Scaling of High-Field Transport and Localized Heating in Graphene Transistors

Micro & Nanotechnology Lab, University of Illinois, Urbana-Champaign, Illinois 61801, United States.
ACS Nano (Impact Factor: 12.88). 09/2011; 5(10):7936-44. DOI: 10.1021/nn202239y
Source: PubMed

ABSTRACT We use infrared thermal imaging and electrothermal simulations to find that localized Joule heating in graphene field-effect transistors on SiO(2) is primarily governed by device electrostatics. Hot spots become more localized (i.e., sharper) as the underlying oxide thickness is reduced, such that the average and peak device temperatures scale differently, with significant long-term reliability implications. The average temperature is proportional to oxide thickness, but the peak temperature is minimized at an oxide thickness of ∼90 nm due to competing electrostatic and thermal effects. We also find that careful comparison of high-field transport models with thermal imaging can be used to shed light on velocity saturation effects. The results shed light on optimizing heat dissipation and reliability of graphene devices and interconnects.

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    • "The simulations are based on our electro-thermal self-consistent simulator,[5] [18] adapted here for suspended graphene. Suspended devices which reach higher, saturating current and break down at lower voltage are expected to be representative of cleaner, less disordered samples. "
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    ABSTRACT: This paper reviews our recent results of high-field electrical and thermal properties of atomically thin two-dimensional materials. We show how self-heating affects velocity saturation in suspended and supported graphene. We also demonstrate that multi-valley transport must be taken into account to describe high-field transport in MoS2. At the same time we characterized thermal properties of suspended and nanoscale graphene samples over a wide range of temperatures. We uncovered the effects of edge scattering and grain boundaries on thermal transport in graphene, and showed how the thermal conductivity varies between diffusive and ballistic heat flow limits.
    SPIE Defense + Security; 06/2014
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    • "Conversely, out-of-plane heat transfer to deposited metals or dielectrics has received less attention, despite significant implications for thermal management in graphene transistors [3], interconnects [4], or as interfacial materials to heatsensitive memory materials [5]. A single previous study [6] performed time-domain thermoreflectance (TDTR) measurements on exfoliated 1-10 layer graphene flakes, transferred to SiO 2 substrates and contacted by a 2 nm Ti adhesion layer/100 nm Au optical transducer. "
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    ABSTRACT: We present an experimental study of cross-plane thermal conductance in metal-graphene-oxide stacks employing time-domain thermoreflectance (TDTR) measurements on Al/m/graphene/SiO2 structures with monolayer graphene for varying adhesion metals m. Thermal conductance G in the range of 15-60 MWm-2K-1 are found across several metals - a two-to-fourfold decrease over Al/m/SiO2 reference values, charted against metal Debye temperature over a 274-630 K range, as well as electronic work function. The results of this study help with a better understanding of the roles of electron and phonon transport in thermal conduction across graphene-metal interfaces, revealing potential trade-offs between electrical contact resistance and heat management in graphene devices.
    IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITHERM) 2014; 05/2014
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    • "Increased heat loss to the contacts is also seen as a sub-linear rise of current degradation in Fig. 2(d) for the shorter devices. Our present model numerically accounts for heat spreading into the substrate and the contacts [10], however this can also be treated to a good approximation analytically as in Ref. [13]. "
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    ABSTRACT: We use simulations to examine current saturation in sub-micron graphene transistors on SiO2/Si. We find self-heating is partly responsible for current saturation (lower output conductance), but degrades current densities >1 mA/um by up to 15%. Heating effects are reduced if the supporting insulator is thinned, or in shorter channel devices by partial heat sinking at the contacts. The transient behavior of such devices has thermal time constants of ~30-300 ns, dominated by the thickness of the supporting insulator and that of device capping layers (a behavior also expected in ultrathin body SOI transistors). The results shed important physical insight into the high-field and transient behavior of graphene transistors.
    IEEE Electron Device Letters 12/2012; 34(2):166-168. DOI:10.1109/LED.2012.2230393 · 2.75 Impact Factor
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