Conformal Coating with Atomic Layer Deposition

Homogeneous layers for complex shaped substrates as well as micro- and nanostructures


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.


Overview of the advantages of Atomic Layer Deposition:

  • 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 for conformal coatings


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 range of 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
  • 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
  • Support for technology transfer
  • Licensing of patented processes

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. 

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 in the field of conformal coatings

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


Research reports

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:

  • "Conformal coating for high-efficiency spectrometer gratings"
  • "HfO2 and SiO2 ALD coatings for laser applications"
  • "Properties of oxides on a new PEALD coating system"
  • "3D conformal antireflective coatings by ALD"
  • "Conformal nanoporous SiO2 films with tailored refractive index"
  • "Atomic layer deposition of antireflective coatings"

Full texts of research reports


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. 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:

Selection of scientific publications

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

Do you have questions about our services?  

In a personal meeting, we will advise you on our (individual) range of services and our core competencies. Please contact us. 

You would like to work with us?
Then apply with us!

We are always looking for creative minds and committed people who want to develop innovative solutions with light together with us. Visit our job portal or send us a speculative application: