With a large Ultra HD TV, you almost feel that you are on the playing field, experiencing the tackles, passes, and goals in a soccer match as if you were part of the team. But because it is not only the size that matters when people are choosing a TV, but also the resolution and price, Evonik has developed iXsenic®, a metal oxide semiconductor technology that improves the resolution of large screens and also reduces their production costs.
TVs are becoming larger and larger. Screen diagonals of sixty inch and more are not unusual these days. The number of pixels per inch also increases: Full-HD displays with more than two million pixels and six million subpixels for the primary colors red, green, and blue are now standard, and manufacturers are already working intensively on increasing the number of pixels by factors of four and even 16. After all, what good is a large TV without sharp images and brilliant colors? Although smaller than classic flat screens for PCs and laptops, smartphones and tablets are just as popular. The resolution and picture quality of these mobile devices is definitely not lagging behind the TV screens.
Function of semiconductors in thin-film transistors
The task of thin-film transistors is to fulfill viewers’ high demands and enable high definition television (HDTV). Modern full HD TVs contain about six million of them. They control the individual subpixels and refresh several 100 frames per second, which the human eye perceives as flowing movement. The thin-film transistors are able to do this only because the electrons move fast enough through the semiconductor layer that is integrated in the thin-film transistors and transport the signals. The larger the screen, the faster the electrons have to be in order to guarantee a high resolution.
This is where the display industry faces major technological challenges. At large displays with high resolutions, the amorphous silicon that is currently being used as a semiconductor material is stretched to its limits. This is due to the material properties: ultimately, the speed at which the thin-film transistors can be switched depends on the electron mobility in the semiconductor layer. A large, high-resolution LCD TV needs enormous electron mobility: between 1 and 10 square centimeters per volt-second. Speeds like this are generally not possible with amorphous silicon or can be achieved only with enormous technical effort. The result would be a very large TV with blurred moving images and streaking effects. Other technologies – experts talk of LTPS and sputtered IGZO – also offer high-performance semiconductors, but they are time, cost, and resource intensive to produce, since they require large equipment and high vacuum.
Crisper image and larger display
This is where iXsenic® from Evonik comes in and offers display manufacturers an optimum solution: Instead of semiconductor technologies with high vacuum processing, this technology uses inorganic metal oxide semiconductor material that is liquid processable and can be applied with a coating process – without vacuum. This not only simplifies the production of flat screens, it is also more costeffective, as this process reduces energy costs and effort for display manufacturers. Depending on the area of application, the metal oxide semiconductors can exhibit electron mobilities of more than 10 square centimeters per volt-second and, under ideal conditions, even up to 20 square centimeters per volt-second. With these properties, they are perfect for high-resolution in extremely large format LCD and OLED TVs: with iXsenic®, TV has no limits.
In collaboration with SCREEN Finetech Solutions Co., Ltd., the market leader of coating equipment for the display industry, Evonik goes even one step further. By offering a mature manufacturing technology suite the introduction of the iXsenic® semiconductor technology will be significantly facilitated.
“In order to offer a complete solution for TFT backplane mass production we need to work on the whole process design,” says Hirofumi Yoshino, General Manager at SCREEN FT. “We plan to finalize the optimization for all the processes which realize the highest performance of iXsenic® by the end of this year.”