Investigation of the mechanism of SrRuO3/SrTiO3 bipolar resistive switching device by transmission electron microscopy

Abstract

Nowadays, as Information technology (IT) makes rapid advance and the contemporary memory devices have reached its limit in application, high potential memory devices are needed which are not based on the existed memory devices way. Therefore, a number of more powerful and functional nonvolatile memory (NVM) have been extensively explored, and resistive random access memory (ReRAM) device is becoming one of the candidates which displays distinct advantages such as fast switching speed, large resistance ratio, low riving voltage and simple structure. ReRAM is based on the resistive switching (RS) phenomenon, of which the resistance of the metal-insulator-metal (MIM) structured device could be repeatedly set to different resistance by external electric field and these resistance states are corresponding to the binary data storage of 0 and 1. ReRAM can be clarified into two categories by resistive switching behavior, unipolar resistive switching which resistance depends only on magnitude of voltage and bipolar resistive switching which resistance is only depends on the polarity of voltage. In unipolar mode, the mechanism of the resistive switching has been already researched enough and it was revealed that formation and rupture of conductive path, filament, in insulating thin film is the origin of resistive switching phenomenon. However, in case of bipolar mode, there are lots of models which explain the resistive switching. One of them is the formation and rupture of the filament as well as unipolar switching. Many researchers have been proposed for homogeneous bipolar resistive switching by the change at the interface state. In this mechanism, microstructure of interface is the most important factor to determine the resistance change, however, there are not enough experimental evidences for microstructural change directly. Here, we investigated the SrRuO3 and SrTiO3 single crystal junction device as the most ideal system for investigation of homogeneous bipolar resistive switching model for TEM experiment. We confirmed the resistive switching and electrical property by I-V curve and did TEM, STEMEELS analysis to observe the microscopic mechanism. Beside, by using the In-situ STM/TEM holder, we observed the operation of the device and the microscopic change simultaneously. The variation of oxygen vacancy concentration at the interface which has been used for explaining the homogeneous bipolar resistive switching was not detected by electron energy loss spectrum in this experiment. Therefore, these results mean that there is another possibility of determining the resistive switching or the amount of oxygen vacancies is too small to detect in well-defined interface. Finally, the finding may be of help to know about the homogeneous bipolar resistive switching mechanism.