Electrical properties of phthalocyanine based field effect transistors prepared on various gate oxides

We have investigated the electrical properties of top-contact type copper phthalocyanine (CuPc) based field effect transistors prepared on various high dielectric constant (high-K) gate oxide thin films, such as tantalum oxide (ɛr ∼ 20), tantalum oxide/silicon dioxide (ɛr ∼ 6), and aluminum oxide (ɛr ∼ 8) prepared by RF magnetron sputtering. A low operating voltage of less than 6 V and a field effect mobility μCuPc of 3.8 × 10− 3 cm2/V s, which is higher than μCuPc obtained with Al2O3 ant Ta2O5 + SiO2, was obtained in the CuPc FET prepared on 200-nm-thick Ta2O5. The FET properties were then combined with the electrical properties of metal–insulator–semiconductor (MIS) capacitors. The doping profile in CuPc was calculated from the capacitance–voltage (C–V) measurement using the FET with patterned CuPc, and it was found that there is a very high density of electronic states exist especially near the interface, which were considered as a origin of the large interfacial capacitance. It was also found that the subthreshold slope depends on the gate capacitance and the considerable interfacial capacitance with a thickness of only 3–4 nm in the CuPc based FETs prepared on various oxide films.