Papers by Author: Sheng Bo Sang

Abstract: With new applications in the area of diagnostics, drug discovery and genetics, the need for Biological Micro-Electro-Mechanical Systems (BioMEMS) has increased tremendously in the last decade. Especially, surface stress-based BioMEMS has been investigated extensively in the recently years. In this paper, a new BioMEMS is proposed, which can be used to detect cells. It consists of microfluidics, square membrane and a fiber optic interferometer. The square membrane as the crucial and sensitive part includes three layers, self-assembled monolayer (SAM), gold and substrate material. Based on the BioMEMS, some fundamental study has been done, especially for the membrane due to its crucial role in the whole system. The finite element (FE) method has been used to study the membrane with different substrates. By the fundamental study, some important conclusions have been acquired: (1) The square membrane will reach maximal deflection at different ratio values (P: membrane size) to different substrates; (2) To a certain substrate, such as PDMS, the ratio making the membrane reach maximal deflection is different to dissimilar PDMS layer thickness; (3) If young’s modulus (E) of the substrate is too small, separation may happen between the gold layer and substrate layer when the gold size becomes smaller.

Abstract: With the development of MEMS, the mechanical properties of micro crystals must to be determined to know the defect, reliability and characterization of MEMS. Young’s modulus is one of the most important properties, which indicates the ability of resisting the elastic deformation. Many methods, such as natural frequency measurement, beam bending tests, membrane bulge test and uniaxial tension test, have been used to measure Young’s modulus of Si, SiN and metals. But there are some limitations when they are used to measure micro crystals in MEMS. This paper puts forward a high accuracy and convenient method----using Raman spectrum to measure Young’s modulus of micro crystals in MEMS, and sets up the measurement system. Measured Young’s modulus of Si and GaAs in [100] crystallographic orientation are 161.113GPa and 84.128GPa respectively, which correspond with the Yong’s modulus in common use now. Based on the values, it can be analyzed if there are some defects in the micro crystals.

Abstract: A trench is used as a storage capacitor in dynamic memory (DRAM) technologies (deep storage trenches), or as an isolation structure in CMOS, bipolar and BiCMOS technologies. But a shallow trench structure has also been shown to be a major factor in substrate defect generation during processing. Such defect generation is directly related to mechanical stresses existing around the trench. This stress can be monitored, using Raman spectroscopy, to a stress resolution of 10MPa and a spatial resolution of 0.2μm. In this paper, a trench structure is designed and fabricated, and the test results for local stresses within the trench are shown to be in good correspondence with theory.

Abstract: The stress is an important parameter of nano-thin film of the micro-structure. It is essential for the successful design and operation of many micro-machined devices. In this paper, the experiment idea that using Raman spectrometer to quantitate the stress in the nano-thin film of MEMS was put forward and the formula of the stress of Si and GaAs crystal was derived. In the experiment, the Si nano-thin film and AlAs/GaAs nano-thin film on GaAs substrate were grown by MBE (molecular beam epitaxy). The uniaxial pressure is exerted to nano-thin film by using the pressurization instrument designed by ourselves. Raman spectrums of the nano-thin film of MEMS are measured with the pressure exerted varying. Through the processing of the experiment data, the error of measurement to stress in nano-thin film is maximally 0.9% to Si and 7.5% to GaAs. So, Raman spectrum can be used to accurately quantitate stress in nano-thin film of MEMS in order to assessment of the reliability of micromachined structure. And the method can be applied to quantitate the stress in the experiment of testing the piezoresistor effect of double-quantum-well nano-thin film.