Present-day society totally depends on the various kinds of high-tech devices such as semiconductor integrated circuits and flat panel displays. Those devices themselves have become quite large industries. For example, the worldwide markets of semiconductor industry and flat panel display one are more than 300 billion $ and 100 billion $, respectively. However, it is not necessary good if we look at them from the global environmental point of view. Because, the currently used production methods for these devices, i.e. vacuum process for depositing films and photolithography for patterning, have not been optimized in terms of efficiency in the use of energy and materials. Therefore, enormous amount of energy and materials are consumed as much as that reached at the level to threaten the global environment.
Instead of vacuum and photolithography processes, solution process and printing one have been investigated actively worldwide. Printing of devices needs sophisticated functional liquids (inks), so that the solution process technology ought to be the base of device printing. In the early stage of research and development of these processes, functional organic materials were intensely investigated and several attractive applications were developed including thin film transistors (TFTs), organic solar cells, organic electroluminescence devices and some parts for liquid crystal displays. Some of them have already appeared in marketplace and some are ready to do. As the next generation of functional material for solution and printing processes, inorganic materials are good candidates. Those would give devices both higher properties and stability than organic ones. For semiconductor materials, many kinds of suspended solutions using compound semiconductor nano-particles have been developed and liquid silicon materials were also developed. Liquid based silver and copper materials are now commercially available for making metal patterns. Recent progress of oxide materials are so great that considerableattention have been paid for solution and/or printed processed oxide devices.
As for the printing technology itself, the current technology level is far from to cover the all aspects required for electronics devices. For example, the minimum pattern size by printing is limited to more than 5 um even though the most precise printing technology adopted, while state of the art semiconductor technology already reached at the resolution around 20nm. As for the shape of patterns by printing, they are flat and around at the corners even though most devices require patterns sharp-edged and having a high aspect ratio. These drawbacks should be solved by innovative processes and materials.
In this talk, recent status of solution and printing processes will be addressed and some of new materials and processes which are expected to solve the above mentioned drawbacks will be introduced.
Author: Masahiko Tomitori