Thermal stability parylene

Polybenzyls polyphenethyls Parylenes (poly-p-xylylene) Fusible, soluble, and stable at 400°C (752°F) low molecular weight. Melt above 520°C (968°F) insoluble capable of forming films poor thermal stability in air stable to 400-525° C (752-977°F) in inert atmosphere. 

The Parylene family has very attractive properties for use as dielectric materials as was noted above, but their thermal stability at the temperatures used in the fabrication of electronic devices is less than optimum. When considering alternatives as possible precursors for VDP, the isomeric ortho-xylylene (o-quinodimethane) is a likely candidate (Scheme 4). This approach involves the thermolysis ofbenzocyclobutene derivatives to generate a reactive dieneoid intermediate (o-quinodimethane),... 

Although Parylene-N possesses an outstanding combination of physical, electrical, and chemical properties, the benzylic C—H bonds present are potential sites for thermal and oxidative degradation. It is well known that replacing a C— bond with a C—F bond not only enhances the thermal stability of the resulting polymer, but also reduces the dielectric constant. Because incorporation of fluorine is known to impart thermal and oxidative stability, it became of interest to prepare poly(a,a,a, a -tetrafluoro- p -xylylene), Parylene-F Joesten reported that the decomposition temperature of poly(tetrafluoro-j9-xylylene) is ca. 530°C. Thus, it seemed that the fluorinated analog would satisfy many of the exacting requirements for utility as an on-chip dielectric medium. 

Thermal stability is an important criterion for microelectronic applications and hence has been the focus of several studies. Figure 9 shows the dynamic thermogravimetric analysis (TGA) of Parylene-N in both inert and oxygen environments. It is clear that, Parylene-N is stable up to about 480°C in inert ambient, beyond which it gradually decomposes. 

It was observed that, these copolymers have superior properties as compared to homopolymers of parylene with respect to dielectric constant and thermal stability. Copolymerization of PPX-C with perfluoro-octylmethacrylate resulted in reduction of dielectric constant from 2.68 to 2.19 at optical frequencies. Copolymerizing PPX-N with vinylbiphenyl yielded an increased thermal stability in oxygen to 450°C. ° ° Although the... 

The molecular weights of these polymers were estimated to be as high as 500,000. The total process is sometimes called transport polymerization. Poly(p-xylylene) films are produced commercially. The value of Tm for this polymer, which is crystalline, is 400 °C and it carries the trade name of Parylene. Films of poly(p-xylylene) have only fair thermal stability and are brittle, but exhibit good chemical resistance and are very good electrical insulators. Pyrolysis of xylene in steam at 950 °C yields the dimer intermediate. The yield is reported to be 15%. ... 

The thermal stability of parylene HT eleetrets was studied by means of thermally stimulated diseharge measurements. Figure 6 illustrates the TSD surfaee potential and eurrent of the as-deposited and annealed parylene HT samples. The peak temperatures of the TSD eurrent speetra oeeur at about 160 °C and 230 °C for the as-deposited and the annealed sample, respeetively, higher than those of the TSD speetra of Teflon. 

Besides, high-performance polymer electrets, sueh as Parylene HT and certain types of CYTOP, were introduced to the family of electret materials. They exhibit not only excellent electret properties (high surfaee charge density with exceptional long-term and thermal stability) but also good compatibility with MEMS fabrication process. 

The comparison of physical and chemical properties of Parylene-N and Parylene-F is shown in Table 18.4. Parylene-N is considerably less stable in air than in nitrogen as a result of oxidative degradation. However, the similarity between its behavior in air and in nitrogen suggests that Parylene-F has very good thermal oxidative stability, which is most likely the result of the high stability of the C—F bond, and provides evidence that oxidative attack starts at the benzylic C—H bonds in Parylene-N.15... 

The reference ISFET can be modified by chemically reacting the SiOH groups with trimethoxysilanes [7]. An alternative method involves deposition of a hydrophobic polymer on the surface, for example by thermal deposition of parylene [85]. These layers tend to be chemically bound to the SiOH surface, leading to enhanced stability and long lifetimes. Also the layers are very thin, which is essential because of decreased electrical sensitivity as the insulator thickness increases [9]. For ion-blocking layers, a stable attachment has been realized by plasma deposition [86,87]. 

The results of the above polymerization thermodynamics calculations for parylene are compared to similar data for typical addition poljuners in Table 2. The Tc quantifies the stability of the polymer only with respect to reversion to monomer. When PPX is thermally degraded (ca 500°C), a mixture of degradation... 

The Parylene conformal coatings are ultrathin, pinhole-free polymer coatings that provide a number of high-value surface treatment properties, such as, excellent moisture, chemical and dielectric barrier properties, thermal and UV stability, and dry-film lubricity. These properties make Parylene coatings the ideal choice for a number of industrial applications throughout the medical device, electronics, automotive, military, and aerospace industries. Some examples are listed [155]. 

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