Fabrication and Characterization of Bi-metallic, Structured Films with Ultra-low Thermal Expansion

We fabricate and characterize bi-metallic structured thin films (~1 um thick) with ultra-low effective coefficient of thermal expansion (CTE). The films consist of a periodic array of aluminum (Al) hexagonal plates attached to a titanium (Ti) frame. In this designed discontinuous geometry, the self-standing films present ultra-low effective CTE through local release of the thermal strains by relative rotation of the lattice elements. We fabricated this structured film by a combination of conventional micro-fabrication process steps, and we measured its CTE as ultra-low (−0.6 × 10^(−6)/°C) using 3D digital image correlation. This new thin film can lead to the creation of low-cost, adaptive structures that operate in extreme thermal environments, such as reflective layers for space telescopes