Research Project Highlight

Layer-Based NTCDI Transistors with Side Chain Dielectrics that Operate Below 1V

layerbasedWe designed a new naphthalenetetracarboxylic diimide (NTCDI) semiconductor molecule with long fluoroalkylbenzyl side chains. The side chains, 1.2 nm long, not only aid in self-assembly and kinetically stabilize injected electrons, but also act as part of the gate dielectric in field-effect transistors. On Si substrates coated only with the 2-nm thick native oxide, NTCDI semiconductor films were deposited with thicknesses from 17 nm to 120 nm. Top contact Au electrodes were deposited as sources and drains. The devices showed good transistor characteristics in air with 0.1-1 µA of drain current at 0.5V of VG and VDS and W/L of 10 ~ 20, even though channel width (250 µm) is over 1000 times the distance (20 nm) between gate and drain electrodes. The extracted capacitance-times-mobility product, an expression of the sheet transconductance, can exceed 100 nS V-1 , two orders of magnitude higher than typical organic transistors. The vertical low-frequency capacitance with gate voltage applied in the accumulation regime reached as high as 650 nF/cm2 , matching the harmonic sum of capacitances of the native oxide and one side chain, and indicating  that some gate-induced carriers in such devices are distributed among all of the NTCDI core layers, though the preponderance of the carriers are still near the gate electrode.    Besides demonstrating and analyzing thickness-dependent NTCDI-based transistor behavior, we also showed <1 V detection of dinitrotoluene vapor by such transistors.

Organic semiconductors for use in plastic electronic devices and other alternative active circuits such as display backplanes are generally hole-transporters. It is much more challenging to design electron transporters, which are often needed to complete a circuit or even a single device.

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