The Ni-al Thin Films And Thermal Performance

Ni-Al thin film is a promising material as thermal resistor. In thisdissertation Ni-Al thin-films were deposited using direct current (DC)magnetron co-sputtering from Ni and A1 targets. The integrity of the filmsand their elemental compositions were assessed using a scanning electronmicroscope (SEM) equipped with an energy dispersive spectroscope(EDS) analyzer. The morphology of the thin-films was characterized byatomic force microscope (AFM) and SEM. The microstructures ofas-deposited and annealed films were identified using a X-raydiffractometer (XRD). The defects of the thin-films were detected bySlow Positron Annihilation Technology (SPAT). The sheet resistance ofthin-films was measured by Four Point Probes (FPP). The temperaturecoefficients of electrical resistance (TCR) of the alloy thin-films werealso determined based on the set-up system for sample heating controland data processing. Based on these measurements and analysis, someconclusions can be made. They are as follows:Ni-Al thermal resistor thin-films with expected stoichiometricproportion can be prepared by adjusting the sputtering power of Ni and A1targets. Sputtering is a good way to fabricate Ni-A1 thermal resistorthin-films for these films are compact and smooth. The films are wellcrystallized with strong (111) preferred orientation. The grains are veryfine and after thermal annealing they become more crystallized. Theresults of defects study show that Al antisite defects are the main defects,the surface layer of thin-films is very thin and the distribution of defectsin the middle layer is lower and more uniform. Through annealing thedefects become less. As 1% O₂ was introduced into the vacuum chamberduring sputtering, the crystallization processes blocked and amorphousAl₂O₃ phase is found in the annealing samples through XRD patterns.The result of SPAT study shows that the amorphous Al₂O₃ phase results inserious lattice distortion.The electrical properties of the thin films show that the sheetresistance of films decreases with the input power of each target. Thesheet resistance increases after rapid thermal annealing protected by N₂. From room temperature to 200℃, the resistance of the thin filmsincreases linearly as a function of temperature which shows a positivetemperature coefficient of resistance. The temperature coefficient ofNi-Al thin-films decreases after annealing and increases if 1% O₂ isintroduced into the vacuum chamber during sputtering. Further analysisshows that the Al₂O₃ present in the samples plays a decisive role.Experimental results show that Ni-Al thin-films are suitable astemperature sensor chips for it has a very wide temperature measurementrange from room temperature to 200℃, with E_f(nonlinearity)＜±2.7%,E_max (outstanding non-repeatability)≤±5.2% and good TCR of 2.06×10^-3/K.