Understanding the Region of Resistance Change in Pr_0.7Ca_0.3MnO₃ RRAM

Pr1–xCaxMnO3 (PCMO)-based resistance random access memory (RRAM) is attractive in large-scale memory and neuromorphic applications as it is nonfilamentary and area scalable and has multiple resistance states along with excellent endurance and retention. The PCMO RRAM exhibits area-scalable resistive switching when in contact with the reactive electrode. The interface redox reaction-based resistance switching is observed electrically. Yet, whether the resistance change occurs near the reactive interface or spread over the entire bulk is largely debated. Essentially, a two-terminal device is unable to provide direct evidence of the resistance change region in the PCMO RRAM. In this paper, we propose and experimentally demonstrate a three-terminal RRAM (3T-RRAM) device in which a thin third terminal (∼20 nm) is inserted laterally in close proximity to a typical vertical two-terminal RRAM device of PCMO thickness ∼80 nm. It is well known that the reactive interface participates in the resistive switching. However, using the 3T-RRAM, we demonstrate that the resistance change also occurs in the region near the inert electrode. We further show that the resistance measured by T3 is exclusively sensitive to the region near the inert electrode as opposed to the reactive electrode. Finally, the highly symmetric space charge limited current (SCLC) characteristics with polarity at various resistance levels, typical of two-terminal RRAM, are undisturbed because of the slightly adjacent placement of the nanoscale inert third terminal while providing resistance change read sensitivity. It is the first time that an interface redox and bulk SCLC-based resistance change has been experimentally shown as correlated and consistent, enabled by the third terminal of the RRAM. Such a study details a critical understanding of the device which can enable the design and development of PCMO RRAM for large memory and neuromorphic computing applications.