Hexagonal boron nitride (hBN) has emerged as a unique platform for room temperature quantum photonics, yet translating its optically active defects into a practical single molecule sensing technology requires two stringent conditions: (i) deterministic and spatially controlled generation of emitters and (ii) engineering nanoscale confinement geometries that reliably bring labelled biomolecules in proximity to the hBN emitters while suppressing background fluorescence. This dissertation develops and connects these two capabilities through complementary routes based on optical and strain nano-engineering in layered hBN.

We initially establish a microsphere-assisted femtosecond-laser approach to enhance light–matter interaction during defect formation and readout. By exploiting the combination of photonic nanojets with whispering gallery mode-assisted signal collection, the method enables deterministic emitter generation with improved spatial confinement and higher collection efficiency compared to microsphere-free processing. Specifically, the approach reduces the emission area by a factor of five and increases fluorescence collection efficiency by approximately tenfold.

A second result is the generation and characterization of hBN wrinkle networks in multilayer hexagonal boron nitride,which form from thermal expansion coefficient mismatch with the substrate during annealing. We demonstrate that wrinkles function as planar nanoscale confinements, and can therefore be used as a feature rather than a limitation. Liquid infiltration and retention are validated by time dependent optical imaging, Raman mapping of the water OH stretch band, and capacitance gradient mapping, consistent with liquid retention exceeding 10 h. This self-assembly process provides a lithography-free route to obtain 1D nanochannels and multi-junctions directly on-chip.

For the purposes of biomolecule confinement and imaging, however, such confinements alone do not guarantee clear optical readouts because wide-field imaging remains limited by fluorescence background from surface adsorbed molecules. This shortcoming motivated a background suppression strategy that we implement via vertical hBN/graphene stacks. By using few-layer hBN as a precise physical spacer between biomolecules and graphene, non-radiative energy transfer can be tuned in a predictable manner. This yields a parameter i.e. spacer thickness, that can be exploited to control the degree of quenching and fluorescence recovery. In this way, graphene suppresses unwanted background fluorescence from molecules adsorbed on hBN wrinkles, while preserving the emission from molecules confined deeper inside the wrinkle volumes. As a result, the imaging contrast is starkly improved.

Overall, this dissertation demonstrates how hBN emitter engineering, strain defined confinement, and interface controlled background suppression can be combined into a framework for high-throughput, fluorescence based biosensing using hBN, forming the first steps towards optical protein fingerprinting at 2D material interfaces. ... Read more

Diamagnetic levitation provides a frictionless and entirely passive method of actuation, operating even in vacuum and at cryogenic temperatures. It has been explored in fields ranging from seismology to microfluidics handling, and its qualities make it attractive for MEMS devices by reducing production costs and improving robustness. This work develops a diamagnetic motion stage aimed at extending the achievable range of motion beyond prior nanometer-scale demonstrations. This objective is formulated as the following research question: What would be an optimal design for a long range actuator to create maximum move- ment range using diamagnetic levitation to eliminate contact friction and electrostatic force as propulsion method using only feedforward control, while keeping the cost low?. Magnet arrays were modeled, with a railroad configuration selected for its levitation properties. An electrostatic actua- tion model was derived, showing that force depends on both electrode area and its change as a result of movement, and that stable control requires balancing charged and grounded electrodes. Two systems were implemented: a low-voltage (0–200 V) setup with high control but low force, and a high-voltage (0–1200 V) setup with greater force but less control. Characterization revealed Duffing- type nonlinear dynamics. The low-voltage stage enabled three-phase frequency control, useful for resonance testing, while the high-voltage stage achieved up to 5.5 mm controlled travel and 23.47 mm one-way displacement, though with the end position being unrecoverable using electrostatics. The results show that longer travel requires repeating magnet arrays where all potential local minima support levitation. Another important finding was that electrostatic force has both x and z components, with their ratio depending on levitation height and stage surface area, highlighting the importance of thin electrodes. Scaling analysis suggests further potential for MEMS integration. ... Read more

