Imaging, Simulation, and Electrostatic Control of Power Dissipation in Graphene Devices

Abstract

We directly image hot spot formation in functioning mono- and bilayer graphene field effect transistors (GFETs) using infrared thermal microscopy. Correlating with an electrical-thermal transport model provides insight into carrier distributions, fields, and GFET power dissipation. The hot spot corresponds to the location of minimum charge density along the GFET; by changing the applied bias, this can be shifted between electrodes or held in the middle of the channel in ambipolar transport. Interestingly, the hot spot shape bears the imprint of the density of states in mono- vs bilayer graphene. More broadly, we find that thermal imaging combined with self-consistent simulation provide a noninvasive approach for more deeply examining transport and energy dissipation in nanoscale devices.

Theoretical analysis of high-field transport in graphene on a substrate

“…As the current saturation is an important metric which determines the transistor gain, a better understanding of velocity saturation and the role of the substrate is needed to advance the development of graphene-based electronics. As in the case of other materials and devices, 24,25 high current in graphene-based devices leads to lattice heating, 26 which must also be considered in realistic models.…”

Thermal conductivity of chirality-sorted carbon nanotube networks

“…We use the Quantum Focus Instruments (QFI) InfraScope to measure the temperature of suspended SWNT films at slightly elevated background temperature, T 0 ¼ 80 C, which improves the signal-to-noise ratio. 3,13,16 Suspending the samples across the thermometry platform enables one-dimensional (1D) heat flow and sufficient mechanical support for the suspended film. 5,17 (This is in contrast to our earlier work 3,13 that used much thinner samples on SiO 2 /Si substrates, where the parasitic heat flow path into the substrate could not be avoided, preventing an analysis of the in-plane thermal conductivity.)…”

Prospective for graphene based thermal mid-infrared light emitting devices

“…Although this makes it attractive for potential use as an incandescent source, 3 thermal emission from graphene has primarily been used over the last few years as a means of probing the electronic structure of graphene transistor devices under bias. [4][5][6][7] However, there is a continuing need for the development of new infrared sources to enable low cost, intrinsically safe, portable infrared gas sensors for applications such as mine safety. Most existing infrared (IR) sensors use conventional incandescent sources which have several shortcomings including slow response time, limited wavelength range (due to the glass envelope of the source), limited lifetimes due to the fragility of the source, relatively high power consumption, and a requirement for explosion proof housings to prevent the source from igniting flammable gases that may be present.…”

“…devices, [3][4][5][6][7] and also in large area CVD devices, 8 where the thermal emission is dominated by Joule heating governed by the charge distribution along the channel. In this case given the symmetrical nature and scaling of the emission we estimate the hotspot to be approximately half-way between the source and the drain contacts.…”

“…Note that in previous studies [4][5][6] either continuous currents, or pulsed currents at a fixed frequency, have been used to heat the graphene. In our frequency measurements, the emission was measured via the spectrometer, but using a mirror rather than a diffraction grating.…”