Silicon varistor

Fig. 4.15 (a) Silicon carbide varistors, and (b) zinc oxide varistors. (Courtesy of P.D. Devices Ltd. UK.) (c) PTC thermistors for motor protection and (d) NTC thermistors inset, catheter fitted with biomedical NTC thermistor for measuring blood temperature. (Courtesy of Thermometries.)... 

Varistor. A material having an electrical resistance that is sensitive to changes in applied voltage. A typical example is the varistor made from a batch consisting of granular silicon carbide, mixed with carbon, clay and water the shaped components are fired at 1100-1250 C in H2 or N2. 

Similar research has been necessary to optimize formulations for applications on alternative substrate types such as BeO, low-temperature tape, and nonhybrid substrates such as glass substrates for displays, silicon (Si) for photovoltaic apphcations, and various ceramic bodies for component apphcations such as titanates for MLCs, zinc oxide varistors, and zir-conia sensors. In each apphcation, not only wiU the chemistry vary, but the particle size, surface area, and volume percentage of the respective glass compositions wiU also vary. 

In the case of the two prototype substances, water and silicon, mentioned at the beginning, we know that boundary layer effects frequently exceed the voliune effects in their importance one may think, on the one hand, of p-n junctions, transistors, photoelements, varistors, Schottky diodes, and, on the other, of electrode/liquid electrolyte junctions or colloid chemistry. First let los look at five particularly illustrative examples (Fig. 5.70). 

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