The presence of wear, friction, and material stiffness limits the robustness and sensitivity of traditional accelerometers with mechanical connections between the base and the proof mass. The diamagnetic levitation system can achieve stable levitation at zero energy consumption and offers mechanical isolation between the magnet base and the levitated mass. Its intrinsically low stiffness makes it promising for the development of better accelerometers. In this project, an accelerometer is designed based on a diamagnetically levitated resonator that consists of a two-by-two magnet array in checkerboard layout and a 10×10×0.3 〖mm〗^3 pyrolytic graphite plate. The accelerometer explores a coplanar capacitive sensing scheme and achieves readouts with σ = 66.84 aF. The accelerations in all six degrees of freedom can be extracted with the results of FEM simulation and experiments. For the in-plane translation mode, it has a sensitivity of 30.28 fF/m∙s^(-2) and a resolution of 6.63e-3 m /s^2. Performances are also carefully characterized in static and dynamic scenarios. Being the first 6-axis levitation accelerometer, it verifies the great potential of the diamagnetic levitation system in the development of a high-performance functional device and indicates the feasibility of using coplanar capacitors for measurement of levitated objects. ... Read more

Early detection of plant diseases is crucial to minimize crop losses and reduce the usage of pesticides. Electronic Nose (E-Nose) detect volatile organic compounds (VOCs) emitted by stressed or diseased plants, and one such device is a pixelated capacitive sensor (PCS). We designed and built a setup to investigate the influence of light (wavelength and intensity) on the sensitivity of a functionalized PCS for VOCs detection. Our test results indicate that UV illumination, particularly at 375 nm, enhances the sensitivity of the PCS, with a 3-fold enhancement compared to dark conditions. The sensor showed fast saturation (<1 min) and recovery (<2 min) times, confirming the effectiveness of the chamber design for repeatable gas exposure. ... Read more

Acoustic-structural interactions present significant engineering challenges, particularly in the domains of noise reduction and vibration control. At ASML, measurement-based analyses have revealed that acoustic disturbance paths often dominate the dynamic behavior of atmospheric lithography machines. This project focuses on enhancing ASML’s current one-way coupled acoustic-structural modelling approach by developing a two-way coupled, known as vibro-acoustic, modelling framework. However, this advancement introduces substantial computational complexity, necessitating effective model reduction techniques. The primary objective of this work is to reduce vibro-acoustic models in a way that preserves their ability to be modularly coupled with other system components. To this end, three Component Mode Synthesis (CMS)-based reduction methods were evaluated, with only one proving suitable for both academic and industry-scale models. The resulting reduced-order models successfully retained the dynamic fidelity of the full system and enabled efficient coupling with other substructures. When applied to harmonic excitation analyses, the reduced models achieved a dramatic reduction in computational time, from several hours to approximately one minute, while accounting for the cost of model reduction. ... Read more

This thesis investigates the forces and torques acting on acoustically levitated cuboids, with the aim of improving translational and rotational control in acoustic transportation applications. Traditional trans port methods rely on mechanical pick-and-place systems, which introduce challenges such as fragility and contamination. Acoustic levitation presents a contactless alternative that eliminates these issues. To address the research question: “1: Can we develop a model to determine the stiffness and torsional stiffness values of acoustically levitating cuboids of arbitrary shape, in an arbitrary pressure field?” the study begins by reviewing the fundamental principles of acoustic levitation, including acoustic radiation force, the Gorkov potential, and phased array transducer (PAT) configurations. It then explores various modeling approaches for determining the forces and torques on levitated objects, comparing the strengths and limitations of Gor’kov-based, finite difference time domain (FDTD), finite and boundary element method (FEM/BEM), and a proposed simplified trapping model.
The findings show that while the simplified trapping model lacks predictive accuracy, a Finite Element Method (FEM) model was introduced as a more reliable alternative. The FEM model, using a sound hard boundary assumption, agrees well with prior models of forces on non-spherical particles, that cannot be predicted with Gorkov’s or King’s method, and its implementation in Comsol makes it more accessible to a broad audience. In addition, the model predicts accurately the torques that act on non spherical particles and for the first time such a model is experimentally verified for all three translational and three rotational degrees of freedom....
... Read more

