A new process developed by the Karlsruhe Institute of Technology, KIT, allows printing of quartz glass structures at nanometer-scale directly onto semiconductor chip. As a feedstock, a hybrid organic-inorganic resin is used for 3D printing silicon dioxide. As the process is not sintering-based, temperatures are much lower. Nanophotonics with visible light is enabled by increased resolution. Researchers report their findings in Science.
Printing micro- and ultra-nanometer-scaled quartz structures out of pure silicon dioxide offers many new applications to optics, photonics and semiconductor technologies. Processes have so far been based on traditional sintering. Temperatures required for sintering silicon dioxide nanoparticles are above 1100°C, which is much too hot for direct deposition onto semiconducting chips. Dr. Jens Bauer, head of KIT’s Institute of Nanotechnology, has developed a process that produces transparent quartz glass at lower temperatures with high resolution and good mechanical properties.
Hybrid Polymer Resins as Feedstock
Bauer, the Emmy Noether Junior Research Group leader at KIT and his collaborators from the University of California Irvine, Edwards Lifesciences, and Irvine’s Edwards Lifesciences Company, describe the process. Science. The feedstock is a hybrid inorganic-organic polymer. This liquid resin is composed of molecules known as polyhedral, oligomeric silsesquioxane(POSS), which are small silicon dioxide molecule cages with organic functional group.
After cross-linking the material via 3D printing to form a 3D nanostructure, it is heated to 650°C in air to remove the organic components. The inorganic POSS cells coalesce at the same time to form a continuous microstructure or a nanostructure of quartz glass. The temperature needed to achieve this is less than half of the temperature necessary for processes that rely on sintering nanoparticles.
Even in the face of challenging thermal and chemical conditions, structures remain stable
Bauer explains: “The lower temperatures enable the free-form-printing of robust optical-grade glasses structures with the necessary resolution for visible light nanophotonics on semiconductor chips,” Bauer explains. The quartz glass is not only excellent in optical quality but has good mechanical properties.
Researchers from Karlsruhe and Irvine printed various nanostructures using the POSS resin, including free-standing photonic crystals with 97 nm beams and parabolic microlenses. They also created a micro objective that had nanostructured elements and multiple lenses. Bauer states that the process produced structures that remained stable, even when subjected to harsh chemical or temperature conditions.
Oliver Kraft, Vice president Research at KIT, says that the INT group led by Jens Bauer belongs to the 3DMM2O Cluster of Excellence. “The results of the research, which have been published in Science, are just one example of the success that cluster researchers can achieve in supporting early-stage scientists.” 3D Matter Made to Order (or 3DMM2O) is a Cluster of Excellence that KIT and Heidelberg University have jointly established. The project combines natural sciences with engineering to create a highly inter-disciplinary approach. The aim is to raise 3D additive production to the next step — from the molecule level up to macroscopic dimension.