Step by step

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

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| 6.1 Step by step

We break this assignment into smaller subassignments to make it simpler to follow:

- Make a thin membrane with edges defined by the deep n-well. This is equivalent to what was done in Step by step: Thin circular membrane . Layers needed are NOWEL and BETCH.
- Design of the Venturi channel

Getting started

- Open the cell 'THROUGH_HOLE_AND_CHANNEL'
- Only Cell Assist layer provided

Thin membrane

- We are to make a thin membrane that will enable us to make a 1000 micron wide opening through to the other side.
- The dimensions of the resulting [BETCH] mask should be 1200 microns x 800 microns.
- Position the [BETCH] mask centered over the origin of the cell.
- Use the bulk etch calculator to find the dimensions for BETCH.
- Add a NOWEL mask that will allow a channel of at least 1000 microns width and that will give the best control over channel length.

The deep n-well has a soft transition region stemming from diffusion. As illustrated to the right, it means that the recess etch will punch through at different locations depending on the etched depth (10 μm ±4μm.). Please see the MultiMEMS design handbook for exact details on the soft transition region.
It might be tempting to use the anisotopic etch and terminate directly against the thin membrane, but if you use the bulk etch calculator and look at the different data available, you will find that the variation in the dimensions from the backside etching, vary more than what a solution using NOWEL and RETCH will.

Venturi channel

- The Venturi channel is simply a front side DRIE etch with a nominal depth of 10 μm ±4μm.
- The effectiv length of the Venturi channel is the region of constant height.
- It is therefore important to make room for fluid ports to the channel at both ends(See illustration below).

Challenge | Improve the electrical contact to the region under the thin membrane. |

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Last updated: June. 2009 24.06.2009