Source-drain potential

Viewed as a ftmction of the potential bias 4> (the source-drain potential), the molecular conduction also shows resonance behavior. This can be realized by examining the integral in Eq. (17.33). The transmission function T( , 4>) is given by Eq. (17.36), perhaps with a bias-dependent resonance energy,... 

For correct function of the ISFET, a sufficiently large gate voltage, Vq, must be applied between the leads to the reference electrode and to the substrate, so that a sufficiently large potential difference is formed between the surface and the interior of the substrate for formation of the n-type conductive channel at the insulator/substrate interface. This channel conductively connects drain 1 and source 2, which are connected with the substrate by a p-n transition. On application of voltage Vj between the drain and the source, drain current /p begins to pass. Under certain conditions the drain current is a linear function of the difference between Vq and the Volta potential difference between the substrate and the membrane. 

The electrical current flows from the source, via the channel, to the drain. However, the channel resistance depends on the electric field perpendicular to the direction of the current and the potential difference over the gate oxide. Should this surface be in contact with an aqueous solution, any interactions between the silicon oxide gate and ions in solution will affect the gate potential. Therefore, the source-drain current is influenced by the potential at the Si02/aqueous solution interface. This results in a change in electron density within the inversion layer and a measurable change in the drain current. This means we have an ion-selective FET (an ISFET), since the drain current can be related to ion concentration. Usually these are operated in feedback mode, so that the drain current is kept constant and the change of potential compared to a reference electrode is measured. 

This chapter summarizes some of our recent work in printing techniques and plastic electronics. It also presents new data from printed transistors that use several different organic semiconductors in a variety of device geometries. In all cases, we observed good performance. pCP for the source/drain electrodes is attractive because it provides a simple and potentially low-cost route to high resolution (i.e. small channel lengths, L) structures that can be used to build transistors which... 

The electrical stability of the TFT was measured using dc bias followed by a pulsed recovery measurement. The dc bias conditions were applied with the gate potential set at 20 V and the source/drain bias at 1 V. The devices were stressed for 60 min followed by the pulsed recovery measurement having an on-time pulse of 25 ms. and an off time of 10 s. Figure 11.17 shows the measurement of the... 

In practice the source-drain current is kept constant by adjusting the potential between the reference electrode and bulk of the semiconductor. 

One should also invoke Fermi statistics. A typical tunnel curve is shown in Fig. 12 for SET model with D = 14 a.u., a = 1 a.u., the work function of electrodes W = 0.4 a.u., the Fermi energy Ee = 0.2 a.u., and the polarizability a = 200 a.u. (of Na atom). The potential drops near the interface of the source-drain electrodes, as it should for the ballistic regime. The tunnel curve has a single shallow well at a small bias voltage. When the latter increases, the well becomes deeper, and the dot is attracted to the inter-electrode gap center... 

For the saturation regime (Fj Fq - Ft) the aeeumulation within the channel is incomplete. This so ealled pinch off arises due to the superposition of the gate and drain potential. The source-drain eurrent ff in the saturation regime reads ... 

---