High-Rate Glass Etching Process for Transferring Polycrystalline Silicon Thin-Film Transistors to Flexible Substrates

We report on a process technology that makes possible the transfer of polycrystalline silicon thin-film transistor (poly-Si TFT) arrays from an original rigid glass substrate to another flexible plastic substrate. The transfer technology is characterized by its high-rate glass etching process, using a newly developed apparatus. After a description of the transfer sequence free from adhesive contamination, we present experimental observations for high-rate glass etching in hydrofluoric (HF) and hydrochloric (HCl) acid solution mixtures. The etching apparatus provides jets of the solution mixtures to the glass surface in order to achieve good circulation of the solutions in the bath, as well as to remove etch products effectively from the surface. We successfully achieved etch rates as high as 6 m/min with the etched surfaces almost as smooth as the original glass. In order to gain insight into the chemical mechanism of the etching, we developed a simplified kinetic etching model based on a Langmuir isotherm. The model and experimental etch-rate data are generally in good agreement, indicating that the basic modeling approach captures much of the essential chemistry for the high-rate glass etching. The transfer technology allows us to obtain TFT flexible substrates with good electrical characteristics and flexibility even after an annealing process at as high as 150 . These results demonstrate that the transfer technology is a promising candidate for achieving entirely new lightweight electronic devices such as flexible displays and radio frequency identification tags based on TFT flexible substrates.