Figure 2: Electrical characteristic of the fabricated OFETs in various environments.
(a) Transfer characteristics (source-drain current, Isd, versus back-gate voltage, Vbg) in ambient. Isd is plotted on a semi-logarithmic scale (left axis, black dots) and a constant source-drain voltage (Vsd) of −1 V is applied. The dimensions of the Au source-drain electrodes are length=50 μm and width=4,000 μm. Arrows indicate the gate sweep direction. Only a small hysteresis is observed. The right axis shows the square root plot of Isd (red-dashed lines). The inset shows the schematics of the measurement set-up. (b) Output plots (Isd versus source-drain voltage, Vsd) for different fixed Vbg in ambient. (c) Transfer characteristics measured in DI water. For this purpose, a PDMS flow cell was mounted on top of the OFET. The polymer OFET shows a slightly higher hysteresis under aqueous operating conditions. (d) Output characteristics for various fixed Vbg measured in DI water. (e) Transfer characteristics of the OFET in 10 μM NaCl solution using a liquid gate. For this purpose, a flow-through Ag/AgCl reference electrode was placed in close vicinity to the PDMS flow cell and in-line with the tubing. Isd current was recorded while sweeping the liquid-gate potential (Vlg) applied to the reference electrode at a constant Vsd (−0.6 V). A much smaller hysteresis and an on/off ratio over ~103 was observed over a small Vlg range (<0.5 V). The inset shows the schematics of the measurement set-up. (f) Output characteristics for various fixed Vlg.
