Structural, optical, electrical and resistive switching properties of ZnO thin films deposited by thermal and plasma-enhanced atomic layer deposition

In this study, we report on a systematical investigation on the crystal structure, optical and electrical properties of ZnO thin films grown by thermal and remote plasma-enhanced atomic layer deposition (Thermal ALD and PEALD) and their applications in resistive switching devices. The conductivity of ZnO films grown by Thermal ALD at 200 °C is ∼169 S/cm, demonstrating a good potential for the applications in transparent conducting films. It is possible to deposit ZnO films with good structural quality and few defects at lower temperatures by PEALD. The Al/PEALD-ZnO/Pt devices show good resistive switching properties, while the devices using Thermal ALD ZnO films failed to show any resistive switching behavior, but a perfect Ohmic behavior. The thickness ZnO active layer has a strong effect on the device properties. When the thickness of ZnO film is ∼23 nm, the high state-resistance to low state-resistance ratio maintains at larger than 103, while the current compliance for safe operation is ∼1 mA much smaller than those for devices with thick active layers. The results have demonstrated the PEALD grown ZnO films have the excellent properties for the applications in high-density 3D resistive random access memory.