Chemically sensitive semiconductor device

Nanowires and nanobelts of inorganic oxides have been fashioned into chemically sensitive semiconductor devices. These include tin and zinc oxides [9], and indium oxide [30], Once again, ammonia and NO2 gases were used for initial demonstrations. Oxygen had very little effect on the sensing action. Because of the low concentrations detected and the speed of the response, it was suggested that single-molecule response could be within reach with these ultraminiaturized sensors. 

P. Bergveld and N. F. De Rooij [1981] History of Chemically Sensitive Semiconductor Devices, Sensors and Actuators, 1, 5-15. 

Bergveld (7 ) was, of course, the first to report an ISFET as a chemically sensitive semiconductor device (CSSD). A broader grouping is that of chemically sensitive electronic devices CSEDs), sub-classified by Bergveld and van der Schoot (75) into ISFETs as "active electronic components as one member of a four-class system. Other categories are passive electronic components (resistor, capacitor, etc.), electronic and opto-electronic systems (oscillating crystal sensors, etc.), and systems with a chemical feedback (dynamic oxygen sensor, and coulometric sensors). 

The technique is referred to by several acronyms including LAMMA (Laser Microprobe Mass Analysis), LIMA (Laser Ionisation Mass Analysis), and LIMS (Laser Ionisation Mass Spectrometry). It provides a sensitive elemental and/or molecular detection capability which can be used for materials such as semiconductor devices, integrated optical components, alloys, ceramic composites as well as biological materials. The unique microanalytical capabilities that the technique provides in comparison with SIMS, AES and EPMA are that it provides a rapid, sensitive, elemental survey microanalysis, that it is able to analyse electrically insulating materials and that it has the potential for providing molecular or chemical bonding information from the analytical volume. 

Among the methods of anodic and chemical etching of semiconductors, widely used both in the production of semiconductor devices and in investigations (see, for example, Schnable and Schmidt, 1976 Turner and Pankove, 1978), the so-called light-sensitive etching is of great importance. It is based on the variation, under illumination, of the concentration of minority carriers, which often determines, as was shown above, the rate of anodic dissolution and corrosion of semiconductors. 

Photoelectrochemical conversion from visible light to electric and/or chemical energy using dye-sensitized semiconductor or metal electrodes is a promising system for the in vitro simulation of the plant photosynthetic conversion process, which is considered one of the fundamental subjects of modern and future photoelectrochemistry. Use of chlorophylls(Chls) and related compounds such as porphyrins in photoelectric and photoelectrochemical devices also has been of growing interest because of its close relevance to the photoacts of reaction center Chls in photosynthesis. 

The ion controlled diode was an initial attempt to isolate the active electronics from the chemical solution by producing a metallic-like via that allows the isolation of the chemically sensitive region from an area where electronic components could be deposited (41,42). However, the limited precision of the non-standard microfabrication techniques made this process difficult and costly. Since this device is still essentially a capacitive membrane-insulator-semiconductor structure like the chemfet, the same problems of hermetic isolation of the gate remain. 

A wide range of physical parameters are suitable for chemical sensing applications, consequently, there is a very wide variety of different transducers. Some examples of frequent transducing techniques are metal oxide semiconductor devices (MOS diodes and field effect transistors) relying e.g. on changes in electrical fields or opt(r)odes concerning optical phenomena such as absorbance and fluorescence, but also miniaturised capacities [1]. Mass-sensitive, or acoustic, devices constitute another very popular class of transducers. Within this chapter we will focus on this transducing technique and introduce its abihties and properties in combination with selective artificial interaction materials. 

Sensors based on adsorption of species onto or into lattice structures have been reported for molecules besides water. For example, devices based on the detection of carbon dioxide adsorption onto semiconductor materials have been developed [10]. In other cases, dielectric materials that have some degree of chemical specificity have been used for making chemically-sensitive layers. One such application is the use of the highly porous zeolite lattice to detect adsorbed hydrocarbons [11]. The specific dimensions and shape of the zeolite pores allows for size and chemical selectivity in the lattice. As in the case of the humidity devices, the adsorbed molecules dipoles cause a local change in the electric fields that can be detected through a capacitive effect. 

Semiconductor materials have had to meet progressively more stringent requirements as the density and performance of semiconductor devices has increased. This trend will continue. The purity of the matoial, the dimensions of the devices, and the electrical properties require higher precision in their measurement and the ability to determine the device parameters to a resolution and sensitivity that pushes measurement techniques to their very limit. Semiconductor measurements cover a broad range of techniques and disciplines. After a brief listing of optical and physicall chemical characterization methods we give in this chapter a discussion of the general trend in electrical characterization and present a few examples of the charactmzation techniques used today. 

To facilitate a self-contained description, we will start with well-estahlished aspects related to the semiconductor energy hand model and the electrostatics at semiconductor-electrolyte interfaces in the dark . We shall then examine the processes of light absorption, electron-hole generation, and charge separation at these interfaces. The steady state and dynamic aspects of charge transfer are then briefly considered. Nanocrystalline semiconductor films and size quantization are then discussed as are issues related to electron transfer across chemically modified semiconductor-electrolyte interfaces. Finally, we shall introduce the various types of photoelectrochemical devices ranging from regenerative and photoelectrolysis cells to dye-sensitized solar cells. 

Various techniques are used for the fabrication of semiconductor sensors. Conductance sensors from structurized sintered polycrystalline ceramics can be produced by thick- or thin-film technology. Chemically sensitive materials in the form of single crystals or whiskers can be attached to electrodes by thin- or thick-film techniques as well. Mass production of sensors requires that the resulting devices be characterized by a defined level of conductance. For example, the conductance of polycrystalline Sn02 can be adjusted by subsequent thermal treatment >800°C under a controlled partial pressure of oxygen. Another approach to defined conductance involves doping the semiconductor with antimony or fluorine. The reproducibility and stability of a sensor signal... 

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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