Abstract
In this paper, we propose an optimum access method for a phase change memory (PCM) with NAND strings. A PCM with a block erase interface is proposed. The method, which has a SET block erase operation and fast RESET programming, is proposed since the SET operation causes a slow access time for conventional PCM;. From the results of measurement, the SET-ERASE operation is successfully completed while the RESET-ERASE operation is incomplete owing to serial connection. As a result, the block erase interface with the SET-ERASE and RESET program method realizes a 7.7 times faster write speed compared than a conventional RAM interface owing to the long SET time. We also give pass-transistor design guidelines for PCM with NAND strings. In addition, the write-capability and write-disturb problems are investigated. The ERASE operation for the proposed device structure can be realized with the same current as that for the SET operation of a single cell. For the pass transistor, about 4.4 times larger on-current is needed to carry out the RESET operation and to avoid the write-disturb problem than the minimum RESET current of a single cell. In this paper, the SET programming method is also verified for a conventional RAM interface. The experimental results show that the write-capability and write-disturb problems are negligible.
