Fabrication of TiNi shape memory actuator for micropump

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Abstract
We are attempting to develop a shape memory alloy (SMA) actuated micropump as a component for use in micro analysis or micro dosage systems. In this paper, we will discuss the fabrication process and dynamic actuation properties of an SMA actuator. TiNi thin film of about 6 micrometers in thickness was deposited onto a Si wafer with a square recess on its reverse side, and annealed at 500 degrees C for 1h in a vacuum to memorize an initial flat shape. The TiNi thin film and a Pyrex glass cap of 500 micrometers thickness with a square recess were then anodically bonded together in a vacuum to form a chamber to which a bias pressure was to be applied to deform the TiNi thin film. After removing the remaining 50 $mUm thick Si layer beneath the TiNi thin film by RIE in SF6 plasma, a shape memory diaphragm of 5mm square in size was completed. The fabricated actuator was driven by resistive heating and air-cooling under a bias pressure of 200 kPa, which was applied by a nitrogen gas flow through a small hole pieced in the Pyrex glass cap. Under these conditions, the actuator gave displacements of about 95 micrometers at the center during repeated thermal cycles. A Si check valve structure, to be assembled with the actuator to construct a micropump, was also fabricated through a process of anisotropic etching and fusion bonding. The flow resistance for forward flow proved to be about one-three hundredths of that for backward flow.

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