Modified resistive switching performance by increasing Al concentration in HfO2 on transparent indium tin oxide electrode

Abstract

In this work, a detailed improvement in the resistive switching behavior of Al-doped HfAlO-based resistive random-access memory (RRAM) devices was studied by controlling the Al ratio during atomic layer deposition (ALD) on a transparent indium tin oxide (ITO) electrode. The deposition of Al-doped HfO2 at 280 °C demonstrated a significant reduction in In and Sn diffusion from the ITO electrode compared with the ALD of HfO2 when examined by transmission electron microscopy and energy-dispersive X-ray spectroscopy. X-ray photoelectron spectroscopy confirmed that the bandgap energy increased with increasing Al content, further reducing the leakage current and creating additional extrinsic defects. A higher concentration of trivalent Al into HfO2 intrinsically distributes oxygen vacancies (Vo) in a uniform manner, further controlling the gradual resistive switching in the RRAM device. Improved cycle-to-cycle variability with a maximum on/off ratio of ~44 was achieved with better retention properties of as much as 5 × 103 s. Multilevel conductance modulation under DC and pulse conditions was successfully demonstrated, together with synaptic properties of potentiation/depression and spike time-dependent plasticity, for Al-doped HfO2 RRAM devices.