Thick film technology screen-printing

Two common forms of soHd-membrane ISEs are the coated-wire electrode and structures made by thick-film technology (screen printing). 

Applications of electrochemical transducers have relied on conventional and bulky disk (C, Au) or mercury drop electrodes, as well as on mass-producible, single-use, thick-film carbon screen-printed electrodes. The sensitivity of such devices, coupled to their compatibility with modern microfabrication technologies, portability, low cost (disposability), minimal power requirements, and independence of sample turbidity or optical pathway, make them excellent candidates for DNA diagnostics. In addition, electrochem-... 

Most electrochemical immunosensors use screen-printed electrodes produced by thick-film technology as transducers the importance of screen-printed electrodes in analytical chemistry is related to the interest for development of disposable and inexpensive immunosensors. A thick-film is based on the layers deposition of inks or pastes sequentially onto an insulating support or substrate the ink is forced through a screen onto a substrate and the open mesh pattern in the screen defines the pattern of the deposited ink. 

The first miniaturized electrochemical device for measuring glucose in whole blood was a mediated system produced in thick-film technology by screen printing [73]. This disposable, single-shot system is produced and actually marketed widely by the company Medisense. Several other companies are now following with similar approaches [74,75]. 

Thick-film technology consists of depositing inks on a substrate in a film of controlled pattern and thickness, mainly by screen-printing (Fig. 1). 

Commercializes electrochemical biosensors based on thick-film hybrid technology (screen-printed electrodes)... 

Challenges facing the development of in vitro amperometric biosensors (interference rejection, rapid response, reproducibility, response range) have been met in many cases, and commercially available devices based on disposable test strips that incorporate miniature two-or three-electrode electrochemical cells are available for a variety of analytes (see Sect. 10.3.7). Thin-fihn and thick-film technology [80] have been used to mass-produce reproducible sensing elements, and amperometric detection in oxidase-based devices occurs by peroxide oxidation or the oxidation of freely diffusing mediators such as ferricyanide and ferrocene derivatives. The screen-printing process for disposable sensor preparation has also been reviewed [144]. 

The lowest resolution limit of screen printing is typically about 50 jm. The thickness of the layers fabricated by thick-film technologies is commonly in the range 2-300 jm. In many ways, the microstructure of the thick-film compares with that of ceramics and is a function of grain sintering conditions. As a rule, films prepared by thick-fihn technology are porous. Reproducibility of sensors fabricated by thick-film technology is better than for ceramic elements. 

Thick-film technology is an additive process that utilizes screen printing methods to apply conductive, resistive, and insulating films, initially in the form of a viscous paste, onto a ceramic substrate in the desired pattern. The films are subsequently dried and fired at an elevated temperature to activate the adhesion mechanism to the substrate. 

The composihon and characterishcs of the paste are critical factors in screen printing. The cermet (combinahon of ceramic and metal) pastes commonly used in the thick-film technology have four major ingredients (1) an active element that establishes the frmction of the film, (2) an adhesion element that provides the adhesion to the substrate, (3) an organic binder a matrix that holds the active particles in suspension and which provides the proper fluid properhes for screen printing, and (4) a solvent or thinner that establishes the viscosity of the vehicle phase [21,22]. 

Both thin- and thick-film technology allow planar microstrip or coplanar transmission lines. However, requirements on line and coupling-gap accuracy do not always permit traditional screen printing. Etching techniques or photosensitive paste systems offer a potential solution. LTCC provides more design freedom. Impedance-matched line transitions (e.g., from microstrip to stripline or to an embedded waveguide) are possible. 

For thick-film technology, a broad range of materials is available. Costs for materials and production are comparatively low. Small series can be produced with reasonable effort on the laboratory scale. On the other hand, production of a large number of pieces also is not a problem since automatic screenprinting machines are available. Disadvantages are the low resolution and the high surface roughness of the screen printed layers, in particular after thermal... 

Thick Film. In its simplest form, thick-film technology involves the deposition of metal circuitry on a dense ceramic substrate by screen-printing technology. 

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