Chapter 7 - Case Studies in Modulus-Limited Design

Anodic bonding is a widely used process in research and industry for MEMS Applications. The main advantage is that it is a very reliable process, that results in a strong and hermetically sealed bond. The bonding process is also very stable to perform. These properties are due to the process sequence of heating the wafers, to be bonded, to a temperature in the range of 300 to 450°C. One of these two wafers has to be made of borosilicate glass (e.g., SCHOTT Borofloat33®). In such glasses, sodium ions (network modifier) are dissolved out of the glass network in the temperature range mentioned and thus become free and mobile. If now a negative voltage of typically 1000V is applied to the glass wafer, the free positively charged sodium ions will move away from the contact area of both wafers, the later bonding interface, under the influence of the electric field. This results in a displacement current, which decreases again after a maximum is reached, due to the limited available number of charge carriers (sodium ions). This ultimately leads to a depletion of the charge carriers in the glass. It is generally assumed that a linked effect occurs in the bond field, namely that oxygen ions migrate from the glass to the bond interface, where they cause the actual bond formation via anodic oxidation.Even though this basic concept of the anodic bonding corresponds to state of the knowledge of how the anodic bond is actually formed [1], it is difficult to prove in practice. In order to gain a deeper insight into the formation of anodic bonding and thus open up new applications and even wider utilization of anodic bonding, a first basic experiment was done as follows: A glass wafer was provided with a thin aluminum layer by a sputtering process and another glass wafer was anodically bonded to this aluminum layer. The typical bonding current (depletion and current drop) was observed and the resulting composite of two glass wafers with a very thin intermediate aluminum layer was examined and tested for bonding quality. First of all, it can be stated that bonding formation has taken place locally between the the 6" wafers. Unfortunately, particle contamination could not be completely avoided during processing leading to larger unbonded areas, especially in the center of the wafer. Nevertheless, the bonded areas allow for evaluation of bonding quality. The sputtered aluminum layer has a higher thickness in the center, due to the fact that the glass wafer was eccentrically rotated below a small sputter target. This inhomogeneity effect enables the characterization of different Aluminum layer thicknesses in one sample. The sputter time was set, that at the wafer center an untransparent Aluminum layer was deposited, while at the wafer edge just a few nanometers of aluminum forming a semitransparent layer. After the bonding experiment it was noticed that in all the bonded area the aluminum appears rather homogeneously transparent. According to that it can be concluded that the aluminum layer is oxidized during anodic bonding transforming into transparent Aluminum oxide. This finding is a clear confirmation of the general thesis, that during anodic bonding an anodic oxidation takes place at the bond interface. In further examinations the influence of the bonding parameters on this oxidation process will be investigated. It is expected that with higher temperature and bonding voltage the oxidation will be enhanced, ending up with an optically highly transparent layer of Aluminum oxide. This might be relevant for emerging optical applications requiring anodic bonding as reliable bonding process together with optical transparence for visual light. As blade tests have shown the bonding conditions in the first process are not yet optimal – the bonding strength was rather low, but darker spots in the crack opened area indicate a transfer of the aluminum oxide layer. By variating and improving bonding conditions, a deeper insight into the details of the oxidation process during anodic bonding will be available. So far it is known that easy to oxidize materials (Silicon and Aluminum) can be well anodically bonded while rather inert materials (Silicon Nitride) are hardly or not bondable with this procedure. For that reason, some materials like Platinum, Gold, and Titanium these predictions will be evaluated in practice. With this more profound knowledge it might be possible to predict the anodic bonding behavior of different materials in the future.Literature:[1] Lapadatu, A. C., & Jakobsen, H. (2015). Anodic bonding. In Handbook of Silicon Based MEMS Materials and Technologies (pp. 599-610). William Andrew Publishing. Figure 1

