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It’s the little things
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06/10/2006
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It is tempting, when thinking of microelectrical mechanical systems (MEMS) to only consider the moving elements that give these systems their novel properties. However, in design, the emphasis needs to be on the word ‘systems’.
The most effective MEMS devices are those that exploit the combination of micromachining with the analogue and digital signal processing – even on chip memory – possible with MEMS compatible processes.
The key to designing with MEMS, therefore, is integration. A tool that aims to satisfy the needs of MEMS needs also to support the different requirements of a potentially complex combination of micromachining and electronic circuit design. And it needs to support designers when those elements are brought together into the final chip assembly phase.
Any tool aimed at MEMS engineers needs features beyond those found in classic mixed signal ic design tools – and support for arbitrary shapes is uppermost.
For electronic devices, the almost universal use of rectilinear structures does not place restrictions on what it possible with them. In contrast, the use of micromachined structures for mechanical, optical or fluidic systems involves arbitrary geometries composed of arcs, curves, circles and other shapes.
A host of features differentiates MEMS layout tools from those of the ic field, due to the free form nature of the structures. Most ic based layout tools do not support the precision drawing of curves, which are needed for elements such as gear wheels. Using ic oriented tools, the user must create additional macros in order to define the flow channel accurately point by point using a coordinate data file. Editing these free form polygonic shapes accurately becomes tedious because most layout tools are grid based. What is really needed is the ability to snap to these curved geometries arbitrarily – a common feature in mechanical cad tools.
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Author
Paul Double
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