Hermetic Metallization of Aluminum Nitride for Radio Frequency Devices

65072 The use of high thermal conductivity aluminum nitride (AlN) components can boost the performance of power electronic and microwave devices significantly. However, the lack of suitable metallization and brazing technologies, required to join the AlN components to each other and to metallic members, hampers AlN insertion into vacuum electron devices and power semiconductor packages. This project will develop a hermetic refractory metallization technology, along with associated brazing technologies, to attach AlN composites to copper members for microwave tube and power semiconductor packaging applications. Phase I investigated refractory Mo-Mn thick film metallization, active metal brazing, and diffusion bonding techniques to attach AlN and lossy AlN dielectrics to copper members. The adhesive strength of the thick-film-metallized, active-metal-brazed, and diffusion-bonded AlN-Cu joints were measured; hermeticity of the joints was evaluated using leak tests; and chemical and microstructural characterization of the metallized and brazed interfaces was performed. Phase II will develop a molybdenum thick film metallization based on the glasses identified in Phase I, along with associated nickel-plating and brazing techniques, to attach AlN components to copper members. Commercial Applications and Other Benefits as described by the awardee: Almost every medium-to-high vacuum electron device would benefit from new hermetic, refractory metallization that is compatible with high-thermal-conductivity aluminum nitride composites. Applications include klystrons and gyrotrons to supply microwave energy in chemical processes, materials processing, direct broadcast satellites, magnetic fusion, and microwave communications.