| 1. |
- Fashandi, Hossein, et al.
(författare)
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Single-step synthesis process of Ti3SiC2 ohmic contacts on 4H-SiC by sputter-deposition of Ti
- 2015
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 99, s. 53-56
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Tidskriftsartikel (refereegranskat)abstract
- We report a single-step procedure for growth of ohmic Ti3SiC2 on 4H-SiC by sputter-deposition of Ti at 960 degrees C, based on the Ti-SiC solid-state reaction during deposition. X-ray diffraction and electron microscopy show the growth of interfacial Ti3SiC2. The as-deposited contacts are ohmic, in contrast to multistep processes with deposition followed by rapid thermal annealing. This procedure also offers the possibility of direct synthesis of oxygen-barrier capping layers before exposure to air, potentially improving contact stability in high-temperature and high-power devices.
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| 2. |
- Jonsson, Jonas, et al.
(författare)
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Instrumentation and vehicle platform of a miniaturized submersible for exploration of terrestrial and extraterrestrial aqueous environments
- 2012
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Ingår i: Acta Astronautica. - : Elsevier BV. - 0094-5765 .- 1879-2030. ; 79, s. 203-211
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Tidskriftsartikel (refereegranskat)abstract
- An example of an extraterrestrial environment likely to support life is the vast liquid body believed to hide underneath the frozen crust of Jupiter's moon Europa. The hypothetical exploration of this, as well as the more accessible subglacial lakes on Earth, has been used as model applications for the development of a heavily miniaturized, yet qualified, submersible with the potential to be deployable either in itself through a long and narrow borehole or as the daughter craft of an ice-penetrating cryobot.Onboard the submersible, which is only 20 cm in length and 5 cm in diameter, accommodation of a versatile set of sensors and instruments capable of characterizing and imaging the surroundings, and even collecting water samples with microorganisms for return, is facilitated through the use of miniaturization technologies. For instance, together with a small camera, a laser-based, microoptic device enables the 3-D reconstruction of imaged objects for topographical measurements. As a complement, when the water is turbid or a longer range is wanted, the world's smallest side-scanning sonar, exhibiting centimeter resolution and a range of over 30 m, has been developed. The work on miniaturizing a CTD, which is a widely employed oceanographic instrument used to measure and correlate conductivity, temperature, and depth, has commenced. Furthermore, a device employing acoustics to trap microscopic particles and organisms, and, by this, enrich water samples, is under development. To ensure that the gathered samples are pristine until analyzed at the end of a mission, the device is equipped with high-pressure, latchable valves.Remote operation and transfer of measurement data and images, or even live streaming of video, is made possible through a kilometer-long fiber optic cable being reeled out from the vehicle underway and tethering it to a terminal. To extend the missions, the same fiber shall also be capable of charging the onboard batteries.In this paper, the vehicle and its subsystems are summarized. Subsystems essential for the vehicle's operation, e.g., hull structure, communication and power management, are treated separately from those of more mission-specific nature, like the instruments mentioned above.
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| 3. |
- Jonsson, Jonas, et al.
(författare)
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Miniaturized submersible for exploration of aqueous environments on Earth and beyond
- 2011
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Konferensbidrag (refereegranskat)abstract
- Some of the most likely environments to support extraterrestrial life in our solar system are the ice-covered moons, suchas Europa, thought to harbor a liquid ocean underneath its frozen crust. Exploration, however, necessitates an ice-penetratingcryobot, or a long and narrow borehole, and the subsequent deployment of a small submersible, a hydrobot, with severe sizerestrictions imposed on its scientific payload. As a stepping stone for exploration of such environments, a small instrumentladenedsubmersible vehicle is currently under development.Employment of a large set of instruments capable of characterizing the aqueous environment, imaging the surroundingsand collecting microorganisms is essential for the determination of habitability. Despite the submersible being only 20 cm inlength and 5 cm in diameter, a high degree of functionality is facilitated here through the use of miniaturization technologies. Forinstance, a compact laser-illuminated diffractive optical element, paired with a high-resolution camera, enable photogrammetryand the reconstruction of objects’ shapes in 3-D space. Also for imaging, the world’s smallest side-scanning sonar has beendeveloped to acoustically image, either where water is too turbid for the camera, or where longer range is necessary. Currently,the sonar exhibits centimeter resolution and ranges over 30 meters. On the sensor side, a most vital oceanographic instrument, theCTD, used to measure the conductivity, temperature, and depth of water, has been heavily miniaturized and preliminaryevaluated. Additionally, a water sampler combining integrated selection and enriching capabilities to filter out and accommodate,e.g., microbes in the size range of 1-10 μm, is under development. Among other parts, its high-pressure valves and microfluidicacoustic traps have already been realized.For remote operation and upload of measurement data or images, or even live streaming of video, the submersible will betethered with a bi-directionally transmitting fiber optic cable, also capable of charging the onboard batteries for long missions.The one kilometer long fiber will be fitted within the hull, and by reeling out the fiber from the submersible, drag will be reduced.Herein, test results and images of the vehicle and its complete, and continuously developed, subsystems are presented.The vehicle, and its subsystems as stand-alone instruments, will enable the exploration of previously unreachable analogenvironments on Earth, vital to the field of astrobiology, and act as a forerunner to a submersible hydrobot that can explore icecoveredoceans elsewhere in our solar system.
