  We observed two types of unipolar resistance switching (RS) in NiO film:
memory RS at low temperature and threshold RS at high temperature. We explain
these phenomena using a bond percolation model that describes the forming and
rupturing of conducting filaments. Assuming Joule heating and thermal
dissipation processes in the bonds, we explain how both RS types could occur
and be controlled by temperature. We show that these unipolar RS are closely
related and can be explained by a simple unified percolation picture.
