Conformal deposition of lithium phosphate thin film electrolytes for 3D solid state batteries by MOCVD

A metal-organic chemical vapor deposition (MOCVD) process was developed to deposit high quality lithium phosphate (Li3PO4) thin films using lithium dipivaloylmethanate (Li(DPM)), triethyl phosphate (TEP) and H2O as the precursor materials. The use of water as an activating agent helps stimulate the formation of a lithium phosphate structure and tailor the process to the reaction-controlled regime. Consequently, lithium phosphate thin films were deposited uniformly with ~ 46% step coverage on trenched substrates with an aspect ratio of 6:1, demonstrating the feasibility of the three-dimensional (3D) deposition of Li3PO4 by MOCVD. In the temperature range of 300-450 °C, an increase in temperature led to the development of crystallinity, increased growth rate, and decreased lithium concentration. The concentrations of Li, P, and O were homogeneous along the film depth. The films deposited at 400 °C exhibited the highest ionic conductivity (5 × 10− 8 S cm− 1) due to the optimal elemental ratio and crystallinity. The method developed in this study can also be applied for the uniform deposition of other materials on 3D geometries by using suitable activating agents.