ASTM E2246 Strain gradient measurements of thin films using an Optical Interferometer

Scope:

ASTM E2246 test method defines a standard for calculating the strain gradient of thin, reflecting films that help design and fabricate the microelectromechanical systems. Moreover, the strain gradient value can contribute to the application of Young’s Modulus. It obtains 3-D data sets by using a non-contact optical interferometric microscope which can help determine the properties of the cantilever. The strain gradient value impacts the structural and conductivity properties of thin films.

Procedure:

In ASTM E2246, a surface-micromachined cantilever is fabricated and made to bend out of the plane in the z-direction. An optical interferometer forms a topographical 3-D data set, resulting in 2-D data traces which are used for calculating the strain gradient. The transitional edges are obtained and aligned, along with determining the attachment position of the cantilevers. The endpoints and uncertainties are determined, and the misalignment is adjusted. A circular arc is used to specify the misalignment of the cantilevers. The strain gradient is obtained from the circle’s radius by taking the average of the strain gradient values from the traces.

Specimen size

For ASTM E2246, the specimen size should be as required, that is 5 µm wide and 350 µm long.

Data:

The strain gradient s_g is obtained by taking the average of the residual strain values of the traces b, c, and d, as follows:

Conclusion:

ASTM E2246 test method defines a standard for calculating the strain gradient of thin, reflecting films that help design and fabricate the microelectromechanical systems.