A new silicon-based micropump is described in this paper. The key element of the device is a thick-film/silicon micromachined hybrid actuator. The actuation principle relies on the flexure of a screen printed piezoelectric lead zirconate titanate (PZT) layer on a silicon membrane ( 8 mm X 4 mm X 70 km). An investigation into the deposition technology of the bottom electrode for the piezoelectric material showed that a gold resinate or Pt evaporated electrode on a 500 nm thick SiQ covered silicon wafer achieved best results for the membrane actuator. Met and outlet valves are of the cantiiever type and use deep boron diffusion together with KOH etching. Pump rates of up to I20 ~1 min-' have been achieved. A maximum backpressure of 2 kPa was measured when using a 600 V,, sinusoidal drive voltage at 200 Hz across a 100 pm thick PZT layer. The pump was compared with a conventional surface mounted piezoelectric driven micropump. The conventional pump achieves a performance which was a factor of 3-6 more efficient, but does not allow mass production, 0 1998 Elsevier Science S.A. AU rights reserved.

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 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 µl min −1 and a maximum backpressure of 1 kPa were achieved at a driving voltage of 600 V pp. 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.

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.

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 µl min −1 . The measurements were compared with diffusive mixing simulations with a CFD simulator and agreement of both was observed.