Adhesively bonded joints in wind turbine blades, particularly trailing edge joints, are prone to damage due to high-intensity stress concentrations, missing adhesive, or deficient bonds at the bonding surfaces. If not detected early, cracks or disbonds in the trailing edge might propagate rapidly resulting in catastrophic failure of the whole blade. No dedicated in situ sensor system is, as of now, available for real-time damage monitoring in the critical adhesively bonded joints. This article discusses the use of in situ triboluminescent optical fiber sensors for damage monitoring in adhesively bonded composite joints. Double cantilever beam and three-point bend end-notched flexure samples were fabricated from a thick glass fiber/vinyl ester composite and glued with a two-part methacrylate-based structural adhesive. The in situ triboluminescent optical fiber sensors were embedded into the adhesive layer. Double cantilever beam and three-point bend end-notched flexure tests were performed to determine the mode I and mode II fracture toughness of the adhesive joints, respectively. The results show that the triboluminescent emissions occur at the onset of damage when performing double cantilever beam and three-point bend end-notched flexure fracture tests on adhesively bonded composite panels of different adhesive thicknesses. The triboluminescent response increases with the fracture toughness of adhesive joints. The double cantilever beam and three-point bend end-notched flexure specimens undergo cohesive failure in the adherend thickness. Optical microscopy was utilized to obtain better insights of fracture lines. Results indicate that in situ triboluminescent optical fiber sensors can monitor damage in adhesive in real-time without generating false alarms.

Chapter 28 - Case studies in design

Cortical bone distribution in the femoral neck of strepsirhine primates

A case study in interface design The CHI'89 Information Kiosk

Higher power circuits in steadily decreasing structures are changing failure mechanisms that were previously uncritical for the semiconductor industry into critical ones. Such a failure mechanism is, for example, the material fatigue of thin metal layers induced by cyclic loading, leading to disruption the failure mode of the metal layer. If a corrosive medium penetrates in addition, due to a crack in the device housing, the degradation of the metal can be accelerated. In this study corrosion sensitivity of thin aluminium and copper layers to iodine was verified in a feasibility study. A test vehicle is available for characterising disrupted, thin metal layers. It is a micro cantilever beam with a meander-shaped thin metal layer on top. After an optimisation and calibration phase, 1 µm thick aluminium layers were disrupted by alternating mechanical loading ((70 - 180). 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> cycles) in a newly developed, low-cost, tabletop vibration tester in a thermally stable environment. The test vehicles are then corroded in an iodine vapour corrosion tester at an accelerated rate. Preliminary tests on the corrosion of thin aluminium and copper layers were performed within a feasibility study and the iodine vapour corrosion tester was thus confirmed. A dependence of the corrosion sensitivity on the disruption could be proven. These results need to be verified within further investigations.

Flexoelectricity is a size-dependent electromechanical mechanism coupling polarization and strain gradient. It exists in a wide variety of materials, and is most noticeable for nanoscale objects, where strain gradients are higher. Simulations are important to understand flexoelectricity because experiments at very small scales are difficult, and analytical solutions are scarce. Here, we computationally evaluate the role of flexoelectricity in the electromechanical response of linear dielectric solids in two-dimensions. We deal with the higher-order coupled partial differential equations using smooth meshfree basis functions in a Galerkin method, which allows us to consider general geometries and boundary conditions. We focus on the most common setups to quantify the flexoelectric response, namely, bending of cantilever beams and compression of truncated pyramids, which are generally interpreted through approximate solutions. While these approximations capture the size-dependent flexoelectric electromechanical coupling, we show that they only provide order-of-magnitude estimates as compared with a solution fully accounting for the multidimensional nature of the problem. We discuss the flexoelectric mechanism behind the enhanced size-dependent elasticity in beam configurations. We show that this mechanism is also responsible for the actuation of beams under purely electrical loading, supporting the idea that a mechanical flexoelectric sensor also behaves as an actuator. The predicted actuation-induced curvature is in a good agreement with experimental results. The truncated pyramid configuration highlights the critical role of geometry and boundary conditions on the effective electromechanical response. Our results suggest that computer simulations can help understanding and quantifying the physical properties of flexoelectric devices.

Chip reliability becomes a great threat to the design of future microelectronic systems with the continuation of the progressive downscaling of CMOS technologies. Hence increasing the robustness of chip implementations in terms of error tolerance becomes an important issue. In this paper we present a case study in reliability-aware design tolerating transient errors. A state-of-the-art WiMAX channel decoder for LDPC codes is investigated on all design levels to increase its reliability for a given system performance with minimum hardware overhead. We show that an efficient exploitation of the algorithmic fault-tolerance yields a fairly small area overhead with nearly no degradation in communications performance even under high error injection rates.

