Abstract

TiNi shape memory thin films have great potential as an effective actuation material for microsized actuators. However, a high temperature (above approximately 723 K) is required in order to obtain crystalline thin films either during deposition (e.g., sputtering) or in post-annealing. Such a high temperature is not fully compatible with the traditional integrated circuit techniques, and thus brings additional constraint to the fabrication process. Laser annealing provides an ideal solution to this problem, as the high temperature zone can be confined well within a desired small area at a micrometer scale. In this chapter, we demonstrate the feasibility of local laser annealing for crystallization in as-deposited amorphous TiNi thin films and present a systematic study of the theories behind this technique.

Introduction

TiNi shape memory thin films have great potential as an effective actuation material for microsized actuators [1]. As compared with other materials, such as electrostatic, electromagnetic and piezoelectric thin films, the work output per unit volume of TiNi shape memory thin films is significantly higher, because they are able to provide not only a larger force but also over a longer displacement [2]. In addition, the disadvantage of slow response speed in bulk shape memory alloys (SMAs) can be dramatically improved due to a larger surface-area-to-volume ratio in thin films. 20 Hz frequency has been achieved in a TiNi thin film based microvalve [3]. Furthermore, TiNi shape memory thin films can be fabricated by techniques which are compatible with the well-established batch-processing technology of Si micromachining [1, 4]. A number of microdevices have been realized using TiNi shape memory thin films, as presented in Chapters 10 to 19.