Fig.1 The cross sectional TEM image of the 40nm WOX ReRAM cell. The ring of TiNOX produced during RTO of W plug is non-conducting. Fig.3 RESET and SET voltages for WOX devices of various size. The switching voltages are independent of device size, an indication of filament forming/rupturing mechanism [4-5].Fig.4 RESET/SET current and initial resistance for various WOX devices.Switching current for 40nm device decreases drastically, while the initial state resistance increases as device scales. The smaller devices are more power efficient. Fig.2 Operation of the 40nm WOX device. A negative forming pulse is used to obtain the first SET state. Then the cell can be switched in bipolar operation: Positive pulse for RESET, and negative pulse for SET.
Abstract40nm WO X ReRAM has several unique characteristics that are very favorable for MLC application. (1) Although the resistance has strong temperature dependence (as for all ReRAM's) the J-V characteristics can be accurately described, thus all MLC levels are easily modeled. (2) The device is immune to over-erase, thus allow fast MLC programming. (3) The programming is self-converging (as Flash memories) and is independent of history. Thus an algorithm similar to ISPP (Incremental Step Pulse Programming), commonly used by MLC NAND flash, is designed to achieve accurate MLC states. Consequently, fast 50ns switching, 2-bit/cell and 3-bit/cell MLC states with good cycling characteristics and low read disturbance (> 10 10 ) is achieved.
The resistance of phase-change-memory (PCM) cells measured during RESET programming (dynamic resistance, R d ) is found to be inversely proportional to the amplitude of the programming current, as R d = [A/I] + B. We show that parameters A and B are related to the intrinsic properties of the memory cell, and demonstrate by means of experimental data that they could be used to characterize the cell-to-cell process-induced variability of PCM cells.Index Terms-Chalcogenide, electrothermal simulations, nonvolatile memory, phase-change memory (PCM).
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