Fabrication of low thermal expansion coefficient electrodeposited Invar alloy films by hydrogen annealing for OLED fine metal masks

Abstract

Electrodeposited Invar alloy film is considered an ideal material for fabricating OLED fine metal masks (FMMs) due to its advantages of a simple preparation process, cost-effectiveness, and highly controllable thickness. However, electrodeposited Invar alloy films exhibit a high thermal expansion coefficient (CTE). In this study, the phase transition temperature range of electrodeposited Invar alloy films was obtained and hydrogen annealing experiments were conducted. The results indicate that grain size, carbon (C) and sulfur (S) impurity contents, as well as compositional homogeneity, influence the CTE of electrodeposited Invar alloy films, with grain size dominating. The CTE is inversely proportional to grain size, as the CTE at the grain boundaries of electrodeposited Invar alloy films is significantly higher than at crystallites. After hydrogen annealing at 1073 K, the average grain size is approximately 3.3 μm, with the C content decreasing to 50 ppm and the S content dropping below 10 ppm. The CTE of electrodeposited Invar alloy film is reduced to 1.0 × 10⁻⁶ K⁻¹, comparable to that of conventionally manufactured Invar alloy. Consequently, electrodeposited Invar alloy films with near-zero inclusions and extremely low CTE were obtained. This study enables the application of electrodeposited Invar alloy films in FMM fabrication.