# Fabrication of Stretchable Transparent Electrode by Utilizing Self-Induced Vacuum Force
## 4 Summary and Conclusions  
A curing method, using a self-induced vacuum force for the fabrication of stretchable electrodes, was proposed in this study. The self-induced vacuum force inside the electrode conductor resulted in the full penetration of the elastomer into the electrode pattern. In the tests, the complete penetration of the elastomer into the intaglio pattern was only observed for the electrode fabricated using Ketjen Black, which has superior adsorption/desorption characteristics. Furthermore, the fabrication exhibited an extraordinary transfer ratio of the electrode conductor from the silicon substrate to the elastomer. However, in the case of the electrode slurry, synthesized using Denka Black, which has low adsorption/desorption characteristics, the elastomer could not penetrate the particles completely. This result indicates that the particles contained insufficient amounts of solvent due to their poor adsorption/desorption characteristics, thereby, resulting in a weak vacuum force.  
Additionally, the effect of solvent volatility on the proposed method was investigated. Here, three solvents, namely, acetone, THF, and ethanol, were considered. When ethanol was used, which has inferior volatility compared with the others, bubble defects were observed in the cured elastomer. This is because ethanol could not evaporate completely before the elastomer was cured due to its inferior volatility. Therefore, the gasified solvent (ethanol) was captured in the elastomer. However, a clear  
Figure 14: Advantage of the selective thermal curing on a hot plate. The void caused by the trapped solvent gas is disappeared after heating the conductive-slurry region prior to elastomer substrate.  
Figure 13: Solvent gas trapped by highly viscous elastomer during the thermal curing process in a convection oven for the slurry synthesized with excessive solvent. The void in the elastomer substrate is observed only for the fabrication with excessive amount of solvent in slurry (thin-slurry case).  
transparent electrode was fabricated using acetone and THF as the solvents, because of their higher evaporation rates than that of ethanol.  
Finally, we analyzed the effect of the curing method used on the fabrication quality. The curing process was performed on a hot plate, and the resultant electrode was compared with an electrode cured in a convection oven. The full penetration of the elastomer into the particles was observed by curing the electrode on a hot plate, even with the inferior slurry using Denka Black. However, this level of fabrication quality could not be obtained by curing the elastomer in a convection oven. This result indicates that curing on a hot plate provokes the evaporation of the solvent prior to the thermosetting of the elastomer, thereby, further inducing the penetration of the elastomer. Based on these results, it can be concluded that the vacuum force is a key factor for achieving a high transfer ratio of the electrode conductor from the silicon substrate to the elastomer. Furthermore, the penetration can be enhanced by considering the adsorption/desorption characteristics of the particle, volatility of solvent, and curing method.  
Investigation, C.L., Writing-review & editing, J.S., Funding acquisition, C.B., Writing-original draft preparation, K.Y. This paper was prepared in the contributions of all authors.  
This research received no external funding.  
This work was supported by a 2016 Yeungnam University Research Grant.  
The authors declare no conflict of interest.