Individually addressable electrodes

Electrochemical experiments have been carried out on materials deposited by PVD on silicon microfabricated arrays of Au pad electrodes [Guerin et al., 2006a]. The substrate is made up of a square silicon wafer capped with silicon nitride (31.8 mm x 31.8 mm), which has an array of 100 individually addressable Au pad electrodes. These electrodes make up a square matrix on the wafer, which can be masked when placed in a PVD chamber, allowing deposition of thin films on the Au electrodes. Figure 16.3 is a schematic drawing of the configuration. Small electrical contact pads in Au for the individual addressing of electrodes (0.8 mm x 0.8 mm) are placed on the boundaries. 

Figure 16.3 Silicon nitride pacified silicon wafer with an array of 100 individually addressable square Au electrodes.

Electronically active chips (e.g.. Nanogen s NanoChip Electronic Microarray) are true microchips in which microelectrodes (pads) become elements of the array (Figure 2.13). The microelectrodes are covered with materials that allow immobilization of probes. Each electrode is individually addressable so that specific probes can be attached to different electrodes. Hybridization is accelerated by electromotive force (emf) on the target. Enhanced stringency is also achieved by modulation of the emf (Heller et al., 2000). 

Different methods are described to construct ultramicro electrodes48-62 such as insulation in glass or epoxy resin, the construction of ultramicro electrode arrays (an array of individual ultramicro electrodes to increase the current signal without losing the benefits of ultramicro electrode behaviour) by template synthesis, metal depositions in pores of membranes and by using the connecting wires in microchips. The latter has the advantage that each ultramicro electrode is individually addressable. 

Fig. 11.2 A 64-element, individually addressable, Ti electrode array on a 3" diameter quartz wafer for the synthesis of electrocatalyst libraries.

It is rarely addressed in the literature that for molecular versions of circuit elements to be useful, there has to be the possibility to connect them together in a way where their electrical characteristics — measured individually between electrodes — would be preserved in the assembled circuit. However, it has been recently shown that such a downscaling of electrical circuits within classical network theory cannot be realized due to quantum effects, which introduce additional terms into Kirchhoff s laws and let the classical concept of circuit design collapse [16]. Circuit simulations on the basis of a topological scattering matrix approach have corroborated these results [34]. 

Figure 1. Side-view of digital micro fluidic platform with a conductive glass top plate (left). A diagram of materials and construction of the actuator is shown (right). By adding a conductive top plate and adding individually addressed buried electrodes in the bottom plate, the droplet can be actuated from one electrode position to the next by the application of voltage.

Figure 15. The electrowetting effect. (According to Mugele et al. [260].) (a) If a voltage V is applied between a liquid and an electrode separated by an insulating layer, the contact angle of the liquid-solid interface is decreased and the droplet flattens , (b) Hydrophobic surfaces enhance the effect of electro wetting. For electrowetting on dielectrics (EWOD) several individual addressable control electrodes (here on the bottom) and a large counter-electrode are used. The droplet is pulled to the charged electrodes.

Figure 10.26 Schematic diagram of a structure used for electrochemical wire growth (a) electrodeposited wire connected between electrodes (b) cross-sectional view of the Si substrate, silicon nitride (1 gm), Au contacts, and thermally evaporated SiO. Channels for the electrolyte solution are formed between electrodes by e-beam patterning of the SiO. (Reprinted with permission from Nano Letters, Electrochemical ly grown Wires for Individually Addressable Sensor Arrays by M. Yun et al., 4, 3. Copyright (2004) American Chemical Society)...

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