Low-power Phase Change Memory Research Articles

Realization of fast-speed and low-power phase change memory by optimizing Ge10Sb90 film with samarium doping

In this paper, the Sm-doped Ge10Sb90 films were proposed and the effect of Sm doping on the crystal structure and electrical properties were investigated. The crystallization process of materials with different Sm concentrations was carried out by an in situ resistance measurement system, demonstrating that doping Sm can significantly improve the amorphous resistance, thermal stability, and bandgap of Ge10Sb90 film and alleviate the structural relaxation. X-ray diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy show that the appropriate content of Sm doping can hinder the grain growth process, limiting the grain size to a certain extent. The phase change memory devices with Sm-doped Ge10Sb90 were prepared based on the CMOS process, and their electrical properties were evaluated. The outcomes indicate that Sm doping can remarkably ameliorate the high RESET current required for Sb-rich Ge10Sb90 films during erasing/writing operation.

Probing the Melting Transitions in Phase-Change Superlattices via Thin Film Nanocalorimetry

Phase-change superlattices with nanometer thin sublayers are promising for low-power phase-change memory (PCM) on rigid and flexible platforms. However, the thermodynamics of the phase transition in such nanoscale superlattices remain unexplored, especially at ultrafast scanning rates, which is crucial for our fundamental understanding of superlattice-based PCM. Here, we probe the phase transition of Sb2Te3 (ST)/Ge2Sb2Te5 (GST) superlattices using nanocalorimetry with a monolayer sensitivity (∼1 Å) and a fast scanning rate (105 K/s). For a 2/1.8 nm/nm Sb2Te3/GST superlattice, we observe an endothermic melting transition with an ∼240 °C decrease in temperature and an ∼8-fold decrease in enthalpy compared to those for the melting of GST, providing key thermodynamic insights into the low-power switching of superlattice-based PCM. Nanocalorimetry measurements for Sb2Te3 alone demonstrate an intrinsic premelting similar to the unique phase transition of superlattices, thus revealing a critical role of the Sb2Te3 sublayer within our superlattices. These results advance our understanding of superlattices for energy-efficient data storage and computing.

Low-power phase-change memory cell based on a doped GeTe/InP heterostructure: a first-principles study

Low-power phase-change memory cell based on a doped GeTe/InP heterostructure: a first-principles study

All‐Photonic Phase‐Change Memories: Low‐Power Phase Transition of Chalcogenide Glass Using Au Nanoparticle Plasmon Resonance (Advanced Optical Materials 6/2020)

A cluster of gold nanoparticles (Au NPs) is dispersed on chalcogenide film to reduce the phase transition power of the chalcogenide layer, as shown by Tun Cao and co-workers in article number 1901570. This reduced power is owing to the enhanced light absorptance through the strongly localized surface plasmon resonance of the Au NPs. Such a design is suitable for high-speed, low-power phase-change memory and for a new type of tunable surface-enhanced Raman scattering substrate.

Low Power Phase Change Memory at High Endurance With a Slice Bottom Electrode

Phase change memory (PCM) is a promising candidate for nonvolatile data storage and reconfigurable electronics, but the high programming current presents a challenge to realize low-power operation. In this paper, PCM cells based on a new bottom electrode contact (BEC) structure called the slice BEC are introduced to reduce the programming current. Compared with T-shaped PCM cells, the RESET current was found to be significantly reduced for cells with slice bottom electrodes, which is consistent with the simulation results. The dynamic resistances for cells with different electrodes during RESET programming were also studied. The theoretical calculations showed that the power was greatly reduced by using the slice bottom electrode. The endurance characteristics of the new type cells were investigated to evaluate the cell performance.

Surface Energy Driven Cubic-to-Hexagonal Grain Growth of Ge2Sb2Te5 Thin Film

Phase change memory (PCM) is a promising nonvolatile memory to reform current commercial computing system. Inhibiting face-centered cubic (f-) to hexagonal (h-) phase transition of Ge2Sb2Te5 (GST) thin film is essential for realizing high-density, high-speed, and low-power PCM. Although the atomic configurations of f- and h-lattices of GST alloy and the transition mechanisms have been extensively studied, the real transition process should be more complex than previous explanations, e.g. vacancy-ordering model for f-to-h transition. In this study, dynamic crystallization procedure of GST thin film was directly characterized by in situ heating transmission electron microscopy. We reveal that the equilibrium to h-phase is more like an abnormal grain growth process driven by surface energy anisotropy. More specifically, [0001]-oriented h-grains with the lowest surface energy grow much faster by consuming surrounding small grains, no matter what the crystallographic reconfigurations would be on the frontier grain-growth boundaries. We argue the widely accepted vacancy-ordering mechanism may not be indispensable for the large-scale f-to-h grain growth procedure. The real-time observations in this work contribute to a more comprehensive understanding of the crystallization behavior of GST thin film and can be essential for guiding its optimization to achieve high-performance PCM applications.

