Phase change memory employing a Ti diffusion barrier for reducing reset current

Abstract

Phase Change Memory (PCM) has the potential for use as the flash memories for the next generation due to its scalability, long endurance, high speed, and the possibility of random access. To successfully integrate phase change materials of a GeSbTe (GST) alloy in the device fabrications, the presence of a Ti layer is required to obtain proper contact resistance characteristics and also to improve the adhesion property between the GST alloys and the top TiN electrode. The findings reported herein indicate that Ti can readily diffuse into the GST layer and reduce the set resistance when the subsequent device fabrication involves the heating process. As a result, the reset current significantly increases and the endurance cycles of the PCM device are significantly degraded. We proposed the use of a Highly Nitrogen doped GST (HNGST) layer as a barrier to Ti diffusion, in which the presence of the barrier was able to restore the reset current of the PCM devices down to the level of as-etched PCM cell by the use of a 9nm thick HNGST barrier. In addition, endurance cycles were significantly enhanced from 106 to over 108 by blocking the diffusion of Ti into the program volume of the cell with the HNGST barrier layer.