Diversity and feasibility of direct bonding: a survey of a dedicated optical technology

TLDR

Bondability depends on geometry and surface states, and direct bonding offers vacuum‑tight, jointless, glueless interfaces that enable buried layers and loss‑free optical connections. The paper reviews nearly a decade of Philips Research direct‑bonding work, focusing on its diversity and feasibility. The review surveys a range of materials—including refractory metals, semimetals, boron, diamond, carbides, fluorides, nitrides, oxides, and chalcogenides—and discusses applications in interface engineering, waveguiding, and fiber‑plate bonding.

Abstract

The aim of this paper is to review almost a decade of direct-bonding activities at Philips Research including the diversity and feasibility of direct bonding. The bondability of a material is determined by its geometrical shape and mechanical, physical, and chemical surface states. Physically direct bonding provides a vacuumtight bond, which is jointless and glueless, and it permits engineering of the interfaces to be bonded. Layers can be buried, and reflective–lossless bonds between optical elements can be created. A variety of materials are investigated: (refractory) metals, a semimetal, boron, diamond, a carbide, fluorides, nitrides, oxides, and a chalcogenide. The applications that we describe relate to interface engineering, waveguiding, and the direct bonding of a fiber plate.