Temperature Data Retention Research Articles

Ta alloy doped InSbTe ensuring high thermal stability and fast operation speed in phase change memory

The excellent performance of phase change memory (PCM) in non-volatile and storage density makes it one of the most attractive solutions for storage-class memory and neuromorphic computing, whereas the slow operation and low thermal stability limit its extensive applications. Here Ta-doped In0.43Sb2Te3has been proposed, which enhances the amorphous stability without sacrificing its operating speed. Ta0.12(In0.43Sb2Te3)0.88 film possess excellent 10-year data retention temperature of 184.5 °C and the PCM based on Ta0.12(In0.43Sb2Te3)0.88 achieved an operating speed of 6 ns. Both experimental results indicate that Ta doping reduces grain size, enhances the ability to maintain face-center cubic phase, and improves phase separation caused by In doping. A long endurance of 1 × 106 has been achieved, which is originating from the small volume change of 1.71 %. Therefore, Ta0.12(In0.43Sb2Te3)0.88 material is a potential candidate for application in PCM.

Reduction of write current with improved thermal stability in GeSe2 doped Sb2Te3 films for phase change memory applications

Chalcogenide alloy-based semiconductors have gained significant attention in recent decades due to its applications in phase change memory (PCM). Sb2Te3 has proven to be an alternative to Static and Dynamic Random Access Memory and can be a suitable candidate for commercial memory devices due to their fast switching speed. However, Sb2Te3 suffers from low amorphous phase stability and high RESET current, which needs further improvement for high power efficiency. In this work, we have prepared (Sb2Te3)1−x (GeSe2) x (x = 0.06, 0.12, 0.18, 0.24, 0.3) films to investigate their PCM properties. The films showed a rise in transition temperature to transform from high resistive amorphous (RESET) to low resistive crystalline (SET) states with doping that leads to significant enhancement in amorphous phase stability. For 30% doping of GeSe2 in Sb2Te3, the data retention temperature increases from 20.2 °C to 84.6 °C, and the resistance contrast also increases from 102 to 105. The rise in electrical resistance with doping in the amorphous as well as crystalline states leads to a drop in threshold current (I th) from 3.5 to 0.8 mA. This also reduces the RESET and SET currents. By analyzing the samples using finite element method, it was found out that the high resistance materials produce more heat, resulting in a lower write current in an energy efficient PCM device.

Development of Sb phase change thin films with high thermal stability and low resistance drift by alloying with Se

A single Sb phase demonstrates potential for use in phase change memory devices. However, the rapid crystallization of Sb at room temperature imposes limitations on its practical application. To overcome this issue, Sb is alloyed with Se using a reactive co-sputtering deposition technique, employing both Sb and Sb2Se3 sputter targets. This process results in the formation of Sb-rich Se thin films with varying compositions. Compared to pure Sb, the Sb-rich Se thin films exhibit enhanced thermal stability due to the formation of Sb–Se bonds and reduced resistance drift. In particular, the Sb86.6Se13.4 thin film demonstrates an exceptionally low resistance drift coefficient (0.004), a high crystallization temperature (Tc = 195 °C), a high 10-year data retention temperature (116.3 °C), and a large crystallization activation energy (3.29 eV). Microstructural analysis of the Sb86.6Se13.4 reveals the formation of a trigonal Sb phase with (012) texture at 250 °C, while Sb18Se and Sb2Se3 phases form at 300 °C. Conversely, the Sb98.3Se1.7 thin film shows the formation of the single Sb phase with (001) texture, a Tc of 145 °C, and a low resistance drift coefficient (0.011). Overall, this study demonstrates that the alloying strategy is a viable approach for enhancing thermal stability and reducing resistance drift in Sb-based phase-change materials.

Understanding the microstructure evolution of carbon-doped Sb2Te3 phase change material for high thermal stability memory application

The Sb2Te3 phase change material shows a growth-dominated crystallization mechanism with fast phase transition but poor thermal stability of the amorphous state. This work investigated the effects of carbon doping on the thermal stability, microstructure, and electrical properties of the Sb2Te3 material. The 10-year data retention temperature of the material increased to ∼147.3 °C and the size of the grains was limited to ∼10 nm by carbon doping. The formation of the C cluster upon crystallization was found at the grain boundaries, which was accelerated as the temperature increased due to the break of the Sb–C bonds. The memory device based on the carbon-doped Sb2Te3 material exhibited a switching speed of 15 ns and an endurance of ∼105 cycles with a resistance ratio of more than two orders of magnitude. This work suggests that the carbon-doped Sb2Te3 material is a promising candidate for memory applications that require high thermal stability, fast speed, and high endurance.

