| 1. |
- 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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| 2. |
- 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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| 3. |
- Abdalla, Munir A, et al.
(författare)
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An integrating CMOS APS for X-ray imaging with an in-pixel preamplifier
- 2001
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 466:1, s. 232-236
-
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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| 4. |
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| 5. |
- 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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| 6. |
- 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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| 7. |
- Badel, Xavier, et al.
(författare)
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Metallized and oxidized silicon macropore arrays filled with a scintillator for CCD-based X-ray imaging detectors
- 2004
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Ingår i: IEEE Transactions on Nuclear Science. - : IEEE. - 0018-9499 .- 1558-1578. ; 51:3, s. 1001-1005, s. 1006-1010
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Tidskriftsartikel (refereegranskat)abstract
- Silicon charge-coupled devices (CCDs) covered with a scintillating film are now available on the market for use in digital medical imaging. However, these devices could still be improved in terms of sensitivity and especially spatial resolution by coating the CCD with an array of scintillating waveguides. In this paper, such waveguides were fabricated by first etching pores in silicon, then performing metallization or oxidation of the pore walls and finally filling the pores with CsI(TI). The resulting structures were observed using scanning electron microscopy and tested under X-ray exposure. Theoretical efficiencies of macropore arrays filled with CsI(TI) were also calculated, indicating that the optimal pore depth for metallized macropore arrays is about 80 mum while it is around 350 mum for oxidized ones. This result, together with the roughness of the metal coating, explains why lower SNR values were measured with the metallized macropores. Indeed, the macropore arrays had depths in the range of 210-390 mum, which is favorable to oxidized structures.
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| 8. |
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| 9. |
- Bertilsson, Kent, et al.
(författare)
-
Monte Carlo simulation of vertical MESFETs in 2H, 4H and 6H-SiC
- 2001
-
Ingår i: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 10:3-7, s. 1283-1286
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Tidskriftsartikel (refereegranskat)abstract
- The 4H-SiC static induction transistor (SIT) is a very competitive device for high frequency and high power applications (3-6 GHz range). The large breakdown voltage and the high thermal conductivity of 4H-SiC allow transistors with extremely high current density at high voltages. The SIT transistor shows better output power capabilities but the unity current-gain frequency is lower compared to a MESFET device. In this work we show, using a very accurate numerical model, that a compromise between the features given by the SIT structure and the ordinary MESFET structure can be obtained using the vertical MESFET structure. The device dimension has been selected very aggressively to demonstrate the performance of an optimized technology. We also present results from drift-diffusion simulations of devices, using transport parameters obtained from the Monte Carlo simulation. The simulations indicate that 2H-SiC is superior to both 4H and 6H-SiC for vertical devices. For lateral devices, 2H-SiC is slightly faster compared to an identical 4H-SiC device
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| 10. |
- Bertilsson, Kent, et al.
(författare)
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Simulation of a low atmospheric-noise modified four-quadrant position sensitive detector
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 466:1, s. 183-187
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Tidskriftsartikel (refereegranskat)abstract
- A modified four-quadrant position sensitive detector (PSD) is developed. This structure is less sensitive to atmospheric turbulence that is a major drawback with the traditional four-quadrant detector. The inter-electrode resistance is as high as for the four-quadrant detector, which is an advantage compared to the lateral effect PSD. The linearity for the modified four-quadrant detector is good in the whole active range of sensing. The structures are limited to small sensing areas with well focused beams and are suitable for use in detectors up to 1 mm in size.
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| 11. |
- Bertilsson, Kent, et al.
(författare)
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Simulation of anisotropic Breakdown in 4H-SiC Diodes
- 2000
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Ingår i: IEEE Workshop on Computers in Power Electronics. - : IEEE. ; , s. 118-120
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Konferensbidrag (refereegranskat)abstract
- The breakdown characteristics of two-dimensional 4H-SiC diode structures have been studied using an anisotropic drift-diffusion model. The degree of anisotropy was estimated from recent full band Monte Carlo simulations. Identical diode structures have previously been used in the literature to measure the hole impact ionization coefficients of 4H-SiC. The reported measurements from different research groups show large differences in the impact ionization coefficients. Our numerical simulations show that the differences in these measurements can be explained by the difference in device geometry used by the research teams if one considers an anisotropic impact ionization process. This indicates that it is very important to consider anisotropic impact ionization in design and characterization of 4H-SiC power devices.
