Microwave bolometers based on carbon nanotube thin films and CVD-grown graphene

摘要

We have investigated microwave power detection based from carbon nanotube (CNT) thin films and chemical vapor deposition (CVD) grown graphene. Our experiments indicate that power detection from the CNT devices is primarily due to bolometric mechanisms. While, power detection from the graphene devices is primarily due to signal rectification. Both enabling materials are relatively inexpensive and easily blanketed on a variety of substrates-enabling low-cost/disposable, surface-conformal power sensors for wideband spectrum sensing applications. However, it is significantly less challenging to pattern and integrate CNT thin films than it is to do the same with graphene. CNT thin film and graphene power detectors were realized by fabricating metallic Corbino disc test structures over these enabling materials. Such test structures are convenient for on-wafer characterization with ground-signal probes. The CNT devices were also evaluated with transient current-versus-voltage traces and microwave reflection spectroscopy to respectively measure thermal time constants and values of complex conductivity. The bolometer performance of these devices was gauged in terms of power detection sensitivity, noise equivalent power, and dynamic range. The measurements were performed with 915 MHz test signals and yielded sensitivities as high as 0.36 mV/mW at room temperature and 2.3 mV/mW when cooled with liquid nitrogen. Similarly, graphene Corbino disc test structures were characterized with 433.92 MHz test signals and yielded power detection sensitivities of 3.25 mV/mW (at room temperature) and 5.43 mV/mW (at 80 K). These devices feature gate control over the channel conductance, which contributed a frequency-limiting parasitic capacitance. Our investigations revealed that rectification, due to characteristic nonlinear current versus voltage behavior, was more prevalent in the graphene than bolometric detection, due to Joule heating.