Tuning inverter behavior through threshold voltage adjustment

Voltage transfer characteristics of inverters fabricated with four different threshold configurations.
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.