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| 12. |
- Bertilsson, Kent, et al.
(författare)
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The Effect of Different Transport Models in Simulation of High Frequency 4H-SiC and 6H-SiC Vertical MESFETs
- 2001
-
Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 45:5, s. 645-653
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Tidskriftsartikel (refereegranskat)abstract
- A full band Monte Carlo (MC) study of the high frequency performance of a 4H-SiC Short channel vertical MESFET is presented. The MC model used is based on data from a full potential band structure calculation using the local density approximation to the density functional theory. The MC results have been compared with simulations using state of the art drift-diffusion and hydrodynamic transport models. Transport parameters such as mobility, saturation velocity and energy relaxation time are extracted from MC simulations
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| 13. |
- Bocelli, S, et al.
(författare)
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Experimental identification of the optical phonon of CoSi2 in the infrared
- 1995
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 91:1-4, s. 30-33
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Tidskriftsartikel (refereegranskat)abstract
- A weak but clear optical structure was detected at 329 cm−1 by both reflectance and transmittance measurements in the far infrared on a 430 Å film of CoSi2 grown on Si(100). This is the first observation of the IR vibrational mode of the cubic structure of CoSi2 and the result is in very good agreement with theoretical calculations. In order to characterize the sample, the reflectance was extended up to 5.2 × 104 cm−1 and the refractive index was also directly obtained in a more limited spectral range by spectroscopic ellipsometry. The IR structure was then quantitatively analyzed by means of a fit procedure, obtaining the values of ω0 = 327 cm−1 for the phonon energy, of γ = 10.5 cm−1 for the damping parameter and of 0.006 electronic charges for the screened effective ionic charge.
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| 14. |
- Dejanovic, Slavko, 1964-
(författare)
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Manufacture and characterization of elastic interconnection microstructures in silicone elastomer
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of this thesis is a new chip to substrate interconnection technique using self-aligning elastic chip sockets. This work was focused on the technology steps which are necessary to fulfill in order to realize the suggested technique. Elastic chip sockets offer a solution for several assembly and packaging challenges, such a thermo-mechanical mismatch, effortless rework, environmental compatibility, high interconnection density, high frequency signal integrity, etc. Two of the most challenging technology aspects, metallization and etching of the silicone elastomer were studied, but also, air bubble free casting of the silicone elastomer was taken into consideration. Elastic chip sockets and single elastic micro-bump contacts of different shapes and sizes were manufactured and characterized. The contact resistance measurements revealed that the elastic micro-bump contacts manufactured by using the developed methods require less than one tenth of the contact force to achieve the same low contact resistance as compared to commercial elastic interconnection structures. The analysis and measurements of the high frequency properties of the elastic micro-bump structures have shown that they can operate up to several tens of GHz without a serious degradation of the signal quality. The same methods were applied to manufacture very high density contact area array (approximately 80000 connections/cm2), which until now was achieved only using so called chip-first techniques. The low contact resistance, the absence of environmentally harmful materials, no need of soldering, easy rework as well as capability of very high interconnecting density and very high frequency compatibility, indicates a high potential of this technique for assembly and packaging. Moreover, the presented technology of the silicone elastomer micromachining (metallization and RIE in particular) can be used for manufacturing of other microstructures, like chemical or biological micro reactors.
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| 15. |
- Duan, M., et al.
(författare)
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Deposition of Scintillating Layers of Bismuth Germanate (BGO) Films for X-ray detector applications
- 1998
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Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 45:3, s. 525-527
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Tidskriftsartikel (refereegranskat)abstract
- Bi4Ge3O12 films were deposited by pulsed laser ablation on glass and SiO2/Si substrates. The crystal structures of the films depend on the deposition temperature. XRD patterns indicate that the films deposited at substrate temperature less than 400°C are amorphous. The as deposited amorphous films can be crystallized by post rapid thermal annealing (RTA) in the temperature window from 750°C to 800°C for 2 minutes in a oxygen ambient environment. RBS measurements confirm that the films have the same chemical composition as that of the target. The surface morphology of the films were characterized by atomic force microscopy (AFM)
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| 16. |
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| 17. |
- Dubaric, Ervin, et al.
