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Courses Contents

Plenary Lectures

From concept to commercialization: growing a microfluidics start-up company

Dr. Kieran Curran

Becton Dickinson and Company, Ireland

Kieran Curran led GenCell Biosystems as founder and CEO until its acquisition by Becton Dickinson and Company in 2014. Established in early 2011, GenCell Biosystems grew from a side-line interest of a consultancy company into a microfluidics engineering business focused on developing technology to enable DNA analysis, specifically Next Generation DNA Sequencing. Based in Ireland, GenCell’s microfluidic technology mimics nature by enabling biological testing in an encapsulated “cell” known as a Composite Liquid Cell. As an inventor of the company’s core microfluidic technology, Kieran Curran participated in the design, development and commercialization of a new approach to genetic testing. Currently employing over 90 people in Ireland and with applications as broad as helping to improve human, animal and plant health – the company’s technology is helping researchers to explore the complexity of DNA at unprecedented speed and detail.

Modelling Flow in the Transition Regime: From Canonical Problems to Applications

David R. Emerson and Xiao-Jun Gu

STFC Daresbury Laboratory, United Kingdom

Despite the tremendous progress made in the design, development, and fabrication of today’s micro-electro-mechanical systems (MEMS), they remain a fairly recent technological advancement. From exploratory work in the 1980s it was only in the mid-1990s that publications began to appear in any number. Indeed, work related to microfluidics was considered quite distinct from MEMS even when the device was clearly using a fluid, either gas or liquid. Since the mid-1990s, however, the growth in publications has grown exponentially and the subject of microfluidics is now a major research topic in its own right. One fact has remained true throughout the development of microfluidics and MEMS is that modelling has not kept pace with the tremendous advances in fabrication and design.

A subject that exemplifies the challenge is the modelling of gaseous transport in MEMS. As a consequence of the small length scales involved, the traditional Navier-Stokes-Fourier (NSF) equations quickly break down and become a poor predictor of properties such as mass flow rates, stresses at the wall etc. This has led to many extensions of the NSF equations from velocity-slip through to extended hydrodynamic approaches such as the Method of Moments and various levels of the Burnett equations. Alternatively, solutions of the Boltzmann equation can be applied either directly or using the direct simulation Monte Carlo (DSMC) method. For practical MEMS geometries, the flow speed is very low, with Mach numbers << 1 and Knudsen numbers ranging from 0.01 to 1.0, making DSMC prohibitively expensive whilst directly solving the Boltzmann equation, with its high-dimensionality and complicated collision integral, is generally limited to geometrically-simple fundamental studies.

In this lecture, we will consider how we reduce the computational burden by exploiting the significant advances made in Computational Fluid Dynamics and show how the Method of Moments can be applied to low-speed gaseous flows in the low- to mid-transition regime, i.e. where the Knudsen number is < 1, for a range of classic problems including flow past cylinders, the Graetz problem, Knudsen pumps, thermal flows in eccentric cylinders etc. where the classic NSF equations are no longer safe to use.

Silicon and Polymer based Micro and Nano Components Fabrication Processes

Laurent Mazenq

Laboratoire d'Analyse et d’Architecture des Systèmes, University of Toulouse, France

This lecture will present an overview of various methods for deposition, patterning and characterization of thin films for silicon and polymer based micro and nano components fabrication processes.

After a photolithography introduction, the principle, the aim and the limits, this presentation will provide several techniques of conventional process manufacturing: Physical Vapor Deposition, CVD, ion implantation, wet and dry etching. We will also mention alternative methods to structure polymers devices: 3D laser lithography, nanoimprint, electroplating, copolymer self-assembly, ink jet, dry films…

In another part, we will see the advantages of these fabrication techniques of silicon and polymer components for various applications, biology, environment and health, energy.

Kinetic theory modeling of liquid-vapor systems

Aldo Frezzotti

Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano, Italy

Kinetic theory of fluids plays an important role in understanding and modeling mass, momentum and energy transfer between the vapor and liquid phase in non-equilibrium two-phase flows, in which evaporation and/or condensation occur. The lecture presents a review of kinetic modeling of the vapor-liquid flows next to interfaces. Starting from the studies of the Knudsen layer structure in evaporation and condensation, the problem of the formulation of kinetic boundary conditions is described and discussed. The problems arising in matching theory to experimental data from evaporation of water are described and discussed.

