Gate electrode, features

C Linewidth Control, This parameter refers to the necessity of maintaining the correct features size across an entire substrate and from one substrate to another. This is important since the successful performance of most devices depends upon control of the size of critical structures, as for example in the gate electrode structure in an MOS device. As feature size is decreased and circuit elements packed closer together, the margin of error on feature size control is reduced. The allowable size variation on structures is generally a fixed fraction of the nominal feature size. A rule of thumb is that the dimensions must be controlled to tolerances of at least 1/5 the minimum feature size. Linewidth control is affected by a variety of parame-... 

Future developments of OLETs operating with higher power and speed are expected from the optimization of the device structure, such as the thickness of the organic layers and the dimensions of the gate electrode. In particular, the modulation depth and operational frequency of the OLETs are strongly dependent on the edge features of the gate electrode. 

Fig. 5. Density of states of the Au-C60-Au junction versus energy, for electrode separation of 13.7 A, V(, = 0. The curves are for three different gate voltages. Other system parameters are the same as in Fig. 4. Positions of the molecular levels are depicted over the peaks of IK )S( the triangles, circles, and squares correspond to Vg = 2.7 V, Vg = 0 V, and Vg = —2.7 V, respectively. The degeneracy of the original LUMO level is removed due to the presence of Au leads. Inset excess charge SQ (in units of e) in the C60 versus gate voltage. Due to the wider electrode separation, the equilibrium excess charge is smaller, 0.5e, and the DOS features are sharper due to a weaker coupling of the C60 to the leads.

Thiol end-capped oligothiophenes 105a-c were used to form the SAMs between the electrodes. A series of distinct periodic steps in the conductance was observed for all samples at low temperature (<100 K). These features were suggested to originate from vibrational modes in the molecules. A (weakly coupled) gate potential could be applied to the molecular junction, which shifted the step position in the I(V) curves but not the step widths. This observation was taken as an indication that only a single molecule was electrically active in the molecular junction. 

This feature of the FET is transformed into high sensitivity in the ISFET. That is, in order to go over from the FET to the ISFET it is sufficient to replace the insulating layer by an ion-selective membrane permeable only to one sort of iont and the metal gate by an electrolyte solution, which contains a reference electrode needed to short circuit the electric circuit (Fig. 19b). The potential, which develops across the membrane in the presence in the solution of that sort of ions for which the membrane is selectively permeable, acts here as an external voltage on the gate. This potential can be determined from Nernst s equation [cf. Eq. (4)]... 

The reduction potential of the 42a-monolayer is controlled by the pH of the electrolyte and is positively shifted as the pH decreases (e.g. E° = -0.65 V vs. SCE at pH = 7.5 and E° = -0.51 V vs. SCE at pH = 5.0). This movement allows the use of pH as an additional controller of the interfacial electron transfer features of the functionalized monolayer. At pH = 5.0, the 42a-monolayer is thermodynamically prohibited from stimulating electron transfer to BV2+ (E° = -0.58 V vs. SCE). Only the weak electrical response of the 42a-monolayer is observed, without the activation of the electron transfer cascade. Thus, the phenoxynaphthacenequinone-functionalized monolayer-electrode can be described as an AND gate with optical and pH inputs that act cooperatively in the activation of an electrochemical output. 

As a supplement for widely used glass electrodes, ISFET sensors provide some unique features. One of them is the capability of dry storage, which helps to avoid the problem of shelf-life and the hydration requirement time for glass electrodes. Fast response is another feature of an ISFET pH sensor. In a comparison study of commercial pH sensors reported by Smit et al. [84], the ISFET sensor showed about a ten times faster response than that of glass electrodes, and a response similar to that of an iridium oxide-based electrode [100, 104], This fast response time of ISFET sensors was attributed to its sensing mechanism, which is based on the electrostatic interaction of H+ ions with surface charge at the gate surface [66]. 

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