SbO_x thin films are deposited by atomic layer deposition (ALD) using SbCl₅ and Sb(NMe₂)₃ as antimony reactants and H₂O and H₂O₂ as oxidizers at low temperatures. SbCl5 can react with both oxidizers, while no deposition is found to occur using Sb(NMe₂)₃ and H₂O. For the first time, the reaction mechanism and dielectric properties of ALD-SbO_x thin films are systematically studied, which exhibit a high breakdown field of ≈4 MV cm⁻¹ and high areal capacitance ranging from 150 to 200 nF cm⁻², corresponding to a dielectric constant ranging from 10 to 13. The ZnO semiconductor layer is integrated into a SbO_x dielectric layer, and thin film transistors (TFTs) are successfully fabricated. A TFT with a SbO_x dielectric layer deposited at 200 °C from Sb(NMe₂)₃ and H₂O₂ presents excellent performance, such as a field effect mobility (µ) of 12.4 cm² V⁻¹ s⁻¹, I_on/I_off ratio of 4 × 10⁸, subthreshold swing of 0.22 V dec⁻¹, and a trapping state (N_trap) of 1.1 × 10¹² eV⁻¹ cm⁻². The amorphous structure and high areal capacitance of SbO_x boosts the interface between the semiconductor and dielectric layer of TFT devices and provide a strong electric field for electrons to improve the device mobility.