Conformal coating of complex shaped substrates places high demands on the coating process. For strongly curved, three-dimensional, micro- or nano-structured components, the technology of Atomic Layer Deposition (ALD) is particularly suitable. A key advantage of Atomic Layer Deposition is the precise control of layer thickness and composition. This enables conformal and homogeneous coatings.
Fraunhofer IOF offers customers from industry and research application-specific and flexible solutions. Our services regarding conformal coatings range from process development for thermal and plasma-enhanced ALD coatings to developments of tailored functional ALD coatings on complex shaped substrates (such as lenses, spheres, aspheres, cylinders, microlens arrays, domes, covers etc.).
ALD coatings have already been transferred to large-scale technical applications in the semiconductor industry. However, optical coatings have to meet further special requirements. Based on our expertise in ALD as well as optics, we want to establish this coating process in the optical industry together with our partners.
Atomic Layer Deposition is a high-performance coating technology based on self-limiting surface reactions of precursors (starting materials for chemical reactions) and reactants (substances consumed during chemical reactions, e.g.: H2O, O2 plasma etc.).
In conformal coating, the substrate material to be coated is placed in a vacuum chamber. During the ALD process, the gaseous precursors and reactants are alternately pulsed into the vacuum chamber. They react with the functional groups (atomic groups in a compound) of the substrate surface or the already deposited layer. New reactive groups are formed on the surface. The reaction is self-limited by the number of functional groups and comes to a halt after a sufficient pulse time. Between pulses, the vacuum chamber is purged so that no gas phase reaction can occur. The reactions are confined to the surface. Accordingly, an ALD cycle typically consists of four consecutive steps: precursor pulse, purge step, reactant pulse, purge step. The ALD cycle is repeated, depositing films of the same thickness in the sub-nanometer range sequentially. The thickness of the deposited film is exactly defined by the number of ALD cycles.
The deposition of conformal films with precise thickness plays a crucial role in the manufacturing of high-quality optical systems. Conventional technologies, such as evaporation and sputtering techniques, are suitable for depositing layers on flat surfaces. On curved surfaces, however, a non-uniform thickness is generated, leading to distortions of the function of optical layer systems.
Due to its self-limiting surface reactions, the ALD technique enables excellent conformality of the coating, no matter the shape of the surface to be functionalized.
Conformal coatings can be used to advantage in many different industries and applications. These include aerospace, laser optics, automotive industry, telecommunications, medical technology/biology, microelectronics, display technology or semiconductor industry.
Our range of services is characterized by versatility as well as a wide range of functional combination possibilities. In addition, we develop new processes as well as solutions for our customers.
In addition to conformal coatings, we offer our customers solutions along the entire photonic process chain - from the functional coating of surfaces to the realization of optical components and complete systems.
On request, we also carry out tailor-made material developments.
Thanks to our many years of experience and extensive knowledge in the field of optical ALD coatings, we can provide you with specific solutions tailored to your complex requirements.
Our researchers have access to several ALD coating facilities. These can perform both thermal and plasma-enhanced atomic layer deposition. Plasma-enhanced atomic layer deposition is particularly relevant for temperature-sensitive substrate materials in order to avoid exposing them to too high temperatures (in contrast to thermal ALD).
With the available ALD equipment, up to eight precursors (+ H2O + O3) can be used for conformal coating. This allows the realization of a wide range of materials and tailored compositions for various functionalities.
The articles in the annual report show, among other things, the research strength of our experts at Fraunhofer IOF. Every year, selected research results from the previous year (archive annual reports) are published in the annual report. You can find the articles on developments regarding Atomic Layer Deposition from the past years in the following list:
In addition, our researchers publish many of their scientific results in scientific journals. Both the large number of scientific publications and patents speak for the excellence of our researchers. We offer licenses for our patented processes.
A list of scientific papers as well as patents on the subject of atomic layer deposition can be found below:
Invention of: Pfeiffer, Kristin; Schulz, Ulrike; Szeghalmi, Adriana
Status: published September 19, 2019
German file reference: DE 10 2018 105 859 A1
Abstract: A reflection-reducing layer system (20) is described which comprises an arrangement of alternating first layers (1) with a refractive index n1 and second layers (2) with a refractive index n2 > n1 as well as a cover layer (3) with a refractive index n3 < n1, wherein the first layers (1) comprise Al2O3, a proportion of the first layers (1) to the total thickness of the reflection-reducing layer system (20) is at least 40 %, a proportion of the second layers (2) to the total thickness of the reflection-reducing layer system (20) is less than 25 %, and the second layers (2) are each less than 35 nm thick. Furthermore, a method for producing the reflection-reducing layer system (20) by atomic layer deposition is described.
Invention of: Schulz, Ulrike; Szeghalmi, Adriana; Ghazaryan, Lilit (IAP); Kley, Ernst-Bernhard (IAP)
Status: granted July 18, 2019
German file reference: DE 10 2016 100 907 B4
Abstract: A method for producing a reflection-reducing layer system (4), comprising the steps:
Invention of: Kley, Ernst-Bernhard; Szeghalmi, Adriana; Schulz, Ulrike; Ghazaryan, Lilit
Status: granted July 4, 2019
German file reference: DE 10 2016 100 914 B4
Abstract: A method of making a porous refractive index gradient layer (20) comprising the steps of:
Invention of: Ghazaryan, Lilit (IAP); Szeghalmi, Adriana (IAP); Kley, Ernst-Bernhard
Status: granted February 22, 2016
German file reference: DE 10 2015 203 307B3
Abstract: The invention relates to a process for the production of optically active elements, in particular optical gratings, in which a structuring with depressions/interstices formed in the surface or a structuring is formed on the surface of a substrate and the structuring is covered with a layer. In a process step i), the formed depressions or interstices between elevations of the patterning are filled or sealed with a filler material, the filler material material differing from the material of the substrate and from the material from which the nanoporous covering layer is formed. In a subsequent process step ii), the filler material is removed to such an extent that no filler material is present on outwardly facing end faces of webs formed between and adjacent to the interstices. In a process step iii), the surface with the structuring and the filled interstices is coated with the covering layer, which is or is formed from a nanoporous material, and in a further process step iv), decomposition of the filler material is achieved by a treatment, and at least the decomposition products of the filler material formed are removed through open pores of the covering layer, so that cavities free of filler material are obtained in the region of the depressions, which are enclosed by substrate material and the material of the covering layer.
Fraunhofer Institute for Applied Optics and Precision Engineering IOF