This thesis focuses on the development and characteristics of a resonant sensor based on MEMS, which is used for real-time measurement of blood viscosity. The research mainly concentrates on the non-Newtonian fluid behavior related to immediate medical diagnosis. To understand the rheological properties of human blood, including its shear thinning characteristics, Preparation of blood mimicking fluid,we conducted a comprehensive literature review. Based on these insights, we prepared a  blood blood mimicking fluid using xanthan gum and a water-glycerol mixture to replicate the shear-dependent viscosity observed under physiological conditions. The sensor operates by monitoring the changes in its resonant frequency and quality factor when interacting with the fluid, and captures the mechanical response through impedance analysis and Doppler vibrometry. The rheological behavior is modeled using the power law method, allowing the extraction of viscosity over a range of shear rates. Experimental results demonstrate the sensitivity of the system to changes in fluid viscosity, verifying its potential for low-cost, compact, and rapid diagnosis in portable or clinical settings.

Neurons are fundamental to cognitive and motor functions, relying on intricate electrical and chemical signaling. However, neurological diseases such as Parkinson’s, Alzheimer’s, and Amyotrophic Lateral Sclerosis impair neural function, posing a growing challenge due to aging populations and limited regenerative capacity of the nervous system. Advances in induced pluripotent stem cells (iPSCs) have enabled human-derived neuronal models for disease study, while neural interfaces, particularly microelectrode arrays (MEAs), facilitate electrophysiological investigation both in vivo and in vitro.

This thesis explores the use of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), a conductive polymer with mixed ionic-electronic conductivity, as a superior neural interface for in vitro neuronal cultures. The study addresses three key objectives: (1) elucidating the electrochemical mechanisms underlying PEDOT:PSS’s performance, (2) validating its biocompatibility and functionality in recording neuronal activity, and (3) establishing protocols for neuronal differentiation and maturation on PEDOT:PSS substrates.

First, a scientific literature search was performed to understand the current standing of PEDOT:PSS as a neuronal interface, exploring the different applications and approaches scientific peers have established, and understanding the working mechanisms of the conduction behind their work. This was complemented with the practical experience with PEDOT:PSS, showcasing its biocompatibility and methods to improve conductivity.

Secondly, neuronal recordings in vitro were made to assess the performance of a custom-built PEDOT:PSS-based MEA and the meaning behind the electrophysiological recordings. Data acquisition, pre-processing, and analysis are discussed to understand the results obtained. Key findings include the performance success of the MEA, while also explaining the shortcomings of the implemented processing algorithms.

Lastly, a motor neuron differentiation protocol from iPSCs was established to further investigate the role of PEDOT:PSS in such context for later studies. The success of the protocol was assessed by morphological, functional, and immunostaining assays.

Future directions include optimizing conductivity through acid treatments, integrating PEDOT:PSS into motor neuron maturation protocols, and exploring electrical stimulation and 3D culture systems. This work contributes to the development of advanced bioelectronic tools for neuronal models and engineering.

During most cardiac surgeries, a Cardiopulmonary bypass (CPD) is used. This is a machine which takes over the respiration and circulation functions of the heart during surgery. However, the blood supply to the heart and thus the supply of oxygen and nutrients, will be cut off when this occurs. This is also known as myocardial ischemia, which can lead to damage to the heart tissue and could even be fatal. Therefore, it is of paramount importance to detect ischemia before it causes irreversible damage.

There are several parameters that can indicate ischemia, including pH, oxygen and lactate. This work focuses on measuring the pH level of the heart tissue, since this could be measured noninvasively and is relatively simple. In order to get a clear picture of the consequences of ischemia throughout the heart, the pH level should be measured at different locations. To achieve this an optical fluorescence sensor is designed. This sensor consists of a sensor layer, two LEDs and an optical fibre connected to a spectrometer.

The fluorescent indicator dye used in the sensor layer is 8-Hydroxypyrene-1,3,6-trisulfonic acid
trisodium salt (HPTS). This fluorescent dye has two excitation peaks, one at 405nm and one at 470nm and two emission peaks one at 440nm and one at 515nm. These different excitation and emission bands enable ratiometric sensing which improves accuracy and sensitivity. This is due to the fact that the intensity of the fluorescent emission at 515nm is directly proportional with the pH level, where the intensity of the fluorescent emission at 440nm is inversely proportional to the pH level. By taking the ratios of these measured intensities the pH can be determined.

The indicator dye is immobilized in a hydrogel which is thereafter deposited on a thin glass slide. This slide is placed above two LEDs which are matched with the excitation peaks of HPTS. Adjacent to the LEDs an optical fibre is placed to capture the fluorescent emission and direct it to the spectrometer which is connected to a computer. The designed sensor system shows a 5 fold increase in ratio of intensities over a pH range of 6.2-8.2, with a significant improvement in response time compared to other HPTS and hydrogel based pH sensors reported in literature.

Organ-on-a-chip (OoC) technology has revolutionized the biomedical research field by offering dynamic platforms which accurately mimic physiological environments of human tissue. This technology has become a promising option to study human biology in vitro, including disease modeling, drug screening and personalized medicine. Organoids, 3D cell cultures derived from human stem cells, represent a promising tool to investigate 3D tissue growth in vitro. However, integration of vasculature in these organoids remains a significant challenge. Establishment of vasculature is essential to enable significant organoid growth, allowing nutrient and oxygen supply and waste removal.

