Andre Bossche

Characterizing size-dependent effective elastic modulus of silicon nanocantilevers using electrostatic pull-in instability

This letter presents the application of electrostatic pull-in instability to study the size-dependent effective Young’s Modulus ? ( ~170–70?GPa) of [110] silicon nanocantilevers (thickness ~1019–40?nm). The presented approach shows substantial advantages over the previous methods used for characterization of nanoelectromechanical systems behaviors. The ? is retrieved from the pull-in voltage of the structure via the electromechanical coupled equation, with a typical error of ? 12%, much less than previous work in the field. Measurement results show a strong size-dependence of ?. The approach is simple and reproducible for various dimensions and can be extended to the characterization of nanobeams and nanowires.

Magnetic-field measurements using an integrated resonant magnetic-field sensor

The present paper introduces a magnetic-field sensor based on a resonating single-crystal silicon structure. The excitation of the resonator is achieved by the Lorentz force generated by a sinusoidal current flowing through a rectangular coil deposited on the surface of the structure. The amplitude of the vibration, which is proportional to the magnetic field, is detected by sensing capacitors. Because of the high-quality factor of the resonator, a lower detection limit of 1 nT, or even smaller might be realised when the device is vacuum-packaged. This paper describes the working principle, the fabrication procedure as well as open- and closed-loop measurement results.

Quality factor of torsional resonators in the low-pressure region

Abstract This paper reports the calculation of the Q -factor of a torsional resonator in the low-pressure region if the vibration occurs in free space or close to another surface. The calculation is based on the model used by Christian but a modified Maxwell-Boltzmann distribution, the Maxwellian-Stream distribution, is applied to describe the velocity distribution of the gas particles colliding with the resonator. The result is an increased damping factor or lower quality, which matches much better with published measurements.

Effects of size and defects on the elasticity of silicon nanocantilevers

The size-dependent elastic behavior of silicon nanocantilevers and nanowires, specifically the effective Youngs modulus, has been determined by experimental measurements and theoretical investigations. The size dependence becomes more significant as the devices scale down from micro- to nano-dimensions, which has mainly been attributed to surface effects. However, discrepancies between experimental measurements and computational investigations show that there could be other influences besides surface effects. In this paper, we try to determine to what extent the surface effects, such as surface stress, surface elasticity, surface contamination and native oxide layers, influence the effective Youngs modulus of silicon nanocantilevers. For this purpose, silicon cantilevers were fabricated in the top device layer of silicon on insulator (SOI) wafers, which were thinned down to 14 nm. The effective Youngs modulus was extracted with the electrostatic pull-in instability method, recently developed by the authors (H Sadeghian et al 2009 Appl. Phys. Lett. 94 221903). In this work, the drop in the effective Youngs modulus was measured to be significant at around 150 nm thick cantilevers. The comparison between theoretical models and experimental measurements demonstrates that, although the surface effects influence the effective Youngs modulus of silicon to some extent, they alone are insufficient to explain why the effective Youngs modulus decreases prematurely. It was observed that the fabrication-induced defects abruptly increased when the device layer was thinned to below 100 nm. These defects became visible as pinholes during HF-etching. It is speculated that they could be the origin of the reduced effective Youngs modulus experimentally observed in ultra-thin silicon cantilevers.

Size-dependent trajectories of DNA macromolecules due to insulative dielectrophoresis in submicrometer-deep fluidic channels

In this paper, we demonstrate for the first time that insulative dielectrophoresis can induce size-dependent trajectories of DNA macromolecules. We experimentally use lambda (48.5 kbp) and T4GT7 (165.6 kbp) DNA molecules flowing continuously around a sharp corner inside fluidic channels with a depth of 0.4 mum. Numerical simulation of the electrokinetic force distribution inside the channels is in qualitative agreement with our experimentally observed trajectories. We discuss a possible physical mechanism for the DNA polarization and dielectrophoresis inside confining channels, based on the observed dielectrophoresis responses due to different DNA sizes and various electric fields applied between the inlet and the outlet. The proposed physical mechanism indicates that further extensive investigations, both theoretically and experimentally, would be very useful to better elucidate the forces involved at DNA dielectrophoresis. When applied for size-based sorting of DNA molecules, our sorting method offers two major advantages compared to earlier attempts with insulative dielectrophoresis: Its continuous operation allows for high-throughput analysis, and it only requires electric field strengths as low as approximately 10 Vcm.

