Chaohui Zhang

Progress in material removal mechanisms of surface polishing with ultra precision

Chemical mechanical polishing (CMP) process is commonly regarded as the best method for achieving global planarization in the field of surface finishing with ultra-precision. The development of investigation on material removal mechanisms for different materials used in computer hard disk and ultra-large scale integration fabrication are reviewed here. The mechanisms underlying the interaction between the abrasive particles and polished surfaces during CMP are addressed, and some ways to investigate the polishing mechanisms are presented.

A New Postulation of Viscosity and Its Application in Computation of Film Thickness in TFL

In this paper, a viscosity modification model is developed which can be applied to describe the thin film lubrication problems. The viscosity distribution along the direction normal to solid surface is approached by a function proposed in this paper. Based on the formula, lubricating problem of thin film lubrication (TFL) in isothermal and incompressible condition is solved and the outcome is compared to the experimental data. In thin film lubrication, according to the computation outcomes, the lubrication film thickness is much greater than that in elastohydrodynamic lubrication (EHL). When the velocity is adequately low (i.e., film thickness is thin enough), the pressure distribution in the contact area is close to Hertzian distribution in which the second ridge of pressure is not obvious enough. The film shape demonstrates the earlobe-like form in thin film lubrication, which is similar to EHL while the film is comparatively thicker. The transformation relationships between film thickness and loads, velocities or atmosphere viscosity in thin film lubrication differ from those in EHL so that the transition from thin film lubrication to EHL can be clearly seen.

Effect of external electric field on liquid film confined within nanogap

A strong and reproducible effect of an external electric field (EEF) on liquid films confined within a nanogap between a highly polished steel ball and a smooth glass disk is described. Induced by the EEF, microbubbles were observed at the edge of the contact region. This phenomenon is more obvious in polar liquid films than that in nonpolar ones. A stronger EEF causes a decrease in the film thickness in the contact region initially, and then the variation becomes much smaller. When the ball is applied with a positive EEF, the emergence of microbubbles is stable over time, while it becomes much less as time progresses. Different mechanisms of these experimental phenomena have been discussed.

Multigrid technique incorporated algorithm for CMP lubrication equations

Abstract Chemical mechanical polishing (CMP) is a manufacturing process used to achieve required high levels of global and local planarity, which involves a combination of chemical erosion and mechanical action. The study on mechanical removal action of CMP with hydrodynamic lubrication involved will help us to get some insights into the mechanism of CMP and to solve the lubrication problem of CMP. In this paper, a full approach scheme of multigrid technique incorporated with line relaxation is introduced for accelerating the convergence. The effects of various parameters on load and moments are simulated and the results of computation are reported.

Effect of liquid properties on the growth and motion characteristics of micro-bubbles induced by electric fields in confined liquid films

The effect of liquid properties on gas bubble growth and motion characteristics in liquid films confined within a nanogap between a highly polished steel ball and a smooth glass disc under an electric field is reported. Experimental results show that the critical voltage for the appearance of bubbles has insignificant dependence on liquid viscosity and surface tension. The bubble size after detachment increases with liquid viscosity, and bubble instability and coalescence tend to occur when bubbles move some distance away from where they were formed. An increase in liquid surface tension results in larger bubbles at the growth stage. Also, the bubble motion characteristics are greatly influenced by liquid viscosity, and the dielectrophoresis force is demonstrated to be the dominant driving force for bubble movement. Theoretical models and analyses have been used to discuss the bubble formation and describe the bubble movement characteristics.

Lubrication Theory for Thin Film Lubrication Accounting for the Ordered Film Model

In this paper, the features in thin film lubrication (TFL) are investigated with the use of nematic theory accounting for the ordered film. In TFL, in which dominated by the ordered molecules, the alignments of molecules can roughly be described by a unit vector, the director, and then the phenomena can be construed accordingly. The fundamental continuum flow theory is applied to the two-dimensional lubrication geometry. The angular distribution profile is solved from the angular momentum equation which couples the viscosity and elastic effects. Other than in nematic case, in which the Leslie coefficients are the properties of lubricant, the Leslie coefficients are determined by the combination of solid walls and the lubricants in TFL. A parameter named as viscosity-to-elasticity ratio is introduced to account for the relative effect of viscosity to elasticity.

Properties of Ti-Si-N Nanocomposite Coatings Deposited by Closed-Field Unbalanced Magnetron Sputtering

Ti-Si-N coatings with different silicon contents were deposited by reactive magnetron sputtering. These coatings were characterized and analyzed by using a variety of analytical techniques. The Ti-Si-N coating shows a denser structure as compared with TiN coating, and consists of TiN crystallites and amorphous Si3 N4 phase. The maximum hardness and Young’s Modulus of 52 GPa and 360 GPa respectively are achieved as the Si content was 8.6 at.%. The Ti-Si-N coating with 8.6 at.% Si shows the excellent oxidation resistance behavior and perfect anti-wear performance.Copyright