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The effects of phosphorus doping on the bending strength of a single crystal silicon (SCS) microbeam are reported. First, a specially designed bending micro structure test and a simple bending test device are presented. Secondly, the results of bending strength tests for six groups of specimens with different phosphorus doping concentrations are presented. The test results are comparatively analysed using a Weibull distribution, revealing that the bending strength has a monotonically increasing relationship with the phosphorus concentration. The effect of surface roughness on the bending strength is also investigated. Finally, the mechanism underlying this phenomenon is demonstrated. The results indicate that the bond strength of a phosphorus-silicon pair is larger than that of a silicon-silicon pair, and the phosphorus atoms increase the energy necessary to create new surfaces. Therefore more energy is required to fracture the microbeam, and the fracture strength increases. Research on this topic therefore shows some practical significance for improving the bending strength of a SCS microstructure.
1. Introduction: Microelectromechanical systems (MEMS), as a multidisciplinary field, are broadly applied in almost all the natural sciences, including aerospace, national defence and biomedical engineering. Typical working environments for MEMS, such as in the transportation industry and its applications, include both shocks and vibrations. These environments require that MEMS withstand high-impact stress and vibration loads, particularly for military and aerospace applications. Therefore it is increasingly necessary to investigate methods to improve the strength characteristics of microstructures to minimise the hazards caused by shocks or vibrations. Generally, there are two effective methods for this task: optimising the structure by reducing surface roughness to overcome stress concentrations [1] and enhancing the fracture resistance of the microstructure material itself. This Letter focuses on the latter.
Silicon MEMS products are the most prevalent today. Single-crystalline silicon (SCS), one of the most widely used MEMS structural materials, is brittle at room temperature and has good mechanical properties and sensing characteristics, such as the piezoresistive, Hall effects [2] and so on. The fracture strength of the SCS can be described statistically by a Weibull distribution [3]. For the macroscale SCS structures, numerous studies have con- cluded that doping is an effective way to enhance the mechanical strength [4-6], Phosphorus is a commonly used electrically active doping agent for silicon. Numerous...