Direct Micro Mechanical Testing Method for MEMS Materials

Abstract

Mechanical properties of MEMS materials are crucial for MEMS performance and reliability. Micro scale mechanical test has been challenging to MEMS community, due to the difficulties in handling micro scale specimens. In this article, a novel micro mechanical tensile testing method has been developed in combining a stiff microscale specimen developed with MTS Tytron Micro Force Tester. The advantages of this method include that it is a standard direct test of micro machined specimens, simple boundary conditions, and easy specimen handling/mounting in characterization. A novel specimen with micro features has been designed and fabricated for the direct mechanical testing. The specimen consists of three micro beams in parallel. The width of the center beam is 40 μm and the outer two beams’ width is 90 μm. The length of all three beams is 4 mm long. An optimized design has been achieved with finite element analysis, which shows that 98% of the total deformation occurs on the beams’ gage length. The stress is uniformly distributed over the three beams with a difference less than 0.5% among them. Both UV-LIGA fabricated nickel and SU-8 specimens have been tested. The UV-LIGA fabricated nickel has fracture strength of 1000±70 MPa and the results of SU-8 show a brittle behavior with fracture strength of 48±3 MPa.