OFETs CMOS inverters

In a second approach to generate a CMOS inverter, OFETs with a PMMA insulator were utilized. For one of the OFETs the otherwise electron trap free PMMA dielectric was UV irradiated prior to the pentacene deposition [44]. 

Fig. 19 Circuit of an unipolar inverter (a) and an inverter based on a CMOS-like circuit (b). Electrical losses in the ON state of the unipolar inverter exist, since the OFET is open and hence, a substantial current flows due to the finite resistivity of the resistor. For the CMOS inverter on the other hand only little current can flow at each logical state since one of the employed OFETs is always closed. The resistivities of the involved unipolar p- and n-type OFETs are named R and / 2 respectively...

On the basis of the evaluated description of OFETs in Sect. 2.1, the CMOS inverter can be modeled, namely the output voltage Vout as a function of the input voltage Vin. The CMOS inverter acts as a voltage divider with the output bias of... 

Fig. 20 Simulated inverter characteristics of a CMOS inverter for different field-effect mobility ratios. In Eq. (11), and )tn are set to zero and thus truly unipolar OFETs have been considered...

Fig. 21 Simulated inverter characteristics of a CMOS inverter where ambipolar OFETs have been considered. While jlip = /tj and have been assumed, the ratio fiS/fip varies from 0 to 1...

Fig. 22 Schematic setup and characteristics of a CMOS inverter consisting of OFETs both fabricated by vacuum-deposition of pentacene on a PMMA/Si02 dielectric. The transport character is achieved by proper choice of source- and drain contact metals...

Fig. 23 Characteristic of an organic CMOS inverter stage reaching a maximum gain of 24. The inverter has been realized using Ca passivated SiOz. In the insets, the inverter circuit and the stiuctuie of the employed complementary oiganic OFETs arc depicted...

Fig. 25 Characteristic of a CMOS-like inverter based on ambipolar transistors, operating in the first and the third quadrant. The inverter comprises two identical ambipolar OFETs with a blend of OCiCio-PPV and PCBM as active material. The solid lines are simulated inverter characteristics. Reprinted with permission from Macmillan Publishers Ltd Nature Materials [35], copyright (2003)...

From Fig. 28 it can be concluded, that the voltage losses in the final logical states are rather low, since truly unipolar complementary OFETs have been used (see Fig. 27). This is an advantage if compared to CMOS-like inverters based on ambipolar OFETs because those disclose in the contrary substantial voltage losses. 

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