ИСТИНА

Using of printing technologies is simple, ecological and safe approach allowing to fabricate easy scalable cheap sensors with wide range of applications. Transition from traditional silicon substrates to printed polymer ones supposed to avoid a lot of difficulties associated with device fabrication as well as to create flexible and/or stretchable sensors. The main task of our work was to develop a reliable technique to fabrication of fully printed polymer field-effect transistor (PPFET) for gas sensing. To achieve this goal it is necessary to elaborate suitable PPFET architecture and a method of sequential printing of additive layers such as electrodes, interface, dielectric, semiconductor on polymer substrate. All devices were fabricated on glass or polyethylene naphthalate (PEN) substrates in bottom contact – bottom gate geometry (Fig.1a). In order to provide sufficient adhesive properties of silver (Ag) inks to substrate, the substrate surface has been treated by oligomeric 3-aminopropyltriethoxysilane using spin-coating1 . The bottom gate was printed by two ways: screen and inkjet printing. To ensure compatibility with the previously elaborated electronics required to sensory properties measurement, the same pattern of electrodes configuration was used. 2 For inkjet printing conditions such as pulse shape, firing frequency, piezo voltage, meniscus pressure and permission were selected and optimised. Commercial silver inks were used for printing. To provide contact layer stability post-treatment annealing was carried out at 150 degrees in a vacuum oven. It should be notice that annealing at a lower temperature or without vacuum doesn't provide the required layer stability, which leads to the damage of the electrodes during a dielectric layer formation. The dielectric layer was deposed by Dr. Blade technique as a kind of screen printing. The dielectric layers fabrication conditions such as molecular weight (MW) of polystyrene (PS), PS concentration and solvent composition were optimized. The dielectric layer quality was estimated by AFM morphology, layer capacitance and density of leakage current. The best characteristics of layer (RMS = 0.26nm, specific capacitance = 27 nF/cm2 ) were achieved for the device fabricated on glass substrate with inkjet printed electrodes and dielectric layer obtained from toluene (90%)/o-xylene (10%) solution of PS with MW= 280k g/mol at concentration of 60 mg/ml. Obtained characteristics allow to concluded that fabricated printed substrates should be suitable for further PPFET fabrication.