On-Chip MEMS Material Characterization

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NATO Advanced Study Institute RESPONSIVE SYSTEMS … / MEMS Course Brussels, September 10-19, 2001

Laboratoire de Mécanique Appliquée – UMR CNRS 6604 – Université de Franche Comté Institut des Microtechniques de Franche Comté

5.3 Applications of High- Driving Force Actuation Cells

on the Micrometer Scale

On-Chip MEMS Material Characterization

NATO Advanced Study Institute RESPONSIVE SYSTEMS … / MEMS CourseBrussels, September 10-19, 2001

Laboratoire de Mécanique Appliquée – UMR CNRS 6604 – Université de Franche Comté Institut des Microtechniques de Franche Comté

Investigation of Micro World using Microactuators

Macroscopic machines naturally scale with humans

“B ot to m -Up ” Ap pr oac h

Micrometer Size Actuation Cells

M acr os co pic M ach in es

“T op -D ow n” A pproa ch

Investigation of microand nano World Visible Effectsup to theHuman Scale

ArrayedElementaryActuators Conventional Machining Limits

M icr om ac hine s

Silicon Processing Technology Limits 10 0m

10–3 m

10–6 m

? !

Visible Effects up to the Human Scale

Investigation of Micro World

Standard Process (From CRONOS INTEGRATED MICROSYSTEMS)

Non-Stabilized Process

Various Textures of LPCVD Polysilicon Films

Industrial Development of IC-Compatible Polysilicon Surface Micromachining Technology Requires Tools to Expertise Process, Material & Structure Properties as a Function of Deposition Conditions

Design Rules Toward Self-Consistent Testing Method

- a) Small Area on the Chip

- b) IC-Compatible Actuation Electrostatics

- c) No Special Handling Electrostatic Probing - e) Ideal Boundary Conditions Monolithic Structure - d) Large elastic deflections Image Processing

Driving Force Capabilities on the Silicon Wafer Level !

IC-Compatible Polysilicon Surface Micromachining Hybridization of Polysilicon Samples and Macroscopic Test Machines

- Human Intervention - Incompatibility in Size

- Inappropriate Boundary Conditions - Parasitic Friction

- Misalignment Between Sample and External Grippers

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Fully Integrated On-Chip Laboratories for MEMS-Based Material & Structure Mechanical Analysis

4 Inches Wafer Integrating Micro Laboratories for Testing Mechanical Properties of Polysilicon Structures.

Doc. LMARC / web site: www.micromachines.univ-fcomte.fr (in Cooperation with EPFL-Lausanne) Micro Labs :

- Actuator Test Beds - Bending Test Units - Tensile Test Units According to the micrometer size of test structures, most of the wafer surface remains dedicated to the industrial application…

On-Chip Bending Strain Analysis of LPCVD PolySi Beams

Doc. LMARC / web site: www.micromachines.univ-fcomte.fr

Critical Bending Stress

~ 1700 MPa

Critical Bending Strain

~ 1%

On-Chip Bending Strength Measurement of LPCVD PolySi Beams

0 1000 1500 2000 2500

Contrainte à rupture (MPa)

Valeur moyenne : 1799MPa

longueur des poutres : 300µm longueur des poutres : 440µm Valeur moyenne :

1995MPa

500

Doc. LMARC / web site: www.micromachines.univ-fcomte.fr

On-Chip Bending Strength Measurement on PolySi Beam Arrays

Doc. LMARC / web site: www.micromachines.univ-fcomte.fr Bending Fracture Strength:

σ

fract

= 2500 MPa

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Bending Fracture of Arrayed Polysilicon Beams using Electrostatic Probing of Silicon-Based Actuators

web site: www.micromachines.univ-fcomte.fr

- Bending Fracture Strength: σ

fract

= 2500 Mpa - External Driving Torque: Γ

fract

> 10µNm

On-Chip Tensile Strength Measurement of LPCVD Polysilicon Films: First Generation Tensile Test Unit

Pro

Ver Actu Gr

PolysiSpec

0 0.2 0.4 0.6 0.8 1

700 1000 1300 1600 1900 2200 2500

Tensile Fracture(MPa) FractureProbabilityPf

Pf = 0.5

MPa mean 1735

f =

σ 0

500 1000 1500 2000 2500

n°1 n°2 n°3 n°4 n°5 n°6 n°7 n°8 n°9 n°10

Tensile Fracture (MPa)

a)

- Critical Tensile Stress : 1735 MPa

b)

- Critical Tensile Strain : 1 % - Test Duration : 5 s - Overall Test Unit Surface : 1.5 mm

²

Doc. LMARC / web site: www.micromachines.univ-fcomte.fr

Polysilicon Specimen

Vernier

Actuation Grid Probe

Integrated Tensile Test Units: Second Generation Prototype

Doc. LMARC / web site: www.micromachines.univ-fcomte.fr

Integrated Tensile Test Units: Second Generation Prototype

*

Hair’s Cross Section ~ 3000 µm²

Each actuation cell must develop up to 1500 µN In order to initiate fracture within the tensile specimen

- Tensile Specimen Nominal Length : 270µm - Critical Elongation : 4µm

- Critical Strain : 1.48%

- Tensile Fracture Strength : 2520 MPa - Overall Test Unit Surface : 0.075 mm

² Actuation Grid involving

6 Actuation Cells

Polysilicon Tensile Specimen:

Cross Section:2 x 1.5 µm

*

Fracture Elongation Reading Using

High Resolution CCD Camera