| 1. |
- Nguyen, Hugo, 1955-, et al.
(författare)
-
Controllable growth of ZnO nanowires grown on discrete islands of Au catalyst for realization of planar-type micro gas sensors
- 2014
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 193, s. 888-894
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Tidskriftsartikel (refereegranskat)abstract
- The proper engineering design of gas sensors and the controlled synthesis of sensing materials for the high-performance detection of toxic gas are very important in the fabrication of handheld devices. In this study, an effective design for gas sensor chips is developed to control the formation of grown ZnO nanowires (NWs).The design utilizes the dendrite islands of Au catalyst deposited on and between Pt electrodes of a planar-type micro gas sensor so that NWs can grow on instead of a continuous Au seed layer. This method results in an increase of NW-NW junctions on the device and also eliminates current leakage through the seed layer, which results in a higher sensitivity. The results show that the developed gas-sensing devices could be used to monitor NO2 at moderate temperature (~250 °C) and/or ethanol at a high temperature (~400 °C).
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| 2. |
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A design of high performance gas sensor array withdiscrete islands of Au catalyst for increasing of ZnO nanowire junctions
- 2013
-
Proceedings (redaktörskap) (refereegranskat)abstract
- In this study, an effective design for growth of ZnO nanowires directly on gas sensor chips is introduced. The design utilizes the dendrite islands of Au catalyst deposited between and on the Pt electrodes for the nanowires to grow on instead of a continuous seed layer or Au film. This lead to an increase of the nanowirenanowire junctions in the devices, as well as a reduction of the leak current that would occur through the mentioned alternative seed layer; resulting in a higher sensitivity. The results showed that the developed gas sensors could be used for monitoring of NO2 at low concentration.
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| 3. |
- Tan, Ha Minh, 1989-, et al.
(författare)
-
Self-heating Effect on Tin Oxide Nanowire Network Gas Sensor
- 2014
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Self-heated gas sensors have attracted much of interests owing to the ultra-low power consumption as well as simple device fabrication. However, it still requires further improvement to overcome some technical difficulties such as high operation voltage, long-term stability, and mass production. In this work, we propose a nanowire nework structure to solve these problems. The self-heating effect on fabricated structures was tested and working temperature was evaluated by base resistance measurement and infrared emission microscopy methods. The fabricated sensor consumed an electric power of about 40 mW to reach the working temperature up to 250 oC. The NO2 sensing properties were initially studied on this sensor structure.
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| 4. |
- Vu Trong, Thu, 1982-, et al.
(författare)
-
Tiềm năng lớn của vệ tinh siêu nhỏ đáp ứng nhu cầuquản lý hàng hải của Việt Nam
- 2011
-
Ingår i: REV/ComNaVi-11, Workshop on Communications and Navigations for the Development of Vietnam's Marine Economy, Da Nang city Vietnam, August 2-4, 2011.
-
Konferensbidrag (refereegranskat)abstract
- Trong 10 năm gần đây, loại vệ tinh siêu nhỏ có kích thước 10x10x10 cm và trọng lượng 1 kg với tên gọi CubeSat từ công cụ thực hành của sinh viên đại học đang dần trở thành nền tảng cho những vệ tinh có khả năng ứng dụng trong thực tiễn. Ngày nay, người sử dụng có thể tự thiết kế hoặc mua sẵn linh kiện điện tử và cơ khí lắp thành vệ tinh cỡ 1, 2, 3... kg với các tính năng mong muốn. Ưu điểm của loại vệ tinh siêu nhỏ này là thời gian chế tạo ngắn, chi phí thấp và càng phát huy năng lực khi sử dụng cả một chùm vệ tinh. Nhờ có thể thích hợp hóa dễ dàng với từng nhu cầu thực tiễn và nhờ những tiến bộ nhanh chóng trong lĩnh vực điện tử và công nghệ thu nhỏ các hệ thống cảm ứng, nhiều nhu cầu quản lý hàng hải của Việt Nam được đánh giá là khả thi ngay trong thời điểm hiện tại. Nhiều trường đại học trên thế giới đã sử dụng thành công vệ tinh siêu nhỏ trong các chương trình viễn thám và khoa học vũ trụ. Gần đây, Trường đại học FPT cộng tác với Đại học Uppsala Thụy Điển đã đưa ra ý tưởng sử dụng loại vệ tinh này trong công tác quản lý hàng hải Việt Nam và đã được Trường đại học Tokyo, Nhật Bản tuyển chọn, mời sang trình bày đề án tại hội thảo “2nd Nano-satellite symposium” ngày 13-15/3/2011. Nói tóm tắt, đây là đề án dùng chùm vệ tinh siêu nhỏ loại 3kg có trang bị máy thu tín hiệu định vị (AIS) của tàu thuyền lưu thông trên biển, nhằm hỗ trợ công tác quản lý hàng hải và tìm kiếm, cứu nạn. Bài viết này đề cập đến loại vệ tinh siêu nhỏ CubeSat có thể áp dụng cho các nhu cầu thiết thực của Việt Nam, đồng thời cũng trình bày về đề án theo dõi sự di chuyển của tàu biển từ vệ tinh làm ví dụ điển hình cho thấy tiềm năng lớn của vệ tinh siêu nhỏ đáp ứng nhu cầu quản lý hàng hải hiện nay của đất nước.
