PART 4 • POLYMUMPS FABRICATION

A process you can order

Not every engineer has their own cleanroom. Most don't — and PolyMUMPs is how they build MEMS anyway.

🏭 → 📦

PolyMUMPs is a real, commercially available MEMS fabrication process. You design a chip, submit it, and a foundry builds it for you alongside dozens of other customers' designs on the same wafer.

Key idea: Everything in this part is a real process you can actually order — not a hypothetical.

MULTI-USER FOUNDRIES

Sharing a wafer with strangers

MUMPs stands for Multi-User MEMS Processes.

It's a well-established commercial program, running since 1992, that gives engineers economical access to MEMS prototyping without requiring their own fabrication facility. Hundreds of complete runs have shipped since then.

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Think of it like a shared shipping container: you don't need to own the ship, you just need to buy space on the next voyage.

HOW IT WORKS

Buy a tile, get a chip

1. Reserve a tile Purchase a 1 cm × 1 cm die location on a scheduled run

2. Submit a design Following the foundry's process design rules

3. Wait 8 to 12 weeks for the run to complete

4. Receive chips 15 identical copies of your design

You don't need your own fab. You need a design that follows the rules.

THE MUMPS FAMILY

Four processes, one foundry model

PolyMUMPs

A three-layer polysilicon surface micromachining process. The most popular of the four.

SOIMUMPs

Built on a silicon-on-insulator wafer instead of deposited polysilicon layers.

PiezoMUMPs

Adds a piezoelectric material for sensing and actuation.

MetalMUMPs

Uses an electroplated metal structural layer instead of polysilicon.

PolyMUMPs is the one you'll learn in depth here — it's the most widely used, and the one most universities teach MEMS design with.

POLYMUMPS OVERVIEW

PolyMUMPs by the numbers

8 mask levels Photolithography steps in the process

7 physical layers Built from those 8 masks

3 polysilicon layers Poly0, Poly1, Poly2 — structural material

2 sacrificial layers PSG, removed at release

1 metal layer Probing, bonding, and mirrors

2 µm Minimum feature size

Eight masks is a small number of steps to memorize compared to the hundreds of individual fabrication operations they represent.

APPLICATIONS

What can you build with it?

🎤 📟 💧 🪞

Acoustics

MEMS microphones

Sensors

Accelerometers and other motion sensors

Micro-fluidics

Channels and valves for tiny fluid volumes

Display technology

Micromirrors and optical devices

WORKED EXAMPLE

An electrostatic micromotor

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Two classic PolyMUMPs demonstration devices are an electrostatically driven rotary motor and a MEMS micromirror.

Both are built from the exact same three-layer polysilicon process you're about to walk through, step by step.

We'll build this same kind of device, layer by layer, over the next several slides.

UNIT 13 STUDY COMPLETE

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Ready for the Fab Challenges?

You've covered Multi-User Foundries & the MUMPs Family.