Using continuous approximation we study the static and high-frequency heat dissipation in multi-layer graphene on a ferroelectric. We demonstrate that the Joule heating effect, caused by a high-frequency ac electric current in graphene, creates a pronounced temperature gradient in a ferroelectric substrate. The pyroelectric effect transforms the gradient into the spontaneous polarization gradient.. Therefore, the high-frequency depolarizing electric field occurs and penetrates in the

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... graphene. Free charges in graphene immediately screen the electric field and thus their density oscillates at high-frequency. Performed calculations had proved that the pyroelectric effect can modify essentially the free carrier density at the graphene-ferroelectric interface and consequently the conductivity of multi-layer graphene channel. So, pyroelectric mechanism can be critical for understanding of the complex physical thermal and electrical processes taking place across and along graphene-ferroelectric interfaces at terahertz frequencies.