Etched silicon channels

FIGURE 2.1 Process steps of a standard one-mask micromachining procedure to etch a channel structure into silicon [3]. Reprinted with permission from Elsevier Science. 

Figure 2.13 Examples of RIE etched silicon, with friendly permission of the Technical University of llmenau, Faculty of Mechanical Engineering, Department of Micromechanical Systems.(a) Circular channels, (b) channel with a through-hole and (c) adjustment mark.

A third way to build up pFCs based on MEMS-polymers such as poly-dimethylsiloxane (PDMS) or polymethyl methacrylate (PMMA) or PCB-materials such as polyimid (PI) or FR4. These polymers can be micro-machined by molding or by laser ablation. Shah et al. [22,23] have developed a complete PEMFC system consisting of a PDMS substrate with micro-flow channels upon which the MEA was vertically stacked. PDMS micro-reactors were fabricated by employing micro-molding with a dry etched silicon master. The PDMS spin coated on micro-machined Si was then cured and peeled off from the master. The MEA employed consisted in a Nafion - 12 membrane where they have sputtered Pt through a Mylar mask. Despite an interesting method, this FC gave poor results, a power density of 0.8 mW cm was achieved. 

Representative results of microdevices fabricated with hot embossing are illustrated in Fig. 9. An SEM of a microchaimel array of a flow cytometry system embossed in PC using an RIE-etched silicon master [17] is illustrated in Fig. 9a. Small micrometer-sized channels... 

Another silicon membrane microreactor, composed of an aluminum bottom plate, a microstructured silicon layer carrying the channel system, and a 3 pm thick SiN membrane as a cover of the reactor, was developed [60]. Pt as an active component was put on the membrane either by wet chemistry or by PVD on a Ti adhesion layer. The reactor was manufactured by photolithography and plasma etching. The channels were introduced either by wet-etching or deep reactive ion etching. By increasing the thickness of the membrane from 1 to 1.5 and 2.6 pm. 

Ozone is a god target reagent for microreactor applications since it is toxic, difficult to handle and very reactive. A silicon-etched 16-channel (600 (tm x 300 pm x 22.7 mm) microreactor covered with Plexiglas was used for oxidation of 1-decene into nonanal with quantitative conversion and selectivity [20]. This reaction proceeds in fact through the formation of the very reactive intermediate ozonide, which formally results from [3 + 2] addition of O3 to the C=C bond. A consecutive reduction step with P(OEt)3-EtOAc is required to yield the aldehyde. The reaction time is as short as 0.32 s. From the published data, a daily production of ca. 1600 g of nonanal per day may be obtained, which is well suited for preparation in fine chemistry. 

Turner et al. (2004) studied the independent variables relative surface roughness, Knudsen number and Mach number and their influence on the friction factor. The micro-channels were etched into silicon wafers, capped with glass, with hydraulic diameters between 5 and 96 pm. Their surface roughness was 0.002 < ks< 0.06 pm for the smooth channels, and 0.33 < / < 1 -6 pm for the glass-capped ones. The surface roughness of the glass micro-channels was measured to be in the range 0.0014 [Pg.39]

We have designed, manufactured and tested a prototype that may be applied in thermal control of electronic devices. It was fabricated from a silicon substrate and a Pyrex cover, serving as both an insulator and a window through which flow patterns and boiling phenomena could be observed. A number of parallel triangular micro-channels were etched in the substrate. The heat transferred from the device was simulated by different types of electrical heaters that provided uniform and non-uniform heat fluxes, defined here respectively as constant and non-constant values... 

In the study by Hetsroni et al. (2006b) the test module was made from a squareshaped silicon substrate 15 x 15 mm, 530 pm thick, and utilized a Pyrex cover, 500 pm thick, which served as both an insulator and a transparent cover through which flow in the micro-channels could be observed. The Pyrex cover was anod-ically bonded to the silicon chip, in order to seal the channels. In the silicon substrate parallel micro-channels were etched, the cross-section of each channel was an isosceles triangle. The main parameters that affect the explosive boiling oscillations (EBO) in an individual channel of the heat sink such as hydraulic diameter, mass flux, and heat flux were studied. During EBO the pressure drop oscillations were always accompanied by wall temperature oscillations. The period of these oscillations was very short and the oscillation amplitude increased with an increase in heat input. This type of oscillation was found to occur at low vapor quality. 

There are other, nonhydrogel, new materials for chromatographic and electrophoretic separations [7,8,103,164,199,214,377,407], Eor example, Volkmuth and Austin [407] proposed electrophoretic studies in microlithographic arrays of posts and channels etched into sihcon wafers. This material may be useful for studying fundamental transport characteristics of macromolecules in defined media, and many recent studies have been conducted to develop chromatography and electrophoresis on silicon wafers with micron-scale channels... 

Flockhart, S. M., Dhariwal, R. S., Experimental and numerical investigation into the flow characteristics of channels etched in (100) silicon, J. Fluids Eng. 120 (1998) 291-295. 

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