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| 5. |
- Han, Hoang Van, et al.
(författare)
-
Single-crystal zinc oxide nanorods with nanovoids as highly sensitive NO2 nanosensors
- 2013
-
Ingår i: Materials letters (General ed.). - : Elsevier BV. - 0167-577X .- 1873-4979. ; 94, s. 41-43
-
Tidskriftsartikel (refereegranskat)abstract
- Design and synthesis of nanostructured materials with a highly porous crystal structure and high specific surface area are the key issues to an enhanced gas sensing performance. This letter introduces a simple and scalable hydrothermal method to fabricate single-crystal ZnO nanorods (NRs) with nanovoids (NVs) for highly sensitive NO2 nanosensors. The fabricated ZnO NRs have a single-crystal structure with an average length and diameter of about 900 nm and 23 nm, respectively. NVs of less than 5 nm size are found frequently along the NRs. Gas-sensing characterizations revealed that the ZnO NR sensors exhibited a relatively high response to sub-ppm NO2 with excellent stability after 8 cycles of switching from NO2 to dry air without significant response reduction.
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| 6. |
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| 7. |
- Jonsson, Jonas, 1979-, et al.
(författare)
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A compact projection system enabling topographical measurements for a miniaturized submersible explorer
- 2011
-
Ingår i: Proceedings of the 16th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS), 2011. - : IEEE conference proceedings. - 9781457701573 ; , s. 2518-2521
-
Konferensbidrag (refereegranskat)abstract
- To enable photogrammetry of underwater images using a miniaturized submersible explorer, a compact projection system has been developed. By registering the deformation of a known projected pattern, using a laser and a diffractive optical element (DOE), the distance to, shape and size of an object can be calculated. The DOE has been designed, using in-house developed software, and manufactured using microstructure technology. Distances to objects 45 to 30 cm away were determined to within 0.5 cm, and the developed GUI was able to recreate the shape from the measurements for easier examination of the object.
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| 8. |
- Jonsson, Jonas, et al.
(författare)
-
A compact system to extract topography information from scenes viewed by a miniaturized submersible explorer
- 2012
-
Ingår i: Sensors and Actuators A-Physical. - : Elsevier BV. - 0924-4247 .- 1873-3069. ; 188:SI, s. 401-410
-
Tidskriftsartikel (refereegranskat)abstract
- In images taken underwater, it is generally difficult to correctly extract distances and geometric informationof objects. Different techniques, collectively referred to as photogrammetry, exist to measurefeatures in images. One of these is to project a reference pattern onto an object in a scene viewed by acamera, and register the distortion of this pattern, to calculate the shape of, and distance to, that object.This method is implemented here on a miniaturized submersible explorer equipped with, among manyother instruments, a camera. Diffractive optical elements (DOEs) have been designed and manufacturedusing microsystems technology, to, together with a laser diode, camera, and in-house developed software,provide a compact system for projecting reference patterns and analyzing their deformations. Thesystem has been characterized by measuring the distances and angles of objects in a water tank, andattempting to reproduce their shapes. The range of operation of the system, verified to be at least onemeter, is limited by the compact mounting in the small submersible and the cameras’ performance.The system was found to work well under turbid conditions as well as in water containing larger particles.Together with a vehicle-mounted camera, the compact and low-power DOE laser projection systemenables topographical measurement.
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| 9. |
- Jonsson, Jonas, et al.
(författare)
-
Instrumentation and vehicle platform of a miniaturized submersible for exploration of terrestrial and extraterrestrial aqueous environments
- 2012
-
Ingår i: Acta Astronautica. - : Elsevier BV. - 0094-5765 .- 1879-2030. ; 79, s. 203-211
-
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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| 10. |
- Jonsson, Jonas, 1979-
(författare)
-
Microsystems Technology for Underwater Vehicle Applications
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work has been to investigate how miniaturization, such as microsystems technology, can potentially increase the scientific throughput in exploration of hard-to-reach underwater environments, such as the subglacial lakes of Antarctica, or other challenging environments, including cave systems and wrecks. A number of instruments and subsystems applicable to miniature submersibles have been developed and studied, and their potential to provide a high functionality density for size-restricted exploration platforms has been assessed.To provide an onboard camera system with measurement capabilities, simulation and design tools for diffractive optics were developed, and microoptics realized to project reference patterns onto objects to reveal their topography. The influence of murky water on the measurement accuracy was also studied.For longer-range mapping of the surroundings, and under conditions with even less visibility, the performance of a very small, high-frequency side-scanning sonar was investigated using extensive modeling and physical testing. In particular, the interference on the acoustic beam from tight mounting in a hull was investigated. A range in excess of 30 m and centimeter resolution were obtained.Besides these systems, which can be used to navigate and map environments, a two-dimensional, thermal sensor for minute flows was developed. Measuring speed and direction of water flows, this sensor can aid in the general classification of the environment and also monitor the submersible’s movement. As the flow of waters in subglacial lakes is estimated to be minute, the detection limit and sensitivity were investigated.Measurements of water properties are facilitated by the chip-based conductivity, temperature, and depth sensor system developed. Macroscopically, this is an essential oceanographic instrument with which salinity is determined. Contrary to what was expected, MHz frequencies proved to be advantageous for conductivity measurements.Finally, sampling of water using an acoustically enriching microdevice, and even enabling return of pristine samples via the use of integrated latchable, high-pressure valves, was realized and evaluated. Particularly, investigations of the device’s ability to capture and hold on to microorganisms, were conducted.Further developed and studied, these devices – as subsystems to miniature submersibles, or as stand-alone instruments – should enable exploration of previously unreachable submerged environments.