This report aims to develop a Pluronic F127 based hydrogel as a transient barrier in an OoC-platform that combines cell cultures of Vasculature-on-a-Chip and cortical brain organoids. This transient barrier separates the two cell cultures until sufficient maturation of the cortical organoid. Due to thermoreversible gelation, the Pluronic F127 hydrogel barrier can be removed from the barrier channel by a decrease in temperature. Pluronic F127 and di-acrylated Pluronic F127 hydrogels were synthesizes and characterized using rheometry, differential scanning calorimetry and degradation testing to determine the optimal Pluronic F127 hydrogel. Simultaneously, optimization of the OoC-platform was done by fabrication of the platform using Polydimethylsiloxane (PDMS).

It was shown that the OoC platform for Vascularized Organoids-on-a-Chip could effectively by fabricated using PDMS molding. This was achieved through both PDMS-PDMS and PDMS-glass bonding. Pluronic F127 hydrogels were shown to be a viable option to function as a transient barrier for Vascularized Organoids-on-a-Chip. Pluronic F127 hydrogels effectively blocked fluid flow through the barrier channel for seven days. To increase this time, di-acrylated Pluronic F127 was synthesizes. A degree of acrylation of 57% was achieved. This was shown to be insufficient to significantly increase the longevity of Pluronic F127 hydrogels.

Further research needs to be done to find the optimal synthesis and photo-polymerization conditions of di-acrylated Pluronic F127 hydrogels. Ideally, di-acrylated Pluronic F127 hydrogels exhibit a low degradation rate while maintaining the thermoreversible properties of Pluronic F127 hydrogels.

Electronic interfaces, particularly microelectrode arrays (MEAs), are crucial for studying electrophysiological processes in the body, with applications ranging from implants to deep brain simulators. In neuroscience, they play a vital role in exploring neuronal cell distribution and behaviour, as well as disorders like epilepsy and Alzheimer’s disease. However, electrophysiological recordings have limitations, that have led to the exploration of optical approaches like calcium imaging. To address the shortcomings, a promising strategy involves integrating electrophysiology and optical methods for simultaneous cellular activity measurement, capitalising on their combined temporal and spatial resolution. The challenge lies in developing fully transparent MEAs to overcome the limitations of traditional opaque electrodes.
Graphene’s versatile properties, spanning from electrical conductivity to mechanical flexibility, position it as an ideal material for transparent and flexible electronics, particularly in neural recording and stimulation. Due to these properties, graphene MEAs (gMEAs) allow integration with various optical techniques, overcoming limitations associated with traditional opaque MEAs.
In this project, we designed and fabricated a transparent gMEA, intended to perform electrical signal recordings and optical voltage mappings simultaneously from photostimulated optogenetic cell lines. The design allows for photostimulation from a source beneath the gMEA, while enabling unobstructed optical measurements from above. The electrodes were crafted from multilayer chemical vapour deposition (CVD) graphene, chosen for its transparency and favourable electrical properties. Quartz and sapphire were evaluated as potential substrates for the device. After demonstrating the synthesis of multilayer graphene was possible on both substrates, quartz was selected as the preferred material due to its resistance to graphene delamination.
Characterisation of the gMEAs was done using various techniques, including optical transmittance (OT), electrochemical impedance spectroscopy (EIS), and measurements of the signal-to-noise ratio (SNR). The stability of the gMEAs was also assessed by immersing the devices in cell culture medium and with ageing tests performed in PBS. Initial electrochemical characterisation of the gMEAs exhibited promising signal detection despite a relatively high baseline noise of ∼ 23 μV . In comparison, commercially available MultiChannel Systems MEA (60MEA200/30iR-Ti), showed a lower baseline noise (∼ 4 μV ), but gMEAs achieved comparable signal sensitivity. EIS of gMEAs revealed an impedance at 1 kHz ranging from 3.2 to 9.89 MΩ, largely surpassing values in other studies. However, when area normalised, the impedance remained comparable to reported values. Stability tests identified issues related to the permeability of the encapsulation layer and degradation of molybdenum structures, causing large variations in the SNR and EIS measurements after exposure to liquid media.

In the emerging research field of bioelectronic medicine, it has been indicated that neuromodulation of the Vagus Nerve (VN) has the potential to treat various conditions such as epilepsy, depression, and autoimmune diseases. In order to reduce side effects, as well as to increase the effectiveness of the delivered therapy, sub-fascicle stimulation specificity is required. In the electrical domain, increasing spatial selectivity can only be achieved using invasive and potentially damaging approaches like compressive forces or nerve penetration. To avoid these invasive methods, while obtaining a high spatial selectivity, a 2 mm diameter extraneural cuff-shaped proof-of-concept design with integrated Lead Zirconate Titanate (PZT) piezoelectric ultrasound transducers is proposed. For the development of the proposed concept, wafer-level microfabrication techniques are employed. Moreover, acoustic measurements are performed on the device, in order to characterize the ultrasonic beam profiles of the integrated PZT-based piezoelectric ultrasound transducers. A focal spot size of 200 μm by 200 μm is measured for the proposed cuff. Moreover, the curvature of the device leads to constructive interference of the ultrasound waves originating from multiple piezoelectric ultrasound transducers, which in turn leads to an increase of 45% in focal pressure compared to the focal pressure of a single piezoelectric ultrasound transducer. Integrating piezoelectric ultrasound transducers in an extraneural cuff-shaped design has the potential to achieve high-precision ultrasound neuromodulation of the Vagus Nerve without requiring intraneural implantation.

