Flexible Graphene Field-Effect Transistors With Extrinsic ${f}_{{{\mathrm{max}}}}$ of 28 GHz

Graphene field-effect transistors (G-FETs) on flexible substrates have demonstrated much higher strain limits than that on rigid substrates. In this letter, G-FETs with an extrinsic f
_max
of 28 GHz on flexible polyethylene terephthalate (PET) substrates are presented. Polyimide film benzocyclobutene with 50-nm thickness is coated on a PET substrate surface for optimizing the carrier transport. The results show that the hole mobility can reach up to 1738 cm
²
/V.s. An Au-supported graphene transfer technology is used to facilitate the quality of graphene in G-FETs and reduce the output parasitic resistance to 50 Ω. The measured figure of metric of “f
_max
· L
_g
” is 8.4 GHz·μm, which is 105% higher than the highest reported results on polymeric substrates. The RF performance of flexible G-FETs under the bending condition is also studied. The results of the letter will be useful for developing the millimeter-wave flexible graphene integrated circuits.