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Atomic Layer Deposited Alumina for Micromachined Resonators. Y. J. Chang, K. Cobry, and V. M. Bright University 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. - PowerPoint PPT Presentation
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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
2
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
3
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)…
4
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
5
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
7
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
8
Al2O3 85nm
Cr 5nm
Fabrication ProcessFabrication Process
85nm
5nm
Figure 4 SEM image of ALD Al2O3 micro-resonators
9
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
10
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
11
Measurement (II): FrequencyMeasurement (II): FrequencyResonant frequency
EI
Lnfn
nEIWHLff o
oon 2
22
2
2
2)( ...,3,2,1 , )1(1
12
Experimental ResultsExperimental Results
• Theoretical and experimental data of resonance modes
13
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
14
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
18
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
20
Distributed LoadqPoint Load F
Types of Loads