# Design and Development of OECT Logic Circuits for Electrical Stimulation Applications
## 3 Results
Figure 7: Current throughput vs. time for various OECT channel widths. The current was measured in the two parallel branches of the OECT characterization testbed for four different OECT architectures: 1 mm, 2 mm and 3 mm channel widths and the 6 \(\times\) 1 mm interdigitated design. The branch with an OECT switched to its non-conductive state is shown in the left panel, and the branch with an OECT in its conductive state is shown in the right panel. The plots show the corresponding currents. The measurements obtained when comparing the performance of devices with a 1 mm channel width in 25 and 65 %RH conditions are shown in Figure 10. Here, the measured currents in the non-conductive (left) and conductive (right) branches were obtained while a 40 V maximal output voltage and current levels of either 5 mA or 10 mA were provided by the generator set-up. The results indicated a current leakage of less than 0.5 mA for both input currents at 65 %RH conditions, while the current leakage was close to one half of the input current at 25 %RH. Figure 8: Estimated leakage current in the closed branch for various current levels at an output voltage of 30 V (**left panel**) and 40 V (**right panel**), respectively. The bounds of the expected current leakage were estimated based on measurements in both states of the parallel branches, where exactly one branch was conductive at each instant. Figure 9: Effects of maximal output voltage of the stimulation system, ranging from 20 V to 60 V, on the switching capabilities of the OECT architecture with a 1 mm channel at a 5-mA stimulation current. The current was measured in both parallel branches of the OECT characterization testbed, with the non-conductive branch shown in the left panel and conductive branch shown in the right panel. The results from the experiment with the screen-printed OECT-based 2-4 demultiplexer circuits for control of the stimulation current in multi-pad electrodes are shown in Figure 11. The currents measured in each of the four output nodes of the demultiplexer circuit are shown in a testing sequence where the conductive branch was changed every 2 s, with the stimulation pulse from the pulse generator set at 2 mA at a 20 V maximal output voltage. It can be noted that there was a slight variability of the output signals of the printed logic circuit and some expected leakage in the closed channels. However, in all experiments, the conductive branch of the demultiplexing unit was selected correctly and at the appropriate time. In addition, the current in that branch was significantly higher than in all other branches, and at the same time, it almost reached the targeted level of 2 mA. Figure 11: Current propagation through the OECT-based demultiplexer circuit measured on the testbed for validation of the switching capabilities of printed circuits. The four signals represent the four currents measured at the different outputs of the 2-4 demultiplexer circuit when a 2 mA current controlled pulse train with a pulse width of 400 us was supplied at the input. The logic signals were changing the state of the demultiplexing unit every 2 s.  
Figure 10: Effects of variations in relative humidity. The currents were measured in two parallel branches of the OECT characterization testbed. The same set of OECTs was used in these measurements at relative humidity levels of 25 and 65 %RH.