Passive fabrication techniques

In designing a microscale fuel cell, there are several considerations that need to be accounted for. These include the following is the fuel cell to be completely active or passive will it operate at room temperature or elevated temperatures will the fuel be at atmospheric pressure or elevated pressure will external humidification be required and finally, will the fabrication techniques... 

Oxidation reactions of a metallic substrate are excluded. Generally the substrate plays only a passive role in CVD processes. Many examples of such reactions are listed in the review papers [68], [69] and in the books and proceedings of CVD conferences such as [70]. In addition, there are different fabrication techniques in use... 

The flow control is broadly classified as (a) passive control, where no auxiliary power source is required, and (b) active control, where there is expenditure of energy. In passive control, parameters like geometry, compliance, temperature, and porosity, etc. are varied. Boundary oscdlation, acoustic waves, blowing, sucticai, etc. are used for active control. The active control schemes use actuators for manipulating the flow behavior. The size of these actuators depends on the nature of the flow. When the Reynolds number is increased, the required size of the actuator is reduced. The availability of MEMS fabrication technique has contributed toward small-scale actuator development. 

PRISM employs passive safety, digital instrumentation and control, and modular fabrication techniques to expedite plant construction [1-4]. PRISM has a rated thermal power of 840 MW and an electrical output of 311 MWe. Each PRISM module has an intermediate sodium loop that exchanges heat between the primary sodium coolant from the core with water/steam in a sodium-water steam generator (SG). The steam from the sodium-water SG feeds a conventional steam turbine. A diagram of the PRISM nuclear steam supply system (NSSS) is shown in Figure 6.2. 

For micro fuel cells, miniaturization of the fuel-cell system is a key issue. Research in this area includes developing passively operating fuel cells in order to reduce the peripheral spends and the parasitic energy losses and minimize the system complexity. Development must also focus on low-cost production materials such as silicon or thermoplastics, and fabrication techniques such as MEMS technology or injection molding. 

OLEDs grown and encapsulated using these techniques are beginning to show significant promise. Recently, Chwang et al. demonstrated the effects of flexing a 64x64 (180 dpi) passive-matrix flexible OLED (FOLED) display fabricated on a PET substrate with thin film encapsulation [166], In addition, lifetimes of thin-film-encapsulated OLED test pixels on flexible substrates have now been demonstrated to be thousands of hours [162,167],... 

A prerequisite for all etch-stop techniques discussed so far is an electrical connection to an external power supply. However, if the potential required for passivation in alkaline solutions is below 1 V, it can be generated by an internal galvanic cell, for example by a gold-silicon element [As4, Xil]. An internal galvanic cell can also be realized by a p-n junction illuminated in the etchant, as discussed in the next section. Internal cells eliminate the need for external contacts and make this technique suitable for simple batch fabrication. 

We have demonstrated that micron-scale passive waveguide structures including "Y splitters" and crossovers can be fabricated in organic films using a photodelineation technique. This methodology provides for the spatial delineation... 

The silicon detectors were made of n-typed single crystal of 1 mm thick. They have a MOS structure of gold, tungsten oxide, n-typed silicon and aluminum back contact. Since these layers can be deposited on the silicon wafer by evaporation techniques, the fabrication process is so simple as to be applicable to fabrication of the detectors for a special use. No surface treatment for passivation is given to them so that their performance is affected by ambient gases. For example, some good detectors show a leakage current of half micro-ampere at room temperature in the atmosphere, but a few micro-ampere in vacuum. So, in order to stabilize their performance, the silicon detectors were operated at the dry ice temterature. 

Several techniques for miniaturization of simple chemical and medical analysis systems are described. Miniaturization of total analysis systems realizes a small sample volume, a fast response and reduction of reagents. These features are useful in chemical and medical analysis. During the last decade many micro flow control devices, as well as the micro chemical sensors fabricated by three dimensional microfabrication technologies based on photofabrication, termed micromachining, have been developed. Miniaturized total analysis systems (pTAS) have been studied and some prototypes developed. In microfabricated systems, microfluidics , which represent the behavior of fluids in small sized channels, are considered and are very important in the design of micro elements used in pTAS. In this chapter microfluidics applied flow devices, micro flow control devices of active and passive microvalves, mechanical and non-mechanical micropumps and micro flow sensors fabricated by micromachining are reviewed. 

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