Thin film metallization for micro-bimetallic actuators

In this study, eleven different thin film metallization systems were evaluated for use in micro-bimetallic actuators for microelectromechanical structures. These films were evaporated or sputtered onto silicon wafers. The film stress and stress relaxation were determined by measuring changes in the wafer curvature. The phases and micro-structure of these films were evaluated with, scanning electron microscopy, transmission electron microscopy, Auger electron spectroscopy, electron probe micro-analysis, X-ray diffraction and line shape analysis, and atomic force microscopy.; Bimetallic actuator may be operated to generate either force or displacement. The displacement mode is dominated by the coefficient of thermal expansion while the force mode is a function of both Young's modulus and coefficient of thermal expansion of the active layer material. In both modes the maximum displacement or force is determined by the material's yield strength. A figure of merit was developed to aid in material selection.; The 5052 aluminum alloy films showed that solid solution strengthening can double the yield strength of a thin film. The T201 aluminum alloy films showed that precipitates can increase yield strength by 2.5 times. The 2090 alloy film oxidized during the first heating. Based on isothermal stress relaxation data and changes in the micro-structure of the 5052 and T201 alloy thin films, two mechanisms involving logarithmic creep have been postulated to cause stress relaxation. One mechanism is movement of dislocations in slip systems that terminate at the surface while the other is dislocations moving in slip systems that terminate at grain boundaries.; Copper gold intermetallics films oxidized and plastically deformed before the order-disorder transformation occurred, but showed that ordered intermetallics have a lower stress relaxation rate than the solid solution phase. The Al{dollar}sb3{dollar}Ti films showed no stress relaxation at 450{dollar}spcirc{dollar}C, plastically deformed only above 500{dollar}spcirc{dollar}C, and had limited oxidation up to 800{dollar}spcirc{dollar}C.; Nickel, copper, titanium, and manganese films all oxidized on their first heating to 350{dollar}spcirc{dollar}C. The copper film also oxidized at 50{dollar}spcirc{dollar}C over 48 hours. Calculations also showed that the passivation oxide on aluminum alloys can significantly reduce performance a bimetallic actuator. Thus oxidation resistance is a significant requirement for materials for thermal actuation.