Conducting Channels

Figure 14-9. Schematic view of normally on (a) and normally off (b) MESFETs at zero gate voltage. In (a) a conducting channel already exists, while in (b) the depletion layer extends all over the channel.

To calculate the current-voltage characteristic of a MESFET, we assume that the conducting channel is at thermal equilibrium, and the space-chaige layer completely depleted. Eq. (14.28) becomes... 

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... 

Fig. 4.15 Effect of axial conduction, channel between two parallel plates (Maranzana et al. 2004) (schematic view) 1 cover plate, 2 micro-channel, 3 silicon block 1,...

Aluminum trichloride, a cheap, abundant waste product of the chemical industry, forms a gel under certain conditions with carbonates and on mixing with alkalis. Laboratory and field tests showed that aluminum trichloride can be used as a gel-forming agent for reducing the permeability of water-conducting channels [674]. 

Urry, D. W., A molecular theory of ion-conducting channels A field dependent transition between conducting and non-conducting conformations, Proc. Natl. Acad. Sci. USA, 69, 1610 (1972). 

Another way to reduce membrane potentials is to introduce conducting channels into the membrane. Gramicidin A, for example, acts as an ion channel for monovalent... 

Brandbyge M, Kobayashi N, Tsukada M (1999) Conduction channels at finite bias in singleatom gold contacts. Phys Rev B 60(24) 17064... 

Heurich J, Cuevas JC, Wenzel W, Schon G (2002) Electrical transport through singlemolecule junctions from molecular orbitals to conduction channels. Phys Rev Lett 88 (25) 256803... 

Solomon GC, Gagliardi A, Pecchia A, Frauenheim T, Di Carlo A, Reimers JR, Hush NS (2006) Molecular origins of conduction channels observed in shot-noise measurements. Nano Lett 6(11) 2431-2437... 

---