A memory may include a phase change memory element and series connected first
and
second selection devices. The second selection device may have a higher resistance
and a larger threshold voltage than the first selection device. In one embodiment,
the first selection device may have a threshold voltage substantially equal to
its holding voltage. In some embodiments, the selection devices and the memory
element may be made of chalcogenide. In some embodiments, the selection devices
may be made of non-programmable chalcogenide. The selection device with the higher
threshold voltage may contribute lower leakage to the combination, but may also
exhibit increased snapback. This increased snapback may be counteracted by the
selection device with the lower threshold voltage, resulting in a combination with
low leakage and high performance in some embodiments.