(författare)
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Resolution and noise properties of scintillator coated X-ray detectors
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 466:1, s. 178-182
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Tidskriftsartikel (refereegranskat)abstract
- The imaging properties of X-ray pixel detectors depend on the quantum efficiency of X-rays, the generated signal of each X-ray photon and the distribution of the generated signal between pixels. In a scintillator coated device the signal is generated both by X-ray photons captured in the scintillator and by X-ray photons captured directly in the semiconductor. The Signal-to-Noise Ratio in the image is then a function of the number of photons captured in each of these processes and the yield, in terms of electron-hole pairs produced in the semiconductor, of each process. The spatial resolution is primarily determined by the light spreading within the scintillator. In a pure semiconductor detector the signal is generated by one process only. The Signal-to-Noise Ratio in the image is proportional to the number of X-ray photons captured within the sensitive layer. The spatial resolution is affected by the initial charge cloud generated in the semiconductor and any diffusion of carriers between the point of interaction and the readout electrode. In this paper we discuss the theory underlying the imaging properties of scintillator coated X-ray imaging detectors. The model is verified by simulations using MCNP and by experimental results. The results from the two-layer detector are compared with those from a pure semiconductor X-ray detector.
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| 18. |
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| 19. |
- Fröjdh, Anna, et al.
(författare)
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An alpha particle detector for measuring radon levels
- 2010
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Ingår i: Proceedings of Nuclear Science Symposium Conference Record (NSS/MIC), 2010. - : IEEE conference proceedings. - 9781424491063 ; , s. 460-461
-
Konferensbidrag (refereegranskat)abstract
- An alpha particle detector for measuring radon levels through measurement of radon progeny concentration has been developed. The detector is a silicon diode optimized for these measurements. Different alternating and non-alternating guard ring structures and different doping profiles have been investigated.
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| 20. |
- Fröjdh, Anna, et al.
(författare)
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An optimized system for measurement of radon levels in buildings by spectroscopic measurement of radon progeny
- 2011
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 6:12, s. art. no. C12018-
-
Tidskriftsartikel (refereegranskat)abstract
- Radon gas, Rn-222, is a problem in many buildings. The radon gas is not harmful in itself, but the decay chain contains charged elements such as Po-218, and Po-214 ions which have a tendency to stick to the lungs when inhaled. Alpha particles from the decay of these ions cause damages to the lungs and increase the risk of lung cancer. The recent reduction in the limits for radon levels in buildings call for new simple and efficient measurement tools [1]. The system has been optimized through modifications of the detector size, changes to the filters and the design of the chamber. These changes increase the electric field in the chamber and the detection efficiency.
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| 21. |
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| 22. |
- Fröjdh, Christer, 1952-, et al.
(författare)
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New sensors for dental X-ray imaging
- 1999
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 434:1, s. 24-29
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Tidskriftsartikel (refereegranskat)
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| 23. |
- Fröjdh, Christer, et al.
(författare)
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Processing and characterisation of an etched groove Permeable
- 1994
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Ingår i: Physica scripta. T. - 0281-1847. ; T54, s. 56-59
-
Tidskriftsartikel (refereegranskat)abstract
- The Permeable Base Transistor (PBT) is generally considered as an interesting device for high speed applications. PBTs have been fabricated on Silicon and Gallium Arsenide by a number of groups. In this paper we reported on the fabrication of an etched groove PBT structure on 6H-SiC using Ti as contact metal for all electrodes. The devices have been characterised by DC-measurements. The transistors show the normal IV-characteristics for a such a device except for a parasitic series diode at the drain electrode. The breakdown voltage of the gate-drain diode is generally as high as around 60 V even without passivation of the sidewalls of the grooves.
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| 24. |
- Fröjdh, Christer, et al.
