Thick film pastes electrode

Electronic Applications. The PGMs have a number of important and diverse appHcations in the electronics industry (30). The most widely used are palladium and mthenium. Palladium or palladium—silver thick-film pastes are used in multilayer ceramic capacitors and conductor inks for hybrid integrated circuits (qv). In multilayer ceramic capacitors, the termination electrodes are silver or a silver-rich Pd—Ag alloy. The internal electrodes use a palladium-rich Pd—Ag alloy. Palladium salts are increasingly used to plate edge connectors and lead frames of semiconductors (qv), as a cost-effective alternative to gold. In 1994, 45% of total mthenium demand was for use in mthenium oxide resistor pastes (see Electrical connectors). 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

MCPE = magnet carbon paste electrode, SWASV = square wave anodic stripping voltammetry, ASV = anodic stripping voltammetry, PSA = potentiometric stripping analysis, SPEs = screen-printed electrodes, TFGE = thick-film graphite electrode, GCE = glassy carbon electrode. 

Several useful schemes for attaching nucleic acid probes onto electrode surfaces have thus been developed [2-8]. The exact immobilization protocol often depends on the electrode material used for signal transduction. Common probe immobilization schemes include attachment of biotin-functionalized probes to avidin-coated surfaces [15], self-assembly of organized monolayers of thiol-functionalized probes onto gold transducers [16], carbodiimide covalent binding to an activated surface [17], as well as adsorptive accumulation onto carbon-paste or thick-film carbon electrodes [15-30]. 

The thick-film design consists of four layers, to be separately screen printed and fired on a 1 in square alumina substrate (figure 14.9). Commercial formulations were used for electrodes, bridge trimming resistors, and passivation layers. The first attempted sensor layer was a commercial silver/palladium paste modified by the addition of palladium powder. Based on the performance of the first thick-film sensors, DuPont Electronics (Research Triangle Park, NC) specifically formulated a palladium-based thick-film paste for this application. 

Rhodium alloys find most of their applications in electrical contacts for radio frequency circuits, precision potentiometers, and spark plug electrodes. The trend is toward lower usage in electronics, mainly because of price. Osmium has minor uses in electrical equipment, mainly in contacts. Ruthenium is used in electrical contacts and high-voltage relays up to 500°C because even RuO c is conductive. A ruthenate thick-film paste is used for printed circuit resistance elements. The ruthenate is converted to RuOa, which has very low resistance drift, 0.10%. 

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. 

FIG. 14 Dependence of the steady-state limiting current 4 on the concentration of o-glucose Cs h was measured at 0.5 V versus Ag/AgCl with film-coated glucose oxidase (180 rg)-BQ (30%)-carbon paste electrodes at a film thickness of (a) 50 /xm (nitrocellulose film), (b) 50 fim (dialysis membrane), and (c) 100 fjm (dialysis membrane). (From Ref. 33.)... 

This structure is of particular interest as it employs a Pt metal wire and it can be easily adapted to the thick film methods Pt metal is added to thick film conductor pastes to aid solderability, thus a Pt-based conductor is very desirable. Most of the electrodes of the kind described above are generally reported to perform adequately , but little information is available on their longevity and operating mechanisms. 

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