10. |
- Chmeissani, M, et al.
(författare)
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First experimental tests with a CdTe photon counting pixel detector hybridized with a Medipix2 readout chip
- 2004
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Ingår i: IEEE Transactions on Nuclear Science. - : IEEE. - 0018-9499 .- 1558-1578. ; 51:5, s. 2379-2385
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Tidskriftsartikel (refereegranskat)abstract
- We present preliminary tests of hybrid pixel detectors consisting of the Medipix2 readout chip bump-bonded to a 1-mm-thick CdTe pixel detector. This room temperature imaging system for single photon counting has been developed within the Medipix2 European Collaboration for various imaging applications with X-rays and gamma rays, including dental radiography, mammography, synchrotron radiation, nuclear medicine, and radiation monitoring in nuclear facilities. The Medipix2 + CdTe hybrid detector features 256 × 256 square pixels, a pitch of 55 μm, a sensitive area of 14×14 mm2. We analyzed the quality of the detector and bump-bonding and the response to nuclear radiation of the first CdTe hybrids. The CdTe pixel detectors, with Pt ohmic contacts, showed an ohmic response when negatively biased up to less than 60 V (electrons collection mode). Tests were also performed in holes collection mode, where a nonresistive behavior was observed above +15 V. We performed a series of imaging tests at low voltage bias with gamma radioactive sources and with an X-ray tube. Under uniform irradiation, we observed for all detectors the presence of numerous, stable structures in the form of small circles of about 200 μm diameter, with the central pixels showing a reduced counting efficiency with respect to the periphery (in electrons counting regime). Also long filament structures have been observed. Further investigations will reveal whether they are due to an intrinsic detector response (e.g., due to Te inclusions) or to the bump-bonding process.
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