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Temperature‐Dependent Thermal Conductivity and Interfacial Resistance of Ge‐Rich Ge 2 Sb 2 Te 5 Films and Multilayers
Abstract
This article reports on the thermal characterization of Ge-rich Ge2Sb2Te5 films and Ge2Sb2Te5/Ge-rich Ge2Sb2Te5 multilayers designed for high-temperature applications in the field of phase-change memory. The thermal conductivities of such materials and the thermal boundary resistance with the Si3N4 dielectric material are characterized by two different photothermal techniques. The phase change in Ge-rich Ge2Sb2Te5 is found to occur at a temperature higher than that of the Ge2Sb2Te5 alloy. The Ge2Sb2Te5/Ge rich Ge2Sb2Te5 multilayer has been observed to feature two phase changes corresponding to Ge-rich Ge2Sb2Te5 and Ge2Sb2Te5. Finally, it is estimated that the thermal resistance of the interface separating Ge-rich Ge2Sb2Te5 and Ge2Sb2Te5 nano layers constitutes the multilayer structure and its contribution has been realized to be significant in enhancing the thermal resistance of the multilayer structure.
... There is a linear trend, that is, described by Eq. (3), where N is proportional to the thickness of the MLS. The thermal resistance of a single 100 nm thick GeGST layer (measured in previous works 19 ) is also reported in (2). References are also indicated for each parameter. ...
... References are also indicated for each parameter. 19 An in situ structural analysis of the samples from room temperature to 450 C and back to room temperature has been conducted in order to investigate this behavior. ...
... This increase in the crystallization temperature can explain the unexpected lower drop in RTH (Fig. 3) compared to previous work. 19 In order confirm that the TiN encapsulation might be at the origin of this behavior, we need to make sure that the interfaces between the layers of the MLS are still intact after annealing. Otherwise, the hypothesis would be wrong. ...
In the domain of phase change memories (PCMs), intensive research is conducted to reduce the programming cycle cost. The RESET operation is done by melting the PCM and then quenching the liquid phase to put it back to the amorphous state. In most of the devices, the heating is realized by the Joule effect with a titanium nitride (TiN) component put in contact with the PCM itself. One of the crucial points to improve the efficiency of this technology is to characterize the thermal contact between TiN and PCM. Having a low thermal resistance between the heater and the PCM ensures the heat transfer between the two is as efficient as possible. In this work, the interfacial thermal resistance between Ge-doped G 2 Sb 2 Te 5 (GeGST)/TiN in multilayer systems has been characterized, and the influence of the compressive stress exerted by the TiN layers on the GeGST crystallization has been highlighted. Published under an exclusive license by AIP Publishing. https://doi.
... They found high data retention properties which they attributed to the long-range diffusion of Ge atoms, responsible for the high crystallization temperature of 275 °C for Ge-rich regions and still relatively high 245 °C for a reduced amount of excess Ge. Similarly, Ge-rich GeSbTe films were investigated by Kusiak et al. who found a higher phase change temperature and an enhanced thermal resistance [30]. Cecchi et al. investigated the undesired decomposition of such Ge-rich GeSbTe alloys and reported Ge-rich Ge 2 Sb 2 Te 5 to be less susceptible to decomposition than Ge-rich Sb 2 Te 3 [31]. ...
--- Applied Research ---
Graphical Abstract Phase change memory (PCM) belongs to the non-volatile solid-state memory techniques. Data are stored by setting each cell to a low-resistance (crystalline) or a high-resistance (amorphous) state. While fast switching and multi-level data storage are advantageous, writing currents and data retention still show potential for optimization. This review gives an overview of the most recent developments in new material compositions and material-related optimization of PCM in comparison with already produced PCM. Abstract Phase change memory (PCM) belongs to the non-volatile solid-state memory techniques. Usually, a chalcogenide is sandwiched between two conductive electrodes, and data are stored by setting each cell to a low-resistance (crystalline) or a high-resistance (amorphous) state. Switching between these states is relatively fast, which makes phase-change random access memories (PCRAMs) highly interesting for non-volatile memories. Multi-level cells, which can store more than one bit per cell, and multilayer high-density memory arrays have also been reported as advantages of PCRAM. Writing currents and data retention, on the other hand, still show potential for optimization. This review gives an overview of the most recent This article is protected by copyright. All rights reserved. Accepted Article developments in new material compositions and material-related optimization of PCM in comparison with already produced PCM.
