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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 \(4.92 \times 10^{-8}\) A/cm \(^{2}\) at −3 MV/cm, which is \(\sim 70\) % smaller than its HfO2 counterpart. In addition, copper phthalocyanine (CuPc) OTFT with HfAlO dielectric has an average mobility \(\mu ~(2.58\pm 0.32\times 10^{-3}\) cm \(^{2}\) /Vs) increased by 58%, sub-threshold slope SS (0.9 ± 0.11 V/decade) decreased by 11%, and ON/OFF ratio \(I_{\mathrm{{\scriptstyle ON}}}/I_{\mathrm{{\scriptstyle OFF}}}\) (3.1 ± 1.3 \(\times \) \( 10^{3}\) ) increased by 86% as compared with those with HfO2 as gate dielectric ( \(\mu =1.63\pm 0.27\times 10^{-3}\) cm \(^{2}\) /Vs; \({\rm SS}=1.01\) ±0.1 V/decade; \(I_{\mathrm{{\scriptstyle ON}}}/I_{\mathrm{{\scriptstyle OFF}}}=1.7\pm 0.77\times 10^{3}\) ). 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. [ABSTRACT FROM AUTHOR]