Abstract
The miniaturization of electronic components and the excessive heating produced by the increased power densities in these small devices has heightened the need for on-chip cooling solutions. This has prompted a search for materials with large thermoelectric power factor and thermal conductivity that could be integrated in active thermoelectric coolers. Here, we report record thermoelectric power factors achieved in graphene on hexagonal boron nitride devices, corresponding to more than doubling the highest reported room temperature bulk values. In these devices, the smooth and highly efficient gating between electron- and hole-doped sectors, which facilitates switching the polarity of the Seebeck coefficient, extends a distinct advantage for on-chip thermoelectric cooling applications. Based on these results, we propose an integrated graphene-based active on-chip cooler.
Fast and controllable cooling at nanoscales requires a combination of highly efficient passive cooling and active cooling. Although passive cooling in graphene-based devices is quite effective due to graphene’s extraordinary heat conduction, active cooling has not been considered feasible due to graphene’s low thermoelectric power factor. Here, we show that the thermoelectric performance of graphene can be significantly improved by using hexagonal boron nitride (hBN) substrates instead of SiO
2
. We find the room temperature efficiency of active cooling in the device, as gauged by the power factor times temperature, reaches values as high as 10.35 W⋅m
−1
⋅K
−1
, corresponding to more than doubling the highest reported room temperature bulk power factors, 5 W⋅m
−1
⋅K
−1
, in YbAl
3
, and quadrupling the best 2D power factor, 2.5 W⋅m
−1
⋅K
−1
, in MoS
2
. We further show that the Seebeck coefficient provides a direct measure of substrate-induced random potential fluctuations and that their significant reduction for hBN substrates enables fast gate-controlled switching of the Seebeck coefficient polarity for applications in integrated active cooling devices.