Charge-modulated field-effect devices

Nanocrystals are receiving significant attention for nano-electronics application for the development of future nonvolatile, high density and low power memory devices [1-3]. In nanocrystal complementary metal oxide semiconductor (CMOS) memories, an isolated semiconductor island of nanometer size is coupled to the channel of a MOS field effect transistor (MOSFET) so that the charge trapped in the island modulates the threshold voltage of the transistor (Fig. 1). 

P. G. LeComber and W. E. Spear, The Development of the a-Si H Field-Effect Transistor and Its Possible Applications D. G. Ast, a-Si H FET-Addressed LCD Panel S. Kaneko, Solid-State Image Sensor M. Matsumura, Charge-Coupled Devices M. A. Bosch, Optical Recording A. D Amico and G. Fortmato, Ambient Sensors H. Kukimoto, Amorphous Light-Emitting Devices R. J. Phelan, Jr., Fast Detectors and Modulators J. I. Pankove, Hybrid Structures... 

If the semiconductor surface bears localized bound states (surface states), part of the induced charge will reside in these states, thus decreasing the conductivity modulation induced by the transverse field. For a long time, field effect was therefore not used in devices but was a very useful tool for studying semiconductor surfaces and surface states [249] (see also Ref. 236, p. 285). 

CHEMFET devices or chemically sensitive field-effect transistors are potentiometric devices in which the metal layer of a solid-state insulated gate field-effect transistor (IGFET) f29] is replaced with a chemically sensitive electroconductive polymer membrane film. Changes in polymer membrane potential modulate the drain impedance of the space-charge region beneath the insulator. The result is a change in drain current /o under a fixed drain voltage Vd- The potential of the membrane may be modulated in the standard way (as in po-tentiometry, above) or may be modulated by an inert electrode placed beneath the film (but isolated from both the source and drain electrodes) and connected to an efficient electrode for the candidate analyte [30]. 

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