Micro-fabrication techniques

Sichere Chemie in Mikroreaktoren, Frankjurter Allgemeine Zeitung, December 1995 Plant cells as model for micro-reactor development micro-fabrication techniques DuPont s investigations DECHEMA s initiation of micro-reactor platform BASF s investigations general advantages of micro flow [238]. 

In the mid-IR, routine infrared spectroscopy nowadays almost exclusively uses Fourier-transform (FT) spectrometers. This principle is a standard method in modem analytical chemistry45. Although some efforts have been made to design ultra-compact FT-IR spectrometers for use under real-world conditions, standard systems are still too bulky for many applications. A new approach is the use of micro-fabrication techniques. As an example for this technology, a miniature single-pass Fourier transform spectrometer integrated on a 10 x 5 cm optical bench has been demonstrated to be feasible. Based upon a classical Michelson interferometer design, all... 

Anisotropic etching of silicon is routinely used in the fabrication of three-dimensional structures [1,2]. These micro fabrication techniques take advantage of orientation-dependent etch rates where the planes of lowest etch rate, usually the (111) planes, act as etch stops for the dissolution process [3, 4]. In electrolytes such as KOH, the etch rates of the (100) and the (110) planes may be more than two orders of magnitude faster than those of the (111) planes. In buffered NH4F solutions, etch rate enhancements as high as 15 have been reported for the (100) plane in comparison with the (111) surface [5]. 

Figure 25.1 Schematics of typical nano and micro fabrication techniques Photolithography, soft lithography, hot embossing, and direct writing. See color plates.

Chen R (2004) Micro-Fabrication Techniques. Wireless Des Develop 16-20... 

We have also provided evidence that the behavior of microorganisms in confined micro-environment is substantially different and that their desired metabolic activities can be maximized through the modification of the surface characteristics as well as the size of the pores. These characteristics can therefore be utilized in BI as well as in the enhancement of cell penetration and cell proliferation in tissue engineering and when such polymers are grafted. Micro-fabrication technique has also been used in the development of highly porous catalysts with arterial channels feeding nano-pores which provide an extended surface area. Such materials can be used as micro-reactors as well as catalysts. 

As the base material for MEMS technologies. Si is also the most common material encountered in MEMS-based FC. Its properties and the micro-fabrication techniques associated to it such as photolithography, wet or dry etching, depositing (sputtering, CVD, thermal oxidation, etc.) are now well known and mastered. Another advantage of Si-based FC may also be to facilitate the possible integration of the FC with other electronic devices on the same chip. 

The Tohoky University, Japan (Min et al.) reported a p-PEFC using micro-fabrication techniques [3]. This FC is based on two different designs, the alternatively inverted structure and the coplanar structure . These structures use Si substrates with porous SiOj layers with Pt-based catalytic electrodes and gas feed holes, glass substrates with micro-gas channels and a polymer membrane (Flemion S). In spite of a reported enhancement [4], the FC reached poor results, the power density is only 0.8 mW cm . ... 

The handbook chapter Porous Silicon Membranes reviews the different fabrication routes and applications of mesoporous and macroporous silicon membranes. Among inoiganic membrane materials, porous silicon has been the most studied for immunoisolation (macroencapsulation). Desai and Ferrari developed a micro fabrication technique to produce controlled slit pores in 0.5-5 pm-thick Si membranes (see Fig. 2) (Leoni and Desai 2004 Desai et al. 1998, 2000a, b, 2004). The width of these pores (constant length of 45 pm) can be varied from 7 to 100 nm with less than 5 % of variation. The pores are produced by dissolution of a thermally grown sacrificial silicon oxide layer. These membranes present a porosity of 1 % (Leoni and Desai 2004 Desai et al. 2000b). 

These devices feature the use of micro-fabrication techniques adapted from the micro-electronics industry. These encompass substrate etching, thin-fihn deposition, lithography, and film-etching steps. This field has recently been reviewed by Evans et al. [11], and all devices exhibit the beautiful structural quality resulting from the micro-fabrication techniques. An example of a micro-planar SOFC fabricated on a silicon substrate is illustrated in Fig. 19.4 [12]. Figure 19.4a shows the sequence of fabrication steps used to make the edge-supported SOFC membrane which spans an aperture with dimensions 600 x 600 pm. The yttria stabilized zirconia (YSZ) electrolyte, which is only 70-nm thick, was deposited by... 

In this process, a prototype is manufactured using mechanical micro-fabrication techniques. The actual mold insert is manufactured in an electroplating process. This mold insert can range from several tenths of a millimeter in thickness up to 10 mm. The advantage is that the positive-negative impression can be used and that several mold inserts can be shaped by a prototype. 

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