Research On Transfer Printing With A Sacrificial Layer For PDMS Metallization

Polydimethylsiloxane(PDMS)has been increasingly applied in fabricating various micro/nano devices as a kind of silicone polymer owing to its stretchability,transparency,ease of fabrication and biocompatibility.In order to expand application field of PDMS,metallic material is increasingly integrated on PDMS to realize various functions.However,since PDMS has a low elastic modulus and a high coefficient of thermal expansion,irregular wrinkles usually occur on the metal thin-film in PDMS metallization which makes negative impact on the stability and reliability of micro/nano devices even damages availability of micro/nano devices.In this article,we introduce a method of transfer printing with a sacrificial layer for PDMS metallization.Firstly,poly(acrylic acid)(PAA)was employed as the sacrificial layer after comparison of various water-soluble materials and the relationships between the spin-coating speed and the thickness,uniformity,roughness and elastic modulus of PAA thin-films were investigated.Secondly,the specific process of the method was introduced and various metallic patterns with diverse dimensions were fabricated on PDMS via transfer printing with the help of water-soluble sacrificial layer.Besides,the morphology of the metallic patterns was observed with scanning electron microscope(SEM)and it was found that the surface was smooth without obvious wrinkles and cracks.In addition,atomic force microscope(AFM)was employed to evaluate the surface quality of the smooth metal thin-film and the metal thin-film via direct sputtering was also fabricated on PDMS as a comparison.Compared with the metal thin-film via direct sputtering,the amplitude of wrinkles on the smooth metal thin-film was decreased by one order of magnitude and the wavelength was increased by a factor of 4 approximately,so the wrinkles were mitigated significantly.Moreover,the production mechanism of the slight wrinkles of metal thin-film on PDMS via transfer printing with the help of water-soluble sacrificial layer was studied and the small deformation of PDMS in the process of transfer printing led to the slight wrinkles.Meanwhile,the roughness was decreased by a factor of 5 due to the fact that the PDMS elastomeric surface was free from the physical impingement of plasma ions and metal atoms by avoiding the direct sputtering on PDMS.Finally,a metallic tunable grating with a period of 4?m was obtained on PDMS via transfer printing with the help of water-soluble sacrificial layer and the diffraction efficiency,the tensile correspondence and the durability of the grating was measured and investigated.The results showed that the diffraction efficiency of gratings fabricated by transfer printing with the help of water-soluble sacrificial layer was higher than that of the gratings fabricated by direct sputtering,and the calculated actual grating constant corresponded with the theoretical grating constant basically when the grating was stretched by 50%,and the grating maintained its good diffraction efficiency and tensile correspondence after 1000 cycles of stretching.Therefore,the grating exhibited excellent stability,reliability and durability.