Modelling, design and realization of microfluidic components

R.E. Oosterbroek

    Research output: ThesisPhD Thesis - Research UT, graduation UT

    107 Downloads (Pure)

    Abstract

    During the last decades, miniaturization of electrical components and systems has assumed large proportions. The reason for these developments is the application of etch and deposition techniques in the IC-production (integrated circuit), which allows a large amount of functionality per surface area. The IC-production techniques can also be used for the fabrication of functional elements, operating in other physical domains. This has led to the research area of micromechanics. With use of existing and to specific demands adapted or newly developed etch and deposition techniques, miniaturized sensors and actuators can be obtained with typical dimensions in the order of microns to millimeters. The described micromechanics research is carried out at the Micromechanical Transducers Group of the Faculty of Electrical Engineering, University of Twente and took place within the fast growing area of μTAS: micro Total Analysis Systems. The aim of the research is to design miniaturized chemical analysis systems by applying micromechanical fabrication methods to exploit the benefits from downscaling. These advantages can be: reduction of analysis costs, obtaining more compact, energy and reagents economical systems, performing a faster and / or more precise analysis, or performing of chemical analysis which are difficult or not possible with “macrosystems��?. The research is focussed in particular on modeling, designing and fabrication of components of a μTAS. The effects of downscaling on the influence of the different physical mechanisms on the behavior of microcomponents can be well analyzed with use of dimensionless numbers. In the considered microcomponents, the flow regime is in the range of Reynolds numbers around 1. Within this range, simplified models according to Stokes can be used. For stationary, fully developed flow in straight channels with typical microchannel cross-section geometries, analytical expressions have been derived to describe the velocity profile and the hydraulic resistance. The application of the virtual work principle (variational method) and the analogy of the mathematical description for torque of beams turns out to be very successful. Stoke’s theory is applied to modeling both the quasi-dynamic behavior of the pressure / flow sensor and the stationary, domain-coupled behavior of the valves. The hydraulic resistance of passive valves can be described well with use of the dimensionless relation Eu4.Re = constant, in which Eu forms the Euler number and Re the Reynolds number. A good prediction of the behavior of microvalves turns out to be rather difficult though. The relative fabrication accuracy is poor, despite the used high absolute accurate fabrication precision, such that substantial differences between the measured and aimed valve behavior can occur. In this thesis different fabrication techniques and process designs are presented for the realization of the sensors and valves. For the manufacturing of a well-closing valve, selective bonding is an essential step. To achieve this, two methods are presented: selective anodic bonding of silicon to glass, with use of a chromium layer of less than 1 nm thickness and selective silicon to silicon bonding with use of siliconnitride layers. Besides waferbonding, much attention is paid to the application of anisotropic wet chemical etching of mono-crystalline silicon. By optimally using the crystal orientations in different wafertypes, combined with directional and anisotropic etching, powerful designs for microstructures arise. An example is the possibility to etch thin plates with high accuracy by using the switching of {111} planes in <100> silicon during etching through the wafer, in combination with a suitable mask design. These plates can be used to create among others passive valve arrays with a limited number of process steps. For both <100> and <111> oriented silicon design rules are given for optimally using the possibilities offered
    Original languageEnglish
    Awarding Institution
    • University of Twente
    Supervisors/Advisors
    • van den Berg, Albert , Supervisor
    • Elwenspoek, Michael Curt, Supervisor
    Award date12 Nov 1999
    Place of PublicationEnschede
    Publisher
    Print ISBNs90-36513464
    Publication statusPublished - 12 Nov 1999

    Keywords

    • EWI-14535
    • IR-13884
    • METIS-111374

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  • Cite this

    Oosterbroek, R. E. (1999). Modelling, design and realization of microfluidic components. Enschede: Universiteit Twente.