Voltage transfer characteristics of inverters fabricated with four different threshold configurations.
We have shown a hybrid fabrication technique that relies on photolithography plus mechanical peel-off. This new process enables, for the first time, the patterning of positive and negative charges spatially on n- and p-type organic field effect transistors, respectively, on the same wafer.
Utilizing this new fabrication method and threshold adjusting technique, the first organic FET-based CMOS inverter has been fabricated that employs threshold adjustment for both p- and n-type transistors. Both n- and p-type transistors are biased so that the inverter’s gain is maximized. Figure 1 shows voltage transfer characteristics of four inverters; device 1 is the control sample of uncharged dielectrics. Dielectrics on PMOS/NMOS areas charged with -25 V/0 V, 0 V/ +25 V, -25 V/ +10 V for devices 2, 3, 4, respectively. The optimum operating switching point and gain in the inverters went from -74 on control samples to a maximum of -105 by simultaneous tuning of the threshold voltage on both n- and p-type transistors. The figures for the inverter gain as a result of fine-tuning both n- and p-type threshold voltages are the highest ever attained in organic semiconductor inverters.