Most micro- and nanomechanical devices are designed to operate within the linear dynamic range by using simple geometries, primarily due to the limited knowledge in utilizing nonlinearity and constraints in fabrication techniques. However, it is anticipated that the scope of applications and fundamental research can be significantly expanded, if these tiny systems can be precisely engineered to account for and exploit their various nonlinear dynamic behaviors. This thesis provides a comprehensive study on the optimization of dynamical properties of high-Q nanomechanical resonators, spanning from linear to nonlinear dynamics and evolving from single-mode to multi-mode analysis.

We first give an introduction to the development of micro- and nanomechanical resonators in Chapter 1. We focus on their unique mechanics, including very low dissipation and strong nonlinearities. Furthermore, we elaborate on the motivation behind this thesis and the need for linking engineering optimization with micro- and nanomechanical resonators. Followed by Chapter 2, we elaborate on the methodology we use throughout this thesis, including fabrication techniques of nanomechanical Si3N4 devices, characterization approaches by optical measurements, and modeling procedures for structural dynamics. Among all methodologies, we highlight the Finite Element (FE)- based Reduced Order Models (ROMs) that can accurately capture the geometric details and boundary conditions, which facilitate the design of resonators with predictable dynamical properties.

We start from investigating linear dynamics of Si3N4 nanostrings in Chapter 3, where the tuning effects of their soft-clamping supports on resonance frequency and Q-factor are evaluated. We experimentally and theoretically reveal a trade-off between maintaining high stress and low stiffness of the supports in designing high-Q resonators fabricated with initial strain. By optimizing this trade-off with our soft-clamping design, we obtain a 50% enhancement of Q-factor compared to doubly-clamped string resonators. With stronger drive levels, in Chapter 4, we show that the nonlinear dynamics can also be substantially tailored by soft-clamping supports. Through careful engineering of support geometries, we introduce softening nonlinearity by stress-induced buckling, allowing precise control over the nonlinear dynamic responses in doubly supported nanostrings, which conventionally exhibit hardening behaviors.

Based on the accurate modeling of both linear and nonlinear dynamics that is validated by experiments, we integrate our FE-based ROM technique with a derivative-free optimization algorithm for the design of nonlinear mechanical resonators in Chapter 5. By optimizing the support’s geometry of our nanostrings, we show that the proposed methodology is not only capable of handling a single optimization goal, but also multiple conflicting objectives, such as the simultaneous enhancement of Q-factor and the Duffing constant. Besides, we generate Pareto frontiers that visualize the trade-offs among multiple optimization objectives, verify the optimized results with brute-force simulations and validate the numerical framework with experiments.

Apart from the dynamics in a single mode, we observe modal interactions between multiple vibrational modes of our nanostrings in the strong nonlinear regime. In Chapter 6, we demonstrate that soft-clamping techniques, commonly utilized to achieve high-Q resonators, can be employed to engineer mode coupling. We verify the analytically derived two-degree-of-freedom system between the lowest two out-of-plane modes by FE-based ROMs and experiments. We further reveal the significant impact of multi-mode interactions on the nanostrings’ frequency response, demonstrating additional opportunities to tailor the nonlinear dynamics of mechanical resonators facilitated by soft clamping. Moreover, we highlight the design potential of soft-clamping supports through the geometric optimization of two-mode coupling, showcasing the effective Duffing constant of the driven mode can be increased by 70%, as well as the onset of mode coupling can be geometrically programmed to either facilitate or inhibit its occurrence.

