Properties of Lithium Phosphorus Oxynitride Films Prepared By Metalorganic Chemical Vapor Deposition Method

Abstract

3D-structured thin-film batteries draw attention to applications like IoT, wearable, and medical devices because of their having non-flammability, electrochemical stability, and flexibility; furthermore, their capacity density can be enhanced by designing the structure, e.g. the aspect ratio (AR) of trench and pillar structures. For realizing 3D-structured batteries with high-capacity density, the step coverage for high AR-patterned structures is a crucial process parameter. In the case of conventional physical vapor deposition (PVD) method, the coverage is not conformal enough to deposit onto a high AR-patterned surface. On the other hand, chemical vapor deposition (CVD) method is attractive to deposit much more conformal films than PVD. In this study, properties of lithium phosphorus oxynitride (LiPON), which is a promising thin-film electrolyte material due to high-chemical stability and nontoxicity, films deposited using metalorganic (MO) CVD are investigated in detail. In this experiment, utilized precursors were lithium tert-butoxide, tris(dimethylamino)phosphine, O2, and NH3. Chemical composition and microstructure of prepared films were evaluated by various analytical methods such as XPS, RBS/NRA, Raman spectroscopy, and XRD. In addition, electrochemical properties of the film were evaluated by AC impedance (Nyquist plot) and cyclic voltammetry methods. Using this MOCVD system, Li4.1PO4.2N0.7 film with 7.5 nm of crystallite size and 5.0 nm/min of deposition rate shows 5.9x10-6 S/cm at 200 nm and 3.3x10-6 S/cm at 50 nm of ionic conductivity, and an excellent step coverage on a patterned substrate is also shown by SEM and EDX (Fig. 1). These results demonstrate the LiPON film deposited by MOCVD would be successfully available for 3D-structured thin-film batteries. Figure 1