Accession Number:

ADA422530

Title:

Mechanical Properties of MEMS Materials

Descriptive Note:

Final rept. Oct 1999-Sep 2002

Corporate Author:

JOHNS HOPKINS UNIV BALTIMORE MD

Report Date:

2004-03-01

Pagination or Media Count:

60.0

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 Youngs modulus of 160 GPa and a Poissons 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.

Subject Categories:

  • Inorganic Chemistry
  • Test Facilities, Equipment and Methods
  • Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE