Papers by Author: Xiao Zhong Song

Abstract: Various novel 3D micro machining technologies were researched and developed for silicon micro mechanical system fabrication. Micro EDM is one of them. The material removal mechanism is thermal sparking erosion and is completely independent with regards to the crystalline orientation of silicon, therefore there is no orientation constraint in processing the complex 3D geometry of silicon wafers. As thermal sparking implied, the process features local area high temperature melting and evaporating, and this characteristic has an adverse side-effect on the sparked surface integrity. One important concern is the generation of micro cracks, which would provide an adverse effect on the fatigue life of the micro feature element made of silicon. For this consideration, in this paper, with the experiment and SEM picture analysis approach, the author explored the micro crack generation characteristics on mono crystalline silicon wafers under micro EDM with available sparking energies and on the different crystal orientation surface machining. The generation of micro cracking is not only related with the sparking energy but also related with the crystalline orientation. The {100} orientation is the strongest surface to resist crack generation. For a strong-doped P type silicon wafer, there exists a maximum crack energy threshold. If single sparking energy is over this threshold, micro cracks unavoidably would be generated on any orientation surface. Two types of chemical etching post processes that can remove cracks on sparked surfaces are also tested and discussed.

Abstract: Silicon-hydrogen crystalline models are proposed to estimate theoretical hydrogen storage capacity in porous silicon media with nanostructure features like cubic nodules, columnar forests and thin wall honeycomb like networks. To simulate these nanostructure features and their hydrogen storage capacities, three basic crystalline types (cubic, column and plate) have been developed as building blocks for constructing H-Si weight storage models under the assumption of that hydrogen is chemically bonded to available surface silicon atoms. Using these models, the hydrogen weight storage capacity for all feature dimensions from unit to infinitely long can be estimated. According to these theoretical models, the best nanostructure for hydrogen storage is cubic nodule, columnar forest and thin wall network in that order. They have weight storage capacity limits of 5.77%, 5.21% and 2.78% respectively for infinitely large feature dimensions.

Abstract: HVOF WC-Co spraying coating can enhance greatly the anti-wear performance of workpiece, but it is just the high hardness of spraying coatings that makes the polishing of workpiece very difficult, the application of HVOF was limited. In this paper, we discuss the feasibility of apply ECP(electrochemical polishing) to spraying coatings, include the study of electrolyte, the optimization of machining parameters et al., the experiment results show that it is not only feasible that apply ECP to machining spraying coatings, but also high machining efficiency, high quality surface can be obtained. The surface roughness can be reduced from Ra=4.0μm to Ra=0.7μm with suitable machining parameters during a very short time.