Paper GR+EM+MS+NS+SP-FrM4
1/f Noise in Epitaxial Graphene Field Effect Transistors using Al₂O₃ and HfO₂ High k -Dielectrics

Friday, November 1, 2013, 9:20 am, Room 101 A

It has been shown that graphene has substantially low 1/f noise, a characteristic potentially advantageous for electronic sensor applications. Most reports have been from studies of devices on flakes, which lack the desirable scale-up potential for practical applications. Here, we report the 1/f noise behavior for gated graphene devices formed on SiC substrates using low pressure sublimation (LPS) of Si in an Ar ambient. In general, we found that the 1/f characteristics of LPS graphene to be similar to or superior to all prior studies.

The LPS graphene was synthesized in an Aixtron VP508 reactor on ~2.5 cm² nominally on-axis 6H(0001) semi-insulating substrates from the same boule. The process was designed to produce nominally 1 ML of graphene on the terraces of the samples; the samples should be identical as the synthesis process has been demonstrated to be uniform and run-to-run reproducible. Samples were processed using typical photolithographic methods before dielectric deposition; a Ti/Au stack was used for ohmic and gate contacts. High-k dielectric deposition was accomplished via a two-step process that includes functionalization of graphene by Fluorine followed by atomic layer deposition (ALD) of 20 nm thick Al₂O₃ and HfO₂. Previously, we have shown that F-functionalization results in pinhole-free coverage of dielectrics and the films possess Dirac voltage shifts of 0.5V and 1.5V and dielectric constants of 9 and 18, for Al₂O₃ and HfO₂, respectively. The 1/f noise data was acquired using a fast Fourier transform analyzer coupled with low noise amplifier and was averaged over 5 different samples on the same substrate for each oxide case; V_GS was controlled forward and reverse in the range -3 to 2V.

The 1/f noise magnitude, S_i/I²,was found to scale with channel dimension and was comparable or smaller in magnitude to reports by others on graphene flakes thus suggesting that the underlying SiC and interface layer does not add an appreciable number of noise generation sites. Comparing samples with a gate oxide to those processed identically but without oxide shows the noise magnitude was similar implying that the F-functionalization-based ALD process does not degrade the graphene channel by inducing interfacial traps. For the gated samples, the composition of the gate oxide had a minor effect on the channel noise magnitude relative to non-gated samples. For HfO₂ devices having an oxide surface coverage of 20 x 4 m m², S_i/I²=4x10^-11 Hz^-1 (at 20 Hz). For gated measurements, the 1/f noise magnitude were not flat but showed a slight (20%) dependence on V_GS. Both oxides showed noise hysteresis (~15%) although it was more pronounced for the HfO₂ devices.