Effects of oxygen flow rate on the physical properties of PCMO thin films

抄録

Resistive Random Access Memory (ReRAM) has various advantages such as low power consumption, high integration, and fast read out time. PCMO is one of the promising candidates of materials used in ReRAM. Although ReRAM has already been partially in practical use, its operating mechanism is not yet fully understood.

In this study, we focused on the oxygen deficiency model, which is one of the models of ReRAM operation, and researched how the physical properties of PCMO thin films are affected by the oxygen flow rate during film deposition.

PCMO(Pr_0.7Ca_0.3MnO₃) thin films were deposited by RF magnetron sputtering with the oxygen flow rates of 0, 0.8, and 1.6 sccm during deposition. During this process, the flow rate of argon gas was kept constant, and the total pressure was maintained at 2.0 Pa. STO(100) and LAO(100) substrates were used and films were deposited at a substrate temperature of 650°C.STO(100) and LAO(100) have lattice constants of 0.3975 nm and 0.3821 nm, respectively. These lattice constants are close to that of PCMO, but the tensile and compressive stresses are introduced on STO and LAO substrates, respectively. To evaluate the crystallinity, chemical bonding states, and film thickness of these thin films, X-ray diffraction (XRD), Electron Spectroscopy for Chemical Analysis (ESCA), and stylus profilometry were used.

The thickness of the PCMO film was approximately from 10 nm to 45 nm.

Figure 1 shows the XRD patterns of PCMO thin films fabricated on the LAO(100) substrate. The diffraction peak from PCMO deposited on the LAO(100) substrate appeared at slightly lower angles than that of the substrate peak. This indicates that the PCMO grows epitaxially. Furthermore, with increasing the oxygen flow rate during deposition, the intensity of PCMO(200) peak decreases. Oxygen was introduced to compensate for oxygen deficiencies during deposition. The present result, however, shows a deterioration of the crystallinity of the PCMO thin films by the supply of oxygen. Therefore, it is required to investigate the chemical states of Mn and O atoms in PCMO film to discuss the reason of the deterioration of the crystallinity.

The details of results of the evaluation of chemical bonding states by Electron Spectroscopy for Chemical Analysis (ESCA) will be shown in the conference.