Thin-film deposition parylene

Fig. 3 Different synthesis techniques studied for parylene thin film deposition. ...

The quantitative models developed enabled a thorough understanding of the parylene deposition process.Further, these models suggested several deposition parameters that could be varied to tailor the thin film deposition for various applications. They indicate that the rate of consumption of the monomer during propagation is much larger than that during initiation, and is determined primarily by the monomer partial pressure and the substrate temperature. Influence of these two parameters viz., pressure and substrate temperature will be discussed here. 

Table 1 summarizes aU the above mentioned properties of parylene thin films deposited using CVP. 

This polymer is of interest in that extremely thin films can be deposited when the vapour is condensed onto a cooled surface. Parylene film has been shown to offer a reasonable barrier to water vapour and a good barrier to essential oils. For example, LDPE coated with a thin film of parylene has substantially increased the retention of lemon oil which would otherwise have been lost rapidly. It also withstands high temperatures of around 220°C. It is, however, an expensive plastic and has been used as a coating onto rubber. 

Stevens, M. P. Polymer Chemistry An Introduction, 3rd ed., Oxford University Press Oxford, 1998. Fortin, J. B. Lu, T. -M. Chemical Vapor Deposition Polymerization The Growth and Properties of Parylene Thin Films, Springer Berlin Heidelberg New York, 2003. 

Conventionally, SiO thin films are deposited at temperatures exceeding 600°C by thermal CVD. Therefore to enable co-deposition of SiO and parylene thin films in the form of nanocomposites, it was necessary to first develop a near room temperature silica (SiO ) synthesis technique. Desu first demonstrated the possibility of near room temperature deposition... 

Transmission electron spectroscopy (TEM) studies of the co-deposited thin films revealed a continuos polymer phase with a largely inter-dispersed SiOj regions on a 5-50 nm scale, confirming the nanocomposite morphology. As mentioned in section 3.1.3, parylene thin films obtained are typically highly crystalline. In contrast, SiO is an amorphous material. From X-ray diffraction analyses, it was observed that by increasing the relative amount of polymer in the nanocomposite, the crystallinity was... 

Parylene polymers are not manufactured and sold directly. They are deposited from the vapor phase by a process which in some respects resembles vacuum metalizing. Parylene polymers are formed at a pressure of about 0.1 torr from a reactive dimmer in the gaseous or vapor state. Unlike vacuum metalizing, the deposition is not line of sight, and all sides of an object to be encapsulated are uniformly impinged by the gaseous monomer. Due to the uniqueness of the vapor phase deposition, Parylene polymers can be formed as structurally continuous films from as thin as a fraction of a micrometer to as thick as several mils. 

Binh-Khiem et al. investigated a method to change the volume of the encapsulated liquid by electrostatic force [11]. The authors chemically deposited parylene directly on non-volatile liquids under low pressure conditions. The liquid surface was covered with a flexible thin polymer film and the liquid droplets had both shape and surface flexibility. Furthermore, the deposited... 

After the aluminum layer was completely removed, the substrate surface had liquophilic circular domains in which glass surface surrounded by liquophobic areas, where CYTOP still covered the surface, was exposed. Liquid droplets were deposited, by dipping or spin coating onto the substrate surface. These liquophobic and liquophilic patterns force the liquid to form droplets of the desired shape and size on the substrate surface. After depositing parylene onto the droplet surface, the upper electrode, a 5 nm layer of gold (sufficiently thin to be transparent) was deposited on the parylene film. The total transmittivity of the lenses was about 62% at a wavelength of 650 nm. 

Eortin JB, Toh-Ming Lu. Chemical vapor deposition polymerization the growth and properties of parylene thin films. New York Springer 2004. 

---