MOSFET-based sensors

Bergveld P. (1985) The impact of MOSFET based sensors. Sensors Actuators, 8,109-127. 

This work is divided into four main sections. First, in Part II, we discuss the influence of adsorbate effects on the conductivity of a-Si H material. In Part III the possibility of using a-Si H for thermistor applications is considered and justified. Part IV covers in some detail the studies of a-Si H-based MIS structures for hydrogen detection, while Parr. V deals with ACS devices based on a-Si H FETs. We will consider the specific example of a Pd MOSFET H2 sensor. 

Electronic noses The so-called electronic noses consist of chemical gas sensors that are able to monitor changes in the offgas composition of fermentation processes. The different sensors of electronic noses are based on conductive polymers (CP), metal oxide semiconductors (MOS), metal oxide semiconductor field effect transistors (MOSFET), or quartz crystal microbalance (QCM). CP-based sensors use the electrochemical properties of polymers like polypyrrole or polyindole. The absorbance of selected molecules of the off-gas into the polymer film causes changes in the sensors conductivity. MOS sensors possess an electrochemically active surface of metal oxides like tin oxide or copper oxide. The sensitivity... 

The ISFET is an electrochemical sensor based on a modification of the metal oxide semiconductor field effect transistor (MOSFET). The metal gate of the MOSFET is replaced by a reference electrode and the gate insulator is exposed to the analyte solution or is coated with an ion-selective membrane as illustrated in Fig. 

Pd MOS STRUCTURES The Pd MOS device (capacitor and field effect transistor) has been extensively studied as a model chemical sensor system and as a practical element for the detection of hydrogen molecules in a gas. There have been two outstanding reviews of the status of the Pd MOS sensor with primary emphasis on the reactions at the surface (7,8). In this section, the use of the device as a model chemical sensor will be emphasized. As will be seen, the results are applicable not only to the Pd based devices, they also shed light on the operation of chemfet type systems as well. Because of its simplicity and the control that can be exercised in its fabrication, the discussion will focus on the study of the Pd-MOSCAP structure exclusively. The insights gained from these studies are immediately applicable to the more useful Pd-MOSFET. 

The advantage of GasFETs in comparison with conventional MOSFET- and FET-based gas sensors is the free choice of the sensing material. Moreover, in contrast to classical semiconducting metal-oxide... 

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