Design and performance investigation of short channel bottom-contact organic thin-film transistors

Abstract

This paper presents an investigation on the design of organic thin-film transistors (OTFTs) with short channel lengths required to achieve higher integration density organic circuits for various DC and RF applications. The DC and AC performance parameters of an OTFT with channel lengths 5, 2, 1.5, 1.0, 0.9 and 0.7 $$\upmu \hbox {m}$$ have been evaluated through carefully calibrated two-dimensional numerical simulation. The designed OTFT uses pentacene as the active layer in the bottom-contact configuration. The various performance parameter metrics, i.e., threshold voltage ( $${V}_\mathrm{TH}$$ ), transconductance ( $${G}_\mathrm{M}$$ ), gain ( $${A}_\mathrm{V}$$ ), I $$_\mathrm{ON}$$ /I $$_\mathrm{OFF}$$ , DIBL, cutoff frequency ( $${f}_\mathrm{T}$$ ) and breakdown voltage ( $${V}_\mathrm{BR}$$ ), have been evaluated. The results have revealed that OTFTs with short channel lengths show improved performance compared to long channel transistors. The second-order effects of V $$_\mathrm{TH}$$ roll-off and DIBL are less pronounced in OTFTs. Results show that the $$\mathrm{V}_\mathrm{TH}$$ reduces only by 10.73% from $$L=5\,\upmu \hbox {m}$$ to $$L=0.7 \,\upmu \hbox {m}$$ . The results have shown that OTFTs have a high I $$_\mathrm{ON}$$ /I $$_\mathrm{OFF}$$ ratio of the order of 10 $$^{13}$$ and thus are effective for fast switching applications. The cutoff frequency of the simulated device for $$L=0.7\,\upmu $$ m is 2.3 GHz suggesting the application of OTFTs for RF applications. The role of trap states on the device conduction has also been investigated. The simulation study has revealed that OTFTs exhibit well-defined mobility degradation and impact ionization behavior which becomes pronounced for channel lengths below 1 $$\upmu \hbox {m}$$ . Further the capacitive behavior of the designed device has been evaluated, and it has been observed that the device capacitance can be defined from the MOSFET theory except for the role of trap states.