Demand for high density, high bandwidth, and low power Integrated Circuits (ICs) is rapidly increasing even as Moore's Law is starting to plateau. Among the new wave of technologies that are meant to continue the prevalent trend of semiconductor device scaling, 3D System Integration promises many advantages over traditional single-planar designs. This technology enables designers to stack multiple dies and unlock new functionality by reducing the footprint of the final device package. Using 3D Integration, multiple different types of chiplets (Digital IC, Analog IC, MEMS) can be integrated into a single package, potentially bypassing an expensive move to a newer process node and unlocking even more functionality from the same package.

These downscaling issues are not limited to traditional CMOS technologies but extend to Quantum Computers. Due to the highly heterogeneous nature of Quantum ICs, and especially their requirement of low qubit decoherence noise, we require high-density connections from the Qubit layer to the Microelectronics Control layer while maintaining appropriate spacial separation between the two. In this project, the qubit layer is comprised of Diamond Colour Centers in a Photonic IC with other optical components such as SNSPDs, and MEMS switches. On the other hand, the microelectronics control layer is a Cryogenic CMOS chip.

The main goal of this project is to design an Interposer and related technologies like Through Silicon Vias (TSVs) and Microbumps to successfully integrate these two chiplets in a single 3D assembly. We conduct thermal analysis of multiple 3D assembly designs using Finite Element Modelling to derive optimum fabrication specifications. Subsequently, fabrication recipes are developed and optimised for TSV etching, coating, and patterning with superconductive sidewall liners. Recipes are also developed to fabricate Indium Microbumps using techniques like evaporation, liftoff, and atmospheric reflow. Utilizing these microbumps, we conduct cold-compression flip-chip experiments. Finally, we establish cryogenic measurement setups to electrically characterize these fabricated devices.

The mm-wave operational band (24-30 GHz) is becoming increasingly important for various practical applications. However, at such high frequencies, the issue of propagation losses arises, emphasizing the necessity for these systems to achieve high radiation efficiency. Dielectric Resonator Antennas (DRA) are promising candidates to replace traditional radiating elements like patches since they do not suffer from conductor losses and have a radiation efficiency of over 90% when suitably excited. Additive manufacturing has emerged as a promising technique for producing DRAs due to its numerous benefits, such as the ability to fabricate complex shapes and structures, rapid prototyping, and reduced waste. Additionally, 3D printing can enable the incorporation of varying permittivities within the DRA, further enhancing its performance. The influence of such permittivity profiles in DRAs, particularly in finite phased array setups, is yet to be thoroughly investigated. It is important to understand the impact of this technique on the mutual coupling, cross-polarization, and scanning performance of the array. In this work, we discuss the theory behind the radiation characteristics, the modelling of the DRA designs and the analyses of these designs based on performance criteria such as bandwidth, coupling, gain, cross-polarization and axial ratio bandwidth. This thesis demonstrates for the first time, to the best of author’s knowledge, that the incorporation of permittivity profiles in mm-wave DRAs can improve the bandwidth by 7%, reduce the cross-polarization (at broadside) by around 3 dB and improve the axial ratio bandwidth by around 10% compared to single-permittivity DRAs. Furthermore, it is also shown that in an array environment, the active S-parameters of the elements are better matched across a wider frequency band, upon scanning from 0 to 45 degrees, when a permittivity profile is used.

Several promising photovoltaic (PV) concepts are supported by transistors. Along with the growth of PV capacity in the urban environment, issues related to partial shading highlight the interest in more shade-tolerant PV systems. An example of technologies improving a PV module’s energy yield under partial shading is the submodule power optimizer, including a power converter that operates sub-module maximum power point tracking (MPPT). Alternately, reconfigurable PV modules enable dynamic reconfiguration of the solar cells’ interconnections to optimize the energy yield depending on the irradiance distribution. Both technologies make use of transistors as fundamental components. Integrating the latter into the solar cell wafer might be a solution for cost reduction and reliability improvement and thus support such concepts. Moreover, that kind of transistor integration can have applications in solar cell-embedded electronic and digital devices.

In this thesis, a lateral metal-oxide-semiconductor field-effect transistor (MOSFET) and an interdigitated back-contacted (IBC) solar cell are integrated into the same crystalline silicon (c-Si) wafer. A combined process flow is developed to manufacture both components with a minimum number of additional steps compared to single-component manufacturing processes. One criterion for this is a high similarity in the design of the device. Therefore, a tunneling oxide passivated contact (TOPCon) solar cell structure is used, involving polycrystalline silicon (poly-Si) at the device’s backside. Similarly, the MOSFET’s gate is made of a highly doped poy-Si film. Ion implantation is used as a common doping process.