Exploration of the optoelectronic memristor is required to investigate the photoelectric properties of materials. The traditional memristor material GeAs 2 Te 4 is hopeful to be developed into a new type of optoelectronic memristor. However, acquiring high-quality single crystals remains challenging, and the electrical properties of single crystals of GeAs2Te4 need to be explored. Herein, a controlled method is introduced to grow reliable quality GeAs 2 Te 4 single crystals, and the electrical and optoelectronic properties are studied. The photodetector based on GeAs 2 Te 4 exhibits acceptable optoelectronic performance at designed low temperatures. The responsivity and detectivity of the GeAs 2 Te 4 -based photodetector reached the value of about 0.137 A W ⁻¹ and 6.9×10 ⁷ Jones, respectively. It is promising to introduce this family of materials into the field of photodetector and also maybe further in the area of optoelectronic memristors.
Phase change memories (PCRAM) are often made of chalcogenide alloys in the form of multilayer systems (MLS). The mostly used alloys are Ge 2 Sb 2 Te 5 and Ge‐rich Ge 2 Sb 2 Te 5 . The current article reports on the thermal characterization of very thin (<5 nm) Ge‐rich Ge 2 Sb 2 Te 5 /Ge 2 Sb 2 Te 5 MLS by modulated photothermal radiometry (MPTR). The MPTR method allows for the investigation of such samples by determining, with an inverse method, the total thermal resistance of the stack deposited on the substrate. With the measurement of the total thermal resistance, it is possible to determine the thermal conductivity of the deposit and the interfacial thermal resistances between layers. The interfacial thermal resistance between Ge‐rich Ge 2 Sb 2 Te 5 /Ge 2 Sb 2 Te 5 is characterized, which is an important parameter to reduce the energy cost of the PCRAM functioning. It is also possible to highlight a decrease in interface quality inside the MLS after the beginning of the phase transition around 250 °C.
GeTe/Sb2Te3 superlattices (SLs) obtained by sputtering are integrated in phase‐change memory (PCM) devices with a “wall structure”. The high structural quality of SLs deposited on TiN or SiNx layers, used as metallic bottom heater and dielectric bottom layer in PCM devices, is established by X‐ray diffraction, for as‐grown SLs and after an annealing corresponding to the maximum thermal budget during the integration process. Scanning transmission electron microscopy (STEM) images of SLs within PCM cells confirm that the SL structure is kept after integration. A robust statistical analysis on a large number of devices demonstrates unambiguously that the RESET current is lower in SL devices than in GeTe reference devices and decreases when the Sb2Te3 layer thickness in the SL increases from 2 to 8 nm. STEM imaging of a PCM cell incorporating an SL demonstrates that switching from the low‐ to the high‐resistance state occurs through a melting–quenching process and is not due to crystal–crystal transition or defect reorganization in the SL, in contrast to what is commonly stated in the literature on interfacial phase‐change memories (iPCMs). The origin of the improved switching performance of SL‐based PCM devices is discussed, linked with the impact of swapped bilayers. GeTe/Sb2Te3 superlattices are successfully integrated in phase‐change memory (PCM) devices. Superlattice devices require lower RESET current than standard PCM ones. Electron microscopy imaging of a superlattice device evidences its amorphization in the RESET state. A novel explanation of the origin of the decrease in the RESET current in superlattice devices when increasing the thickness of Sb2Te3 layers is proposed.
This article presents three photothermal methods dedicated to the measurement of the thermal properties of chalcogenide alloys, used as a central element in the new generations of non-volatile memory. These materials have two phases, amorphous and crystalline, possessing a sharp contrast in their electrical and thermal properties. In the crystalline phase, the properties also change very significantly with temperature. The control of the temperature of the samples, the choice of transducers, and the time or frequency characteristic values of the photothermal excitation are thoroughly discussed. Each photothermal technique is described from the experimental point of view as well as from the inverse method, performed to identify the parameters of interest. The identified thermal properties mainly concern the thermal conductivity and the thermal resistance at the interfaces between the phase-change materials and the materials in contact as encountered in the production of the microelectronic memory device. Assessing various photothermal techniques, the study suggests that pulsed photothermal radiometry is the most effective method for sensitive high-temperature measurements of thermal properties of the phase-change materials.
The crystallization process of melt quenched Ge-rich GeSbTe films, with composition optimized for memory applications, has been studied by optical reflectance measurements. The optical properties have been related to the structure and composition by means of the effective medium approximation. The compositional variations have been investigated by transmission electron microscopy and electron energy loss spectroscopy. Amorphous materials prepared by melt-quenching with different laser energy densities have been studied. For the energy density of 1.5 J cm⁻², a uniform amorphous layer, with embedded Ge crystalline grains, is obtained. The film exhibits a crystallization temperature of 275 °C and no relevant phase separation during crystallization. For a lower energy density of 1 J cm⁻², only half of the film thickness is quenched to the amorphous phase, with Ge depletion. The crystallization temperature of the Ge depleted film is 245 °C, and a partial phase separation occurs.
