Synthesis of ion conducting Li_xAl_ySi_zO 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 (LixAlyO), lithium aluminosilicate (LixAlySizO) 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.