(författare)
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Schottky Barriers on 6H-SiC
- 1999
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Ingår i: Physica scripta. T. - 0281-1847. ; T79, s. 297-302
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Tidskriftsartikel (refereegranskat)abstract
- Schottky diodes have been fabricated by deposition of Ti, Ni, Cu on epitaxial layers of p-type and n-type 6H-SiC. The fabricated devices have been characterised by CV, IV and photoelectric measurements. The results from the different characterisations are compared. The effect of incomplete ionisation of dopants and high series resistance on the results from CV-measurements is discussed. In addition to the results obtained from the experiments presented in this paper data has also been collected from other research groups in order to investigate the mechanism of Schottky barrier formation on Silicon Carbide. The results show that for a number of metals the barrier height is strongly correlated to the difference between the electron affinity of the semiconductor and the metal work function, while other metals show significant deviation from the Schottky-Mott theory.
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| 25. |
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| 26. |
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| 27. |
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| 28. |
- Hatzikonstantinidou, S., et al.
(författare)
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Process Optimisation and Characterisation of PBT structures
- 1994
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Ingår i: Physica scripta. T. - 0281-1847. ; T54, s. 226-229
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Tidskriftsartikel (refereegranskat)abstract
- The Permeable Base Transistor (PBT) is considered to be a high frequency device with simulated fT and fmax values in the order of 100 GHz. In this work we present several PBT devices in silicon. The fabrication process steps have been developed and optimised in order to meet the demands of a future integration in a standard CMOS processing. Cobalt disilicide is used for the emitter metallization and base metallisation in order to form a good Schottky contact. The important issues of a fabrication process reliability and controllability are discussed in this paper. The process steps had been analysed by standard analysis methods. Electrical (DC) characterisation of the devices has been performed. The obtained results are in a good agreement with the 2D simulations.
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| 29. |
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| 30. |
- Kleimann, P., et al.
(författare)
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An x-ray imaging pixel detector based on a scintillating guides screen
- 2000
-
Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 47:4, s. 1483-1486
-
Tidskriftsartikel (refereegranskat)abstract
- We have developed and preliminary tested a new digital X-ray imaging sensor based on a scintillating guide screen. The scintillating guides are used to channel the emitted visible light to the pixel detector. This enables us to avoid the well-known tradeoff between detection efficiency and spatial resolution which is encountered when a non-patterned scintillating layer is used on top of a CCD. A prototype has been fabricated using microtechnologies. The scintillator is CsI:T1 and the low-index cladding material used to channel the light is silicon dioxide. The performance of this prototype has been compared to that of a thick CsI single crystal. The results concerning the spatial resolution are quite promising and demonstrate a proof-of-principle. However, the performance in terms of signal to noise ratio and sensitivity have to be improved. These problems are currently addressed.
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| 31. |
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| 32. |
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| 33. |
- Kleimann, P., et al.
(författare)
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Formation of wide and deep pores in silicon by electrochemical etching
- 2000
-
Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 69, s. 29-33
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical etching of n-type silicon in hydrofluoric acid electrolyte is now well known as a technique for micro- or macroporous silicon formation. It is commonly admitted that the width of pores can extend over four orders of magnitude, from 2 nm to 20 mu m. In this study the feasibility of using this technique to form larger pores is demonstrated. The use of a water-ethanol solvent mixture (1:1) is shown to modify the electrochemistry of silicon dissolution and pore formation. The formation of stable wide pores requires adjustment of the etching current during the pore formation as a function of the evolution of the current-voltage curve with etching time. An array of 42-mu m wide pores with 2-mu m wall thickness and 200-mu m depth were etched using this method. The feasibility to etch pores up to 100 mu m in width is also presented. The results enable to conclude that the electrochemical etching of n-type silicon could be used to form vertical structures, without restrictions concerning the wall spacing. This provides a useful tool for micro-machining.
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| 34. |
- Kok, A., et al.
(författare)
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Silicon sensors with pyramidal structures for neutron imaging
- 2014
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 9, s. C04011-
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron detection is a valuable tool in nuclear science research, homeland security, quality assurance in nuclear plants and medical applications. Recent developments and near future instrumentations in neutron imaging have a need for sensors with high spatial resolution, dynamic range, sensitivity and background discrimination. Silicon based neutron detectors can potentially fulfil these requirements. In this work, pad and pixel detectors with pyramidal micro-structures have been successfully fabricated that should have an improved detection efficiency when compared to conventional planar devices. Titanium di-boride (TiB2) and lithium fluoride (LiF) were deposited as the neutron converters. Excellent electrical performances were measured on both simple pad and pixel detectors. A selection of pad detectors was examined by alpha spectroscopy. Measurement with thermal neutrons from a 241Am-Be source shows an improvement in relative efficiency of up to 38% when compared to conventional planar devices.