Thermal transport properties bear a pivotal role in influencing the performance of phase change memory (PCM) devices, in which the PCM operation involves fast and reversible phase change between amorphous and crystalline phases. In this paper, we present a systematic experimental and theoretical study on the thermal conductivity of GeTe at high temperatures involving fast change from amorphous to crystalline phase upon heating. Modulated photothermal radiometry (MPTR) is used to experimentally determine thermal conductivity of GeTe at high temperatures in both amorphous and crystalline phases. Thermal boundary resistances are accurately taken into account for experimental consideration. To develop a concrete understanding of the underlying physical mechanism, rigorous and in-depth theoretical exercises are carried out. For this, first-principles density functional methods and linearized Boltzmann transport equations (LBTE) are employed using both direct and relaxation time based approach (RTA) and compared with that of the phenomenological Slack model. The amorphous phase experimental data has been described using the minimal thermal conductivity model with sufficient precision. The theoretical estimation involving direct solution and RTA method are found to retrieve well the trend of the experimental thermal conductivity for crystalline GeTe at high temperatures despite being slightly overestimated and underestimated, respectively, compared to the experimental data. A rough estimate of vacancy contribution has been found to modify the direct solution in such a way that it agrees excellently with the experiment. Umklapp scattering has been determined as the significant phonon-phonon scattering process. Umklapp scattering parameter has been identified for GeTe for the whole temperature range which can uniquely determine and compare Umklapp scattering processes for different materials.
Ge-rich Ge–Sb–Te alloys are materials with potential for new non-volatile memories named Phase
Change Memories offering an extended range of possible applications. However, the origin of their
superior properties, notably their much higher transition temperature and increased thermal stability, is
unknown. Using a variety of transmission electron microscopy based techniques, we have investigated
the changes that affect the structure and composition of such alloys during thermal annealing. We show
that, although Ge-rich Ge–Sb–Te materials can be grown as amorphous layers of homogeneous
compositions, the primary effect of annealing is to activate phase separation between stable Ge and
Ge–Sb–Te phases. This phase separation starts at 380 °C while the material is still amorphous and leads
to the nucleation of the first Ge nanocrystals. Increasing the annealing temperature to 400 and then to
450 °C allows the crystalline Ge phase to grow by driving the Ge excess out of the matrix, which, finally,
leads to the formation of large (30–50 nm) crystals with the face-centered-cubic Ge–Sb–Te structure.
After annealing at 500 °C for 30 minutes, the layer fully crystallizes and consists of a population of large
(50–100 nm) face-centered-cubic Ge–Sb–Te crystals with a stoichiometry close to 225 buried in a
matrix composed of small Ge nanocrystals. This study evidences that the superior properties of Ge-rich
alloys do not result from the intrinsic properties of some Ge-rich crystalline phases but from kinetic
factors. The formation of a two phase Ge/Ge–Sb–Te material involves long range diffusion of atomic
species, first and foremost, Ge.
The global demand for data storage and processing has increased exponentially in recent decades. To respond to this demand, research efforts have been devoted to the development of non- volatile memory and neuro- inspired computing technologies. Chalcogenide phase-change materials (PCMs) are leading candidates for such applications, and they have become technologically mature with recently released competitive products. In this Review , we focus on the mechanisms of the crystallization dynamics of PCMs by discussing structural and kinetic experiments, as well as ab initio atomistic modelling and materials design. Based on the knowledge at the atomistic level, we depict routes to improve the parameters of phase-change devices for universal memory. Moreover, we discuss the role of crystallization in enabling neuro-inspired computing using PCMs. Finally , we present an outlook for future opportunities of PCMs, including all- photonic memories and processors, flexible displays with nanopixel resolution and nanoscale switches and controllers.
By confining phase transitions to the nanoscale interface between two different crystals, interfacial phase change memory heterostructures represent the state of the art for energy efficient data storage. We present the effect of strain engineering on the electrical switching performance of the –GeTe superlattice van der Waals devices. Multiple Ge atoms switching through a two-dimensional Te layer reduces the activation barrier for further atoms to switch; an effect that can be enhanced by biaxial strain. The out-of-plane phonon mode of the GeTe crystal remains active in the superlattice heterostructures. The large in-plane biaxial strain imposed by the layers on the GeTe layers substantially improves the switching speed, reset energy, and cyclability of the superlattice memory devices. Moreover, carefully controlling residual stress in the layers of –GeTe interfacial phase change memories provides a new degree of freedom to design the properties of functional superlattice structures for memory and photonics applications.
