Dielectric encapsulation

Figure 3.16 Different steps in the fabrication of MWNT nanoelectrode arrays, (a) metal film deposition, (b) catalyst deposition, (c) plasma-enhanced chemical vapor deposition for CNT growth, (d) dielectric encapsulation with Si02, (e) planarization with a chemical mechanical polishing to expose the ends of the carbon nanotubes, (f) electrochemical characterization. Readapted from Ref [6].

Besides semiconducting SWCNTs, properly doped diamonds can also be nsed as the channel material for fabricating FETs for biosensing as demonstrated by Song et al. [75]. DNA probes are immobilized directly on the aminated snr-face of a p-type polycrystalline diamond film which serves as the conduction channel between the source and drain electrodes. Since a diamond surface is chemically stable and presents a wide potential window, it permits direct contact of biomolecules with the channel surface, eliminating the needs of a polymer coating (in CNT FETs) or dielectric encapsulation (in Si-FETs). As a result, diamond FET is potentially a much more sensitive and faster biosensor, which can operate in solution. Hybridization with complementary and 3-mer mismatched DNA targets in 10 pM can be discriminated in cyclically repeated hybridization and denatnre experiments. 

MAJOR APPLICATIONS Release agents, rubber molds, sealants and gaskets, surfactants, water repellents, adhesives, foam control agents, biomedical devices, personal care and cosmetics, dielectric encapsulation, glass sizing agents, greases, hydraulic fluids, heat transfer fluids, lubricants, fuser oil, masonry protectants, process aids. 

Electrical. Glasses are used in the electrical and electronic industries as insulators, lamp envelopes, cathode ray tubes, and encapsulators and protectors for microcircuit components, etc. Besides their abiUty to seal to metals and other glasses and to hold a vacuum and resist chemical attack, their electrical properties can be tailored to meet a wide range of needs. Generally, a glass has a high electrical resistivity, a high resistance to dielectric breakdown, and a low power factor and dielectric loss. 

W. R. Grace Co. dielectric and conductive adhesives, encapsulants, heat dissipating materials, manufacturing aid coatings... 

If dielectric separation of fasteners in noncompatible joints cannot be implemented readily, fasteners should be coated with a zinc chromate primer and exposed ends encapsulated. This is illustrated in Figure 2.4. 

Silicones Highest heat resistance, low water absorption, excellent dielectric properties, high arc resistance Compression molding, injection molding, encapsulation... 

The effects of the intramicellar confinement of polar and amphiphilic species in nanoscopic domains dispersed in an apolar solvent on their physicochemical properties (electronic structure, density, dielectric constant, phase diagram, reactivity, etc.) have received considerable attention [51,52]. hi particular, the properties of water confined in reversed micelles have been widely investigated, since it simulates water hydrating enzymes or encapsulated in biological environments [13,23,53-59]. 

An important class of materials that originates from the precursor core-shell particles is hollow capsules. Hollow capsules (or shells ) can be routinely produced upon removal of the core material using chemical and physical methods. Much of the research conducted in the production of uniform-size hollow capsules arises from their scientific and technological interest. Hollow capsules are widely utilized for the encapsulation and controlled release of various substances (e.g., drugs, cosmetics, dyes, and inks), in catalysis and acoustic insulation, in the development of piezoelectric transducers and low-dielectric-constant materials, and for the manufacture of advanced materials [14],... 

Figure 19.7. Fully encapsulated Cu line (a) metal (alloy) top barrier (b) dielectric top barrier.

Organic coatings are used in the electronics industry, both as resists and as encapsulants and insulating, intermediate dielectrics, and perhaps in the not too distant future, as conducting elements. The goal of the symposium organizers has been to emphasize the chemical aspects of these materials and their uses. This emphasis concerns mechanisms of formation and utilization, chemical stability, change, and reliability, as consequences of chemical composition and reactions. 

It is of interest primarily for very uniform ultra-thin films and coatings (0.002-5 mils) in applications such as electrical resistors, thermistors, thermocouples, stator cores, connectors, fast-sensing probes, photo cells, memory units, dropwise steam condensers for recovery of sea water, pellicles for beam splitters in optical instruments, windows for nuclear radiation counters, panels for micrometeorite detection, dielectric supports for planar capacitors, encapsulation of reactive powders, and supports in x-ray and optical work. Any significant growth would depend upon a major breakthrough in process techniques and a consequent lowering in price. 

An other interesting strategy is the modification of the surface of the electrodes with multiwalled carbon nanotubes (MWNTs) or single-walled carbon nanotubes (SWNTs) [13,32]. The MWNTs are grown on the electrodes covered with a nickel catalyst film by plasma-enhanced chemical vapour deposition and encapsulated in Si02 dielectrics with only the end exposed at the surface to form an inlaid nanoelectrode array [13]. In the other case, commercial SWNTs are deposited on SPE surface by evaporation [32], The carbon nanotubes are functionalised with ssDNA probes by covalent attachment. This kind of modification shows a very efficient hybridisation and, moreover, the carbon nanotubes improve the analytical signal. 

A ZnS coating 46 is used to encapsulate the detectors. A dielectric filler is deposited in the channels between the detector elements to provide a supporting surface for a common electrode and to provide lateral mechanical support for the detector elements. Next, diode junctions 54 of the detectors are created by ion-implantation of boron ions. Indium contact pads 56 are formed in holes formed in the coating 46, and a common indium electrode 58 is formed on top of the dielectric material 50. 

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