A NICAM processor comprises a first memory for temporarily storing a current frame of A-channel and B-channel input data, wherein the current frame data is stored into the first memory at a first clock rate. The inventive method includes the steps of: depositing a zirconium-titanium oxide layer containing zirconium, titanium and oxygen on a substrate; and performing a reforming process for densifying the zirconium-titanium oxide layer and for stuffing oxygen in a surface of the zirconium-titanium oxide layer. User keys created to identify lower-level nodes connected to all nodes of the tree are assigned as first user keys of the nodes for all nodes of the tree, and node identification user keys of the son nodes except for the son node included in the unit tree among node identification user keys that identifies son nodes included in unit trees are assigned as second user keys of the son nodes.