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Effect of thickness of bilayer dielectric on 1,7‐dibromo‐N,N′‐dioctadecyl ‐3,4,9,10‐perylenetetracarboxylic diimide based organic field‐effect transistors
Author(s) -
Subbarao Nimmakayala V. V.,
Gedda Murali,
Vasimalla Suresh,
Iyer Parameswar K.,
Goswami Dipak K.
Publication year - 2014
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201431304
Subject(s) - threshold voltage , electron mobility , dielectric , materials science , diimide , field effect transistor , field effect , gate dielectric , optoelectronics , analytical chemistry (journal) , chemistry , transistor , voltage , electrical engineering , molecule , organic chemistry , perylene , engineering
1,7‐dibromo‐N,N′‐dioctadecyl‐3,4,9,10‐perylenetetracarboxylic diimide (PTCDI‐Br 2 ‐C 18 ) was synthesized and employed in the fabrication of n‐type organic field‐effect transistors (OFETs). Lower operating voltage was achieved by using a bilayer dielectric containing anodized Al 2 O 3 and poly‐(methyl methacrylate) (PMMA) layers. We have studied the effect of individual dielectric layer thickness and the roughness on the threshold voltage ( V T ) as well as on the field‐effect carrier mobility ( μ FE ) and achieved a threshold voltage of <1 V with a subthreshold swing of <0.2 V/decade. We observed the reduction in V T while the thickness of Al 2 O 3 layer is reduced. This has been attributed to the reduction of charge trap density present at the active channel and at the interface between active channel and the dielectric layer. The trap states density is apparently influenced by the roughness of the Al 2 O 3 layer. In such cases, gate‐field ( E ) dependent carrier mobility is almost evident. In this work, we have demonstrated gate‐field independent carrier mobility, which are about 0.040 cm 2 V −1 s −1 in the saturation region and 0.035 cm 2 V −1 s −1 in the linear region. This indicates the significant reduction of trap states, which are completely full at the voltage below V T . As a result, the carrier mobility is relatively unaffected by trap scattering of the mobile charges.