References

[1] Ytrehus, T., Molecular  flow effects in evaporation and condensation at interfaces, Multiphase Science and Technology, Vol.9, No.3 (1997), pp. 205-327.

[2] Sone, Y., Kinetic theoretical studies of the half-space problem of evaporation and condensation, Transport Theory and Statistical Physics, Vol.29, No.2-5 (2000), pp. 227-260.

Influence of intermolecular potential on rarefied gas flows

Felix Sharipov

Physics Department, Federal University of Parana, Curitiba, Brazil

The intermolecular interaction plays a crucial role in rarefied gas dynamics. In order to carry out a direct simulation Monte Carlo or to solve the Boltzmann equation, we need to assume some intermolecular potential. The simplest model of such a potential is the hard sphere, which neglects the attractive intermolecular force. This model significantly simplifies numerical and analytical solutions of the Boltzmann equation and the direct simulation. However, it does not provide a correct dependence of the transport coefficients on temperature. Other models, like Lennard-Jones and ab inito, lead to more realistic description of the transport phenomena, but they require more effort to implement them into both Boltzmann equation and direct simulation. A comparative analyze of works based on various intermolecular potentials shows that the degree of potential influence varies for different kinds of gas flows. Some phenomena are quit sensitive and require more realistic potential, while other phenomena are not sensitive to the potential and can be described by a simple model. The presentation contains numerical examples of the potential influence and then some general recommendations to choose an appropriate potential are given.

Surface Acoustic Wave microsensors. Overview, modeling and applications.

Pascal Nicolay

Carinthian Tech Research (CTR AG), Villach, Austria

Surface Acoustic Wave (SAW) devices are omnipresent, around us. They can indeed be found in any mobile phone, where they act as tiny radiofrequency filters and signal processing elements. Due to their sensitivity to environmental conditions (temperature, pressure, adsorbed mass …), they also have found applications as sensors. SAW sensors are intrinsically very small and robust. They are indeed made of a single piece of piezoelectric material (substrate), on which thin Inter Digital Transducers (IDTs) are deposited. An IDT is used to convert electrical signals into acoustic waves. The waves propagate on the substrate, where they are influenced by the environmental conditions. They are later picked-up and converted back to electrical signals by another IDT. As the IDTs can be connected to antennas, it becomes possible to interrogate the sensors wirelessly, without any embedded electronics. That’s why SAW sensors are one of the best solutions, to monitor temperature or deformation in extreme conditions. As they are also very sensitive to minute temperature changes, heated SAW Sensors can be used as miniaturized (and possibly, wireless) flowmeters or Pirani-type vacuum sensors. Finally, as surface waves can interact with fluids, it is possible to use SAW to mix, actuate or heat small liquid droplets. This makes SAW devices an attractive building block of future Lab-on-Chips microsystems.

In this talk, we will present the basics of SAW technology. This will include a brief presentation of the theoretical background and simulation models that are required to compute the actual behavior of SAW sensors. Some selected applications will be described. Especially, CTR SAW wireless sensors for very high temperature monitoring and intracranial pressure monitoring will be presented. An example of SAW Biosensor will be described as well. We will then focus on heated SAW sensors for flow and vacuum monitoring. We will present the state-of-the-art of these two technologies, as well as their current limitations. A presentation of Lab-on-Chips possible applications will conclude the talk.

Industry led innovation research and the importance of creating value chains

Ann O’Connell

Advanced Materials Ireland

As Europe falls behind in economic growth, the competitiveness that research innovation and the creation of value chains can bring is crucial to transform research and inventions into marketable products and services. The Europe 2020 Flagship Innovation Union (2010) states: “We need to get more innovation out of our research”. The EC is demanding improved systems and methodologies for knowledge capture and transfer, and demonstrable impact from EU-funded research. The EU’s Commissioner for Research, Innovation and Science, Máire Geoghegan-Quinn (2010-2014) stated that “Europe needs to better capitalise on its inventions … it needs to build a fully functioning ‘Single Market for Innovation’”.

