Films of chalcogenide Ge–Sb–Te materials were grown by pulsed liquid injection chemical vapor deposition (CVD) technique. Simple thermal CVD without additional process activation and CVD with remote ...activation of precursor decomposition process by a hot-wire were investigated and compared. Ge(NMe
2)
4, Sb(NMe
2)
3 and Te(i-Pr)
2 precursors in a form of diluted solutions in toluene were used for depositions. Film composition was controlled by injection parameters, while the thickness was directly related with number of pulses. Hot-wire activated CVD process allows the growth of chalcogenide films of clearly better quality compared to films grown by standard thermal CVD. Uniform, smooth, crystalline Ge
2Sb
2Te
5 films were grown at substrate/wire temperature 300
°C/550
°C and pressure
⩽
15
Torr, using nitrogen as a carrier gas, on Si, Si/SiO
2, Si/Si
3N
4 and glass substrates. Forty to forty five nanometer thick films on Si/SiO
2 substrates showed reversible electrical and optical phase switching behavior.
The amorphous-to-crystal transition has been studied through in situ resistance measurements in Ge2Sb2Te5 thin films doped by ion implantation with nitrogen, oxygen or fluorine at different ...concentrations. Enhancement of the thermal stability has been observed in O and N amorphous doped Ge2Sb2Te5. Larger effects have been found in the case of nitrogen doping. On the contrary, doping with Fluorine produced a decrease in the crystallization temperature. The electrical properties have been related to the structural phase change through in situ transmission electron microscopy analysis. The comparison between undoped and doped Ge2Sb2Te5 shows that the introduction of oxygen or nitrogen modifies in a different way the kinetics of the amorphous-to-fcc transition and gives new insight on the effects of doping with light elements in GeSbTe alloys.
Resistance distributions for the reset state in phase-change-memory arrays are studied as a function of the programming conditions. The statistical distribution displays a low-resistance tail, which ...may potentially affect the resistance window between the two states in the memory device. The majority of tail cells are found to result from the statistical dispersion of the quenching properties of the chalcogenide material and can be corrected by optimizing the programming operation. On the other hand, a residual tail is found, which is characterized in terms of programming, switching, and conducting characteristics. The measured behavior is consistent with extrinsic low-resistance paths in the programmable volume, which shunts the high-resistance amorphous phase and prevents reaching a fully reset resistance. Removal of this extrinsic tail in the reset distribution is demonstrated by careful optimization of the integration process.
This letter investigates the extraction of activation energy for the crystallization of an amorphous chalcogenide material in phase-change memories. It is demonstrated for the first time that the ...critical resistance, which is the value of resistance defining the crystallization time for the chalcogenide material, has a major impact on the extraction of the activation energy for crystallization. Applying a statistical Monte Carlo model for crystallization coupled with an electrothermal model for both the amorphous and crystalline phases, we analyzed the standard methodology for the extraction of the activation energy. It is shown that a careful choice of the critical resistance is mandatory and a new accurate technique is proposed, resulting in a reliable value for the crystallization activation energy of 2.6 eV in the Ge 2 Sb 2 Te 2 -based devices.
In order to validate phase change memory (PCM) technology, the programming reliability, in terms of reading window between the programmed and erased state, must be guaranteed at array level with an ...error less then 1 part-per-billion. The reset distribution is significantly influenced by the quenching operation Mantegazza D, Ielmini D, Pirovano A, Gleixner B, Lacaita A L, Varesi E, et al. Electrical characterization of anomalous cells in phase change memory arrays. IEDM Tech Dig 2006:53–56. In this paper this phenomenon is explained in terms of PCM active material crystallization statistics. A significant spread in the crystallization times among PCM cells is detected both in the write-reset operation from the melted-amorphous state (quenching) and in the erase-set operation from the solid-amorphous state. At statistical level, a correlation between set at high and low temperatures and quenching behavior of cells is found, allowing to describe the programming distributions uniquely in terms of crystallization times statistics.
To support reliable large array products, phase-change memory (PCM) technologies must be able to retain data over the product's lifetime with very low defect rates. PCM stores data in a chalcogenide ...material which can be placed in either a high resistance amorphous phase or a low resistance crystalline phase. Data retention is limited by resistance loss of the amorphous phase of the material, a process that is controlled by the kinetics of crystallization. This paper presents array-level data retention results on a statistical distribution of PCM cells that shows the failure rate with temperature to be well-described by the Arrhenius equation and distributed lognormally with time. For typical cells, the retention capability exceeds 100,000 hours at 85degC and is capable of meeting product requirements. In non-optimized devices, however, we observe cells that fail earlier than the lognormal distribution would predict. The failure distribution of these cells is Weibull with time but shows similar temperature acceleration to the intrinsic distribution, indicative of a defect in the amorphous chalcogenide. Characterization of these cells shows that their retention behavior is erratic. Furthermore, it is not significantly changed by write cycling. We then show that this defect distribution can be suppressed by process architecture or write algorithm optimization. Retention data collected on cells at both the 180nm and 90nm lithography nodes show that the intrinsic behavior is maintained with process scaling
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