Graphene radio frequency receiver integrated circuit.

Graphene has attracted much interest as a future channel material in radio frequency electronics because of its superior electrical properties. Fabrication of a graphene integrated circuit without significantly degrading transistor performance has proven to be challenging, posing one of the major bottlenecks to compete with existing technologies. Here we present a fabrication method fully preserving graphene transistor quality, demonstrated with the implementation of a high-performance three-stage graphene integrated circuit. The circuit operates as a radio frequency receiver performing signal amplification, filtering and downconversion mixing. All circuit components are integrated into 0.6 mm(2) area and fabricated on 200 mm silicon wafers, showing the unprecedented graphene circuit complexity and silicon complementary metal-oxide-semiconductor process compatibility. The demonstrated circuit performance allow us to use graphene integrated circuit to perform practical wireless communication functions, receiving and restoring digital text transmitted on a 4.3-GHz carrier signal.

Current saturation in submicrometer graphene transistors with thin gate dielectric: experiment, simulation, and theory.

Recently, graphene field-effect transistors (FET) with cutoff frequencies (f(T)) between 100 and 300 GHz have been reported; however, the devices showed very weak drain current saturation, leading to an undesirably high output conductance (g(ds)= dI(ds)/dV(ds)). A crucial figure-of-merit for analog/RF transistors is the intrinsic voltage gain (g(m)/g(ds)) which requires both high g(m) (primary component of f(T)) and low g(ds). Obtaining current saturation has become one of the key challenges in graphene device design. In this work, we study theoretically the influence of the dielectric thickness on the output characteristics of graphene FETs by using a surface-potential-based device model. We also experimentally demonstrate that by employing a very thin gate dielectric (equivalent oxide thickness less than 2 nm), full drain current saturation can be obtained for large-scale chemical vapor deposition graphene FETs with short channels. In addition to showing intrinsic voltage gain (as high as 34) that is comparable to commercial semiconductor FETs with bandgaps, we also demonstrate high frequency AC voltage gain and S21 power gain from s-parameter measurements.

State-of-the-art graphene high-frequency electronics.

High-performance graphene transistors for radio frequency applications have received much attention and significant progress has been achieved. However, devices based on large-area synthetic graphene, which have direct technological relevance, are still typically outperformed by those based on mechanically exfoliated graphene. Here, we report devices with intrinsic cutoff frequency above 300 GHz, based on both wafer-scale CVD grown graphene and epitaxial graphene on SiC, thus surpassing previous records on any graphene material. We also demonstrate devices with optimized architecture exhibiting voltage and power gains reaching 20 dB and a wafer-scale integrated graphene amplifier circuit with voltage amplification.

High-frequency graphene voltage amplifier.

While graphene transistors have proven capable of delivering gigahertz-range cutoff frequencies, applying the devices to RF circuits has been largely hindered by the lack of current saturation in the zero band gap graphene. Herein, the first high-frequency voltage amplifier is demonstrated using large-area chemical vapor deposition grown graphene. The graphene field-effect transistor (GFET) has a 6-finger gate design with gate length of 500 nm. The graphene common-source amplifier exhibits ∼5 dB low frequency gain with the 3 dB bandwidth greater than 6 GHz. This first AC voltage gain demonstration of a GFET is attributed to the clear current saturation in the device, which is enabled by an ultrathin gate dielectric (4 nm HfO(2)) of the embedded gate structures. The device also shows extrinsic transconductance of 1.2 mS/µm at 1 V drain bias, the highest for graphene FETs using large-scale graphene reported to date.

Wafer-scale graphene integrated circuit.

A wafer-scale graphene circuit was demonstrated in which all circuit components, including graphene field-effect transistor and inductors, were monolithically integrated on a single silicon carbide wafer. The integrated circuit operates as a broadband radio-frequency mixer at frequencies up to 10 gigahertz. These graphene circuits exhibit outstanding thermal stability with little reduction in performance (less than 1 decibel) between 300 and 400 kelvin. These results open up possibilities of achieving practical graphene technology with more complex functionality and performance.

High-frequency, scaled graphene transistors on diamond-like carbon.

Owing to its high carrier mobility and saturation velocity, graphene has attracted enormous attention in recent years. In particular, high-performance graphene transistors for radio-frequency (r.f.) applications are of great interest. Synthesis of large-scale graphene sheets of high quality and at low cost has been demonstrated using chemical vapour deposition (CVD) methods. However, very few studies have been performed on the scaling behaviour of transistors made from CVD graphene for r.f. applications, which hold great potential for commercialization. Here we report the systematic study of top-gated CVD-graphene r.f. transistors with gate lengths scaled down to 40 nm, the shortest gate length demonstrated on graphene r.f. devices. The CVD graphene was grown on copper film and transferred to a wafer of diamond-like carbon. Cut-off frequencies as high as 155 GHz have been obtained for the 40-nm transistors, and the cut-off frequency was found to scale as 1/(gate length). Furthermore, we studied graphene r.f. transistors at cryogenic temperatures. Unlike conventional semiconductor devices where low-temperature performance is hampered by carrier freeze-out effects, the r.f. performance of our graphene devices exhibits little temperature dependence down to 4.3 K, providing a much larger operation window than is available for conventional devices.

Utilization of a buffered dielectric to achieve high field-effect carrier mobility in graphene transistors.

We utilize an organic polymer buffer layer between graphene and conventional gate dielectrics in top-gated graphene transistors. Unlike other insulators, this dielectric stack does not significantly degrade carrier mobility, allowing for high field-effect mobilities to be retained in top-gate operation. This is demonstrated in both two-point and four-point analysis and in the high-frequency operation of a graphene transistor. Temperature dependence of the carrier mobility suggests that phonons are the dominant scatterers in these devices.

Operation of graphene transistors at gigahertz frequencies.

Top-gated graphene transistors operating at high frequencies (gigahertz) have been fabricated and their characteristics analyzed. The measured intrinsic current gain shows an ideal 1/f frequency dependence, indicating a FET-like behavior for graphene transistors. The cutoff frequency f(T) is found to be proportional to the dc transconductance g(m) of the device, consistent with the relation f(T) = g(m)/(2piC(G)). The peak f(T) increases with a reduced gate length, and f(T) as high as 26 GHz is measured for a graphene transistor with a gate length of 150 nm. The work represents a significant step toward the realization of graphene-based electronics for high-frequency applications.