Synthesis, Characterization and Laser Patterning of Pulsed DC Magnetron Sputtered NiTi Shape Memory Alloy and TiN Thin in Films

Abstract

The preparation, characterization, and applications of nickel-titanium (NiTi) shape memory alloy (SMA) and titanium nitride (TiN) thin films are investigated in this thesis. The vacuum diagnoses of the process chamber using a residual gas analyzer (RGA) and its importance in the high-quality thin film process environment have been discussed. An optical emission spectroscope has been employed for analyzing the in- situ plasma characteristics of both pulsed DC magnetron sputter (PDCMS) deposition technique and the conventional DC magnetron sputter deposition (DCMS) techniques. The PDCMS NiTi plasmas exhibited higher intensity than the DCMS NiTi plasmas. The enhancements of the NiTi plasma and thin film properties of the PDCMS deposition technique over those of the conventional DCMS technique have been investigated. In the next attempt, the influence of deposition pressure and pulse frequencies on the NiTi thin films properties has been investigated. The NiTi films deposited at 10-3 mbar order pressure exhibited austenitic phase at room temperature, whereas the NiTi films deposited at 10-2 mbar order were in martensitic phase at room temperature. The NiTi films deposited at various pulse frequencies (50 to 350 kHz) did not significantly improve the film properties because the variation of pulse frequencies from 50 to 350 kHz was not adequate to impact the film properties substantially. The second material, TiN, has also been synthesized using the PDCMS technique. The electrical properties of the TiN thin films have been fine-tuned by varying their microstructures using various process adjustments like substrate temperature and nitrogen partial pressures. The TiN film with better electrical resistivity was chosen to fabricate micro-heaters. Focused Ion Beam (FIB) and Ytterbium fiber laser bulk micromachining techniques were utilized to fabricate the micro-heater patterns. By adjusting the input powers, the temperature attained was nearly 400 °C. Similarly, femtosecond laser and Ytterbium fiber laser bulk micromachining techniques were used to fabricate NiTi micro-devices, such as micro- cantilevers and micro-wrappers micro-combs, micro-mesh, etc. TiN micro-heaters were fabricated alongside the NiTi micro-devices to provide the required temperatures for actuation. Since both NiTi and TiN are biocompatible materials, these devices could be used in bio-friendly environments.