We report on our progress and development of high speed flexible graphene field effect transistors (GFETs) with high electron and hole mobilities (~3000 cm2/V·s), and intrinsic transit frequency in the microwave GHz regime. We also describe the design and fabrication of flexible graphene based radio frequency system. This RF communication system consists of graphite patch antenna at 2.4 GHz, graphene based frequency translation block (frequency doubler and AM demodulator) and graphene speaker. The communication blocks are utilized to demonstrate graphene based amplitude modulated (AM) radio receiver operating at 2.4 GHz.

High-frequency performance of graphene field-effect transistors (GFETs) has been limited largely by parasitic resistances, including contact resistance (RC) and access resistance (RA). Measurement of short-channel (500 nm) GFETs with short (200 nm) spin-on-doped source/drain access regions reveals negligible change in transit frequency (fT) after doping, as compared to ∼23% fT improvement for similarly sized undoped GFETs measured at low temperature, underscoring the impact of RC on high-frequency performance. DC measurements of undoped/doped short and long-channel GFETs highlight the increasing impact of RA for larger GFETs. Additionally, parasitic capacitances were minimized by device fabrication using graphene transferred onto low-capacitance quartz substrates.

In this paper we report on the simulation, fabrication, and characterization of planar graphite antennas on flexible polyimide (kapton) substrate, operating in the ISM band. The patch antennas are constructed from pyrolytic graphite sheets adhered to the flexible substrate, and designed to resonate at 2.4 GHz. Simulation and measurements show that the antenna is relatively immune to changes in impedance match induced by bending, although the gain is adversely affected by several dB. For the first time, single-port convex bending measurement is performed on these graphite antennas, revealing only minimal change in resonant frequency as the antenna is bent, and little to no memory effect from the induced curvature. We conclude by showing the possibility of fabrication of an all carbon-based RF receiver.

Graphene transistors using hexagonal boron nitride as the gate dielectric are implemented on mechanically flexible polyimide films. Current saturation is observed for the first time in graphene transistors on a plastic substrate. An atomically smooth insulating surface is achieved with the proposed capture-release process and two-step annealing process, resulting in subnanometer surface roughness. The device shows strong electrical performance: Extracted mobility exceeds 2300 cm2/V·s for both electron and hole transport, and drive current is over 300 μS/μm. This transport symmetry affords frequency doublers with high spectral purity and a conversion gain of - 29.5 dB and output power of -22.2 dBm, representing the highest performance for graphene transistors on flexible substrates.

The graphene field-effect transistor has generated attention in recent years for its potential for fast electronics, with theoretical transit frequencies in the THz range, and fabricated devices operating at hundreds of GHz. Previously published models are based on numerical iteration or neglect the equilibrium quantum capacitance, leading to reduced accuracy around the Dirac point. We have derived a compact, physicsbased closed-form equation for drain-source current that can be implemented in a circuit level simulator. This model demonstrates strong agreement with both DC and RF measurements, as well as linear and non-linear circuits. The model also enables simulation of circuits to enable design of topologies that take advantage of the unique properties of the graphene transistor. The model also affords parameter variation analyses to quantify the adverse effects of non-idealities such as contact resistance. Finally, we have developed a quantum capacitance limited model to benchmark the performance of realistic devices against the ideal quantum capacitance limit, and elucidate the effects of oxide scaling.

Despite the widespread interest in graphene electronics over the past decade, high-performance graphene field-effect transistors (GFETs) on flexible substrates have been rarely achieved, even though this atomic sheet is widely understood to have greater prospects for flexible electronic systems. In this article, we report detailed studies on the electrical and mechanical properties of vapor synthesized high-quality monolayer graphene integrated onto flexible polyimide substrates. Flexible graphene transistors with high-k dielectric afforded intrinsic gain, maximum carrier mobilities of 3900 cm(2)/V·s, and importantly, 25 GHz cutoff frequency, which is more than a factor of 2.5 times higher than prior results. Mechanical studies reveal robust transistor performance under repeated bending, down to 0.7 mm bending radius, whose tensile strain is a factor of 2-5 times higher than in prior studies. In addition, integration of functional coatings such as highly hydrophobic fluoropolymers combined with the self-passivation properties of the polyimide substrate provides water-resistant protection without compromising flexibility, which is an important advancement for the realization of future robust flexible systems based on graphene.

The authors report a flexible transistors based on 2D atomic sheets such as graphene and MoS2 that features record electrical-mechanical properties and offer the highest prospects for realizing Si-CMOS like performance on arbitrary plastic substrates. Graphene is ideal for analog RF devices while MoS2 is ideal for digital low-power FETs.

