The thermo-chemical effect (TC) lies conceptionally in-between the two other variants. The effect occurs in oxides and presumably some sulfides. It is a thermal effect triggered by a forming process which is a controlled electrical breakdown located at crystal defects, resulting in a nanosized filament. Different current levels lead to temperature-related changes of the local composition of the filament – including local valence and phase changes – and, hence, to different resistance states. This phenomenon is also known as a fuse – antifuse effect. The thermo-chemical (TC) and the phase change (PC) effects being of a thermal nature, show a unipolar switching.