Analysis of Contact Forces Using AFM Data of Polycrystalline Silicon Surfaces

The atomic force microscope (AFM) has evolved to the point of enabling the resolution of sub-nanometer features on a surface. Rather than artificially generated surfaces, high-resolution AFM images of polycrystalline silicon can be used to characterize the contact forces in microand nanoscopic devices. In this work, finite element models of characteristic features of the polysilicon surface are developed to explore the evolution of contact forces during a frictional sliding event. In conjunction with these analyses, discrete contact models are developed and applied to a novel MEMS device. This work also illustrates some of the fundamental limitations of Greenwood-Williamson and other homogenized surface models when attempting to characterize the contact and frictional properties encountered in MEMS devices. There is evidence that accurate contact analyses of MEMS devices involving either very light loads or small numbers of contacting asperities can only be performed if spatial information for the contacting surfaces is retained. In investigating that hypothesis, 2D and 3D geometrically based contact simulations are performed to characterize an experimentally observed phenomenon during frictional sliding.