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Accurate alignment between the cavities in cavity-SOI (c-SOI) wafers and lithography on the wafer surface is essential to advanced MEMS production. Existing alignment methods are well defined, but often require specialized equipment or costly software packages available only in professional manufacturing environments. It would be beneficial for the microfabrication world to be able to utilize standard alignment techniques and tools that are easily available also in smaller MEMS fabrication units and especially the majority of research facilities. Therefore, we demonstrate a feasible method for c-SOI wafer alignment using an ASML PAS5500/100 wafer stepper with standard software configuration by relocating ASML alignment markers towards wafer's edges and utilizing a terracing process to reveal them for alignment. Moreover, we characterize the magnitude and behavior of image offset errors that are introduced using this method. The offset error is found to be inversely proportional to the value of the coordinate in each axis, resulting in images being shifted towards the center of the wafer. The measured offset errors are

For both single-phase and multiphase metallic materials, it is necessary to understand the mechanical behavior on the grain-size scale in detail to get information that is not obtainable from macro-scale mechanical characterizations. This paper presents a methodology for uniaxial tensile testing of micro-specimens isolated from a bulk material. The proposed concept of multiple parallel micro-tensile specimens at the tip of a macro-sized wedge reduces the alignment work and offers an easy way for specimen handling. The selection of site-specific specimens is based on detailed microstructural and crystallographic characterization. Three kinds of representative specimens are presented to illustrate the wide range of application of the methodology for a variety of materials. Accurate, reproducible measurement of force (2.5 μN resolution) and displacement (~10 nm resolution) is demonstrated, while accurate alignment (in-plane rotational and out-of-plane tilt misalignment of

This paper reveals potential micro mechanisms underlying time-dependent anelasticity observed in Al-(1 wt%)Cu thin films. The analyzed deformation mechanisms involve dislocation motion and interaction with solute diffusion, grain boundaries and precipitates. In order to investigate the role of these mechanisms, Al-(1 wt%)Cu alloy thin films are heat treated to systematically change the precipitation state, while characterizing the grain boundary distribution with electron backscatter diffraction. Micromechanical characterization is performed by microbeam bending, nano-tensile creep testing and nano-indentation. Results in microbeam bending reveal, for all precipitate and grain boundary states considered, a similar time-dependent evolution of the anelastic strain after load release. The magnitude of the recovered strain is also observed to be independent of the precipitate or grain boundary configuration. The nano-tensile creep test also indicates the same time-dependent anelastic evolution, indicating that the loading state does not affect the underlying mechanisms. Analysis of strain bursts in nano-indentation shows that pinning of dislocations by Cu solutes is unaffected by the precipitation state. Based on uniaxial creep and time-dependent anelasticity measurements in pure Al specimens, it is made plausible that the time-dependent anelasticity originates from diffusion-limited glide or climb of dislocation segments that are pinned at Cu solutes or in dislocation structures, which provide an internal driving force.

Understanding the healthy and diseased state of skin is important in many areas of basic and applied research. Although the field of skin tissue engineering has advanced greatly over the last years, current in vitro skin models still do not mimic the complexity of the human skin. Skin-on-chip and induced pluripotent stem cells (iPSC) might be key technologies to improve in vitro skin models. This review summarizes the state of the art of in vitro skin models with regard to cell sources (primary, cell line, iPSC) and microfluidic devices. It can be concluded that iPSC have the potential to be differentiated into many kinds of immunologically matched cells and skin-on-chip technology might lead to more physiologically relevant skin models due to the controlled environment, possible exchange of immune cells, and an increased barrier function. Therefore the combination of iPSC and skin-on-chip is expected to lead to superior healthy and diseased in vitro skin models.

