Controlling the Threshold Voltage of Organic Thin-Film Transistors by Transition Metal Oxides

We demonstrate an effective, noble metal-free method to control the threshold voltages
$(V_{T})$
of organic thin-film transistors (OTFTs). Through covering an Al gate electrode with a high work function (WF) transition metal oxide (TMO) layer of
${\rm WO}_{3}$
or
${\rm MoO}_{3}$
,
$V_{T}$
is shifted in a positive direction from
${-}{\rm 2.15}~{\rm V}$
to
${-}{\rm 1.40}~{\rm V}$
or
${-}{\rm 0.89}~{\rm V}$
, respectively, with respect to that of OTFTs with a bare Al gate electrode. Together with a thin dielectric layer of cross-linked Cytop, the reduced magnitude of
$V_{T}$
allows for a low-voltage switching operation with a gate voltage as small as 2 V. The amount of
$V_{T}$
shift is shown to correlate well with the change in the WF of the gate electrode upon TMO deposition.