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FEATURE: DISPLAYS


SCREEN TIME


Gemma Church finds that lasers are playing a crucial role in increasing the functionality of modern displays


Displays give us a portal into the digital domain. But the physical world now demands high-quality, ultra-durable and even bendable screens, requiring advanced laser systems to enable their manufacture. These laser systems are used for a range


of tasks during the multi-phase display manufacturing process, with applications in the welding, cutting, scribing, and drilling of glasses, metals and organic layers. For example, the excimer laser annealing


process converts amorphous silicon to high-quality polycrystalline silicon, which is then used as the base material on which a display’s electronic circuits are fabricated. In addition, during the manufacture of flexible displays – which have shown promise in applications such as wearable technology, foldable phones, rollable TVs and automotive displays – excimer laser lift-off is a process now commonly used to separate the flexible panels from their rigid transport glass substrates. Excimer laser annealing and laser lift-off


are two ‘quite mature’ processes where there has been ‘no significant development in terms of [the] process principle’ in the last couple of years, according to Jong Kab Park, director of the R&D centre at AP Systems – a developer of manufacturing equipment for displays and semiconductors. However, there have been advances


in the realm of ultrashort pulse lasers, as Rainer Pätzel, director of strategic marketing at Coherent, explained: ‘Display manufacturing is one of the major success stories for lasers and ultrashort pulse lasers. Today, ultrashort pulse lasers are the preferred tool for several process steps for advanced display manufacturing. They have reached very high maturity with a range of specifications from picosecond


30 LASER SYSTEMS EUROPE AUTUMN 2019


to femtosecond pulses and infrared to UV wavelengths, and they enable multiple applications for the mass-production of displays.’ The rise of ultrashort pulse laser


manufacturing techniques has occurred in parallel to the growth of OLED displays, which have now snatched market share from LCD display technologies, according to Pätzel, who said: ‘The emerging OLED technology offers more opportunities for lasers, partly because the manufacturing processes involved were developed with lasers and ultrashort pulse lasers in mind.’ Ultrashort pulse lasers bring a unique set


of advantages to display manufacturing, including a minimal heat-affected zone, the capability to create extremely fine features, and minimal post-processing. ‘Flat panel displays, such as LCD and especially OLED, are still innovating at an impressive speed, posing process challenges that are perfectly suited to


this type of laser,’ Pätzel said. ‘The wide variety of materials from glass to organic layer stacks, together with demand for the highest precision, creates an opportunity for lasers and ultrashort pulse lasers to add value. With more than 100 serial process steps to manufacture an OLED display, it becomes clear that the process quality, process window and process yield is key. This is where ultrashort pulse lasers shine.’ Coherent launched its Monaco


femtosecond and HyperRapid NXT picosecond lasers earlier this year, both of which are suitable for multiple applications in display manufacturing. The manufacture of fine metal masks (FMM), which are used to deposit organic RGB pixel materials, is one example of where ultrashort pulse lasers are being used in the creation of high-resolution OLED displays. The lasers are used to drill holes in the mask while achieving fine control of their taper angle, and without the creation of burr. According to Park, of AP Systems, while currently chemical etching methods were often used to make FMM, as display resolutions get higher, such methods face technical limitations in their ability to create the fine patterns required to achieve such high-resolutions. AP Systems has therefore been developing FMM using ultrashort pulse lasers for more than four years, and with them are able to achieve 1,000+


Flexible displays could be used to address the increasing amount of surface area being dedicated to displays in car interiors


@LASERSYSTEMSMAG | WWW.LASERSYSTEMSEUROPE.COM @researchinfo | www.researchinformation.info


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