Microfabrication tools

An excellent overview and in-depth description of miniaturization techniques is given in Ref. [2]. Here, only a few examples of how miniaturized biosensors can he fabricated are described. A clear distinction can be made between the miniaturization of the biosensor fluid flow system and the use of a miniaturized transducer. Both result in different advantages for the biosensor assay, as it will be discussed below. In the case of biosensor fluid flow system, microfabrication tools used are by far fewer than those applied to the fabrication of micro/nanotransducers, which can span all of the micro/ nanofabiication techniques developed. 

Microfabrication technology has provided a plethora of tools and methods to engineer the position and microenvironment of cells in vitro. The unprecedented level of control over the mechanical, chemical, and electrical nature of the cellular microenvironment allows investigation of questions not addressable with conventional tools and methods. The unique insight into normal and abnormal cell behavior afforded by microfabricated tools and methods may one day lead to cures for injuries and diseases, and the ability to direct cell growth and behavior for tissue engineering or industrial applications. 

The development of microfluidic devices has been both limited and spurred by limitations of and advances in the materials they are built from and how they are made. Without a doubt, the microelectronics industry gave a critical first impulse to the field by lending its microfabrication tools. Even today, the fabrication techniques used to make microfluidic devices are influenced by advances in the microelectronics industry. 

Tunnel or nano-gap junctions can be prepared based on microfabrication tools and with elegant tricks such as electro-migration. Break... 

Innovation - advocates and opponents origin from microtechnology list of microfabrication techniques selectivity and efficiency as main driver for industrial implementation special properties and general advantages of micro reactors process-development issues BASF investigations on liquid/liquid and gas-phase reactions micro reactors as ideal measuring tools production in micro reactors as exception, the rule will be transfer to mm-sized channels [111],... 

Microfabrication of the parallel channels was performed by mechanical surface cutting of metal tapes [31]. In the case of aluminum alloys, ground-in monocrystalline diamonds were used [45]. In the case of iron alloys, ceramic micro tools have to be used owing to the incompatibility of diamonds with that material. Such a microstructured platelet stack is provided with top and cover plates, diffusion bonded and connected to suitable fittings for the inlet and withdrawal ducts by electron beam welding (Figure 3.9). 

In contrast to other analytical methods, ion-selective electrodes respond to an ion activity, not concentration, which makes them especially attractive for clinical applications as health disorders are usually correlated to ion activity. While most ISEs are used in vitro, the possibility to perform measurements in vivo and continuously with implanted sensors could arm a physician with a valuable diagnostic tool. In-vivo detection is still a challenge, as sensors must meet two strict requirements first, minimally perturb the in-vivo environment, which could be problematic due to injuries and inflammation often created by an implanted sensor and also due to leaching of sensing materials second, the sensor must not be susceptible to this environment, and effects of protein adsorption, cell adhesion, and extraction of lipophilic species on a sensor response must be diminished [13], Nevertheless, direct electrolyte measurements in situ in rabbit muscles and in a porcine beating heart were successfully performed with microfabricated sensor arrays [18],... 

From the very beginning, continuous reactor concepts, an alternative to the truly microfabricated reactors, were used, for example, static meso-scaled mixers or HPLCs and other smart tubing (see Iwasaki et al. 2006 for an example). This completed functionality by filling niches not yet covered by microfabricated reactors or even by replacing the latter as a more robust, more easily accessed or more inexpensive processing tool. Further innovative equipment, coming from related developments in the process intensification field, is another source e.g., structured packings such as fleeces, foams, or monoliths. 

The present chapter reviews recent research efforts aimed at developing new devices for in situ and on-site electrochemical stripping analysis of trace metals. It is not a comprehensive review, but rather focuses on new tools for decentralized metal testing, including remotely deployed submersible stripping probes, hand-held metal analyzers coupled with disposable microfabricated strips, and newly developed green bismuth film sensors. 

Since it will take several years to realize such an integral software toolbox, individual approaches with separate steps have to be applied to meet gradually the requirements of microreactor design. Standard software for computational fluid dynamics is directly applicable in this context, and there are also powerful software tools for the simulation of special steps in microfabrication processes. However, there has been rather little experience with materials for microreactors, optimization of microreactor design, and, in particular, the treatment of interdependent effects. Consequently, a profound knowledge of the basic properties and phenomena of microreaction technology just described is absolutely essential for the successful design of microreaction devices. 

