Diffusion processes for integrated waveguide fabrication in glasses: A solid-state electrochemical approach

Abstract

The process of solid-state film ion exchange (Ag +-Na +) in glass substrates for the fabrication of integrated, optical waveguides has been investigated as a solid-state electrochemical process. The ion exchange process is initiated by establishing a space-charge distribution in the more mobile charge carrier. The space charge establishes an intense electric field that drives oxygen to the surface to fuel dopant oxidation and subsequent diffusion. A one-dimensional model is presented in space-charge effects in glass having charge-blocking and permeable electrodes. The model results show that the rate-limiting step for initiating Ag + diffusion in glass is the motion of oxygen ions towards the silver anode to form a layer of silver oxide. The predictions of oxygen diffusion time compare favorably with the “dead times” in the current vs time curves observed during the ion exchange process. The dead time corresponds to the period of negligible diffusion of silver into glass and formation of a stable oxide layer. This was experimentally confirmed by Rutherford backscattering analysis. The variation of maximum diffusion current as a function of applied voltage and temperature was also studied and a theoretical electrochemical treatment is presented.