Tribological Properties Of Textured Silicon Surfaces

With the miniaturization of structural dimension of micro/nano-sized mechanicaldevices, surface-to-volume ratio increases, and thus surface effects become markedlyenhanced. As a result, serious adhesion, friction and wear problems lead to poor workingperformance, reduce service life and hinder the development and application ofmicro/nano-electro-mechanical systems(MEMS/NEMS). Surface texturing is an effectiveway to solve the problems for MEMS/NEMS. Therefore, in this paper the tribologicalproperties of textured silicon surfaces in micro/nano-scale are studied through experiments.The main work and conclusions are as follows:The pillar textures are prepared on a Si(100) single crystal via optical lithography andinductively coupled plasma etching. The morphologies of textured silicon surfaces arecharacterized using scanning electron microscope and atomic force microscope respectively.Observations suggest that regular cylinder arrays are produced on silicon surfaces. Whenthe interval between adjacent patterns is fixed, both the texture coverage and root meansquare roughness increase along with the increase of the diameter.Adhesion tests are performed by the atomic force microscope equipped with acolloidal probe. Adhesive forces are measured in the environment of atmosphere anddeionized water respectively at room temperature in order to investigate the effect of pillartextures on the adhesive behavior of silicon surfaces. Measurement results show that pillartextures play a significant adhesion-reduction role, reducing both the van der Waals forceand capillary force. When the interval is fixed, textures with smaller diameters are morebeneficial to adhesion-reduction. Besides, the capillary force plays an important role incontributing to the total adhesive force.Friction tests are also carried out using the colloidal-probe atomic force microscope tostudy the frictional behavior of textured silicon surfaces. Experimental results show thatpillar textures reduce the sliding friction between the probe and silicon surfaces. Likewise,when the interval is constant, the smaller the diameter is, the lower the friction on thesurface will be. In addition, by varying load and sliding velocity, it is also found that thefrictional force on textured silicon surfaces increases as the load or sliding velocityincreases, while the relative coefficient of friction decreases with increasing load.The surface topography of silicon wafer is measured through the atomic forcemicroscopy to study the multiscale characteristic. Then a multiscale contact model for rough surfaces is established to explore the relationship between real contact area andnumber of scales. Calculation results suggest that when the scale is getting smaller andsmaller, more and more smallest asperities begin to appear. The real contact area betweensurfaces continues to decrease with increasing number of scales.