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

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.