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| 35. |
- Krapohl, David, et al.
(författare)
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Simulation of a silicon neutron detector coated with TiB 2 absorber
- 2012
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 7:1, s. Art. no. C01096-
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Tidskriftsartikel (refereegranskat)abstract
- Neutron radiation cannot be directly detected in semiconductor detectors and therefore needs converter layers. Planar clean-room processing can be used in the manufacturing process of semiconductor detectors with metal layers to produce a cost-effective device. We used the Geant4 Monte-Carlo toolkit to simulate the performance of a semiconductor neutron detector. A silicon photo-diode was coated with vapour deposited titanium, aluminium thin films and a titaniumdiboride (TiB 2) neutron absorber layer. The neutron capture reaction 10B(n, alpha)7Li is taken advantage of to create charged particles that can be counted. Boron-10 has a natural abundance of about SI 19.8%. The emitted alpha particles are absorbed in the underlying silicon detector. We varied the thickness of the converter layer and ran the simulation with a thermal neutron source in order to find the best efficiency of the TiB 2 converter layer and optimize the clean room process. © 2012 IOP Publishing Ltd and SISSA.
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| 36. |
- Ljungberg, K., et al.
(författare)
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Buried Cobalt Silicide Layers in Silicon Created by Wafer Bonding
- 1994
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 141:10, s. 2829-2833
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Tidskriftsartikel (refereegranskat)abstract
- A buried conductive layer in silicon has been created using wafer bonding technique, with a cobalt interfacial layer.Co-coated silicon wafers were brought into contact with either similar or uncoated wafers at room temperature. CoSi2 wasthen formed through a solid-phase reaction, during an anneal at 700 to 900°C. A 700 Å buried CoSi2-layer, with a resistivityof approximately 21 µ cm, was achieved. Good adhesion, as measured by tensile strength testing, between the wafers wasachieved. Transmission electron microscopic investigations (Co-coated wafer bonded to bare silicon) showed that thesilicide has not grown into the opposite wafer, and that an amorphous layer exists between the silicide and the siliconsurface. The presence of such a layer has been confirmed by electrical characterization.
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| 37. |
- Mbairi, Felix D.
(författare)
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Some Aspects of Advanced Technologies and Signal Integrity Issues in High Frequency PCBs, with Emphasis on Planar Transmission Lines and RF/Microwave Filters
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main focus of this thesis is placed on high frequency PCB signal Integrity Is-sues and RF/Microwave filters using EBG structures. From the signal Integrity aspect, two topics were mainly discussed. On one hand, the effect of increasing frequency on classical design rules for crosstalk reduction in PCBs was investigated experimentally and by full-wave simulations. An emphasis was placed on the 3×W spacing rule and the use of guard traces. Single-ended and differential transmission lines were considered. S-parameter measurements and simu-lations were carried out at high-frequency (up to 20 GHz). The results emphasize the necessity to reevaluate traditional design rules for their suitability in high frequency applications. Also, the impacts of using guard traces for high frequency crosstalk re-duction were clearly pointed out. On the other hand, the effect of high loss PCB ma-terials on the signal transmission characteristics of microstrip lines at high frequency (up to 20 GHz) was treated. Comparative studies were carried out on different micro-strip configurations using standard FR4 substrate and a high frequency dielectric ma-terial from Rogers, Corporation. The experimental results highlight the dramatic im-pact of high dielectric loss materials (FR4 and solder mask) and magnetic plating metal (nickel) on the high frequency signal attenuation and loss of microstrip trans-mission lines. Besides, the epoxy-based SU8 photoresist was characterized at high frequency (up to 50 GHz) using on-wafer conductor-backed coplanar waveguide transmission lines. A relative dielectric constant of 3.2 was obtained at 30 GHz. Some issues related to the processing of this material, such as cracks, hard-skin, etc, were also discussed. Regarding RF/Microwave filters, the concept of Electromagnetic Band Gap (EBG) was used to design and fabricate novel microstrip bandstop filters using periodically modified substrate. The proposed EBG structures, which don’t suffer conductor backing issues, exhibit interesting frequency response characteristics. The limitations of modeling and simulation tools in terms of speed and accuracy are also examined in this thesis. Experiments and simulations were carried out show-ing the inadequacies of the Spice diode model for the simulations in power electronics. Also, an Artificial Neural Network (ANN) model was proposed as an alternative and a complement to full-wave solvers, for a quick and sufficiently accurate simulation of interconnects. A software implementation of this model using Matlab’s ANN toolbox was shown to considerably reduce (by over 800 times) the simulation time of microstrip lines using full-wave solvers such as Ansoft’s HFSS and CST’s MWS. Finally, a novel cooling structure using a double heatsink for high performance electronics was presented. Methods for optimizing this structure were also discussed.
