As a novel alternative for conventional seed disinfection methods, a new design has been proposed in this report using a surface dielectric barrier discharge (SDBD) fractal electrode. The discharge mechanism for this electrode is a diffuse microdischarge under AC or short-pulsed DC mode operation. In this way, cold plasma could be generated that is applicable for seed disinfection. Furthermore, the electrodes were designed to be part of a proof of concept fluidized bed reactor with a reactor size of 10×20×20[𝑐𝑚] for disinfecting cabbage seeds with a diameter of 2𝑚𝑚. Because of this application, the efficacy of seed decontamination using plasma with its generated reactive agents was discussed. The used gas mixture in which the electrodes created plasma was ambient air without increased humidity. This means that the main reactive agents for sterilisation are reactive oxygen species (RON) like ozone (O3) and reactive nitrogen species (RNS). The electrical and physical parameters required to make cold-plasma were investigated to come up with a proper design for the electrode. From this theoretical analysis, five different initial designs emerged. The analysed designs include a wire-to-wire, wire-to-sheet, multi-hollow DBD, fractal SDBD and a coplanar DBD fractal electrode. All electrode designs were made based on the state-of-the-art dielectric barrier discharge principle. Moreover, in the design consideration, different materials for the conductor and dielectric were discussed, mainly based on electrical properties, plasma generation and manufacturing possibilities were considered. Based on previously set trade-off requirements, together with the results of measured power and turn on voltage of the plasma electrodes, the best designs tested design for seed disinfection are the double-sided 5𝑡ℎ order Hilbert fractal with a 1.6 𝑚𝑚 barrier and the single-sided 5𝑡ℎ order Hilbert fractal with a 0.8 𝑚𝑚 barrier. ... Read more

The exponential increase in the number of microsatellite launches over the past decade has generated a research gap within the realm of satellite propulsion, needed to maintain the orbit of such satellites and hence increase their lifetime. The research towards the miniaturisation of propulsion systems has hence steadily gained traction within universities and other educational institutions. With this in mind, in collaboration with the Else Kooi Laboratory (EKL), the TU Delft is developing a novel resistojet thruster with integrated Titanium heaters based on Micro-Electromechanical Systems (MEMS) technology, called the Low Pressure Micro-Resistojet (LPM). Using their resistance, the newly fabricated thruster chips were characterised as temperature sensors for the range of 40-140 C. A new interface was designed and manufactured out of Teflon, allowing for the necessary mechanical and electrical connections to the thruster and adhering to Delfi-PQ system requirements. A maximum thrust of 0.37 mN was found during preliminary testing. ... Read more

With the price of launching satellites remaining high, many companies and universities are turning towards smaller satellites as more affordable options. This requires the miniaturisation of their different components, including the propulsion subsystem. At TU Delft, Vaporising Liquid Microthrusters (VLM) are being developed, with the latest iteration being a new generation Micro-Electromechanical System (MEMS) design. In this work, the updated design of this microthruster is remanufactured and prepared for future operational validation, heat transfer and instabilities studies. This is done by simplifying the manufacturing process, creating a testing interface, and performing measurements and extensive experimental characterisation of the thruster and test set-up. The newly-created interface allows for the study of heat transfer efficiency and convection heat transfer coefficient (HTC) from the silicon wall to the propellant, as well as multiple ways to study the instabilities in the system. One interface + thruster assembly was shown to survive to at least 180 °C temperature and 6-7 bar relative pressure. On the manufacturing side, the fabrication process was streamlined by reducing the number of steps by 13%, most significantly by the use of a soft photolithography mask instead of a hard silicon dioxide one. The deviations in horizontal dimensions are in the same order of magnitude as the ones obtained by the previous student working on this project, and lower than other previous attempts at the Faculty of Aerospace Engineering. The etching process encountered some difficulties, leading to inconsistencies in the feature depth between wafers. Across wafers, etching rate deviations as large as 8% were observed. Within the final production wafer, the range of deviation from the design values on throat depth was from +3.5% to −16.5%, showing a measurable higher etching rate at the edges of the wafer than in the centre. Recommendations were given on which features’ depths are most important to be measured, in order to increase the confidence in the predicted values. With these results, future researchers are ready to use the produced thrusters and testing interfaces. It is recommended to continue with the experimental studies, especially by measuring the heat transfer efficiency, thrust levels, HTC, and by studying any instabilities that could appear. ... Read more

