Parylene encapsulation

A subtractive process using pentacene as the semiconductor material based on [76] is shown in Fig. 4.14. The process uses parylene as the gate dielectric and the encapsulation layer for a semiconductor layer using pentacene. The encapsulation layer process protects the pentacene against exposure to the solvents and other reagents used in the photolithographic process. 

Gate dielectric/ inter-level dielectric (parylene-C) 

Semiconductor and blanket deposited encapsulation (pentacene and parylene) 

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Fig. 5.12. A schematic showing the self-aligned process flow implemented in the parylene encapsulation process. An extra exposure step and mask is required to fill in interconnect shadowed by the gate layer, but these exposures are performed on the same photoresist and the total number of layers remains the same.

Porous membranes using a parylene encapsulated vertically aligned forest of multi-walled carbon nanotubes with an inner diameter of 7 nm have been fabricated [111]. The transport of charged particles in electrolyte systems through these membranes has been studied under an electric field and under pressure. Using an electric field in the range of 44 kV m , electrophoresis, instead of electroomosis, has been found as the main mechanism of ion transport. 

Several types of parylene dimer are commercially available (and many more have been synthesized and reported in the scientific and patent literature), the most popular are C, D, and N. Parylene-C is often used as an encapsulant for organic semiconductors, and is also sometimes used as a gate dielectric. 

The solution to photolithographically patterning the active layer of OFETs is to protect the semiconductor from materials it is not compatible with (i.e. organic solvents and water). One approach is to use water soluble resists which do not induce the phase transformation [57]. Another is to encapsulate the transistors using parylene first, and then proceed with normal photolithography and patterning [58]. A third approach is to use fluorinated or supercritical C02"based resist materials which also do not interact with pentacene or other organic semiconductors [59]. 

An alternative to encapsulating OFETs with parylene is to use an aqueous photoresist system which does not induce the destructive phase transformation which is observed when metastable oligomeric semiconductors are exposed to other solvents. Since the resist is developed in pure water, exposure to strong bases or solvent developers is also avoided. The process shown is based on Kane, et al. [57]. 

An encapsulation scheme that combines AI2O3 by atomic layer deposition with parylene-C for implantable electroiuc systems has been presented [85]. The so formed AI2O3/parylene-C bi-layer was used to encapsulate interdigitated electrodes. Accelerated lifetime test showed a very good performance so that the method of encapsulation has been claimed to be suitable for chronic implants. 

Implanted neural prostheses must be encapsulated in order to protect their electronics against aggressive body fluids and in turn to protect the body tissue against degradation products from the electronics. The use of parylene-C as an encapsulation material... 

An encapsulation scheme that combines atomic layer deposited AI2O3 and parylene-C has been presented for the encapsulation of implantable devices... 

The encapsulation performances of combining AI2O3 and parylene-C were compared to those of the individual layers of parylene-C or AI2O3. The bilayer coating exhibits superior encapsulation properties. 

Xie X, Rieth L, Merugu S, Tathireddy P, Solzbacher F. Plasma-assisted atomic layer deposition of AI2O3 and parylene C bi-layer encapsulation for chronic implantable electronics. Appl Phys Lett 2012 101(9) 093702. 

Hsu JM, Rieth L, Normann RA, Tathireddy P, Solzbacher F. Encapsulation of an integrated neural interface device with parylene c. IEEE Trans Biomed Eng 2009 56(l) 23-9. 

Hassler C, von Metzen RP, Ruther P, Stieglitz T. Characterization of parylene C as an encapsulation material for implanted neural pros-theses. J Biomed Mater Res Part B Appl Biomater 2010 93(l) 266-74. 

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. 

Figure 15.14 Fabrication process for freestanding Parylene-C membranes for pressure compensated encapsulation of the actuation electrolyte.

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... 

Chen, C.-L., Lopez, E., Jung, Y.-J., Miiftii, S., Selvarasah, S., Dokmeci, M.R., 2008a. Mechanical and electrical evaluation of parylene-C encapsulated carbon nanotube networks on a flexible substrate. AppUed Physics Letters 93, 093109. 

Other approaches to encapsulating nanoelectrodes with an insulating material include chemical vapour deposition of silicon nitride or Parylene C ... 

Another example is poly-para-xylylene (Parylene), which is obtained by the generation, through pyrolysis, of radicals of a para-xylylene dimmer that readily polymerize on a substrate held at room temperature. This is a solvent free process so that the polymer can be deposited on any kind of substrate, including organic ones. Although the main application of parylene remains encapsulation [49], its dielectric properties have also been put into profit to use it as a gate dielectric [50,51]. 

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