Phase change memory (PCM) is an emerging technology that combines the unique properties of phase change materials with the potential for novel memory devices, which can help lead to new computer architectures. Phase change materials store information in their amorphous and crystalline phases, which can be reversibly switched by the application of an external voltage. This article describes the advantages and challenges of PCM. The physical properties of phase change materials that enable data storage are described, and our current knowledge of the phase change processes is summarized. Various designs of PCM devices with their respective advantages and integration challenges are presented. The scaling limits of PCM are addressed, and its performance is compared to competing existing and emerging memory technologies. Finally, potential new applications of phase change devices such as neuromorphic computing and phase change logic are outlined.
Thermoelectric effects on phase change memory elements are computationally analyzed through 2-D rotationally symmetric finite-element simulations of reset operation on a ${rm Ge}_{2}{rm Sb}_{2}{rm Te}_{5}$ (GST) mushroom cell with 10-nm critical dimension. Temperature-dependent material parameters are used to determine the thermoelectric contributions at the junctions (Peltier heat) and within GST (Thomson heat). Thermal boundary resistances at the GST interfaces enhance the Peltier heat contribution. Peak current densities and thermal gradients are in the order of 250 ${rm MA}/{rm cm}^{2}$ and 50 K/nm. Overall, thermoelectric effects are shown to introduce significant voltage polarity dependence on the operation dynamics, peak temperatures, thermal gradients, volume of the molten region, energy required, and resistance contrast. Resistance contrasts of ${sim}{8.8},times,10^{3}$ were realized with 155 $mu{rm A}$ for the positive polarity and 245 $mu{rm A}$ for the negative polarity.
The thermal conductivity of thin films of the phase-change material Ge2Sb2Te5 is measured in the temperature range of 27 degrees C < T < 400 degrees C using time-domain thermoreflectance. From the low thermal conductivity of amorphous phase, the conductivity increases irreversibly with increasing temperature and undergoes large changes with phase transformations. Thermal transport in the amorphous and early cubic phases can be described by a random walk of vibrational energy, i.e., the minimum thermal conductivity. In the hexagonal phase, the electronic contribution to the thermal conductivity is larger than the lattice contribution. Crystallization by laser processing produces a cubic phase with a lower thermal conductivity than cubic phases produced by thermal annealing; the authors attribute this difference in conductivity to a larger degree of atomic-scale disorder in films that are crystallized on short time scales. (c) 2006 American Institute of Physics.
Amorphous films having a component of the stoichiometric GeTe‐Sb 2 Te 3 pseudobinary alloy system, GeSb 2 Te 4 or Ge 2 Sb 2 Te 5 representatively, were found to have featuring characteristics for optical memory material presenting a large optical change and enabling high‐speed one‐beam data rewriting. The material films being sandwiched by heat‐conductive ZnS layers can be crystallized (low power) or reamorphized (high power) by laser irradiation of very short duration, less than 50 ns. The cooling speed of the sandwiched film is extremely high: more than 10<sup>10</sup> deg/s, which permits the molten material to convert to the amorphous state spontaneously; whereas, a low‐power pulse irradiation of the same duration changed the exposed portion into the crystalline state. The optical constant changes between the amorphous state and the crystalline state of them were measured to be large: from 4.7+i1.3 to 6.9+i2.6 and from 5.0+i1.3 to 6.5+i3.5, respectively. The crystallized portion was known to have a GeTe‐like fcc structure by an analytical experiment using transmission electron microscopy, differential scanning calorimetry, and x‐ray and electron diffraction methods. The high crystallization speed is ascribed to (1) the pseudobinary system which can form crystalline compositions without any phase separation, (2) the high symmetry of the fcc structure which is the nearest to the random amorphous structure, (3) the high‐energy difference between the amorphous state and the fcc crystal state.
Thermal interfaces play a key role in determining the programming energy of phase-change memory (PCM) devices. This letter reports the picosecond thermoreflectance measurements of thermal boundary resistance (TBR) at TiN/GST and Al/TiN interfaces, as well as the intrinsic thermal conductivity measurements of fcc GST between 30??C and 325??C. The TiN/GST TBR decreases with temperature from ~26 to ~18 m<sup>2</sup>??K/GW, and the Al/TiN ranges from ~7 to 2.4 m<sup>2</sup>??K/GW. A TBR of 10 m<sup>2</sup>??K/GW is equivalent in thermal resistance to ~192 nm of TiN. The fcc GST conductivity increases with temperature between ~0.44 and 0.59 W/m/K. A detailed understanding of TBR is essential for optimizing the PCM technology.
