Anti-sticking behavior of DLC-coated silicon micro-molds

Abstract

Pure carbon-(C), nitrogen-(N) and titanium-(Ti) doped diamond-like carbon (DLC) coatings were deposited on silicon (Si) micro-molds by dc magnetron sputtering deposition to improve the tribological performance of the micro-molds. The coated and uncoated Si molds were used in injection molding for the fabrication of secondary metal-molds, which were used for the replication of micro-fluidic devices. The bonding structure, surface roughness, surface energy, critical load and friction coefficient of the DLC coatings were characterized with micro-Raman spectroscopy, atomic force microscopy (AFM), contact angle, microscratch and ball-on-disc sliding wear tests, respectively. It was observed that the doping conditions had significant effects on Raman peak positions, mechanical and tribological properties of the coatings. The G peak shifted toward a lower position with N and Ti doping. The DLC coating deposited with 1 sccm N 2 flow rate showed the lowest G peak position and the smoothest surface. The surface energies of the pure carbon and Ti-doped DLC coatings were lower than that of the N-doped DLC, which was more significant at a higher N 2 flow rate. In terms of adhesion and friction coefficient, it was observed that the Ti-doped DLC coating had the best performance. Ti incorporated in the DLC coating decreased the residual stress of the coating, which improved the adhesive strength of the coating with the Si substrate.

Tribological properties of platinum/ruthenium/nitrogen doped diamond-like carbon thin films deposited with different negative substrate biases

“…The main peaks found at the higher binding energies are the overlapped C 1s and Ru 3d 3/2 bands and the smaller peaks found at lower binding energies are Ru 3d 5/2 bands. An unsymmetrical shape of the spectra becomes more significant with higher negative substrate bias due to the stronger C-C sp 3 peaks. The increased negative substrate bias increases the kinetic energy of impinging ions, resulting in the increased content of sp 3 bonds in the PtRuN-DLC films and the consequently increased bond disorder in the films [4,29].…”

“…As a result, the full-width-at-half-maximum (FWHM) of the C1s peaks increases from about 2.82 to 2.95 eV with increased negative substrate bias from 0 to -120 V [30]. Normally, an introduction of N into an amorphous carbon structure tends to a decrease of sp 3 bonding configuration because it encourages C to be in sp 2 bonding configuration [31,32]. It is therefore supposed that the decreased N content in the PtRuN-DLC films with increased negative substrate bias contributes to the increased formation of sp 3 bonds in the films.…”

“…However, the lifetime of Si micromolds has been significantly shortened by their high brittleness and friction. Recently, Saha et al [3] reported that coating of Si micromolds with DLC films could successfully extend the lifetime of the micromolds.…”

Effect of sputtering power on friction coefficient and surface energy of co-sputtered titanium and molybdenum disulfide coatings and its performance in micro hot-embossing

“…The dispersive (c lm d ) and polar (c lv p ) components of surface energy for DI water are 21.8 and 51 dyne/cm, respectively. The dispersive and polar components for ethylene glycol are 29.3 and 19 dyne/cm respectively (Saha et al 2009(Saha et al , 2010a.…”

“…Silicon's poor tribological properties can cause defects when separating the part from the mold (demolding) (Hirai et al 2003;Hsueh et al 2006;Fu et al 2008;Dirckx 2010). Several researchers have attempted to improve the tribological performance of silicon micromolds by applying surface coatings, including fluoropolymers (Hirai et al 2001;Yeo et al 2006;Gao et al 2006) and hard coatings (Saha et al 2009(Saha et al , 2010a. Because fluoropolymer coatings have been found to have limited lifetime (Jaszewski et al 1999), hard coatings have the greatest promise for improving the performance of silicon micromolds.…”