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| 38. |
- Nilsson, Hans-Erik, et al.
(författare)
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A semi-analytic model of the Permeable Base Transistor
- 1994
-
Ingår i: Physica scripta. T. - 0281-1847. ; T54, s. 159-164
-
Tidskriftsartikel (refereegranskat)abstract
- The I-V characteristics of the Permeable Base Transistor (PBT) has been investigated in order to find a simple and practical model for use in circuit designs. Two possible approaches has been discussed, a one-dimensional analytical solution and a semi-analytical solution mixing analytical and empirical methods. The semi-analytical model developed in this paper offers high accuracy and a simple and fast evaluation. All model parameters can be extracted from a set of I-V curves from two typical transistors with different threshold voltages. An analytical small signal model has been developed that agrees very well with two-dimensional simulations.
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| 39. |
- Nilsson, Hans-Erik, et al.
(författare)
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An Investigation of the blocking characteristics of the Permeable Base Transistor
- 1998
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 42:3, s. 297-305
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Tidskriftsartikel (refereegranskat)abstract
- A numerical study of the blocking characteristics of the Permeable Base Transistor (PBT) is presented. The PBT is regarded as a promising transistor structure for high voltage and high frequency applications. Numerical studies of the PBT were focused on the high frequency figure of merits or the breakdown characteristics of the Schottky gate. A device designed for high frequency and high voltage switching should be optimized for large blocking and fast switching. The trade off between blocking and speed is a complicated matter which depends strongly on the geometry and doping level. In this work we studied the blocking characteristics for a Silicon PBT with regard to the doping level and doping profile, gate thickness and gate to drain distance. A scaling formalism was developed in order to estimate the transistor performance for a wide range of doping levels and geometrical combinations. A design example is presented of a normally off transistor that can block a drain to source voltage of 10 V while the unity current gain frequency fT value for Vgs = 0.2 V is higher than 7 GHz.
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| 40. |
- Nilsson, Hans-Erik, et al.
(författare)
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Different methods of noise reduction in Monte Carlo simulations of a Schottky diode
- 1994
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Ingår i: Physica scripta. T. - 0281-1847. ; T54, s. 268-272
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Tidskriftsartikel (refereegranskat)abstract
- Methods of decreasing the noise and increasing the computational efficiency in Monte Carlo simulations of semiconductor devices are investigated. A lookup table approach to the charge assignment to mesh points has been implemented which is independent of the complexity of the assignment function. Using this approach reduces the CPU time of the charge assignment to about one third. Potential fluctuations in low field regions are compared for different assignment function, which shows the advantage of using more complex schemes than those generally used. Results from a full band Monte Carlo simulation of a submicron Schottky diode are presented and the values of the current density for different assignment schemes are compared, showing a lower noise for the higher order schemes. Statistical enhancements by splitting of superparticles in the depletion region has been investigated. The combination of a high order assignment scheme and statistical enhancement by splitting decreases simulation runtimes considerable for a given noise tolerance.
