Papers by Keyword: Phase Change Memory (PCM)

Abstract: Carbon-doped Sb-rich Ge-Sb-Te (Sb-CGST) is proved to be a promising candidate for phase change memory because of it high crystallization temperature (higher than 200°C) and 10-year data retention temperature (higher than 120°C). The carbon-doped Sb-rich Ge-Sb-Te (Sb-CGST) films were deposited on SiO₂/Si (100) substrate by RF magnetron co-sputtering using CGST alloy target (a GST target containing 16 at. % C) and Sb targets at room temperature. The content of Sb in the films was controlled by adjusting the sputtering power ratio of CGST and Sb. The results showed that both of these two properties increase firstly and then decreases with increasing the content of Sb, which are superior to that of Ge₂Sb₂Te₅. Furthermore, Sb-CGST based PCM cells were fabricated to investigate the property of material. 6ns pulse could realize SET operation, and 3.2 x 10^-11J energy can realize RESET operation.

Abstract: Stability is one of the most important criterions to judge the quality of products, especially for the phase-change memory (PCM), which is regarded as the most promising candidate for next-generation non-volatile memory. Due to the lack of resistance stability, read errors can occur easily and the reliability of PCM will be influenced. Using Sb₂Te as a base material, the resistance stability of Sb₂Te was studied, and the results indicated that in the whole cooling process, the resistance of Sb₂Te crystalline film was extremely steady under different annealing temperatures and different cooling rates. To unravel the reason why the resistance of Sb₂Te crystalline film has good stability, further study was carried out and the results showed that there was no new diffraction peak in the XRD pattern, and the HRTEM images showed the similar hexagonal phase for the films under different annealing temperatures. Moreover, it was observed that the resistance in Sb₂Te-based PCM device was still stable for crystalline state and amorphous state. These results revealed that the stability of Sb₂Te crystalline films at a micro level and the stability of microscopic structure resulted in the stability of resistance. Therefore, based on the present study, the stability of phase-change material Sb₂Te can be applied to exploit more reliable PCM for near-future application.

Abstract: Power consumption has long been a great obstacle in phase change memory technology. Silicon carbide was introduced to be a buffer layer between the phase change material and the metal electrode in this work. The results showed that the new structure mitigated the energy consumption and maintained the advantage of high speed. This is attributed to the thin SiC buffer layer that helps confine the generated Joule heat inside the active phase change volume and form more conducting paths by the high efficiency of the heat utilization. Additionally, another key role — inhibition of the material separation, is conducive to achieving stable and sustainable electrical operations.

Abstract: Reliability (or stability) of multi-level storage (MLS) is the critical characteristics for multi-level cells. In order to improve reliability of MLS of phase-change memory, there are two effective approaches, (i) enlargement of the ratio between resistance levels and (ii) reduction of scattering of resistance level. On the basis of our experimental results, it is demonstrated that the Ge₂Sb₂Te₅-based double-layered cell has a high ratio of highest to lowest levels up to two-to-three orders of magnitude, implying high reliability. The cells exhibit the possibility of stable switching for four-level storage.

Abstract: Crystallization behaviors of dc sputtered Ge2Sb2Te5 films were studied by X-ray diffraction and transient optical transmittance. Crystalline peak at 29.0° in diffraction patterns appeared after thermal annealing at 180 and 210 °C. Crystallization rate increased after thermal annealing below crystallization temperature. These observations indicate that heat-induced structural change enhances crystallization rate of Ge₂Sb₂Te₅ films.

Abstract: Phase change memory materials of Ge-Sb-Te system [(GeTe)m(Sb2Te3)n (m : n = 1:1; 1:2; 2:1)] were studied during thermal cycling by differential scanning calorimetry, and thermal properties were determined. Reproducible endothermic peak in the range of 390-415°C was revealed in Ge2Sb2Te5, GeSb2Te4, GeSb4Te7, which may possibly influence on the kinetics and endurance of data reading processes in phase-change memory devices. The nature of this endothermic peak is discussed. It was shown that additional annealing of synthesized Ge2Sb2Te5 increase stability of structure and thermal properties of the material.

Abstract: This paper reports on the confined-chalcogenide phase change memory with thin metal interlayer (CCTMI) with the operating reset current of 0.6mA-30ns. This cell offers low reset current with simple architecture and fabrication. Thermal and heat flux distribution of both the normal-bottom-contact (NBC) and a proposed CCTMI PCM cells were carefully analyzed and simulated by two-dimensional finite element modeling. It is intriguingly found that the reset operation current of the CCTMI cell is 44% lower than that of the NBC. CCTMI has capability to solve an over-programming fail issue due to confined heat dissipation in active area.