研究目的
To report on the performance of graphene field-effect transistors (GFETs) with improved extrinsic transit frequency (fT) and maximum frequency of oscillation (fmax) and their scaling behavior with gate length.
研究成果
GFETs with high extrinsic frequency values of fT = 34 GHz and fmax = 37 GHz at Lg = 0.5 μm were achieved, showing improved scaling behavior. Enhancements came from process modifications minimizing extrinsic limitations. Analysis indicates that further optimization could enable fmax above 100 GHz for gate lengths below 100 nm, making GFETs suitable for high-frequency applications.
研究不足
The GFETs are still below the performance of some Si MOSFETs at comparable gate lengths. Further optimizations are needed to compete with shorter-gate-length Si MOSFETs, such as increasing saturation velocity, reducing gate oxide thickness, gate resistance, and contact resistance in access areas.
1：Experimental Design and Method Selection:
The study involved designing and fabricating two-finger gate GFETs with modifications to the process flow to enhance fmax and fT. A small-signal equivalent circuit model was used for simulations to analyze performance.
2：Sample Selection and Data Sources:
High-quality chemical vapor deposition (CVD) graphene with a Hall mobility of up to 7000 cm2/Vs was used. Devices were fabricated on high-resistivity silicon/silicon oxide substrates with varying gate lengths and widths.
3：List of Experimental Equipment and Materials:
Equipment includes a Keithley 2612B dual-channel source meter for DC measurements and an Agilent N5230A network analyzer for AC measurements. Materials include graphene, Al2O3 for protective layers, Ti/Pd/Au for contacts, and Au for electrodes.
4：Experimental Procedures and Operational Workflow:
The fabrication process involved transferring graphene to a substrate, depositing a protective Al2O3 layer, patterning the graphene mesa and contacts using e-beam lithography and etching, depositing metal contacts, thickening the gate oxide with atomic layer deposition, and forming gate electrodes. Measurements included DC characterization and S-parameter measurements from 1 to 50 GHz.
5：Data Analysis Methods:
Data were analyzed using a drain resistance model to estimate contact resistance, mobility, and charge carrier concentration. S-parameters were used to calculate small-signal gains and frequencies. Simulations based on equivalent circuit models were performed to predict performance.
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