Research progress of graphene radio frequency devices

Abstract

Graphene, the first realized two-dimensional material, has received much attention in electronic applications in recent years. With ultra-high carrier mobility and one atom thick structure, graphene becomes a promising semiconductor candidate for solving the problem of short channel effect in nanoscale metal-oxide-semiconductor field-effect transistor (MOSFET), and exploring its applications in radio frequency devices. How to develop the advantages of graphene transistor in radio frequency is an attractive research area. The first step is to obtain high quality graphene material. In this article we summarize the graphene growth methods commonly used in electronic field, including chemical vapor deposition on metal substrates and epitaxial method on wide bandgap semiconductor and insulator substrates. Another key factor to improve graphene transistor performance is to carefully design the device structure and process flow. Multi-finger gate and T-shaped gate are widely used in MOSFET. These two structures can significantly reduce gate resistance, and result in a better radio frequency performance. Inverted process is introduced for graphene FET fabrication, which is compatible with silicon-based back-end-of-line technology. It can reduce the damages to graphene during fabrication. Another improved self-aligned gate deposition process can lead to a good gate coupling and less parasitic parameters. These newly developed process play a prominent part in increasing the cut-off frequency and maximum oscillation frequency of graphene radio frequency devices. In addition, single crystal graphene is helpful in eliminating carriers scattering and improving the radio frequency properties of graphene transistor. So far, the highest cut-off frequency of graphene transistor reaches over 300 GHz by a few groups, but the maximum oscillation frequency remains low. Record-high maximum oscillation frequency is 200 GHz when gate length is 60 nm. Further improvement of maximum oscillation frequency needs to be tried out. Several graphene radio frequency circuits are also discussed in the paper. Some of the circuits have similar structures to silicon-based circuits, and others are designed based on the unique property of graphene transistor, like ambipolar transport properties. The new concept circuits have simpler structures than conventional circuits. With the rapid development of graphene growth and related integrating technology, the potential to use graphene in radio frequency field will be further increased.