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 × 10^-8 A/cm² at -3 MV/cm, which is ~70% smaller than its HfO₂ counterpart. In addition, copper phthalocyanine (CuPc) OTFT with HfAlO dielectric has an average mobility μ (2.58± 0.32 × 10^-3 cm²/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 × 10³) increased by 86% as compared with those with HfO₂ as gate dielectric (μ = 1.63 ± 0.27 × 10^-3 cm²/Vs; SS = 1.01 ± 0.1 V/decade; ION/IOFF = 1.7 ± 0.77 × 10³). 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.