MEMS Final Presentation - imechanica Final Presentation... · 2014-06-04 · MEMS DESIGN PROJECT GROUP D GROUP D Adam Hurst1 John Regis1 Chou Ying-Chi1 Andrew Lie2 Adrian Podpirka3

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MEMS Comb Drive Actuator to Vary Tension &Compression of a Resonating Nano-Doubly Clamped Beam

for High-Resolution & High Sensitivity Mass Detection

MECE E4212 FALL ‘05

MEMS DESIGN PROJECT

GROUP D

GROUP D

Adam Hurst1 John Regis1 Chou Ying-Chi1 Andrew Lie2

Adrian Podpirka3

1. Graduate Student in Mechanical Engineering, Columbia University2. Undergraduate in Mechanical Engineering, Columbia University3. Undergraduate in Material Science and Engineering, Columbia University

Today’s Presentation

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Theory & Design

Fabrication

Packaging

Overview


MEMS DESIGN PROJECT

GROUP D

Today’s presentation will cover the following:

• Application & Functionality• Types of Actuators• Theory behind selected Actuator• Thermal Time Constant• Fabrication• Packaging• Questions

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MEMS DESIGN PROJECT

GROUP D

NEMS Resonating Beam

• Applications- Hyper-sensitive mass detector (hydrogen sensor)- Anti bio-terrorism (organic compound sensor)- Mechanical signal processing- Parametric Amplification

• Functionality- NEMS Doubly-clamped Au/Pd beam (10 microns x 80nm x

100nm)- Resonant frequency shifts as a result of mass loading- Detection of frequency shift through magneto-motive technique- Frequency shift corresponds to loading or beam dimension

changes

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MEMS Device for Adjusting Tension of NEMS Resonators


MEMS DESIGN PROJECT

GROUP D

• Motivation- Residual tensile stresses in beam due to fabrication- Increased sensitivity under compressive loading- Desired loading +/- 200Mpa

• MEMS Actuators- Capacitance-driven electrostatic actuator

- Advantage: Easy fabrication

- Disadvantage: Non-linear relationship between input voltage and resultant force/displacement

- Magneto-motive actuator- Disadvantage: Semi-linear relationship between input voltage and resultant force/displacement

- Comb drive electrostatic actuator- Advantage: Linear relationship between input voltage andresultant force/displacement, simple fabrication

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MEMS DESIGN PROJECT

GROUP D

Proposed Comb Drive Design

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MEMS DESIGN PROJECT

GROUP D

Comb Drive Design

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MEMS DESIGN PROJECT

GROUP D

Theory & Design of Comb Drive Electrostatic Actuator

PdAuAF

P/

=

Resonating Beam Equations:

Required Force on beam is given by: (P = +/- 200MPa)

Beam axial deflection under +/- 200 MPa:

0/

LE

LPdAu

σ=Δ

F = 1.6 micro N

L = 25.6nm

PdAu

PdPdAuAuPdeAu AA

AEAEE

+

+=/

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MEMS DESIGN PROJECT

GROUP D


Comb Drive Equations:

Energy in charged parallel plates:

d

AVU r

20

21 εε

=

d

wVF rx

20εε=

Differentiating with respect to x (lateral direction):

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MEMS DESIGN PROJECT

GROUP D


Comb Drive Equations:

Side Instability Voltage:

VSI = 2fo bnd2ky

2 ky

kx + d2

yo2

- dyo

d n

Beams supporting suspended comb drive resonator structure:

3

34

L

bhEk ex =

(Assumed to be cantilever beams)

)3(6

)( 32

/

xLxIE

Fxv

PdeAu

−=xkF effx ⋅=

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MEMS DESIGN PROJECT

GROUP D


Critical Dimensions Based on Governing Equations:

Cantilevered Support Beams: 2 µm x 5 µm x 50 µm

Comb Drive (50 Fingers): 2 µm x 5 µm x 8 µm

VerticalDisplacement duegravity (into page):96.7pico-m

Side instabilityvoltage: 1320V

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MEMS DESIGN PROJECT

GROUP D


Voltage Input vs. Force:Voltage Input vs. Comb Drive Lateral Force

0.00E+00

2.00E-06

4.00E-06

6.00E-06

8.00E-06

1.00E-05

1.20E-05

1.40E-05

1.60E-05

0 20 40 60 80 100 120 140 160

Voltage (V)

Co

mb

Dri

ve L

ater

al F

orc

e (N

)

Force Dependence on Voltage 200MPa on Beam

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MEMS DESIGN PROJECT

GROUP D


Voltage Input vs. Lateral Displacement:Voltage vs. Lateral Displacement

0

5

10

15

20

25

30

35

40

0 20 40 60 80 100 120 140 160

Voltage (V)

Lat

eral

Dis

pla

cem

ent

(nm

)Lateral Displacement Dependence on Voltage Lateral Displacement at 200MPa

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MEMS DESIGN PROJECT

GROUP D

Theory & Design: Thermal Time Constant

Thermal Time Constant:

• Thermal time constant of an actuator is the measure of time required foractuator to cool to ambient temperature following actuation.

