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MICRO FLUIDICS | ARTICLE


<< Figure 3: Scribing at Micronit Microfluidics. >>


density and high aspect ratio structures in glass (fused silica) and silicon substrates. This technique makes etching with steep side walls (anisotropic etching) as well as with rounded walls (isotropic etching) in substrates possible, with depths varying between 1 µm cavities and complete wafer-through holes.


Bonding Different techniques are also used for bonding. The most common technique is bonding at high temperature. Direct aligned bonding is done at high temperature, which makes the bond very strong (high-pressure resistant up to 150 bar / 2175 psi for certain structures). In the basic chip manufacturing process, a glass layer with holes is bonded to another glass layer with channels. For more complex devices, multi-stack bonding is required. This is also suitable when a large internal volume is required. Devices can then be stacked in order to raise the internal volume.


The other technique, low temperature bonding is gaining interest from the micro fluidics field. By using this technique it is possible to process electrical and biochemical components on the devices the functionalities of which would normally be altered or destroyed by using high temperature bonding. Bonding can be offered direct glass to glass and glass to silicon (without an intermediate layer).


<< Figure 4: Micronit substrate. >>


Electrode Integration Electrodes can be integrated into the micro fluidic devices, e.g. inside channels and reservoirs for detecting and sensing capabilities. Common used electrode materials include Pt, Au, Cu, and ITO (Indium Tin Oxide). Depending on the electrode material sputtering, evaporation or plating is used. The electrodes inside fluidic channels are used for example for electrical impedance spectrometry, contact or contactless conductivity detection, amperometric detection, electrical heating and temperature sensing. Electrodes inside fluidic compartments are mainly used to apply high voltages to generate electroosmotic flow or to perform electrophoresis. Electrodes can be integrated in between two glass or silicon layers or placed on top of the chip. Also thin insulating layers between electrodes and fluidic channels can be applied.


32 | commercial micro manufacturing international Vol 7 No.3


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