Research On Bipolar-Pulse Modulating Property Of Phase Change Random Access Memory Cells

Compared with other kinds of semiconductor memories,phase-change random access memory(PCRAM)has obvious advantages on R&W speed,power consumption,cost,radioresistance and multi-level storage,which makes it possible for PCRAM to be the mainstream of new type semiconductor memories.The tremendous resistance differences in the two states of PCRAM allow it to achieve multi-level storage and analog storage.The previous studies on PCRAM multi-level modulating methods are based on changing the parameters and the number of electrical pulse.These studies only use single-polarity pulses,and resistance drift is not considered.Resistive drift is an important factor influencing the multi-level storage performance of PCRAM.Resistance drift is caused by ionic segregation caused by the Joule heating and ionic migration drived by the electric field.A depleted layer forms at the electrode interface,or close to the boundary between the crystalline area and the amorphous area.This unstable area is the origon of the formation of the resistance drift.Bipolar pulse modulating create a negative electric field to suppresses the depleted area.Modulating method by taking advantage of bipolar pulse is proposed in this thesis.A batch of PCRAM samples has been prepared,by which IV-sweep test,RV test,bipolar pulse modulating test and resistance drift test have been accomplished.The simulation results of bipolar pulse modulating test are obtained.A kind of bipolar pulse modulating method is proposed,which is proved to be a good way to suppresses the resistance drift in PCRAM.