We conclude all works presented for achieving the optimization of nonlinear dynamics in nanomechanical resonators, and give an outlook for future directions in Chapter 7.
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Ultra-thin drums play a crucial role in sensing applications due to their slender construction and relatively low bending rigidity. These properties render them highly sensitive to external forces. The emergence of graphene and other 2D materials has profoundly impacted the development of these devices, allowing for the creation of exceptionally thin membranes, even as thin as a single atomic layer. However, the extreme thinness of these structures introduces challenges, such as susceptibility to large deformations and nonlinear behaviour, making linear models unsuitable for mechanical analysis.

To fully harness the potential of ultra-thin resonators in practical applications, it is thus essential to comprehend their nonlinear mechanical behaviour thoroughly. Consequently, mathematical modelling and numerical simulations play a pivotal role in studying the nonlinear mechanics governing the motion and resonant behavior of these devices. This doctoral thesis investigates the nonlinear mechanics of ultra-thin membranes. Its primary objective is to develop analytical and numerical methodologies that will facilitate the future design and analysis of these structures for various applications... ... Read more

3D imaging of subsurface structures at the nanoscale is a longstanding challenge in microscopy. Ultrasound enables subsurface imaging, but nanometer depth resolution requires high-frequency sound waves, achieved by heating with pulsed lasers. Combined with Atomic Force Microscopy (AFM), which offers atomic-scale surface resolution a promising candidate for full 3D nanoscale imaging emerges.

This thesis focuses on the development of such a combined ultrasound-AFM system.
Novel optical detection techniques are introduced for both the ultrasound and the AFM, enabling simultaneous operation.

Acoustic waves up to 100 GHz are generated and detected, used to characterize the thickness and adhesion of thin films. We demonstrate that the conical AFM tip acts as an acoustic lens, focusing the wave into the tip apex. When in contact with a sample, changes in the reflection signal confirm acoustic transmission—opening the door to true 3D nanoscale imaging. ... Read more

This thesis provides an overview of research focused on fabricating high-performance nanomechanical resonators from amorphous silicon carbide (a-SiC) and (super)conducting metallic niobium titanium nitride (NbTiN), and subsequently characterizing the superconducting NbTiN resonators using scanning tunneling microscopy (STM). The installation of on-chip nano mechanics with a minimally invasive STM detection technique enables the probing of subtle variations in the Casimir force between superconductors during their phase transition. This thesis consists of four parts.

With the aim of maximizing the coupling of the Casimir force to a large superconducting nanomembrane suspended over a sub-micron vacuum gap, we initially employed atomic layer deposition (ALD). Prior to using ALDto construct the high-aspect-ratio superconducting cavity, we investigated a novel amorphous silicon carbide (a-SiC) material in Chapter 2. Our study demonstrated that a-SiC exhibits high chemical inertness, remarkable ultimate tensile strength, and—most importantly—the capability to support nanomechanical resonators with high quality factors. Leveraging these excellent properties, we fabricated high-aspect-ratio a-SiC nanomembranes suspended over a sub-micron vacuum gap.

Subsequently, using the on-chip cavity formed by the strained a-SiC nanomembrane and the substrate with flat surface, we performed ALD to conformally coat all cavity surfaces with metallic NbTiN, thereby filling the vacuum gap atomically layer-by-layer. By optimizing the deposition conditions with the method described in Chapter 3, we achieved a high-aspect-ratio NbTiN cavity with a gap size of less than 100 nm. During this optimization, we also observed that metallic nanomechanical resonators fabricated via ALD can operate at room temperature with quality factors significantly higher than those of fully coated metallic resonators produced by other deposition techniques.

To measure the superconducting nanomembranes with minimal perturbation to their superconducting state, we installed the NbTiN nanomembrane fabricated by ALD into a scanning tunneling microscope (STM) and performed dynamic measurements in a cryogenic environment, as detailed in Chapter 4. In studying the tip–membrane interaction, we developed three measurement techniques to precisely determine the resonant frequency of the nanomembrane. One technique relies on the homodyne method, while the other two exploit the Van der Waals interaction between the STM tip and the nanomembrane.