Both solar cells and transistors that were manufactured with the combined process flow are first characterized separately. The highest efficiencies obtained for n-type and p-type solar cells are 20.29% and 20.66%, respectively. This is achieved thanks to multiple combined passivation approaches including TOPCon, wet poly-Si etching, a front-side hydrogenated amorphous silicon (a-Si:H) film, and hydrogenated silicon nitride on both sides of the device. Different MOSFET layouts are explored to make the device able to handle relatively large currents. It is found that introducing several drain-source pairs in parallel is more efficient than increasing the channel width to reduce the on-resistance. The on-resistance is further minimized with a gate length reduction and wet chemical poly-Si etching. As expected, the comparison of PMOS and NMOS (MOSFETs built on n-type and p-type wafers, respectively) shows better on-performance for the latter. A minimum on-resistance value of 1 Ω is then obtained. However, a higher leakage current consistently seems to come along with reduced on-resistance; i.e., higher on-performance is coupled with lower off-performance. Finally, experiments are performed combining both components. Under illumination, the MOSFET exhibits lower off-performance due to the photovoltaic effect. However, this effect does not affect the on-performance of the component. The monolithically connected components exhibit I-V characteristics that depend on the applied MOSFET’s gate potential. In the on-mode, the solar cell maintains more than 95% of the conversion efficiency compared to the efficiency measured with the same solar cell without the transistor. However, a non-zero current is obtained in the off-mode, exhibiting low transistor blocking capability. Nevertheless, the large difference in characteristics obtained between the on- and off-modes proves the feasibility of integrating a solar cell and a transistor on the same substrate with a minimum number of additional processing
steps.

Atrial fibrillation (AF) is the most commonly occurring arrhythmia in clinical practice and can have a significant impact on the current and future wellbeing of the patient. By placing an unipolar sensor array directly on the epicardium during an open-heart surgery to measure the electrical activity of the atrium, more insight about this disease can be obtained. One method to obtain these insights is by applying common signal processing models to the measured electrogram (EGM). This thesis further investigates this application and argues why the most common array processing signal models are fundamentally incompatible with this application and proposes two different signal models to rectify the identified discrepancies. The proposed signal models are subsequently analyzed and the conclusion is drawn that both novel signal models better fit the EGM signals, but one signal model in particular shows promising results. This potential is exemplified by using this signal model to formulate a novel LAT estimation technique that can compete with state of the art LAT estimation methods in terms of estimation accuracy and execution time. This result shows the potential of the proposed signal model and opens the door to explore more applications in the future.

Cardiorenal Syndrome (CRS) is a multi-organ disease characterized by a reciprocal pathological interaction between the heart and kidneys during acute or chronic injury. Yet, a complete understanding of the underlying bi-directional pathophysiological mechanisms is lacking, hence obscuring effective diagnostic strategies, patient stratification and adequate administering of intervention therapies. Thus far, CRS has only been modelled in in vivo animal models, which are inherently limited in terms of experimental control and translatability of results to humans physiology. This underlines the need to develop more advanced in vitro models that accurately recapitulate the complex inter-organ cross talk responsible for the onset and progression of CRS. However, to date no such disease model system has been reported.

This project set out to design, develop and validate a microfluidic set-up, which would then enable the investigation of CRS in a three-dimensional environment. To that end, a theoretical framework covering all aspects related to Multi-Organ-On-Chip (MOoC) design was developed. This framework then formed the foundation for an extensive list of requirements to establish an ideal microfluidic set-up for a heart-kidney disease model. Various conceptual circuit designs were proposed and evaluated on the basis of the set requirements and their associated priority.

By executing feasibility studies, simulating computational fluid dynamics, designing specific organoid inserts and eventually setting-up the proposed microfluidic circuits, a better understanding of the technological and biological challenges to be addressed was obtained. Proof-of-principle experiments were promising, but more experimental iterations with a focus on in-depth biological tissue characterization are required to further evolve and fully validate the
proposed cardiorenal model. Pressing issues entail establishing physiologically relevant scaling ratios, reducing required medium volume and identifying the exact disease models to incorporate once the physiological organoid system is functional and has been validated.

With the high-speed development of the Internet of Things (IoT), powering such a massive number of wireless IoT sensors with chemical batteries become more and more unpractical. To make the IoT sensors self-sustained, Piezoelectric Energy Harvesting (PEH) technology provides an excellent solution to power the devices with a relatively long service time. By harvesting the ambient mechanical vibrations, PEH could generate a stable power source without wind or light.

Currently, the famous bearing manufacturer, SKF, collaborates with TU Delft to design a self-sustained smart IoT roller with PEH technology, which will be implanted in huge bearings, such as the bearing in the wind turbines. This thesis project is a feasibility study investigating the possibility of replacing the chemical battery with the Piezoelectric Energy Harvester in SKF's smart IoT roller, called Sensor Roller.

The objective of this project includes the system design of two generations of the prototype harvester. The first prototype concentrates on the properties of the piezoelectric material, while the second prototype focuses on the structure of the harvester. The design work consists of the raw data analysis of the target roller from SKF and the prototype construction and simulation in COMSOL Multiphysics. Besides, to make the results more reliable, two stages of the test with the practical components are made to study the harvester's performance under the actual working condition of the roller in the bearing. As a result, a tube shape Piezoelectric Energy Harvester with suitable materials and parameters is built. According to the simulation results, under a safe pressure level of the piezoelectric material, the proposed harvester achieves 8.1mW output power, which is enough for the loading sensors. The designed Piezoelectric Energy Harvester is being manufactured at present, and it is planned to be installed in the target roller to get the system-level test in the future.

