A poly(styrene-co-methyl methacrylate)/room-temperature sputtered hafnium oxide bi-layer dielectrics as gate insulator for a low voltage organic thin-film transistors

In this study, we present a low voltage pentacene organic thin film transistor (OTFT) with poly(styrene-co-methyl methacrylate) grafted hafnium oxide (PS-r-PMMA/HfOx) as gate dielectrics. The HfOx was sputtered at room temperature to approach low temperature and meet low cost requirements of organic electronics. The thickness of the PS-r-PMMA can be controlled to be extremely thin (<10 nm). Consequently, the gate overdriving voltage as low as 3 V was achieved for an OTFT. Furthermore, by applying PS-r-PMMA on top of the HfOx surface, the traps on the HfOx surface and possible pinholes of the HfOx can be passivated. Therefore, the gate dielectric properties in terms of interface states and leakage current were improved. The leakage current reduced to approximately two orders of magnitude and the interface states reduced to nearly one order of magnitude. The reduction of the interface state density was observed by capacitance–voltage measurement. As a result, the subthreshold swing and on/off current ratio were improved significantly from 1.01 V/dec. and 103 to 0.41 V/dec. and 105, respectively.

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► A pentacene OTFT with polymer grafted hafnium oxide as gate dielectrics.
► The OTFT could be operated at low voltage by the nanometer thick polymer dielectric.
► The leakage current and interface states reduced more than one order of magnitude by polymer grafting.