Atomic Layer Deposition of a Magnesium Phosphate Solid Electrolyte

Atomic layer deposition (ALD) was used to fabricate magnesium phosphate thin films as a magnesium-ion conducting solid electrolyte. The deposition was carried out at lower deposition temperatures, ranging from 125 to 300 °C. The film exhibits an amorphous nature and excellent step coverage, even in narrow trenches with a higher aspect ratio. The growth rate and the ionic conductivity were found to increase with a decrease of the deposition temperature. This can be explained by increased disordering of the phosphate matrix, giving rise to enhanced hopping conduction of magnesium ions. The film deposited at 125 °C showed an ionic conductivity of 1.6 × 10–7 S cm–1 at an ambient temperature of 500 °C, with an activation energy of 1.37 eV. These values are better than those of the film deposited at 250 °C as well as of a sputtered film. Our results indicate that ALD has great potential for the fabrication of magnesium-based solid electrolyte films.