Chemical activities in the field of mass screening are often related to combinatorial chemistry [51,52]. One major goal, especially in the field of solid phase chemistry involving polymers like DNA or peptides, aims at the increase in the number of compounds per reactor volume and time. Commercially available microtiter plates are established as reactors in this case whereby robotic feed systems fit perfectly to their dimensions. A drastic reduction of reaction volume and increase in number of reaction vessels ( wells ) leads to the so-called nanotiter plates (e.g. with 3456 wells). Microfabrication methods such as the LIGA process are ideal means for the cost effective fabrication of nano-titer plates in polymeric materials by embossing or injection molding techniques so that inexpensive one-way tools are realized. 

Schlautmann, S., Wensink, H., Schasfoort, R., Elwenspoek, M., van den Berg, A., Powder-blasting technology as an alternative tool for microfabrication of capillary electrophoresis chips with integrated conductivity sensors. J. Micromech. Microeng. 2001, 11, 386-389. 

The above example demonstrates the power of utilizing modeling tools when designing microstructures for high-performance bioanalytical systems. Trivial design errors are easily avoided and preliminary optimization of a microfluidic structure may thus be accomplished in silico, prior to extensive and expensive processing rounds in the microfabrication laboratories. 

Separation of simple mixtures [13,44] to more complicated biofluidic mixtures with CE-NMR and CEC-NMR have been reported [51,52], Several instrumental modifications and methodologies have been described to use CE/CEC-NMR as a diagnostic tool [44,53-55], Though still in its infancy, chip-based CE-NMR with microfabricated microcoils may be able to analyze picoliter volume samples [56,57]. 

The advancements of microelectronics with its increasing device performance and decreasing structure dimensions, which recently fell below the 100-nm mark, follow the path given by Moore s law. In contrast, microfabrication deals with a broad range of structure dimensions between submicrometers and millimeters [7]. The main developments in CMP are traditionally connected to those in advanced IC manufacturing. In recent years, however, the CMP equipment and consumable communities have also paid close attention to microfabrication. It is recognized that MEMS-specific CMP processes require dedicated consumables [8] and optimized tool sets [9] due to their diversity in structure dimension and materials to be processed. 

The differences and similarities in the requirements of CMP for microelectronics manufacturing and microfabrication are summarized in Table 14.1. This comparison gives an overview of the parameters relevant to CMP and is intended to serve as a guideline for CMP practitioners, consumable suppliers, equipment manufacturers, and others. Polishing tools and consumable sets capable of handling MEMS-specific tasks will be discussed at the end of this section. The following is a list of these terms for comparison. 

Throughput Due to the high productivity demands in microelectronics, the typical throughput of the manufacturing tools lies between 20 and 50 wafers/h. Larger vertical dimensions in microfabrication ease the throughput requirements to <10 wafers/h. 

Equipment CMP tools for microfabrication are not covered by the large equipment manufacturers as it is still regarded as a niche market. Therefore, the supply situation for MEMS CMP tools consists not only of older, used polishers for small wafer sizes but also of specialized, highly M EMS dedicated polishers and cleaners from smaller companies. The bandwidth varies between simple tabletop polishers for R D and fully automated CMP cluster tools for production. As the process requirements are equal to or even exceed those of microelectronics, simple polishers or refurbished older generation CMP equipment often carmot meet the demands of the planarization process for microfabrication. 

Tools for microfabrication have also been prepared based on the unique characteristics of carbon nanotubes. In the microtool shown in Fig. 5.23, two carbon nanotubes are fixed on gold electrodes that are deposited either side... 

A new alternative to solve this problem is atomic force microscopy (AFM) which is an emerging surface characterization tool in a wide variety of materials science fields. The method is relatively easy and offers a subnanometer or atomic resolution with little sample preparation required. The basic principle involved is to utilize a cantilever with a spring constant weaker than the equivalent spring between atoms. This way the sharp tip of the cantilever, which is microfabricated from silicon, silicon oxide or silicon nitride using photolithography, mechanically scans over a sample surface to image its topography. Typical lateral dimensions of the cantilever are on the order of 100 pm and the thickness on the order of 1 pm. Cantilever deflections on the order of 0.01 nm can be measured in modem atomic force microscopes. 

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