An outer assembling mechanism of a backpack for carrying a detachable skate. The carrier has a core portion comprising a cubic or tetragonal stabilized zirconia-based composite oxide containing at least one stabilizing element, and a surface layer portion including a heat resistant zirconia-based composite oxide formed on a surface of the core portion. In the circuitry area, additional main reference cells are provided, which are configured to also have a threshold voltage corresponding to an erased or programmed state of a memory cell.