The development of microelectromechanical systems (MEMS) has focused, in recent years, more on the manufacturing process than on issues related to reliability and the relationship with mechanical properties.

Many issues related to tribology, mechanics, surface chemistry, and materials science must be considered in the operation and fabrication of many MEMS devices. Currently, very few analytical tools are available for the accurate characterization of localized properties and specific areas of interest.

Instrumented indentation techniques provide a very powerful method for measuring the load and depth response of bulk and coated materials, but they can also be used to measure the mechanical properties of very small micromachined silicon structures. Beam structures, such as those used for accelerometers, are a good example, as they must be characterized in terms of the number of cycles to failure, the spring constant, or the energy required to bend the beam by a required amount. These localized tests must be adapted to work at various distances from the beam origin with good positioning accuracy.

The indentation method for evaluating mechanical properties at low loads and shallow depths is already well established for the characterization of thin films and bulk materials. The depth-sensing indentation method produces a load-displacement curve from which quantitative property values can be calculated using a variety of approaches. In addition, the indenter (of defined geometry) can be precisely controlled in terms of application load, depth and speed. As long as the indenter can be precisely positioned at a site of interest, the technique can be used to test the local mechanical properties of different structures, either with unique or more complicated loading cycles.

A wide range of electrical applications are possible with the Alemnis Standard Set (ASA), ranging from electrical contact resistance measurements during material deformation to electrochemical studies using the Liquid Cell (LIC).

Liquid Cell (LIC) can be used for a wide range of experiments where the sample must be immersed in liquid. Therefore, it is normally used ex situ with the Alemnis Standard Assembly (ASA) mounted vertically and the LIC mounted on the load cell. Some examples of how the LIC can be used are:

Immersing biomaterials in saline or body-mimicking fluid (BMF) to assess their mechanical properties when hydrated. Electrochemical tests where the indenter can be used as a current probe and the electrolyte (liquid) can be activated using an external potentiostat for corrosion studies or passivation.Studies of the mesoporous effects of the hydrogel, that is, how the mechanical properties change depending on the level of hydration.Tribological studies of interaction between the indenter and the sample when immersed in lubricant (liquid oil or grease), including experiments of tribocorrosion.

An example of a typical LIC application is the study of thin passive layers that can have significant effects on the recrystallization of nanograins in tribological contacts. The LIC is optimized to allow a metallic sample to be indented under various electrochemical conditions by applying passive or cathodic potentials in a suitable solution (for example, pH 8.5 borate solution, made from an aqueous mixture of boric acid and sodium hydroxide ). The liquid cell is converted to an electrochemical cell as shown. The sample is sandwiched between two polymer components with screws and a rubber O-ring provides a tight seal while ensuring reliable electrical contact between the sample and the working electrode.

Therefore, the design allows for reuse between samples, variation in sample geometry, and lateral movement of the indenter tip. The LIC is designed to hold approximately 1 mL of electrolyte solution.

The working electrode is made of stainless steel, 5 mm thick and 20 mm in diameter, to which a wire is welded. Four (M2) screws hold the top and bottom polymer components together. The rubber O-ring has an outer diameter of 12 mm and an inner diameter of 10 mm, thus defining the area of the sample in contact with the electrolytic solution.

The entire cell is attached to the ASA with a single screw at the base. thus defining the area of the sample in contact with the electrolytic solution.

The Alemnis Standard Assembly (ASA) has been used for a large number of studies on coatings in various forms. These can be standard coatings deposited on reference substrates, coated 3D structures manufactured by additive manufacturing, coatings used in microelectronics and MEMS, or multilayer micropillars produced by focused ion beam milling (FIM) or selective lithography processes.

Modern hard coatings, especially those used in the cutting tool industry, have become so hard in some cases that conventional nanoindentation may not be the most appropriate method to test their mechanical properties such as hardness and elastic modulus. This is due to the fact that the hardness of the coating (for example, diamond-like carbon layers with a hardness of 30-40 GPa) is not much less than that of the diamond indenter itself (̴ 70 – 120 GPa). Also, many coating companies now want to know the properties of their thin films at service temperatures, which can be on the order of 500 to 900°C. At such high temperatures, the hardness of the diamond indenter will be significantly reduced and therefore dramatically deformed, rendering point area function calibration useless for calculating mechanical properties.

ASA in situ scratch testing is also used to investigate failure mechanisms in coatings. In the scratch test, a diamond stylus is passed through the sample under a constant or progressively increasing load. Elastic and/or plastic deformation occurs at specific points along the scratch path; said critical points are observed in situ, by optical microscopy or by variations in acoustic emission and friction force.

In many cases, the scratch test has now been accepted as a versatile tool for assessing the mechanical integrity of a coated surface and has found application in many different fields of materials research. The driving forces for failure of a coating-substrate system in scratch testing are a combination of elastic-plastic indentation stresses, frictional stresses, and residual internal stresses present in the coating. The normal load at which failure occurs is called the critical load, Lc.

When scoring with progressive loading, several consecutive events of coating failure may be observed as the loading increases, the final event generally corresponding to full delamination. The critical load depends on the adhesion of the coating, but also on several other parameters; some are directly related to the test itself (intrinsic parameters) while others are related to the coating-substrate combination (extrinsic parameters).

Example of micropillar compression test on a micropillar built from a multilayer pile of different coatings.

Example of scratch tests on coatings to better understand their failure mechanisms.