OLED microdisplays are increasingly establishing themselves for use in future consumer-compatible wearables and data glasses.In order to meet the requirements of higher efficiency, higher contrasts and resolution of the applications, scientists of the Fraunhofer FEP have developed a new approach to the microstructuring of OLED on silicon. In the future, this would eliminate the need for color filters and shadow masks and develop full-color displays with a new process. Increases in efficiency and a significantly broader color spectrum have already been demonstrated in initial experiments. The results will be presented during the IMID 2018, from 29 to 31 August 2018 in Busan, South Korea, at booth 50 of the Fraunhofer FEP and the Poster Session.
About 88 times a day, the average smartphone user looks at a display. Not counting the view of the smaller smart watches or other display elements. Displays in a variety of ways are omnipresent and soon irreplaceable in daily life.
If one focuses on the world of OLED microdisplays, one quickly finds oneself in current and future applications in data glasses for the representation of virtual (VR) and augmented reality (AR), whose core is the microdisplay. It’s not just since the hype surrounding Pokémon Go that anyone has an idea of what AR means – additional information that you can interact with is displayed in the real world. In addition to industrial use in production 4.0, in medicine or consumer electronics, AR and VR applications have also been established for years in the advertising and education sectors. Gone were the days of chunky audio guides in museums. And not just about previous solutions with tablets or smartphones.
Due to their low depth due to the self-illuminating properties of the OLED and the excellent contrast ratios, manufacturers are increasingly turning to OLED microdisplays for AR / VR glasses. The Fraunhofer FEP has been working for years on the continuous development of this technology. Furthermore, there are still some technological challenges to be overcome in order to exploit the full potential of OLED technology for use in user-friendly data glasses or other AR / VR applications. Very high brightness and efficiency, good yields with large (chip) area, curved surfaces, integrated eye tracking and transparent substrates are some tasks that are still on the researchers’ agenda.
Currently, the OLED technology is facing the hurdle that full-color displays can only be realized by using color filters or shadow masks. These limit the efficiency or the resolution of the OLED. New approaches are being researched at high pressure to enable the microdisplays to be produced in a high-resolution, yet efficient and long-lasting manner. The structuring of the organic layers into the OLED represents one of the biggest challenges since conventional methods (eg photolithography) are not applicable to organic semiconductor materials. Two years ago, the use of electron beam technology for microstructuring at Fraunhofer FEP was successfully demonstrated. The patented process succeeded
Now the further development of the electron beam method succeeded, which now also permits full-color OLED structuring without color filter. To generate red, green and blue pixels, an organic layer of the OLED itself is patterned by a thermal electron beam process. This structuring causes a change in the thickness of the layer stack, which makes the emission of different colors possible. This marks the first major step in the development of full-color displays without the use of restrictive color filters in the process. Elisabeth Bodenstein, developer in the project team of Fraunhofer FEP, explains the advantages: “With our electron beam process, it is possible to thermally structure such sensitive, organic materials without damaging underlying layers.”
The results were obtained through simulations and initial estimation of the hole transport layer (HTL) thicknesses patterned with the electron beam. The researchers actually achieved the decoupling of red, green and blue from the white OLED. With proofs of principle at the Fraunhofer FEP, the colors could be demonstrated on first test substrates with comparable performance of the OLED.
In addition to the use of this new process for OLEDs, electron beam structuring can also be used for other applications in organic electronics or for inorganic layers. In addition, a microstructuring process by means of electron beam can be used very flexibly in the fields of photovoltaics, MEMS and thin-film technology.
Now the scientists are facing promising milestones ahead of the next milestones. The ultimate goal is to develop in the coming years together with partners the production of OLED microdisplays with this new method and to establish it by licensing in the industry. For this purpose, among other things, the structures are to be further miniaturized and process optimization promoted together with interested partners from the industry. In the next step, the integration of microstructuring into existing process flows is planned in order to gain further know-how for and with industrial partners. The aim is to develop the future transfer of the test results into an existing process line in order to enable the later establishment of the technology at industry level.
Accompanying this, the scientists are planning an extended simulation of the OLED. With an adaptation of materials and layer thicknesses, the color spectrum of the OLED is to be broadened even further. Perspectively, the use of displays in data glasses, eg for special applications in industry or medicine, should be opened up via this process.
The results of the new technology were developed within a project funded by the Fraunhofer-Gesellschaft. Now the scientists of the institute are ready for concrete further developments of the technology within the framework of partnerships and project work together with display, plant, material or system manufacturers. The results will be presented during the International Meeting on Information Display – IMID 2018, 29th to 31st August 2018 in Busan, South Korea, at booth 50 of the Fraunhofer FEP and poster session III.
Source : Fraunhofer-Gesellschaft