| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
CC7, Frequency Domain THz Characterization of Graphene |
| Author(s) |
Berardi Sensale-Rodriguez, Rusen Yan, Michelle Kelly, Tian Fang, Kristof Tahy, Debdeep Jena, Lei Liu, Huili Grace Xing |
| On-Site Speaker (Planned) |
Berardi Sensale-Rodriguez |
| Abstract Scope |
Graphene has been intensely investigated for various electronic applications such as flexible electronics, RF amplifiers, transparent conductors, and potential replacement of Si channel in high performance MOSFETs. There are also a few reports and proposals on THz lasers and photodetectors based on graphene. However, to date only photodetectors and mode-locked ultrafast lasers have been demonstrated in the lab. In this work we present frequency domain characterization of large area graphene (single-layer and double-layer) over the THz range and demonstrate that THz absorption by graphene can be electrically tuned. Based on this observation, broadband and tunable attenuators for THz quasi-optical systems can be designed and fabricated. In this study we aim to discover applications for graphene in THz communication systems. Single-layer graphene was grown using the copper-catalyzed chemical vapor deposition (CVD) approach recently developed by Li et al in a quartz tube furnace using CH4 and H2. Following the growth, graphene sheets of over 1 cm2 are transferred to the host substrates (in this study quartz or SiO2/p+silicon) using PMMA and wet etch methods; double-layer graphene sheets were obtained by transferring twice the single-layer CVD graphene. For the single-layer graphene sample transferred onto SiO2/Si substrate, top and bottom ring contacts were fabricated to contact graphene and p+Si respectively. Transmission was measured in frequency domain using a VDI (Virginia Diodes, Inc.) THz source that produces CW radiation in the 570-630 GHz frequency band. THz radiation was coupled by a four off-axis parabolic mirror setup into a zero bias Schottky diode broadband detector. Samples were scanned by a 2D positioning stage, and then a 2D transmission attenuation image was generated. Using this technique, graphene on quartz substrate samples were imaged. It was found a single layer graphene introduces an attenuation of 0.5 - 1.0 dB while the double-layer graphene leads to another 0.5 dB of attenuation. Though not yet tested, we expect a linear increase in attenuation with respect to the number of graphene layers. From the relation between graphene sheet conductivity and transmission ratio of the graphene/substrate sample to that of the substrate, local sheet conductivity of a single layer graphene was found to range between 0.4 - 0.9 mS. THz attenuation can be tuned by tuning the graphene conductivity. To this end, we applied DC voltage across the single layer CVD graphene and SiO2/Si substrate while monitoring the THz transmission as a function of this voltage. It was found that the transmission clearly changes with the applied voltage (by sweeping it from -35 to +35 V at 600 GHz, attenuation changes by 0.25 dB). The above observations indicate graphene can be potentially used to fabricate precision and tunable THz attenuators. |
| Proceedings Inclusion? |
Undecided |