Electronic properties of GST for non-volatile memory (original) (raw)
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Electrical properties of the Ge2Sb2Te5 thin films for phase change memory application
AIP Conference Proceedings, 2016
In this study I-V characteristic, temperature dependence of resistivity, thermopower, switching and memory effect were investigated for GST225 thin films. Resistivities, ratio of the resistivities of amorphous and crystalline states, activation energies of conductivity, temperature of phase transition, Seebeck coefficient, transition time due to the transformation from OFF to ON states and full recording time were estimated. It was shown that transport mechanism based on the two-channel model has a good correlation with experimental results for Ohmic region of I-V characteristic, while space-charge limited current mechanism for power region.
Si doping in Ge2Sb2Te5 film to reduce the writing current of phase change memory
Applied Physics A, 2007
The characteristics of phase change memory devices in size of several micrometers and with pure Ge 2 Sb 2 Te 5 (GST), N-doped GST, and Si-doped GST films were investigated and compared with each other. The Si-doped GST device can perform SET and RESET cycles, even if the Si dopant is as small as 4.1 at. %. But the GST and N-doped GST device cannot perform the RESET process, though the SET state resistance of N-doped device is almost the same as that of Si-doped device and larger than that of GST device. In order to explain this phenomenon, the electrical and DSC characteristics of three kinds of films were investigated. Phase separation was found in Si-doped GST films. The reason of the RESET ability of Sidoped GST devices is supposed to be the existence of rich Si phases which act as micro-heaters. Thermal conduction simulations confirmed this supposition and indicate that the separated high resistance phase (rich Si phase) can heat the active volume of device efficiently and reduce the writing current largely.
Applied Surface Science, 2006
The effects of Si doping on the structural and electrical properties of Ge 2 Sb 2 Te 5 film are studied in detail. Electrical properties and thermal stability can be improved by doping small amount of Si in the Ge 2 Sb 2 Te 5 film. The addition of Si in the Ge 2 Sb 2 Te 5 film results in the increase of both crystallization temperature and phase-transition temperature from face-centered cubic (fcc) phase to hexagonal (hex) phase, however, decreases the melting point slightly. The crystallization activation energy reaches a maximum at 4.1 at.% and then decreases with increasing dopant concentration. The electrical conduction activation energy increases with the dopant concentration, which may be attributed to the increase of strong covalent bonds in the film. The resistivity of Ge 2 Sb 2 Te 5 film shows a significant increase with Si doping. When doping 11.8 at.% of Si in the film, the resistivity after 460 8C annealing increases from 1 to 11 mV cm compared to the undoped Ge 2 Sb 2 Te 5 film. Current-voltage (I-V) characteristics show Si doping may increase the dynamic resistance, which is helpful to writing current reduction of phase-change random access memory.
2011 IEEE International Interconnect Technology Conference, 2011
Phase change memory technology is considered as one of the most promising resistive memory solution. One issue, however, is the high electrical current required to reset the information. Indeed large energies are mandatory for amorphization of the crystalline phase change material. It has been demonstrated that energies can be highly decreased by reduction of the active volume and confinement of the phase change material. To do so, phase change materials deposition route with high filling capacity is needed. Atomic Layer Deposition (ALD) is well known for its high conformity. However, such a process is still a challenge for phase change materials such as Ge x Sb y Te z (GST). In this work, (i) ALD GST films are processed and characterized and (ii) realisation of phase change memory devices using ALD GST is demonstrated on 200mm wafers.
Advances in OptoElectronics, 2012
Germanium antimony (Ge-Sb) thin films with tuneable compositions have been fabricated on SiO2/Si, borosilicate glass, and quartz glass substrates by chemical vapour deposition (CVD). Deposition takes place at atmospheric pressure using metal chloride precursors at reaction temperatures between 750 and 875°C. The compositions and structures of these thin films have been characterized by micro-Raman, scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) techniques. A prototype Ge-Sb thin film phase-change memory device has been fabricated and reversible threshold and phase-change switching demonstrated electrically, with a threshold voltage of 2.2–2.5 V. These CVD-grown Ge-Sb films show promise for applications such as phase-change memory and optical, electronic, and plasmonic switching.
