Effect of source/drain undercut on the performance of pentacene thin-film transistors on plastic

We studied the electrical properties of bottom contact pentacene thin-film transistors (TFTs) on plastic with and without source/drain undercut. The undercut depends on the Cr thickness in $\mathrm{Au}∕\mathrm{Cr}$ source/drain electrodes, where Au is used for the ohmic contact with pentacene, and the Cr is to enhance the adhesion of Au to the cross-linked poly-4-vinyphenol gate insulator. The undercut can be removed by reducing the Cr thickness less than $5\mathrm{nm}$ . The TFTs with and without undercut exhibited the field-effect mobility in the saturation region of 0.96 and $1.3{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ , respectively, but in the linear region the field-effect mobility of the TFT with source/drain undercut is $\sim 1∕9$ that of the organic TFT without undercut.