CMOS

What does CMOS mean?

CMOS stands for Complementary Metal-Oxide-Semiconductor.

CMOS fabrication creates electronic devices through repeated processing of many patterned layers.

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Complex microdevices are usually not made in one operation. They are built through many sequential fabrication steps.

CMOS PROCESSING

The fabrication toolbox

CMOS processing can involve many layers and repeated combinations of several core processes.

Oxidation

Form an oxide layer.

Photolithography

Define patterns.

Etching

Remove selected material.

CVD

Deposit thin films.

Diffusion

Introduce dopants.

Ion Implantation

Introduce dopants.

Evaporation

Deposit material.

Sputtering

Deposit material.

MEMS MATERIALS

Why silicon?

Silicon became an important MEMS material because it combines useful electrical properties with strong mechanical properties and an established fabrication infrastructure.

Electrical

Excellent electrical characteristics and convenient integration with electronics.

Mechanical

High elasticity, high yield strength, low density, and good hardness.

Manufacturing

Well-established microelectronics fabrication methods already exist.

Micromachining

Silicon can be patterned and etched into mechanical structures.

Silicon can serve as both an electronic material and a mechanical material.

MEMS MATERIALS

Silicon by the numbers

Silicon isn't just convenient to fabricate — its mechanical properties rival traditional engineering materials.

Elastic modulus 130–190 GPa (steel ≈ 200 GPa)

Yield strength ≈7 GPa, higher than steel

Density Low, compared to metals

Hardness Comparable to quartz

Crystal structure Single-crystal, diamond cubic lattice

Because single-crystal silicon has no grain boundaries, it deforms almost perfectly elastically, with no hysteresis, and can support resonating structures with a very high quality factor (Q).

Key idea: Silicon combines near-ideal elastic behavior with strength and stiffness on par with steel, at a fraction of the density.

UNIT 8 STUDY COMPLETE

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Ready for the Fab Challenges?

You've covered CMOS & Silicon as a MEMS Material.