In addition to the harvester, some rectifiers are designed and taped out to improve the performance of the proposed Piezoelectric Energy Harvesting system. Three rectifiers are made with the Silicon Carbide (SiC) process to obtain a high voltage and temperature tolerance: a Full Bridge Rectifier (FBR), a Passive Rectifier, and a Synchronized Switch Harvesting on Inductor (SSHI) rectifier. Meanwhile, another SSHI rectifier is made with the 0.18um Silicon BCD process that focuses on solving the cold-startup problem. Consequently, simulated with the real transducer of the proposed harvester, both the FBR circuit and the Passive Rectifier circuit with the SiC process achieve over 10mW output power, and the SiC SSHI circuit achieves 37.1mW output power. As for the cold-startup SSHI rectifier circuit, it successfully reduces the required open circuit voltage by 4x to start up the SSHI system from the cold state.

The results of this project show the great potential for applying the Piezoelectric Energy Harvesting technology to power the IoT sensors in the roller of bearing. Although some future works should be finished to build the commercial version of the energy harvesting roller, we are convinced that the fully self-sustained Sensor Roller with Piezoelectric Energy Harvesting technology will possibly show up in the near future.

Silicon solar cells account for about 95% of the total photovoltaic market share. Poly-Si passivating contacts are promising techniques enabling high performance c-Si solar cells with conversion efficiency over 26.0%. The highly absorptive nature of poly-Si materials makes the transparent passivating contacts attractive, such as poly-Si(O_x). However, the research of p⁺ poly-Si(O_x) passivating contacts on a textured surface with an in-situ doping nature is still missing. Therefore, in this thesis, the optimization of p⁺ poly-Si(O_x) carrier selective passivating contacts on double side textured wafers are given and the application in solar cells is demonstrated.
Firstly, the influences of different interfacial tunnelling oxides fabrication methods, nitric acid oxidation of silicon (NAOS-SiO_x), plasma assisted N₂O oxidation (PANO-SiO_x), and thermal oxidation (t-SiO_x) on the passivation of p⁺ poly-Si(O_x) passivating contacts are explored. It is found that Si⁴⁺ stoichiometry in the tunnelling oxide layer is an indicator for its quality. There is a positive correlation between Si⁴⁺ and SiO_x density. The t-SiO_x can be denser with higher Si⁴⁺ compared to its counterparts NAOS-SiO_x and PANO-SiO_x. And fewer boron dopants in-diffuse phenomenon can be observed in the t-SiO_x samples. Then, different intrinsic layer deposition approaches are explored. The intrinsic layer deposited by LPCVD results in higher iV_oc compared to PECVD counterpart. The enhanced iV_oc is given by suppressing the blistering which is caused by hydrogen accumulation at the interface between intrinsic layer and SiO_x. It is assumed that less hydrogen accumulation exists in intrinsic layer deposited by LPCVD. Next, p⁺ doping layer thickness is changed from 0 nm to 200 nm to observe its effect on the passivation quality. The optimum p⁺ doping layer thickness is found to be 100 nm with the highest iV_oc. After that, the hydrogenation process is introduced to enhance chemical passivation by coating SiN_x:H and performing forming gas annealing. The highest iV_oc with the standard hydrogenation process is 674 mV. In order to improve the hydrogen level of p⁺ poly-Si(O_x) passivating contacts, AlO_x:H inserted layer is used for the hydrogen reservoir together with SiN_x:H. It results in an improved iV_oc of 685 mV. It is assumed that the hydrogen in AlO_x:H diffuses into c-Si/p⁺ poly-Si(O_x) interface and enhances the chemical passivation.

Besides, metallization methods of p⁺ poly-Si(O_x) passivity contacts are also studied. There are two approaches to complete the metallization process. Firstly, with thin p⁺ poly-Si(O_x) passivating contacts, TCO is required to provide with the lateral and vertical carrier transport as respect to the carrier collection. However, it commonly brings with the TCO introduced sputtering damage. The iV_oc losses are 70-90 mV when TCO is sputtered on p⁺ poly-Si(O_x) passivating contacts. When the thickness of p⁺ doping layer is over 50 nm, sufficient lateral conductivity can be provided with thick p⁺ poly-Si(O_x) passivating contacts. Therefore, it can directly contact with metal which is the second method of metallization. However, when utilizing this metallization method, the metal induced recombinations need to be taken into consideration when contacting with p⁺ poly-Si(O_x) passivating contacts. Thus, the plot of J_o,total along with different metal fractions is fitted to extract J_o,metal of p⁺ poly-Si(O_x) passivating contacts with 100 nm p⁺ doping layer. When contacting with evaporated aluminum, the measured J_o,metal is around 91 fA/cm². In addition, after calculating, there is 24 mV iV_oc loss when p⁺ poly-Si(O_x) passivating contacts contacting with metal. It is smaller than the loss induced by TCO sputtering. Therefore, the thick p⁺ poly-Si(O_x) passivating contacts with 100 nm p⁺ doping layer directly contacting with metal is used as metallization method for the application in c-Si solar cell. In addition, after linear fitting and calculating, ρ_c between p⁺ poly-Si(O_x) passivating contacts with 100 nm boron doped layer and c-Si is about 23 mΩ· cm².