• Speed at which frequency of the beam can be tuned is highly dependanton time constant.

2t2u

- k dx2

22u= Cp

Q (x, t)• Heat Flow Equation:

• Applied DC Current: I = (Io)*(t); I2 = (Io)2*(t)Thus, Q(x,t) = ((Io)2*(t)*(R))/(h*w*L)

• Boundary conditions (1-D): u(0,t)=Tw; u(L,t)=Tw

Initial condition: u(x,0)=Tw

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MEMS DESIGN PROJECT

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Theory & Design: Thermal Time Constant

v (x, t) = an(t)zn(x)n=1

3

/

where zn(x) = sin( Lnrx

)

• New function: v(x,t)=u(x,t)-Tw

v(0,t)=Tw-Tw=0; v(L,t)=Tw-Tw=0;

v(x,0)=Tw-Tw=0

• New Heat Flow Equation:

• Eigen-function Expansion:

2t2v

- k dx2

22v= Q(x, t)

B.C. (1): v(0, t) = 0

B.C. (2):v(L, t) = 0

I.C.:v(x,0) = 0

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MEMS DESIGN PROJECT

GROUP D


dtdan + mn kan =

Qn2(x)dx

0

L

#

Q (x, t)zn(x)dx0

L

#/ qn(t)

where Q (x, t) = qn(t)zn(x)n=1

3

/

• Sturm-Liouville

• Eigenfunction Expansion<->Heat Flow equation Generalized Fourier Series forQ(x,t).

• Rules of orthogonally (to solve for Fourier coefficients):

• Orthogonally equation continuous. To make it integratable, usethe Integrating Factor:

e_nkt

Fourier Coefficient solved Longest time to reach steady state (n=1eigenmode) Thermal time constant = 0.169 micro-seconds

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MEMS DESIGN PROJECT

GROUP D

Fabrication

Mask #1: Au/Pd Contacts and Beam Mask #2: RIE Comb Drives

Close-Up View

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MEMS DESIGN PROJECT

GROUP D

Fabrication

Step DescriptionStarting Material SOI (5µm-1µm-125µm)Clean Standard RCA cleanPhoto Resist Spin on photoresistPhotolithographyMask #1 (contacts)develop Remove area for contact and beam placementclean Standard RCA cleanE-beam evap. Au/Pd e-beam evaporation to a depth of 80nmstrip Remove photoresistclean Stardard RCA cleanPhoto Resist Spin on photoresistPhotolithographyMask #2 (basic structure)develop Develop and remove used photoresistetch RIE to Silicon Dioxide surfacestrip Remove photoresistclean Standard RCA clean

Etch (optional)

Optional - if by using SEM we notice the the underside of the beam is not cut, we will purge the system with XeF2

clean Standard RCA cleanEtch 5:1 BOE etchDrying Supercritical CO2 dryingClean Standard RCA cleanContacts Place contacts. Wire bond to package.Test Test structureMount Pryrex mountTest Test structure

Process Flow

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MEMS DESIGN PROJECT

GROUP D

Proposed Comb Drive Design

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MEMS DESIGN PROJECT

GROUP D

Fabrication to Packaging

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MEMS DESIGN PROJECT

GROUP D

Packaging Solution

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MEMS DESIGN PROJECT

GROUP D

Packaging

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MEMS DESIGN PROJECT

GROUP D

Conclusion

• For this application, comb-drive actuator is superior to other mechanisms

• Design will allow accurate and feasible application

• Design will be relatively easy to fabricate using Columbia Universityresources

• Future Improvements: Feed back loop to determine distance traveled byblock structure

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MEMS DESIGN PROJECT

GROUP D

Acknowledgements & References

We would like to thank Prof. Wong, Prof. Hone, WeiXiaoding and Michael Mendalais for their guidance

References:

• Haber, Richard. Applied Partial Differences Equations. Prentice Hall. 2004

• Math World. Stephen Wolfram. March 10,2005. Wolfram Research, Inc<http://mathworld.wolfram.com>• G. Abadal. Eletromechanical model of a resonating nano-cantilever-based sensorfor high resolution and high sensitivity mass detection. Nanotechnology 12 (2001)100 – 104• Z.J. Davis. High mass and spatial resolution mass sensor based on nano-cantilever integrated with CMOS. Transducers ’01 Conference Technical Digest,pp72-75 (2001)• Senturia, Stephen D. Microsystem Design. Springer. 2001

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MEMS DESIGN PROJECT

GROUP D

Questions

QUESTIONS?

MEMS Final Presentation - imechanica Final Presentation... · 2014-06-04 · MEMS DESIGN PROJECT GROUP D GROUP D Adam Hurst1 John Regis1 Chou Ying-Chi1 Andrew Lie2 Adrian Podpirka3

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