Bringing nanomechanical measurements into the real-world 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.

NanoTesting techniques Nanoindentation Nano-scratch testing Impact testing* Contact fatigue testing* Dynamic hardness testing* High temperature testing* * = Micro Materials techniques – Worldwide patents pending

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

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 CTE (10-6/oC) CVD Diamond 2.0 Beryllium Oxide 7.4 Aluminium Nitride 3.2 Silicon 3.0 Copper 16.8 Gold 14.3 testing at service temperature is necessary for optimisation …particularly where coating-substrate CTE mismatch is an issue…

Higher test temperatures 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

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)

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”

Hardness and modulus decrease with increasing Temperature on soda-lime glasses…

Applications Softening parameters Tg determination on ultra-thin films

High temperature nanoindentation testing Indentation to 50 mN on gold Applications include... temperature-dependent phase changes repeat indentations thermal cycling studies of creep processes loss and storage moduli Temp/0C H/GPa Er/GPa 25 0.84 86.3 200 0.59 74.1 400 0.38 68.8

Impact 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

Impact Impact testing - simulating fatigue wear and failure adhesion failure fracture

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

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 test probe piezoelectric or pendulum impulse sample oscillation film 1 film 2/subsrate Assess adhesion/delamination (e.g. between metal-dielectric) Investigate fracture behaviour

Contact fatigue testing of conductive ITO coatings 349 nm 423 nm more conductive ITO coating less conductive ITO coating the less conductive coating shows more brittle fracture larger change in depth

Pendulum impulse - DLC 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

Pendulum impulse - DLC 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

Pendulum impulse - DLC time to failure differentiate samples by... Test conditions for all samples:- 1 mN applied load 8 repeat impact tests of 30 min each (on different areas of the samples) time to failure type of failure differentiate samples by... Illustrative behaviour on sample deposited at 105 W RF power 105 W sample exhibited cohesive failure in only 12.5 % of tests

Pendulum impulse - DLC Illustrative behaviour on sample deposited at 115 W RF power 115 W sample exhibited cohesive failure in 37.5 % of tests

Pendulum impulse - DLC Illustrative behaviour on sample deposited at 125 W RF power 125 W sample exhibited cohesive failure in 62.5 % of tests

Calculation of energy required for failure Pendulum impulse - DLC 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

Summary Pendulum impulse - DLC (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?

Pendulum impulse - DLC Fatigue performance of these DLC much higher load necessary for failure Fatigue performance of these DLC coatings is worse than FS and Si! (DLC is in highly stressed state)

To summarise…. Bringing nanomechanical measurements into the real-world 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….

Current NanoTest application areas include… Automotive Bearings Biomedical Devices Ceramics Composites Contact Lenses Cutting Tools Hard Coatings Laminates Magnetic Disks Microelectronics Nanocomposites Optical Coatings 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?