On the size-dependent elasticity of silicon nanocantilevers: impact of defects

Recent measurements have indicated that the elastic behaviour of silicon nanocantilevers and nanowires is size-dependent. Several theoretical models have been proposed to explain this phenomenon, mainly focused on surface stress effects. However, discrepancies are found between experiments and theories, indicating that there could be other influences in addition to surface effects. One of the important issues, which was experimentally confirmed and has not been considered, is accounting for the fact that experimentally tested nanocantilevers and nanowires are not defect free. In this paper molecular dynamics (MD) is utilized to study the effects of defects on the elasticity of silicon. The effective Young’s modulus ˜ E of [100] and [110] oriented silicon nanoplates is extracted in the presence of defects, showing that such defects significantly influence the size-dependent behaviour in ˜ E. The MD results are compared with the results of continuum theory, showing that continuum theory holds, even for very small defects. Taking into account the surface effects, native oxide layers together with fabrication-induced defects, the experimental measurements can be explained. The studied example involved nanocantilevers, but can be extended to nanowires. (Some figures in this article are in colour only in the electronic version)

Computer-aided fault tree synthesis I (system modeling and causal trees)

Abstract This paper is devoted to fault tree synthesis and is split up into three parts. Part I starts with the introduction of component models that show all fault propagation through the components and fault initiation by the components in both directions (upstream and downstream). Subsequently, it is shown how to create system models that interconnect a systems components and environmental variables. Then a fault tree construction algorithm is introduced which is able to generate fault trees from the given system and component models in two steps. First a causal tree is constructed showing the propagation paths for all basic events leading to any deviation in the top parameter. All control loops (feedback and feedforward loops) in this causal tree must be traced prior to any fault tree construction since they might prevent some faults from reaching the top parameter. They consequently require a special treatment. Part I ends showing how to adapt the causal trees for these loops. Part II discusses the final step of the fault tree construction algorithm, i.e. it shows how fault trees can be abstracted from the causal diagram and ends with a comprehensive example. Finally, Part III discusses a method for real-time fault location which is based on the causal tree construction procedure introducted in Part I.

Through-wafer interconnect technology for silicon

This paper presents a novel method for creating through-wafer interconnects via an anisotropically etched groove in a (100)-silicon wafer. The idea is based on the realization of interconnection lines on the inclined sidewalls of the anisotropically etched grooves, which transfer the metalization to the back side of the wafer without open through-holes. The process itself is compatible with standard semiconductor technology and can be applied at the wafer level resulting in low packaging costs. All post interconnect processes are developed independently and can be added to any IC fabrication process. They are performed at the back side of the wafer at the packaging step, so during this processing the front side of the wafer can be protected from scratches and pollution. The key feature of the method presented is the coating of the anisotropically etched grooves with a polyimide and an electrodeposited photoresist. Further, methods to improve the photoresist uniformity over three-dimensional structures are discussed. Copper interconnects have been realized to show the feasibility of this through-wafer technique for front-to-back electrical interconnections. The thickness of the copper interconnects has been increased by copper electroplating to reduce their electrical resistance further and to increase their mechanical strength.

Low-cost plastic sensor packaging using the open-window package concept

Abstract This paper presents a low-cost transfer mould packaging concept for sensors, based on a direct-mould principle. The advantage of this new packaging concept, which we call the open-window package, is that up to the moulding step the whole assembly process is compatible with the standard lead-frame processing. The open-window package concept allows plastic sensor packaging with one or more environmental access paths to be created in a single moulding step. As an application of this new packaging concept, a plastic sensor package with a single access path has been developed for commercial production. The performances of this new low-cost package are satisfactory and lifetime performances show promising results. Furthermore, packaging of other types of sensors is in preparation.

Monitoring enzymatic reactions in nanolitre wells.

We have developed a laboratory‐on‐a‐chip microarray system based on nanolitre‐capacity wells etched in silicon. We have devised methods for dispensing reagents as well as samples, for preventing evaporation, for embedding electronics in each well to measure fluid volume per well in real‐time, and for monitoring the fluorescence associated with the production or consumption of NADH in enzyme‐catalysed reactions. Such reactions can be found in the glycolytic pathway of yeast. We describe the design, construction and testing of our laboratory‐on‐a‐chip. We also describe the use of these chips to measure both fluorescence (such as that evidenced in NADH) as well as bioluminescence (such as evidenced in ATP assays). We show that our detection limit for NADH fluorescence is 5 µm with a microscope‐based system and 100 µm for an embedded photodiode system. The photodiode system also provides a detection limit of 2.4 µm for ATP/luciferase bioluminescence.