Nanosecond Switching in Superlattice-Like GeTe/Sb Thin Film for High Speed and Low Power Phase Change Memory Application

Superlattice-like GeTe/Sb thin films were investigated for their potential application in phase change memory. Compared with monolayer GeTe thin film, GeTe/Sb thin film has lower crystallization temperature (208°C), crystallization activation energy (2.38 eV) and thermal conductivity (0.15 W/(m·K)). In GeTe/Sb thin film, GeTe and Sb phases exist independently. The superlattice-like structure is observed even after annealing at 250°C for 10 min. The shorter phase change time is achieved for GeTe/Sb thin film (4.3 ns). The GeTe/Sb-based phase change memory devices show an operation speed of as fast as 9 ns and a low RESET operation power of 4.09 × 10−13 J.

SET and RESET states of As2Se3 doped GeTe4 bulk glasses probed by Raman spectroscopy

Te based chalcogenide glasses are being explored for non-volatile memory applications. We report the electrical switching studies on bulk Ge0.20Te0.80 glass alloyed with As0.40Se0.60 in different proportions. The addition of As0.40Se0.60 increases the electrical resistivity and the threshold voltage of (As0.4Se0.6)x(Ge0.2Te0.8)1−x glasses in the composition range 0 ≤ x ≤ 0.40. Glasses in the range 0 ≤ x ≤ 0.10 are found to exhibit memory switching, whereas glasses with x ≥ 0.15 exhibit threshold switching. The memory (SET) state can be brought back to RESET state by passing a current of 3–5 mA. Particularly, the glass with x = 0.10 is identified to be very stable, and it can be cycled between the SET and RESET state consistently with 3 mA current. The Raman spectra of SET and RESET states indicate that the SET sample has GeTe and Te crystalline units while the structure of RESET state is analogous to the as-quenched glass. Interestingly, the variation in the local structure is minimal for SET and RESET states for x = 0.10. And also the resistance of the SET state is relatively high. So they can be set to RESET state with less current and can be explored for low power phase change memory applications.

Low power phase change memory switching of ultra-thin In3Sb1Te2 nanowires

We report on the fabrication and electrical characterization of phase change memory (PCM) devices formed by In3Sb1Te2 chalcogenide nanowires (NWs), with diameters as small as 20 nm. The NWs were self-assembled by metal organic chemical vapor deposition via the vapor–liquid–solid method, catalyzed by Au nanoparticles. Reversible and well reproducible memory switching of the NWs between low and high resistance states was demonstrated. The conduction mechanism of the high resistance state was investigated according to a trap-limited model for electrical transport in the amorphous phase. The size of the amorphized portion of the NW and the critical electric field for the transition to the low resistance state were evaluated. The In3Sb1Te2 NW-based devices showed very low working parameters, such as RESET voltage (∼3 V), current (∼40 μA), and power (∼130 μW). Our results indicated that the studied NWs are suitable candidates for the realization of ultra-scaled, high performance PCM devices.

Impact of Dielectric Resistive Heater, Bottom Contact and Reading Scheme on the Reliability of Nanoscale Low Power Phase Change Memory (PCM) Cell: 3-D-ADI Modeling

This paper discusses the impact of silicon nitride dielectric resistive-heater, copper bottom contact, and reading scheme on the reliability of a precycled nanoscale phase change memory cell. Through the calibrated run-time efficient 3-D— alternating direction implicit (ADI), numerical modeling we have found that due to the presence of nitride heater, RESET power saving can be significantly achieved with a 1.1-nA RESET current pulse of 75-ps duration mitigating excessive heating within the heater, but at the same time, downsizing amorphous-Ge2Sb 2Te5 (GST) thickness to 2 nm. In contrast, we found that low resistance offered by such 2-nm-thin amorphous-GST is inappropriate for conventional reading used for sensing both SET and RESET states. Furthermore, we found that for having low thermal conductivity, nitride heater tends to store heat for a long time following RESET, which has been identified as a major reliability concern in the cell, although the benefit of the nitride heater toward RESET current scaling has been found prevalent. In this respect, we have demonstrated that the read current window can be reliably maintained to 0.14 mA through a novel in-plane reading in a thin-film GST cell, with 2-nm amorphous-GST. Furthermore, through 3-D-ADI modeling, we have demonstrated that reverse heat relaxation time can be significantly reduced to 30 ps using copper bottom contact, when supported by a nitride heater.

Si/Sb superlattice-like thin films for ultrafast and low power phase change memory application

After compositing with Si, the superlattice-like (SLL) Si/Sb thin film had higher crystallization temperature (~231°C), larger crystallization activation energy (2.95eV), and better data retention ability (126°C for 10years). The crystallization of Sb in SLL Si/Sb thin films was restrained by the multilayer interfaces. The reversible resistance transition could be achieved by an electric pulse as short as 10ns for [Si(22nm)/Sb(2nm)]2-based PCM cell. A lower operation power consumption of 0.02mW and a good endurance of 1.0×105cycles were achieved. In addition, SLL [Si(22nm)/Sb(2nm)]2 thin film showed a low thermal conductivity of 0.11W/(m·K).

