Microfabricated structures microfabrication processes

GP 8[ [R 7[ The structure of the rhodium catalyst changed during operation. Owing to the microfabrication process (thin-wire pEDM), the surface of the micro channels was rough before catalytic use [3]. After extended operational use, small crystallites are formed, especially in oxygen-rich zones such as the micro channels inlet. Thereby, the surface area is enlarged by a factor of 1-1.5. 

The actual device consists of two parallel rows of five mixing elements each [125, 126], The lateral displacement and recombination of the sub-channels are done via 90° angles. In contrast, the variation of channel depth and width is done in a continuous fashion, yielding a curved horizontal and vertical structure. In particular, the curved floor structure is demanding, since a real 3-D and not just a multi-level microfabrication process is needed. 

The actual retina contact structure incorporates 12 or 24 independent electrodes, respectively. The electrodes were arranged concentrically to minimize the electrical stray field during stimulation. We established the microfabrication process for double metallization layers needed to obtain concentric microelectrodes. In a temper step, the electrodes were formed into a convex shape according to the curvature of the eye. The generation of convex shapes was possible since the stimulator was designed in concentric rings interconnected by s-shaped bridges (Fig. 26). 

Microfabrication processes have been used successfully to form micro-fuel cells on silicon wafers. Aspects of the design, materials, and forming of a micro-fabricated methanol fuel cell have been presented. The processes yielded reproducible, controlled structures that performed well for liquid feed, direct methanol/Oj saturated solution (1.4 mW cm ) and direct methanol/H O systems (8 mA cm" ). In addition to optimizing micro-fuel cell operating performance, there are many system-level issues to be considered when developing a complete micro power system. These issues include electro-deposition procedure, catalyst loading, channel depth, oxidants supply, and system integration. The micro-fabrication processes that have... 

Since advanced lithography tools with resolution down to sub 100 nm may not be readily available, some novel techniques to fabricate ID nanochannels have been developed and reported. One of these techniques uses standard microfabrication process and has the potential to make integrated nanofluidic devices [2]. This technique is similar to the spacer technique developed in solid-state electronic device fabrication. A spacer is the thin side wall achieved by conformal deposition of selected thin film on the side wall of a sacrificial structure. With the fine control of the LPCVD deposition process, a spacer as thin as 10 nm can be made. After removing the sacrificial structure, a spacer as thin as 10 nm is left on the substrate, which can be subsequently used as a mask to pattern nanometer lines or used as a sacrificial line to make a nanochannel. Other novel techniques involve shrinking a larger channel made by standard micromachining to smaller sizes by methods such as filling the channel with other materials [3]. 

From the very beginning, continuous reactor concepts, an alternative to the truly microfabricated reactors, were used, for example, static meso-scaled mixers or HPLCs and other smart tubing (see Iwasaki et al. 2006 for an example). This completed functionality by filling niches not yet covered by microfabricated reactors or even by replacing the latter as a more robust, more easily accessed or more inexpensive processing tool. Further innovative equipment, coming from related developments in the process intensification field, is another source e.g., structured packings such as fleeces, foams, or monoliths. 

Figure 4 shows the impact of process intensification for this hypothetical case. With a temperature increase of only 41°C, the number of reactors for such comparatively big units is reduced from 20, hardly feasible in view of costs and process control, to four, feasible for the same reasons. Thus, the costs decrease by almost a factor of five (not exactly, since fixed costs have a small share). Another 21°C temperature increase halves the number of reactors again, and at 249°C, which is 149°C higher than the base temperature, an equivalent of 0.2 micro-structured reactors is needed. This means that practically one micro-structured reactor is taken and either reduced in plate number or in the overall dimensions. The costs of all microstructured reactors scales largely with their number only at very low numbers do fixed costs for microfabrication lead to a leveling off of the cost reduction. 

The ion controlled diode was an initial attempt to isolate the active electronics from the chemical solution by producing a metallic-like via that allows the isolation of the chemically sensitive region from an area where electronic components could be deposited (41,42). However, the limited precision of the non-standard microfabrication techniques made this process difficult and costly. Since this device is still essentially a capacitive membrane-insulator-semiconductor structure like the chemfet, the same problems of hermetic isolation of the gate remain. 

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