Research:  Graphene Devices & Circuits

 

Impact of Edge and Bulk Disorder on the Minimum Conductivity of Graphene

Graphene has been proposed as a promising material for future nanoelectronics because of its unique electronic properties. Understanding the scaling behavior of this new nanomaterial under common experimental conditions is of critical importance for developing graphene-based nanoscale devices.

We present a comprehensive experimental and theoretical study on the influence of edge disorder and bulk disorder on the minimum conductivity of graphene ribbons, relating this disorder to a discovered strong nonmonotonic size scaling behavior featuring a peak and saturation in the minimum conductivity. This study elucidates the quantum transport mechanisms in realistic experimental graphene systems, which can be used as a guideline for designing graphene-based nanoscale devices with improved performance (see Nano. Lett., 11, 1319).

 

 

 

Graphene Logic Inverters for Digital Applications

Though graphene has recently emerged as a promising nanoelectronic material, the inherent zero band gap by nature has raised many questions in terms of graphene's usefulness for digital applications. Several recent experimental studies have demonstrated graphene based inverters, but issues remain, such as, low inverter gain (<< 1) at room temperature and a mismatch between input/output voltage levels.

We report the first room-temperature, electrostatic-doping-controlled, complementary graphene inverter with a gain > 1. In-plane graphene side gate structures are used to facilitate electrostatic doping in graphene channels, which permits the optimization of inverter gain (see DRC 2011).

 

 

 

 

Graphene Nanomesh

It is widely understood that width scaling of graphene nanoribbons leads to a modification of the electrical performance of the material and extensive efforts on creating isolated graphene ribbons with very thin widths (<15nm) have been reported. At these dimensions scattering plays a significant role in governing the electrical properties and tends to dominate any effect due to the opening of a bandgap. Recently, a mesh-like graphene structure was reported using a block copolymer lithography approach, rather than creating a single continuous ribbon.

Our approach focuses on creating large-scale, higher-fidelity, and more periodic graphene nanomeshes than are possible using the block copolymer approach. A uniform and scaled nanomesh could potentially lead to the formation of a graphene super-lattice that is useful for a variety of nanoelectronic applications.

 

 

 

Low-Noise Graphene Nano-Ribbon

In this study, we examine the ideal bandgap value in graphene devices (e.g. through size quantization in graphene nano-ribbons) to enable graphene-based, high-performance RF applications. Considering a ballistic graphene nano-ribbon low noise amplifier (GNR-LNA), including aspects like stability, gain, power dissipation and load impedance, our calculations predict a finite bandgap on the order of Eg ≈ 100meV to be ideally suited. GNR-LNAs with this bandgap, biased at an optimum operating point are ultra-fast (THz) low noise amplifiers exhibiting performance specs that show considerable advantages over state-of-the-art technologies. The optimum operating point and bandgap range is found by simulating the impact of the bandgap on several device and circuit relevant parameters including transconductance, output resistance, band-width, gain, noise figure and temperature fluctuations (see RFIC 2011 and IEEE Trans. Nanotechnol., 10, 1093).