Board-level reliability (BLR) looks at the reliability problem in the package and PCB interconnection, which is an important topic in microelectronics. The current criterion in the BLR test is to look if the connection is open, which can only detect the failure and there is no available method that can detect the degradation of the solder joints. This project mainly focuses on the degradation process of solder joints in board-level vibration tests and thermal cycle tests.

Special methods and test programs are developed tailored for two test vehicles, and some of the test results are collected and analyzed. Assisted by the failure analysis technique, the physical change of solder joints can be observed.

Findings in this study show the parameter shift during the solder joint degradation and also the mathematic model that describes the relationship between the crack of the solder joints and resistance increment.
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Propulsion systems capable of providing attitude and orbit control are an essential part of small satellites. In particular, Micro-Electro-Mechanical Systems (MEMS) Vaporizing Liquid Micro- thrusters (VLM), using water as a propellant, meets the requirements for launch-safety, simplicity and cost. Moreover, MEMS technology also enables the integration of sensors to fabricate smart thrusters. This thesis reports the design and fabrications of a smart vaporizing liquid microthruster for the applications in small satellites. The thruster is fabricated with a conventional anodic bonded silicon-glass wafer stack with a glass capped microfluidic channel but the novelty here is that in-channel heaters and sensors on the glass wafer are combined with on-channel heater and sensors on the silicon wafer. For example, an on-silicon piezo resistive pressure sensor is combined with an in-channel temperature sensor. To enable close proximity and stacking of heaters and sensors, a combined front-side/back-side silicon wafer processing is applied.
Furthermore, the on-silicon heater is built in a recess on the silicon wafer to minimize thermal resistance between heater and channel. The modular designed layout allows the integration of different sensor / heater combinations in the wafer stack to meet an application specific thruster performance, which enables cost effective flexible manufacturing. A preliminary characterization was performed which showed that integration of all designed modules was successful. The proposed fabrication process could therefore be a fabrication platform for VLMs.
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Small satellites require efficient propulsion systems for attitude and orbit control. This thesis focuses on the development and characterization of two distinct types of micro-resistojet thrusters, namely Vaporizing Liquid Micro-resistojet (VLM) and Low Pressure Micro-resistojet (LPM). Both concepts are developed at TU Delft and are designed to use water as a propellant, conforming to launch-safety, simplicity, and cost-effectiveness criteria.
In VLM, liquid water is vaporized and accelerated through a convergent-divergent nozzle. In contrast, LPM operates by reducing water vapor pressure to below 300 Pa and then accelerating it through expansion slots under a rarefied flow regime. Both types of thrusters are built on Micro-Electro-Mechanical Systems (MEMS) chips to accommodate the size constraints of nano- and pico-satellites.
The thesis introduces refined designs for both VLM and LPM thrusters. Specifically, the VLM design features an optimized nozzle shape and improved inlet flow, while the redesigned LPM assembly is more space-efficient. These modifications increase the thrust-to-size ratio for both thruster types.
The thesis presents a fabrication process for these thrusters, employing an anodic bonded silicon-glass wafer stack with a capped microfluidic channel. Fabrication was executed at the EKL lab, using a simplified manufacturing process that is detailed within the report.
Post-fabrication, the thrusters underwent mechanical and electrical characterization. The results indicate incremental improvements in both design performance and manufacturability. The new VLM design yielded a 15% increase in thrust efficiency, while the new LPM assembly reduced the occupied volume by 30%.
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Airspeed information plays a crucial role in the takeoff, flight, and landing processes in animal flyers and aerial vehicles. Among the aerial vehicles, Flapping Wing Micro Air Vehicles (FWMAVs) represent the novel engineering approach of learning and mimicking animal flyers in the past two decades. A few prototypes of various sizes and functionalities of FWMAVs have been developed by MAVLab in the TU Delft Aerospace department since 2005. For these small and lightweight platforms, stable control under disturbances remains a challenge, and could further benefit from integrating effective airflow sensing into control system design.