Finally, p⁺ poly-Si(O_x) passivating contact is applied in c-Si solar cells together with n⁺ poly-Si(O_x) passivating contact as front surface field. The poly-poly solar cell of the highest quality has the following electrical performance: V_oc is 648 mV, J_sc is 35.9 mA/cm², FF is 73.1% and η is 17.0%. A roadmap to realize 22% is given by addressing the bottlenecks of poly-Si(O_x) passivating contacts based c-Si solar cells.

Capillary self-alignment shows the potential to keep small components aligned using soft liquid contact when disturbed by external forces. Whilst this concept has been promising, mostly static situations have been investigated, making it unclear how a receptor-droplet-chip (RDC) configuration behaves dynamically and where its stability limits are.

The primary aim of this research was to determine the stability limits of such a configuration and explore its failure modes. Two non-linear analytical models simulate the situation and investigate the parameters exposed to the system. These models predict the relative lateral displacement of the chip and its tilt, which can predict when failure should occur. Results from Surface Evolver, a computational software, and experimental data from a laboratory setup validate these models. A shaker induced one DOF linear accelerations, and high-speed cameras observed these tests. The validated model was then used to investigate the effects of variables such as lubricant height, chip dimensions and acceleration magnitudes.

This project gives an insight into how a chip behaves dynamically on a liquid meniscus and was the first to investigate the tilt of the component during accelerations. The key finding is a stable region showing what amount of liquid results in reaching the highest possible acceleration without failure. Secondly, the models and experiments showed that smaller liquid volumes and chip sizes increase the attainable acceleration. Chips of L = 2mm were able to be accelerated up to a = 27g without failure, parts of L = 1mm even reached an acceleration of a = 35g at which the RDC configuration remained intact. Moreover, possible eigenfrequencies were observed, and the system could re-align at specific frequencies from a tilted pose. Therefore, this research has demonstrated that, under the right conditions, capillary interfaces can be useful to transport components under high accelerations.

In this thesis, the realization and qualification of an anechoic dome chamber for 5G antenna’s is discussed. As with audio, where no echoes or noise from outside is wanted when listening to music, when characterizing an antenna it must be prevented to get internal reflections or electromagnetic (EM) radiation from outside. For this reason, a measurement setup was simulated, using that setup, different absorbers were tested and characterized. And a Faraday cage shielding is designed and evaluated, to remove EM interference. To make the anechoic chamber physically possible, rebuilding the minidome was also required, so that the absorber and Faraday cage could be mounted on the inner wand of the dome. Eventually, a suitable test environment for 5G antenna’s is build. In the end, the assessment of the absorbing materials was completed, and the chamber achieved all requirements. Despite the space of improvement, the idea of building an anechoic chamber is successfully verified.

Myocardial ischaemia induced by cardioplegia is the most prominent risk during open-heart surgery. To achieve adequate protection of the cardiomyocytes during surgery, the cardioplegia must arrive at all cardiomyocytes. Local obstruction can lead to regional ischaemia. For surgeons and perfusionist, the arrested heart is a black box. They know how much cardioplegia they are administering to the heart. However, they do not know if cardioplegia is reaching all cells. This work describes which parameters can be measured during cardioplegia induced cardiac arrest and compares the methods used in the literature to detect these parameters. Following this, it is the goal to create a proof-­of-­concept sensor for the detection of myocardial ischaemia. A literature review indicated that a fluorescent optochemical pH sensor has the most potential. To be able to develop a proof-­of-­concept, optical, chemical, and medical knowledge needs to be combined. This is necessary to map what is required and what is possible for optochemical in vivo sensing. First, a framework is designed and used to select the best technique and material suited for this project. In this framework, the medical requirements and the resources available are combined. As a result, this thesis work will use a dual wavelength pH­-sensitive fluorescent dye encapsulated in a biocompatible hydrogel. In preparation for the proof-­of-­conceptsensor, multiple samples are fabricated and extensively tested to achieve the optimal sensing layer. Using the optimised concentrations, a proof-­of-­conceptsensor is created using a miniature reflection probe and an USB spectrometer. This proof-­of-­conceptsensor shows that it can measure the changes in pH and can be corrected for multiple interferences. It also shows the potential to be further miniaturised and to be used during cardiac surgery. Before this can happen, chemical optimisation of the sensing layer is needed, and the consistency of the sensing layer needs to be improved. However, besides this, the work succeeded in selecting an optochemical sensing technique and material which shows the potential to be used in cardiac surgery

