Fracture strength of polysilicon at stress concentrations

被引:85
作者
Bagdahn, J [1 ]
Sharpe, WN
Jadaan, O
机构
[1] Fraunhofer Inst Mech Mat, D-06120 Halle Saale, Germany
[2] Johns Hopkins Univ, Dept Mech Engn, Baltimore, MD 21218 USA
[3] Univ Wisconsin Platteville, Coll Engn Math & Sci, Platteville, WI 53818 USA
关键词
fracture; polysilicon; strength; stress concentration; Weibull statistics;
D O I
10.1109/JMEMS.2003.814130
中图分类号
TM [电工技术]; TN [电子技术、通信技术];
学科分类号
0808 ; 0809 ;
摘要
Mechanical design of MEMS requires the ability to predict the strength of load-carrying components with stress concentrations. The majority of these microdevices are made of brittle materials such as polysilicon, which exhibit higher fracture strengths when smaller volumes or areas are involved. A review of the literature shows that the fracture strength of polysilicon increases as tensile specimens get smaller. Very limited results show that fracture strengths at stress concentrations are larger. This paper examines the capability of Weibull statistics to predict such localized strengths and proposes a methodology for design Fracture loads were measured for three shapes of polysilicon tensile specimens-with uniform cross-section, with a central hole, and with symmetric double notches. All specimens were 3.5 mum thick with gross widths of either 20 or 50 mum. A total of 226 measurements were made to generate statistically significant information. Local stresses were computed at the stress concentrations, and the fracture strengths there were approximately 90% larger than would be predicted if there were no size effect (2600 MPa versus 1400 MPa). Predictions based on mean values are inadequate, but Weibull statistics are quite successful. One can predict the fracture strength of the four shapes with stress concentrations to within 10 % from the fracture strengths of the smooth uniaxial specimens. The specimens and test methods are described and the Weibull approach is reviewed and summarized. The CARES/Life probabilistic reliability program developed by NASA and a finite element analysis of the stress concentrations are required for complete analysis. Incorporating all this into a design methodology shows that one can take "baseline" material properties from uniaxial tensile tests and predict the overall strength of complicated components. This is commensurate with traditional mechanical design, but with the addition of Weibull statistics.
引用
收藏
页码:302 / 312
页数:11
相关论文
共 23 条
  • [1] *ASTM, 1995, 123995 ASTM C
  • [2] Size effect on the mechanical properties of microfabricated polysilicon thin films
    Ding, JN
    Meng, YG
    Wen, SZ
    [J]. JOURNAL OF MATERIALS RESEARCH, 2001, 16 (08) : 2223 - 2228
  • [3] Specimen size effect on mechanical properties of polysilicon microcantilever beams measured by deflection using a nanoindenter
    Ding, JN
    Meng, YG
    Wen, SZ
    [J]. MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 2001, 83 (1-3): : 42 - 47
  • [4] DOWLING NE, 1999, MECH BEHAV MAT, P803
  • [5] In situ tensile strength measurement and Weibull analysis of thick film and thin film micromachined polysilicon structures
    Greek, S
    Ericson, F
    Johansson, S
    Schweitz, JA
    [J]. THIN SOLID FILMS, 1997, 292 (1-2) : 247 - 254
  • [6] Johnson C.A., 1991, Eng. Mater. Handb., V4, P709
  • [7] Johnson G. T., 2000, P SOC PHOTO-OPT INS, V3874, P94
  • [8] JONES PT, 2000, P SOC PHOTO-OPT INS, V3880, P20
  • [9] Fracture strength and fatigue of polysilicon determined by a novel thermal actuator
    Kapels, H
    Aigner, R
    Binder, J
    [J]. IEEE TRANSACTIONS ON ELECTRON DEVICES, 2000, 47 (07) : 1522 - 1528
  • [10] Cross comparison of direct strength testing techniques on polysilicon films
    LaVan, DA
    Tsuchiya, T
    Coles, G
    Knauss, WG
    Chasiotis, I
    Read, D
    [J]. MECHANICAL PROPERTIES OF STRUCTURAL FILMS, 2001, 1413 : 16 - 27