Inkjet printed graphene as an interconnect for optoelectronic devices
A comparative study of inkjet-printed graphene films (IPGFs) with mechanically exfoliated, highly crystalline graphene platelets have been conducted. Inkjet-printed graphene films were obtained using liquid-phase exfoliation of bulk graphite, while crystalline, residue-free graphene was obtained from highly-oriented-pyrolytic-graphite (HOPG) using mechanical exfoliation through a viscoelastic transfer process. Optical absorption spectroscopy was used to infer the density of platelets in the graphene-based ink dispersion. Temperature-dependent Raman spectroscopy revealed the presence of the defect D-band peak in the IPGFs, which was not observed in the HOPG-based samples at room temperature, confirming the higher crystalline quality of the latter. Full-width-half-maximum (FWHM) of the G-band was measured to be ~ 26.4 cm−1 for IPGFs compared to ~ 18.6 cm−1 for HOPG-based samples. Moreover, the D-band intensity decreased as temperature increased up to 600 °C for IPGFs, suggesting the possibility of annealing effects that may arise at these temperatures to reduce defect densities. In both HOPG-based samples and IPGF patterns, the G-band and G′-band red-shifted with increasing temperature which can be attributed to elongation of the C–C bond due to thermal expansion, resulting in the anharmonic coupling of the phonon modes. Moreover, a power study demonstrated the IPGFs even with printing passes as low as 10 passes, dissipate ~ 1.03 mW of power at 1 V, which was similar to the power dissipated in the HOPG samples (~ 1.05 mW at 1 V) suggesting good adherence of graphene platelets and high conductivity in IPGFs, which suggests that the inks are favorable for use in interconnects for device platforms in printed electronics. A natural follow-on from this work, was the use of the conductive graphene inks as an interconnect in devices, specifically WS2-based photodetectors, where prototype devices were fabricated and characterized that are also discussed here.
We greatly appreciate the support received from the Army Research Office (grant number W911NF-15-1-0425) that enabled us to pursue this work. A.B.K. also acknowledges support from the PACCAR Technology Institute at the University of North Texas.