  We report on the growth and characterization of
Ti/$La_{1/3}$$Ca_{2/3}$Mn$O_3$/Si$O_x$/n-Si memristive devices. We demonstrate
that using current as electrical stimulus unveils an intermediate resistance
state, in addition to the usual high and low resistance states that are
observed in standard voltage controlled experiments. Based on thorough
electrical characterization (impedance spectroscopy, current-voltage curves
analysis), we disclose the contribution of three different microscopic regions
of the device to the transport properties: an ohmic incomplete metallic
filament, a thin manganite layer below the filament tip exhibiting
Poole-Frenkel like conduction, and the SiOx layer with an electrical response
well characterized by a Child-Langmuir law. Our results suggest that the
existence of the SiOx layer plays a key role in the stabilization of the
intermediate resistance level, indicating that the combination of two or more
active RS oxides adds functionalities in relation to single-oxide devices. We
understand that these multilevel devices are interesting and promising as their
fabrication procedure is rather simple and they are fully compatible with
standard Si-based electronics.
