Compressive stress profiles of chemically strengthened glass after exposure to high voltage electric fields

The ion exchange process for chemical strengthening of glass involves an inter-diffusion of alkali ions between the glass and a molten salt bath. In most commercial glasses, this comprises an exchange of Na⁺ ions in the glass for larger K⁺ ions from the salt bath. The stuffing of K ⁺ ions into sites previously occupied by Na⁺ in the glass results in the formation of a compressive stress profile in the glass. In the absence of stress relaxation, this compressive stress profile largely follows the concentration profile of the K⁺ ions. Any subsequent migration of K⁺ ions within the glass would result in a change in this stress profile, which could lead to different mechanical behaviors of the glass. In particular, a reduction of the surface compressive stress could lead to a compromise in the retained strength of the glass, making it more susceptible to failure. Recent work has shown that chemically strengthened glass can be used as an effective substrate material for organic thin film transistors (TFTs), since the temperatures involved with organic TFT deposition are low enough to avoid any compromise in the compressive stress profile. This opens the possibility of fabricating high strength organic TFT displays. However, the question remains as to whether the exposure of the glass to an electric field may lead to the diffusion of the alkali ions and a corresponding alteration of the stress profile, which could compromise the strength of the organic TFT device. In this paper, we demonstrate that there is no change in the stress profile of Corning® Gorilla® Glass 3 after subjecting the glass to much higher voltage dc fields compared to the maximum field that would be exhibited in an organic TFT device. The stress profile is modified only after treating the glass at sufficiently high temperature, where alkali migration becomes thermally activated.