Percolation threshold related to field-effect transistors using thin multi-walled carbon nanotubes composites

We fabricated thin-film field-effect transistors (TF-FETs) using thin multi-walled carbon nanotubes (t-MWCNTs) and poly (methyl methacrylate) (PMMA) composites as the active layer. The gate-dependent current–voltage characteristics, the current on/off ratio (I_on/off), and the dc conductivity (σ_dc) were measured as a function of various weight (wt.%) of t-MWCNTs. The typical p-type FET characteristics were observed. We found that the field-effect I_on/off increased rapidly for TF-FETs with a wt.% of t-MWCNTs below 0.6. For the TF-FETs with a wt.% of t-MWCNT above 0.6, the I_on/off was relatively low. From the measured σ_dc as a function of the wt.% of t-MWCNTs, the percolation threshold (p_c) was observed to be approximately 0.6 wt.% for the t-MWCNT composites. We infer that the TF-FET characteristics are closely related to the p_c for the charge conduction of the t-MWCNTs composites.