Role of Oxygen in Microstructure Development at Solid‐State Diffusion‐Bonded Cu/α‐Al₂O₃ Interfaces

Abstract

Role of Oxygen in Microstructure Development atSo I id -S t a t e D iff u s i o n -Bonded C u/a -A I 0 I n t e r f aces Microstructure development at solid-state diffusion-bonded Cda-Al,O, interfaces has been studied using optical and electron microscopy. High-purity Cu foil was bonded between basal-oriented a-Al,O, single-crystal plates at 1040°C for 24 h in a vacuum of -1.3 X Pa (1 X lo-' torr). Optical microscopy of as-bonded specimens revealed a large Cu grain size, fine pores, and long needles of Cu,O at the interface. Bulk specimens were annealed at 1000°C for various times under controlled oxygen partial pressures in CO/CO, mixtures. Consistent with a thermochemical analysis, CuAIO, could be formed at the interfaces. The CuAIO, was acicular and discontinuous, but occurred in a uniform distribution over the bulk specimen interfaces.

Joining of alumina via copper/niobium/copper interlayers

“…In the work of Rogers et al [71], cuprous oxide needles were present at the interface between 99.95% pure copper and sapphire after 24 h hv diffusion bonding at 1040°C even though the ambient p O 2 during diffusion bonding (≈3 × 10 -10 atm) was well below the copper-cuprous oxide equilibrium p O 2 (≈1.6 × 10 -6 atm). s The copper foil was found to contain ≈1200 atomic ppm (ppma) oxygen.…”

“…Studies by Rogers et al [71] and Rühle et al [57] have shown that the levels of dissolved oxygen in even high-purity copper foils are sufficient to induce formation of interphases that impact the mechanical properties of copper/sapphire assemblies. In the work of Rogers et al [71], cuprous oxide needles were present at the interface between 99.95% pure copper and sapphire after 24 h hv diffusion bonding at 1040°C even though the ambient p O 2 during diffusion bonding (≈3 × 10 -10 atm) was well below the copper-cuprous oxide equilibrium p O 2 (≈1.6 × 10 -6 atm).…”

“…Controlled p O 2 anneals (1000°C, 24 h) were used by Rogers et al [71] to study interphase formation at copper/sapphire interfaces. Sapphire/copper/sapphire diffusion-bonded assemblies were annealed at a p O 2 of ≈10 -7 atm to reduce the cuprous oxide particles, and induce the formation of a copper aluminate at the interface.…”

Electron Energy-Loss Near-Edge Structure of Metal-Alumina Interfaces

“…The chemical composition can be determined from the intensity of the ionization edges which are element specific. Furthermore, the energy-loss near-edge structure (ELNES) in the region from the onset of the edge to approximately [20][21][22][23][24][25][26][27][28][29][30] eV above the edge contains information about the bonding and the electronic structure [1]. Different oxidation states of metals can be distinguished either by chemical shifts or by changes in the shape of the absorption edge.…”

“…Depending on the processing conditions, either an atomically abrupt interface or reaction layers are formed. Possible phases in the Cu-Al-0 system are the two aluminates CuA102 and CuA1204 [22]. Formation of these compounds at the interface is only expected for bicrystals prepared in a non reducing atmosphere [23].…”