Semiconductor-based gas sensors

The history of electrochemical sensors began in the thirties of the twentieth century, when the pH-sensitive glass electrode was deployed, but no noteworthy development was carried out till the middle of that century. In 1956, Clark invented his oxygen-sensor based on a Ft electrode in 1959, the first piezoelectric mass-deposition sensor (a quartz crystal microbal-ance) was produced. In the sixties, the first biosensors (Clark and Lyons, 1962) and the first metal oxide semiconductor-based gas sensors (Taguchi, 1962) started to appear. 

Electrochemical, such as ion-selective electrodes (ISE), ion-selective field affects transistors (ISEET), solid electrolyte gas sensors, semiconductor-based gas sensors, and conducting polymer sensors. Most electrochemical sensors are based on potentiometry, voltammetry, or amperometry although coulometry and conductimetry have also been utilized. 

Recent advances in wide bandgap semiconductor-based gas sensors... 

Fergus JW (2007) Perovskite oxides for semiconductor-based gas sensors. Sens Actuators B Chem 123(2) 1169-1179... 

M. (1997) A novel electronic nose based on semiconductor films gas sensor to distinguish different types of milk. In Authenticity and Adulteration of Food the Analytical Approach, Proceedings of Euro-FoodChem IX, Interlaken, Switzerland, 24-26 September 1997, pp 89-94. 

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. 

In the field of SMOX-based gas sensors, by far the most studied material is the n-type Sn02. Moreover, most of the commercial sensors marketed today are based on it, generally in combination with noble metal additives (Ihokura and Watson, 1994 Williams, 1999). The other material used in commercial sensors in applications involving the detection of oxidizing gases is WO3, which is also an n-type semiconductor. This is intriguing, because since... 

Various materials and fabrication methods have been investigated to produce metal oxide semiconductor CO2 gas sensors. The most widely-used materials based on tin dioxide have largely been found to be insuffident for the task. Typically, poor response behaviour to CO2 and high cross-sensitivity are major problems for tin dioxide-based materials. Examples are work conducted by Patel et al. (1994) and Hoefer et al. (1994). The sensors in the study by Hoefer et al showed a marked response in the concentration range of 1000-10000 ppm CO2 at an operating temperature of 270°C. The most significant responses were above CO2 concentrations of 5000 ppm but. 

As can be seen, II-VI semiconductor compounds can be used as sensing materials in all types of gas sensors, including chemiresistors, SAW, heterojunction based, and optical. They can be applied to surface functionalizing and composites forming as well. The application of II-VI saniconductor compounds in quantum dots-based gas sensors will be discussed in Chap. 5 (Vol. 2). Operating characteristics of several Il-VI-based gas sensors are shown in Figs. 5.18 and 5.19. 

It is important that the sensitivity of Il-VI-based gas sensors of the conductometric type for various semiconductors changes according to the value of S from Fig. 5.17. For example, in the couple CdS-CdSe, CdS-based sensors had much better sensitivity to vapors of water, ethanol, ammonia, acetone, and iodine (Nesheva et al. 2006). We also need to note that aU regularities established for metal oxides work in Il-VI-based gas sensors as well (Lantto and Golovanov 1995). This means that for better sensitivity, II-VI semiconductor compounds should be porous with small both the grain size... 

Monchev B, FUenko D, Nikolov N, Popov C, Ivanov T, Petkov P, Rangelow IW (2007) Investigation of the sorption properties of thin Ge-S-AgI films deposited on cantilever-based gas sensor. Appl Phys A 87 31-36 Monroy E, Omnes F, CaUe F (2003) Wide-bandgap semiconductor ultraviolet photodetectors. Semicond Sci Technol 18 R33-R51... 

As indicated before, the semiconductor, which interacts with analyte, is the main element in thin-fihn transistor-based gas sensors. Research has shown that for fabrication of these devices both organic and inorganic semiconductors can be used. 

---