Step by step: Thin circular membrane

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Hands-on design training for MultiMEMS
D. Lapadatu and P. Ohlckers

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| 5.1 Step by step: Thin circular membrane

Open cell '6X6B_MEMBRANE' in file from or your own file saved in Assignment 3:Fluid flow through, alternatively open it from the file available under Support material, Files, Layout with emptied cells |
Add a NOWEL circle of Ø=1600 micron in the centre. If you use LayoutEditor, please see 'How to draw circles in LayoutEditor' |

Calculate and draw a BETCH mask that embeds the NOWEL circle

- To fit a circle of Ø=1600 micron, we need a square with sides of 1700.
- Add a 1700 micron X 1700 micron rectangle on the [BETCH] help mask layer.
- Use the membranes sheet on the bulk etch calculator to find the required dimensions for BETCH

Add a rectangle with a hole in it surrounding the NOWEL circle on the NOBOA layer

In regions with NOBOA, the surface oxide will kept. Oxide on the membrane will cause it to bend due to the internal stress of the oxide.The internal stress of the oxide is due to mismatch in the coefficient of thermal expansion between silicon and silicon dioxide. Below is an image of the buckling of a silicon dioxide membrane left after all the silicon under it has been etched away.
If oxide is present on top of a thin membrane, the membrane will be bent, offsetting the sensor output.

Your design should now look like this |

Save the file. Sub assignment finished

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STIMESI training on MULTIMEMS |
Last updated: June. 2009 24.06.2009