Disclosed is a method for the manufacture of a CEM device comprising forming a thin film of a correlated electron material having a predetermined electrical impedance when the CEM device in its relatively conductive (low impedance) state, wherein the forming of the CEM thin film comprises forming a d- or f-block metal or metal compound doped by a physical or chemical vapour deposition with a predetermined amount of a dopant comprising a back-donating ligand for the metal.