Thermal stability and high speed for optoelectronic hybrid phase-change memory based on Cr doped Ge2Sb2Te5 thin film

Non-volatile memory, which can simultaneously store data and compute in memory, is a promising candidate to break through “memory bottleneck”. However, its operation speed and thermal stability are still contradictory and difficult to meet the requirement of in-memory computing especially in high-temperature applications. In this work, optoelectronic hybrid phase-change memory based on Cr doped Ge2Sb2Te5 material is proposed, where the picosecond laser is used to perform the information recording/erasing operation based on the reversible phase-change characteristics while resistance signal is detected to realize the information readout. Results imply that the Cr doped Ge2Sb2Te5 film with Cr concentration of 10.7 at. % has high crystallization temperature (289 °C) and ten-year data-retention temperature (221 °C), low density-change rate (2.3%) and small resistance drift coefficients (0.022 at 85 °C, 0.056 at 120 °C, 0.070 at 150 °C, and 0.00131 for the laser induced SET state). The corresponding memory device has the SET/RESET operation speeds of as fast as 1820 ps/13 ps accompanied by the RESET/SET resistance ratio of higher than two orders of magnitude. The structural analyses indicate that Cr doping can suppress the growth of grains and reduce the grain size, improving the thermal stability of amorphous Ge2Sb2Te5 thin film while the octahedral/defective octahedral motif ensures its fast phase-change speed. Therefore, Cr doped Ge2Sb2Te5 based optoelectronic hybrid phase-change memory with superior thermal stability and ultrafast operation speed may be one of the promising solutions for in-memory computing.

Development of Sb2Se3 alloys by Ti-doping with ultralow resistance drift and improved microstructure for nonvolatile memory applications

The Sb2Se3 and Ti-doped Sb2Se3 phase change thin films were prepared by magnetron sputtering. The relationship between resistance drift and crystallization behavior of Sb2Se3 and Ti-doped Sb2Se3 thin films were thoroughly investigated. The results revealed that when Ti-doping concentration reaches 5.4 at. %, Ti5.4(Sb2Se3)95.4 thin film exhibited a high thermal stability with crystallization temperature of 225 °C and 10-year data retention temperature of 129.5 °C. This benefits to lower resistance drift coefficient from 0.067 for Sb2Se3 to 0.002 for Ti5.4(Sb2Se3)95.4. Further microstructural analysis revealed the suppression of large grain growth in Ti-doped Sb2Se3 thin films, while the formation of Ti–Sb and Ti–Se bonds being responsible for enhanced stability of the amorphous Ti-doped thin films. Moreover, the Ti doping promoted one-dimensional growth-dominated crystallization mechanism of the studied alloys, leading to the reduced nucleation index compared to Sb2Se3. The present study sheds valuable light on the effectively reducing nucleation randomness in chalcogenide-based phase-change materials.

Multilevel optoelectronic hybrid memory based on N-doped Ge2Sb2Te5 film with low resistance drift and ultrafast speed

Multilevel phase-change memory is an attractive technology to increase storage capacity and density owing to its high-speed, scalable and non-volatile characteristics. However, the contradiction between thermal stability and operation speed is one of key factors to restrain the development of phase-change memory. Here, N-doped Ge2Sb2Te5-based optoelectronic hybrid memory is proposed to simultaneously implement high thermal stability and ultrafast operation speed. The picosecond laser is adopted to write/erase information based on reversible phase transition characteristics whereas the resistance is detected to perform information readout. Results show that when N content is 27.4 at.%, N-doped Ge2Sb2Te5 film possesses high ten-year data retention temperature of 175 °C and low resistance drift coefficient of 0.00024 at 85 °C, 0.00170 at 120 °C, and 0.00249 at 150 °C, respectively, owing to the formation of Ge–N, Sb–N, and Te–N bonds. The SET/RESET operation speeds of the film reach 520 ps/13 ps. In parallel, the reversible switching cycle of the corresponding device is realized with the resistance ratio of three orders of magnitude. Four-level reversible resistance states induced by various crystallization degrees are also obtained together with low resistance drift coefficients. Therefore, the N-doped Ge2Sb2Te5 thin film is a promising phase-change material for ultrafast multilevel optoelectronic hybrid storage.