Although the NbTiN nanomechanical resonators exhibit high performance, their superconducting properties are compromised by the absence of plasma bombardment on the inner cavity surfaces. Drawing on our experience with suspending large nanomembranes over small gap sizes in Chapter 3, we developed a new fabrication process in Chapter 5 to suspend a bare superconducting NbTiN nanomechanical membrane over another superconducting NbTiN film, with a sub-micron vacuum gap between them.

This configuration minimizes unwanted interactions that could otherwise affect the precision of measuring the variation in the Casimir force between superconductors during the phase transition. The high force sensitivity of the nanomembrane allows us to detect subtle force changes associated with the superconducting phase transition, including those arising from abrupt changes in the Casimir force.
... Read more

Multiple recent events have shown the alarming vulnerability of infrastructure on sea to sabotage. This infrastructure can be monitored and protected with passive sonar systems, which provide a number of advantages over other surveillance methods such as RADAR or active sonar. An overview of different localisation methods suitable for the Dutch littoral zone that perform bearing estimation, ranging or complete localisation on the surface plane is made from methods available in literature. From this overview a proposal is made to select cepstral ranging for further research, as there is a limited amount of literature available on this subject. Experimental data from the Dutch coastal area has been gathered with a RHIB and stationary sensor to verify important parameters for both computation and the ranging environment. An effective cepstral ranging method based on experimental data has been developed, although ranging with tidal effects and SNR mismatch remains somewhat problematic. To compensate for this a novel ray tracing method based on open-source measurements has been developed that offers a significant increase in accuracy while effectively compensating for variations in bathymetry and tide. ... Read more

The nonlinear dynamics of nanomechanical resonators has drawn great interest for applications in sensing, material characterisation, and for uncovering fundamental interactions at the nanoscale. In this thesis, we explore multi-tone excitation as a route towards extracting the full nonlinear reduced order model of a multi-mode nanomechanical resonator. By driving at two frequencies, the nonlinear terms in the equation of motion will cause the generation of motion at sum-frequencies. For certain combinations of the fundamental tones and at sufficient drive levels, this motion can be detected. By analysing the amplitude of the response, the relevant nonlinear reduced order model parameters can be extracted.
In this thesis we present a theoretical analysis of a general nonlinear reduced order model excited by two-tone excitation, a description of the methodology to estimate nonlinear terms, and an experimental setup to perform these experiments. The methodology is applied on a string resonator with non-ideal supports, to estimate most nonlinear terms in its modal equations of motion for the first two modes. These results are in relatively good agreement with results estimated using backbone curve estimation and numerical simulations for a string.
The reduced order model, resulting from these measurements done with the presented methodology, could be used for validating nonlinear models, by characterizing nonlinearities in resonant systems, and for designing nonlinear mechanical systems with accurately tuned nonlinear properties. ... Read more

Diamagnetism can be used for energy-less levitation, while allowing for friction-free movement of objects in vacuum conditions. A very suitable material can be found in Highly Oriented Pyrolytic Graphite(HOPG), which not only has relatively high diamagnetic properties, but also electrical properties which allow for contactless actuation through electrostatic forces. These properties open up the possibility for the design of a multiple degree-of-freedom(DOF) levitating precision motion stage. To this end a design was created consisting of a permanent magnet array, which is covered by a thin PCB, housing multiple electrodes. Above this PCB a square HOPG plate was made to levitate, which can be actuated in the vertical and lateral directions, as well as be rotated out-of-plane. Analytical models and FEM simulations were produced to find the dimensions of this design so that optimal performance could be achieved. An experimental setup was designed and manufactured to measure the performance of the design. It was shown that for voltages below Dutch main's voltage (230V), movements within the micrometer and millirad range could be achieved. Because of environmental disturbances, it was not possible to show movement at the nanometer scale, since these disturbances were in the submicron range. It can however be analytically calculated that for actuations of 1V, displacements of less than 1nm can be achieved. Another design challenge provided itself in the separation of the DOF's, since the electrostatic force always acts in the vertical direction, due to the attraction between the electrodes and the levitating plate. That's why the electrode set-up on the PCB was engineered in a way that rotations produced by lateral displacements could be cancelled by counter-actuation. This method was experimentally proven to work. It was then also shown that with this multiple electrode set-up, movement could be produced along a diagonal line, which shows that the plate could be made to move in multiple dimensions at once, as to be expected of a multiple DOF precision motion stage. This precision motion stage was manufactured at a fraction of the costs of comparable commercial multiple DOF precision motion stages that are currently available. ... Read more

