Transfer Processes for Thermally Stable Large-Size TFT Flexible Substrates

Abstract

We report on glass etching transfer processes to obtain thermally stable large-size TFT flexible substrates on plastic film bases. The transfer processes include high-pressure jet etching that allows us to achieve good etch-rate uniformity over the large area and the utilization of an adhesive having a low elastic modulus. From the experiments and simulations, we find that using an adhesive having a low elastic modulus is effective in reducing bend of the flexible substrate under thermal stresses. The simulations also predict that the reduction in the bend corresponds to the reduction in the principal stress of the adhesive, leading to the suppression of the film peeling off from the thinned glass. Using the transfer processes, we have successfully fabricated thermally stable TFT flexible substrates (300 mm 350 mm 200 m) that have satisfactory electrical characteristics.

Development of rollable silicon thin‐film‐transistor backplanes utilizing a roll‐to‐roll continuous lamination process

“…In order to gain an insight into the force balance among the materials, we numerically solved the following stress-strain equation 16 :…”

“…We numerically estimated deformation of the flexible TFTbackplane sheet and the principal stress generated in the permanent adhesive resulting from 150°C thermal stress, a typical temperature for curing polyimide films in an LCD production process. 16 We compared permanent adhesives having a low elastic modulus (0.07 MPa) and a high elastic modulus (27.5 MPa) in terms of the differences between them in deformation and principal stress at 150°C. Here, the plastic film was a high-E film.…”

“…In this paper, we first review our recent work on the TFT transfer process, focusing on the use of high-rate, uniform glass-etching to transfer TFT arrays fabricated on a glass substrate to a flexible plastic base film 14,15 as well as on the thermal stability of the adhesive used to glue thinned TFT glass sheets to base film. 16 Thermal stability is discussed in terms of the generation of mechanical tensile stress in the adhesive, which results from thermal stress. This tensile stress is found to cause deformation in flexible TFT backplanes, leading to peeling-off of the base film from the thinned TFT glass sheet.…”