Mechanical Properties of MEMS Materials
Abstract
New techniques and procedures were developed to measure the mechanical properties of the thin-film structural materials used in microelectromechanical systems. Tensile stress-strain curves were measured for polysilicon, silicon nitride, silicon carbide, and electroplated nickel. For example, polysilicon has a Young's modulus of 160 GPa and a Poisson's ratio of 0.22. It is a linear brittle material with fracture strength as high as 3 GPa. The mechanical properties of electroplated nickel are found to be highly dependent on the manufacturing process. Preliminary tests were conducted on silicon germanium, aluminum-glass composites, and diamond (amorphous carbon). Tests on specimens with stress concentrations show a definite size effect, i.e.,increase in fracture strength with decrease in size of highly stressed region, that is explained with Weibull statistics. Scanning and transmission electron microscopy studies of these materials relate the microstructure to the mechanical behavior. X-ray and atomic force microscopy studies show texture and surface roughness to be important features. Methods were developed to test polysilicon up to 600 deg C, and it is seen to be ductile and subject to creep at these temperatures. The coefficient of thermal expansion of polysilicon is larger than predicted from single crystal data. New axial fatigue tests at 6 kHz show polysilicon to behave much like a metal with decreased loading leading to increased life. Creep and fatigue tests were also conducted on nickel.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2004
- Accession Number
- ADA422530
Entities
People
- K. J. Hemker
- R. L. Edwards
- W. N. Sharpe Jr.
Organizations
- Johns Hopkins University