Development of High Temperature Structural Metal MEMS Materials and Devices
To date, the majority of commercial MEMS devices are fabricated out of silicon. Si is compatible with conventional very-large scale integration (VLSI) fabrication technologies and exhibits a highly desirable linear elastic response with excellent dimensional stability at room temperature. These aspects make silicon as an attractive mechanical MEMS material; however, mechanical properties(such as creep or fracture strength) of Si are significantly degraded at thermally harsh environments. Accordingly, the development of materials that possess improved mechanical, functional properties at wider temperature range in addition to the ability to be shaped on micro-scale would greatly expand the design space for the future electronic systems. Metallic materials are especially attractive in MEMS applications that require high density, electrical and thermal conductivity. In this research, we are looking into Ni-based alloys with the exceptional mechanical properties and dimensional stability.
Recently, we developed direct current (DC) magnetron sputter deposited Nickel (Ni)-Molybdenum (Mo)-Tungsten (W) films. The films deposited as single-phase nanotwinned solid solutions and possess ultra-high tensile strengths of approximately 3 GPa, but negligible ductility. Subsequent heat treatments resulted in grain growth and nucleation of Mo-rich precipitates. While films annealed at 600℃ or 800℃ for 1 h still showed brittle behavior, films annealed at 1,000℃ for 1 h were found to exhibit strength greater than 1.2 GPa and near 10% tensile ductility. In addition to the excellent mechanical properties, alloy films further exhibit remarkably improved dimensional stability i.e. a lower coefficient of thermal expansion and greater microstructural stability. An excellent balance between mechanical properties and dimensional stability make sputter deposited Ni-Mo-W alloys promising structural materials for MEMS applications.
To date, the majority of commercial MEMS devices are fabricated out of silicon. Si is compatible with conventional very-large scale integration (VLSI) fabrication technologies and exhibits a highly desirable linear elastic response with excellent dimensional stability at room temperature. These aspects make silicon as an attractive mechanical MEMS material; however, mechanical properties(such as creep or fracture strength) of Si are significantly degraded at thermally harsh environments. Accordingly, the development of materials that possess improved mechanical, functional properties at wider temperature range in addition to the ability to be shaped on micro-scale would greatly expand the design space for the future electronic systems. Metallic materials are especially attractive in MEMS applications that require high density, electrical and thermal conductivity. In this research, we are looking into Ni-based alloys with the exceptional mechanical properties and dimensional stability.
Recently, we developed direct current (DC) magnetron sputter deposited Nickel (Ni)-Molybdenum (Mo)-Tungsten (W) films. The films deposited as single-phase nanotwinned solid solutions and possess ultra-high tensile strengths of approximately 3 GPa, but negligible ductility. Subsequent heat treatments resulted in grain growth and nucleation of Mo-rich precipitates. While films annealed at 600℃ or 800℃ for 1 h still showed brittle behavior, films annealed at 1,000℃ for 1 h were found to exhibit strength greater than 1.2 GPa and near 10% tensile ductility. In addition to the excellent mechanical properties, alloy films further exhibit remarkably improved dimensional stability i.e. a lower coefficient of thermal expansion and greater microstructural stability. An excellent balance between mechanical properties and dimensional stability make sputter deposited Ni-Mo-W alloys promising structural materials for MEMS applications.