Research project "FlexPAET"

Energy-efficient lighting – a challenge for microtechnology

The further development of light-emitting diodes (LEDs) has led to efficient, resource-saving light sources during the last years. The use of such light sources, however, has so far been restricted to only a few applications, although the advantages with regard to energy-efficiency and durability are well known. Within the context of the research project "FlexPAET", the Fraunhofer IPT is currently developing processes and equipment that will allow the cost-effective production of flat optics, paving the way for an even wider use of LED technology in the future.

Structured and planar light guidance systems are ideally suited to serve as optical components for lighting and backlight technology, with complex and 3-dimensional microstructures ensuring high levels of visual functionality. The production of large-components with microstructured surfaces, however, has so far posed a serious problem to the industrial production process engineers. The new technique of flexible microstructuring with step-and-repeat hot embossing processes now appears capable of providing a solution. Within the context of the research project "FlexPAET", the Fraunhofer IPT is developing an adaptive hot embossing process, integrating the technology into a process chain of a cost-effective production of planar lighting optics. The project is funded by the European Commission through the 7th framework programme.

The main focus of the research project is put on the development of a machine system which systematically imprints the structure of complex micro-tools into a thermoplastic component. In contrast to the conventional process of hot embossing, individual structural elements are combined one-by-one on a single surface. The machine can provide surfaces of up to 1 x 2 m² with imprinted microstructures, guarantee-ing a positioning accuracy of 2 µm. This creates boundless opportunities for the production of visually functionalized surfaces in terms of flexibility and speed.

The optical function of the embossed component is measured directly in the machine system by means of integrated metrology. Errors in the optical design can therefore be detected directly on the machine. An algorithm compares the optical function of the embossed component with the required values. In this manner, the system identifies those positions on the surface where the structure has to be improved. The optimization process will be continued until the measured optical properties correspond to the required specifications.

The process is part of a replication process chain that is suitable for mass production. Similar to the approach of CD and DVD production, form tools will be produced out of the embossed component by means of galvanic electroforming processes, enabling the cost-efficient production of high quality optics.