Making a Capacitive Accelerometer EE 147247 A Fall

Outline • Simple SOI process – Etching – Design rules • Simple capacitive accelerometer

Simple SOI process • Start with 20 um thick SOI on 2 um Si.

Maximum distance between etch holes in a free plate?

Design Rules: example • • • minimum line/space: 2 um etch hole size: 2

Design Rules • Design rules are a contract between the manufacturer and the designer

Design rules, cont. • Note that this does not guarantee that a 2 um

ST 3 axis accelerometer LIS 44 AHL https: //memsblog. wordpress. com/2011/01/05/chipworks-2/

Possibly the ST LIS 331 EB? (probably not) Moving mass (with etch holes) Spring

MEMS racetrack and racecar Pham, Dao, Sugiyama, “A micro transportation system […] J. Micromech.

Slides: 21

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Making a Capacitive Accelerometer EE 147/247 A Fall 2016 Week 2, Lecture 1 K. Pister

Outline • Simple SOI process – Etching – Design rules • Simple capacitive accelerometer – Anchor, spring, mass, capacitor • Performance – Spring constant, mass, frequency response – Capacitance vs. acceleration

Simple SOI process • Start with 20 um thick SOI on 2 um Si. O 2 • spin, expose, develop, hardbake photoresist with mask STRUCT • DRIE (deep reactive ion etch) silicon etch (plasma) • strip photoresist • 5 minute etch in 49% HF (liquid) • rinse, dry

Minimum size for an anchor?

Maximum width of a free beam?

Maximum distance between etch holes in a free plate?

Design Rules: example • • • minimum line/space: 2 um etch hole size: 2 um square etch hole spacing: 6 um center-to-center minimum width, fixed beam: 20 um max width, free beam: 8 um

Design Rules • Design rules are a contract between the manufacturer and the designer • “obey these rules and we guarantee this level of performance” – free beams will be free – fixed beams will be fixed – 2 um lines (e. g. springs) will still be there – 2 um gaps (e. g. capacitors) will be cleared

Design rules, cont. • Note that this does not guarantee that a 2 um line will be 2 um wide when it is fabbed • Design rules are a good idea even when you are both the designer and the manufacturer (maybe “especially when”)

Simplest accelerometer

ST 3 axis accelerometer LIS 44 AHL https: //memsblog. wordpress. com/2011/01/05/chipworks-2/

Possibly the ST LIS 331 EB? (probably not) Moving mass (with etch holes) Spring Capacitor fingers? Anchor http: //www. pcbheaven. com/opendir/index. php? show=4109 sg 7239 pu 0 d 6729 c 0

MEMS racetrack and racecar Pham, Dao, Sugiyama, “A micro transportation system […] J. Micromech. Microeng. 2007 http: //iopscience. iop. org/article/10. 1088/0960 -1317/17/10/026/pdf

Spring, mass, damper, capacitor

Spring

Mass

Deflection under gravity

Capacitor