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.

Thick-film printed lead zirconate titanate (PZT) structures can be combined with micromachined silicon structures and offer relatively large actuation forces compared to alternative techniques. This paper describes the initial investigation into the compatibility issues of micromachining silicon wafers with PZT layers printed on the surface. It assesses the effect of many standard photolithography and micromachining upon the printed PZT layer. In particular the adhesion of the printed layer to the substrate and its internal structure have been studied after exposure to each process. Standard photolithography using positive resists has been found to destroy the adhesion of the platinum electrode and an alternative masking technique using a thick-film printed dielectric polymer has been developed. Aluminium top electrodes have been fabricated using this masking technique combined with ion beam milling. Finally many standard micromachining etching processes have been carried out on a range of silicon substrates incorporating platinum electrode/thick-film PZT structures. Wet silicon and silicon dioxide etches were found to be unsuitable since they also attacked the adhesion of the bottom electrode. Plasma etching processes appear to be well suited for the combination of materials since there is a wide range of etches available that do not affect the PZT. These can therefore be used for the micromachining of the silicon substrate after thick-film processing greatly expanding the range of applications suited to this combination of technologies.

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Abstract-This paper investigates the application of analog adaptive techniques to the area of dynamic sensor compensation, of which there is little reported work in the literature. The case is illustrated by showing how the response of a load cell can be improved to speed up the process of measurement. The load cell is a sensor with an oscillatory response in which the measurand contributes to the response parameters. Thus, a compensation filter needs to track variation in measurand, whereas a simple fixed filter is only valid at one specific load value. To facilitate this investigation, computer models for the load cell and the adaptive compensation filter have been developed. To allow a practical implementation of the adaptive techniques, a novel piecewise linearization technique is proposed in order to vary a floating voltage-controlled resistor in a linear manner over a wide range. Simulation and practical results are presented, thus, demonstrating the effectiveness of the proposed techniques.

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