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| 11. |
- Jonsson, Jonas, et al.
(författare)
-
Miniaturized submersible for exploration of aqueous environments on Earth and beyond
- 2011
-
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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| 12. |
- Jonsson, Jonas, et al.
(författare)
-
Miniaturized submersible for exploration of small aqueous environments
- 2011
-
Ingår i: Oceans’11 MTS/IEEE Kona, Hilton Waikoloa Village, Kona, Hawai‘i September 19-22, 2011.
-
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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| 13. |
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| 14. |
- Nguyen, Hugo, et al.
(författare)
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Experimental Studies of Sealing Mechanism of a Dismountable Microsystem‑to‑Macropart Fluidic Connector for High Pressure and a Wide Range of Temperature
- 2010
-
Ingår i: Advances in Mechanical Engineering. - : Hindawi. - 1687-8132 .- 1687-8140. ; 2010
-
Tidskriftsartikel (refereegranskat)abstract
- As fluidic microelectromechanical devices are developing and often attached to, or embedded in, large, complex and expensive systems, the issues of modularity, maintenance and subsystem replacement arise. In this work, a robust silicon connector suitable for high-pressure applications – likely with harsh fluids – in the temperature range of +100 to –100°C is demonstrated and tested together with a stainless steel nipple representing a simple and typical macropart. With a micromachined circular membrane equipped with a 5 μm high ridge, this connector is able to maintain a leak rate below 2.0´10-8 scc/s of gaseous helium with a pressure of up to 9.7 bar. Degradation of the sealing performance on reassembly is associated with the indentation of the ridge. However, the ridge makes the sealing interface less sensitive to particles in comparison with a flat reference. Most evaluation is made through so called heat-until-leak tests conducted to determine the maximum working temperature and the sealing mechanism of the connector. A couple of these are followed by cryogenic testing. The effect of thermal mismatch of the components is discussed and utilized as an early warning mechanism.
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| 15. |
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| 16. |
- Nguyen, Hugo, 1955-, et al.
(författare)
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Material- and fabrication-governed performance of a tunnelling magnetometer
- 2010
-
Ingår i: Advances in Natural Sciences. - : Institute of Physics (IOP). - 2043-6254 .- 2043-6262. ; 1:4, s. 045006-
-
Tidskriftsartikel (refereegranskat)abstract
- Miniaturization of sensitive magnetic sensors for nano- and picosatellites has come to the point where the traditional sensors with magnetic coils soon can be replaced. Thin film technology offers the possibility of making extremely small magnetic field sensors that employ the effect of anisotropic, giant and tunneling magnetoresistance (AMR, GMR and TMR). In this paper, the development status of sensors based on microelectromechanical systems technology (MEMS), starting from a TMR layer structure is presented. The sensors have been successfully fabricated and integrated onto an electronic circuit designed for space application. The system as a whole, and the sensors in particular, have not only been characterized with respect to sensitivity, resolution, and noise level, but also to launch vibration and space radiation. The sensor performance and limitations are strongly dependent on the deposited materials, sensor design, and fabrication process. Since the sensor elements are small and sensitive (with lateral dimensions of some tens of micrometres, and resolution of 100 pT at frequencies of MHz), they are also promising for other MEMS applications.
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| 17. |
- Nguyen, Hugo, 1955-, et al.
(författare)
-
Tailoring the properties of a magnetic tunnel junction to be used as a magnetic field sensor
- 2011
-
Ingår i: Conf. on solid state physics and materials VII (SPMS 2011), Ho Chi Minh, 7-9 November 2011.
-
Konferensbidrag (refereegranskat)abstract
- A magnetic tunnel junction (MTJ) can be used as an effective magnetic field sensor thank to its high magnetoresistance ratio. To be used as a magnetic field sensor in different applications, the possibility of tuning the performance of the MTJ is important. Different means of tuning, such as voltage and magnetic field biasing, can be used. In this work, an external magnetic field from a permanent magnet was used to bias the sensing layer of a MTJ along its hard axis, and the effect of the biasing on the sensitivity, detection limit, and hysteresis of the MTJ was investigated. The experiments showed that the hysteresis of the MTJ languished away at a certain applied magnetic field. Moreover, the sensitivity and noise level decreased, whereas the detection limit increased with increasing bias field strength. The motivation of this experiment is not only to find a power- and cost-effective method of tuning the MTJ, but also to study what happens with the sensing layer, and with electron transport within the MTJ when an external magnetic field is applied.
