Crystalline backplanes for vivid displays – Bye-bye, pixels!

(f.l.t.r.) Dr. rer. nat. Ralph Delmdahl, Dipl.-Ing. Rainer Pätzel, Dr.-Ing. Kai Schmidt

Dipl.-Ing. Rainer Pätzel (Spokesperson)
Dr. rer. nat. Ralph Delmdahl
Dr.-Ing. Kai Schmidt

Coherent LaserSystems GmbH & Co. KG, Göttingen

The old-fashioned cell phone is passé - what the market now demands are smart phones with wireless capability and touch-sensitive displays. To be able to work with these new devices without difficulty and to display web content, the relatively small screen naturally still has to be able to deliver razor-sharp, high-resolution images and texts. The question is, how?

Dipl.-Ing. Rainer Pätzel, D. rer. nat. Ralph Delmdahl und Dr.-Ing. Kai Schmidt found the solution. They have developed an innovative laser system capable of producing large-area backplanes made of crystalline silicon on glass - the basis for manufacturing high-quality smart phone displays whose appeal lies in their excellent resolution. Rainer Pätzel is head of marketing at Coherent, a laser technology company based in Göttingen, Ralph Delmdahl works for the company as product marketing manager, Kai Schmidt is the director of the Research & Development division.

Demand for smart phones continues to grow. In three years, it is assumed that two billion people worldwide - twice as many as today - will own one of these multi-talented devices that combines a cell phone and portable mini-computer. The success of the small-sized high-tech devices is primarily based on their large touch-screen displays that allow easy handling and display of high-resolution pictures, animations and video clips. The only requirement is a pixel density of at least 250 dpi: the display's individual pixels are so close together that they cannot be seen by the human eye. With the pixels the underlying electronic circuits also have to be shrunk to minute dimensions. This can only be achieved by using thin layers of polysilicon - a material consisting of numerous small silicon crystals and produced by selectively melting amorphous silicon onto a glass substrate.

To use this process with great accuracy, rapidly and on large-area glass substrates, the scientists and developers at Coherent developed a unique optical procedure. It is based on high-energy short pulses of ultraviolet light emitted by two connected oscillators of an innovated excimer laser. The laser pulses are synchronized to an accuracy of a billionth of a second using a specially developed, patented high-voltage circuit. Laser optics in addition bundle the beams into a 75 cm long line-shaped thin beam that sweeps the glass surface, creating the polysilicon layer. This process is used to manufacture glass substrates several square meters in diameter, stepping up the throughput rate in production of the displays.

The VYPER/Linebeam technology was introduced to the market in spring 2011. It is the only process available for manufacturing large-area polysilicon layers and suitable for industrial mass production. In the meantime, all major producers of high-quality smart phone displays are using the system whose most important components are all manufactured at Coherent. Worldwide over 60 systems are currently in operation. In Göttingen alone, around 150 new jobs were created in production. Demand for the technology is expected to grow over the next few years, particularly since the displays for tablet computers, ultra-thin notebooks and the next generation of TV screens can be made of thin, organic light-emitting diodes (OLED).

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