All skin diseases have an underlying immune component. Owing to differences in animal and human immunology, the majority of drugs fail in the preclinical or clinical testing phases. Therefore animal alternative methods that incorporate human immunology into in vitro skin disease models are required to move the field forward. This review summarizes the progress, using examples from fibrosis, autoimmune diseases, psoriasis, cancer and contact allergy. The emphasis is on co-cultures and 3D organotypic models. Our conclusion is that current models are inadequate and future developments with immune-competent skin-on-chip models based on induced pluripotent stem cells could provide a next generation of skin models for drug discovery and testing.

Organ-on-Chips (OOCs) are micro-fabricated devices which are used to culture cells in order to mimic functional units of human organs. The devices are designed to simulate the physiological environment of tissues in vivo. Cells in some types of OOCs can be stimulated in situ by electrical and/or mechanical actuators. These actuations can mimic physiological conditions in real tissue and may include fluid or air flow, or cyclic stretch and strain as they occur in the lung and heart. These conditions similarly affect cultured cells and may influence their ability to respond appropriately to physiological or pathological stimuli. To date, most focus has been on devices specifically designed to culture just one functional unit of a specific organ: Lung alveoli, kidney nephrons or blood vessels, for example. In contrast, the modular Cytostretch membrane platform described here allows OOCs to be customized to different OOC applications. The platform utilizes silicon-based micro-fabrication techniques that allow low-cost, high-volume manufacturing. We describe the platform concept and its modules developed to date. Membrane variants include membranes with (i) through-membrane pores that allow biological signaling molecules to pass between two different tissue compartments; (ii) a stretchable micro-electrode array for electrical monitoring and stimulation; (iii) micro-patterning to promote cell alignment; and (iv) strain gauges to measure changes in substrate stress. This paper presents the fabrication and the proof of functionality for each module of the Cytostretch membrane. The assessment of each additional module demonstrate that a wide range of OOCs can be achieved.

The reliability of metallic microelectromechanical systems (MEMS) depends on time-dependent deformation such as creep. Key to this process is the interaction between microstructural length scales and dimensional length scales, so-called size-effects. As a first critical step towards studying these size-effects in time-dependent deformation, a purely mechanical experimental methodology has been developed, which is presented here. The methodology entails the application of a constant deflection to a lm-sized free-standing aluminum-alloy cantilever beam for a prolonged period of time. After this load is removed, the deformation evolution is immediately recorded by acquiring surface topographies through confocal optical profilometry. Image correlation and an algorithm based on elastic beam theory are applied to the full-field beam profiles to correct drift and improve limited optical profilometry precision, yielding the tip deflection as function of time with a precision of 7% of the surface roughness. A proof-of-principle measurement reveals a remarkable time-dependent deflection recovery. Assumptions and errors of the methodology are analyzed. Finally, it is concluded that the methodology is most suitable for the investigation of creep due to the simplicity of specimen handling, preparation and setup design, while maximizing long term stability and deformation precision.

Time-dependent mechanical investigations of on-wafer specimens are of interest for improving the reliability of thin metal film microdevices. This paper presents a novel methodology, addressing key challenges in creep and anelasticity investigations through on-wafer tensile tests, achieving highly reproducible force and specimen deformation measurements and loading states. The methodology consists of a novel approach for precise loading using a pin-in-hole gripper and a high-precision specimen alignment system based on three-dimensional image tracking and optical profilometry resulting in angular alignment of?

Free-standing metallic thin films are increasingly used as structural components in MEMS. In commercial devices, long-term reliability is essential, which requires determining time-dependent mechanical properties of these films. The uniaxial tensile test is a preferred method due to uncomplicated determination of the stress and strain state. However, at the MEMS-scale this method is not straightforward: specimen handling and loading, force and deformation measurement need careful consideration. Here we discuss the challenges of the application and measurement of nano-Newton forces, nanometer deformations and micro-radians rotation alignment ensuring negligible bending in on-chip tensile test structures during long periods. We then present a novel tensile-testing instrument with in-situ capabilities in SEM and Optical Profilometry. The design solutions to measure these small forces and deformations whilst ensuring a uniaxial stress state will be presented.