Nonvolatile RAM using resistance contrast in phase-change materials [or phase-change RAM (PCRAM)] is a promising technology for future storage-class memory. However, such a technology can succeed only if it can scale smaller in size, given the increasingly tiny memory cells that are projected for future technology nodes (i.e., generations). We first discuss the critical aspects that may affect the scaling of PCRAM, including materials properties, power consumption during programming and read operations, thermal cross-talk between memory cells, and failure mechanisms. We then discuss experiments that directly address the scaling properties of the phase-change materials themselves, including studies of phase transitions in both nanoparticles and ultrathin films as a function of particle size and film thickness. This work in materials directly motivated the successful creation of a series of prototype PCRAM devices, which have been fabricated and tested at phase-change material cross-sections with extremely small dimensions as low as 3 nm × 20 nm. These device measurements provide a clear demonstration of the excellent scaling potential offered by this technology, and they are also consistent with the scaling behavior predicted by extensive device simulations. Finally, we discuss issues of device integration and cell design, manufacturability, and reliability.
Phase-change memory technology relies on the electrical and optical properties of certain materials changing substantially when the atomic structure of the material is altered by heating or some other excitation process. For example, switching the composite Ge(2)Sb(2)Te(5) (GST) alloy from its covalently bonded amorphous phase to its resonantly bonded metastable cubic crystalline phase decreases the resistivity by three orders of magnitude, and also increases reflectivity across the visible spectrum. Moreover, phase-change memory based on GST is scalable, and is therefore a candidate to replace Flash memory for non-volatile data storage applications. The energy needed to switch between the two phases depends on the intrinsic properties of the phase-change material and the device architecture; this energy is usually supplied by laser or electrical pulses. The switching energy for GST can be reduced by limiting the movement of the atoms to a single dimension, thus substantially reducing the entropic losses associated with the phase-change process. In particular, aligning the c-axis of a hexagonal Sb(2)Te(3) layer and the 〈111〉 direction of a cubic GeTe layer in a superlattice structure creates a material in which Ge atoms can switch between octahedral sites and lower-coordination sites at the interface of the superlattice layers. Here we demonstrate GeTe/Sb(2)Te(3) interfacial phase-change memory (IPCM) data storage devices with reduced switching energies, improved write-erase cycle lifetimes and faster switching speeds.
Phase-change materials are characterized by a unique property portfolio well suited for data storage applications. Here, a first treasure map for phase-change materials is presented on the basis of a fundamental understanding of the bonding characteristics. This map is spanned by two coordinates that can be calculated just from the composition, and represent the degree of ionicity and the tendency towards hybridization ('covalency') of the bonding. A small magnitude of both quantities is an inherent characteristic of phase-change materials. This coordinate scheme enables a prediction of trends for the physical properties on changing stoichiometry.
Measurements of the thermal conductivity above 30 K of mixed crystals with controlled disorder, (KBr)1-x(KCN)x, (NaCl)1-x, (NaCn)x Zr1-xYxO2-x/2, and Ba1-xLaxF2+x, support the idea of a lower limit to the thermal conductivity of disordered solids. In each case, as x is increased, the data approach the calculated minimum conductivity based on a model originally due to Einstein. These measurements support the claim that the lattice vibrations of these disordered crystals are essentially the same as those of an amorphous solid.
In this paper we compare the performances of SiN with respect to an optimized SiC encapsulation in Wall based Phase-Change Memory (PCM) integrating a Ge-rich Ge-Sb-Te alloy (GGST) suitable for high temperature stability in automotive applications. Thanks to the electrical characterization of 4kb arrays, 3D electro-thermal simulations and TEM analyses performed on programmed devices, we demonstrate the higher programming efficiency in SiC-based PCM devices, thanks to the lower thermal conductivity of the optimized encapsulation. Indeed, the uniform temperature profile achieved in the active layer of SiC encapsulated PCM leads to a retention of one hour at 250°C. A theoretical model is here proposed to describe the electro-thermal behavior of the device, linking the electrical properties, such as the resistance as a function of current characteristics, to the thermal conductivity of the materials that constitute the device. Finally, thanks to our findings, we provide some guidelines to achieve drastic current reduction via the thermal engineering of the next generation PCM technology.
In phase change memory cells, the majority of heat is lost through the electrodes during the programming process, which leads to significant drops in the performance of the memory device. In this Letter, we report on the thermal properties of thin film carbon nitride with a modest electrical resistivity of 5–10 mΩ cm, a low thermal conductivity of 1.47 ± 0.09 W m⁻¹ K–1, and a low interfacial thermal conductance between carbon nitride and phase change material for length scales below 40 nm. The thermally insulating property of carbon nitride makes it a suitable thermal barrier, allowing for less heat loss during Joule heating within the memory unit. We compare the thermal properties of carbon nitride against the commonly used electrodes and insulators such as tungsten and silicon nitride, respectively, to demonstrate the promise of carbon nitride as a potential material candidate for electrode applications in phase change memory devices.
