A type of hybrid thin-layer film that could make touch screen displays in tablets, smart phones and computer monitors last longer has been developed in a new study by two polymer scientists from Kyungpook National University in Daegu, South Korea. The flexible thin films are comprised of both inorganic and organic materials using a sol–gel fabrication process, and could help in producing screens that are flexible and durable but still offer the same electrical and optical properties as existing screens.
Touch screens are usually made up of layered thin films of indium–tin oxide of only billionths of a meter in thickness. This oxide is electrically conductive and allows electrical signals to travel from the touch location to the edge of the display where they can be sensed by the device. However, these inorganic materials are brittle and shatter easily, and use acids that corrode the metals and metal oxides in the electronic components. An acid-free sol-gel method of synthesizing organic–inorganic hybrid materials was therefore required for optical thin-film applications.
The research by Soo-Young Park and A-Ra Cho, as published in Optical Materials Express [Cho, A.-R. & Park, S.-Y. Opt. Mater. Express (2015) DOI: 10.1364/OME.5.000690], involved a co-polymer composed of two organic materials combined with a co-polymer called trialkoxysilane. When this reacts with two other inorganic chemicals, it synthesizes hybrid layers with high and low refractive indexes. The refractive index measures the amount that light is bent as it passes through the material.
However, inorganic thin-layer and hybrid films have layers with different refractive indexes, which helps tune the wavelengths of the light passing through the film (or touch screen). Tests undertaken on the new hybrid films show that both the high and low refractive index layers are highly transparent compared to just glass. Also, films that have higher resistance have less electrical conductivity, so more voltage must be applied to send a signal through it, further degrading the material. For these new hybrid films, resistance increases less over time, allowing displays from this type of film to last longer.
The materials were produced in solution and at low temperature, making their production much cheaper. In addition, the hybrid films demonstrated less depreciation in their flexibility after 10,000 bending cycles than the inorganic layered films. The process means multi-layered films can be created where the layers have thicknesses usable for anti-reflective coatings, leading to potential new applications.