Creep is a time-dependent deformation mechanism that affects the reliability of metallic MEMS. Examples of metallic MEMS are RF-MEMS capacitors/switches, found in wireless/RF applications. Proper modeling of this mechanism is yet to be achieved, because size-effects that play a role in MEMS are not well understood. To understand this better, a methodology is setup to study creep in Al-Cu alloy thin film micro-cantilevers micro-fabricated in the same MEMS fabrication process as actual RF-MEMS devices. The methodology entails the measurement of time-dependent deflection recovery after maintaining cantilevers at a constant deflection for a prolonged period. Confocal profilometry and a simple mechanical setup with minimal sample handling are applied to control and measure the deformation. Digital image correlation, leveling and kinematics-based averaging algorithms are applied to the measured surface profiles to correct for various errors and improve the precision to yield a precision < 7% of the surface roughness. A set of measurements is presented in which alloy microstructure length scales at the micrometer-level are varied to probe the nature of this creep behavior.

This paper presents an accurate yet straightforward methodology for characterizing time-dependent anelastic mechanics of thin metal films employed in metalic microelectromechanical systems (MEMS). The deflection of microbeams is controlled with a mechanical micro-clamp, measured with digital holographic microscopy and processed with global digital image correlation (GDIC). The GDIC processing directly incorporates kinematics into the three-dimensional correlation problem, describing drift-induced rigid body motion and the beam deflection. This yields beam curvature measurements with a resolution of

Experiments for characterization of time-dependent material properties in free-standing metallic microelectromechanical system (MEMS) pose challenges: e.g. fabrication and handling (sub)-μm sized specimens, control and measurement of sub-μN loads and sub-μm displacements over long periods and various temperatures [1]. A variety of experimental setups have been reported each having their pros and cons. One example is a micro-tensile tester with an ingenious electro-static specimen gripping system [2] aiding simple specimen design giving good results at μN and sub-μm levels, but without in-situ full-field observations. Other progressive examples assimilate the specimen, MEMS actuators and load cells on a single chip [3,4] yielding significant results at nN and nm levels with in-situ TEM/SEM observability, though not without complications: complex load actuator/sensor calibration per chip, measures to reduce fabrication failure and unfeasible cofabrication on wafers with commercial metallic MEMS. This work aims to overcome these drawbacks by developing experimental methods with high sensitivity, precision and in-situ full-field observation capabilities. Moreover, these should be applicable to simple free-standing metallic MEMS that can be co-fabricated with commercial devices. These methods will then serve in systematic studies into size-effects in time-dependent material properties. First a numeric-experimental method is developed. It characterizes bending deformation of onwafer μm-sized aluminum cantilevers. A specially designed micro-clamp is used to mechanically apply a constant precise deflection of the beam (zres

Reliability of microelectromechanical systems (MEMS) depends a.o. on time-dependent deformation such as creep and fatigue [1]. It is known from literature that this behavior is affected by size-effects: the interaction between microstructural length scales and dimensional length scales [2,3]. Not much research has focused on characterizing size-effects in time-dependent material behavior, specifically for free-standing thin films [3]. This study investigates size-effects caused by grain statistics in timedependent deformation in µm-sized free-standing aluminum cantilever beams. A numeric-experimental method is used to determine material parameters. The experiment entails applying a constant deflection to the micro-beams for a prolonged period. The deflection is achieved with 50 nm resolution via a micro-clamp. The beams are then released. Immediately the deformation evolution is recorded by acquiring surface height profiles with a confocal optical profiler. Image correlation of the full-field beam profiles is applied to correct for specimen drift and tilt. The experiment yields the tip deflection as function of time with ~3 nm precision. In the numerical part, this data is combined with a finite element model based on a standard-solid material model. In this way material parameters describing time-dependent behavior are extracted. The time constant for the deflection evolution is determined within 20%, as verified by predicting a different experiment. Figure 1 shows the model and the numeric prediction of an experiment.