Liga process

Fig. 2.73a-d The LIGA process. Reprinted from Kan-dlikar and Grande (2002) with permission... 

Chemiefabrik in der Grojie eines Chips, Handdsblatt, May 1996 Vision of shoe box-sized micro reactors plant cells as model for micro-reactor development cost, performance, and safety advantages LIGA process numbering-up safety processing of hazardous substances [237]. 

Zhu et al. [76] designed and fabricated microfluidic devices on polymethylmethacrylate (PMMA) substrates for electrochemical analysis applications using an improved UY-LIGA process. The microchannel structures were transferred from a nickel mold onto the plastic plates by the hot embossing... 

Fabrication of capillary electrophoresis microchip by UV-LIGA process... 

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. 

The fabrication of microelectromechanical systems (MEMS), e.g. actuators and sensors, is also one of the promising applications for nickel films. Nickel is currently electroplated into preform molds. One typical process is the LIGA process, where pure or alloyed nickel films are... 

As stated above, the development of the LIGA process began at the Research Center in Karlsruhe (FZK), Germany, in the 70s as a rather inexpensive method of producing very small slotted nozzles of any lateral shape for uranium-isotope separation by the nozzle process. Its usage is now wide spread globally as well as to a much... 

A combined fabrication technology made possible through a sacrificial layer technique was developed to obtain partly or totally movable microstmctures together with fixed structures on a single substrate. Many practitioners consider this ability to be the hall mark of the LIGA process. 

The substrate is first coated, for instance, via electroless or physical vapor deposition with a thin (< 1 pm) metallic layer, which in turn is patterned by photolithography and wet etching. This layer serves two roles, as a plating base and as an electrically conducting layer for the finished structures. In the subsequent step a sacrificial layer, of about 5 pm in tliickness, is deposited on the substrate and also patterned by photolithography and wet etching. Titanium is used most often as the sacrificial material because it adheres well to the resist and to the electrodeposited layer and can be etched with hydrofluoric acid that does not attack other materials such as chromium, silver, nickel, copper, and which are usually used in the LIGA process. 

The standard LIGA process is then followed polymerization of the thick X-ray resist directly on to the substrate, exposure to synchrotron radiation through a precisely adjusted mask, development of the resist, and electrodeposition. Some parts of the metallic microstructures are built up on the first metal layer, while other parts lie on top of the sacrificial layer. After stripping the resist, the sacrificial layer is etched selectively against all the other materials. 

The plastic molding process may be combined with deep etch X-ray lithography to fabricate microstructures with different shapes in the third dimension" In the first step, only the upper part of a very thick resist layer is patterned with the embossing technique using a mold insert fabricated by the standard LIGA process. The relief structure obtained by this first patterning process is subsequently exposed to synchrotron radiation through a precisely... 

Fig. 13.2 The LIGA process consists of first exposing a thick PMMA resist coUimated, synchrotron x-rays.

Fig. 13.3 A prototype scroll pump for a miniature GCMS system fabricated using the LIGA process, (a) 3 mm PMMA mold, (b) schematic of scroU pump, (c) electroformed scroll pump...

Fig. 2 X-ray absorption spectra calculated for the polymers PMMA and PTFE. PMMA is mainly used in deep x-ray lithography, namely the LIGA process, while PTFE is mainly used in SR direct photoetching, namely the TIEGA process...

Fig. 3 SEM picture of the high aspect ratio structure made of PMMA by the LIGA process. Typically, the structural height (depth) is 100-500 jizm and the feature size is 2-20 //m thus, the aspect ratio is between 5 and 100...

Fig. 4 Synchrotron radiation spectrum of AURORA-2S between 0.1 and 100 nm as well as the typical spectra used for x-ray lithography and the LIGA process...

The PMMA polymer is the best known resist, due to the fact that it has the best resolution down to at least 5 nm [23]. It has been used exclusively in the LIGA process since the thick resist layer of the order of a few 100 jum could be made readily [14]. Many previous studies, including those on the self-development phenomena [2, 3] and laser ablation [5, 10, 12, 17], have been carried out on this polymer. Therefore, there are relatively more data... 

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