Printed Electronics Applications

Sintering is defined as a process in which distinct particles in a powder weld together and interdiffuse with each other at temperatures below their melting point. The concept has been employed in the fields of powder metallurgy and ceramics for hundreds of years. Sintering allows metal particles, whether nanoparticles for inkjet applications or larger particles for other printed electronics applications, to join together at a temperature below the melt phase in order to form the conductive path. 

As discussed above, the driver for many printed electronics applications is the printed transistor. The printed transistor is essentially a thin film transistor fabricated using printable materials. In other words, in its ultimate implementation, all three major material components of the printed transistor, i.e., the conductive electrodes, the insulating gate dielectric, and the semiconducting channel material, are printed. 

Just as polymers may be used to form printable semiconductors, so they may be used to form dielectrics as well. Indeed, polymer dielectrics are in widespread use in conventional microelectronics as well. For printed electronics applications, polymer dielectrics are therefore a natural choice for use in printed transistors. Several families of polymer dielectrics have been studied and used in printed transistors. These include various polyimides and other polymer dielectrics such as pol)rvinylphenol (PVP). In general, these dielectrics are characterized by the following properties ... 

As with other techniques, the material requirements for rotogravure printing depend on the curing process. For drying (solvent removal), a viscosity of between 0.01 and 0.2 mPa s is appropriate, resulting in a film about 1 p,m thick [23], which is more than sufficient for many printed electronics applications. UV curing the film allows for thicker films, up to about 8 p,m thick. 

Today, electronics are manufactured with expensive materials that often contribute to the increase of pollution and are rarely recyclable. The market of printed electronic is expanding rapidly and therefore needs new materials that could help revolutionize the electronic industry and would be relative inexpensive. Nanocellulose, one of the most common, cheapest, and reqrclable substrate materials, is believed to be able to successfully replace plastic, metallic foil or paper substrates currently used for manufacturing flexible electronics [81, 82]. The authors of article [81] studied composites made of inoi anic filler particles and cellulose nanofibers for printed electronics applications. In their research, nanocellulose was assumed to fill voids of the structure. On the other hand, Caspar et al. worked on "nanocrystalline cellulose applied simultaneously as the gate dielectric and the substrate in flexible field effect transistors [82]. Figure 21.42 presents transmittance of two NCC membranes produced by two approaches NCC evaporation and NCC casting. 

About half of epoxide resin production is used for surface coating applications, with the rest divided approximately equally between electronic applications (particularly for printed circuit boards and encapsulation), the building sector and miscellaneous uses. In tonnage terms consumption of epoxide-fibre laminates is only about one-tenth that of polyester laminates, but in terms of value it is much greater. 

Copper is plated on printed circuit boards to provide electrical conductors and for a variety of other electrical and electronic applications. ... 

Although high-performance TFTs are needed for several electronic applications, the potential for printed, inorganic electronics encompasses other devices and applications. A major opportunity is in optoelectronic applications, which impose different requirements, challenges, and opportunities (see Chapters 6, 7, 9, and 11 for discussion of solution-processed solar cells and other printed optical devices). 

Electrical Properties. Polysulfones offer excellent electrical insulative capabilities and other electrical properties as can be seen from the data in Table 7. The resins exhibit low dielectric constants and dissipation factors even in the GHz (microwave) frequency range. This performance is retained over a wide temperature range and has permitted applications such as printed wiring board substrates, electronic connectors, lighting sockets, business machine components, and automotive fuse housings, to name a few. The desirable electrical properties along with the inherent flame retardancy of polysulfones make these polymers prime candidates in many high temperature electrical and electronic applications. 

DNQ—novolac resist chemistry has proved to have remarkable flexibility and extendibility. First introduced for printing applications, DNQ—novolac resists have been available since the eady 1960s in formulations intended for electronics applications. At present, most semiconductor manufacturing processes employ this resist chemistry. Careful contemporary research and engineering support the continuing refinement of this family of materials. 

Very low cost, medium performance printed electronics A less controversial area is printed (or organic) electronics. The objective in this rapidly developing field is to develop alternatives to silicon and conventional photolithography as the basis for electronic systems151"153. Initially, the devices produced using this technology would have relatively low performance, but very low cost. These devices would be directed toward applications (for example, RF ID tags154) where one-time use would dictate cost and performance. 

The second approach has the advantage that it provides flexibility in the choice of means to perform the printing. Figure 10.14 shows a stamp with this construction, designed for plastic electronics applications [42]. It consists of a thin layer of PDMS on top of a sheet of polyimide. The relatively high in-plane modulus of the poly-imide prevents distortions that can frustrate registration. Its small thickness enables the stamp to be bent in a manner that facilitates printing. 

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