**5. Conclusions**

Thin film flexible polymeric devices, such as a parylene-metal-parylene system, are being used for measuring nerve impulse from the central or peripheral nerve systems. Such thin-film polymeric devices provide advantages of flexibility and biocompatibility, but they are prone to delamination and carry concerns about their mechanical robustness. Therefore, metal adhesion strength to polymer substrate is important. The adhesion of metal electrodes to parylene substrate was measured by the scotch tape test. Thin and long metal electrodes was patterned on a parylene substrate in which the surface was modified by CF<sup>4</sup> plasma etch before the metal deposition through e-beam evaporation. Metal adhesion strength was estimated by measuring force-displacement curve of the scotch tape test. The estimated metal adhesion was 1.3 J/m<sup>2</sup> . Experiment result was verified through FEM modeling of the scotch tape test. The proposed modeling method provided adhesion force having good agreement with experimental result. Although a thin-film parylene-based device can provide excellent short-term reliability, there exists one significant drawback of poor adhesion to metallic layer. The failure of the metal electrode on the parylene substrate is accelerated in the wet environment of a human body and under mechanical forces originating from body movement. Therefore, mechanical integrity in conditions of a human body implant or movement will be performed to assess long-term reliability of the parylene-metal devices, along with the biocompatibility of the parylene-base neural probe.

**Author Contributions:** Conceptualization, S.S. and J.K.; methodology, H.P.; software, H.P.; validation, S.S., H.P. and J.K.; formal analysis, S.S.; investigation, H.P.; resources, H.P.; data curation, H.P.; writing—original draft preparation, S.S.; writing—review and editing, S.S.; visualization, S.S.; supervision, J.K.; project administration, J.K.; funding acquisition, J.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the convergence technology development program for bionic arm through the National Research Foundation of Korea (NRF) funded by the Ministry of Science & ICT (No. 2017M3C1B2085292). This work was also supported by the Korea Institute of Science and Technology institutional program (2E30090 and 2V08590).

**Conflicts of Interest:** The authors declare no conflict of interest.
