Thermal sensors pellistor

The coefficients for Pt are A = 4 x 10 3, B = 5.8 x 10 7, and po = 1 x 10-5 Q cm. With these parameters, the sensitivity, expressed as the temperature coefficient, is 0.4%°C 1 over a wide range of temperatures. Resistivities of other metals, as well as their temperature coefficients, are tabulated in standard reference tables (e.g., the CRC Handbook of Chemistry and Physics, 2006). Because the geometry of the resistor does not change with temperature, (3.8) is often written in terms of change of resistance R. Because of their chemical inertness and high temperature coefficient, platinum resistors are most common. They are the key part of the most successful thermal sensors, pellistors, which are discussed in Section 3.6.2. 

This is the reaction taking place at the surface of the thermal sensor, the pellistor, discussed in Chapter 3. An example of a biocatalyst is the enzyme glucose oxidase (GOD) which highly selectively promotes oxidation of D-glucose to gluconic acid. 

Microhotplates, however, are not only used for metal-oxide-based gas sensor applications. In all cases, in which elevated temperatures are required, or thermal decoupling from the bulk substrate is necessary, microhotplate-like structures can be used with various materials and detector configurations [25]. Examples include polymer-based capacitive sensors [26], pellistors [27-29], GasFETs [30,31], sensors based on changes in thermal conductivity [32], or devices that rely on metal films [33,34]. Only microhotplates for chemoresistive metal-oxide materials will be further detailed here. The relevant design considerations will be addressed. 

In biomedical sensing, some of the solid-state devices based on thermal sensing cannot be used effectively. The reason is that the sensor itself has to be heated or is heated quite hot by catalytic surface reactions. Thus pellistors (oxides with catalytic surfaces and embedded platinum wire thermometer), chemiresistors, and Figaro sensor smoke detectors have not found many biologic applications. 

One of the most popular approach is to periodically change the operation temperature, for example, metal oxide gas sensors or pellistors (see also Figure 22.33). Sears et al. [154] proposed to monitor conductance/time curves for different gases under conditions of thermal cycling. Kunt et al. [155] described an optimization... 

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