'Thin films & coatings' Roadmap - Nano Mahidol

2.3.1.2 Physical Vapour Deposition (PVD):
This method consists of converting the precursor material into the gas phase (e.g.
resistive heating, electron beam, etc.) and then depositing it onto the surface.
Several techniques are available for depositing the thin film material. Thermal
evaporation, magnetron sputtering and pulsed laser deposition are probably the most
widely used.
Main barriers to success and research paths
As for most of the coating processes, experts highlight difficulties to coat 3-D
geometries as well as to get a good adhesion coating-substrate. A better
understanding of the relation of the process parameters and final properties is also
required.
According to the experts, the control at the nano level is still limited and getting the
required properties probably requires expensive substrates (e.g. non conventional
single crystal substrates) that favour thin film growth in the desired direction and with
the desired structure. With regard to material precursors, for some materials the
process is considered to perform well (e.g. parylene) whilst for some others the
materials are still in their development phase to achieve the required performance.
According to the experts, this is a capital-intensive process that requires expensive
equipment to coat large areas (e.g. wafers in semiconductors’ industry). The fact that
this process requires vacuum chambers also limits the size of the areas to be coated.
2.3.1.3 Other Gas/Vapour synthesis methods
According to the experts, several scientific and technical barriers persist. There’s still
basic research needed mainly on the chemical synthesis onto surfaces and to get the
proper crystal orientation required for many en-user applications.
With regard to the process itself, according to the experts there’s the need to improve
the process reproducibility and uniformity (ultimately leading to improved material
quality) as well as the process throughput (deposition rate). With respect to specific
materials, the variety of materials that could be processed is rather limited and there
are difficulties to model polymer thin film properties.
According to some experts, there isn’t a major barrier and there are a lot of
opportunities for exploitation. The transfer of process capabilities to industrial endusers
would speed up this process development, which in itself could result in new
research needs.
2.3.1.4 Sol-gel
In the sol-gel process the precursor is dissolved in a solvent (forming a sol or gel
depending on the reactor conditions) and precipitates due to chemical reactions. The
sol-gel process consists on 4 basic steps: hydrolysis, condensation and
polymerisation of particles, growth of particles and agglomeration and formation of
networks. The outcome of the process depends on several factors that influence the
hydrolysis and condensation rates. Among them, there are few that are considered to
have a greater impact: pH, nature and concentration of catalysts, H 2 0/precursor
molar ratio and temperature.
13 Roadmap report on
Thin films and coatings