  We fabricated Pt/NiO/Pt capacitor structures with various bottom electrode
thicknesses, $t_{BE}$, and investigated their resistance switching behaviors.
The capacitors with $t_{BE} \geq 50$ nm exhibited typical unipolar resistance
memory switching, while those with $t_{BE} \leq 30$ nm showed threshold
switching. This interesting phenomenon can be explained in terms of the
temperature-dependent stability of conducting filaments. In particular, the
thinner $t_{BE}$ makes dissipation of Joule heat less efficient, so the
filaments will be at a higher temperature and become less stable. This study
demonstrates the importance of heat dissipation in resistance random access
memory.
