Correlation of Growth and Surface Properties of Poly(\(p\)-xylylenes) to Reaction Conditions

Abstract

Parylene, a non-critical, non-toxic layer material, which is not only a candidate for low-K dielectrics, but also well suited for long-term applications in the human body, has been deposited by (plasma-enhanced) chemical vapor deposition of the monomeric species. To that end, a specially-designed reactor exhibiting a cracker tube at its entrance, which serves as the upstream control, and a cooling trap in front of the downstream control has been applied. The process of polymerization has been traced and is explained by evaporating the dimeric species followed by dissociation in the cracker at elevated temperatures and, eventually, to the coating of the polymeric film in terms of thermodynamics. Alternatively, the process of dissociation has been accomplished applying a microwave plasma. In both cases, the monomerization is controlled by mass spectrometry. The window for surface polymerization could be clearly defined in terms of a factor of dilution by an inert gas for the chemical vapor deposition (CVD) case and in the case of plasma-enhanced chemical vapor deposition (PECVD), additionally by the power density. The characterization of the layer parameters has been carried out by several analytical tools: scanning electron microscopy and atomic force microscopy to determine the surface roughness and density and depth of voids in the film, which influence the layer capacitance and deteriorate the breakdown voltage, a bulk property. The main issue is the conduct against liquids between the two borders' hydrophilic and hydrophobic conduct, but also the super-hydrophobic character, which is the condition for the Lotus effect. The surface tension has been evaluated by contact angle measurements. Fourier-transform infrared spectroscopy has proven the conservation of all of the functional groups during polymerization.

Bi-layer sandwich film for antibacterial catheters

“… (a,b) Deposition rate of parylene-N as a function of the reactor pressure; (c,d) deposition rate of parylene-N as a function of the percentage of the partial pressure of parylene-N p p = f PX /( f PX + f Ar ) for two models. By diluting the vapor with argon, the reaction is forced to surface polymerization (reaction of first order), best visible by the linear logarithmic slope [ 60 ]. In the model in panel c, the rate-limiting step is the condensation of the monomer; in the Beach model in panel (d) surface diffusion is the rate-limiting step.…”

“…At constant partial pressure of the monomer, the volume polymerization at low pressure is effectively suppressed. Reprinted from [ 60 ], copyright 2015 the authors.…”

“…(a) Without diluent, 6 mTorr (0.8 Pa), (b) 37.5 mTorr (5 Pa), (c) 75 mTorr (10 Pa). Reprinted from [ 60 ], copyright 2015 the authors.…”

Carbon electrode obtained via pyrolysis of plasma-deposited parylene-C for electrochemical immunoassays

“…During plasma deposition of parylene-C, the temperature deviation (dissociation energy of the parylene-C dimer) during pyrolysis was minimized, and the generated parylene-C radicals exhibited far higher energies compared with those of the radicals produced via thermal pyrolysis. 12,28 The properties of plasma-deposited parylene-C are very sensitive to the ratio of the applied power (W) to mass flow rate (F). 14 This ratio represents the average energy applied to the unit amount of parylene-C dimer and is closely correlated to the concentration of reactive radicals during polymerization on the substrate, as in conventional thermal pyrolysis.…”

“…Therefore, parylene-C is used in applications requiring micrometer-scale thicknesses. [11][12][13] Recently, a plasma deposition method was reported for the deposition of parylene-C, 14,15 wherein reactive radical production from the parylene-C dimer was performed using plasma instead of conventional thermal deposition. As the plasma exhibits a relatively high energy density compared with that of thermal energy, the pyrolysis of the parylene-C dimer is faster, e.g., parylene-C with a thickness of 100-200 nm may be deposited within 20 min.…”