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| 4. |
- Jonsson, Jonas, et al.
(författare)
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Miniaturized submersible for exploration of small aqueous environments
- 2011
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Ingår i: Oceans’11 MTS/IEEE Kona, Hilton Waikoloa Village, Kona, Hawai‘i September 19-22, 2011.
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Konferensbidrag (refereegranskat)abstract
- Remotely operated vehicles (ROVs) are commonlyused for sub-surface exploration. However, multi-functionalROVs tend to be fairly large, while preferred small and compactROVs suffer from limited functionality. The Deeper Access,Deeper Understanding (DADU) project aims to develop a smallsubmersible concept using miniaturization technologies to enablea high functionality. An operator is able to maneuver the vehiclewith five degrees of freedom using eight small thrusters, while aset of accelerometers and gyros monitor the orientation of thesubmersible. A single fiber optic cable will connect thesubmersible to a control station and enable simultaneous dataand command transfers. Rechargeable battery packs providepower to the submersibles subsystems during operation. Thesewill be rechargeable through the fiber connection. A forwardlooking camera is aided by a laser topography measurementsystem, where distances, sizes and shapes of objects in view canbe determined to within 0.5 cm. For murkier environments, orwhen a more extensive mapping of the surroundings is needed,the small high-frequency side-scanning sonar can be used.Salinity calculations of the water will be available throughmeasurements of the conductivity, temperature and depth.Samples of water and particles within it will be enabled through awater sampler with an enriching capability. Flow sensors will beable to measure the water movement around the submersible’shull. The submersible and its subsystems are under continuousdevelopment. The vehicle itself, and its subsystems as stand-aloneinstruments, will enable the exploration of previouslyunreachable submerged environments, such as the sub-glaciallakes found in Iceland and Antarctica, or other submerged smallenvironments, such as pipe and cave systems.
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| 5. |
- Jonsson, Jonas, et al.
(författare)
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Towards chip-based salinity measurements for small submersibles and biologgers
- 2013
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Ingår i: International Journal of Oceanography. - : Hindawi Publishing Corporation. - 1687-9406 .- 1687-9414. ; 2013, s. 529674-
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Tidskriftsartikel (refereegranskat)abstract
- Water’s salinity plays an important role in the environment. It can be determined by measuring conductivity, temperature, anddepth (CTD). The corresponding sensor systems are commonly large and cumbersome. Here, a 7.5 × 3.5mm chip, containingmicrostructured CTD sensor elements, has been developed. On this, 1.5mm2 gold finger electrodes are used to measure theimpedance, and thereby the conductivity of water, in the MHz frequency range. Operation at these frequencies resulted in highersensitivities than those at sub-MHz frequencies. Up to 14 kΩ per parts per thousand salt concentration was obtained repeatedlyfor freshwater concentrations.This was three orders of magnitude higher than that obtained for concentrations in and above thebrackish range. A platinumelectrode is used to determine a set ambient temperature with an accuracy of 0.005∘C.Membranes withNichrome strain gauges responded to a pressure change of 1 bar with a change in resistance of up to 0.21Ω. A linear fit to data over7 bars gave a sensitivity of 0.1185Ω/bar with an R2 of 0.9964. This indicates that the described device can be used in size-limitedapplications, like miniaturized submersibles, or as a bio-logger on marine animals.
