Improved Performance of Bottom-Contact Organic Thin-Film Transistor Using Al Doped HfO2 Gate Dielectric

Aluminum doped HfO2 (HfAlO) prepared by atomic layer deposition is investigated as gate dielectric for low-voltage organic thin-film transistors (OTFTs). The HfAlO film exhibits a low leakage current density of 4.92 x 10(-8) A/cm(2) at -3 MV/cm, which is similar to 70% smaller than its HfO2 counterpart. In addition, copper phthalocyanine (CuPc) OTFT with HfAlO dielectric has an average mobility mu(2.58 +/- 0.32 x 10(-3) cm(2)/Vs) increased by 58%, sub-threshold slope SS (0.9 +/- 0.11 V/decade) decreased by 11%, and ON/OFF ratio I-ON/I-OFF (3.1 +/- 1.3 x 10(3)) increased by 86% as compared with those with HfO2 as gate dielectric (mu = 1.63 +/- 0.27 x 10(-3) cm(2)/Vs; SS = 1.01 +/- 0.1 V/decade; I-ON/I-OFF = 1.7 +/- 0.77 x 10(3)). All these could be ascribed to the inclusion of Al in the HfO2 film, which increases the conduction band offset and the bandgap and improves the dielectric and interface quality. The temperature effect on the performance of OTFTs is also investigated.