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| 41. |
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| 42. |
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| 43. |
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| 44. |
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| 45. |
- Nordell, Nils
(författare)
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Metall organic vapour phase epitaxy for advanced III-V devices
- 1993
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metalorganic vapour phase epitaxy (MOVPE) has proven to be a successful method for growth of structures for advanced optoelectronic semiconductor devices in III-V compounds. This thesis deals with technological and process related aspects of MOVPE from an experimental perspective. Special attention is given to three main questions: uniformity over large areas, p-type dopant diffusion and redistribution in structures for heterostructure bipolar transistors, and planar embedding of high mesas for buried heterostructure lasers.A uniformity within a few per cents for thickness, alloy composition, and dopant incorporation over large areas is fundamental for growth of advanced device structures. We present a new horizontal reactor with a large width-to-height aspect ratio operating at reduced pressure, and with a rotating susceptor for single wafers with a diameter of up to 75 mm. The obtained uniformity over 40 mm diameter is within 1 % for thickness, composition and doping, and within 1 nm for the wavelength of quaternary InGaAsP at = 1560 nm. The doping distribution has been used to estimate the temperature gradient over the wafer to a few tenths of a degree, and the uniformity is most probably limited by gas phase diffusion and depletion of the reactants.Abrupt doping profiles are important for some devices. An example is the high frequency performance of the n-p-n heterostructure bipolar transistor (HBT), which is improved by a very narrow and highly doped p-type base. We have compared Zn and Mg for this application. The memory effect of Mg in the reactor gives doping tails towards the surface, but with Zn we obtained an abruptness of three decades over 60 nm at a maximum doping level exceeding 21019 cm-3. However, a highly n-doped layer of AlGaAs adjacent to the Zn-doped region gives rise to a significant re-distribution of Zn into the AlGaAs layer. At a reduced growth temperature this effect is diminished and the maximum doping level is simultaneously increased.Growth on partly masked and non-planar substrates has become an important field for realisation of devices designed in three dimensions. We have focused on planar regrowth of semi-insulating InP around high mesas of buried heterostructure lasers. Unwanted growth over the masked mesa top usually occurs. These depositions are reduced at high growth temperatures and for growth around low mesas (< 2 m). Addition of CCl4 in the MOVPE process considerably improves the morphology, especially for growth around high mesas. When chlorine is provided to the growing surface nucleation is prevented on the phosphorus-faced {111}B lattice planes and the mask, and this effect permits reproducible planar regrowth not limited by the mesa height.
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| 46. |
- Petersson, Sture, et al.
(författare)
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Oxygen distribution profiles in thin evaporated contacts on single crystal silicon
- 1978
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Ingår i: Nuclear instruments and methods. ; 149, s. 285-288
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Tidskriftsartikel (refereegranskat)abstract
- The nuclear resonance in the l6O(a, a)l6O elastic scattering reaction at 3.045 MeV has been used in concentration profilemeasurements ol oxygen in thin-film structuresThe concentration profile can be deduced lrom an energy scan ol the incoming a-particies, thus shifting the resonanceto different depths in the sample. The methocl has been applie
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| 47. |
- Petersson, Sture, et al.
(författare)
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Tunable acoustic wave device
- 2002
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Patent (populärvet., debatt m.m.)abstract
- The invention discloses a tunable acoustic wave device (100; 200) comprising a piezoelectric material (120; 220) with a tunable dielectric permittivity. The dielectric permittivity of the material is tuned by applying a tuning electric field (190), preferably a DC-bias field, low frequency AC field, pulsed electric field or AC electric field superimposed onto an electric field pulse, thereto. By tuning the dielectric permittivity, the operation characteristics of the device (100; 200), including the acoustic wave velocity in the material (120; 220) and the resonance frequency and bandwidth of the device (100; 200), may be tuned. The tuning electric field (190) may applied by superimposing it onto the input high frequency electric field signal of the device (100; 200) or by applying it over at least a portion of the piezoelectric material (120; 220). A piezoelectric material (120; 220) with a tunable dielectric permittivity can be found in ceramic crystalline superparaelectric materials, e.g. perovskite niobates-tantalates.
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| 48. |
- Possnert, G, et al.