A reduction of the SET and RESET currents by more than 60% with respect to conventional GeTe‐Sb2Te3 (GST) alloys is demonstrated by using Phase Change Memory (PCM) cells containing (GeTe‐Sb2Te3)/Sb2Te3 Super‐Lattices (SLs), see article no. 1800634 by Mattia Boniardi et al. Moreover, the authors' SL PCM devices feature similar characteristics in terms of the memory transition as conventional memory cells based on GST, even though showing reduced power consumption, indicative of an efficiency augmented SET‐to‐RESET transition. The reduced power consumption is attributed to an increased thermal resistance of the SL stack with respect to the bulk GST alloy.
Phase change memory (PCM) is the most mature among the novel memory concepts. Embedded PCM technology can be a real breakthrough for process cost saving and performances. Nevertheless, for specific applications some improvement in high temperature data retention characteristics is needed. In this paper, we present an optimized GexSbyTez phase change material, able to guarantee code integrity after soldering thermal profile and data retention in extended temperature range. In particular, extrapolation of data retention at 10 years for temperatures higher than 150 C cell level has been demonstrated, thus enabling automotive applications. Despite the tradeoff between the SET speed and RESET data retention, competitive performances with respect to present floating gate memories have been confirmed. Finally, solid data collection based on a 4-Mb test chip integrated in a standard 90-nm CMOS technology platform has been performed. Functionality and performances are well in line with today industrial targets.
Phase Change Memory (PCM) has been proposed for use as a substitute for flash memory to satisfy the huge demands for high performance and reliability that promise to come in the next generation. In spite of its high scalability, reliability, and simple structure, high writing current, e.g., RESET current, has been a significant obstacle to achieving a high density in storage applications and the low power consumption required for use in mobile applications. We report herein on an attempt to determine the level of carbon incorporated into a GeSbTe (GST) film that is needed to reduce the RESET current of PCM devices. The crystal structure of the film was transformed into an amorphous phase by carbon
doping, the stability of which was enhanced with increasing carbon content. This was verified by the small grain size and large band gap that are typically associated with carbon. The increased level of C-Ge covalent bonding is responsible for these enhancements. Thus, the resistance of the carbon
doped
Ge
2Sb2Te5
film was higher than that for an undoped GST film by a factor of 2 orders of magnitude after producing a stable face-centered cubic phase by annealing. As a consequence, the PCM devices showed a significant reduction in RESET current as low as 23% when the carbon content was increased to 11.8 at. %. This can be attributed to the elevated SET resistance, which is proportional to the dynamic resistance of the PCM device, caused by the high resistance due to a carbon
doped GST film.
A rapid and reversible transition between a highly resistive and conductive state effected by an electric field, which we have observed in various types of disordered semiconducting material, is described in detail. The switching parameters and chemical composition of a typical material are presented, and microscopic mechanisms for the conduction phenomena are suggested.
We report the breakdown behavior of a patterned Ge2Sb2Te5 multiline structure during the voltage-driven electric stress biasing. Scanning Auger microscope analysis shows that the breakdown process accompanies with a phase separation of Ge2Sb2Te5 into an Sb, Te-rich phase and a Ge-rich phase. The phase separation is explained by the incongruent melting of Ge2Sb2Te5 based on the pseudobinary phase diagram between Sb2Te3 and GeTe. It is claimed that this phase separation behavior by incongruent melting provides one of the plausible mechanisms of the device failure in a phase change memory.
The thermal conductivity of Ge <sub>2</sub> Sb <sub>2</sub> Te <sub>5</sub> (GST) layers, as well as the thermal boundary resistance at the interface between the GST and amorphous Si O <sub>2</sub> , was measured using a photothermal radiometry experiment. The two phase changes in the Ge <sub>2</sub> Sb <sub>2</sub> Te <sub>5</sub> were retrieved, starting from the amorphous and sweeping to the face centered cubic (fcc) crystalline state at 130 ° C and then to the hexagonal crystalline phase (hcp) at 310 ° C . The thermal conductivity resulted to be constant in the amorphous phase, whereas it evolved between the two crystalline states. The thermal boundary resistance at the GST - Si O <sub>2</sub> interface was estimated to be higher for the hcp phase than for the amorphous and fcc ones.
The self-assembly of Ge(1)Sb(2)Te(4) nanowires (NWs) for phase change memories application was achieved by metal organic chemical vapor deposition, catalyzed by Au nanoislands in a narrow range of temperatures and deposition pressures. In the optimized conditions of 400 °C, 50 mbar, the NWs are Ge(1)Sb(2)Te(4) single hexagonal crystals. Phase change memory switching was reversibly induced by nanosecond current pulses through metal-contacted NWs with threshold voltage of about 1.35 V.
