Thin-film screen printing

In order to address the needs of field sensing of explosives, it is necessary to move away from traditional bulky electrodes and cells (commonly used in research laboratories). The exploitation of advanced microfabrication techniques allows the replacement of conventional ( beaker-type ) electrochemical cells and electrodes with easy-to-use sensor strips. Both thick-film (screen-printing) and thin-film (lithographic) fabrication processes have thus been used for high-volume production of highly reproducible, effective and inexpensive electrochemical sensor strips. Such strips rely on... 

Both AC and DC PDFs have been used to produce fuU-color, flat-panel large area dot-matrix devices. PDP systems operate in a memory mode. Memory operation is achieved through the use of a thick-fihn current-limiting series capacitor at each cell site. The internal cell memory capability eliminates the need for a refresh scan. The cell memory holds an image until it is erased. This eliminates flicker because each cell operates at a duty cycle of one. The series cell capacitor in an AC-PDP is fabricated using a thick-film screen-printed dielectric glass, as illustrated in Fig. 7.41. The gap separation between the two substrates is typically 4 mil. The surface of the thick-fihn dielectric is coated with a thin-film dielectric material such as magnesium oxide. 

Other small molecule species decompose and volatilise. The glass frit fuses, wetting the surface of the functional phase, providing adhesion and sealing of the composite to the substrate. Because of the screen printing process, resolution is modest. Fired film thicknesses, which range from 10 to 50 p.m (0.4 to 2.0 mils), are large compared to thin-fHm microelectronics. Some photosensitive pastes are also ia use. 

Peng, R. Xia, C. Peng, D. Meng, G. 2004. Effect of powder preparation on (Ce02)o.8(Sm203)o.i thin film properties by screen-printing. Mater. Lett. 58 604-608. 

Furthermore, other solid-state sensors have been developed and introduced, ranging from thin film and screen-printed sensors to ceramic sensors and - latterly polymeric sensors. 

The LEC structure that involves the addition of ionic dopants and surfactants to the printable inks enables the ability to print a top electrode without restriction by the work function of the metal. Silver, nickel, or carbon particle-based pastes are generally the preferred printable electron injecting electrodes however, the shape and size of the particles combined with the softening properties of the solvent can create electrical shorts throughout the device when printed over a thin polymer layer that is only several hundred nanometers thick. For optimal performance, the commercially available pastes must be optimized for printing onto soluble thin films to make a fully screen-printed polymer EL display. 

Two methods are applicable for preparing 2 thin films One is the doctor blade method and the other is the screen-printing method. 

In one report, a thick-film C electrode (by screen printing) was constructed. Carbon ink (10 p.m thick) was first printed on an alumina plate, and cured thermally. Then the silver ink (28 p,m thick) was printed and cured to partially overlap with and hence connect to the C layer. The thick-film C electrode was found to enhance the detection sensitivity, as compared to the thin-film amperometric detector [753]. 

Another major technology area that can utflize conductive IJ ink is the display market. Inkjet can be applied for both flexible and rigid displays such as electroluminescent and electrophoretic displays (including e-paper), hquid crystal displays (LCD), plasma display panels (PDP) and touch screens some functionalities have already been printed by IJ technology in certain display apphcations, for example RGB color filters. Conductive IJ is also appropriate for use in thin film transistors (TFT), disposable batteries, radio-frequency identification (RFID) tags, and a range of chemical and electronic sensors. 

The ability to provide more processable inherently conducting polymers, as described above, enables new approaches to device fabrication, including ink jet printing [153] and screen printing [154]. Photolithography has also been used to produce ICP patterns [155-157], while spin coating has been used to produce thin, even films [158]. 

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