Patterned Ti-based shape memory alloy films have attracted considerable research effort in recent times owing to their favorable characteristics for potential applications as micro-actuators in microelectromechanical systems. Titanium-Nickel-Palladium (TiNiPd) shape memory alloy film can be used to fabricate micro actuators for high temperature applications. These films are to be patterned to realize the microactuators. We have made an attempt to laser pattern amorphous TiNiPd shape memory alloy films on a silicon substrate, deposited by DC-magnetron sputtering using a Ti54Ni36.8Pd9.2 alloy target. These films were micromachined by KrF excimer laser induced ablation at 248nm. Two different mask patterns have been used, one having an array of squares and circular features and the other having lines of varying widths and pitch. Three types of film removal mechanisms were observed i) due to amorphous to crystalline phase transformation, ii) due to solid to liquid transition followed by crystallization and iii) removal of the film along with silicon substrate melting. These mechanisms of TiNiPd film removal from silicon substrate appear to be similar to the mechanisms of TiNi film removal from silicon substrate reported in the literature. This paper presents the dependence of TiNiPd material removal mechanisms and feature quality on laser parameters such as fluence, pulse repetition frequency and number of shots.
Ti-based shape memory alloy (SMA) thin films have the potential to become high performance actuator materials for microelectromechanical systems. The major challenge in fabricating Ti-based SMA thin films is composition control, since a small compositional deviation can result in very large changes in the phase transformation temperatures. Owing to extreme reactivity of titanium, oxygen contamination is a major problem during the sputter deposition of TiNi and TiNiPd SMA thin films as it alters the Ni/Ti ratio. Oxygen as a contaminant has deleterious effects both on shape memory properties and mechanical properties of these alloys. Not much work in this field has been focussed on identification, determination and elimination of oxygen contamination. Rutherford Backscattering Spectrometry (RBS)is a useful technique for accurate determination of stoichiometry and depth profiling of these alloy films. RBS is less
sensitive to light elements. For this reason RBS has been complemented by Heavy Ion Elastic Recoil Detection Analysis (HIERDA) for the determination of oxygen. TiNi and TiNiPd films were deposited by DC- Magnetron Sputtering on unheated Silicon substrates by using Ti1.08Ni0.92 and Ti1.08 Ni 0.74 Pd 0.18 alloy targets. RBS measurements were carried out with 2 MeV He ions whereas HIERDA used 77 MeV I10+ ions with a ToF-E detector. It was found that oxygen contamination is almost negligible in TiNiPd films compared to TiNi films deposited under similar conditions. Palladium is effective as a catalyst in removing the oxygen from the deposition system resulting in reduced oxygen pick-up. This paper presents the stoichiometric analysis and depth profiling of these films by RBS and HIERDA
Actuators made from patterned Ti-based shape memory alloy films have potential applications in micro systems owing to their high mechanical output and other favourable characteristics. Micro fabrication techniques such as chemical etching and electrolytic photo etching have been used for patterning these alloy films. The latest trend is to use laser micromachining owing to its advantages in terms of non-contact processing, achievable resolution and pattern flexibility. Successful excimer laser micromachining of TiNi in the forms of as- rolled strips (bulk) and RF Sputter deposited, free - standing foils, with different combinations of laser parameters have been recently reported. However, sufficient data pertaining to laser micromachining of these alloy films deposited on silicon substrates are required for their applications to silicon based MEMS. We have attempted to micromachine TiNi shape memory alloy films on silicon substrate deposited by DC- magnetron sputtering using a Ti54Ni46 alloy target. These films were micromachined by KrF excimer laser induced ablation at 248nm. The dependence of TiNi material removal mechanisms and feature quality on laser parameters such as fluence, pulse repetition frequency and number of shots are presented.