Voltage polarity effects in Ge2Sb2Te5-based phase change memory devices
Journal of Applied Physics, 2011
We assess voltage polarity effects in phase-change memory (PCM) devices that contain Ge 2 Sb 2 Te 5 (GST) as the active material through the study of vertically asymmetric pore-cell and laterally symmetric bridge-cell structures. We show that bias polarity can greatly accelerate device failure in such GST-based PCM devices and, through extensive transmission electron microscopy-based failure analysis, trace these effects to a two-stage elemental segregation process. Segregation is initially driven by bias across the molten region of the cell and is then greatly enhanced during the crystallization process at lower temperatures. These results have implications for the design of pulses and PCM cells for maximum endurance, the use of reverse polarity for extending endurance, the requirements for uni-or bi-polar access devices, the need for materials science on active rather than initial stoichiometries, and the need to evaluate new PCM materials under both bias polarities.
Enhanced Thermal Efficiency in PhaseChange Memory Cell by Double GST Thermally Confined Structure
IEEE Electron Device Letters, 2007
A novel phase-change memory cell with a doubleconfinement structure was proposed and fabricated in this work. By having an additional bottom Ge 2 Sb 2 Te 5 layer under the electrically confined active region, the heat loss can be effectively prevented. The temperature uniformity over the active region significantly improves and so does the thermal efficiency. Therefore, a low I RESET of about 0.3 mA and a reset power can be achieved. For the SET performance, a pulsewidth as low as 200 ns can be used without compromising the R SET .
Characteristics of Phase Change Memory Devices based on Ge-doped SbTe and its derivative
2007
As a promising candidate for a phase change material of a highly fast and scalable non-volatile memory, Ge-doped SbTe with a certain range of Sb and Te content has interesting material properties such as a low melting temperature, fast crystallization with a high crystallization temperature, and a low electrical resistivity. Using test vehicles based on a cell structure with a contact pore of 100 to 200nm in size, Ge-doped SbTe of two different compositions (Sb/Te atomic ratio of 4.53 and 2.08) were examined and compared with Ge 2 Sb 2 Te 5 in term of important device characteristics such as SET speed, SET resistance as well as RESET current. Between the two compositions, Gedoped SbTe of the higher Sb content was found superior by far in SET speed, which is considered to arise from fast growth-dominated crystallization characteristics of the material combined with the nature of a SET process within the device that does not necessarily require nucleation of crystallites in the presence of movable inter-phase boundaries. Ge-doped SbTe of the higher Sb content was also shown to provide a higher SET speed by more than two orders of magnitude and a lower SET resistance by about one tenth than Ge 2 Sb 2 Te 5. As for RESET current, the material was observed to require a higher current than Ge 2 Sb 2 Te 5 for a stable operation but there appears much room for improvement with a proper understanding of the apparently incomplete RESET at a much lower current level than the one for a stable RESET. Lastly, a derivative of Ge-doped SbTe of the higher Sb/Te content was formed by addition of nitrogen, which turned out to provide an effective means to reduction in RESET current without significantly decreasing SET speed.
Journal of Applied Physics, 2008
We present chemical state information on contamination-free Ge 2 Sb 2 Te 5 thin film using high-resolution x-ray photoelectron spectroscopy ͑HRXPS͒ and the corresponding theoretical understanding of the chemical states, on both amorphous and metastable phases, illuminating the phase-change mechanism of the system. HRXPS data revealed that the Sb 4d shallow core level was split into two components having different binding energies and that the spin-orbit splitting feature of the Ge 3d level was enhanced as the system became metastable. Negligible change was observed in the Te 4d shallow core level, and in contrary to the previous report's prediction less change in valance band spectra was observed. The results imply that Sb movement is also involved in the phase-change mechanism and that acquisition of shallow core-level spectra can be a useful measure for understanding phase-change mechanism. Hydrogenated SbTe 6 octahedral-like cluster model was introduced to schematically interpret the generation of the two components in the Sb 4d level in metastable state, having an isotropic six-bonds configuration, and an anistropic six-bonds ͑three-short and three-elongated bonds͒ configuration. The amorphous state was modeled to have three-short bonds configuration. Finally, Stibnite-like building block model was used to show that the existence of the above two configurations for Sb atoms is feasible in the Ge 2 Sb 2 Te 5 system.