The aim of the SELF-FLEX-APP project is the realization of high performance and flexible complementary inverters based on ultrathin free-standing films that involve a spontaneous phase separation between the polymer dielectric and the organic semiconductor (Figure 2). This approach is considered to reduce the number of production steps of flexible organic/inorganic based transistors. The free-standing films will be obtained by deposition of the polymer dielectric and organic semiconductor together on a temporary standard sacrificial substrate and a subsequent phase separation between both fractions during solution evaporation or/and during a post-treatment step (Figure 2). These additional post-treatment steps can include thermal or solvent annealing. After the phase separation, a bi-layer structure is formed with preferential crystallization of the organic semiconductor on the top film surface creating in this way the active layer (Figure 2). Finally, the free-standing film will be carefully removed from the temporary sacrificial substrate. It should be pointed out that such reduction of the fabrication steps will show significant impact on dielectric/semiconductor interface engineering. Parameters like: insulator surface roughness, surface energy, surface polarity will not affect the crystallization process and molecular arrangement of the semiconductor. Thanks to our idea the charge trapping at the dielectric/isolator interface will be reduced to a minimum. Additionally, the dielectric capacitance will be designed and controlled by application of insulators with well-defined thickness. The most innovation point of our idea is fact that the polymer acts as the carrier substrate and as a dielectric at the same time for substrate thicknesses between 1-3 µm. This low thickness additionally ensures the flexible character of the final device (Figure 1).

Figure 1. Scheme of self-standing film fabrication by spontaneous phase separation.

As the further part of this project, all transistor electrodes, source, drain, and gate, as well as the electrical paths of the complementary inverter will be printed on the top and bottom side of self-standing composites by using a conductive ink of electrochemically exfoliated graphene (Figure 2). For the printing of graphene on the organic semiconductor, an orthogonal solubility of both systems is an important requirement. In this way, the electrode/semiconductor interface will not be damaged by graphene inkjet printing electrodes.

Figure 2. Scheme of graphene electrodes and conductive paths fabrication.

The combination of the self-standing dielectric/semiconductor bi-layers composites with printed conductive graphene electrodes will allow fabricating high performance and flexible complementary inverter and finally logic gates in a new approach opening the door towards low-cost processing (Figure 3).

Figure 3. Scheme towards complementary inverters based on self-standing dielectric/semiconductor composites and graphene printed electric paths.