PMMA interlayer-modulated memory effects by space charge polarization in resistive switching based on CuSCN-nanopyramids/ZnO-nanorods p-n heterojunction

Resistive switching (RS) devices are commonly believed as a promising candidate for next generation nonvolatile resistance random access memory. Here, polymethylmethacrylate (PMMA) interlayer was introduced at the heterointerface of p-CuSCN hollow nanopyramid arrays and n-ZnO nanorod arrays, resulting in a typical bipolar RS behavior. We propose the mechanism of nanostructure trap-induced space charge polarization modulated by PMMA interlayer. At low reverse bias, PMMA insulator can block charges through the heterointerface, and V(-)Cu and V(+)o trapped states are respectively created on both sides of PMMA, resulting in a high resistance state (HRS) due to wider depletion region. At high reverse bias, however, electrons and holes can cross PMMA interlayer by Fowler-Nordeim tunneling due to a massive tilt of energy band, and then inject into the traps of ZnO and CuSCN, respectively. V(+)Cu and V(-)O trapped states are created, resulting in the formation of degenerate semiconductors on both sides of PMMA. Therefore, quantum tunneling and space charge polarization lead to a low resistance state (LRS). At relatively high forward bias, subsequently, the trapped states of V(-)Cu and V(+)o are recreated due to the opposite injection of charges, resulting in a recovery of HRS. The introduction of insulating interlayer at heterointerface, point a way to develop next-generation nonvolatile memories.