(författare)
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Oxygen content and depth profiling in silicon surface technology studied by the 16O(α, α)16O resonance at 3.045 MeV
- 1978
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; 18, s. 353-356
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Tidskriftsartikel (refereegranskat)abstract
- The use of the t6O(o,o)160 elastic scattering resonance reaction forthe study of low concentration of oxygen such as found in interfacesin silicon technology is described. We have investigated the depth resolution and the limit of the sensitivity that can be obtained with thismethod. The method has been applied to the study of AlrQ{r "sandwich" film structures and to Au and amorphous Ge contacts to silicon.
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| 49. |
- Siebert, Wolfgang Peter, 1944-
(författare)
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Alternative electronic packaging concepts for high frequency electronics
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the research work presented here, is to contribute to the adaptation of electronic packaging towards the needs of high frequency applications. As the field of electronic packaging stretches over several very different professional areas, it takes an interdisciplinary approach to optimize the technology of electronic packaging. Besides this, an extensive knowledge of industrial engineering should be an essential part of this undertaking to improve electronic packaging. Customary advances in technology are driven by new findings and a continuous development of processes in clearly defined fields. However, in the field of the higher levels of the interconnection hierarchy, that is external to the chip level interconnections and chip packaging, it is supposed that a wide combination of disciplines and technical creativity, instead of advanced technology in a special area should produce most added value. The thesis is divided into five areas, interlinked by the overall aim of there advantages to the common goal. These areas are the Printed Wiring Board (PWB) technology, PWB connections using flexible printed circuit boards, multiconductor cable connections, shielded enclosures and the related EMC issues, and finally the cooling of electronics. A central issue was to improve the shielded enclosures to be effective also at very high frequencies; it will be shown that shielded enclosures without apertures can cope with frequencies up to and above 15 GHz. Due to this enclosure without apertures, it was necessary to develop a novel cooling structure. This cooling structure consists of a heat sink where the PCB’s are inserted in close contact to the cooling fins on one side, whereas the other side of the heat sink is cooled by forced ventilation. The heat transfer between these parts is completely inside the same body. Tests carried out on a prototype have shown that the performance of the cooling structure is satisfactory for electronic cooling. Another problem area that is addressed are the interconnect problems in high frequency applications. Interconnections between parts of a local electronic system, or as within the telecom and datacom field between subscribers, are commonly accomplished by cable connections. In this research work multiconductor cables are examined and a patented novel cable-connector for high frequency use is presented. Further, an experimental complex soldering method between flexible printed circuits boards and rigid printed circuits boards, as part of connections between PCBs, is shown. Finally, different sectors of the PCB technology for high frequency applications are scrutinized and measurements on microstrip structures are presented.
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| 50. |
- Sjöberg, Niklas B., 1972-
(författare)
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Eel migration - results from tagging studies with relevance to management
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In response to the drastic decline of the European eel (Anguilla anguilla (L.)) fisheries have been reduced and elvers are stocked in areas where natural abundances are low. Are these measures adequate? To answer different aspects of this question, we have analysed more than a century of eel tagging, using both traditional and more novel capture – recapture analyses. Based on these long-term data, we have evaluated the impact of the Swedish eel coastal fisheries using Survival analysis. Our analysis indicates that the fishing mortality just prior the 2009 fishing restrictions were in the order of 10%.More recent tagging programs have focused on issues related to the fate of stocked fish. If and how they migrate out of the Baltic Sea and further on towards the Atlantic Ocean. Both earlier and our new studies reveal that all eels recaptured on the Swedish East Coast, no matter of their origin, migrate at a reasonable speed and direction towards the outlets of the Baltic Sea. Even though it is sometimes difficult to determine their origin, our analyses indicate that stocked fish were scarce among the recaptures. In an experiment on the Swedish West Coast, we knew the individuals’ origin (stocked or wild) and they had similar migration patterns.In contrast, silver eel in Lake Mälaren – assumed to have been stocked as elvers or bootlace eels – seemed to have difficulties in finding the outlets. Instead they overwintered and lost weight. However, weight losses are also significant among non-stocked individuals in the Baltic Sea, both if they overwinter and if they appear to be on their way out from the area. It remains an open question whether eels from the Baltic region in general, and whether the overwintered fish in particular, manage to reach the spawning area in the Atlantic Ocean.Based on current knowledge, I advocate invoking the precautionary approach and to concentrate Swedish eel stockings to the West Coast and allow the young fish to spread out on their own.
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