A. D. Johnson, TiNi Alloy Company, San Leandro, CA; V. Martynov, TiNi Aerospace, San Leandro, CA
Thin film Nitinol has been fabricated in laboratory quantities by many researchers since 1989. A number of high quality publications exist. This paper attempts to trace the development of technology, publications, people involved, and applications, from the perspective of a group involved in the process.
Some experience gained and lessons learned will be discussed. Vacuum sputter deposition produces TiNi film with desirable thermo-mechanical properties if several critical process parameters are controlled. Microlithography and chemical milling, the MEMS processes, have been used to fabricate microactuators combining TiNi with silicon and to make patterned free-standing superelastic film. For these, selective etching places requirements on selection of chemicals and sequences of operations.
Use of TiNi thin film in products has been limited. Some examples of efforts to market TiNi film will be cited, with suggestions about future directions.
Thin film TiNi was introduced at Engineering Aspects of Shape Memory Alloys conference in Lansing MI in 1989. Much has happened since then. Both high-temperature actuator material and superelastic material are produced. There are MEMS devices, patents, and conference papers. But no large-scale application has happened. One consequence is that thin film material remains expensive. It is increasingly apparent that each application requires significant investment: there is no one-size-fits-all advantage.
Anticipated applications were microactuators, particularly valves, medical, especially intravascular, miniature instruments (gas chromatographs), and fuel cells. We will describe efforts in some of these areas and suggest where the technology is currently moving.
