Fig. 4. (Color online) Electrical properties and schematics for advanced device fabrication process. (a–e) Schematics and transfer curves of the LM device during annealing with PR and erasing: After annealing under vacuum (a), after coating with PR (b), after annealing the PR under vacuum (c), after erasing the PR using acetone (d), and after the third annealing under vacuum (e). (f) Combined fabrication method with EP and annealing processes to remove all polymer residues. After transferring graphene with PMMA as an assist layer, the PMMA is erased using acetone and removed by heat treatment under vacuum. After developing with PR to make source/drain electrodes, the PR residue on the contact part is removed by vacuum annealing. After depositing electrodes and the lift-off process, the residual PR on the graphene channel is removed by final heat treatment. Green and red circles on graphene surface represents adsorbates generated after removal of PMMA and PR, respectively. (g) Transfer curve of the EP device according to the process in (f). (h) Parameters extracted from transfer curves of 16 conventional EP devices and 10 new EP devices after vacuum-assisted annealing. The upper and lower graphs display the distributions of VCNP and hole mobility of channel, respectively.
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