BACKGROUND

Phase change memories may use chalcogenide semiconductors for storing states. The chalcogenide semiconductors have a crystalline state and an amorphous state. In the crystalline state, the phase change materials have a low resistivity, while in the amorphous state they have a high resistivity. The resistivity ratios of the phase change materials in the amorphous and crystalline states are typically greater than 1,000, and thus the phase change memory devices are unlikely to have erroneous reading. The chalcogenide materials are stable at certain temperature ranges in both crystalline and amorphous states and can be switched back and forth between the two states by electric pulses.

Phase change memories has several operating and engineering advantageous features, including high speed, low power, non-volatility, high density, and low cost. For example, phase change memories are non-volatile and may be written-into rapidly, for example, within less than about 50 nanoseconds. The Phase change memory cells may have a high density. In addition, phase change memories are compatible with CMOS logic and can generally be produced at a low cost compared to other types of memory cells.