Highly bendable graphene field-effect transistors are fabricated on polyimide films. The device offers robust performance against various conditions including immersion in liquids, and dynamic loading tests, which are hazardous to conventional electronics. Bendability of the sample is tested with the bending radius of down to 1.3 mm; the devices remain fully functional with less than 8.7% reduction and no reduction in the electron and hole mobility after repeated bending tests, respectively. Multi-finger electrodes are implemented on flexible substrates to enhance its current drive. Silicon-nitride passivation offers efficient chemical protection over diverse liquids and robust mechanical protection against impacts.

Highly bendable graphene field-effect transistors are fabricated on polyimide films. The device offers robust performance against various conditions including immersion in liquids, and dynamic loading tests, which are hazardous to conventional electronics. Bendability of the sample is tested with the bending radius of down to 1.3 mm; the devices remain fully functional with less than 8.7% reduction and no reduction in the electron and hole mobility after repeated bending tests, respectively. Multi-finger electrodes are implemented on flexible substrates to enhance its current drive. Silicon-nitride passivation offers efficient chemical protection over diverse liquids and robust mechanical protection against impacts.

We report a 500nm graphene field-effect transistor operating at the Dirac point for frequency doubling with maximum output power of −23dBm and a record bandwidth of 3GHz, 2× higher than the state-of-the-art. The experimental device exceeds its ft and fmax by about 50%. Contact resistance degrades the performance of the experimental GFET. In the limit of negligible non-idealities and maximum gate capacitance, the conversion gain approaches lossless frequency doubling. The record performance of the graphene doubler is enabled by the growth of high-quality graphene affording carrier mobilities as high as 5000cm2/V-s and 2200cm2/V-s on smooth quartz and flexible substrates respectively.

We demonstrate a 500-nm graphene frequency doubler with a record 3-GHz bandwidth, exceeding the device transit frequency by 50%, a previously unobserved result in graphene, indicating that graphene multiplier devices might be useful beyond their transit frequency. The maximum conversion gain of graphene ambipolar frequency doublers is determined to approach a near lossless value in the quantum capacitance limit. In addition, the experimental performance of graphene transistor frequency detectors is demonstrated, showing responsivity of 25.2 μA/μW. The high-frequency performance of these gigahertz devices is enabled by top-gate device fabrication using synthesized graphene transferred onto low capacitance, atomically smooth quartz substrates, affording carrier mobilities as high as 5000 cm 2 /V ·s.

We explore the ultimate behavior of the graphene transistor in the quantum capacitance limit. The quantum capacitance formulation allows for an exactly solvable model, and the ideal assumptions provide an upper bound on performance, including peak currents of 1 mA/mu m with mobilities as low as 2000 cm(2)/V s for channel length of 1 mu m, as well as linearly increasing transconductance not observed in conventional transistors. A negative differential resistance is predicted under certain conditions, with a maximum peak-to-valley-current ratio of 4. Finally, the effects of oxide scaling are elucidated and the oxide capacitances required for quantum capacitance limited behavior are quantified. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739943]

We report graphene field-effect transistors on hexagonal boron nitride, high-k, and polymeric films featuring state-of-the-art electrical and mechanical properties on flexible substrates. The record electrical performance includes the highest ON current (~0.3mA/μm), the first demonstration of current saturation on flexible films and intrinsic gain, and the highest conversion gain flexible graphene frequency doubler. Extrinsic transit frequency of 2.23GHz, and maximum frequency of 1.15GHz are also achieved. In addition, robust electrical response down to 0.7mm mechanical bending radius is realized.

A highly bendable, high mobility graphene field-effect transistor with embedded-gate structure is fabricated on commercial polyimide films. Multi-finger configuration consisting of 10 and 18 fingers is used to increase the current drivability. Bendability measurements for the device show that it is fully functional at the bending radius of down to 1.3mm. The shift in the dirac point is less than 0.6V, which is the result from the high uniformity of the grown graphene films and the simplified process minimizing the exposure of graphene to chemicals and the risk of chemical contamination. Plasma enhanced chemical vapor deposited silicon nitride is used as a capping layer to prevent contamination of the device from environments and provides robust protection over exposure to liquids.

Interest in graphene device physics and technology has been growing rapidly, especially for very high frequency transistor applications. However, the predicted intrinsic performance has not been fully realized due to impurity and parasitic issues introduced in device fabrication. Through a self-consistent model, we show that the normalized contact resistance has an exponentially detrimental impact on the peak transconductance, which is a defining transistor parameter. In addition, we reveal that very high current-gate voltage linearity or input invariant transconductance can be achieved in the limit of negligible contact resistances, a desirable feature for linear electronic systems.