Through research developments and innovative the EU aims to create a world leading position in Manufacturing. As such it is intended to be a key component that contributes to the “Europe 2020” goal of smart, inclusive and sustainable growth for Europe. The European commission is encouraging growth within the area of advanced manufacturing through research and innovation investments to support sectoral development in manufacturing. Therefore instrumental in bridging the gap between research and industry, with an overriding objective to contribute to the establishment of sustainable collaboration between research and industry is the creation of both horizontal and vertical value chains.

Theory & Design Session

Gas flow simulations in MEMS devices: review of main approaches

Irina Graur

IUSTI Laboratory, Aix Marseille University, France

The lecture presents the main properties of the gas flows in MEMS devices showing their difference from the conventional devices. The review of the main approaches for modeling and simulations of gas flows at microscale is presented. Three methods are reviewed: the continuum approach usually based on the Navier-Stokes (NS) equation with the special type of the boundary conditions; the kinetic approach based on the kinetic theory of gases, involving deterministic (Boltzmann equation and its kinetic models) and statistical (the DSMC) methods and the molecular dynamic (MD) approach. For all approaches the main advantages and disadvantages are presented along with the range of most appropriate physical parameters for each method.

Heat and mass transfer within gas flows in the slip flow regime

Stéphane Colin

Institut Clément Ader, INSA, University of Toulouse, France

Gas microflows must be accurately controlled for a lot of microsystem applications (micro-heat exchangers, pressure gauges, fluidic micro-actuators for active control of aerodynamic flows, mass flow and temperature micro-sensors, micropumps and microsystems for mixing or separation for local gas analysis, mass spectrometers, vacuum and dosing valves…). The main particularity of gas microflows is a local thermodynamic disequilibrium which appears first at the walls, in the so-called Knudsen layer. It is a consequence of rarefaction resulting from an increase of the Knudsen number, which represents the ratio of the mean free path over a characteristics length of the fluidic microsystem. Most of the above listed microsystems are partly or totally operating in the so-called slip-flow regime. In this slightly rarefied regime, the Navier-Stokes-Fourier equations are still valid, provided they are supplemented with appropriate boundary conditions that correctly describe the velocity slip and temperature jump observed in the Knudsen layer close to the walls.

These boundary conditions are physically explained and discussed, with a focus on the viscous slip, thermal slip and temperature jump coefficients. The consequence of the associated effects are illustrated by various applications. The main steps for a correct implementation of these boundary conditions to extend the classic no-slip analytical solutions for mass flow rate and convective heat transfer in microchannels are detailed.

Mesoscale tools for simulation of transport phenomena in gases: Applications in micro-devices and vacuum systems

Steryios Naris

Department of Mechanical Engineering, University of Thessaly, Greece

Gas flows where the characteristic dimension of the flow is of the same order with the mean free path, can not be simulated by the typical hydrodynamic models. Alternative tools are applied, mostly based on the Boltzmann equation. Various numerical methods can be used following both deterministic and stochastic approach, such as DVM and DSMC respectively.

Here, a brief introduction on mesoscale modeling of real flows is given, focusing on specific theoretical and numerical aspects. In addition examples where such an approach is required for gas flow simulation are presented, including flow in micro-devices and vacuum systems, as well as possible new fields where the kinetic theory of gases could be applied.

Experiments & Microfabrication Session

Rarefied gas experiments - Measurement of accommodation coefficients

Marcos Rojas

Institut Clément Ader, INSA, University of Toulouse, France

An interesting characteristic of gas flows in micro-systems is related to the fact that gas can be often considered to be in a state of slight or even strong rarefaction, which means a gas having its molecular mean free path (λ) of the same order of dimensions of the characteristic length (L_c) of the system itself. The mean free path is the average distance traveled by a molecule before colliding against another molecule and it is inversely proportional to the gas pressure and directly proportional to temperature, for example the gas mean free path of air at ambient pressure and temperature is around 70nm. Thus, if the gas is rarefied, local thermodynamic disequilibrium may appear in the fluid flow and this may generate phenomena such as slip at the wall, temperature jump at the wall or thermal transpiration. Gas/surface interaction at the solid boundaries of the system plays a fundamental role in respect to these non-equilibrium phenomena and more specifically in respect to the quantitative values obtained of viscous and thermal velocity slip at the wall and temperature jump at the wall. Due to the practical impossibility of considering each molecule/surface interaction, it is of great interest to study statistical coefficients that can give us information about the global momentum and energy exchange between gas molecules and surface. These so-named accommodation coefficients can vary as a function of the gas molecule and the solid surface material and roughness. In this talk we will treat the experimental measurement of these coefficients which is often achieved by indirect measurement methodologies.

