MIcrowave GRAphene QUantum ELectronics – MIGRAQUEL

Two demonstrators will be realized that exploit the unique microwave properties of graphene. The first one is a graphene transistor used as a nanosecond (GHz) single electron pulse detector. It uses high mobility mono or bi-layer graphene foils or nano-ribbons coupled to top gates with ultrathin oxide in a stacked-gate transistor architecture. The GHz bandwidth would correspond to an improvement by a factor of ten in the speed of single electron detectors, and provides the possibility of single shot experiments in the quantum regime which is an emerging new field of physics. The second is an attempt to overcome Klein Tunneling which is responsible for the poor ON-OFF switching of graphene transistors. Two innovative solutions to produce local tunable tunnel barriers in single-layer graphene will be investigated that are detailed in the proposal. Another originality is to include optical characterization, with micro-Raman experiment to provide in situ diagnosis of out-of-equilibrium phonon populations in complement to the electronic temperature deduced from noise thermometry. A unique RF-optics cryogenic setup will be developed with high resolution both in the optic and RF transport sides. This approach will bring new clues on the dissipation process at work in actual devices. The setup will be well suited for preliminary investigations in ultrafast photo-detection which is another promising field of applications for graphene. Phenomena involve electron-phonon interaction which is known to be the main scattering mechanism leading to current saturation and noise in biased devices. Finally, the project will give a significant impetus to the French graphene community in the intense international competition in the field, especially with the US groups. The angle of attack with microwave dynamical properties is likely to carry applications which may be relevant for the RF transistor market of space based radars and high-bandwidth telecommunications and mobile platforms.

1) production of high mobility graphene on SiC films for microwave transistors.

2) demonstration of transistors with a 80 GHz transit frequency using exfoliated graphene on saphire.

3) demonstration of flexible GHz transistors derived from solution-based single-layer graphene.

4) theoretical description and similation of two new HF transistors principles : i) graphene nanomesh transistor for bandgap engineering ii) Dirac fermion reflector, using saw-tooth gate geometries, to realize tunable electrostatic barriers.

5) Investigation of electron cooling by acoustic phonons: ordianry and extra-ordinary phonon collisions.

1) The availability of high mobility graphene on SiC films will allow to fabricate conventional microwave transistors with state of the art transit frequencies.
2) The fabrication of nanomesh transistors will allow to improve the SOA in terms of maximumu amplification frequency.
3) The use of graphene on boron nitride and local, saw-tooth shaped, back gates will allow to demonstrate graphene reflectors proposed in the projet.

28 scientific papers in international journals
29 oral présentations in international conferences or workshops.

The Microwave Graphene Quantum Electronic (MIGRAQUEL) project investigates the new possibilities of graphene in the field of ultra-high-speed, low-power, low-noise field effect transistors for RF/mm-wave circuits. Expectations rely on the high mobility, Fermi velocity, current carrying capability and thermal conductivity of graphene. The small and controllable number of conducting channels and the ultrathin geometry of top-gated transistors gives access to a regime where conductance, transconductance and gate capacitance approach the "quantum limit". Carbon based devices are therefore also model systems for basic quantum mesoscopic physics. The new concept that explains the unique properties of graphene is that of Dirac Fermions (DFs), associated with the honeycomb lattice, characterized by an enhanced forward scattering due the Klein tunneling. Well documented at dc, DFs can be used to realize innovative RF/microwave electronic devices.
The MIGRAQUEL program proposes a unique global approach integrating high mobility graphene film production, ultimate nano-device fabrication, magneto-transport, RF and microwave-frequency scattering and noise characterization as well as their theoretical modeling. High mobility sample production will rely on exfoliation, CVD growth and SiC graphitization techniques on various substrates, including flexible films, adapted for microwave electronics. A variety of ultimate microwave device design with top gates on utltrathin oxide will be realized using etching and e-beam nanolithography. Device simulations will rely on a non equilibrium Green's function technique to calculate microwave device characteristics and noise using realistic device parameters. The efficient feedback to experiment will help optimizing sample design and fabrication with the objective of producing W-band Low Noise Amplifiers with a transit frequency of 100 GHz and a 1dB noise.
Two demonstrators will be realized that exploit the unique microwave properties of graphene. The first one is a graphene transistor used as a nanosecond (GHz) single electron pulse detector. It uses high mobility mono or bi-layer graphene foils or nano-ribbons coupled to top gates with ultrathin oxide in a stacked-gate transistor architecture. The GHz bandwidth would correspond to an improvement by a factor of ten in the speed of single electron detectors, and provides the possibility of single shot experiments in the quantum regime which is an emerging new field of physics. The second is an attempt to overcome Klein Tunneling which is responsible for the poor ON-OFF switching of graphene transistors. Two very innovative solutions to produce local tunable tunnel barriers in single-layer graphene will be investigated that are detailed in the proposal.
Another originality of MIGRAQUEL is to include optical characterization, in particular micro-Raman experiment to provide in situ diagnosis of out-of-equilibrium phonon populations in complement to the electronic temperature deduced from noise thermometry. A unique RF-optics cryogenic probe station setup will be developed with high resolution both in the optic and RF transport sides. This global approach will bring new clues on the dissipation process at work in actual devices. The setup will be well suited for preliminary investigations in ultrafast photo-detection which is another promising field of applications for graphene. Phenomena involve electron-phonon interaction which is known to be the main scattering mechanism leading to current saturation and noise in biased devices.
Finally, the MIGRAQUEL project will give a significant impetus to the French graphene community in the intense international competition in the field, especially with the US groups. The angle of attack with microwave dynamical properties is likely to carry innovative applications which may be relevant for the RF transistor market of space based radars and high-bandwidth telecommunications and mobile platforms.