Current commercial products are either not suitable due to size, weight, and power (SWaP) restrictions of the drone platform, or have very limited low-speed sensitivity. Therefore, to facilitate this, this thesis aims to develop a MEMS-based capacitive airflow sensor for a miniaturized and low-power implementation. Inspired by the filiform hair structure of arthropods, the sensor design comprises two key parts: the hair structure, whose displacement is governed by the drag force induced by the incident airflow, and the sensing base, located at the hair structure's base, which translates the structural displacement into a change in capacitance. The sensor exhibits the capability to sense airflow in one dimension and can be further adapted for omnidirectional sensing.

This thesis predominately focuses on the design and reliable fabrication of the sensing base. It is comprised of a suspended membrane supported by corner beams, supplemented by a pivoting dimple and anti-stitching dimples to facilitate robust hair movement and ensure optimal sensor functionality. The sensing base is fabricated at the TU Delft EKL cleanroom facility, equipped with sophisticated machinery that enables fabrication at micro and nano scales. Furthermore, the membrane suspension is achieved through the implementation of Vapor HF etching of a sacrificial layer beneath the membrane.

In conclusion, the devised sensors aspire to optimize flight control for FWMAVs within the constraints of SWaP, by drawing profound inspiration from the intricate workings of nature. ... Read more

Since the unravelling of the Covid-19 pandemic, studying methods of virus inactivation have become more important than ever. Many studies focus on the chemical and optical methods of inactivation. Very limited work has been carried out in studying the electrical methods of virus inactivation. The work presented in this thesis attempts to pioneer a study that examines the effect of electric fields generated by micro-electrodes on the survival of the surrogate of the SARS CoV-2 virus.
For this purpose, electrodes with 7 different geometries were micro-fabricated and characterized. A liquid suspension of the phi-6 bacteriophage (a surrogate of the SARS virus) was tested on all the different electrodes with different input voltages, frequencies and medium parameters.
The study showed that the treatment on specific electrode designs tailored with specific voltage and medium parameters showed a decrease in the virus titer ranging from half a log to a maximum of 2 logs. These results are promising for the development of products like electric facemasks, micro-filters and m-TAS systems. ... Read more

This thesis investigates the all-copper fine pitch bonding process with photoimageable underfill. NanoCU paste is used as interconnect material. A bi-layer photo resist structure is manufactured and lithographic stencil printing is used to apply nanoCu paste. A new underfill injection method is realized by using epoxy resin based photo resist as underfill layer. Adhesion of sample is extensively enhanced. Various bonding methods are developed including using AML bonder and Tresky pick-and-place bonder. Electrical measurements for sintered nanoCu interconnect are conducted, sheet resistance and contact resistance are studied. ... Read more

Today’s cars are undergoing the greatest transformation the industry has seen. Power MOSFETs play a crucial role in making electronics more energy efficient by driving down switching losses and Rdson using a combination of next-generation trench technology and ultra-thin dies. Power MOSFET dies are becoming larger ( > 5 X 5 mm ) and thinner ( < 50 μm ) to meet the high performance lifetime requirements of the automotive industry. The high aspect ratio and the new chip designs with trench technology offer challenges for assembly, packaging and testing.

The majority of the research performed in the past, aimed to reduce the risk of die crack by improving equipment and process strategies in back-end semiconductor processing. This thesis study aims at improving die
strength from a front-end approach (device fabrication process) by making dies stronger to stress from die frontside. New chip designs are presented with new metal layer layouts for improved stress distribution. Materials like polyimide are investigated as new die top material for mechanical strengthening of die frontside. Key factors which influence die strength like trench-metal interaction, wafer stress and warpage are also analyzed in this thesis report.

