PART 3 • MICROFABRICATION TECHNOLOGY

From ICs to MEMS

Modern MEMS fabrication grew from many of the same technologies used to manufacture integrated circuits.

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Integrated circuits are fabricated by repeatedly adding, modifying, patterning, and removing materials on a silicon wafer.

MEMS uses many of those same fabrication techniques, but extends them to create mechanical structures as well as electronics.

Key idea: MEMS builds on semiconductor manufacturing, but uses those tools to create mechanical structures too.

SILICON WAFERS

Start with the substrate.

Silicon used in microfabrication begins as a large single crystal.

Thin wafers are cut from the crystal and become the substrate on which devices are fabricated.

Raw silicon Starting material

Single crystal Crystal growth

Silicon wafer Device substrate

The wafer is not just a holder. In many MEMS devices, the silicon itself becomes part of the mechanical structure.

SEMICONDUCTORS

Silicon is a semiconductor whose electrical behavior can be deliberately modified.

Si

By introducing selected impurity atoms into silicon, engineers can change the concentration and type of charge carriers available in the material.

This controlled introduction of impurities is called doping.

DOPING

Group III dopants such as boron increase the concentration of positive charge carriers called holes.

Majority carrier: holes

Group V dopants such as phosphorus increase the concentration of mobile electrons.

Majority carrier: electrons

P-type → holes

N-type → electrons

UNIT 7 STUDY COMPLETE

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You've covered From ICs to MEMS & Semiconductors.