  This letter investigates the bias-dependent low frequency noise of single
layer graphene field-effect transistors. Noise measurements have been conducted
with electrolyte-gated graphene transistors covering a wide range of gate and
drain bias conditions for different channel lengths. A new analytical model
that accounts for the propagation of the local noise sources in the channel to
the terminal currents and voltages is proposed in this paper to investigate the
noise bias dependence. Carrier number and mobility fluctuations are considered
as the main causes of low frequency noise and the way these mechanisms
contribute to the bias dependence of the noise is analyzed in this work.
Typically, normalized low frequency noise in graphene devices has been usually
shown to follow an M-shape dependence versus gate voltage with the minimum near
the charge neutrality point (CNP). Our work reveals for the first time the
strong correlation between this gate dependence and the residual charge which
is relevant in the vicinity of this specific bias point. We discuss how charge
inhomogeneity in the graphene channel at higher drain voltages can contribute
to low frequency noise; thus, channel regions nearby the source and drain
terminals are found to dominate the total noise for gate biases close to the
CNP. The excellent agreement between the experimental data and the predictions
of the analytical model at all bias conditions confirms that the two
fundamental 1/f noise mechanisms, carrier number and mobility fluctuations,
must be considered simultaneously to properly understand the low frequency
noise in graphene FETs. The proposed analytical compact model can be easily
implemented and integrated in circuit simulators, which can be of high
importance for graphene based circuits design.
