Suppressing 1/f Noise in Graphene Transistors By Area Scaling

Flicker noise or 1/f noise refers to processes in which the power spectral density (PSD) is inversely proportional to frequency and is typically the dominant noise source in transistors at low frequency. We report our work on measurements of unprecedentedly low 1/f noise in graphene field effect transistors, which we attribute to large device area. Large area graphene grown by chemical vapor deposition (CVD) has potential for a variety of applications including biomolecular sensors, bolometric photodetectors and ion sensitive field effect transistors (ISFET) [1]. For all these applications, low-frequency 1/f noise is found to be the dominant factor that determines sensor resolution limits. Hence, the absolute value of 1/f noise PSD serves as a crucial performance metric for graphene sensor applications. Previous studies of 1/f noise in graphene devices has been performed using both CVD grown graphene and exfoliated graphene. Balandin et al [2] has studied 1/f noise in exfoliated graphene and how it varies with substrate and charge carrier concentration. Karnatak et al [3] has shown that contact resistance can play a dominant role in 1/f noise. To date, there has been no experimental study of 1/f as the graphene channel is scaled up to mm lengths. We report here our work on 1/f noise measurement of graphene field effect transistors with varying channel and contact geometries. In our experiments, CVD grown graphene on copper was transferred onto fused silica coated with 100 nm of parylene using a standard wet transfer process. Parylene was used as an interface between the graphene and fused silica, which has been shown by Fakih et al [1] to reduce both drift and hysteresis in graphene ISFETs. The transferred graphene was processed with two photolithography steps to fabricate devices with areas ranging from 12µm2 to 36mm2. Electrical contact to the graphene was made directly with Au. The 1/f noise was measured by first applying a dc bias using a low noise lithium-ion battery, and the generated voltage fluctuations were then measured using a low noise voltage pre-amplifier and a 24-bit digitizer. The voltage PSD of 1/f noise in graphene, will typically have the form of SV=Vo 2K/f. Where Vo is the dc voltage applied across the device, f is the frequency, and K is the unitless noise constant. K is experimentally approximated to be (1/N)∑nSVnfn/Vo 2, where SVn is the voltage PSD measured at n different frequencies fn. The work from Balandin et al [2] demonstrates typical K values of 10-8, and work from Karnatak et al [3] shows values as low as 10-9. Our devices have unprecedented low measured K values of 10-14, which we attribute to the large device area of 36 mm2. Our results experimentally demonstrate that the noise parameter can be decreased by orders of magnitude by working with large area devices. Our work suggests that for graphene based sensor applications, large device area is favourable for improved sensor resolution. References: 1. Fakih, I., et al., High resolution potassium sensing with large-area graphene field-effect transistors. Sensors and Actuators B: Chemical, 2019. 291: p. 89-95. 2. Balandin, A.A., Low-frequency 1/f noise in graphene devices. Nature nanotechnology, 2013. 8(8): p. 549-55. 3. Karnatak, P., et al., Current crowding mediated large contact noise in graphene field-effect transistors. Nature Communications, 2016. 7(1).

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