**5. Conclusions**

In summary, we first reported the resistance–temperature relationship for supported graphene since this relationship is critical for explaining the behavior of graphene in thermal characterization. The TCR of our sample reduced from a positive value at RT to a negative value at low temperatures, while the free-standing graphene has a negative TCR throughout the entire temperature range. The abnormal *R–T* relationship is due to the TEC mismatch between graphene and PMMA and rips in graphene appearing at lower temperature. Using the diff-TET technique, the temperature dependence of the thermal conductivity of graphene supported by a flexible substrate is obtained. Through monitoring the blueshift of the Raman peak, compressive strain is confirmed to be built up in the graphene. The large reduction in *k* as temperature decreases from RT to 275 K is partly due to the compressive strain built up in graphene. This work can provide some guidance on the design of graphene-based electrothermal devices.

**Author Contributions:** Conceptualization, J.L. and L.M.; methodology, J.L., S.X. and Y.X.; validation, J.L., P.L.; investigation, P.L. and Q.W.; data curation, Y.X.; writing—original draft preparation, J.L.; writing—review and editing, J.L. and Y.X.; visualization, P.L.; supervision, J.L. and L.M.; project administration, J.L.; funding acquisition, J.L. and L.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** Natural Science Foundation of Top Talent of SZTU 2019209; Guangdong Basic and Applied Basic Research Foundation 2020A1515110389; Project of Youth Innovative Talents in Higher Education Institutions of Guangdong 2020KQNCX069.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** Support of this work by the Natural Science Foundation of Top Talent of SZTU (2019209, to J.L.), the Guangdong Basic and Applied Basic Research Foundation (2020A1515110389, to J.L.), and the Project of Youth Innovative Talents in Higher Education Institutions of Guangdong (2020KQNCX069, to L.M.) is gratefully acknowledged.

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