Flexible and transparent ReRAM with GZO-memory-layer and GZO-electrodes on large PEN sheet

Flexible transparent resistive random access memory (FTReRAM) can be fabricated by sandwiching a wide band gap oxide such as ZnO between transparent electrodes such as tin-doped indium oxide (ITO) on polymer flexible sheets. However, an alternative transparent conducting oxide (TCO) to ITO is desired because of the high cost and scarcity of the indium element. Although one of the best candidates is Ga doped ZnO (GZO), low glass transition temperature of flexible substrates prevents fabrication of GZO films with low resistivity ρ. Moreover, bombardment by energetic oxygen to the position of the substrate facing the erosion area of the target introduces the nonuniformity of the sputtered film. On the other hand, large dispersion of the resistance in the high resistance state, R_HRS, during cycling is a serious problem in ReRAMs which show steep and discontinuous reset switching, where reset means resistance switching from the low resistance state (LRS) to the high resistance state (HRS). This is due to the difficulty in limiting the current that decreases rapidly. In this paper, we have solved all the above mentioned issues by introducing RF plasma assist for DC magnetron sputtering, which has not been practically applied to GZOTCO films, and fabrication of FT-ReRAM consisting of GZO memory layer and GZO electrodes (all-GZO-FTReRAM) was attained.