Designing Sb phase change materials by alloying with Ga2S3 towards high thermal stability and low resistance drift by bond reconfigurations

The pure Sb phase-change thin films alloyed with Ga2S3 alloy have been prepared and the related properties have been investigated. Compared with pure Sb, Ga2S3-alloyed Sb films exhibit higher crystallization temperature (∼250 °C), larger ten-year data retention temperature (∼166 °C), and higher crystallization activation energy (4.10 eV). These thermal parameters indicate that the thermal stability of the Ga2S3-alloyed Sb thin films can be considerably enhanced due to the formation of high binding energy Sb-S and Sb-Ga bonds. Moreover, the enhanced thermal stability can also significantly lower resistance drift coefficient (0.0014). According to the analysis of the crystallization mechanism, the crystallization kinetic index (n) is determined to be 0.625, implying one-dimensional growth type in Ga2S3-alloyed Sb thin films. This can benefit to reduce the nucleation randomness and decrease resistance drift. The work demonstrates that Ga2S3-alloyed Sb materials have excellent potential for embedded memory applications.

Resonant Bonding Dependence of the Phase Change Characteristics of a VO2-Sb2Se Film for Tunable Photonic Devices in the Mid-Infrared Region

Phase change material (PCM) has gained great attraction for being widely used in tunable photonic devices due to its nonvolatility, excellent scalability, high speed, and tunable properties. However, the unclear source of the phase-change characteristics limits PCM for true device-level integrated circuits with high configuration and multifunctional attributes, especially in the mid-infrared (MIR) region. In this paper, the inherent dependences of phase-change characteristics on both the microstructure and bonding environments of the (VO2)x(Sb2Se)100–x film are disclosed for low-loss and nonvolatile tunable photonic devices. (VO2)x(Sb2Se)100–x films possess a tendency that the crystallization temperature, 10 year data-retention temperature, and optical band gap of (VO2)x(Sb2Se)100–x films increase with the increase of VO2 content. The improvement in thermal stability of (VO2)x(Sb2Se)100–x is ascribed to the complex bonding environment consisting of Se–V and Sb–V bonds with the large bonding enthalpy, which disturbs the crystallization. The symbolic value for the contribution of resonant bonding ζ is derived by the real part ε1 and imaginary part ε2 of dielectric functions with a wavelength ranging from 1.7 to 25 μm. With increasing VO2 content, a large structural distortion in the VO2-rich phase leads to a reduction in the level of resonant bonding, which accounts for a decrease in the optical refractive index contrast. These results shed light on intrinsic material science and engineering to the ongoing search for other phase-change materials for tunable photonic devices in the MIR region.

The Effect of Carbon Doping on the Crystal Structure and Electrical Properties of Sb2Te3.

As a new generation of non-volatile memory, phase change random access memory (PCRAM) has the potential to fill the hierarchical gap between DRAM and NAND FLASH in computer storage. Sb2Te3, one of the candidate materials for high-speed PCRAM, has high crystallization speed and poor thermal stability. In this work, we investigated the effect of carbon doping on Sb2Te3. It was found that the FCC phase of C-doped Sb2Te3 appeared at 200 °C and began to transform into the HEX phase at 25 °C, which is different from the previous reports where no FCC phase was observed in C-Sb2Te3. Based on the experimental observation and first-principles density functional theory calculation, it is found that the formation energy of FCC-Sb2Te3 structure decreases gradually with the increase in C doping concentration. Moreover, doped C atoms tend to form C molecular clusters in sp2 hybridization at the grain boundary of Sb2Te3, which is similar to the layered structure of graphite. And after doping C atoms, the thermal stability of Sb2Te3 is improved. We have fabricated the PCRAM device cell array of a C-Sb2Te3 alloy, which has an operating speed of 5 ns, a high thermal stability (10-year data retention temperature 138.1 °C), a low device power consumption (0.57 pJ), a continuously adjustable resistance value, and a very low resistance drift coefficient.

Design of all-phase-change-memory spiking neural network enabled by Ge-Ga-Sb compound

The implementation of artificial spiking neural network (SNN) usually takes advantage of multiple heterogeneous circuits to mimic either neurons which generate spiking pulses, or synapses which store the weights of event correlations. Here, we design a homogeneous device using Ge-Ga-Sb (GGS) as a phase-change-memory (PCM) material which can do both jobs. The GGS compound shows high stability when used in data storage, such as high working temperature (281°C) and high 10-years data retention temperature (230°C), as well as low resistance drift. Interestingly, when the as-fabricated GGS device is set by iterative narrow-width electric pulses, it first experiences an abrupt resistance drop by two orders of magnitude, followed by a continuous resistance decrease. This unique abrupt-to-progressive transition can be used to mimic both neuronal and synaptic functions, mechanistically enabled by the formation of conductive channels and the continuous growth with the phase separation of crystalline areas. To this end, we propose an all-PCM SNN, which is emulated to have high accuracy (90%) in the standard pattern recognition.