In the present study, the effects of an alumina layer and its thickness on the bonding behavior of Al/Al strips were evaluated. To achieve this, aluminum strips were anodized at different times to generate alumina layers with various thicknesses. Furthermore, some samples were produced with alumina powder and the bond strength of these samples was compared with that of samples produced by the alumina layer. After the cold roll bonding process, peel test was carried out to evaluate the bond strength and weld efficiency of Al strips. The results of the peel test indicated that using a thin alumina layer (5 μm) led to a decrease in weld efficiency. However, by increasing the thickness of the alumina layer, weld efficiency also increased, reaching a higher level compared to Al strips without the anodized layer. Moreover, using alumina powder caused the deterioration of the bond strength compared with the samples fabricated by anodized alumina layer.

The MATLAB M language provides constructs for the simple representation of functions, and has been used extensively for algorithm development and verification in embedded system design. The M language processes entire arrays simultaneously, and it is expected that design based on M can be implemented faster and with the same or higher quality as compared with design based on other languages. This paper presents a case study of a design of a filter for signal processing using M-based design flow. The results of the case study demonstrate the high efficiency of the M-based design flow as compared to traditional functional modeling and manual coding using a hardware description language.

Although originally motivated by applications such as image processing, multidimensional (nD) systems have mainly attracted the attention of the research community due to the richness of new theoretical questions raised by their treatment, and are often replaced by other settings when it comes to modelling, identifying and controlling processes in practical situations. The aim of this special issue is to illustrate the application potential of nD systems by presenting several contributions where the nD framework is successfully used either to deal with practical problems or to solve practically relevant questions that arise in other contexts that are not at first sight related to multidimensional systems. In the paper Multidimensional Control Systems: Case Studies in Design and Evaluation, by Rogers et al., after introducing the most commonly used models for the analysis and control of discrete nD linear systems, a series of case studies is presented with the aim of demonstrating the advantages of the nD systems approach in solving certain control problems. Namely, applications in the fields of sensor grid networks, iterative learning control, civil engineering and agriculture are considered. The paper Two-dimensional Generalized Predictive Control (2D-GPC) Scheme for the Batch Processes with Two-dimensional (2D)Dynamics, Shi et al. studies the problem of iterative learning control (ILC) design for batch processes. Based on 2Dcontrolled auto-regressive moving average (2D-CARMA) model, a novel two-dimensional generalized predictive control (2D-GPC) is proposed. The feasibility and effectiveness of the proposed method is validated by the experimental results on packing pressure control of the injection molding process.

Case study in design and transient analysis of hydrogen-propelled aircraft using direct combustion

This paper summarizes various aspects of identifying and using biological analogies in engineering design. To avoid the immense as well as potentially biased task of creating a database specifically for this purpose, the chosen approach searches biological knowledge in natural language format, e.g., books, papers, etc., for instances of functional keywords describing the engineering problem. Strategies developed to facilitate this search as well how text descriptions of biological phenomena were used in problem solving are summarized. Case studies in design for remanufacture and microassembly are used to provide an overview of the method.

Performance evaluation of collaboration in the design process: Using interoperability measurement

One of the most highly cited papers in management is Eisenhardt’s (Acad Manag Rev 14(4):532–550, 1989) piece on the importance of case study research, in particular multiple cases (versus single cases), for theory building. We focus on this distinction between multiple versus single cases in the context of rigor and impact of management case studies (N = 173) published during the period 1996–2006 in Academy of Management Journal, Administrative Science Quarterly, Organization Science, and Strategic Management Journal. We find that this distinction of multiple versus single only crudely captures the reality of case study designs in published article. For this we propose an alternative empirical classification of case study design that is replication and non-replication, in which case studies using a replication logic either in single cases (e.g. comparing teams within an organization, where the case is the organization) or, indeed, multiple cases (e.g. comparing teams across multiple organizations) are more rigorous and also more impactful than cases who do not use replication logic. However, unlike in quantitative research, rigor is not a driver of article citations in qualitative studies. In this regard, our finding makes important contributions to scientrometric research by discussing criteria under which different case study designs can be rigorous and impactful.