Resistive switching (RS) devices with binary and analogue operation are expected to play a key role in the hardware implementation of artificial neural networks. However, state of the art RS devices based on binary oxides (e.g., HfO 2 ) still do not exhibit enough competitive performance. In particular, variability and yield still need to be improved to fit industrial requirements. In this study, we fabricate RS devices based on a TaO x /HfO 2 bilayer stack, using a novel methodology that consists of the in situ oxidation of a Ta film inside the atomic layer deposition (ALD) chamber in which the HfO 2 film is deposited. By means of X-ray reflectivity (XRR) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), we realized that the TaO x film shows a substoichiometric structure, and that the TaO x /HfO 2 bilayer stack holds a well-layered structure. An exhaustive electrical characterization of the TaO x /HfO 2 -based RS devices shows improved switching performance compared to the single-layer HfO 2 counterparts. The main advantages are higher forming yield, self-compliant switching, lower switching variability, enhanced reliability, and better synaptic plasticity.