1. Technical Field
The relates to a phase-change random access memory (PCRAM) device, and more particularly, to a PCRAM device and a method of manufacturing the same.
2. Related Art
With demands on lower power consumption, next-generation memory devices having nonvolatile and non-refresh properties have been studied. A PCRAM device of the next-generation memory devices includes a switching element connected at intersections of word lines and bit lines, which are arranged to cross each other, a lower electrode electrically connected to the switching element, a phase-change layer formed on the lower electrode, and an upper electrode formed on the phase-change layer.
In a conventional PCRAM device, when a write current flows through the switching element and the lower electrode, Joule heat is generated at an interface between the phase-change layer and the lower electrode. The phase-change layer is phase-changed into an amorphous state or a crystalline state by the generated joule heat. Therefore, the conventional PCRAM device stores data using a difference between resistances in the amorphous state and the crystalline state of the phase-change layer.
However, in the conventional PCRAM device, the Joule heat generated when the write current flows affects a phase-change layer of adjacent cell.
The effect on adjacent cells is generally referred to as thermal disturbance. In recent years, the thermal disturbance has an increased effect on adjacent cells when a semiconductor memory device is highly integrated.
FIGS. 1A and 1B are views illustrating thermal disturbance of a conventional PCRAM device.
As shown in FIGS. 1A and 1B, the conventional PCRAM device includes a lower electrode 10 formed on a switching element (not shown), a phase-change layer 20 formed on the lower electrode 10, and an upper electrode 30 formed on the phase-change layer 20. The reference numeral 40 denotes an insulating layer.
As shown in FIG. 1A, if a cell A is written when cells B are written with data “1”, which is a high resistance state, Joule heat is generated at an interface between the lower electrode 10 and the phase-change layer 20 of the cell A (see FIG. 1B), and thus, phase-change material patterns of amorphous states in the cells B are crystallized. Therefore, resistances of the cells B are reduced.
The thermal disturbance generated in the conventional PCRAM device may cause a malfunction, and thus reliability of the conventional PCRAM device is degraded.