Research On The Enhancement Of The Adhesion Between Metal Films And Polymer Substrates By UV-ozone Modification

Polymer provides numerous advantages in terms of cost,mechanical,optical and biological properties,and ease of fabrication.Polymer has been increasingly used in many micro-and nanosystem technologies.Polymer metallization can integrate various metal components on the device,which can improve the device integration and expand polymer applications.However,since the polymer surface is nonpolar and has a low surface energy,the adhesion of deposited metal films on polymer substrates is normally poor,which greatly limits the applications of metal components in polymer micro-and nanosystem technologies.In this paper,ultraviolet(UV)-ozone surface modification was for the first time put forward to enhance the adhesion between metal films and polymer substrates.Prior to depositing metal films,the polymer surface was treated by using a UV-ozone cleaner.The adhesion between metal films and polymer substrates was significantly enhanced.The adhesion of sputtered Cu films on UV-ozone modified polymethylmethacrylate(PMMA)substrates was enhanced by a factor of 6,and that of Au films was improved by a factor of 10.Moreover,Au films deposited on modified PMMA substrates could withstand 30 days of liquid immersion,and no cracks and delamination were observed.To understand the mechanism for the adhesion enhancement,the PMMA surface characteristics in physics and chemistry before and after the UV-ozone modification were studied with contact angle measurements,attenuated total reflection Fourier-transform infrared spectrometry(ATR-FTIR)and atomic force microscopy(AFM).Detailed characterization results indicate that the significant adhesion enhancement is attributed to two aspects.On the one hand,the photolysis and photooxidation of the PMMA surface caused by the UV-ozone modification result in the generation of some polar oxygen-containing functional groups,and these polar functional groups interact strongly with the deposited metal film,which is beneficial for the adhesion enhancement.On the other hand,due to the UV-ozone modification,numerous nanoscale hillocks and pits were formed and the surface roughness was increased.The hillocks and pits provide many mechanical anchoring sites between the metal film and the PMMA substrate,and the increased roughness enlarges the effective surface area at the metal-PMMA surface,both of which contribute to the improvement in the adhesion of metal films on PMMA substrates.To further demonstrate the UV-ozone modification method reported here,a 6-in.PMMA chip with arrays of three-electrode electrochemical sensors was fabricated.An important neurotransmitter dopamine was used as a model analyte to evaluate the electrochemical performance of the sensor.The sensor fabricated on the UV-ozone modified PMMA substrate exhibits excellent reproducibility,uniformity and long-term stability,and has a great potential for a variety of long-time and real-time electrochemical analyses.In addition,by taking advantage of the drawback that metal films exbit a poor adhesion to PMMA substrates,a novel tape-based direct transfer method for fabricating flexible electrodes was put forward.To improve the yield of the transfer process,two PMMA surface treatments were studied.Finally,a taped-based flexible electrochemial sensor was fabricated by this direct transfer method,and the performance of the sensor was preliminarily tested.