Thermoelectric Graphene Nano-Constrictions as Detectors of Microwave Signals

Microwave power detectors were realized using nano-constrictions fabricated from commercially-available monolayer graphene, synthesized by means of chemical vapor deposition. The graphene nano-constrictions (GNCs) were fabricated so as to shunt the inner discs to the concentric outer annuli of micrometer-scale Corbino disc test structures. The test structure was fabricated on a layer of electrically-insulating silicon dioxide situated on an electrically-conductive, doped silicon substrate. The substrate was used as a gate for controlling the Fermi level in the nano-constriction. Probe station measurements were conducted on a detector with nano-constriction dimensions of 500 nanometers in width and 5 micrometers in length. The annulus of this device was electrically grounded and held in thermal equilibrium with chassis of the probe station. Measurements obtained with a vector network analyzer provided the reflection coefficient of the detector. Using a test signal frequency of 433.92 MHz, microwave power detection characterizations, which accounted for signal reflection, revealed a peak detection sensitivity of 60.25 mV/mW. The gate voltage dependence of the power detection sensitivity was found to be strongly correlated with that of the Mott formula used for calculating the Seebeck coefficient of graphene. This observation suggests that localized microwave heating of the inner disc, relative to the temperature of the outer annulus, establishes a thermal gradient across the nano-constriction and results in a thermoelectric response that is proportional to the power level of the incident microwave signal.