Synthesis of ion conducting LixAlySizO thin films by atomic layer deposition

Abstract

Thin films of a solid electrolyte, lithium aluminosilicate, were synthesized by atomic layer deposition (ALD) for potential applications in 3D Li-ion microbatteries. The films were deposited at 290 °C via alternating the ALD growth of the constituents, LiOH, Al₂O₃ and SiO₂. Manipulation of the cation composition and thickness was achieved through well-controlled surface reactions during each precursor pulse cycle. Various compositions were obtained by changing the number of pulse cycles for each precursor, which enabled lithium aluminate (Li_xAl_yO), lithium aluminosilicate (Li_xAl_ySi_zO) and stoichiometric LiAlSiO₄ materials to be prepared. The as-deposited ALD films were amorphous and formed conformal coatings over Si nanowires. Films as thin as 6 nm were found to be free of pinholes. Complex impedance measurements confirmed that the films were ionic conductors with the room temperature conductivity in the range of 10⁻⁷ to 10⁻⁹ S cm⁻¹ and an activation energy between 0.46 and 0.84 eV, depending upon the film composition.