Microstructure Testing – Quantifying the Mechanical Behavior of Microstructures

To optimize the performance and reliability of microstructures, it is crucial to have an accurate knowledge of their mechanical properties. Nanoindentation provides a standardized approach to measure the geometry independent material properties of small structures or thin films. Combined with an accurate measurement of the microstructure’s geometry, its overall mechanical behavior can be determined.

Directly measuring the microstructure’s mechanical behavior on the structure itself is an alternative approach. However, because of the large range of various structures types, shapes, and sizes, a highly versatile instrument is required to handle the requirements of these different structures.

Also, microstructures frequently play an active role in coatings, actuators, or sensors, for example. Examples for such active microstructures include dry adhesives, super-hydrophobic surfaces, electro-active polymer actuators, or micro-capsules. In order to have a quantitative understanding of these active microstructures, their behavior can often not be modeled accurately and should be quantified on microstructure level.

The FT-MTA03 Micromechanical Testing and Assembly System is the most versatile micromechanical testing system that enables a comprehensive analysis of the mechanical properties of microstructures. This article provides an insight into a selection of the testing principles and applications.

Nanoindentation for the Qualification of Young’s Modulus of Micromaterial

The FT-MTA03 can be used for the localized material testing of small volumes, and offers both force-controlled and position-controlled nanoindentation. The tiltable microscope enables visual observation of the sample in real time during the load application.

Nanoindentation into Soft Materials

The FT-MTA03 has a large displacement range and low-force sensing capabilities, making it a perfect tool for soft material characterization. Here, a spherical tip is used to indent the PDMS sample. In addition to the typical material parameters, the raw force- displacement-time data is offered for a variety of material models.

Mechanical Property Mapping of a Suspended Diamond Membrane

This work describes the testing of a nanocrystalline diamond and aluminum nitride membrane for application in tunable micro-optics. Both the stiffness and the topography of the membrane are determined. The upper right graph shows the topography of the micromembrane, while the lower right graph illustrates its stiffness distribution. The lower left graph is a cross-section of the stiffness map going via the central section of the membrane.

Dimensional Metrology of Microstructures

Advances in microtechnology help fabricate much smaller, high aspect ratio structures. This miniaturization leads to an increase in mechanical and dimensional imperfections. The FT- MTA03 can measure the mechanical properties and dimensions of microstructures in order to optimize fabrication methods. (Device courtesy: Prof. Ionescu, Nanolab, EPFL)

Micromechanical Testing Along Different Directions

During the micro-manufacturing process development, several process parameters have an impact on the mechanical properties of the MEMS structures. In this work, both the out-of-plane stiffness and in-plane stiffness of an array of MEMS flexures are analyzed using the FT-MTA03.

By defining a lower and an upper limit for the target stiffness, a chip map is generated to detect the working flexures (green) and flexures that are outside the preferred specifications (red). Flexures that have not been effectively discharged from the wafer (very high stiffness) or flexures with cracks (low stiffness) are detected. It is easy to compute the yield rate by the ratio of green to the total number of devices.

Electro-Mechanical Behavior of Active Materials

Conducting or conjugated polymers are drawing considerable interest as smart materials for the development of innovative microfabricated devices such as sensors and actuators. This application involves testing the time-response, actuation force, and deflection range of the beam-shaped electroactive polymer (EAP) actuator.

The beam-shaped microactuators are secured between two electrodes, enabling the microactutor to be driven by the application of the actuation signal. The top graph shows the EAP actuator beam tip’s maximum deflection versus the actuation voltage, whereas the lower graph illustrates the driving force produced by the EAP actuator and the plot of the square-wave driving signal versus time.

This information has been sourced, reviewed and adapted from materials provided by FemtoTools AG.

For more information on this source, please visit FemtoTools AG.

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