Papers by Keyword: Single Crystal Silicon

Abstract: Mechanical loading and unloading of silicon is a characteristic feature of grinding and diamond turning processes. Such rapid loading and unloading induces damage and phase transformations. While, indentation tests are often used to study such normal loading and unloading via characteristic events in the force-depth plot, such tests involve only normal loading and lack tangential loading. A better alternative is scratch test, both constant and varying depth ones, involving normal and tangential loading on the scratching tool; this better simulates conditions of machining, or grinding. In this research, the mechanical load/unload behavior response of silicon is studied under scratching conditions by comparing increasing and decreasing depth scratch behaviour. In-situ force responses show that after ductile-brittle transition occurs, higher forces, at a given scratch depth, are required to deform the material during increasing depth scratching for a given depth than in decreasing depth scratch. Large surface and sub-surface damages with the presence of radial, median, and lateral cracks are seen to make the material weaker, ahead of the advancing tool, in decreasing depth scratch. Raman intensity ratio of amorphous silicon (a-Si) to nanocrystalline silicon (nc-Si) shows that high amorphization of silicon occurs during increasing depth scratching than decreasing depth. Using such force-depth plots an attempt is made to compare the normal loads while indenting and scratching. This study can help optimize the processing of silicon by grinding and diamond turning.

Abstract: The single-asperity friction of polished single crystal silicon using a cone with a spherical apex tip was quantitatively studied concerning the influence of normal load and scratching cycles. Specific friction equations were presented and the interfacial friction equations were determined by fitting the experiment data obtained in the scratching tests. The influence of different scratch conditions to both the interfacial fiction and the plowing friction was analyzed. This paper aims to understand the mechanisms of friction and material removal of single crystal silicon in micro and nanocutting or polishing.

Abstract: Single crystal silicon has both important application value in the fields of micro-optics and MEMS, and it has been considered as one of the most difficult-to-cut materials because of its hardness and brittleness. Removal mechanism of the silicon was discussed, and the model of undeformed chip thickness was established in this article. According to the data of micro-groove surface roughness from the diamond fly-cutting experiment, the nonlinear relationship curve, between the largest undeformed chip thickness h_max and microgroove surface roughness R_a, were obtained using Gaussian-fitting principle, and the regression equation of the fitting curve was also got. Thus the prediction mathematical model of microgroove surface roughness was derived. The influence laws of the main working parameters on the R_a were obtained based on the result of this experiment and the response surface of the prediction model, and some conclusions were summarized: the surface roughness R_a of microgroove in the single crystal silicon decreases with the decrease of the cutting depth a_p, the feed f and the increase of the spindle speed n under the diamond fly-cutting; the experimental results also showed that feed f affects the value of R_a very much, cutting depth a_p less, and spindle speed n the least.

Abstract: The experiment of cutting mechanical properties of single crystal silicon surface in the micro-nanoscale is researched using nanoindenter and atomic force microscopy. The result of the experiment shows that: in the constant load, the impact of different scratching velocity for single crystal silicon surface scratch groove width and chip accumulation volume are not big; but the cutting force and friction coefficient are not increases with the scratching velocity increases; when the scratching speed is certain, the size of load has a greater impact on the cutting mechanical properties of single crystal silicon surface, with the increase of the load, the cutting force increases, but the cutting force is not linearly growth.

Abstract: In this paper, a method of fabricating single crystal silicon microstructures on oriented silicon wafer is developed. The relationship of the (111) planes on silicon silicon wafer is analyzed based on the crystal lattice of the silicon, the method of judging these (111) planes is given. An anisotropy wet-etching experiment is done to verify the etching characteristics of silicon. The process of fabricating three dimension structures on silicon wafer is then given out and some basic MEMS structures such as cantilever beams, doubly-clamped beams are fabricated. With this method, it is easy to define the shape and thickness of the microstructure and the process is not complicate. Moreover, the structures made in this way have higher structural precision and mechanical strength.

Abstract: A lot of studies on the ultra-precision cutting of single crystal silicon have been reported and they used the single crystal diamond cutting tools having the sharp cutting edge. However, the diamond cutting tools having small chamfer at the cutting edge are usually used in practical machining shops. In addition, studies on the relationship between the tool wear and the machined surface have been reported little although the relationship is important in practical applications. In this study, ultra-precision cutting of single crystal silicon, using cutting fluids, feed rate, and depth of cut as experimental parameters, were carried out by using the single crystal diamond cutting tools having small chamfer and large nose radius, and effects of the cutting fluids, the feed rate, and the depth of cut on the machining accuracy and tool wear were studied. As a result, the optimum cutting conditions was obtained as follows: the cutting fluid was kerosene, the feed rate was 2.0μm/rev, and the depth of cut was 1.0μm.

Abstract: Wear of diamond tool is also very serious, which affects the surface quality of the machined work material, even if ductile mode where an undeformed chip thickness is at a nanoscale is used. During the cutting process, the crystal structure in the cutting zone is destroyed under the high pressures applied by the diamond tool. The silicon atoms adhering to the tool surface reconstruct to be in a crystal state under the effect of adhesion and pressures.

Abstract: The failure components made of silicon is an important issue in the electronic and nano-technological developments. A study on the near-crack-tip deformation of single-crystal silicon wafer under tensile load was presented. The strain formulas around the crack tip of mode I crack were deduced from linear elastic fracture mechanics. The strain fields around the crack tip were simulated and analyzed in detail.

Abstract: Wear of diamond tool has always been a limiting factor in ductile regime machining of large size silicon components. In order to understand the tool wear phenomena, it is non-trivial to know the process outputs especially cutting forces, stresses and temperature during nanometric turning. In this paper, a realistic potential energy function has been deployed through molecular dynamic (MD) simulation, to simulate the process outputs of single diamond turning operation against single crystal silicon. The simulation result suggests that wear mechanism of diamond tool is fundamentally governed by these process parameters and thus critical.

Abstract: A mathematical model to calculate the grit average cut depth in wire sawing single crystal silicon was founded. So the grit average cut depths were calculated theoretically by choosing different process parameters, and influences of process parameters on grit cut depths of slicing silicon crystal were analyzed. Analysis results indicate that the grit average cut depth relates to the silicon mechanical properties, grit shape and size, wire speed and ingot feed speed, etc. And there is a monotone increasing non-linear correlation between grit average cut depth and the ratio i value of ingot feed speed and wire speed, when the i value is lower, the average grit cut depth is lower.