Improved thermal stability and direct hexagonal transition accompanied by metal-insulator transition in Arsenic substituted Ge2Sb2Te5

Amorphous chalcogenides, particularly Ge2Sb2Te5 (GST) based alloys, are well known for their non-volatile phase-change random access memory applications (PCRAM). In this work, the phase change properties of Ge2Sb2−xAsxTe5 (x = 0, 0.5, 1.0, 2.0) thin films deposited by thermal evaporation are reported. The As substituted samples crystallize at higher temperatures compared to parent GST. During the phase change for x > 1.0, a direct transition from amorphous to the stable hexagonal structure has been observed. A distinct two-step transition in Sb rich samples and a single step transition for As rich samples are observed in R-T measurements with a high contrast in electrical resistivity. The transition is becoming sharper and sharper with increasing As substitution. A composition-dependent Metal-Insulator Transition (MIT) is also observed in these samples. Compared to GST, As substituted samples show an increase in crystallization temperature and activation energy for crystallization. For GST, the 10-year data retention temperature is 67 °C, and with complete As substitution, it increases to 169 °C, with a significant rise of 102 °C in the data retention temperature. High thermal stability, sharp transition and increased data retention of As substituted Ge-Sb-Te suggest that they are promising candidates for PCRAM applications.

Pt Modified Sb2Te3 Alloy Ensuring High-Performance Phase Change Memory.

Phase change memory (PCM), due to the advantages in capacity and endurance, has the opportunity to become the next generation of general−purpose memory. However, operation speed and data retention are still bottlenecks for PCM development. The most direct way to solve this problem is to find a material with high speed and good thermal stability. In this paper, platinum doping is proposed to improve performance. The 10-year data retention temperature of the doped material is up to 104 °C; the device achieves an operation speed of 6 ns and more than 3 × 105 operation cycles. An excellent performance was derived from the reduced grain size (10 nm) and the smaller density change rate (4.76%), which are less than those of Ge2Sb2Te5 (GST) and Sb2Te3. Hence, platinum doping is an effective approach to improve the performance of PCM and provide both good thermal stability and high operation speed.

Ruthenium doped Ge2Sb2Te5 nanomaterial as fast speed phase-change materials with good thermal stability

Ge2Sb2Te5 (GST) as phase-change material has the advantage of good thermal stability and long cycle life, however large power consumption and lower phase change speed partly limit large-scale application for phase-change materials (PCM). In this paper, a comprehensive research is investigated on Ru doped GST phase-change material, from properties to performances for PCM application. Ru doping can efficiently improve the thermal stability of GST alloy and the thickness change of Ru0.05(GST)0.95 film is 3.3%. In addition, high 10-year data retention temperature (∼151 °C) and small crystal grain reflect the advantages of data retention and low power consumption for Ru0.05(GST)0.95 film. Furthermore, the structure characteristics show the stable face-centred cubic structure at crystalline state after annealing. As for electrical properties, Ru0.05(GST)0.95-based PCM cell shows excellent reversible SET-RESET properties with a suitable operation window and good endurance up to 106 electrical cycles with a resistance ratio of about 10. And also, it has a dramatically lower power consumption of 1.46 × 10-11 J compared with GST-based cell (4.76 × 10-10 J), making it a promising material for the Internet of Things (IOT) field applications.

Pt-Sb2Te as high speed phase-change materials with excellent thermal stability

Phase change memory (PCM) has been regarded as one of the most promising candidates for the next-generation nonvolatile memory. In this paper, we propose PtSb2Te (PST) phase change material for phase change memory. The doping of Pt improves the crystallization temperature and Ten-year data-retention temperature of Sb2Te to 180 °C, 192 °C, 204 °C and 117 °C,123 °C,137 °C, and refines the grain to about 10 nm. At the same time, the density change of Sb2Te film after phase transition is reduced to 4.19% due to the addition of Pt. There are no other new phases formed in PST film except hexagonal Sb2Te phase. For PST-based phase change memory cell, only 10 ns electrical pulse is required to complete the reversible operation with a Reset voltage lower than 4.3 V. At the same time, the number of cycle operations of the memory cell exceeds 105 and it has a lower resistance drift coefficient as 0.019.

