Nanotransistors using graphene interfaced with advanced dielectrics for high-speed communication

Graphene is emerging as a wonder material for future radiofrequency electronics and is mechanically compatible with the ubiquitous integration on arbitrary substrates-rigid [1,2], flexible [3], stretchable [4], and transparent [5]. Several studies have been performed demonstrating GHz unity-gain frequency (f_t) in graphene transistors [2]; however, there are minimal reports that also achieve GHz maximum oscillation frequency (f_max) [6]. Achieving power gain requires high-performance device characteristics in addition to well-designed device layouts in low-loss configurations. Achieving both high-frequency f_t and f_max is critical for the realization of graphene-based advanced active radio-frequency (RF) circuits such as amplifiers and oscillators. In this chapter, transistors are constructed and examined based on chemical vapor deposited (CVD) graphene. Transistors incorporate scaled (~10 nm) plasma-assisted atomic-layer-deposited (ALD) gate dielectrics and use an RF layout designed for targeting improved RF performance. An extrinsic f_t and f_max in the GHz regime are both achieved under suitable bias conditions that favor large transconductance and low output resistance due to the onset of an observed saturation-like behavior. The dependence of the gain on the applied gate and drain voltages is measured and examined. Increasing f_t and f_max are consistent with bias conditions that correspond to increased g_m and I_d. Simple, small-signal RF models are used to extract the small-signal capacitances and to determine the performance-limiting factors.