We report fabrication of phase change random access memory (PRAM) using nanowires (NWs) of GeTe and In<sub>2</sub>Se<sub>3</sub>. NWs were grown by a vapor-liquid-solid technique and ranged from 40 to 80 nm in diameter and several micrometers long. A dynamic switching ratio (on/off ratio) of 2200 and 2 times 10<sup>5</sup> was realized for GeTe and indium selenide devices, respectively. The programming power for the RESET operation is only tens of microwatts compared to the milliwatt power levels required by the conventional thin-film-based PRAM.
Thermal conduction governs the writing time and energy of phase-change memory (PCM) devices. Recent measurements demonstrated large thermal resistances at the interfaces of phase-change materials with neighboring electrode and passivation materials. In this letter, electrothermal simulations quantify the impact of these resistances on the set to reset transition. The programming current decreases strongly with increasing boundary resistance due to increased lateral temperature uniformity, which cannot be captured using a reduced effective conductivity in the phase-change material. Reductions in programming current from 20% to 30% occur for an interface resistance of 50 m<sup>2</sup>middotK/GW. The precise spatial distribution of thermal properties is critical for the simulation of PCM devices.
BezinSymposium on VLSI Technology Digest of Technical Papers
- F A Pellizzer
- F Pirovano
- M Ottogalli
- M Magistretti
- P Scaravaggi
- M Zuliani
- A Tosi
- P Benvenuti
- S Besana
- R Cadeo T.Marangon
- R Morandi
- A Piva
- R Spandre
- A Zonca
- E Modelli
- T Varesi
- A Lowrey
- G Lacaita
- P Casagrande
- Cappellettiandr
and 2 (IEEE CPMT; Heat Transfer Div K 16; ASME Elect & Photon Packaging Div
- Reifenberg E Pop
- A Gibby
- S Wong
Electron Devices Meeting Technical Digest
- A A Pirovano
- A Lacaita
- F Benvenuti
- S Pellizzer
- R Hudgens
- Bezinieee Int
- S R Ovshinsky
S. R. Ovshinsky Phys. Rev. Lett. 1968, 21(20), 1450-1453
- D Lencer
- M Salinga
- B Grabowski
- T Hickel
- J Neugebauer
D. Lencer, M. Salinga, B.Grabowski, T. Hickel, J. Neugebauer and M. Wuttig NATURE
MATERIALS, 2008, 7, 972-977 ISSN 1476-1122
- S Raoux
- F Xiong
- M Wuttig
S. Raoux, F. Xiong, M. Wuttig and E. Pop MRS Bulletin, 2014, 39, 703-710
- S Raoux
- G W Burr
- M J Breitwisch
- C T Rettner
- Y Chen
- R M Shelby
- M Salinga
- D Krebs
- S Chen
- H Lung
S. Raoux, G. W. Burr, M. J. Breitwisch, C. T. Rettner, Y. Chen,
R. M. Shelby, M. Salinga, D. Krebs, S. Chen, H. Lung, C. H. Lam
IBM J. Res. Dev. 2008, 52, 465-479
- S Tyson
- G Wicker
- T Lowrey
- S Hudgens
- K Hunt
S. Tyson, G. Wicker, T. Lowrey, S. Hudgens and K. Hunt in IEEE AEROSPACE
CONFERENCE PROCEEDINGS, VOL 5 IEEE AEROSPACE CONFERENCE
PROCEEDINGS (IEEE, Aerosp & Electr Syst Soc) pp 385-390 ISBN 0-7803-5846-5 ISSN
1095-323X 2000 IEEE Aerospace Conference, Big Sky, MT, March 18-25, 2000.
