Understanding the Location of Resistance Change in the Pr0.7Ca0.3MnO3 RRAM.

Pr1-xCaxMnO3 (PCMO) based resistance random access memory (RRAM) is attractive in large scale memory and neuromorphic applications as it is non-filamentary, area scalable and has multiple resistance states along with excellent endurance and retention. The PCMO RRAM exhibit area scalable resistive switching when in contact with the reactive electrode. The interface redox reaction based resistance switching is observed electrically. Yet, whether resistance change occurs through partial (close to interface) or entire bulk is largely debated. Essentially, a two-terminal device is unable to provide direct evidence of the resistance change location in the PCMO RRAM. In this paper, we propose and experimentally demonstrate a novel three-terminal RRAM device in which a thin third terminal (~20nm) is inserted laterally in a typical vertical 2 terminal RRAM device of PCMO thickness of ~80nm. Using the 3T-RRAM method, we show that resistance change occurs largely at the upper bulk (near reactive electrode interface) - which is highly asymmetric. Yet it produces SCLC based resistance change with symmetric IV characteristics. 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 3rd terminal of the RRAM. Such a study enables a critical understanding of the device which enables the design and development of PCMO RRAM for memory and neuromorphic computing applications.