Silicon micromachining

The design and fabrication of some gas-phase micro reactors are oriented on those developed for chip manufacture in the framework of microelectronics, relying deeply on silicon micromachining. There are obvious arguments in favor the infrastructure exists at many sites world-wide, the processes are reliable, have excellent standards (e.g. regarding precision) and have proven mass-manufacturing capability. In addition, sensing and control elements as well as the connections for the whole data transfer (e.g. electric buses) can be made in this way. 

Standard silicon micromachining processes were applied. The starting material was a 100 mm silicon (110) orientation wafer covered with thermal oxide. Stand-... 

The latest development are micromechanical sensors. Their development began with the large-scale introduction of silicon micromachined pressure sensors to the automotive industry in the nineties, which entailed a massive price reduction. Then acceleration sensors for airbag firing, yaw rate sensors and more were introduced. Many devices are still being discovered. The next step is product evolution, with introduction times between a few years and over a decade, as shown in Tab. 2.2. Once customers in the industry have accepted a product, investment in large-scale production can go ahead. It helps to find more applications for the product The time scale for the product evolution process varies from about five... 

Figure 23. Processing flow for 3-D electrode array fabrication using silicon micromachining with colloidal filling of the electrode material. The six steps are identified as the following (i) patterned photoresist (PR) on silicon substrate, (ii) PR removal after DRIB micromachining, (iii) insulate silicon mold by oxidation, (iv) colloidal electrode filling material centrifuged into the mold, (v) silver epoxy added to provide mechanical stability and electrical contact, (vi) the electrode flipped over and released from the mold by immersion in a TEAOH solution.

L. Bousse and W. Parce, Applying silicon micromachining to cellular-metabolism, IEEE Eng. Med. Biol. Mag., 13(3) (1994) 396-401. 

Hollow planar waveguides have been fabricated by several techniques, including physical vapor deposition and CVD of silver and dielectric layers on metallic substrates. Nevertheless, better results can be obtained by taking advantage of silicon micromachining techniques. Perhaps the most important advantage of silicon hollow waveguides over other hollow structures is the... 

Standard silicon micromachining was applied for device manufacture using wet-... 

The micro channel system was fabricated by standard silicon micromachining via etching of a silicon wafer with potassium hydroxide using thermal oxide as an etch mask [6], The double mixing tee configuration consists of six micro channels. For fluid connection, an outlet hole was drilled into the silicon chip. The chip was anodically bonded to a glass slide with three inlet holes, clamped in a holder and, thereby, connected to a commercially available quench-flow instrument... 

Miniaturized and integrated sensor systems were developed early for pressure and accelerometer sensors. The technology of silicon micromachining leads to sensitive pressure sensors which were marketed early [4]. Also accelerometers were developed mainly driven by the huge market of air bag application and crash sensors [5]. 

Micro electrode arrays can also be produced by thin film technology and silicon micromachining. Electrochemical analysis using planar thin film metal electrodes as transducer can be done with high performance in vitro [59]. 

For air monitoring a complete miniaturized system made by silicon micromachining has been proposed [86]. Valves,gas fluidics, filters, thin film sensors and pumps are integrated in silicon and mounted on a printed circuit board (Fig. 3). The application of such systems will become apparent in the future. 

According to the different ways in which cells alter their environment, e.g. heat produced, acidification, oxygen consumption or metabolite production, to some extent reflecting metabolic pathways, various sensors can be used to measure metabolic activity. In order to get deeper insight into the cell metabolism, different sensors were integrated into one small test chamber [99]. Even an entire fermenter has been realized by means of silicon-micromachining [105],... 

Hannoe, S., Sugimoto, I., Katoh, T., Silicon-micromachined separation columns coated with amino acid films for an integrated on-chip gas chromatograph. Micro Total Analysis Systems 98, Proceedings pTAS 98 Workshop, Banff, Canada, 13-16 Oct. 1998, 145-148. 

Yun, K-S., Joo, S., Kim, H-J., Kwak, J., Yoon, E. (2004). Silicon micromachined infrared thin-layer cell for in situ spectroelectrochemical analysis of aqueous and nonaqueous solvent system. Electroanalysis 17 959-64. 

Arkilic, E. B., Breuer, K. S., Sehmidt, M. A., (2001) Mass Flow and Tangential Momentum Accommodation in Silicon Micromachined Channels, Journal of Fluid Mechanics, Vol.437, pp.29-43. 

Another reported application of backshock is in filtration using membranes called microsieves, which are very thin and smooth membranes with uniform pores made by silicon micromachining [54]. The thinness (ca. 1.2 p,m) and high porosity of... 

O. Tabata, pH-controlled TMAH etchants for silicon micromachining, Sensors Actuators A 53, 335, 1996. 

A planar substrate, such as silicon wafer, could be micromachined by a sequence of deposition and etching processes. This results in three-dimensional microstructures which can be implemented in cavities, grooves, holes, diaphragms, cantilever beams etc. The process referred to as silicon micromachining often employs anisotropic etchants such as potassium hydroxide and ethylene diamine pyrocatechol. The crystallographic orientation is important as the above-mentioned etchants show an etch-rate anisotropy. The ratio for the (100)-, (110)- and (111)- planes is typically 100 16 1. The technique of electrochemical etch stop could be applied for control of the microstructural dimensions. An alternative... 

Srinivasan, U. Houston, M.R. Howe, R.T. Maboudian, R. Alkyltrichlorosilane-based self assembled monolayer films for stiction reduction in silicon micromachines. J. Microelectromechan. Syst. 1998, 7 (2), 252-260. 

The pressure ranges and environmental requirements differ from application to application therefore, various technologies coexist silicon micromachining and ceramic technologies are mostly used in the low-pressure range (1 kPa to 2 Mpa), and steel membranes are often used for higher pressures. 

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