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| 18. |
- Palmer, Kristoffer, et al.
(författare)
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A highly integratable silicon thermal gas flow sensor
- 2012
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Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 0960-1317 .- 1361-6439. ; 22:6, s. 065015-
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Tidskriftsartikel (refereegranskat)abstract
- Thermal flow sensors have been designed, fabricated, and characterized. All bulk material in these devices is silicon so that they are integratable in silicon-based microsystems. To mitigate heat losses and to allow for use of corrosive gases, the heating and sensing thin film titanium/platinum elements, injecting and extracting heat, respectively, from the flow, are placed outside the channel on top of a membrane consisting of alternating layers of stress-balancing silicon dioxide and silicon nitride. For the fabrication, an unconventional bond surface protection method using sputter-deposited aluminum instead of thermal silicon dioxide is used in the process steps prior to silicon fusion bonding. A method for performing lift-off on top of the transparent membrane was also developed. The sensors, measuring 9.5 x 9.5 mm(2), are characterized in calorimetric and time-of-flight modes with nitrogen flow rates between 0 sccm and 300 sccm. The maximum calorimetric sensor flow signal and sensitivity are 0.95 mV and 29 mu V sccm(-1), respectively, with power consumption less than 40 mW. The time-of-flight mode is found to have a wider detectable flow range compared with calorimetric mode, and the time of flight measured indicates a response time of the sensor in the millisecond range. The design and operation of a sensor with high sensitivity and large flow range are discussed. A key element of this discussion is the configuration of the array of heaters and gauges along the channel to obtain different sensitivities and extend the operational range. This means that the sensor can be tailored to different flow ranges.
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| 19. |
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| 20. |
- Palmer, Kristoffer, 1983-
(författare)
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Development of Microcomponents for Attitude and Communication Systems on Small Vehicles in Space and Extreme Environments
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, components intended for vehicles in space and other extreme environments have been realized using microsystems technology to facilitate miniaturized, yet high-performing systems beneficial for small spacecraft and other vehicles with limited size and power.Cold gas thrusters commonly used on spacecraft basically accelerate a gaseous propellant stored under high pressure. When miniaturized, their performance is reduced because of viscous forces. Here, with a special masking and etching scheme, making silicon micronozzles close to rotationally symmetric, this shortcoming was mitigated as indicated by schlieren imaging of the rocket exhaust and a comparison with conventionally manufactured micronozzles with rectangular cross-sections. Schlieren imaging was also used to detect leakage, quantify thrust vector deviation, and measure shock cell periods in the exhaust. Correlation was made to operational conditions.Similarly operating zirconia thrusters with integrated heaters and flow sensors were developed to allow for higher operating temperature. Successful testing at 1000°C, suggests that the propellant efficiency could be increased by 7.5%, and also makes them candidates for chemical propulsion.A silicon thruster operating in rarefied gas regimes was also developed. Being suspended in a silicon dioxide frame reducing heat losses, a total efficiency of 17% was reached.Relating to the integrated micropropulsion systems, two types of flow sensors were developed. Through finite element modeling, the insertion of sensor fingers in the fluid was shown to be an interesting concept for high-pressure applications.Utilizing the same principle, a velocity sensor for a miniaturized submersible was developed. With a power consumption below 15 mW, it was able to measure directions with an accuracy of ±8º, and speed with an error less than 22%.To enable high-speed optical communication between spacecraft, a Free Space Optics communication system, and particularly its dual-axis beam-steering actuator, was developed. Through thermal actuation, optical angles larger than 40º were obtained. A lumped thermal model was used to study design changes, vacuum operation and feedback control.Understanding and mastering heat transfer in microsystems have been vital in many of the studies conducted. Throughout, advanced micromachining and modeling have been used as a step towards high-performance systems for space and other extreme environments.
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| 21. |
- Palmer, Kristoffer, et al.
(författare)
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Fabrication and evaluation of a free molecule micro-resistojet with thick silicon dioxide insulation and suspension
- 2013
-
Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 0960-1317 .- 1361-6439. ; 23:6, s. 065006-
-
Tidskriftsartikel (refereegranskat)abstract
- A silicon free molecule micro-resistojet (FMMR) with a thermally insulating suspension frame composed of silicon dioxide has been designed, fabricated and tested. The concept was developed to increase the efficiency of FMMRs, especially in silicon-based integrated systems. Fabrication of the thick insulating frame was performed through oxidation of high-aspect ratio silicon trenches. The thermal properties of the 1 cm(2) thruster were evaluated using an IR camera, and it was found that when the volume inside the frame is heated more than 200 degrees C using integrated nickel heaters, the temperature increase in the volume outside the frame is less than 50 degrees C. During operation in vacuum, the thrust range was calculated to be about 13-1070 mu N and the maximum specific impulse 54 s. At maximum thrust, and a power consumption of 1.6 W, the total efficiency of the thruster was 17%. Designs of more efficient and versatile systems are discussed.
