Conformal Coating with Atomic Layer Deposition

Homogeneous layers for complex shaped substrates and lattice structures

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.

Your partner for conformal 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.

What is Atomic Layer Deposition?

 

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.).

 

More information about the process / principle

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.

3D model of a sphere covered with several thin and homogeneous layers.
© Fraunhofer IOF
Schematic visualization of ALD coating on spheres or lenses.
3D model of an optical fiber clad with multiple homogeneous layers.
© Fraunhofer IOF
Schematic visualization of ALD coating on fibers.
Conformal TiO₂ -ALD coating on a grating substrate.
© Institut für Angewandte Physik Jena
Highly efficient transmission grating - achieved by a fused silica grating embedded in ALD layers.

 

The advantages of Atomic Layer Deposition at a glance:

  • Conformal coatings on substrates with geometrically complex shapes (such as lenses, fibers, hemispheres, cylinders, domes, tubes, etc.).
  • Conformal growth of thin films on nano/microstructured substrates (such as gratings, microlens arrays, porous membranes)
  • Tailored material properties through composite materials and nanolaminates
  • Precise control of layer thickness in sub-nanometer ranges
  • Optically homogeneous layers
  • Low surface roughness
  • High uniformity and reproducibility
  • Functionalization of temperature-sensitive substrates at low deposition temperatures using plasma-enhanced ALD (PEALD)

Markets and applications

 

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.

Fields of application:

  • Conformal anti-reflective/high-reflective laser optics
  • Coating of lenses, endoscopes, glasses
  • Antireflection coating of fiber end surfaces
  • Conformal coating of protective covers for camera and sensor systems
  • Barrier/protective coatings for e.g. OLEDs, silver coatings, ...
  • and much more ...
A lens coated with ALD in the hand.
© Fraunhofer IOF
Atomic layer deposition of antireflection coatings and bandpass filters.
3D exploded view of a smartphone camera with the multiple lens setup.
© stock.adobe
An advanced lens of the smartphone dual camera structure provides new functions for the smartphone camera concept.
Camera lens with three coated single lenses.
© Fraunhofer IOF
Conformal coatings on camera lenses enable optimizations in photography.

Our services

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.- High-quality oxide coatings with excellent adhesive properties and high abrasion resistance

  • Customized nanoporous SiO2 coatings with precise control of the refractive index
  • Single layer and broadband antireflection coatings for the UV-VIS-NIR spectral range
  • Double-sided coatings on glass substrates
  • Support for technology transfer
ALD functionalized components: Glass dome with and without antireflection coating system, spherical and hemispherical lenses with narrow band filters.
© Fraunhofer IOF
Various optical components functionalized by ALD: glass domes with and without antireflection coatings, ball and half-ball lenses with a narrow bandpass filter coating.

Possible functional ALD coatings:

  • Interference coating systems such as bandpass filters, beam splitters, polarizers, mirrors, etc.
  • Antireflection coatings
  • X-ray optics
  • Photonic crystals
  • Polarizers
  • Diffractive optical elements
  • High-performance transmission or reflection gratings
  • Resonant waveguides
  • Filling grooves of nanostructured materials
  • Biocompatible or antibacterial surfaces
  • Hydrophobic or hydrophilic coatings
  • Barrier and protective coatings
  • Diffusion membranes
  • Encapsulation, fiber coating, metamaterials, sensors, etc.
Conformal coated substrate with highly curved surface to illustrate ALD technology.
© Fraunhofer IOF
Conformal anti-reflective coating with angle-independent color representation.

 

Our wide range of materials:

  • Oxides (TiO2, Ta2O5, HfO2, Al2O3, SiO2).
  • Nanoporous oxides (SiO2, Al2O3)
  • Metals (Ir, Ru)
  • Doping of thin films
  • Composite materials with tailored composition and properties
  • Nanolaminates
  • Organic or hybrid organic-inorganic MLD coatings (Molecular Layer Deposition)

On request, we also carry out tailor-made material developments.

Atomic layer deposition (ALD) can be used in the coating of optical components such as aspheres, convex and concave lenses, or spherical lenses.
© Fraunhofer IOF
Atomic layer deposition (ALD) can be used for coating optical components such as aspheres, convex and concave lenses or ball lenses.

Your advantages of working with us

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.

  • We maintain a very close connection to basic research at the Institute of Applied Photonics.
  • We have a broad, Fraunhofer-wide network at our disposal.
  • We offer unique selling points with the ownership of patents.
  • We offer access to multiple ALD facilities, which in turn open up a wide range of opportunities.
  • We offer great strength in research and transfer.
  • We work in an applied and customer-oriented way.
Uniform Al2O3 thin film (ca. 100 nm) on an 6 inch silicon wafer, processed using atomic layer deposition (ALD).
© Fraunhofer IOF
Uniform Al2O3 thin film (ca. 100 nm) on an 6 inch silicon wafer, processed using atomic layer deposition (ALD).

Technical equipment

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.

 

Our research strength

Annual report articles

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:

  • "Properties of oxides on a new PEALD coating system" (Annual Report 2018, pages 46-47)
  • "3D conformal antireflective coatings by ALD" (Annual Report 2017, pages 44-45)
  • "Conformal nanoporous SiO2 films with tailored refractive index" (Annual Report 2016, pages 72-73)
  • "Atomic layer deposition of antireflective coatings" (Annual Report 2015, pages 66-67)

 

Scientific publications and patents

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.

A list of scientific papers as well as patents on the subject of atomic layer deposition can be found below:

With ALD (atomic layer deposition) coated lenses.
© Fraunhofer IOF
With ALD (atomic layer deposition) coated lenses.

Have we sparked your interest?

 

Please contact us.

We develop customized solutions for photonic problems from industry and science.

Something is still unclear?

 

Ask us your questions.
We will be happy to help.

If you have any questions about the cooperation with Fraunhofer IOF, you can find more information under the following link:

 

You haven’t found anything that fits your request?

Please contact us anyway.

The possibilities of Atomic Layer Deposition are highly individual - and we will take care of a suitable solution for you just as individually.

Further information

 

Possible characterization and material treatments for ALD-coated substrates and components:

  • Spectrophotometry, ellipsometry, XRR, XRD, AFM, SEM, etc.
  • Thermal stability and annealing
  • Chemical stability and wet chemical etching
  • Handling of moisture sensitive substrates under inert atmosphere

More information and services on surface and thin film characterization

 

Functional surfaces and coatings

Get an overview of all services offered by our scientific department “Functional Surfaces and Coatings” at Fraunhofer IOF.

Overview