Low-Loss Characteristics of Metal-Foil-Based Passive Components by Surface-Activated Bonding Technologies.

Low-loss passive components for RF signals compatible with the on-wafer process are essential for realizing integrated circuits with high-frequency and high-power operations. We successfully fabricate thick-metal-film-based coplanar waveguides (CPWs) and inductors (INDs) by directly bonding a 17- $\mu \text{m}$ -thick Al foil to a sapphire (0001) substrate and wet etching. The surface-activated bonding (SAB) technologies at room temperature are used. RF characteristics of the foil-based passive components are compared with those of components made of 1- $\mu \text{m}$ -thick evaporated Al layers. We obtain a better insertion loss and a higher ${Q}$ -factor for foil-based CPWs and INDs, respectively. The measured characteristics are compared with those obtained by an analysis based on the equivalent circuit scheme. Impacts of side etching of foils and surface oxidation on their characteristics are observed. Characteristics of virtual components made of 1- $\mu \text{m}$ -thick Al foils, i.e., 1- $\mu \text{m}$ -thick Al films with the same resistivity as that of foils, are analytically investigated. [ABSTRACT FROM AUTHOR]