Fabrication pyroelectric sensors

A 200 pm thick, 30 mm diameter, Z-cut, single-crystal LiTaOs wafer, unpolished on both sides, was used to fabricate the pyroelectric flow sensor. The wafer was first degreased by immersing in trichloroethane, acetone, and isopropyl alcohol for 10 min each, and then it was rinsed in deionized (DI) water and blown dry with nitrogen. After cleaning, nichrome (NiCr) and gold films were sequentially deposited on the front surface of the wafer. This was done in a cryopumped electron-beam evaporator at a pressure of about 10 Pa without breaking vacuum between the NiCr and Au evaporations. The last step minimized contamination of the devices. 

During recent years, the study of micro- and nanoscale fluids has shown significant opportunities for high detectivity of elementary devices with small size. For pyroelectric flow sensors, it is highly desirable to develop theoretical models, experimental methods for pyroelectric element preparation and sensor fabrication, and higher sensitivity with excellent mechanical properties. 

Fig. 1.15 Schematic diagrams of (a) pyroelectric and (b) micro-thermoelectric gas sensors fabricated on Si substrates with micromachined membrane [(a) Reprinted with permission from Schreiter et al. (2006) and (b) from Shin et al. (2006). Copyright 2006 Elsevier]...

It is important that all indicated devices can function at room temperatures. This means that polymer-based sensors have low power consumption (of the order of microwatts) because no heater element is required for their operation. Properties of polymers that influence the operating parameters of sensors can be physicochemical, chemical, optical (photo- and electroluminescence, optoelectronic), redox, hydrophobic/ hydrophilic, piezoelectric/pyroelectric, and electrical (conductivity, resistivity). Moreover, the polymer itself can be modified to bind biomolecules to a biosensor (Mulchandani and Wang 1996). It is mentioned above that polymers have considerable potential for fabrication of multisensing arrays required for e-nose fabrication (Janata and Huber 1985). 

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