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| 22. |
- Palmer, Kristoffer, et al.
(författare)
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Finite Element Analysis of the Effect on Employing Thermal Through Vias and Heat Fingers to Increase Heat Transfer to Fluid in Calorimetric Flow Sensors
- 2013
-
Ingår i: Sensors and Actuators A-Physical. - : Elsevier BV. - 0924-4247 .- 1873-3069. ; 201, s. 49-57
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Tidskriftsartikel (refereegranskat)abstract
- Measurement results of a robust silicon calorimetric flow sensor with a 25 μm thick silicon dioxide membrane with thermal silicon vias have been compared with results obtained from three-dimensional Finite Element Analysis (FEA). Based on the fabricated device, the sensor has been further developed to include heat-exchanging fingers extending down into the integrated flow channel for increased heat transfer. Using FEA, different designs of the fingers have been compared with respect to signal strength, sensitivity, power consumption and pressure loss in the channel at flow rates from 0 to about 650 sccm. Using heat fingers, the sensor signal was improved by a factor of five. The sensor signal, i.e. the temperature difference between downstream and upstream elements, was more than 60 °C when the central heater was heated 300 °C above room temperature, which was comparable to a thin-membrane device modeled. The maximum sensitivity using the finger design was about 1.4 °C sccm−1, and the maximum power consumption was almost 700 mW, which is considerably higher than for thin-membrane sensors. A figure of merit used for evaluation, was the ratio of signal strength to power consumption. The results show that the device design is a promising concept that is suitable in systems requiring robust monolithically integratable flow sensors.
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| 23. |
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| 24. |
- Palmer, Kristoffer, 1983-, et al.
(författare)
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Two-Dimensional Thermal Velocity Sensor for Submersible navigation and Minute Flow Measurements
- 2013
-
Ingår i: IEEE Sensors Journal. - 1530-437X .- 1558-1748. ; 13:1, s. 359-370
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Tidskriftsartikel (refereegranskat)abstract
- A 2-D thermal velocity microsensor for use as a navigational aid and for flow measurements on a miniaturized submersible is developed in this paper. The sensor with nickel heater and temperature sensors on a Pyrex substrate, designed for mounting on the outside of the submersible hull, is fabricated and tested in an application-like environment and proven to be able to measure water speed from zero to 40 mm/s with a power consumption less than 15 mW and determine the flow direction with an error less than ±8°. Finite Element Analysis is used to investigate design and operation parameters and possible biofouling effects on the sensor signal. The effect on shape and orientation of the sensor's mounting surface is also studied.
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| 25. |
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| 26. |
- Persson, Anders, et al.
(författare)
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Changing the attitude towards magnetoresistance
- 2011
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Ingår i: Changing the attitude towards magnetoresistance.
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Konferensbidrag (refereegranskat)abstract
- Magnetometers are one of the most common instruments on spacecrafts. They are used for both satellite attitude determination and for scientific purposes, such as mapping of Earth’s magnetic field. The most common magnetometer for low-frequency applications is the fluxgate. High-end fluxgates are generally quite bulky, with a mass of around 1 kg, but there exist miniature version, weighing only around 100 g, but with worse noise figure. Interest in such miniature models has increased with the adaption of the Faster-Better-Cheaper philosophy, and the introduction of small satellite classes. However, downscaling of fluxgates beyond the present 100 g has proven difficult, wherefore other technologies have earned more and more interest, especially those employing different kinds of magnetoresistance.Here, a review of different magnetoresistive techniques, and their past, present and potential use in space is presented. Magnetoresistive sensors based on anisotropic, giant, and tunneling magnetoresistance is covered, and extra attention is directed towards sensors based on the planar Hall effect. The latter have the potential of overcoming some of the major disadvantages of other magnetoresistive sensors, such as poor detectivity at low frequencies, and the need for external biasing coils to improve linearity and reduce hysteresis by, e.g., set-reset protocols and magnetic feedback.Moreover, the design of two such planar Hall effect sensors is tailored to meet the requirements set on a magnetometer aimed for, firstly, attitude determination and, secondly, mapping of Earth’s magnetic field. It is concluded that planar Hall effect sensors is one of the prime candidates for the next generation of miniaturized low-frequency space magnetometers.
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| 27. |
- Persson, Anders, et al.
