Abstract

This chapter summarizes several recent theoretical and computational approaches for understanding the behavior of shape memory films from the microstructure to the overall ability for shape recovery. A new framework for visualizing microstructure is presented. Recoverable strains in both single crystal and polycrystalline films are predicted and compared with experiments. Some opportunities for new devices and improvements in existing ones are also pointed out here.

Introduction

The explosive growth of microsystems has created a great need for the development of suitable microactuators and micropumps. Among these applications, micropumps with large pumping volume per cycle and high pumping pressure are essential to microfluidic devices. This requires a large actuation energy density to transmit a high force through a large stroke. However, common MEMS-integrated actuation schemes can deliver limited stroke and actuation force; specifically, the typical output pressure of these pumps is of the order of several tens of kPa. Therefore, there is an important need for finding suitable materials which are able to deliver a high work output from a small volume. Shape memory alloys show great promise in this aspect since they outperform other actuation material in work to volume ratio; consequently, they are able to recover large strain at high force [1, 2, 3, 4]. A disadvantage of using these alloys is that the frequency of operation is relatively low due to limitations on heat transfer. But this can be improved in thin films because of the increase in the surface area to volume ratio. Currently an operation frequency of 100Hz has been demonstrated using the R-phase transformation [5].