The present disclosure relates generally to Hf-comprising materials for use in, for example, the insulator of a RRAM device, and to methods for making such materials. In one aspect, the disclosure provides a method for the manufacture of a layer of material over a substrate, said method including a) providing a substrate, and b) depositing a layer of material on said substrate via ALD at a temperature of from 250 to 500° C., said depositing step comprising: at least one HfX4 pulse, and at least one trimethyl-aluminum (TMA) pulse, wherein X is a halogen selected from Cl, Br, I and F and is preferably Cl.