Silicon Photonics is a dynamic field of research for developing new sensing technologies. In the domain of biomedical imaging, much effort is put to design photonic sensors as an alternative to commonly used piezo transducers for detecting ultrasounds. Piezo transducers are popular due to their cost effectiveness but they have some disadvantages such as limited bandwidths, difficulty of miniaturisation for achieving higher image resolutions and high sensitivity to electromagnetic noise. On the other hand, photonic sensors can achieve much higher bandwidths, be easily miniaturised and are more energy efficient. The most common photonic sensing device is the micro ring resonator (MRR). When a laser light propagates inside them, for certain laser wavelengths, resonance occurs and causes a sharp change of light intensity. Whenever an ultrasound wave hits the ring resonator, deformation occurs and causes a shift of the resonant frequency. This amount of shift is tracked to characterise the ultrasound wave. Currently, MRRs are not sufficiently sensitive for detecting weak ultrasounds. Therefore, this project was aimed at improving ring resonator sensitivity to ultrasounds by applying a patterned polymer layer on top of a MRR.

To study the effect of a patterned polymer on ultrasound sensitivity: First a FEM simulation was conducted to compute MRRs sensitivity to ultrasounds with different polymer configurations. Then multiple fabrication methods were tested to produce a polymer pattern on top of a MRR. Finally, an ultrasound characterisation was done with the fabricated patterns to determine and compare sensitivity results with the simulation and conclude about the patterning effect. ... Read more

One way to tackle the rise in antibiotic resistance, is to develop new techniques for testing the susceptibility of cells to antibiotics. In this paper, a comparison is made between a novel bacterial susceptibility testing method and a modification on this method. Both methods rely on bacterial samples deposited on graphene cavities, where the bacteria will stick to the graphene by the addition of APTES. By making use of a 632.8 nm He-Ne laser, the sample is probed, and the cavities then serve as ultrasenstive sensors for determining bacterial nanomotion. The existing method (single spot readout) is based on focusing a laser on graphene drums, where the drums are read out one at a time by the use of a photodiode. The modified method (parallel readout) makes, by the addition of one lens, use of an expanded laser, and a CMOS camera. At 100 frames per second, four drums are read out simultaneously. This technique hypothetically makes very high throughput possible for antimicrobial testing.

Both methods rely on converting a signal based on the intensity of the incoming light to the membrane deflection in nanometer, and the bacterial motility is found by taking the variance. The comparison of the two methods is done by performing multiple experiments, in order to relate the quality of the signal by finding the standard deviation (noted as S) of the variance of the deflection σ_z² . 

From an analysis of S, statistical quantities describing the distances between probability distributions have been conceived, and a criterion is proposed to differentiate between the noise levels of the two techniques. One such quantity is the normalized distance between the signals of two types of experiments, the one being an experiment without bacteria as a reference and the other being an experiment with living bacteria.
In the case of hypermotile bacteria, parallel readout has an average variance of deflection of 5.95 nm², it is substantially higher than the method of single spot readout, having average 2.92 nm². The unitless metric D for the distance between two signals however shows that both methods score similarly in probing nonmotile (∆-MotAB) E. Coli, as for the parallel readout the measure has for ∆-MotAB a value 0.34 and for single spot readout it has the value 0.31. In the case of hypermotile (7740) E. Coli, parallel readout scores again better with a value of 2.35 versus 0.39, which is the value obtained for single spot readout.