Carrier selective passivating contacts (CSPC) have proven to effectively curtail the recombination losses emerging at directly metallised contacts of crystalline Silicon (c-Si) solar cells. CSPCs enabled using an ultra-thin interfacial tunnel oxide layer (SiOx) capped by a doped polycrystalline Silicon (poly-Si) layer also referred to as Tunnel Oxide Passivating Contacts (TOPCon) have resulted in efficiencies as high as 25.8%. This thesis project addresses the development of oxygen alloyed poly-Si (poly-SiOx) in combination with an interfacial oxide layer grown by dry thermal oxidation. The limited transparency of poly-Si based contacts brought on by high free carrier absorption (FCA) can be mitigated by the use of poly-SiOx based passivating contacts owing to their wider bandgaps which induce stronger band bending.
To begin with, poly-SiOx CSPC were optimised by determining the optimum thermal budgets for tunnel oxide growth and hydrogenation scheme. Tunnel oxide layers grown at 675 ͦC 6 minutes demonstrated very good passivation for p-type polished and n-type textured CSPCs indicated by their implied Voc of 709 mV and 711 mV respectively. For the p-type textured CSPC identified as the primary limiting factor when deploying in c-Si solar cells, a tunnel oxide layer grown at 675 ͦC 3 minutes in conjunction with a two-step annealing scheme showed a crucial enhancement in passivation quality with a final implied Voc of 687 mV.
The single side textured front back contacted (FBC) solar cell fabricated using the optimised p-type polished and n-type textured poly-SiOx CSPC recorded a conversion efficiency of 20.94% on a 4 cm2 screen printed solar cell. The reported efficiency is the maximum that has been attained so far for the configuration that uses a thermally grown tunnel oxide layer with poly-SiOx CSPCs. Effective carrier transport and carrier collection was illustrated by a fill factor (FF) of 79.6%. A Jsc of 37.91 mA/cm2 was recorded for the same. A comparison with a single side textured FBC solar cell that employed a tunnel oxide layer grown by nitric acid oxidation of Silicon (NAOS) revealed a superiority in performance by the thermally grown tunnel oxide layer resulting in better passivation and carrier selectivity.
Lastly, the optimised n-type textured and p-type textured CSPCs were implemented on a double side textured FBC solar cell. The two-step annealing scheme that showed beneficial results for the p-type textured CSPC was implemented within the FBC solar cell, leading to an implied Voc of 698mV post hydrogenation. It is worth mentioning that this is the highest value achieved until now for this novel cell architecture. Implementation of screen printing resulted in a final conversion efficiency of 19.38% on a 4 cm2 solar cell with a FF and Jsc of 77.89% and 37.65 mA/cm2 respectively.

Interdigitated back-contacted solar cell (IBC) is a successful high-efficiency solar cell concept. Without a metal grid at the front side, the metal shading loss is eliminated. However, the fabrication process of an IBC cell is much more complicated than that of a FBC cell. Within the PVMD group, two poly-Si carrier-selective passivating contacts (CSPCs) IBC cell fabrication methods were developed, namely Self-aligned and Etch-back method. These two methods require respectively to pattern the IBC rear side twice and three times to define the emitter and BSF area. In this project, a novel poly-Si/SHJ hybrid IBC solar cell design using tunneling recombination junction (TRJ) is proposed, which only requires one pattern step to define the emitter and BSF area, thus, significantly simplifies the flowcharts of IBC cells.
The main objective of this thesis is to demonstrate the novel poly-Si/SHJ hybrid TRJ IBC cell concept by fabricating such high-efficiency hybrid IBC cells. With the proposed hybrid IBC cell design, the BSF layers are deposited on the full rear side after the emitter patterning. Thus, a TRJ is introduced at the emitter ((p+)poly-Si). The carrier tunneling efficiency across the TRJ layers should be guaranteed. The BSF layers passivation quality is also crucial for hybrid IBC cell performance, and the shunting due to the full area deposited BSF layers should be limited as well.
The TRJ proof-of-concept was firstly demonstrated in FBC cells due to their easier fabrication processes. And different materials combinations of (i)a-Si:H, (n)a-Si:H and (n)nc-Si:H were used to form TRJ with (p+)poly-SiOx. Firstly, it was found that the existence of (i)a-Si:H is detrimental to the device performance, especially for the cell FF. Secondly, for cells without (i)a-Si:H layer, the cell performance was improved by replacing (n)a-Si:H with more conductive and low activation energy (n)nc-Si:H layer. At last, the TRJ with dual-n-layer, (p+)poly-SiOx/(n)a-Si:H/(n)nc-Si:H, was found to be most promising. And the cell FF decreases with (n)a-Si:H layer thickness. However, instead of only depositing (n)nc-Si:H, the (n)a-Si:H was kept for its better passivation ability than (n)nc-Si:H, as it is directly deposited on the c-Si surface at BSF in hybrid IBC cells.
Then the hybrid design with dual-n-layer was demonstrated and optimized regarding the passivation quality, TRJ efficiency and the Rshunt in IBC cells. We firstly demonstrated that poly-Si delivers better performance than poly-SiOx due to its lower resistivity. With 18 nm(at textured BSF)(n)n-Si:H, the (n)a-Si:H layer thickness optimizes at 3 nm in poly-Si/SHJ hybrid cells. The pitch width was also found to have an influence on cell external parameters as the number of fingers decreases with pitch width. The cell FF increases and the Jsc decreases with pitch widening. The best cell obtained in this project has 3/18 nm (n)a-Si:H/(n)nc-Si:H and a medium pitch width (650 μm). It has a Voc of 665 mV, a Jsc of 39.36 mA/cm2, a FF of 74.33% and an efficiency of 19.45%.

