Detection of the conductive filament growth direction in resistive memories

Resistive switching random access memory (RRAM) is among the leading future non-volatile memory technologies; however, its implementation is hampered by the lack of full understanding of the switching and conduction mechanism as well as the lack of detailed physical models [1]. In particular, there are conflicting reports in the literature on the direction of growth of conductive filaments in valence change memories (VCM). Filament growth is a key aspect in the operation of bipolar RRAM devices as it determines the polarity of the device as well as the 'active' switching location. In some cases, it was shown directly by electron microscopy that filaments grow from the cathode towards the anode during forming, as in typical electrochemical metallization (ECM) cells [2]. In other cases, it was concluded indirectly that filaments originate from the anode [3]. Electron microscopy of filaments is highly challenging, and reports are scarce. Here, we show that the metal-insulator-semiconductor bipolar transistor structure can be used to detect the direction of growth of the conductive filament, and apply this procedure to validate our model of the dynamics of filament growth [4].