- B Yu
- X Sun
- S Ju
- D B Janes
- M Meyyappan
B. Yu, X. Sun, S. Ju, D. B. Janes and M. Meyyappan IEEE Transactions on
Nanotechnology, 2008, 7, 496-502 ISSN 1941-0085
- F Xiong
- M H Bae
- Y Dai
- A D Liao
- A Behnam
- E A Carrion
- S Hong
- D Ielmini
F. Xiong, M. H. Bae, Y. Dai, A. D. Liao, A. Behnam, E. A. Carrion, S. Hong, D. Ielmini
and E. Pop NANO LETTERS, 2013, 13, 464-469 ISSN 1530-6984
- S M S Privitera
- I García
- C Bongiorno
- V Sousa
- M C Cyrille
- G Navarro
- C Sabbione
- E Carria
- E Rimini
S. M. S. Privitera, I. López García, C. Bongiorno, V. Sousa, M. C. Cyrille, G. Navarro,
C. Sabbione, E. Carria and E. Rimini Journal of Applied Physics, 2020, 128, 155105
- S W Nam
- C Kim
- M H Kwon
- H S Lee
- J S Wi
- D Lee
- T Y Lee
- Y Khang
- K B Kim
S. W. Nam, C. Kim, M. H. Kwon, H. S. Lee, J. S. Wi, D. Lee, T. Y. Lee,
Y. Khang, K. B. Kim, Appl. Phys. Lett. 2008, 92, 111913
- H K Lyeo
- D G Cahill
- B S Lee
- J R Abelson
- M H Kwon
- K B Kim
- S G Bishop
- B K Cheong
H. K. Lyeo, D. G. Cahill, B. S. Lee, J. R. Abelson, M. H. Kwon,
K. B. Kim, S. G. Bishop, B. K. Cheong, Appl. Phys. Lett. 2006, 89, 151904.
- N Yamada
- E Ohno
- K Nishiuchi
- N Akahira
- M Takao
N. Yamada, E. Ohno, K. Nishiuchi, N. Akahira, M. Takao, J. Appl. Phys.
1991, 69, 2849.
- D Lencer
- M Salinga
- B Grabowski
- T Hickel
- J Neugebauer
- M Wuttig
D. Lencer, M. Salinga, B. Grabowski, T. Hickel, J. Neugebauer,
M. Wuttig, Nat. Mater. 2008, 7, 972.
- W Zhang
- R Mazzarello
- M Wuttig
- E Ma
W. Zhang, R. Mazzarello, M. Wuttig, E. Ma, Nat. Rev. Mater. 2019, 4,
150.
), (Soc Francaise Metallurg Mat; Deutsch Gesell Mat; Schweizerishcher Verband Mat
- R Bez
- A Pirovano
R. Bez, A. Pirovano, F. Pellizzer in Materials For Information
Technology: Devices, Interconnects and Packaging Engineering
Materials and Processes (Eds. E. Zschech, C. Whelan, T. Mikolajick),
(Soc Francaise Metallurg Mat; Deutsch Gesell Mat;
Schweizerishcher Verband Mat; Federat European Mat Soc), ISBN
1-85233-941-1, ISSN 1619-0181 Biennial Meeting of the
Federation-of-European-Materials-Societies, Springer Lausanne,
Switzerland 2003, pp. 177-188.
- S Tyson
- G Wicker
- T Lowrey
- S Hudgens
S. Tyson, G. Wicker, T. Lowrey, S. Hudgens, K. Hunt in IEEE Aerospace
Conference Proceedings (IEEE, Aerosp & Electr Syst Soc), Vol. 5,
ISBN 0-7803-5846-5 ISSN 1095-323X 2000, IEEE, Big Sky, MT,
March 18-25 2000, pp 385-390.
- F Pellizzer
- A Pirovano
- F Ottogalli
- M Magistretti
- M Scaravaggi
- P Zuliani
- M Tosi
- A Benvenuti
- P Besana
- S Cadeo
- T Marangon
- R Morandi
- R Piva
- A Spandre
- R Zonca
- A Modelli
- E Varesi
- T Lowrey
- A Lacaita
- G Casagrande
- P Cappelletti
F. Pellizzer, A. Pirovano, F. Ottogalli, M. Magistretti, M. Scaravaggi,
P. Zuliani, M. Tosi, A. Benvenuti, P. Besana, S. Cadeo, T. Marangon,
R. Morandi, R. Piva, A. Spandre, R. Zonca, A. Modelli, E. Varesi,
T. Lowrey, A. Lacaita, G. Casagrande, P. Cappelletti and R. Bez in
Symposium on VLSI Technology, Digest of Technical Papers (IEEE
Electron Devices Soc; Japan Soc Appl Phys), Honolulu, HI, June 15-17,
2004, pp. 18-19.
- B Yu
- X Sun
- S Ju
- D B Janes
- M Meyyappan
B. Yu, X. Sun, S. Ju, D. B. Janes, M. Meyyappan, IEEE Trans.
Nanotechnol. 2008, 7, 496.
- R E Simpson
- P Fons
- A V Kolobov
- T Fukaya
- M Krbal
- T Yagi
- J Tominaga
R. E. Simpson, P. Fons, A. V. Kolobov, T. Fukaya, M. Krbal, T. Yagi,
J. Tominaga, Nat. Nanotechnol. 2011, 6, 501.
- A Faraclas
- G Bakan
- L Adnane
- F Dirisaglik
- N E Williams
- A Gokirmak
- H Silva
A. Faraclas, G. Bakan, L. Adnane, F. Dirisaglik, N. E. Williams,
A. Gokirmak, H. Silva, IEEE Trans. Electron Devices 2014,
61, 372.