MEMS Fatigue Testing to Study Nanoscale Material Response

With the advent of microtechnology over the last few decades, designs for new and innovative microscale machines and sensors have been released to market at a record pace. Current life saving devices based on this technology, such as air bag deployment sensors and blood pressure sensors necessitate a high degree of reliability. As a result, it has become increasingly important to determine when and how device failure will occur. It is widely known that once structures enter the microscale, the laws of macro mechanics no longer necessarily dominate the mechanical response. The future of technology demands that the scale shrink even farther to the nanoscale to increase functionality and reduce the size and weight of future devices. Determining and documenting properties at the nanoscale is necessary to take revolutionary designs to market. These new designs offer a multitude of new possibilities. This not only demands reliable and repeatable operation, but also a fundamental understanding of the nanomechanical response when exposed to repetitive loading. An experimental methodology is needed to begin accurate assessment of potential nanoscale structure failure modes. The purpose of this research is to create a standard design and procedure for tensile and fatigue testing at small length scales. Our approach begins with the application of a uniaxial load to a micro test specimen with a gage section that is two by two micrometers. The tensile tester is manufactured using the Multi-User MEMS Process (MUMPS) technology [1]. The loads will be applied using various actuator designs using thermal and comb drive actuation, with a separate comb drive used to monitor cross-head displacement. The tensile tester can deliver a force exceeding 0.65 microNewtons and a deflection range from 0 to 5 micrometers. Numerical simulations using ANSYS [2] and MEMCAD [3] were used to validate the theoretical response. The experimental design allows for the complete fracture process to be examined using Scanning Probing Microscopy (SPM).