Solid-State Chemical Sensors

Each bond represents a pair of bonding electrons 

An activation energy is needed to get the charge carriers to move across the diode For Si, 0.6 V of forward bias Is required before current will flow. For Ge, the requirement is —0.2 V. 

For moderate reverse bias voltages, no current flows. If the voltage is sufficiently negative, breakdown occurs and current flows in the reverse direction. 

Circuit adjusts potential difference between the reference electrode and the source, in response to changing analyte concentration, to maintain constant drain-source current 

This voltage sets the drain-source current at a desired level 

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Janata, J. Chemically Sensitive Field Effect Transistors, in Solid State Chemical Sensors (Janata, J., Huber, R. J., eds.) New York Academic Press 1985, p. 65... 

Cheung, P. W., Fleming, D. G., Ko, W. H., Neuman, M. R., eds. Theory, Design and Biomedical Applications of Solid State Chemical Sensors, West Palm Beach, Florida, CRC Press 1978... 

J.F. Schenck, Technical difficulties remaining to the application of ISFET devices, in Theory, Design and Biomedical Applications of Solid State Chemical Sensors (P.W. Cheung, ed.), pp. 165—173. CRC Press, Boca Raton (1978). 

Theory, Design and Biomedical Applications of Solid State Chemical Sensors... 

Solid-state chemical sensors are fabricated by the same technology used for microelectronic chips. The field effect transistor (FET) is the heart of commercially available sensors such as the pH electrode in Figure 15-24. 

Janata and R.J. Huber (Eds.) Solid State Chemical Sensors. Academic. 

A new solid state chemical sensor for sulfur dioxide utilizing a sodium sulfate/rare earth sulfates/silicon dioxide electrolyte has been developed. The addition of rare earth sulfates and silicon dioxide to the sodium sulfate electrolyte was found to enhance the durability and electrical conductivity of the electrolyte. The electrolyte exhibits a Nernstian response in the range of SC gas concentrations from 30 ppm to 1 %. 

Over the years, the demand for cheap, small, low power consuming but reliable solid-state chemical sensors has continued to grow. Consequently, significant research efforts have been made worldwide to improve on the 3Ss (sensitivity, selectivity and stability), mainly with empirical approaches, but also some basic theoretical research and spectroscopy studies. 

I. Lundstrom and C. Svensson, in Solid State Chemical Sensors , J. Janata and R.J. Huber (Eds), Acad. Press, 1985. 

Boeva, Z. A, Milakin, K., Pesonen, M., Ozerin, A. N., Sergeyev, V. G., and Lindfors, T. (2014). Dispersible composites of exfoliated graphite and polyaniline with improved electrochemical behavior for solid-state chemical sensor applications, RSCAdv., 4, pp. 46340-46350. 

There are two basic types of solid-state chemical sensor (i) potentiometric devices, and (ii) field effect devices, e.g. ion-selective field effect transistors (ISFETs or CHEMFETs). Electrodes of the potentiometric type usually have a metal as the back contact and they also have a high output impedance. Field-effect devices are a variant of the metal oxide field-effect transistor (MOSFET) familiar in electronics, and they have a low output impedance. Hybrid devices attempt to combine the advantages of both. 

Janata J, Huber RJ (eds) (1985) Solid state chemical sensors. Academic, New York, NY... 

J Janata, R H Huber. Solid State Chemical Sensors, Academic Press Inc, Orlando 1985 BA Gregg, A Heller, J Phvs Chem 95 (1991) 5970-5975... 

A number of physical devices with chemical sensitivity have been developed previously, including the quartz crystal microbalance (QCM) and other acoustic wave devices, semiconductor gas sensors, and various chemically sensitive field effect transistors. However, based on their intrinsic detection principles, most of the known solid state chemical sensors are not selective, i.e., they respond to more than one or a few chemical species. There is an urgent demand for new families of selective, microscope sensors that can eventually be integrated into microelectronic circuits. We have embarked on a program aimed at the design of conceptually new microporous thin films with molecular recognition capabilities. On the surface of chemical sensors, these membranes will serve as "molecular sieves that control access of selected target molecules to the sensor surface. 

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