The fracture toughness of polysilicon microdevices: A first report
- PDF / 512,980 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 24 Downloads / 177 Views
MATERIALS RESEARCH
Welcome
Comments
Help
The fracture toughness of polysilicon microdevices: A first report R. Ballarini, R. L. Mullen, and Y. Yin Department of Civil Engineering, Case Western Reserve University, Cleveland, Ohio 44106-7201
H. Kahn, S. Stemmer, and A. H. Heuer Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106-7204 (Received 16 February 1996; accepted 16 December 1996)
Polysilicon microfracture specimens were fabricated using surface micromachining techniques identical to those used to fabricate microelectromechanical systems (MEMS) devices. The nominal critical J-integral (the critical energy release rate) for crack initiation, Jc , was determined in specimens whose characteristic dimensions were of the same order of magnitude as the grain size of the polysilicon. Jc values ranged from 16 to 62 Nym, approximately a factor of four larger than Jc values reported for single crystal silicon. I. INTRODUCTION
Significant research has been conducted on the development of designs, modeling, and production processes for microelectromechanical systems (MEMS) devices. However, long-term durability of various MEMS devices, which requires a fundamental understanding of the fatigue and fracture characteristics of such microfabricated structures (known as “microstructures” in MEMS jargon), has not been fully addressed in a systematic fashion. While there is a significant technology base in the wear, fatigue, and fracture of macro systems, the study of fatigue and fracture on the microscale appropriate for MEMS is very limited. Furthermore, the fracture mechanics base for polysilicon, one of the principal materials currently used in the fabrication of MEMS devices, is sparse at best. The determination of mechanical properties at the scale relevant to MEMS devices is complicated by the anisotropy and heterogeneity inherent in the microfabricated structures, the residual stresses resulting from processing, and the resulting batch-to-batch statistical variations. To our knowledge, the only existing experimental fracture mechanics study at the microscale was conducted by Connally and Brown1 on single crystal silicon, and by Fan, Howe, and Muller2 on CVD-formed silicon nitride and low-stress silicon nitride. Connally and Brown’s goal was to determine whether silicon is prone to static fatigue. By using a bulk micromachined cantilever specimen whose natural frequency is sensitive to small changes in the length of the precrack, they were able to show that in humid air, crack growth does occur, albeit at a relatively slow rate. Fan et al. estimated the fracture toughness, p KIc , of low-stress silicon nitride as 1.8 6 0.3 MPa m. An understanding of the relationships between processing variables and the resulting mechanical behavior J. Mater. Res., Vol. 12, No. 4, Apr 1997
http://journals.cambridge.org
Downloaded: 02 Apr 2015
and durability of microfabricated structures is needed in order to allow rational design of MEMS devices. To quantify the statistical inf
Data Loading...
