Indentation Delamination and Indentation Fracture in ZnO/Si Systems
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INDENTATION DELAMINATION AND INDENTATION FRACTURE IN ZnO/Si SYSTEMS Bin Huang, Ming-Hao Zhao, Tong-Yi Zhanga) Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China ABSTRACT Vickers indentation tests were carried out at room temperature with a microhardness tester on ZnO thin films deposited on (100) Si wafers. The films with thicknesses ranging from 0.202 to 1.535 µm were tested under indentation loads varying from 50 mN to 2.0 N. The experiments exhibited a film thickness dependent deformation behavior. When the film thickness is smaller than a critical value, only indentation-induced radical cracking occurred and for a given load, the radical crack size decreased with film thickness. On the other hand, indentation-induced delamination was observed if the film thickness was larger than the critical value. In this case, the radial crack, if induced, had a size smaller than the size of delamination or even smaller than the size of indentation impression. Under a same indentation load, the delamination size increased with the film thickness. INTRODUCTION Thin film coated structures are widely used in magnetic, optic, microelectronic, and microelectromechanical devices. The durability and reliability of the devices depend greatly on the mechanical properties of the film/substrate structure, including residual stresses and adhesion of a film on its substrate. Therefore, assessments of residual stress and adhesion have become a hot research area. There are many available methods and techniques to assess these properties [1], among which the indentation test is the most attractive method because of its simplicity and easiness. Marshall and Evans [2] and Evans and Hutchison [3] studied the indentation-induced delamination and provided solutions to assess adhesion. Their approach [2, 3] was further developed for multilayer films [4] and for microwedge probes [5, 6]. The indentation-induced delamination tests were carried out to measure the interface fracture toughness of the polyester/glass, ZnO/Si [7], polycrystalline diamond/Si [8], sputtered Cu/Si, W/Si, and W/Cr superlayer/Si systems [9], etc. Furthermore, the indentation test on brittle film/ductile substrate systems was also studied [1, 10, 11]. In the present work, we use the indentation test to estimate the adhesion between a ZnO film and a (100) silicon substrate. Lawn and Fuller [12] proposed to use the indentation fracture technique to measure residual stresses in a film deposited on a brittle substrate. Following Lawn and Fuller’s approach, Gruninger et al. [13] and Kobrin and Harker [14] conducted the indentation fracture tests on SiO2, Si3N4, Al2O3 and ZrO2 thin films deposited on soda-lime glass. Zhang et al. [15] further developed the indentation fracture technique on the basis of the mean stress intensity factor. We a)
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