Papers by Author: Xin Wei

Abstract: A solvent-free cross-linked alternating copolymer electrolyte is synthesized through photo copolymerization of comb-like poly (ethylene glycol) ester maleate and styrene. Phase transitions, thermal properties, ionic conductivities and electrochemical stabilities are investigated to characterize the alternating copolymer electrolyte. The flexible solid polymer electrolyte (spe) with lithium salt content of 15 wt.% and MA/-OH = 1 has a good ionic conductivity of 1.45×10^-5 S cm^-1 at 35 °C and a superior electrochemical stability to 5.2 V. The maleic anhydride on the main chain increases the rigidity of the copolymer matrix and decreases the ionic conductivity.

Abstract: A finite element method (FEM) is used to make the modal analysis of the drive axle housing, the first ten natural frequencies and modal shapes are obtained. The parameter identification method is applied to obtain the experimental modes. There is a great agreement with the calculating modes and the experimental ones, which proves that the finite element method is rational. According to the theoretical analysis, the main deformations are bending and torsion at both ends of the drive axle housing and the deformation of the middle part is relatively high. The natural frequencies are at middle and high frequencies which are close to the mesh frequencies of the drive axle gears. Therefore increasing the thickness and redesigning of stiffened palates are applied to avoid the resonance region effectively.

Abstract: Chemical mechanical polishing (hereinafter referred to as CMP) which is to provide the best global planarization technology has been researched and applied in the field of ultra-precision surface finish. This article outlines the principles of the CMP process, focusing on the development of the major theoretical models such as phenomenological model, contact mechanics model, fluid dynamics model and hybrid model based contact mechanics and fluid dynamics in chemical mechanical polishing process. The hybrid model based contact mechanics and fluid dynamics has been a good developed in recent years. The model based on the molecular / atomic scale is proposed the further research methods of CMP's theoretical model.

Abstract: According to the features of the self–rotating grinding, the real-time grinding force control system was designed. The Fuzzy-PID control method has been proved to be the most suitable control method and fulfill the system’s needs through the modeling, simulation and experiment of the system in this paper.

Abstract: This paper studies the chemical mechanical polishing (CMP) of the wafer's material such as stainless steel, monocrystalline silicon etc, and analyzes how the technological parameters’ impact on the final wafer’s surface material removal rate, surface quality and surface damage like the polishing pad’s speed and the wafer speed, polishing pressure and polishing time.The results show that: when the difference between the polishing pad's rotation speed and the wafer's rotation speed is small and their directions are the same , then the material removal rate of the wafer is larger.when the polishing pressure is selected between 5 to 6.5 kPa, the wafer surface's damage is smaller.The polishing time also play a very important role and affect the surface quality and surface damage of the wafer after polishing.

Abstract: To establish the green laser ablation process more accurately, a detailed knowledge of the exact value of ablation threshold is of great importance. Therefore, the presented paper has investigated the single pulse ablation threshold using four different methods, namely, fitting method via diameter square, fitting method via depth, micro-topography method and the one-dimensional heat conduction model. Through this research, the well-defined threshold in term of laser fluence (J/cm2) is obtained, and the comparison among different methods casts a light on the effective way to determine the ablation threshold. Also, the underlying laser-material interaction mechanism is analyzed.

Abstract: This paper presents a Raman analysis of the monocrystalline silicon wafer scratched by single point diamond. Si-III and Si-XII phases are found to be existence in the scratched silicon surface, which is the result of the phase transformation. A mathematical model was developed to calculating the molar concentration of phase of the silicon. Based on the mathemathical model, the relationship between the molar concentrations of the Si-I phase and the applied load was analysied.

Abstract: In this paper, micro-nano scratching experiments were conducted on mono-crystalline silicon wafer to investigate the material removal mechanism of silicon. Two loading methods (increasing-loading and constant-loading) were used. The characteristics of the scratching grooves, and the relationship between the groove size and the load were analyzed by observing the surface torography and measuring the groove. The results show that there are four distinct regimes existed with an increasing scratching load: elastic regime, ductile regime, ductile-brittle regime and brittle regime. The critical load of the transition from ductile to ductile-brittle regime can be considered as 120mN, within which smooth scratching surfaces have been obtained by ductile removal. The scratching load has very significant effects on the groove sizes of the mono-crystal silicon.

Abstract: The three dimensional (3D) coupling model is set up for analyzing the energy reflection and absorption on the kerf using ray tracing method after the laser beam cutting nonmetallic materials with high absorptance through multiple reflections. The laser beam characterized by focused gauss beam and fresnel absorption on the kerf are taken into account. The influences of the polarization on the absorbed intensity both in the front and the two walls are also discussed. Results indicate the differences of absorptive intensity among the three polarized lights are relatively small compared to metal. Thus, the polarization has little effects on the kerf of nonmetallic materials with high absorptance. The experimental results also agree well with the theoretical analysis.

Abstract: This paper studied the effects of the off-process conditioning parameters on the pad performances. The pad conditioning was evaluated based on the measurement of pad removal rate, the observation of the conditioned pad surface. The performances of conditioned pads were evaluated also by the material removal rate (MRR) and the surface roughness of polished wafers in the CMP experiments of LiTaO3 crystal wafers.