Organic electrochemical transistors (OECTs) are promising
building
blocks for bioelectronic devices such as sensors and neural interfaces.
While the majority of OECTs use simple planar geometry, there is interest
in exploring how these devices operate with much shorter channels
on the submicron scale. Here, we show a practical route toward the
minimization of the channel length of the transistor using traditional
photolithography, enabling large-scale utilization. We describe the
fabrication of such transistors using two types of conducting polymers.
First, commercial solution-processed poly(dioxyethylenethiophene):poly(styrene
sulfonate), PEDOT:PSS. Next, we also exploit the short channel length
to support easy in situ electropolymerization of poly(dioxyethylenethiophene):tetrabutyl
ammonium hexafluorophosphate, PEDOT:PF6. Both variants
show different promising features, leading the way in terms of transconductance
(gm), with the measured peakgmup to 68 mS for relatively thin (280 nm) channel layers
on devices with the channel length of 350 nm and with widths of 50,
100, and 200 μm. This result suggests that the use of electropolymerized
semiconductors, which can be easily customized, is viable with vertical
geometry, as uniform and thin layers can be created. Spin-coated PEDOT:PSS
lags behind with the lower values ofgm; however, it excels in terms of the speed of the device and also
has a comparably lower off current (300 nA), leading to unusually
high on/off ratio, with values up to 8.6 × 104. Our
approach to vertical gap devices is simple, scalable, and can be extended
to other applications where small electrochemical channels are desired.