研究目的
To improve the conversion loss of resistive mixers using Bernal-stacked bilayer graphene by increasing the on/off ratio and demonstrating high-temperature stability.
研究成果
The Bernal-stacked bilayer graphene FET mixers achieve a record low conversion loss of 12.7 dB at 2 GHz due to high on/off ratios enabled by dual-gate control. They exhibit excellent thermal stability with minimal degradation up to 380 K, making them promising for low-loss and high-temperature RF applications. Future work could focus on optimizing materials and device structures for better performance.
研究不足
The bandgap achieved is relatively small (47 meV) due to charge carrier inhomogeneities in wide channels and thick top-gate dielectrics. The on/off ratio and conversion loss could be further improved with higher mobility graphene or thinner dielectrics to reduce LO power requirements.
1：Experimental Design and Method Selection:
The study involves designing and fabricating dual-gate Bernal-stacked bilayer graphene FETs for use as gate-pumped resistive mixers. The theoretical basis includes the relationship between conversion loss and on/off ratio, and the use of dual-gate voltage to adjust the electric displacement field. Methods include CVD growth of graphene, device fabrication using EBL and EBE, and RF characterization.
2：Sample Selection and Data Sources:
Bernal-stacked bilayer graphene films were synthesized via CVD using a copper pocket method and transferred onto SiO2/Si substrates with ALD HfSiO dielectric. Devices were fabricated on single crystalline bilayer graphene domains to avoid grain boundary scattering.
3：List of Experimental Equipment and Materials:
Equipment includes CVD system, SEM, Raman spectrometer, EBL system, EBE system, ALD system, RF test setup with filters and spectrum analyzer. Materials include copper for growth, CH4 and H2 gases, SiO2/Si substrates, HfSiO dielectric, Pd/Au for contacts, Ni/Au for gates, Al and Al2O3 for dielectrics.
4：Experimental Procedures and Operational Workflow:
Steps include graphene growth at 1070°C with H2 and CH4 flows, transfer to substrate, deposition of HfSiO dielectric, device patterning via EBL and EBE, and RF measurements using a test circuit with RF and LO signals, filters, and spectrum analyzer. Measurements were done in vacuum and at varying temperatures.
5：Data Analysis Methods:
Data analysis involved extracting on/off ratios, conversion loss from RF measurements, and using methods from previous reports for bandgap estimation and performance comparison.
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SEM
Used for imaging the transferred graphene film to observe BLG domains.
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Raman Spectrometer
Used to characterize the Bernal-stacked nature of BLG domains by analyzing intensity ratios of 2D and G peaks.
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Electron-Beam Lithography System
Used for defining the channel, source, drain contacts, and gate electrodes in device fabrication.
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Electron-Beam Evaporation System
Used for depositing metal layers such as Pd/Au for contacts and Ni/Au for gates.
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Atomic Layer Deposition System
Used for depositing high-k HfSiO and Al2O3 dielectrics.
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Spectrum Analyzer
Used in the RF test setup to measure IF output power and analyze signals.
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RF Filter
High pass and low pass filters
Used to separate RF and IF signals in the mixer test circuit, providing port isolation.
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Bias Tee
Used in the RF test setup to apply bias voltages.
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