AlSc Alloy Doped Sb2Te as High Speed Phase-Change Material with Excellent Thermal Stability and Ultralow Density Change

The research progress of global nonvolatile phase change memory (PCM) is quite effective. Among them, chalcogenide Sb2Te is considered as one of the important materials with high operation speed. In this work, we put forward a 1:1 AlSc alloy doped AlSc-Sb2Te to enhance the performance of Sb2Te, including thermal stability, density change and transition speed. Experimental results show that AlSc-Sb2Te has better 10-year data retention temperature (146 °C) and higher crystallization temperature (221 °C), which reflects excellent amorphous thermal stability of AlSc-Sb2Te. X-ray reflection analysis shows that this material has much smaller density change (2.6%) than that of reported phase change materials. Importantly, the AlSc-Sb2Te based device has a very low power consumption of 6.78 × 10−12 J and a high operation speed of 6 ns.

Effect of V2O5 interlayers in V2O5/Ge8Sb92 superlattice-like film on thermal stability and size scaling

In this paper, the superlattice-like V2O5/Ge8Sb92 films are studied. Compared with Ge8Sb92 film, V2O5/Ge8Sb92 films have a high crystallization temperature (~233 °C), a large amorphous resistance (~3.4 × 107 Ω) and good data retention temperature (~171.2 °C) for ten years. The volume change rate of V2O5/Ge8Sb92 superlattice-like film is only 1.855% during the crystallization, which can guarantee a better contact with the electrode when it is applied in the phase-change memory. By adding of V2O5 interlayers, the thermal stability and reliability of Ge8Sb92 film have been greatly improved.

High thermal stability and fast operation speed phase-change memory devices containing Hf-doped Ge2Sb2Te5 films

Ge2Sb2Te5 (GST) materials have been widely investigated for applying in phase-change memory (PCM). However, the low amorphous thermal properties limit its application in high-density memory devices, thus doping modified has been the subject of extensive studies in past decades. In this work, the amorphous thermal stability of GST can be significantly improved by doping hafnium elements without reducing operation speed. A higher crystallization temperature (~221 °C) and 10-year data retention temperature (~114 °C) are achieved in Hf0.04(Ge2Sb2Te5)0.96 alloy. The addition of Hf elements helps to suppress crystallization and decrease the grain size of rock-salt phase. Besides, the PCM cell based on Hf0.04(Ge2Sb2Te5)0.96 exhibits a faster operation speed (10 ns) than GST-based one and could be operated repeatedly for over 2́105 cycles, showing that Hf-doped GST is a promising material for PCM devices.

Scaling-down and interfacial effect to break down the trade-off between thermal stability and crystallization speed of the Sb2Se films

Phase change memory (PCM) has been one of the most potential technologies for in-memory computing and neuromorphic integrated systems. It requires phase-change memory scaling toward higher density for such applications. However, the scaling-down and interfacial impact in phase-change materials, which are the core of PCMs, are still unclear. In this paper, the phase transition properties and crystallization behavior of phase-change material Sb2Se were tuned intrinsically by reducing the thickness of the Sb2Se film and coverage of VO2. It is shown that the crystallization temperature increases from 209 °C to 224 °C, and 10-year data retention temperature enhances from 117 °C to 139 °C, as the thickness of the Sb2Se film decreases from 50 nm to 2 nm. The coverage of VO2 could improve the thermal stability and crystallization rate of the Sb2Se film obviously, especially for smaller thickness. The kinetic exponent obtained by the JMA model indicates that the crystallization mechanism varies with film thickness, which could tune the crystallization rate of the Sb2Se film. This study provides a practical solution for on-going optimizing phase-change properties in terms of size and interfacial effects.

Improved thermal stability and contact of antimony film by the interlayer HfO2

The thermal stability was one of the primary obstacles hindering the development of phase-change memory. In this paper, Sb/HfO2 multilayer phase-change films were prepared by multilayer composite method. The transition process of Sb/HfO2 multilayer films from amorphous to crystalline state was studied by in-situ heating. With the decrease of the thickness of Sb layer, the crystallization temperature of Sb/HfO2 increased significantly. At the same time, the data retention temperature for 10 years increased from 14 °C of pure antimony to 147 °C of Sb/HfO2. The bandgap became wider and the surface became smoother. The existence of a large number of Sb microcrystals inhibited the phase transformation process. Compared with single-layer Sb film, Sb/HfO2 multilayer film had smaller volume change before and after phase transformation. The results showed that the addition of HfO2 interlayer significantly enhanced the amorphous thermal stability of Sb and improved the effective contact between the phase-change layer and the electrode. Sb/HfO2 multilayer film was a potential phase-change film with high stability and good reliability.