Plasma thin film sensor fabrication

For thin-film metallization, a thin metallic film is first deposited onto the surface of the substrate. The deposition can be accomplished by thermal evaporation, electronic-beam- or plasma-assisted sputtering, or ion-beam coating techniques, all standard microelectronic processes. A silicon wafer is the most commonly used substrate for thin-film sensor fabrication. Other substrate materials such as glass, quartz, and alumina can also be used. The adhesion of the thin metallic film to the substrate can be enhanced by using a selected metallic film. For example, the formation of gold film on silicon can be enhanced by first depositing a thin layer of chromium onto the substrate. This procedure is also a common practice in microelectronic processing. However, as noted above, this thin chromium layer may unintentionally participate in the electrode reaction. 

Figure 10.6 Procedure for polymer nanowire fabrication. An aqueous PEDOTtPSS solution was spin-coated on a substrate patterned with a 1.3 ym period grating, then coated with a thin Si02 layer and a PDMS homopolymer brush. A PS-PDMS block-copolymer thin film was then spin-coated and solvent-annealed. The self-assembled block-copolymer patterns were transferred into the underlying PEDOT-.PSS film through a series of reactive ion etching steps employing CF4 and O2 plasmas. (Reprinted with permission from Nano Letters, Nanowire Conductive Polymer Gas Sensor Patterned Using Self-Assembled Block Copolymer Lithography by Y. S. Jung et al., 8, 11. Copyright (2008) American Chemical Society)...

Fabrication of polymers for these small and integrated sensors should be by the new processing technologies, which can produce accurate, mass reproducible and thin polymers. The polymers fabricated by conventional methods may have potential problems such as the difficulty of preparing thin (<1 pm) and homogeneous films. A plasma-polymerised film offers a new alternative [19]. The plasma-polymerised film is achieved in a glow discharge or plasma in the vapour phase. Such films are thin (< 1 pm), pinhole-free, flat-surface structures and are chemically and mechanically stable. 

Over the last decades, there have been a lot of efforts to fabricate polymer thin film. However, it is difficult to obtain a conducting polymer in thin film or monolayer owing to lack of processabihty and solubility. Among the conducting polymers, PANI thin film has a great potential to apply for chemical sensor due to its sensing ability and conductivity. Similar to PPy, there have been several methods to fabricate PANI thin film LB technique, self-assembly, electropolymerization, evaporation, and plasma-mediated polymerization. 

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