Polymer films screen printing

The multilayer sensor structure consists of cermet and polymer based layers sequentially deposited on a 96% alumina ceramic substrate using a thick film screen printing process. The cermet layers are of ceramic-metal composition which require firing at a temperature of 850°C and the polymer layers are cured at temperatures below 100°C. Layout of this multilayer sensor structure is shown in Figure 1. 

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. 

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]. 

However, in the development of chemical and biosensors, new pastes must usually be developed. Polymer thick films can be screen printed on cheap polymer substrates with a thickness anywhere between 5 and 50 /xm. Importantly, no high-temperature steps are involved in the deposition process. The first commercial planar electrochemical glucose sensor (the ExacTech by MediSense) was a screen-printed sensor. A comparison of thick-film deposition against thin-film deposition is shown in table 3.10. 

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