Fabrication micromachining

Tonkovich, A. L. Y, Roberts, G. L, Fabrication of a stainless steel microchannel microcombustor using a lamination process, in Proceedings of the SPIE Gonference on Micromachined Devices and Gompo-nents IV, pp. 386-392 (September 1998),... 

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. 

H. Suzuki and H. Arakawa, Fabrication of a sensing module using micromachined biosensors. Biosens. Bioelectron, 16, 725—733 (2001). 

Fig. 7.6 (a) Microscopic image of the micromachined hole introduced on the fiber cross section, (b) Microscopic image of the fabricated sensor head. Reprinted from Ref. 12 with permission. 2008 Optical Society of America... 

The latest advancement in femtosecond (fs)-based micromachining technology has opened a new window of opportunity for fabrication of microdevices. Direct exposure of most solid materials (including fused silica glass) to high power fs laser pulses may lead to the ablation of a thin layer of materials at the laser focal point13. Due to the multiphoton nature of the laser-material interaction, the ablation process can be conducted on the material surface as well as within its... 

Cheng, Y. Tsai, H. L. Sugioka, K. Midorikawa, K., Fabrication of 3D microoptical lenses in photosensitive glass using femtosecond laser micromachining, Appl. Phys. A. 2006, 85, 11 14... 

A cross-sectional schematic of a monolithic gas sensor system featuring a microhotplate is shown in Fig. 2.2. Its fabrication relies on an industrial CMOS-process with subsequent micromachining steps. Diverse thin-film layers, which can be used for electrical insulation and passivation, are available in the CMOS-process. They are denoted dielectric layers and include several silicon-oxide layers such as the thermal field oxide, the contact oxide and the intermetal oxide as well as a silicon-nitride layer that serves as passivation. All these materials exhibit a characteristically low thermal conductivity, so that a membrane, which consists of only the dielectric layers, provides excellent thermal insulation between the bulk-silicon chip and a heated area. The heated area features a resistive heater, a temperature sensor, and the electrodes that contact the deposited sensitive metal oxide. An additional temperature sensor is integrated close to the circuitry on the bulk chip to monitor the overall chip temperature. The membrane is released by etching away the silicon underneath the dielectric layers. Depending on the micromachining procedure, it is possible to leave a silicon island underneath the heated area. Such an island can serve as a heat spreader and also mechanically stabihzes the membrane. The fabrication process will be explained in more detail in Chap 4. 

In the previous section, it was mentioned that Zhang et al. [51,52] developed a technique to micromachine a thin metal film made out of copper. This material had a number of perforations that followed a predetermined pattern and such a design can be changed fairly easily by simply changing one of the masks used in the fabrication process. Although copper is not an ideal material to be used as a DL in a fuel cell due to the contamination issues, the development of fabrication techniques similar to those mentioned... 

Three-dimensional electrode arrays have been fabricated using two very different micromachining methods. One approach, named carbon MEMS or C-MEMS, is based on the pyrolysis of photoresists. The use of photoresist as the precursor material is a key consideration, since photolithography can be used to pattern these materials into appropriate structures. The second approach involves the micromachining of silicon molds that are then filled with electrode material. Construction of both anode and cathode electrode arrays has been demonstrated using these microfabrication methods. 

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.

A second approach for fabricating electrode arrays has involved micromachining of silicon molds, which are filled with electrode material by colloidal processing methods. In contrast to G-MEMS, this fabrication approach is suitable for both anodes and cathodes, as one merely alters the composition of the powders. The process flow for electrode array fabrication is depicted in Figure 23. 

A number of fabrication techniques meet the general requirements for constructing an efficient and compact microreactor. Popular methods include LIGA, wet and dry etching processes, micromachining, lamination, and soft lithography. 

Initially, the reactor was to be built using silicon wafers, 92 but more recent efforts have focused on a stainless steel reactor. The reformer, 7.5 x 4.5 x 11.0 cm (371 cm ), houses up to 15 stainless steel plates (0.5 mm thick) with chemically etched microchannels and heating cartridges. Conventional and laser micromachining techniques were used to fabricate the reformer body. The microchannel dimensions are 0.05 x 0.035 x 5.0 cm . The reactor inlet was carefully designed to allow uniform flow conditions. ... 

Mass-produced cantilever sensors, however, have the potential to satisfy the conditions of selectivity, sensitivity, miniature size, low power consumption, and real-time operation [5, 6], Microcantilevers are micromachined from silicon or other materials and can easily be fabricated in multiple-element arrays. They resemble miniature diving boards measuring 100 to 200 pm long by about 20 to 40 pm wide by 0.3 to 1 pm thick and having a mass of a few nanograms. Their primary advantage originates from their sensitivity, which is based on the ability to detect their motion with subnanometer precision. 

In the positive branch of the i/V graph, anodic dissolution process will remove material from silicon crystals. The conditions for optimal etching of silicon have been extensively explored for micromachining or surface polishing in the fabrication of electronic devices. Most generally, the etch rate of silicon in HE solutions is isotropic among the various crystalKne orientations. The etch rate of silicon at room temperature at the open-circuit potential (OCP) is very low, on the order of 10 nm s , which is equivalent to 100 nA cm , in aqueous HE solutions. 

The term etching refers to the dissolution processes at OCP of silicon samples immersed in an electrolyte solution. The technique has been extensively explored for its useful applications in the fabrication of electronic devices, surface polishing, and micromachining. For example, it is widely used for the production of cantilevers for the AFM technology. 

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