Effects of H_3PO_4 Treated Porous SiO_2 on Proton Conductivity and Performances of EDL-TFTs

Porous SiO2 films were deposited by plasma enhanced chemical vapor deposition and were treated by H3PO4 solution with various concentrations. Then indium-zinc-oxide(IZO) electric-double-layer thin-film transistors(EDL- TFTs) were fabricated by using such porous SiO2 films as the gate dielectrics. The effects of H3PO4 treatments on the proton conductivity and EDL capacitance of porous SiO2 films and on the performances of EDL-TFTs were investigated systematically. The proton conductivity and EDL capacitance of SiO2 films increase with the H3PO4 concentration increase. A high proton conductivity of 1.51×10-4 S/cm and a large EDL capacitance of 6.33 μF/cm2 are obtained for porous SiO2 films which were treated with 60% H3PO4 solution. The operating voltage decreases and the on/off ratio increases with the increasing H3PO4 concentration. The EDL-TFTs gated by porous SiO2 films treated with 60% H3PO4 solution show the best performance with a low operating voltage of 1.2 V,a high mobility of 20 cm2/(V·s),and a large on/off ratio of 4×106. Such EDL-TFTs are promising for biosensors and chemical sensors in the future.