(författare)
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Etch-stop technique for patterning of tunnel junctions for a magnetic field sensor
- 2011
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Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 0960-1317 .- 1361-6439. ; 21:4, s. 045014-045022
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Tidskriftsartikel (refereegranskat)abstract
- Spin-dependent tunnelling devices, e. g. magnetic random access memories and highly sensitive tunnelling magnetoresistance (TMR) sensors, often consist of a large number of magnetic tunnel junctions (MTJs) of uniform quality over the whole device. The uniformity and yield of the fabrication of such a device are therefore very important. A major source of yield loss is the short-circuiting of junctions by redeposition of etch residues. This can be prevented by terminating of the etch in the typically 1 nm thick tunnelling barrier. Here, electron spectroscopy for chemical analysis for monitoring the etching semi-continuously is proposed. The fabrication scheme employs Ar ion milling for etching the MTJs, and photoelectron spectroscopy for analysing the composition of the etched surface in situ. Junctions etched either to or through the barrier were used for this. The quality of the etch stop was investigated using transmission electron microscopy (TEM), and it was confirmed that the etch could be stopped in the MgO barrier. The TEM imaging also showed clear signs of redeposition. Such redeposition was attributed to being partly caused by the reduction of the TMR ratio of the junctions etched through the barrier, which was only 15% as compared with 150% for junctions etched to the barrier. Also, the latter junctions exhibited 2.7 times less noise in the low-frequency regime, resulting in a 27 times improvement of the signal-to-noise ratio with the etch stop. The barrier also proved effective in protecting the bottom contact from oxidation during the capping and contacting of the junctions.
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| 28. |
- Persson, Anders, 1982-, et al.
(författare)
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Ga Implantation in a MgO-based Magnetic Tunnel Junction With Co60Fe20B20 Layers
- 2011
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Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 47:1, s. 151-155
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Tidskriftsartikel (refereegranskat)abstract
- A Co60Fe20B20-based tunneling magnetoresistance multilayer stack with an MgO barrier has been exposed to 30 keV Ga ions at doses corresponding to ion etching and metal deposition in a focused ion beam (FIB) instrument, to study the applicability of these processes to magnetic tunnel junction (MTJ) fabrication. MTJs were fabricated and irradiated to investigate how the exposures affected their coercivity and magnetoresistance. Elemental depth profiles, acquired using electron spectroscopy for chemical analysis, showed that Ga gathered in and around the two Co60Fe20B20 layers. Correlated with the results of the magnetic measurements, this Ga presence was found to cause a reduction of magnetoresistance and an increase in coercivity. Quantitatively, a dose of 1014 Ga+cm-2 reduced the magnetoresistance by 60%, whereas a dose of 1015 Ga+cm-2 reduced the magnetoresistance by 67% and also increased the coercivity by 2 mT and changed the dipole coupling between the sensing and the pinning layers by 1.6 mT. The latter was attributed to an imbalance in the synthetic antiferromagnetic structure, where the stack's Ru spacer served as an implantation barrier. The magnetoresistance was lost at a dose of 1016 Ga+cm-2. Annealing reduced the content of Ga around the magnetic layers but also caused diffusion of Cu from one of the layers in the stack. Apart from the observation and explanation of implantation damages in the multilayer, this work concludes on the applicability of FIB processes for prototyping of MTJs.
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| 29. |
- Persson, Anders, 1982-, et al.
(författare)
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Low-frequency noise in planar Hall effect bridge sensors
- 2011
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Ingår i: Sensors and Actuators A-Physical. - : Elsevier. - 0924-4247 .- 1873-3069. ; 171:2, s. 212-218
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Tidskriftsartikel (refereegranskat)abstract
- The low-frequency characteristics of planar Hall effect bridge sensors are investigated as function of the sensor bias current and the applied magnetic field. The noise spectra reveal a Johnson-like spectrum at high frequencies, and a 1/f-like excess noise spectrum at lower frequencies, with a knee frequency of around 400 Hz. The 1/f-like excess noise can be described by the phenomenological Hooge equation with a Hooge parameter of γH = 0.016. The detectivity is shown to depend on the total length, width and thickness of the bridge branches. The detectivity is improved by the square root of the length increase. Moreover, the detectivity is shown to depend on the amplitude of the applied magnetic field, revealing a magnetic origin to part of the 1/f noise.
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| 30. |
- Persson, Anders, 1982-
(författare)
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Magnetoresistance and Space : Micro- and Nanofeature Sensors Designed, Manufactured and Evaluated for Space Magnetic Field Investigations
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, the interest for miniaturization of spaceborne instruments and subsystems has increased steadily, as this enables development of small and lightweight satellite classes as well as more versatile payloads on traditional spacecraft. In essence, this thesis work is an investigation of the applicability of magnetoresistive technology to a magnetometer intended for space. Two types of magnetoresistive sensors, promising with respect to performance competiveness also after considerable miniaturization, were developed and evaluated, namely magnetic tunnel junctions and planar Hall effect bridge sensors. In the case of the magnetic tunnel junctions, much effort was put on the micromanufacturing process. Two schemes were developed and evaluated for sensor contouring: one employing focused ion beam processes for rapid prototyping, and the other combining sputtering and x-ray photoelectron spectroscopy for precise etch depth monitoring during ion etching. For the former, the resulting implantation damages were investigated with chemical analysis and correlated to the sensor properties. In the latter, the depth of the etching was monitored live with a resolution sufficient to stop the etching in the 1 nm thick tunneling barrier. The effect and extent of redeposition were investigated by transmission electron microscopy and micromagnetic analysis. With the knowledge so gained, the tunneling magnetoresistance of the manufactured junctions could be improved significantly and their inherent noise could be reduced. As a step in space flight qualification, the magnetic tunnel junctions were subjected to both g and particle radiation, leaving them unaffected by the first, but rendering them a reduced tunneling magnetoresistance ratio and an increased coercivity by the latter. In the case of the planar Hall effect bridge sensors, their inherent noise was thoroughly investigated, revealing both electric and magnetic 1/f noise at low frequencies along with thermal noise at higher frequencies. In addition, an analytical model of the magnetic properties of the planar Hall effect bridges was developed, and a design process, based on the model, was established to optimize the bridges for a particular application. In conclusion, both types of sensors show great promises for use in space. Of the two, the planar Hall effect bridge sensors had a better detection limit at low frequencies, whereas the magnetic tunnel junctions were more precise at higher frequencies. However, both sensors had a bandwidth greatly exceeding that of traditional spaceborne magnetometers. A magnetometer employing the magnetic tunnel junctions from this work is currently included as payload onboard the Vietnamese satellite F-1 scheduled for launch this year. A magnetometer using magnetoresistive sensors – planar Hall effect sensors, magnetic tunnel junctions, or both – enables a mass reduction of more than two orders of magnitudes compared with traditional systems.
