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Investigation of the Aging of Micromachined Silicon Actuators

Alex Dommann

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PREFACE

The technological advances of microsystemengineering in the past decade have been truly impressive in both pace of development and number of new applications. Microsystem engineering involves the design, manufacture, and packaging of microelectromechanical systems (MEMS) and peripherals. Applications of Microsystems in the aerospace, automotive, biotechnology, consumer products, defense, environmental protection and safety, healthcare, pharmaceutieal , and telecommunications industries prompted many experts to account for a $82 billion in revenue for the Microsystems and related products in the year 2000.

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The strong demand for MEMS and Microsystems by a rapidly growing market has generated strong interestin quality control and failure analysis.

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X-Ray Diffraction

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Bragg-Equation

Hook Law : σ = ε σ = ε E

d =λ

2 sin ϑ∆d =

λ2

− cosϑsin2 ϑ

∆ϑ

σ = FA

ε:=∆dd

=> ε =−1

tan ϑ

∆ϑ

2 dsin ϑ = nλ

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Diffraction geometries

§ B r a g g r e f l e c t i o n f i x e d ( ω, 2θ ) s a m p l e o r i e n t a t i o n f i x e d ( χ,φ )

§ s a m p l e o r i e n t a t i o n c h a n g e d (χ,φ ) B r a g g p e a k s c a n n e d ( ω, 2θ )

X - r a y s o u r c e

2θd e t e c t o r

s a m p l eX

f o c u s i n gm o n o c h r o m a t o r ω = θ

χ

φ

ω

2θ

d e t e c t o r

X

p r i m a r y b e a m

m o n o c h r o m a t o r

s a m p l e

d i f f r a c t e db e a m a n a l y z e r

X - r a y s o u r c e χ

φ

m i r r o r

texture d i f f ractometry h i g h-r e so lu t ion d i f f r a c tomet ry

- o r i e n t a t i o n a n a l y s i s - - m e t r i c d e t e r m i n a t i o n -

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Exploring the strain situation with thin films

(assuming a cubic metric)

substrate

d⊥ film

d⊥substrate

d⊥ film = d= film

d⊥substrate = d= substrate

d⊥ film,strained ≠ d= film,strained

d⊥substrate ≈ d= substrate

d=film = d=substrate

φstrained

completely unstrained ⇔ pseudomorphically strained

φunstrained

film

φstrained ≠ φunstrained

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Typically a strong argument to usemonocrystalline material and especially silicon is its potential resistance against aging. Aging of a crystal can be documented as a change of the strain and by simulation the strain profile. High Resolution X-ray Diffraction(HRXRD), X-ray standing wave method (XSW) and reciprocal space mapping (RSM) in addition permits to characterize the amount of crystalline defects introduced by cycling and by manufacturing MEMS devices.

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The starting point for our investigations was the observed fact of a hysteresis of the bimorphousactuator, designed as optical deflection system for ophtalmological applications. The beam deflection angle of the bimorphous beam was measured as a function of the input power. Cycling the activation ended in a shift of the zero point. Repeating the process ended in a shift in the same direction, but to a lower amount. While applying no power during one hour, the zero shifted backwards towards the old origin. Thus some relaxation has taken place. With a maximum input power of less than 100 mW no such hysteresis effects were observed.

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SEM photograph of the chip with different bimorphous actuators. The HRXRD measurements were executed on the middle plate of the fourfold symmetrical structure in the middle of the photograph.

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Comparison of the symmetric X-ray rocking curves of the (004) reflection from a (001) cut Si wafer before and after oxidation

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Symmetric x-ray rocking curves of the (004) reflection from a (001) cut Si chip with a bimorphous actuator.

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Symmetric x-ray rocking curves of the (004) reflection from a (001) cut Si wafer. The measurements were executed on the same structure after one week of operation.

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Symmetric x-ray rocking curves of the (004) reflection from a (001) cut Si wafer. The measurements were done on the same structure after removing thealuminium.

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BEHAVIOUR OF A SILICON SPRING FABRICATED BY WIRE ELECTRO DISCHARGE MACHINING.

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alignmenthole

for ASIC-integration

Pyrex Hard Metal,Si

Pyrex SiO 2, Si(P++)

mech.+ electr.coating,

transv. guideelectrodes,el. contacts

bondingand distance

layer mech. contact,spring,

inner electrode

Hard Metal,Si

dopetarea

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Solid line: symmetricx-ray rocking curves of the (004) reflection from a (001) cut Si chip. Dashed line: symmetric x-ray rocking curves of the (004) reflectionfor this chip afterWEDM.

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Symmetric X-ray rocking curves of the (004) reflection from a (001) cut Si wafer. The measurements were executed on the same structure after 3 million of cycles.

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Life Time

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Wave Guide for Intersatellite LinkI µ S

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Werkstückträger

Flexprint

Elektronikbereich

32mm

42mm 10mm

15m

m2m

m

10m

m

10mm

”Gehäuse" herzustellen mitdem Stereolitographieprozess

Packaging

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Symmetric x-ray rocking curves of the (004) reflection from a (001) Si chip after production (x), after molding (+) and encapsulated with a new polymer (^) .

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Structural quality

IµSIµSInstitut für Mikrosystemtechnik

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Acknowledgements

Dr. Reto Holzner, Dr. Peter Müller, Contraves -Space

August Enzler, Dr. Markus Michler, Dr. Matthias Kummer, NTB-I µµ S

Dr.Enver Mukhamedzhanov, Shubnikov Institute

Financial Support: CTI