FET-based sensors

A. Fanighulo, P. Accossato, M. Adami, M. Lanzi, S. Martinoia, S. Paddeu, M.T. Parodi, A. Rossi, M. Sartore, M. Grattarola and C. Nicolini, Comparison between a LAPS and an FET-based sensor for ceb-metabolism detection, Sens. Actuators B Chem., 32(1) (1996) 41-48. 

In this entry, we focus on the discussion of the platform technology for electrochemical sensors, metal oxide semiconductive (MOS) sensors, and piezoelectric based quartz crystal microbalance (QCM) sensors. There are other types of chemical sensors, such as optical sensors, Schottky diode based sensors, calorimetric sensors, field-effect transistor (FET) based sensors, surface acoustic wave sensors, etc. Information of these specific sensors can be found elsewhere and in current journals on sensor technologies. Because of the increasing importance of microfabricated sensors, a brief discussion of microsensors is also given. 

In this section, new type FET-based sensors are described focnsing mainly on the research activities in nanotechnology at Waseda University. 

Fig. 5.10 (a) Response of FET-based sensor shown in Figure 5.9c to NO2 diluted in N. Inset an extended response of the sensor to 20 ppb NO2 (Reprinted with permission from McAlpine et al. 2007, Copyright 2007 Nature Publishing Group), (b) Response to NH3 and NO2 at various concentrations for an ordered, vertically aligned silicon nanowire-based resistive gas sensor with a porous electrode (Reprinted with permission from Field et al. 2011, Copyright 2011 American Chemical Society)... 

Electrical sensors, operating due to a surface interaction with target gas, cover a large group of gas sensors polymer, metal, metal oxide, or saniconductor conductometric sensors capacitance sensors and work-function-type and Schottky barrier-, MOS-, and FET-based sensors (Korotcenkov 2011). 

Sensors based on reactivity of gas Electrochemical sensors Semiconductor sensor Combustible gas sensor/microcalorimetric gas sensor/peUistor Colorimetric paper tape Chemiluminescence Schottky barrier/heterocontact sensor/FET-based sensors... 

There are three major classes of palladium-based hydrogen sensors [4], The most popular class of palladium-based sensors is based on palladium resistors. A thin film of palladium deposited between two metal contacts shows a change in conductivity on exposure to hydrogen due to the phase transition in palladium. The palladium field-effect transistors (FETs) or capacitors constitute the second class, wherein the sensor architecture is in a transistor mode or capacitor configuration. The third class of palladium sensors includes optical sensors consisting of a layer of palladium coated on an optically active material that transforms the hydrogen concentration to an optical signal. 

FET type humidity sensor. Although sensors based on a field-effect transistor (FET) appear to hold promise as a small and low-cost intelligent sensor, relatively few people have been engaged in the research on FET type sensors in Japan. In this respect, it is remarkable that a FET type humidity sensor was developed recently by Hijikigawa of Sharp Corp (9). The sensor is also worth notice as a new type of humidity sensor, which utilizes changes in electric capacitance of humidity sensitive membrane interposed between double gate electrodes. 

Miyahara et al. (1985) developed an integrated enzyme FET based on a silicon-on-sapphire (SOS) sensor for simultaneous determination of glucose and urea. Three ISFETs and two metal insulator semiconductor FETs (MISFETs) were integrated on a surface area of 2.5 mm x 2.5 mm (Fig. 54). One of the ISFETs served as reference sensor in order to compensate the signals caused by pH changes of the solution the two others were covered by GOD and urease, respectively. The MISFETs can be used as pH electrodes. For enzyme immobilization the chip was covered with a laminated photosensitive layer of 75 pm thickness and,... 

The success of FET-based CNT gas sensors quickly attracted interest for use in biosensing applications, particularly since biomolecules such as DNA and proteins are heavily charged under normal conditions. SWCNT FETs are expected to be more sensitive than chemisorbed gas molecules to the binding of such charged species. However, the wet chemical environment with the presence of various ions and other biomolecules makes it much more complicated than gas environments. Studies demonstrated that proteins in the solution tend to adsorb irreversibly onto the bare CNT surface and induce significant change in FET characteristics [67,68]. Thus, extensive efforts have been made to passivate CNT with various polymers, such as PEI, poly(ethylene glycol) (PEG), Nafion, or Tween 20 [67,69,70]. It is conunonly accepted that a polymer or surfactant... 

Exploration to make FET type and oxygen concentration cell type gas sensors more flexible in operating temperature FET-based on silicon cannot function at temperatures higher than ca.l80°C, whereas the cell using zirconia cannot function at temperatures lower than ca. 550°C neither is able to work in the most important temperature range for gas sensing. Exploration for new semiconductors and new solid electrolytes is desired to eliminate these limitations. 

To be used as the addressing matrix switches for individual sensor elements, the on/off state current ratio is the parameter to be considered. For a biosensor array with thousands of sensor elements the off-state resistance must be at least 3 orders of magnitude larger that of the on-state to secure precise measurement of data. This can be easily achieved by the use of a single FET based on either CMOS [5], poly-Si TFT [15], or amorphous-Si TFT [59]. 

Ishige, Y., Shimoda, M., Kamahori, M. Extended-gate FET-based enzyme sensor with ferrocenyl-alkanethiol modified gold sensing electrode. Biosens. Bioelectron. 24, 1096-1102 (2009)... 

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