Memristive Pr_0.7Ca_0.3MnO₃ (PCMO) heterostructures exhibit area-dependent resistive switching via a valence change mechanism, making them promising for neuromorphic architectures. A major challenge in PCMO-based memory is higher-dimensional lattice defects that affect oxygen-vacancy migration and concentration. This study mitigates these defects using highly conductive amorphous PCMO fabricated via a CMOS back-end-of-line-compatible process and compares it with low-conductive amorphous and polycrystalline PCMO. The resistance differences are attributed to changes in electronic mobility, based on the analysis of short- and long-range order, Mn–O hybridization, and Mn valence state. AlO_x/qa-PCMO devices showed the highest ON/OFF ratio compared to low-conductive amorphous and polycrystalline PCMO, because the field-accelerated oxygen vacancy movement switches the mechanism from Poole–Frenkel emission in the LRS to trap-assisted tunneling in the HRS. The mechanism change was identified by systematically analyzing the I–V asymmetry, device band diagrams for different PCMO types, and shape changes in the I–V curve fits. The band diagrams were calculated from the measured bandgaps and work functions of the different PCMO types. Analysis of the electric field distribution in the devices showed a clear correlation between the pre-switching field strength in AlO_x and the resulting ON/OFF ratio.