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MICRO
MATERIALS
Bringing nanomechanical
measurements into the real-world
MEASURING NAN OTEC HNOL OGY
Recent Developments in Nanoscale
Mechanical Property Testing
High Temperature Testing and Impact Testing
Dr Krish Narain, Dr Ben Beake and Dr Jim Smith,
Micro Materials Ltd. Wrexham, UK.
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NanoTesting techniques
• Nanoindentation
• Nano-scratch testing
• Impact testing*
• Contact fatigue testing*
• Dynamic hardness testing*
• High temperature testing*
* = Micro Materials techniques – Worldwide patents pending
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Nanomechanical property testing at high temperatures
Horizontal loading configuration
has advantages for drift-free
high temperature tests
Hot stage specifications
• Indentation to 500 degrees Celsius
• Scratch testing to 500 degrees Celsius
• Thermal drift minimal
The NanoTest high temperature stage
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Why is high temperature testing important?
All materials exhibit
temperature-dependent
mechanical properties
…thermal and mechanical
cycling can lead to increased
residual stresses, particularly
where materials have dissimilar
thermal properties
Properties of Electronic Device
and Packaging Materials
Material
CVD Diamond
Beryllium Oxide
Aluminium Nitride
Silicon
Copper
Gold
CTE (10-6/oC)
2.0
7.4
3.2
3.0
16.8
14.3
• testing at service temperature is necessary for optimisation
…particularly where coating-substrate CTE mismatch is an issue…
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Higher test
temperatures
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High temperature nanoindentation testing of fused silica
Thermal drift measured at
90 % unloading.
Thermal drift would be shown
by discontinuities in unloading
curves at 90 % unloading…
…minimal thermal drift
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High temperature nanoindentation testing of fused silica
Thermal drift normally
very low – some small
drift at 300 deg. C shown
by the discontinuity at 90 %
unload
Usually thermal drift
at elevated temp is as low as
room temp (due to the
thermalisation time and the
horizontal configuration)
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Hardness and modulus results for fused silica
FS shows increasing
Modulus with temp…
…agrees with modulus
determinations by
beam-bending methods
FS is an “anomalous glass”
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Hardness and modulus
decrease with increasing
Temperature on
soda-lime glasses…
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Applications
• Softening parameters
• Tg determination on
ultra-thin films
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High temperature nanoindentation testing
Indentation to 50 mN on gold
Applications include...
• temperature-dependent
Temp/0C
25
200
400
H/GPa
0.84
0.59
0.38
Er/GPa
86.3
74.1
68.8
phase changes
• repeat indentations
• thermal cycling
• studies of creep processes
• loss and storage moduli
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Impact
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NanoTest impact module
for…
• Impact testing
• Contact fatigue testing
• Erosive wear testing
• Fracture toughness
• Adhesion testing
• Dynamic hardness
The only commercial nano-impact tester available
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Impact
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Impact testing - simulating fatigue wear and failure
• adhesion failure
• fracture
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Impact
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Impact Testing of a brittle TiN coating
100 mN applied load is
on throughout test
80 Hz oscillation frequency
Oscillation on 30 s after start
Oscillation off 30 s before end
Film failure after 250 s
• For bulk materials wear rates are determined from changes in probe depth
• For coatings, time-to-failure is related to the bonding strength to the substrate
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Contact fatigue testing
An accelerated test to mimic the mechanical fatigue cycles
which circuit boards and ME devices are subject to in service
Information obtained:
1/ time to failure (durability)
2/ type of failure
(adhesive/cohesive/mixed)
Applied
Load
piezoelectric or
pendulum
impulse
sample
oscillation
test probe
film 1
film 2/subsrate
• Assess adhesion/delamination (e.g. between metal-dielectric)
• Investigate fracture behaviour
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Contact fatigue testing of conductive ITO coatings
349 nm
more conductive ITO coating
423 nm
less conductive ITO coating
the less conductive coating shows
• more brittle fracture
• larger change in depth
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Pendulum impulse - DLC
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AIM: to use the pendulum
impulse technique to
determine the effect of
deposition power on impact
resistance of DLC coating on
Si wafers
...film thickness is
similar for all 3
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Pendulum impulse - DLC
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Operating principle...
Experimental variables include:
Static Force
Impact Angle
Acceleration distance
Impact Frequency
Test probe geometry
Advantage of the impulse technique:
The energy imparted to the sample
surface can be calculated at any
given time point, since the force is
known (static load applied throughout
the test), and the displacement is
also recorded.
• Quantification of adhesion energy
• Determination of total energy delivered to contact point
• Dynamic hardness measurement
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Pendulum impulse - DLC
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Test conditions for all samples:1 mN applied load
8 repeat impact tests of 30 min each
(on different areas of the samples)
differentiate samples by... • time to failure
• type of failure
Illustrative behaviour on sample deposited at 105 W RF power
105 W sample exhibited cohesive failure in only 12.5 % of tests
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Pendulum impulse - DLC
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Illustrative behaviour on sample deposited at 115 W RF power
115 W sample exhibited cohesive failure in 37.5 % of tests
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Pendulum impulse - DLC
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Illustrative behaviour on sample deposited at 125 W RF power
125 W sample exhibited cohesive failure in 62.5 % of tests
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Pendulum impulse - DLC
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Calculation of energy required for failure
(neglecting damping, rebound energy)
• Energy per impact = pendulum swing x Force
• Total energy = number of impacts x energy per impact
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Pendulum impulse - DLC
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Summary
(1) Impact-induced coating failure is a statistical process
(2) tests are sensitive to small changes in deposition conditions
Diamond-like carbon coatings deposited at higher power have...
• shorter time-to-failure
• lower energy-to-failure
• high probability of cohesive failure
• incomplete removal (final depth is lower than thickness)
How does the impact performance of DLC
compare to other brittle materials?
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Pendulum impulse - DLC
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much higher load
necessary for failure
Fatigue performance of these DLC
coatings is worse than FS and Si!
(DLC is in highly stressed state)
Bringing nanomechanical
measurements into the real-world
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To summarise….
1. Nanoindentation techniques are essential in the optimisation of the
mechanical properties of thin films and coatings
2. The NanoTest has large range of testing techniques, and therefore
offers a complete testing capability
3. These techniques are possible due to the unique pendulum design
4. The high temperature option and impact module allow testing under
contact conditions that can closely simulate those in service
5. The versatility and wide range of options have resulted in the system
finding applications in….
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Current NanoTest application areas include…
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Automotive
Bearings
Biomedical Devices
Ceramics
Composites
Contact Lenses
Cutting Tools
Hard Coatings
Laminates
Magnetic Disks
Microelectronics
Nanocomposites
Optical Coatings
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Optical Disks
Packaging Materials
Paints
Paper Coatings
Pharmaceuticals
Photographic Film
Polymers
Powders
Printing Plates
Semiconductors
Thin Film Adhesion
Turbine Blades
Ultra-thin films
...future application areas will be in?