Briefly describe the working principle of filter membrane chemical vapor deposition

Chemical vapor deposition (CVD) is a widely used technology for depositing thin films or coatings on substrates (including filter membranes). During the process, gaseous precursors heat the surface of the substrate and chemically react in a controlled environment , forming a solid film material deposition.

There are many types of materials used in filter membrane CVD, depending on the required properties and specific applications of the deposited film, such as silicon dioxide (SiO₂) with excellent chemical stability, thermal stability and high transparency; high strength and chemical resistance and electrically insulating silicon nitride (Si₃N₄); alumina (Al₂O₃) with high hardness, chemical resistance and dielectric properties; titanium dioxide (TiO₂) with high refractive index, photocatalysis and biocompatibility, etc.

What is the working principle of the CVD process? During the CVD process, one or more volatile precursor gases that constitute the final coating are introduced into the reaction chamber. When these precursor gases come into contact with the heated surface of the filter membrane, It will be adsorbed on the filter membrane and will not react immediately on the surface.

After adsorption to the filter membrane, these precursor gases will thermally decompose under heating or plasma-induced conditions, destroying molecular bonds and producing active substances, breaking down complex molecules into simpler molecules or reactive single atoms. The broken down atoms/molecules migrate across the surface of the membrane and find suitable locations to combine with other atoms/molecules (including those in pre-existing layers) to form clusters or "nuclei", this is called nucleation. If silane (SiH4) is used, it can decompose to produce silicon and hydrogen.

As more and more precursors decompose and react, the core becomes larger and gradually forms a continuous film at the bottom and top of the film. In this process, the film thickness can be controlled by adjusting the reaction time and precursor concentration. At the same time, the CVD chemical reaction process also produces by-products or unreacted precursor gases. These by-products are usually volatile and can be desorbed from the system through vacuuming or continuous gas flow.

Generally speaking, the CVD process mainly converts precursor gases into active substances. The chemical molecular changes that occur depend on the precursor materials, reaction conditions and properties required to deposit the film, the temperature of the process, indoor pressure, etc. , in terms of raw material selection and chemical reaction conditions, they are all controllable operations, so this type of technology is also suitable for customized production of specific membranes.