ABSTRACT
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 (ft) in graphene transistors [2]; however, there are minimal reports that also achieve GHz maximum oscillation frequency (fmax) [6]. Achieving power gain requires high-performance device characteristics in addition to well-designed device layouts in low-loss configurations. Achieving both high-frequency ft and fmax 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 ft and fmax 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 ft and fmax are consistent with bias conditions that correspond to increased gm and Id. Simple, small-signal RF models are used to extract the small-signal capacitances and to determine the performance-limiting factors.
