The scaling of organic field-effect transistors (OFETs) is necessary for high-density integration and for this, OFETs with a top-gate configuration are required. There have been several reports of damageless lithography processes for organic semiconductor or insulator layers. However, it is still difficult to fabricate scaled OFETs with a top-gate configuration. In this study, the lift-off process and the device characteristics of the OFETs with a top-gate configuration utilizing an amorphous (α) rubrene gate insulator were investigated. We have confirmed that α-rubrene shows an insulating property, and its extracted linear mobility was 2.5 ' 10 %2 cm 2 /(V&s). The gate length and width were 10 and 60 µm, respectively. From these results, the OFET with a top-gate configuration utilizing an α-rubrene gate insulator is promising for the high-density integration of scaled OFETs.
Nitrogen-doped (N-doped) LaB 6 is a candidate material for the bottom-contact electrode of n-type organic field-effect transistors (OFETs). However, the formation of a N-doped LaB 6 electrode affects the surface morphology of a pentacene film. In this study, the effects of surface treatments and a N-doped LaB 6 interfacial layer (IL) were investigated to improve the pentacene film quality after N-doped LaB 6 electrode patterning with diluted HNO 3 , followed by resist stripping with acetone and methanol. It was found that the sputtering damage during N-doped LaB 6 deposition on a SiO 2 gate insulator degraded the crystallinity of pentacene. The H 2 SO 4 and H 2 O 2 (SPM) and diluted HF treatments removed the damaged layer on the SiO 2 gate insulator surface. Furthermore, the N-doped LaB 6 IL improved the crystallinity of pentacene and realized dendritic grain growth. Owing to these surface treatments, the hole mobility improved from 2.8 ' 10 %3 to 0.11 cm 2 /(V&s), and a steep subthreshold swing of 78 mV/dec for the OFET with top-contact configuration was realized in air even after bottom-contact electrode patterning.
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