Cholangiocarcinoma (CCA) is a highly aggressive biliary tumor with a poor prognosis and limited treatment options. Various critical aspects of CCA development remain unclear. Lately, the dynamic process of epithelial-mesenchymal transition (EMT) was highlighted to play a crucial role in the fundamental mechanism of metastatic dissemination. However, in vitro EMT studies are mainly limited to conventional 2D models which lack in vivo tumor physiology. Recently, 3D organoid culture methods provide us new model possibilities. Therefore, our research aim was to establish a representative in vitro organoid-based epithelial-mesenchymal transition model in cholangiocarcinoma including its in vivo pathophysiology and tumor microenvironment. This study focusses on three different aspects of the tumor microenvironment regarding EMT activation in CCA organoids: 1.The effects of EMT promoting growth factors and culture media on EMT activation. Various growth factors are highlighted to play a crucial role in EMT activation in different cancer types. To study EMT activation in CCA, various growth factors were added to CCA organoids. We observed round shaped organoid structures consisting of single layered epithelium for all conditions. Additionally, gene expression levels of EMT related markers were increased for specific growth factor conditions. The use of various culture media combined with transforming growth factor β1 (TGF-β1) showed the most substantial differences in mRNA expression of EMT markers in branching medium (BM). Based on these results, specific growth factors and BM were used to find the optimal culture conditions to induce EMT. Although we did not find significant morphological differences between the various conditions, altered gene expression levels of EMT markers were observed after TGF-β1 and tumor necrosis factor alpha (TNF-α) treatment in BM. 2.The effect of the tumor extracellular matrix on EMT activation. The tumor extracellular matrix (ECM) is an important component of the tumor microenvironment that stimulates the malignant behavior of surrounding cells. The combination of CCA organoids and patient-derived ECM resulted in morphological changes. Cells with a polygonal shape adopted an irregular shape after TGF-β1 treatment. On top of that, our data revealed that patient-specific ECM and CCA organoids altered the gene expression of EMT related markers. 3.The effect of the interstitial fluid flow on EMT activation. The use of a microfluidic platform enabled us to study the effect of fluid flow on EMT in vitro. Cells formed organoid structures in the absence and the presence of a fluid flow. However, cells only migrated to the surrounding culture medium due to the presence of a fluid flow. When cells were seeded directly into the chip, cells formed a tube structure with protrusions growing outwards. The protrusions growth was accelerated by the addition of TGF-β1 and led to increased cell migration. Additionally, fluid flow conditions resulted in altered gene expression levels of EMT related markers. Our data suggest that fluid flow could potentially stimulate EMT in CCA organoids. Overall, our findings have demonstrated that growth factors, native ECM and interstitial fluid flow could be used to induce EMT in vitro. Indicating that the tumor microenvironment plays a crucial role in EMT and tumor progression. Our novel in vitro CCA organoid-based EMT model provides a foundation towards a more representative EMT in vitro model to unravel the underlying mechanism of CCA and its progression.

Carrier-selective passivating contacts (CSPC) have been proven to be effective in suppressing recombination losses at metal-silicon interface in high-efficiency crystalline silicon solar cells. The poly-Si-based CSPCs consisting of SiOX/poly-Si stacks are used in this thesis due to their compatibility with high thermal budgets. CSPCs with thin poly-Si layers are preferred since thicker poly-Si layers induce significant parasitic absorption at device level. The bifacial solar cell design could provide a higher energy yield than monofacial solar cells and largely reduce the consumption of metals such as silver, indium due to the contribution of reflected light. The objective of this thesis is to fabricate double-side textured copper (Cu)-plated bifacial poly-Si solar cells. It is achieved by developing thin poly-Si contacts, addressing the TCO sputtering-induced passivation damage, and optimizing the Cu-plating processes.
Firstly, the passivation of the poly-Si symmetric samples and solar cells was optimized. 16 nm-thick n+ poly-Si and 16 nm-thick p+ poly-Si symmetric samples with intrinsic layer grown through PECVD demonstrated good passivation quality indicated by their iVOC of 713 mV and 665 mV respectively. To further improve the passivation quality of the p+ poly-Si, the layer thickness and the doping gas flow ratios were varied. Best passivation was achieved for a solar cell precursor with 42 nm-thick p+ poly-Si layers. The optimum doping gas flow ratio was found to be SiH4-B2H6=20/15 sccm. The highest iVOC achieved was 692 mV.
TCO sputtering caused a severe passivation drop of ~90 mV in solar cell precursors. Post-deposition annealing treatments and 2-step TCO sputtering techniques were used to reduce such a passivation loss. However, it was challenging to reproducibly obtain solar cell precursors with good passivation quality before metallization step. The initial solar cell with double side TCO use showed cell parameters were: VOC 398 mV, FF 56.22%, JSC 30.55 mA/cm2 and η 6.85% (from n-side illumination).
To maintain a good passivation quality of the solar cell precursor, an 8 nm-thick MoOX buffer layer was introduced on top of the p+ poly-Si layer. This approach effectively reduced the passivation drop from 91 mV to 12 mV. However, the MoOX layer was observed to strongly react with the solution which was used for silver seed layer removal in Cu-plating metallization procedure. Different approaches were tested to obtain a well-plated p+ poly-Si side. As for the n+ poly-Si side, a TCO-free design was deployed. To ensure a good adhesion of the plated Cu fingers, a Ti/Ag (8 nm/192 nm) seed layer was employed before Cu-plating step. Moreover, an additional SiOX layer, which acts as the anti-reflection coating, was deposited on the n-side of a complete solar cell. With these adjustments, the solar cell performance was improved to: VOC 610 mV, FF 64.98%, JSC 36.95 mA/cm2 and η 14.64% (from n-side illumination).
Furthermore, with reducing the Ti thickness in the metal seed layer to 2 nm. The solar cell performance was further improved to VOC 611 mV, FF 69.58%, JSC 36.16 mA/cm2 and η 15.38% (from n-side illumination). The bifaciality factor is 89%.