Atomic Layer Deposition of Lithium Tantalate Solid-State Electrolytes

3D all-solid-state microbatteries are promising onboard power systems for autonomous devices. The fabrication of 3D rnicrobatteries needs deposition of active materials, especially solid-state electrolytes, as conformal and pinhole free thin films in 3D architectures, which has proven very difficult for conventional deposition techniques, such as chemical vapor deposition and physical vapor deposition. Herein, we report an alternative technique, atomic layer deposition (ALD), for achieving ideal solid-state electrolyte thin films for 3D microbatteries. Lithium tantalate solid-state electrolytes, with well-controlled film composition and film thickness, were grown by ALD at 225 degrees C using subcycle combination of 1 x Li2O + n X Ta2O5 (1 <= n <= 10). The film composition was tunable by varying Ta2O5 subcycles (n), whereas the film thickness displayed a linear relationship with ALD cycle number, due to the self-limiting nature of the ALD process. Furthermore, the lithium tantalate thin films showed excellent uniformity and conformity in 3D anodic aluminum oxide template. Moreover, impedance testing showed that the lithium tantalate thin film exhibited a lithium ion conductivity of 2 X 10(-8) S/cm at 299 K. The lithium tantalate thin films by ALD, featured with well thickness and composition, excellent step coverage, and moderate ionic conductivity at room temperature, would be promising solid-state electrolytes for 3D microbatteries.