Abnormal Back Channel Leakage Under Large Drain Voltage in Short Channel Organic Thin-Film Transistors

This study investigates short channel (length <; 20 μm) p-type organic thin-film transistor (OTFT) devices which exhibit off-state leakage in their I
_D
-V
_G
characteristics. This phenomenon is attributed to the fact that when a lower positive gate voltage is applied, gate voltage cannot control the back channel, causing back channel leakage. The behavior of back channel leakage is confirmed by the OTFT saturated-regime drain-current formula multiplied by channel length. For dual gate OTFT devices, a top gate voltage sweep and fixed different bottom gate voltages are applied, which indicates that the conduction path is distributed throughout the entire organic semiconductor (OSC) layer, and the back channel leakage can be suppressed by a positive bottom gate voltage. Finally, using dual gate sweeping for a dual gate OTFT device allows the top and bottom gate voltage to simultaneously control the front and back channels, causing a suppression of the back channel leakage, an improvement in subthreshold swing (SS) from 420 to 200 (mV/decade) and an on current increase from 7.8 × 10
^-8
to 3.3 × 10
^-7
A at V
_G
-V
_{sub-threshold}
= -8 V for the W/L = 50/20 μm device.