ASTM E2245 test method determines the residual strain of the films in microelectromechanical systems by a non-contact optical interferometric microscope that can form topographical 3-D data sets. This optical interferometric microscope does not measure the residual strain of fixed-fixed beams that touch the underlying layers.
Scope:
ASTM E2245 test method defines a standard for calculating the residual strain of thin, reflecting films that help design and fabricate the microelectromechanical systems. Moreover, the residual strain 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 fixed-fixed beam.
Procedure:
A surface-micromachined fixed-fixed beam is fabricated and made to bend out of the plane in the z-direction. An optical interferometer forms a 3-D data set which results in 2-D data traces for calculating residual strain. The in-plane length and the curved length of the fixed-fixed beam contribute towards the measurement of residual strain. The endpoints and uncertainties are determined, and the misalignment is rectified. Cosine functions are applied to calculate the in-plane length and the curved length of the fixed-fixed beam. Temperature and humidity are recorded. The residual strain is obtained by taking the average of the residual strain values of the data traces.
Specimen size
The specimen shall be as per the requirements such that it is 5µm wide and 400µm long.
Data:
The residual strain r is obtained by taking the average of the residual strain values of the traces b, c, and d, as follows:
εr=εrb+εrc+εrd/3
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