Fatigue and Fracture of Polycrystalline Silicon and Diamond MEMS at Room and Elevated Temperatures

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)2 14. ABSTRACT A high-resolution Atomic Force Microscopy (AFM)/Digital Image Correlation (DIC) method was developed to investigate the deformation and fracture of tetrahedral amorphous diamond-like carbon (ta-C) and polycrystalline silicon (polysilicon) for microelectromechanical systems (MEMS). Polysilicon and ta-C test structures were fabricated at the Sandia National Laboratories (SNL) and at MCNC-Cronos. Their Young's modulus, Poisson's ratio, strength, and fracture toughness were obtained, many of them for the first time. Compared to polysilicon, ta-C was found to have superior mechanical properties: Its fracture toughness and strength were 3.5 times and two times that of polysilicon, respectively. Its elastic modulus was 4.5 times that of polysilicon and its Poisson's ratio was 30% smaller than polysilicon. The mode I and mixed mode I/I fracture toughness of polysilicon showed 50% scatter due to its polycrystallinity. On the contrary, the mixed mode I/I fracture of the amorphous ta-C was described wellf by deterministic theories for brittle fracture. The stochastic failure of polysilicon was treated by a finite element model that combined NASA's code CARES Life (Ceramics Analysis and Reliability Evaluation of Structures Life). This model provided failure predictions for devices with arbitrary geometries. Finally, the multi-grain nature of polysilicon was found to present a potential risk in the accurate determination of its effective mechanical behavior, especially in MEMS with dimensions equal to a small multiple of the grain size. In general, devices with dimensions larger than 15x 15 grains can be described by using the isotropic properties reported in literature and presented in this report. DI-STRIBUT1O•! STAT,47EWTAApproved for Public Release Distribution Unlimited SUMMARY A high-resolution experimental method was developed to investigate the deformation and fracture properties of tetrahedral amorphous diamond-like carbon (ta-C) and polycrystalline silicon (polysilicon) for microelectromechanical systems (MEMS). The method employed an Atomic Force Microscope (AFM) to record stra...

Research on Crack Measurement Technique in Solids Material with Digital Image Correlation (DIC)

“…Methods such as digital image correlation (DIC) and digital speckle correlation technique (DSCM) are all belong to this category [4,5]. Cross correlation based displacement measuring methods are widely used in material deformation analysis, it is anticipated that the method can also be used in crack width measurement [6][7][8][9][10].…”