Failure Mechanisms of Ge2Sb2Te5 Phase Change Memory Cell

The failure of the Ge2Sb2Te5 (GST) phase change memory cell has been investigated by the High Resolution Transmission Electron Microscopy (HR-TEM). The HR-TEM results indicate that the both of hexagonal structured GeSbTe (GST) and meta stable GeTe phases are appeared after about 10 cycles of set/reset operations. The face centered cubic structured GST seems to be quickly changed from amorphous to crystalline and amorphous. However, the hexagonal GST phases seem to be not easily changed into the amorphous state, which causes an imperfect quenching during the further reset cycles. And, also it is observed that the GST is depleted at the interface between top electrode and GST and such depleted layer widens during the set/reset operations. Therefore, the stable operation of GST memory cell may be difficult for these reasons. Key-Words: PCRAM, Phase Change, Electrical Failure, GST, HRTEM, Memory Device