Multi-level phase change memory devices with Ge2Sb2Te5 layers separated by a thermal insulating Ta2O5 barrier layer

This work investigates multi-level phase change random access memory (PCRAM) devices comprising two Ge2Sb2Te5 (GST) layers sandwiching a thermal insulating Ta2O5 barrier layer. The PCRAM cell comprises a phase change material stack between a top and a bottom electrode. The phase change material stack comprises a nitrogen doped GST (NGST) layer on a thin Ta2O5 barrier layer on an undoped GST layer. It is demonstrated that one of the phase change layers in the GST stack can be selectively amorphized by using a voltage pulse. This enables multi-level resistance switching. The differences in resistivities, as well as the different melting and crystallization temperatures of both the NGST and GST layers, contribute to the multi-level switching dynamics of the PCRAM device. The thermal conductivity of Ta2O5 with respect to GST is also another factor influencing the multi-level switching. Extensive electrical characterization of the PCRAM devices was performed. Thermal analysis was used to examine the physics behind the multi-level switching mechanism of these devices. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672448]