Assignment: Pressure sensor

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

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| 5. Assignment: Pressure sensor

The goal of this session is to illustrate how to make a circular membrane using the pn-junction etchstop and how this, combined with the piezoresistor designed in Assignment 1:Piezoresistor can be used as a pressure sensor.
Before starting
The fabrication of circular membranes is not possible using just anisotropic etching. Also, using anisotropic etching and non stop functionality, the thickness of the membrane will be giverned by timed etching, which for thin membrane does not provide a good control of the dimensions. We will therefore use the thin epitaxial layer to stop against.
A complete pressure sensor require more than a thin membrane. The assignment is therefore divided into several small assignments:

- A thin circular membrane with R=800 micron
- Positioning of the piezoresistors to maximize sensitivity
- Assembly of the Wheatstone bridge
- Improving the reproducibility of the pn-junction etchstop

The starting point of this exercise is the file from Assignment 3:Fluid flow through found under Suggested solution.

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Last updated: June. 2009 24.06.2009