Silicate bonding on silicon and silica

S. Reid, J. Hough, I. Martin, P. Murray, S. Rowan,J. Scott, M.v. Veggel

University of Glasgow

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Introduction: Current applications

Originally developed for NASA’s Gravity Probe B mission, launched April 2004. (Gwo et al., patent)

GEO600 currently operates with quasi-monolithic fused silica suspensions and mirrors. This technology allows improved thermal noise in the suspension systems.

Construction of the ultra-rigid, ultra-stable optical benches for the LISA Pathfinder mission.

Picture of a GEO600 sized silica test mass in Glasgow with silica

ears jointed using hydroxy-catalysis bonding

Silica fibres are welded to the ears in the completion of the lower-

stage of the GEO600 mirror suspension.

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Introduction: Planned applications

The upgrades for Advanced LIGO plan to incorporate the GEO600 technology for significantly improved thermal noise performance – and under consideration for Advanced VIRGO (in addition to other improvements, e.g higher power lasers).

Construction of the ultra-rigid, ultra-stable optical benches for LISA.

Design sensitivity curves for the LIGO and AdvLIGO detectors.

10-21

10-22

10-23

10-24

h

Wire looparm length: 4 km

Quadruple stagesilica ribbons/fibres

eg. LIGO AdvLIGO

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Introduction: Future applications (silicon)

The construction of a 3rd generation gravitational wave observatory within Europe E.T. (Einstein Telescope) and under consideration for the construction of the DUAL resonant mass detector.

Credit: M.Punturo

LIGO 2005 Bars 2005

Advanced LIGO/Virgo (2014)

Virgo Design

GEO-HF

2009

Virgo+ 2008

Einstein GW Telescope

DUAL Mo(Quantum Limit)

M. Punturo et al.

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Studies on silicate bonding of silica in relationto the Advanced generation of GW detectors

Settling time investigate details of the underlying chemistry e.g. Through the Arrenhius

equation time available for bond adjustment and alignment

Bond structural properties Close inspection of bonds through electron microsopy can reveal properties

such as: bond thickness, molecular structures in addition to imperfections/inhomogeneities at the microscopy-scale.

Bond mechanical properties Mechanical strength (studying the factors responsible for strength and

reliability)

Mechanical loss in addition to bond thickness will allow the level of mechanical dissipation associated with the bond layer to be calculated – thus allowing precise modelling of the level of thermal noise expected from silicate bonds in future gravitational wave detectors.

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Studies on silicate bonding of silica in relationto the Advanced generation of GW detectors

Bond mechanicalproperties

Bond structuralproperties

Settling time

experiments

S. Reid et al.,PLA 363 341-345 (2006)

Activation energy:Ea = 0.545 eV permolecule of OH−

Above plot showing settling time as a function of

temperature for silica-silica bonds

Above plot showing two bonded silica cylinders, studied before and after

silicate bonding.

Experiments suggest that the level of loss associated with

silicate bonding may lie:bond ~ (0.3→1.2)×10-1

(across the differentmeasured modes).

SEM SEM

TEM

TEM

AFM

(81±4) nm

7.9 GPa

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Required studies on silicate bondingof silicon in relation to future detectors

Settling time

Bond structural properties

Bond mechanical properties

Surface preparation (oxidisation techniques)

Thermomechanical properties

Temperature cycling effects/failures

In addition to characterising these properties in relation to silicon-silicon bonds,

it is also necessary to understand the required surface preparation and the cooling performance available for bonded silicon components.

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Wealth of literature on oxidation techniques

For example: Deal, B.E., Grove, A.S. General relationship for the thermal oxidation of silicon. Journal of Applied Physics, vol. 36, no. 12, pp. 3770 – 3778, 1965 Found quantitative relations of the rate of growth of thermal

oxide

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Relevant literature knowledge

Qualitative statements B.E. Deal, A.S. Grove Wet oxidised surfaces give a less dense silicon oxide then dry

oxidised surfaces – possibility of having an effect on bond strength and thermal noise.

Carrier gas for wet oxidation doesn’t make a difference in oxidation speed (nitrogen or oxygen). Thus undissociated H2O is the oxidising agent.

In dry oxidation molecular oxygen is oxidising agent. Flow speed in wet oxidation doesn’t influence speed of

oxidation. Higher oxidation temperature gives higher density.

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Visable appearance of thermal oxides on silicon

Color of oxide as a function of thickness Note, this is also dependent on viewing angle.

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Oxidation results (oxide colors) in Glasgow

Shown layer thicknesses are expected layer thicknesses

Colours don’t match with corresponding layer thicknesses on graph in previous slide

Colours don’t match between wet and dry oxidation of the same prospected thickness

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PV flatness change as a function of oxidation regime

-50

0

50

100

150

200

250

300

350

oxidation regime

PV

fla

tnes

s ch

ang

e [n

m]

Delta PV flatnessgood side

Delta PV flatnessbad side

Oxidation results (change in flatness)

50 nmwet1000C

100 nmwet1000C

200 nmwet1000C

100 nmdry920C

50 nmdry1000C

100 nmdry1000C

200 nmdry1000C

Localised dip in surface

Spikes on edge of surface

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Oxidation results (change in flatness)

0

50

100

150

200

250

300

Batch no. 1

PV fl

atne

ss [

nm]

Before oxidisationAfter oxidisation

Batch no. 2

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Bond thickness

Comparison of silica-silicon SEM images

40 nm

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Thermal conductivity of silicate bondsin collaboration with Firenze

The first set of silicate bonded silicon-silicon have been fabricated with varying volumes of 1:6 sodium silicate solution at Glasgow.

Samples sent to Florence for thermal conductivity measurements.

Volumes of bonding solution: 0.4 ml cm-2, 0.2 ml cm-2 and0.1 ml cm-2. (Advanced LIGO specification)

See following talk by Enrico Campagna.

diameter = 25.4 mm 12.7 mm

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Mechanical strength of bonds

Initial tests showed that a pair of silicate bonded 1” silicon disks supported 40Kg for 2 week (~1 MPa).

40Kg load suspended Si-Si sample under load

40Kg

clamped sample wire loop

rubber ring

lightlyclamped

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Test setups for mechanical strengthtesting of silicon-silicon

New strength testing setups have been designed and ready for use.(M. v. Veggel)

pure shearstrength test

Four-point bending test (peeling test)

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The ability of silicate bonds to withstand repeated temperature cycles must be verified, in addition to withstanding the thermal stresses that may be induced during cooling.

Repeated cycles from room temperature to 77K were performed on bonded samples of silicon with no bond failures (in addition to this various samples of different materials including SiO2-ZnSe, SiO2-Ge, SiO2-ULE, SiO2

‐Al2O3, all of whom have different coeff. of thermal expansion)

Temperature cycling

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Conclusion

Silicate bonding appears to be a highly promising technique for the construction of cryogenic and ultra-low loss monolithic suspensions

Current estimates suggest that the thermal noise associated with silicate bonding will have a negligible contribution to the overall thermal noise in Advanced LIGO and likewise Advanced VIRGO.

Future work: extend the studies of bond thermal noise