In this study, ultra-thin power MOSFET dies are realised on 100 mm diameter silicon wafers with dimensions of 6 X 3 X 0.050 mm. These dies are mechanical equivalent in design, robustness to commercial trench power MOSFETs. The processed wafers are grinded from the backside to realise 50 μm thin wafers which are then sawned to obtain singulated dies. The strength of the dies are characterized by three-point bending tests and analyzed using probability plots for weibull distribution. ... Read more

The development of fifth-generation (5G) technology is the beginning of a rapid transition in the world of wireless communications. Gbps data rates, minimal latency, and good connectivity are the ultimate aims of 5G. To achieve them, 5G systems employ the mm-Wave frequency band which has a frequency range above 24GHz and so allows for higher bandwidth and gigabit wireless services. Because the size of the antenna elements and their spacings are so small in mm-Wave, massive antenna arrays in the base station may fit into a smaller area while yet providing high gain. However, the problem with the mm-Wave integrated antenna array system is the excessive heat generated per unit volume as there is not enough surface area to dissipate heat. Thermal management of the antenna system is very important as it affects the reliability and lifetime of the electronic components in the system. Both active and passive cooling strategies have been employed with passive cooling being the cost-effective and energy-efficient solution. Heatsink antennas can enhance the cooling capacity by providing dual functionality in terms of both thermal and electromagnetics. Traditionally, most of the works on heatsink antennas are focused at lower frequencies and a few at the mm-Wave frequency range. However, proper mm-wave thermal modeling in active integrated antennas is missing and there isn’t any research on the performance of heatsink antennas in array designs. This thesis work aims in designing and optimizing a heatsink antenna operating at 28 GHz to achieve dual functionality. The second aim of the thesis is to develop an appropriate thermal model for the designed antenna. Following the conduction-based simulations depending on assumed heat transfer coefficients, proper thermal modeling with appropriate beamformer chip characteristics and a CFD-based natural convective simulation setup has been developed without the assumption of a heat transfer coefficient. Optimal heatsink antenna dimensions are chosen based on the electro-thermal performance. Then, the selected antenna has been used in 1D and 2D arrays. Finally, a comparison study has been made with that of the conventional patch antenna. The results obtained have shown that both 1D (1x8) and 2D (4x4) heatsink antenna arrays can achieve a better heat dissipation by lowering the junction temperature of about 10-20 degrees Celsius (for the investigated cases) with higher realized gain and similar side lobe level compared to the respective patch antenna arrays. Furthermore, amplitude tapering of the heatsink antenna array achieved lower sidelobe levels which make this heatsink antenna a low-sidelobe and low-temperature alternative for the patch antenna array. ... Read more

Analyzing the different signaling pathways of cells is key in understanding the basic functions of the cells in all organic systems from algae to humans. Not only do they help solve our questions on how organisms function, they also allow for new cures to be explored. A large variety of these signaling pathways can be influenced by light and can, for example, stimulate or inhibit cell growth. This research thesis introduces a new lab-on-a-chip MEMS device to help with the cell signaling exploration with a focus on optical cell stimulation. From a culture of HeLa cells, the chip is able to separate individual cells into different chambers by means of microfluidics. These microfluidic channels are processed using SU-8 and place each cell above an LED. In total, each chip houses ten LEDs with four different wavelengths ranging from 450 to 850 nm. Each of these LEDs is individually addressable through an Arduino MEGA with a Matlab user interface. After an introduction into cell signaling, the thesis describes how the chip is build up from two silicon wafers and one glass wafer, and explores novel assembly methods like SU-8 wafer bonding and the use of apertures. ... Read more