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| 31. |
- Persson, Anders, et al.
(författare)
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Modelling and design of planar Hall effect bridge sensors for low-frequency applications
- 2013
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Ingår i: Sensors and Actuators A-Physical. - : Elsevier BV. - 0924-4247 .- 1873-3069. ; 189, s. 459-465
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Tidskriftsartikel (refereegranskat)abstract
- The applicability of miniaturized magnetic field sensors is being explored in several areas of magneticfield detection due to their integratability, low mass, and potentially low cost. In this respect, differentthin-film technologies, especially those employing magnetoresistance, show great potential, being compatible with batch micro- and nanofabrication techniques. For low-frequency magnetic field detection,sensors based on the planar Hall effect, especially planar Hall effect bridge (PHEB) sensors, show promising performance given their inherent low-field linearity, limited hysteresis and moderate noise figure. Inthis work, the applicability of such PHEB sensors to different areas is investigated. An analytical modelis constructed to estimate the performance of an arbitrary PHEB sensor geometry in terms of, e.g., sensitivity and detectivity. The model is valid for an ideal case, e.g., disregarding shape anisotropy effects, andalso incorporates some approximations. To validate the results, modelled data was compared to measurements on actual PHEBs and was found to predict the measured values within 13% for the investigatedgeometries. Subsequently, the model was used to establish a design process for optimizing a PHEB to aparticular set of requirements on the bandwidth, detectivity, compliance voltage and amplified signalto-noise ratio. By applying this design process, the size, sensitivity, resistance, bias current and powerconsumption of the PHEB can be estimated. The model indicates that PHEBs can be applicable to severaldifferent areas within science including satellite attitude determination and magnetic bead detection inlab-on-a-chip applications, where detectivities down towards 1 nT Hz−0.5at 1 Hz are required, andmaybeeven magnetic field measurements in scientific space missions and archaeological surveying, where thedetectivity has to be less than 100 pT Hz−0.5at 1 Hz.
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| 32. |
- Persson, Anders, et al.
(författare)
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Radiation tolerance of a spin-dependent tunnelling magnetometer for space applications
- 2011
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Ingår i: Measurement science and technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 22:4, s. 045204-
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Tidskriftsartikel (refereegranskat)abstract
- To meet the increasing demand for miniaturized space instruments, efforts have been made to miniaturize traditional magnetometers, e. g. fluxgate and spin-exchange relaxation-free magnetometers. These have, for different reasons, turned out to be difficult. New technologies are needed, and promising in this respect are tunnelling magnetoresistive (TMR) magnetometers, which are based on thin film technology. However, all new space devices first have to be qualified, particularly in terms of radiation resistance. A study on TMR magnetometers' vulnerability to radiation is crucial, considering the fact that they employ a dielectric barrier, which can be susceptible to charge trapping from ionizing radiation. Here, a TMR-based magnetometer, called the spin-dependent tunnelling magnetometer (SDTM), is presented. A magnetometer chip consisting of three Wheatstone bridges, with an angular pitch of 120 degrees, was fabricated using microstructure technology. Each branch of the Wheatstone bridges consists of eight pairs of magnetic tunnel junctions (MTJs) connected in series. Two such chips are used to measure the three-dimensional magnetic field vector. To investigate the SDTM's resistance to radiation, one branch of a Wheatstone bridge was irradiated with gamma rays from a Co-60 source with a dose rate of 10.9 rad min(-1) to a total dose of 100 krad. The TMR of the branch was monitored in situ, and the easy axis TMR loop and low-frequency noise characteristics of a single MTJ were acquired before and after irradiation with the total dose. It was concluded that radiation did not influence the MTJs in any noticeable way in terms of the TMR ratio, coercivity, magnetostatic coupling or low-frequency noise.
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| 33. |
- Persson, Anders, et al.
