Chemical microsensors for measurement microsystems

Microsensors for chemical measurement microsystems exploit a wide variety of chemical and physical transduction principles and a correspondingly wide variety of practical electrical and electronic implementation technologies. To keep this article\´s scope manageable, the devices discussed in detail are limited to specialized electrical circuit components - resistors and capacitors - whose parametric values depend on their chemical environment; furthermore, the discussion and examples focus on chemical sensors for gas phase versus liquid phase or biological environments. The article looked in detail at chemiresistors, resistors fabricated of materials whose resistivity changes dramatically with their atmospheric environment, and humidity sensors, which are especially interesting because it is possible to compare commonly available devices based on resistive, capacitive, and thermal conductivity principles. Since many of the most practically important of these sensors are currently at a stage of their miniaturization path that makes it more accurate to call them "minisensors" than "microsensors," devices at this scale are also discussed.