Large scale industries like automobile, agriculture and poultry etc.. are in the need of a reliable technology for gas sensors. Till date various types of sensors have been developed for gas applications but the SiC gas sensing has been a recent trend. With increase study in MEMS technology, the SiC material is gaining importance for sensor applications. Although, Silicon Carbide has been the epitome of research in the field of semiconductors in past couple of years due to its commendable properties and resilience. And being one of most used semiconductor in the field of sensor applications lately, an extensive research is being done and proved that Silicon Carbide is one the best suited sensor material. But very little is known about the possibilities of porous silicon carbide and its applications. Since there is no extensive research available on porous Silicon carbide, this thesis aims at it to show how silicon carbide can be made porous, and the role of it in the gas sensor application. An in-depth study of the silicon carbide including its features, issues, and possible advantages and disadvantages. A detailed procedure on design and fabrication is presented along with various models and its parameters used to fabricate the sensor device. The design parameters, technical and economic feasibility of the device are discussed using the results from the experiments. ... Read more

Wirebonding is an interconnection technology used to connect a chip to its LED package. It is currently not well understood which wirebond characteristics are best to tailor to prevent the failure of wirebonds. The focus of this thesis is to understand the physics-of-failure of wirebonds via an experimental approach. Therefore, an experimental setup is designed which can accurately measure the resistance of the wirebond samples by four-wire resistance measurements. Furthermore, Finite Element simulations are done to understand the physical nature of wirebond failure better.

Gold wirebonds with different loop geometries have been designed and made which are then subjected to temperature cycling. It is found through 4-wire experimental resistance setup that when a significant increase in resistance is reported, wirebond fatigue is imminent. Coffin-Manson based Finite Element
simulations show that stresses at the neck are higher than at the heel. In retrospect, when the wirebond samples are encapsulated in Silicone, there is an increase in the stresses at the heel. ... Read more

The prosthetic eye is created to help people who have lost an eye. The eye itself can only improve the appearance but without any optic function. In order to optimize the appearance, a prosthetic eye with a pupil that can dilate and contract according to the light level, just like the natural eye, is desired. The primary goal of this work is to develop and characterize a dilating pupil based on electrowetting. A droplet of an aqueous solution acts as a pupil.
Electrowetting-on-dielectric (EWOD) has become one of the most popular tools in variety of applications, from microfluidics to electrowetting displays. This thesis presents the design of a low-voltage electrowetting one-pixel display which can act as a pupil. Decreasing the maximum actuation voltage is the main objective and challenge of this project. Different methods to achieve this goal are presented in the thesis, including using dielectric materials with better dielectric properties and using electrowetting liquids with lower surface tension. Ways to minimize the effect of gravity are also investigated. Droplet-based simulations are introduced by two methods. The simulation results are used to sustain the design process and for comparison with the measurement results on the real devices. According to the theoretical background and simulations, a test device is designed and fabricated in the cleanroom of EKL, TU Delft. The fabrication details are described in this thesis. Finally, measurements on the fabricated device are performed under different conditions. The results are shown and discussed in the final conclusions. In general it can be said that an electronic dilating pupil based on EWOD seems possible. Some recommendations for the future improvement are made.
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A driver with high power factor, high efficiency and safety isolation are more attractive in the lighting application. Flyback is an ideal choice to be the power factor stage in LED driver. But one of the most difficulty in flyback topology is the energy stored in its leakage inductance. This part of the energy will introduce very high voltage spike on the main switch. A clamp circuit is needed.Passive clamp flyback converter is with few components and effectively clamping the voltage stress on transistor. But its switching frequency is limited by its switching loss. So the transformer volume in passive clamp flyback is very bulky. The aim of this project is to investigate high switching frequency Active Clamp Flyback converter with GaN transistor as power factor correction in lighting application.With the active clamp loop, the leakage inductance energy and snubber loss could be utilized properly to allow ZVS on switches under all line and load conditions and recycled to input source.So high switching frequency and high efficiency are both achievable.
In this project,specific control method, dead time length and conduction mode are properly designed for active clamp flyback converter as PFC in lighting application.The implementation of closed control loop is not included.A 50W (75V) prototype of active clamp flyback front end converter operation around 1MHz with GaN transistor as Power Factor Correction stage in lighting application is developed to verify the analysis. ... Read more