M Koch

Design and Fabrication of a Micromachined Coulter Counter

This paper reports the design and fabrication of a micromachined Coulter counter. Calculations have been performed to estimate the behaviour of the counter for passing particles. A relative resistance change of 1.8% has been derived for a particle of 1.5 µm radius flowing through a capillary of 5 µm side length and an electrode spacing of 40 µm. The fabrication technology has been based on similar micromachining steps to a micromixer, and allows further design modification to generate other microfluidic devices. Thus, integration of other microfluidic devices is possible with this technology. The fabrication relies on silicon trench etching and subsequent deposition of metal electrodes over the trench edges. Finally, a Pyrex wafer is anodically bonded on top of the silicon to seal the capillaries.

A Novel Micropump Design with Thick Film Piezoelectric Actuation

A new design for a silicon-based micropump is described. Passive cantilever valves are produced by boron etch stop and fusion bonding. Tests of these valves show good performance, as no flow could be detected in the reverse direction. Initial experiments on a thick-film screen printed piezoelectric membrane actuator were undertaken. A study of suitable inks for electrodes on different insulation layers on silicon yielded silicon dioxide and cermet gold ink as the most satisfactory combination. Deflection measurements of a mm PZT (lead zirconate titanate) - bimorph membrane gave movement at an applied voltage of 100 V. A quasi-static simulation package of the flow through a micropump is also presented. The valve action is simulated using ANSYS coupled with FLOW3D. The piezoelectric membrane deflection is simulated with ANSYS. A differential equation for the combined actuation of membrane and valves is solved numerically with Maple. Pump rates of up to and a maximum backpressure of up to 70 kPa for a driving voltage of 40 V have been modelled using bulk values for PZT-5H. A pump rate of up to and a maximum backpressure of up to 35 kPa at 100 V driving voltage are predicted using thick-film parameters extracted from the measurements.

Two simple micromixers based on silicon

This paper reports modelling, fabrication and testing of two micromixers. The principle of mixing used for the devices was diffusion because of the small value of the Reynolds number in microcapillaries. The first mixer separates the main flow into partial flows, which are laterally alternated in order to increase the boundary surface between the liquids. The second mixer superposes two fluids by injection of one liquid into the other. The fabrication technology is based on etching of silicon and anodically bonding with Pyrex glass. The performance of the mixers has been verified by mixing phenolphthalein solution and ammonia dissolved in water. Reasonable mixing was achieved at pressures of around 4 kPa (lateral mixing) and 7 kPa (vertical mixing) with flow rates of approximately 1 . The measurements were compared with diffusive mixing simulations with a CFD simulator and agreement of both was observed.

The dynamic micropump driven with a screen printed PZT actuator

A hybrid actuated silicon-based micropump with dynamic passive valves is described in this paper. The actuator is based on a combination of thick-film and silicon micromachining technology and relies on the flexure of a membrane structure of lead zirconate titanate on silicon. Inlet and outlet valves use the passive dynamic principle, where flow direction is realized with a diffuser and a nozzle shaped element. Pump rates of up to 155 and a maximum backpressure of 1 kPa were achieved at a driving voltage of 600 . Additionally the fluidic modelling of the dynamic passive valves is described, using a CFD simulator. The results of the model agree well with device measurements.

Self-aligning gas/liquid micropump

In this paper a piezoelectrically driven silicon membrane pump with passive dynamic valves is described. It is designed to pump gases and liquids and to be tolerant to gas bubbles. Reducing the dead volume within the pump, and thus increasing the compression ratio, one achieves the gas pumping. The main advantages and novel features of the pump described in the paper are the self-aligning of the membrane unit to the valve unit and the possibility of using screen-printed PZT as actuator, which enables mass production and thus low-cost micropumps. A liquid pump rate of 1500 μl min−1 and a gas pump rate of 690 μl min−1 were achieved.

Thick-film printing of PZT onto silicon

This paper describes a way of screen-printing PZT (lead-zirconate-titanate) onto silicon substrates. Initial experiments of printing a PZT-ink on a native oxide-covered Si-substrate showed contamination of the silicon substrate by lead diffusion during the firing stage of the film. This occurred also on thin-film deposited silicon oxide or silicon nitride layers. The effect of this is potentially catastrophic as conduction occurs between areas required to be electrically isolated by the thin film. The problem was solved by using a screen-printed barrier layer of IP211 (Heraeus), which also reduces the diffusion and prevents the conduction.

Improved characterization technique for micromixers

This paper reports an improved technique to characterize a micromixer. Due to the small dimensions of micromixers, the mixing relies on diffusion only. To date most diffusive micromixers have been tested with phenolphthalein and a base. However, this method does not give any information about the proportional mixing of the device, as the final colour of the mixing depends only on the pH value. For a pH below the critical point, the mixed fluid is colourless, whereas an intensive but almost constant colour is obtained at pH values above. In order to avoid any chemical reactions, the new characterization technique is based on commercially available inks of different colours. For mixing, the colours of the inks change gradually rather than at one specific point. The technique has been successfully employed to characterize a micromixer at various pressure differences. Finally, image processing was used to allow observation of proportional mixing and to characterize the development of the diffusion over time. The latter feature could be an interesting technique to monitor the course of a reaction over the length of the mixer (stopped flow technique).

Micromachined chemical reaction system

Abstract This paper presents a micromachined chemical reaction system, which is based on the integration of several microfluidic devices. The system is realised by anodically bonding two pumps, two flowsensors and a micromixer on top of a micromachined fluidic circuit board. The pumps are membrane pumps with piezoelectric actuation. The pumping rates are from, −220 to 490 μl/min. The flowsensors are based on the temperature difference method. The principle of the mixing/reaction chamber used for this system is diffusion because of the small value of the Reynolds number in micro-capillaries. Two fluids/chemicals join through laterally alternated inlets in order to increase the boundary surface between them. The whole system is functional and leakage through the joints does not occur. Tests have been done with ethanol, flowing through both system inlets and joining at the mixing unit.

Design and Fabrication of a Microfluidic Circuitboard

This paper reports the design and fabrication of a micromachined microfluidic circuitboard. The circuitboard consists of a Pyrex wafer in which trenches and connection holes are etched. Channels are then formed by anodically bonding a silicon wafer to the Pyrex wafer. On top of this, various microfluidic devices can be mounted via the anodic bonding technique. This allows a simple way of mass production of different microfluidic systems. To realize other microfluidic systems only the mask layout for creating the channels in the Pyrex wafer has to be changed. The microfluidic circuitboard has been successfully fabricated and single devices have been surface mounted. A whole system has been tested and it proved to be functional and without any leakage.

Characterization of micromachined cantilever valves

This paper reports the fabrication and simulation of micromachined cantilever valves. For quasi-static fluid-structural simulations, the FEM package ANSYS and the CFD package Flow3D are coupled with a control programme to yield the flow rate for the cantilever valve. The results are compared with micromachined cantilever valves. The fabrication of these valves can be subdivided into the generation of cantilevers and ducts via KOH etching and a final fusion bonding step to join them. For the release of the cantilever, toluene is used to avoid stiction while drying the chips. Agreement between measured and simulated flow rates is shown to be good and gives confidence in the use of this simulator for valve development. Dynamic simulations are established with an impact model of the cantilever sitting on top of the duct. This allows the prediction of the dynamic behaviour of cantilever valves.