Gate insulator

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. 

The most common a-Si H TFT structure is the so-called inverted staggered transistor structure [40], in which silicon nitride is used as the gate insulator. A schematic cross section is shown in Figure 74. The structure comprises an a-Si H channel, a gate dielectric (SiN.v), and source, drain, and gate contacts. 

Another disadvantageous phenomenon in TFTs is the photoconductivity of a-Si H [626]. Electrons and holes are photogenerated and recombine at the back surface (gate insulator). The photocurrent reduces the on/off ratio of the TFT. Illumination, however, cannot always be avoided, e.g., in active matrix displays. A way of circumventing this is to make the a-Si H as thin as possible. 

FIGURE 7.3 Simplified equivalent circuit of an original (unmodified) EIS structure (a) and EIS biosensor functionalized with charged macromolecules (b). Cj, Cx and CML are capacitances of the gate insulator, the space-charge region in the semiconductor, and the molecular layer, respectively / u is the resistance of... 

Dimitrakopoulos, C. D. Purushothaman, S. Kymissis, J. Callegari, A. Shaw, J. M. 1999. Low-voltage organic transistors on plastic comprising high-dielectric constant gate insulators. Science 283 822-824. 

The inkjet-printed (or inkjetted ) TFT operated with a mobility of 6.5cm2/ Vs and an on/off ratio of three digits as shown in Fig. 5.6b. This low mobility is attributed to the poor crystallinity and rough surface, whereas the large off current, which was confirmed to be the current between source and drain rather than a leakage current through the gate insulator, is also attributed to... 

Field effect transistors are miniature, solid-state, potentiometric transducers (Figure 4.22) which can be readily mass produced. This makes them ideal for use as components in inexpensive, disposable biosensors and various types are being developed. The function of these semiconductor devices is based on the fact that when an ion is absorbed at the surface of the gate insulator (oxide) a corresponding charge will add at the semiconductor... 

Collet J, Tharaud O, Chapoton A, Vuillaume D (2000) Low-voltage, 30 nm channel length, organic transistors with a self-assembled monolayer as gate insulating films. Appl Phys Lett 76 1941-1943... 

High electric field in the gate insulator under off-condition due to electric field enhancement at the sharp corner of the U-trenches ... 

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