Figure 3: Stability measurements in aqueous environments.
(a) Source-drain current (Isd) versus back-gate voltage (Vbg) measured over multiple days while stored continuously in DI water. Black arrows indicate gate sweep directions. Channel width (w)/length (l) ratio is 320. A small, unchanging hysteresis is visible. To extract the average threshold voltage (Vth,avg) shift shown in the inset, threshold voltages for the left (Vth,l) and right (Vth,r) slope were obtained by linear fit (dashed lines, guide to the eye) and Vth,avg was calculated by taking their average. Error bars represent the standard deviation. (b) Time-resolved measurement of Isd at a fixed working point (constant Vsd and Vbg) with w/l=80. The aqueous phase is cycled between DI water and seawater, with the pump set to a speed of 1 ml min−1. After the flow cell volume is fully replaced, the system reaches equilibrium and Isd plateaus (dashed red lines). The OFET demonstrated repeatable cycling between DI and seawater samples. (c) Isd versus Vbg of the same device shown in a measured over several weeks while stored in seawater. No degradation of the performance is visible. Extracted Vth,avg shifts are almost constant (inset). Error bars represent the standard deviation. (d) Time-resolved response of Isd to cycled increases in salinity (DI water, 0.01 × seawater, 0.1 × seawater, and seawater) for the same device shown in b. The working point was set to Vsd=−1 V and Vbg=−0.9 V. The pump was set to a speed of 1 ml min−1. After the solution in the flow cell was fully replaced, the pump was switched off. Isd reached repeatable, stable plateaus (indicated by the red-dashed lines).
