R.W. Tjerkstra

Micromachining of buried micro channels in silicon

A new method for the fabrication of micro structures for fluidic applications, such as channels, cavities, and connector holes in the bulk of silicon wafers, called buried channel technology (BCT), is presented in this paper. The micro structures are constructed by trench etching, coating of the sidewalls of the trench, removal of the coating at the bottom of the trench, and etching into the bulk of the silicon substrate. The structures can be sealed by deposition of a suitable layer that closes the trench. BCT is a process that can be used to fabricate complete micro channels in a single wafer with only one lithographic mask and processing on one side of the wafer, without the need for assembly and bonding. The process leaves a substrate surface with little topography, which easily allows further processing, such as the integration of electronic circuits or solid-state sensors. The essential features of the technology, as well as design rules and feasible process schemes, will be demonstrated on examples from the field of /spl mu/-fluidics.

Etching technology for microchannels

Various ways of fabricating channels in silicon are discussed. Some new channels are presented: the GPSICs and the LPCVD covered channels. Also some attention is paid to the problem of making connections of these channels to the outside world.

Etching technology for chromatography microchannels

Half-circular channels, to be used for gas chromatography, were etched isotropically using a mixture of HF, HNO3 and H2O. Two wafers with half-circular channels were bonded on top of each other to yield channels with a circular cross-section. During etching the so-called loading effect was encountered: the etch rate depends on the local structure density. To solve this, extra structures were placed around the channels to create an equal structure density over the wafer and so prevent irregularities in channel width. To eliminate the alignment problems that arise when bonding two wafers with isotropically etched channels together, a method which combines deep trench etching, passivation and isotropic etching was developed to construct channels under the surface of a wafer.

Technologies and Microstructures for (Bio)chemical Microsystems

There is a strong correlation between microreactors and microsystems for chemical and biochemical analysis. Microreactors need to be closely coupled to analysers, whereas in micro analysis systems a microreactor is often an important element. An example of a device that can be considered both as microreactor and as analyser, a catalytic gas sensor is presented. In particular the role of porous silicon material for fabrication and as support for the catalyst is shown. A modular concept for fabrication of micro analysis systems is illustrated with some components. A new capacitive pressure/flow sensor is presented with low power operation and a detection limit of 6 nl/s. Microchannels play an essential role in many micro analysis systems. Simulations made using the Flow3D programme based on the incompressible Navier-Stokes equations, give guidelines for the construction of the flow channel and positioning of sensors whereas the effects of the channel geometry on the profile of the injected plug can be predicted. Finally, a number of different techniques is presented to produce closed microchannels in silicon. Particular attention is paid to techniques that enable the fabrication of electrically insulating microchannels, which are of particular interest for capillary electrophoresis (CE) applications