Silicon-based gas sensors

However, at the same time silicon is a chemically active material and, due to oxidation and interaction with surrounding atmosphere, especially at higher tanperatures, has unstable surface properties. The operation temperature of silicon-based devices is also limited due to the small band gap of silicon. This means that silicon-based devices have strong limitations for operation at high tanperatures and in corrosive atmospheres. Unfortunately, conventional gas sensors mainly operate in such conditions. As a result, silicon-based sensors are absent from the gas sensor market. 

Korotcenkov, Handbook of Gas Sensor Materials Properties, Advantages and Shortcomings for Applications Volume 1 Conventional Approaches, Integrated Analytical Systems, 

The components include flip-chip frame microhotplate temperature sensor, controller, and digital interface (Reprinted with permission from Graf et al. (2004). Copyright 2004 American Chemical Society) 

It was found that amorphous silicon can also be used in gas sensors of resistive (Helwig et al. 2007, 2009) and heterostructure-type devices (Tucci et al. 2004). For these purposes hydrogenated amorphous silicon (a-Si H) is normally used. This material has found widespread commercial application in photovoltaic solar energy conversion and in large-area thin-film electronic devices (Kanicki 1992). In the course of these developments, the basic material properties of a-Si H have been intensively investigated (Luft and Tsuo 1993). It should be noted that a-SiiH is a stable material and the H-termination remains up to annealing temperatures on the order of 800 °C in vacuum (Cui et al. 1999). 

Another major research theme related to silicon is the development of MEMS-based analytical instruments for gas sensing, such as ntiniaturized silicon photoacoustic and thermal conductivity gas sensors, MEMS Fourier transform and other spectrometers, and integrated nondispersive IR absorption (NDIR) sensors. Unfortunately, there are several problans to be overcome here. According to Bogue (2007), part of the difficulty lies with the fact that nuniaturization is not always particularly beneficial miniaturized NDIR optical sensors suffer from low sensitivity due to the necessarily short optical path lengths silicon photoacoustic sensors cannot offer the low limits of detection that characterize their conventional counterparts, and as yet, MEMS spectrometers only offer low resolution. 

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Another variation on solution casting is spin coating. This technique borrows from the methods developed by the semiconductor industry to deposit very thin and uniform layers of photoresist onto silicon wafers. This method has been successfully used in the sensor industry to deposit polymer electrolyte membranes onto silicon-based gas sensors [21]. Some main advantages of spin coating are that very thin and reproducible films can be produced, and that an entire array of sensors can be coated simultaneously using batch fabrication methods. In addition, spin coating equipment is readily available fi"om the semiconductor industry. 

Barillaro, G, Bruschi, E, Lazzerini, G. M. and Strambini, L. M. Validation of the compatibility between a porous silicon-based gas sensor technology and standard microelectronic process , (2010) IEEE Sens. J. 10,893-9. 

With the increase in needs to monitor a variety of gases in our environment, the solid-state gas sensors based on electrical parameters are widely studied, including silicon-based chemical sensors, semiconducting metal oxide sensors, catalysis. 

Recent trends in silicon carbide (SiC) and graphene-based gas sensors... 

Gas sensors based on field ionization from multiwall carbon nanotube arrays grown on PSi templates have been developed (Nikfaijam et al., 2010). Such sensors showed good sensitivity, selectivity and short response times, as well as higher discharge current and good mechanical stability in comparison with those which were fabricated on polished silicon substrates. Validation of the compatibility between PSi-based gas sensor technology and standard microelectronic processes has been demonstrated (Barillaro etal.,2010). 

Multiple micro-hotplate-based gas sensors on a single silicon die (Cambridge CMOS Sensors, UK). 

All the above-mentioned results indicate that, for attainment of the essential parameters of chemical sensors, it is necessary to use porous layers with optimal thickness and porosity, which in most cases are being established experimentally. For example, Connolly et al. (2002) found that if the maximum sensitivity of porous silicon and polysilicon to humidity was achieved using 30 % HF, the best result for humidity sensitivity of porous SiC was obtained using 73 % HF (see Fig. 26.5). The layer microstructure in terms of pore shape, pore size, and pore distribution is very important for the capillary condensation mechanisms. This means that all technological parameters of PSi forming should have very strong control. As a result, we cannot expect that PSi-based gas sensors will have good reproducibility of their parameters. 

Dey D, Munshi S (2008) An artificial neural network based system for measurement of humidity and temperature using capacitive humidity sensor and thermistor. Sens Transducers J 97(10) 1-10 Di Francia G, Noce MD, Ferrara VL, LanceUotti L, MorvUlo P, Quercia L (2002) Nanostractured porous silicon for gas sensor application. Mater Sci Technol 18 767-771... 

In Chapter 5.4, optical ultraviolet radiation sensors are described, including UV-enhanced silicon-based pn diodes, detectors made from other wide band gap materials in crystalline or polycrystalline form, the latter being a new, less costly alternative. Other domestic applications are personal UV exposure dosimetry, surveillance of sun beds, flame scanning in gas and oil burners, fire alarm monitors and water sterilization equipment surveillance. 

We recently published a chapter in the book Silicon Carbide Recent Major Advances by Choyke et al. [19] that describes SiC gas sensor applications in detail. In this book, we emphasize device properties applications are only briefly reviewed at the end. The device and gas sensing properties of various field-effect chemical gas sensing devices based on SiC are described, and other wide bandgap material devices are reviewed. The detection principle and gas response is explained, and the buried channel SiC-FET device is described in detail. Some special phenomena related to the high-temperature influence of hydrogen at high temperature are also reported. 

Most ISEs are based on purely physicochemical and non-catalytic recognition elements solid membranes with fixed ionic sites (e.g. the glass pH electrode), ion-exchange polymer membranes or plasticised hydrogel membranes incorporating ionophores [9], Silicon oxide or metal oxides act as the recognition element in pH-ISFETs, gas-sensitive FETs, solid-state electrolyte, solid-state semiconductor and many conductometric gas sensors. 

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