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issue: May 2007 APPLIANCE Magazine

Technology Report
Next-Generation Display Technology

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Advanced laser technology is said to help consumer electronic manufacturers create brighter displays with crisper images and lower power consumption.

It is safe to say that flat panel displays (FPDs) are one of the fastest growing technology segments in the consumer electronics industry. Consumers continue to ask for higher resolution, brighter displays, as well as faster (video) capabilities for phones, PDAs and other compact products. In an effort to beat out the competition and keep consumers happy, manufacturers are spending enormous amounts of time and energy to achieve these features. Santa Clara, California, U.S.-based Coherent, however, believes the answer is actually quite simple—lasers.

According to the supplier, many high-performance FPD products are based on polycrystalline silicon (poly-silicon), as opposed to the more widely used amorphous silicon. These high-performance products include the latest active matrix organic light emitting displays (AM OLED) and system on panel (SOP) devices. Coherent says that Low Temperature Poly-Silicon (LTPS) annealing is the proven, preferred approach for producing the critical poly-silicon layer during FPD fabrication.

“The increased adoption of LTPS panels is led by consumer demand, and the technology is already being integrated widely in mobile and other hand-held displays,” explains Ludolf Herbst, a product manager of the Lambda SX series based in Coherent’s German facility. “The key benefits are high brightness, crisper images and lower power consumption.”

Creating LTPS displays requires the use of laser technology. According to Coherent, the most important laser characteristics for LTPS are high pulse energy, pulse-to-pulse energy stability and high reliability. The company says its new Lambda SX 315C laser has all of these characteristics, while improving the LTPS process in terms of throughput, yield, device quality, and cost.

“Stable UV laser light is essential for demanding and efficient LTPS LCD display manufacturing,” Herbst tells APPLIANCE. “The Lambda SX 315C offers unique energy stability at high ultra-violet (UV) laser pulse energy (typical 0.5 percent rms at 1 Joule pulse energy). This combination is not met by any other competing UV laser technology such as diode pumped solid-state lasers (DPSSL), diode lasers or fiber lasers.”

The next-generation laser is said to provide the same high pulse energy as its predecessor while delivering a twofold improvement in energy stability. “This is achieved by a proprietary laser discharge design and high-resolution pulse energy control,” Herbst says. The laser’s high-pulse energy is said to enable a wider area to be processed with each pulse, maximizing both the process window (hence, yield) and process speed.

In combination with process control tools, the increased stability of the new laser reportedly results in improved mobility levels, which minimize variations in the threshold voltage (Vth) of the thin film transistors (TFTs) and significantly reduces Mura-effects, enabling mass production of high-performance AM OLED devices. It also improves the yield for larger panel products.

“Improved mobility levels refers to poly silicon electron mobility,” Herbst notes. “High mobility levels result in high-performance and long-term stable TFTs. Conventional amorphous silicon technology shows decreasing TFT performance over time, whereas poly-silicon based TFT keep performance over years.”

Lower total cost-of-ownership is said to be achieved through enhanced predictive maintenance characteristics and longer components lifetime. “[This] is enabled by state-of-the-art E-diagnostic capabilities, which keep track of laser performance,” Herbst says. “With the acquired laser data, consumable laser parts can be used as long as possible in order to save costs. The end of component lifetime is predicted by monitored degradation of performance.”

The company says this feature results in a 20-percent reduction in running costs, compared to earlier lasers used for LTPS.


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