Atomic Layer Deposited Atomic Layer Deposited Alumina for Micromachined Alumina for Micromachined

ResonatorsResonators

Y. J. Chang, K. Cobry, and V. M. BrightUniversity of Colorado, Department of Mechanical Engineering, Boulder, USA

Refer from: MEMS 2008, Tucson, AZ, USA

Team : Cheng-Yi Lin (林政毅 ) Yen-Po Lin (林諺伯 ) Date: November 11, 2008

OutlineOutlineAbstractIntroduction

Resonator Atomic Layer Deposition

FabricationMeasurement of Micor-resonators

Displacement Frequency

Conclusion

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AbstractAbstractAtomic layer deposited (ALD) aluminum

(Al2O3) as the material for micro-resonatorA pinned-pinned beam model with axial stress

of 250MPa is used Higher modes of the resonator were observed

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Introduction (I) : ResonatorIntroduction (I) : ResonatorDevice with a vibratory nature responseApplication : Sensors of pressure, mass, or

force with high resolution Material : Silicon, Aluminum nitride…Method : Chemical vapor deposition (CVD),

Atomic layer deposition (ALD)…

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Atomic Layer Deposition AluminaAtomic Layer Deposition Alumina

Used on structure with high ratio and irregular geometries

High quality Pinhole freeUniform Deposited at low temperature

Advantage

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Deposited MethodDeposited Method(A)(B)

1. Precursor is introduced into the viscous flow reactor 2. A precursor (trimethyl aluminum) is purged form the

chamber with nitrogen3. B precursor (water) reacts with all of the available

sites on the A layer that is introduced4. B precursor is purged from the chamber with nitrogen5. Again this step until the film is of the desired

thickness 6

• AB binary surface reaction sequence for ALD

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Coat 85 nm Al2O3 on SiliconDeposit 5 nm Cr by e-beam evaporationSpin coat PR AZP 4210Pattern and develop PR AZP 4210Etch Cr in CR-7(13s)Etch Al203 in 5 ％ HF (37s) Remove PR AZP 4210Release Al2O3 structure by isotropic silicon etch with SF6 plasma

Fabrication Process of ALD-Fabrication Process of ALD-based Resonatorbased Resonator

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Al2O3 85nm

Cr 5nm

Fabrication ProcessFabrication Process

85nm

5nm

Figure 4 SEM image of ALD Al2O3 micro-resonators

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550 um

Measurement (I): DisplacementMeasurement (I): DisplacementClamped-clamped model

Pinned-pinned model

Distributed transverse electrostatic force

WHN

LkkLkL

Nk o

oo

ostress

;

)2/sinh(1)2/cosh(22

4C-

12 ;

4

3

3

235

p-WHI

LNLEIkstress

]))((

[21F 2

alumina

alumina2

zZHAV

o

oe

EWH12N , 3 oo kWHN

H

ZoZ

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Experimental ResultsExperimental Results

• Theoretical and experimental results of displacement vs. voltage of ALD Al2O3 micro-resonator

• Measured and theoretical calculated profiles of the micro-resonator with different applied voltages

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Measurement (II): FrequencyMeasurement (II): FrequencyResonant frequency

EI

Lnfn

nEIWHLff o

oon 2

22

2

2

2)( ...,3,2,1 , )1(1

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Experimental ResultsExperimental Results

• Theoretical and experimental data of resonance modes

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ConclusionConclusionMicromachined ALD Al2O3 resonators had

been demonstrated High quality thin film Nano-scale resonator

Displacement and resonant frequencies have been calculated by pinned-pinned beam model

Axial stress in the resonators of 250MPa is determined by fitting the experiment data

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ReferenceReference [1] G. Stemme, “Resonant silicon sensors”, J. Micromech.Microeng., vol. 1, pp.113-125, 1991. [2] A.N. Cleland, M. Pophristic, and I. Ferguson, “Single-crystal aluminum nitride nanomechanical

resonators”, Appl. Phys. Lett., vol. 79, pp.2070-2072 2001. [3] N. D. Hoivik, J.W. Elam, R.J. Linderman, V.M. Bright,S.M. George, and Y.C. Lee, “Atomic layer

deposited protective coatings for micro-electromechanical systems”, Sensors and Actuators A, vol. 103, pp. 100-108

2003. [4] M. K. Tripp, C. Stampfer, D.C. Miller, T. Helbling, C.F. Herrmann, C. Hierold, K. Gall, S.M.

George, and V.M. Bright, “The mechanical properties of atomic layer deposited alumina for use in micro- and nano-electromechanical systems”, Sensors and Actuators A, vol.130-131, pp. 419-429, 2006.

[5] M. K. Tripp, C.F. Herrmann, S.M. George, and V.M. Bright, “Ultra-thin multilayer nanomembranes for short wavelength deformable optics”, in Proc. of MEMS’04, Maastricht, The Netherlands, Jan. 25-29, 2004, pp. 77-80.

[6] B. Hälg, “On a nonvolatile memory cell based on micro-electro-mechanics”, in Proc. of MEMS’90, Napa Valley, California, Feb. 11-14, 1990, pp.172-176.

[7] S. D. Senturia, Microsystem Design, Kluwer Academic Publishers, Massachusetts, USA, 2001. [8] R. D. Blevins, Formulas for Natural Frequency and Mode Shape, Van Nostrand Reinhold Co.,

New York, USA, 1979. 39015

Comparison of ALD and CVDComparison of ALD and CVD

ALD Highly reactive precursors Precursors react separately

on the substrate Precursors must not

decompose at process temperature

Uniformity ensured by the saturation mechanism

Thickness control by counting the number of reaction cycles

Surplus precursor dosing acceptable

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CVD Less reactive precursors Precursors react at the same

time on the substrate Precursors can decompose at

process temperature Uniformity requires uniform

flux of reactant and temperature

Thickness control by precise process control and monitoring

Precursor dosing important

WHo WHo

Po

)(Wq

; , 22

2

2

o dxdWHP

HPWHWP

oo

oooo

• Need to compensate the bending when stress is present

oqq 4

4

dxdEI

0;dxd(4) 0;

dxd(3)

;0)((2) ;0)0((1) ..

L0

L

CB

• The form of the polynomial

432 FxDxCx

Types of Support

Fixed Free

Pinned Pinned on Rollers

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Distributed LoadqPoint Load F

Types of Loads