Molecular Tagging Techniques for gas flows velocimetry and thermometry

Christine Barrot

Institut Clément Ader, University of Toulouse, France

One of the local flow characterization techniques widely used for gas flows is the particle image velocimetry (PIV). A second velocimetry technique, which can be shown as an interesting alternative to PIV, is the molecular tagging velocimetry technique (MTV). MTV is a little-intrusive technique based on luminescence phenomenon: the flow is seeded with fluorescent or phosphorescent molecules which emit light when they are activated by photons. Typically, a laser is used to tag a line or a grid. Molecules luminescence is then detected at two successive times and the analysis of the tagged line or displacement and deformation allows the determination of the velocity field. Currently developed to measure velocity fields, this technique is also being developed to measure temperature distribution exploiting the properties of the phosphorescence lifetime dependence on the temperature.

Here, the general principle of MTV and MTT techniques will be explain. Typical experimental setup is described including general experimental considerations (calibration, materials, image analysis, accuracy …) and more specific issues linked to its application for gas flows. The remaining challenges for their applicability to gas microflows will also be discussed.

the ASML Lithography system

Erik Arlemark

ASML, Eindhoven, The Netherlands

The company name ASML abbreviates “Advanced semiconductor material lithography”, and is founded in the Netherlands 1984. ASML is a world leader in the manufacture of technology systems for the semiconductor industry. The company offers an integrated portfolio for manufacturing complex integrated circuits (also called ICs or chips).

ASML’s guiding principles is continuing Moore’s Law in doubling number of transistors per chip every two years. This results in increasingly powerful and capable electronics that enable the world to progress within a multitude of fields, including healthcare, technology, communications, energy, mobility and entertainment.

The critical technology for shrinking transistors in high volume manufacturing is lithography. The lithography process works by projecting the information from a mask (blue print of a chip) with an intense laser light onto a wafer coated with light –sensitive substance, the photo resist. 

To increase resolution in the lithography process it is desirable that the numerical aperture of incident light on wafer is as large as possible and that the exposure light has as short wave length as possible. The former requirement has led ASML to utilize light in extreme ultra violet (EUV) band-width. However, EUV light becomes easily absorbed by all mater (even gas). Therefore the lithography machine has to be operated in medium vacuum condition and utilize mirrors instead of lenses.

Micro heat exchangers

Gian Luca Morini¹ & Juergen J. Brandner²

¹University of Bologna, Italy        ²Karlsruhe Institute of Technology, Germany

The talk is focused on the design of miniaturized heat exchangers based on a series of parallel mini/micro-channels spatially organized in order to obtain different flow configurations (parallel flow, counter-current flows, cross flows). First, the theory for the estimation of pressure drops and overall heat transfer coefficients in presence of mini/micro-channels is recalled and some preliminary calculation is presented in order to highlight the potential of micro heat exchangers in terms of overall thermal performance.

The problem linked to the flow mal-distribution among the parallel channel is discussed and the most useful solutions for the mitigation of this problem are presented. The role of the inlet and outlet manifolds and of the configuration of the inlet and outlet gates on the distribution of the working fluid among the channels is shown by using the results of a series of numerical simulations.

The problem of fouling is also shortly presented by means of a series of experimental data for some working fluid in specific temperature ranges.

The dependence of the overall performances of the heat exchangers on the adopted flow configuration is also discussed by means of a series of numerical and experimental results. It will be highlighted the role played by the conjugate heat transfer between fluids and solid walls on the temperature distributions of the flows. Finally, a series of guidelines are given in order to drive the designers during the design stage of a new micro heat exchangers will be presented.