An integrated circuit memory is based on isolation device free memory cells. The memory cells are passively coupled to bit lines and word lines. The memory cells include an anti-fuse element and an element of phase change material in series. A rupture filament through the anti-fuse layer acts as an electrode for the phase change element. Control circuitry is configured to apply bias arrangements for operation of the memory cells, including a first write bias arrangement to induce a volume of the higher resistivity phase in the phase change material establishing a first threshold for the selected memory cell below a read threshold, a second write bias arrangement to induce a larger volume of the higher resistivity phase in phase change material establishing a second threshold for the selected memory cell above the read threshold, and a read bias arrangement to apply the read threshold to the selected memory cell.