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| 6. |
- Smedfors, Katarina, et al.
(författare)
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Characterization of Ohmic Ni/Ti/Al and Ni Contacts to 4H-SiC from-40 degrees C to 500 degrees C
- 2014
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. - 9783038350101 ; 778-780, s. 681-684
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Tidskriftsartikel (refereegranskat)abstract
- Extreme temperature measurements of Ni/Ti/Al contacts to p-type SiC (N-a = 1.10(18)cm(-3)), with a specific contact resistivity rho(c) = 6.75.10(-4) Omega cm(2) at 25 degrees C, showed a five time increase of the specific contact resistivity at -40 degrees C (rho(c) = 3.16.10(-3) Omega cm(2)), and a reduction by almost a factor 10 at 500 degrees C (rho(c) = 7.49.10(-5) Omega cm(2)). The same response of rho(c) to temperature was seen for contacts on lower doped epitaxial layer. Also N-type nickel contacts improved with higher operational temperature but with a considerably smaller variation over the same temperature interval. No degradation of the performance was seen to either the Ni/Ti/Al or the Ni contacts due to the high temperature measurements.
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| 7. |
- Smedfors, Katarina
(författare)
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Ohmic Contacts for High Temperature Integrated Circuits in Silicon Carbide
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In electrical devices and integrated circuits, ohmic contacts are necessary and a prerequisite for the current transport over the metal-semiconductor junctions. At the same time, a desired property of the ohmic contacts is to not add resistance or in other way disturb the performance. For high temperature electronics, the material demands are high regarding functionality and stability at elevated working temperatures, during and after temperature cycling and during long time of use. Silicon carbide, SiC, is a suitable substrate material for fabrication of high temperature electronics with a large band gap, good thermal conductivity and chemical inertness. The large bandgap causes however difficulties in finding a common material for ohmic contacts to both n- and p-type SiC. The goal of this project is to find a suitable metallization for n- as well as p-type contacts to epitaxially doped SiC for use in integrated circuits. The circuit technology developed and used in KTH for SiC is built on bipolar junction transistors. The p-doped base layer in the transistors is relatively low doped; 5 x 1017 – 1 x 1018 cm-3. P-type SiC is more difficult to form ohmic contacts to than n-type SiC, with such a low doping concentration it is even more complicated. Today, the metallizations used in the contacts consists of Ni for n-type contacts and Ni/Ti/Al to p-type SiC. Experiments of the specific contact resistivity ρc and the sheet resistance Rsh of these contacts, characterized to two types of samples, are presented for the extreme temperature range of -40 °C – 500 °C. Ohmic contact test chips with transfer length method structures have been compared to similar test structures on samples from the KTH SiC integrated circuits. The metals were also tested on the opposite doping polarity. Sputter deposition of Co and Si in layers to form CoSi2 contacts was made to chips from the same contact test wafer for comparison with the behavior of the presently used contacts. Since this was a new metallization, the process development of the high temperature anneal and contact formation made an important part of the work. Out of the tested contacts, Ni has been the best for n-SiC and Ni/Ti/Al for p-SiC. None of the three metallizations formed ohmic contacts to both n- and p-SiC. However, the CoSi2 contacts showed specific contact resistivity ρc <4 x 10-6 Ωcm2 at 25 °C and non-linear I-V characteristics but without barriers to p-SiC after voltage sweeps of ± 75V.
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| 8. |
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| 9. |
- Smedfors, Katarina, et al.
(författare)
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Sputtered Ohmic Cobalt Silicide Contacts to 4H-SiC
- 2015
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 821-823, s. 440-443
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Tidskriftsartikel (refereegranskat)abstract
- Ohmic CoSi2 contacts to n-type 4H-SiC showing low contact resistance have been made by sputter depositing sequential layers of Si and Co on 4H-SiC substrates followed by a two-step rapid thermal anneal at 600 °C and 950 °C. The contacts formed have been characterized at temperatures ranging from-40 °C to 500 °C with a specific contact resistance of 3.80∙10-5 Ωcm2 at 25 °C and a minimum of 6.0∙10-6 Ωcm2 at 500 °C.
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