Finally an outlook is given where interesting findings have been summarized. With the use of power spectral densities and heatmaps of either average intensity or variance of the signal, interesting phenomena are noted and are topics for future research. ... Read more

Nanomechanical resonators made of two-dimensional (2D) materials are the subject of intensive research due to their remarkable properties, allowing them to operate at high frequencies with high sensitivity. However, dissipation losses and manufacturing issues have prevented them from reaching their full potential. This thesis aims to overcome these challenges by dry-transferring 2D materials onto a MEMS and clamping them using electron beam-induced deposition. By in-plane straining the membranes using MEMS, the tensile energy is increased, thereby diluting intrinsic losses. This approach increased the Q-factor of 2D material resonators by 91% and allowed measuring forces down to sub-piconewtons, outperforming commercially available silicon-based force sensors. ... Read more

This thesis discusses several studies on magnetic two-dimensional (2D) materials, focusing on their nanomechanical properties and the behavior of resonance frequencies in response to temperature changes. These studies employ nanomechanical resonators, specifically suspended membranes (drum resonators) of 2D magnetic materials. The frequency response of these resonators is measured using optical excitation combined with an interferometric setup, allowing identification of resonance frequencies. By altering the temperature of the resonators, the resonance frequency shifts as the strain within the 2D material changes. This strain change is partially magnetostrictive in origin due to changes in the magnetic order within the materials, offering a method to study these magnetic characteristics... ... Read more

Hermeticity is a measure of how well a package is leak-tight. Many Micro-Electro-Mechanical Systems (MEMS) sensors, actuators, and microelectronic devices need a defined cavity environment for optimal performance, hence measuring the package leak rate is critical for lifetime prediction. MEMS devices are generally packaged through the wafer-bonding technique. The MEMS device is produced on a wafer with a cavity and bonded to a cap wafer to seal the hole. Reducing the cap wafer thickness allows it to deflect due to the cavity interior-exterior pressure differential. Consequently, if leakage occurs, the deflection will
change. By measuring these deflections, it is possible to quantify leak rates.

In order to use it as an in-line testing process, this research aims to determine the accuracy of the deflection method for determining the leak rates. To achieve this, our approach involved designing and leak testing test structures (or devices) using an experimental setup that can vary pressure, supply desired species
inside a vacuum chamber, and measure deflection using an interferometer to determine leak rates. Deflections are converted to leak rates using a formulated analytical expression, subsequently utilized to determine the error involved in measuring leak rates.

Using the experimental setup, the test devices were effectively characterized for sensitivity using pressure-induced deflection measurements, with experimental sensitivity values closely matching the theory. Further, air leak testing was performed on devices interconnected with nanometer-gap size leak channels to
gain first-hand knowledge of leakage. Experimental leak rates matched well with analytical models, proving that flow through devices having leak channels can be characterized. Ultimately, the setup enabled successful helium leak testing of devices without any defined leak channels.

The helium leak-tested samples were circular membranes of diameters: 2000, 1600, 1400, 1300, and 1100 μm with a thickness of 40 μm bonded to a cavity depth of 3.24 μm. Uncertainty analysis associated with leak rate measurement revealed that when considering a certain cavity depth and membrane thickness,
the membrane with the largest diameter would exhibit the least amount of uncertainty. This was also observed through experiments, for the diameter of 2000 μm, a clear linear trend of deflection reduction due to the helium leakage was observed during a two-week period of deflection measurements. Whereas, for the diameter of 1100 μm, it was not possible to observe the same linear trend of deflection reduction, indicating that even more no.of.days is required to determine an accurate leak rate.

In the end, a short analysis was made using the cavity design having the 2000 μm membrane, which had the least uncertainty in measuring the leak rate. This analysis aimed to ascertain the designed test structure’s usefulness in measuring leak rates of the MEMS packages. Based on the analysis, it was concluded that large-volume wafer-bonded MEMS packages (> 1 mm3) with an acceptable cavity pressure increase of 10 mbar could be tested using the deflection method and our proposed test structure design to guarantee their lifetime. ... Read more