First demonstration of gate voltage-less chemical vapour deposition graphene for non-vacuum thermoelectric study

Graphene has been well studied to be an excellent thermoelectric (TE) material of choice for thermal detection. It is widely considered a key enabler for next-in-class infrared (IR) detectors given its superb carrier mobility, sensitivities and broadband absorption in far-IR range surpassing that of current thermopiles. Normally, TE studies are conducted using graphene exfoliated from graphite crystal. It is then transferred onto Si/SiO2 substrate and fabricated into Hall bar configuration with microheater at one end. A gate voltage (Vg) is passed through the substrate and the response is examined in vacuum condition. By tuning the Vg, one can possibly obtain different thermoelectric power (TEP) values. The challenge is to maintain optimum Vg for the TE device to function which requires higher power consumption. This translate to the need for additional power supply. In this report, we proposed CVDG as TE material. Typically, CVDG are synthesized on Cu film and eventually transferred onto Si/SiO2 substrate. The benefit of CVDG is that it is large area, relatively inexpensive and does not require a Vg with associated circuitry. For the first time, CVDG system was extended to nonvacuum condition to simulate open detector system where detector is exposed to sensing environment. Average TEP was measured to be 168μV/K at 298K. Moreover, CVDG is tested to be stable in air over several months with little or no decrease in performance. A comprehensive characterization between exfoliated and CVDG will be presented. In addition, measurement results for vacuum and non-vacuum detector mode will be compared as well.