MISFET device

Fig. 18. A schematic drawing of a MISFET device. n-Silicon serves as the metal, Si02 is the insulator, and PA is the semiconductor. The top contact layer is made from gold [152].

Polythiophene is a material which is the center of interest of many groups for its possible applications. It shows high conductivity when doped [110], large third order non linear optical properties [111] and it has been used as a semiconducting active material in the first attempts to build MISFET devices [112]. Of more relevant practical importance is the fact that its alkyl-derivatives are soluble thus opening new horizons for workable polyconjugated polymers. 

Defect states in semiconductors affect bipolar junction transistors strongly. Interface states at the dielectric affect MISFET devices strongly. 

Conventional electronic devices are made on silicon wafers. The fabrication of a silicon MISFET starts with the diffusion (or implantation) of the source and drain, followed by the growing of the insulating layer, usually thermally grown silicon oxide, and ends with the deposition of the metal electrodes. In TFTs, the semiconductor is not a bulk material, but a thin film, so that the device presents an inverted architecture. It is built on an appropriate substrate and the deposition of the semiconductor constitutes the last step of the process. TFT structures can be divided into two families (Fig. 14-12). In coplanar devices, all layers are on the same side of the semiconductor. Conversely, in staggered structures gate and source-drain stand on opposing sides of the semiconductor layer. 

Because there is no depletion layer between the substrate and the conducting channel, the equations of the current-voltage curves are in fact simpler in the TFT than in the MISFET, provided the mobility can still be assumed constant (which is not actually the case in most devices, as will be seen below). Under such circumstances, the charge induced in the channel is given, in the case of an /l-channel, by Eq. (14.23). In the accumulation regime, the surface potential Vs(x) is the sum of two contributions (i) the ohmic drop in the accumulation layer, and (ii) a term V(x) that accounts for the drain bias. The first term can be estimated from Eqs. (14.15), (14.16) and (14.19). In the accumulation regime, and provided Vx>kT/q, the exponential term prevails in Eq. (14.16), so that Eq. (14.15) reduces to... 

Device motivation for interface studies, and Optical absorption and emission in conjugated oligomers and polymers. The principles of device physics of metal insulator field-effect transistors (MISFETs) and light emitting diodes (LEDs) are oudined mainly as motivation for the contents of the chapters which follow, but also to point out certain features relevant to developing an understanding of the nature of the polymer-metal interface (chapters 5 and 6). The basic principles of electro-luminescence are reviewed here, at the level consistent with the aims of this work. 

A particularly interesting fact is that in the case of a-sexithiophene, or a6T, work on prototype devices such as MISFETs has shown that thin films of a6T molecules actually exhibit better performance characteristics than the corresponding polymer, polythiophene, and rival those of amorphous silicon41. a6T also has been used in light emitting diodes42-44. 

Device MESFET MISFET/HIGFET JFET MODFET/HFET... 

The MIS capacitor represents the heart of most field effect sensor devices, and the physics of MIS capacitors is of importance and is treated in semiconductor physics and other sensor books (Sze, 1981 Lundstrom, 1995 Dimitrijev, 2000). Here, we will only give the basic physical principles regarding the metal insulator semiconductor field effect transistor (MISFET), since this is the ultimate transducer for commercial sensor devices. 

Usagawa, T. and Kikuchi, Y. (2011), Device characteristics for Pt-Ti-O gate Si-MISFETs hydrogen gas sensors. Sensors and Actuators B, 160(1), 105-14. 

MIS field-effect transistors (MISFETs) and enzyme field-effect transistors (ENFETs) based on conducting polymers have also been fabricated. A schematic diagram of such a device is shown in Figure 13.12. Janata and co-workers have investigated the electrical properties... 

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