(författare)
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Rapid prototyping of magnetic tunnel junctions with focused ion beam processes
- 2010
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Ingår i: Journal of Micromechanics and Microengineering. - : IOP. - 0960-1317 .- 1361-6439. ; 20:5, s. 055039-
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Tidskriftsartikel (refereegranskat)abstract
- Submicron sized Magnetic tunnel junctions (MTJs) are most often fabricated by time-consuming and expensive e-beam lithography. From a research and development perspective, a short lead time is one of the major concerns. Here, a rapid process scheme for fabrication of micrometer size MTJs with focused ion beam processes is presented. The magnetic properties of the fabricated junctions is investigated in terms of magnetic domain structure, tunnelling magnetoresistance (TMR) and coercivity, with extra attention to the effect of Ga implantation from the ion beam. In particular, the effect of the implantation on the minimum junction size and the magnetization of the sensing layer are studied. In the latter case, magnetic force microscopy and micromagnetic simulations, with the Object Oriented Micromagnetic Framework (OOMMF), are used to study the magnetization reversal. The fabricated junctions show considerable coercivity both along their hard and easy axes. Interestingly, the sensing layer exhibit two remanent states: one with a single and one with a double domain. The hard axis TMR loop has kinks at about ±20 mT which is attributed to a non-uniform lateral coercivity, where the rim of the junctions, which is subjected to Ga implantation from the flank of the ion beam, is more coercive than the unirradiated centre. The width of the coercive rim is estimated to 160 nm from the hard axis TMR loop. The easy axis TMR loop shows more coercivity than an unirradiated junction and, this too, is found to stem from the coercive rim, as seen from the simulations. It is concluded that the process scheme has three major advantages. Firstly, it has a high lateral and depth resolution – the depth resolution is enhanced by end point detection – and is capable of making junctions of sizes down towards the limit set by the width of the irradiated rim. Secondly, the most delicate process steps are preformed in unbroken vacuum enabling the use of materials prone to forming oxides in the MTJ film stack. Thirdly, the scheme is both uncomplicated and quick and makes it possible to go from design to characterization in the order of hours.
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| 34. |
- Thorslund, Sara, et al.
(författare)
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A disposable and multifunctional capsule for easy operation of microfluidic elastomer systems
- 2011
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Ingår i: Journal of Micromechanics and Microengineering. - : Institute of Physics (IOP). - 0960-1317 .- 1361-6439. ; 21:12, s. 127001-
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Tidskriftsartikel (refereegranskat)abstract
- The global lab-on-chip and microfluidic markets for cell-based assays have been predicted to grow considerably, as novel microfluidic systems enable cell biologists to perform in vitro experiments at an unprecedented level of experimental control. Nevertheless, microfluidic assays must, in order to compete with conventional assays, be made available at easily affordable costs, and in addition be made simple to operate for users having no previous experience with microfluidics. We have to this end developed a multifunctional microfluidic capsule that can be mass-produced at low cost in thermoplastic material. The capsule enables straightforward operation of elastomer inserts of optional design, here exemplified with insert designs for molecular gradient formation in microfluidic cell culture systems. The integrated macro–micro interface of the capsule ensures reliable connection of the elastomer fluidic structures to an external perfusion system. A separate compartment in the capsule filled with superabsorbent material is used for internal waste absorption. The capsule assembly process is made easy by integrated snap-fits, and samples within the closed capsule can be analyzed using both inverted and upright microscopes. Taken together, the capsule concept presented here could help accelerate the use of microfluidic-based biological assays in the life science sector.
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| 35. |
- Vu Trong, Thu, 1982-, et al.
(författare)
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Constellation of small quick-launch and self-deorbiting nano-satellites with AIS receivers for global ship traffic monitoring
- 2011
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Ingår i: 2nd Nano-Satellite Symposium, Tokyo, Japan, Mars 2011.
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Konferensbidrag (refereegranskat)abstract
- Since December 2004 the International Maritime Organization's International Convention for the Safety of Life at Sea requires that Automatic Identification System (AIS) has to be implemented on all international voyaging ships with gross tonnage of 300 or more tons, and on all passenger ships regardless of size. This stems from the need of collision avoidance, search-and-rescue operations and other maritime purposes. Ground-based AIS receiving station usually cannot cover ships over the horizon, but with space-based AIS signal receivers, the global ship monitoring became possible, providing data service for maritime administrations, cargo liners, and even navies. Since 2007, a number micro-satellites and nano-satellites have been launched for technical demonstration in this respect. However, at present the space-based global AIS data service is not fully operational and international cooperation is limited. In this paper, a constellation of 3 self-deorbiting nano-satellites, with a mass equivalent to 3U cubesats, carrying AIS receivers is proposed to complement the existing systems. The feasible study presented here showed that this mission can be realized at very low cost, and quick-launched. Three other important features of the mission are: international cooperation, making a practical use of smaller nano-satellites and taking the responsibility for deorbiting the satellites at the end of mission. It is also the hope that this mission will become a milestone that marks the maturity of smaller nanosats, and give the "student satellite" projects around the world a new dimension for real application and sustainable business application.
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