# Design and Development of OECT Logic Circuits for Electrical Stimulation Applications
## 3 Results  
In the first test, the aim was to analyse the performance of various OECT architectures designed for high current throughput. The results of the comprehensive tests, including various levels of current amplitudes and pulse generator maximal voltages, are summarized in several representative figures. Figure 7 shows the current measured in both parallel branches when one OECT was switched off (left panel) and the other OECT was in its conductive on state (right panel). Here, the results based on a maximal output voltage of 40 V and a current amplitude of 5 mA are depicted, since these were the output parameters most representative of real stimulation scenarios. It can be noted from the graphs that the 6 \(\times\) 1 mm transistor architecture showed the worst performance, with the leakage current in the closed branch comparable to the current measured in the conducting branch. The OECT with a 3 mm channel width also showed subpar performance, with a current leakage above 1 mA, or 20% of the current level in the conducting state. The OECTs with 1 mm and 2 mm channel widths showed comparable performance, with an average leakage current below 0.5 mA for both designs. Figure 6: **Left**: Image of the testbed for validation of the switching capabilities of the OECT-based printed 2–4 demultiplexer circuits. The testbed enabled connection of up to four demultiplexer circuits, which allowed control of the current propagation over a 16-pad matrix electrode at the output. The flat cable at the input was connected to the MCU and the pulse generator boards shown in Figure 5. **Right**: The schematic of the screen-printed OECT-based 2–4 demultiplexer circuit used to route the stimulation signal to the selected pad of the multi-pad electrode. Further analysis of the current leakage in the closed branch was performed for various levels of stimulation amplitudes in two scenarios: with the maximal output voltage of the pulse generator at 30 V (Figure 8, left panel) and 40 V (Figure 8, right panel). An estimation of the bounds of the expected current leakage was performed based on measurements in both possible states of the parallel branches. (One OECT was conductive, while the other was non-conductive, and vice versa.) It can be noted that for both cases, the current leakage was higher for low amplitudes (1 mA and 2 mA), while the leakage stabilized for currents above 5 mA. At 30 V, the output leakage was around 5% for the 1 mm, 2 mm and 3 mm OECT channel widths, while it was close to 15% for the 6 \(\times\) 1 mm OECT architecture. At 40 V, the output leakage was more pronounced for all architectures. Additionally, the system stability was compromised, which can be noted from the high variability of the measured leakage current when comparing one state (branch 1 open, branch 2 closed) with the other state (branch 1 closed, branch 2 open), as reflected by the estimated bounds of the expected current leakage. Figure 9 shows the measured current levels for various maximal output voltages of the pulse generator. Here, the results are shown for the OECT architecture with a 1 mm channel width and the stimulation current of 5 mA, with the measurements of the nonconductive branch in the left panel and the conductive branch in the right panel. It can be noted that that there was a negative relation between the maximal output voltage and the leakage current. However, for voltage levels of 40 V or below, the current leakage was relatively low (<0.5 mA), meaning that over 90% of the current was flowing through the conductive branch. Conversely, for 50 V and above, the current in the closed branch was comparable to the current in the open branch, with approximately 2.5 mA running through both branches. When analysing the right panel, it can also be noted that for a low maximal output voltage, the required current could not be generated throughout the pulse. In the negative phase, this was evident even for the 40 V maximal output voltage and even more pronounced for lower values, especially for the 20 V level.