CHEMICAL-FREE METAL–PDMS THERMAL BONDING IN FLEXIBLE ELECTRODE FABRICATION
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The objective of this research is to introduce a chemical-free metal Polydimethylsiloxane (PDMS) thermal bonding (CFMPTB) in the flexible electrode fabrication by transferring metal onto a PDMS substrate. PDMS is an excellent biocompatible and elastic material which is widely used in the biomedical engineering and the wearable and implantable devices. However, the use of PDMS in the wearable and implantable devices is limited due to the poor adhesion between metal and PDMS. The current studies to overcome the limitation require extra treatment which increases the complication of the process and the toxicity by surface modification.I recently discovered a simple process of enhancing the adhesion strength between metal and PDMs without any extra treatments, which is CFMPTB. It is a thermally induced process and compatible with various metals (such as copper, silver and gold). CFMPTB enhances the adhesion strength by creating metal oxide bonds between metal (M) and PDMS (M-O-Si bonds). CFMPTB is the same process as the PDMS curing process with a modified curing condition. The modified factors in the conditions are the amount of the curing agent, the baking temperature and the baking time. The effect of these factors on the adhesion strength was studied to determine the optimum condition for the flexible electrode fabrication.Next, as a proof of the concept, the adhesion strength by the standard PDMS curing condition and CFMPTB were compared by two adhesion tests; the cross-hatch adhesion test, and the adhesion ratio test. This proved that no strong adhesion was generated by the standard PDMS curing condition but CFMPTB had significantly enhanced the adhesion between metal and PDMS. As a result, CFTMPB can transfer an electrode structure onto PDMS to create a flexible electrode.As a demonstration of the flexible electrode fabrication, several possible applications of CFMPTB were studied; a flexible capacitive pressure sensor and a dry flexible bio-potential electrode. Furthermore, as a suggestion of possible applications, a fabrication process of a porous PDMS membrane with an electrode integration was introduced. In conclusion, CFMPTB can enhance the adhesion between metal and PDMS in the PDMS curing process by modifying the condition without extra treatment which is compatible with various metals. Moreover, it can be used in the flexible electrode fabrication for developing the wearable and implantable devices.