Resistance switching of thin AlOx and Cu-doped-AlOx films

• AlOx layers are formed by plasma oxidation for resistance memory device (RRAM).
• Al/AlOx/Al and Al/AlOx-CuOx/Al-Cu exhibit unipolar resistance switching.
• Cu doping assists formation of the filaments of mixed Al and Cu in AlOx.
• Cu doping improves endurance and retention of the AlOx-based RRAM.

Thin copper-doped aluminum oxide (Cu-doped-AlOx) and AlOx films of about 5 nm thick were generated by oxidizing the surfaces of Al and Al-5 wt.% Cu (Al-Cu) films in an oxygen plasma. According to X-ray photoelectron spectroscopy analyses, these two oxide films were found to be deficient in oxygen and had gradient concentrations of Al and O. The oxide films were employed as resistor layers sandwiched between an Al top electrode and an Al or Al-Cu bottom electrode to form resistive memory devices. The devices demonstrated unipolar resistance switching between high resistance state and low resistance state (LRS), and their resistance ratios measured at + 0.2 V were around 105. Furthermore, their current–voltage characteristics showed ohmic conduction with the resistance increasing with temperature, in LRS. Conductive filaments were thought to form inside the AlOx film and the Cu-doped AlOx film, causing resistive switching. The resistive memory device using the AlOx film had unstable switching behaviors during cyclic testing, whereas the device using the Cu-doped AlOx film demonstrated stable resistance switching during 100 cycles of testing. The presence of the Cu ingredient in the AlOx film is likely to facilitate the formation and rupture of conductive filaments and induced stable resistance switching.