Low Power Phase Change Memory using Silicon Carbide as a Heater Layer

The amorphous to crystalline transition of germanium-antimony-tellurium (GST) using two types heating element was investigated. With separate heater structure, simulation was done using COMSOL Multiphysic 5.0. Silicon carbide (SiC) and Titanium Sitride (TiSi3) has been selected as a heater and differences of them have been studied. The voltage boundary is 0.905V and temperature of the memory layer is 463K when using SIC as a heater. While the voltage boundary and temperature of memory layer when using TiSi3 are 1.103 V and 459K respectively. Based on the result of a simulation, the suitable material of heater layer for separate heater structure is Silicon carbide (SiC) compared with Titanium Sitride (TiSi3).

Low-power phase change memory with multilayer TiN/W nanostructure electrode

In this paper, multilayer TiN/W with interfacial nanostructure is used as electrode for application in low-power phase change memory (PCM). Compared with single-layer electrode, multilayer electrode has much lower thermal conductive due to the interfacial scattering effect. PCM based on multilayer electrode with different thickness ratio of TiN and W was fabricated and characterized. The device properties including operation voltage and endurance depended critically on the multilayer structure rather than the thickness ratio of TiN and W. The low operation voltage and long cycle life of multilayer-electrode-based PCM result from the increase in overall thermal resistance due to the low thermal conductivity of multilayer electrode.

Study on the Cu-doped Ge2Sb2Te5 for low-power phase change memory

Cu0.10(Ge2Sb2Te5)0.90 is proposed for low power consumption phase change memory (PCM). The thermal stability of Ge2Sb2Te5 is increased by 10at% Cu doping, with the crystallization temperature and data retention increased from 163°C to 202°C and from 87°C to 134°C, respectively. The electric operation results have proved the low power consumption and good cycling ability (>104), which may result from the low melting point (486°C) and the negligible phase separation in Cu0.10(Ge2Sb2Te5)0.90. The good thermal stability, low Tm and good cycling phase change ability have made Cu0.10(Ge2Sb2Te5)0.90 a promising candidate for the low power consumption PCM application.

Cost-Effective Schottky-Barrier Diode Array With Ni–Silicidation Accessing Low Power Phase-Change Memory

A cost-effective fabrication of Schottky-barrier (SB) diode steering element for low power phase-change memory (PCM) application is realized. While superior drivability in conventional PN diode array, SB diode array with 0.0193- μm2 (5F2), performing higher switching speed, sufficient drive current density of ~ 26.30 mA/μm2, disturbance immunity, and lower power consumption has been manufactured under 40-nm standard complementary metal oxide semiconductor technology. Simultaneously, different performance specifications, including integration scheme, JON/JOFF ratio, temperature characteristics, and scalability have been studied in detail and compared in two categories of accessing diode arrays. It manifests that the scaled SB diode array is suitable for full operation of PCM.

Improved phase-change characteristics of Zn-doped amorphous Sb7Te3 films for high-speed and low-power phase change memory

The superior performance of Zn-doped Sb7Te3 films might be favorable for the application in phase change memory. It was found that Zn dopants were able to suppress phase separation and form single stable Sb2Te crystal grain, diminish the grain size, and enhance the amorphous thermal stability of Sb7Te3 film. Especially, Zn30.19(Sb7Te3)69.81 film has higher crystallization temperature (∼258 °C), larger crystallization activation energy (∼4.15 eV), better data retention (∼170.6 °C for 10 yr), wider band gap (∼0.73 eV), and higher crystalline resistance. The minimum times for crystallization of Zn30.19(Sb7Te3)69.81 were revealed to be as short as ∼10 ns at a given proper laser power of 70 mW.

Nitrogen-doped Ge3Te2 materials with self-restricted active region for low power phase-change memory

In this paper, nitrogen-doped Ge3Te2 materials have been investigated for low power phase-change memory. Nitrogen incorporated in Ge3Te2 increases the crystallization temperature, electrical resistance, and band gap significantly. The introduced GeNx pile up at the grain-boundaries and suppress the crystal growth of Ge3Te2, which further leads to larger crystalline resistance and smaller active region. 10-year data retention of nitrogen-doped Ge3Te2 film reaches a peak value with a N2 flow of 2 sccm, while it decreases sharply as the N2 flow reaches 3 sccm. This is due to the formation of inhomogeneous nucleation sites at the GeNx-GeTe interface. Phase-change memory device based on nitrogen-doped Ge3Te2 film shows much lower RESET power consumption than that of pure Ge3Te2. It's considered that the self-restricted active region and effect of GeNx microheaters play an important role in cutting down the power consumption.

Low Power Phase Change Memory via Block Copolymer Self-assembly Technology

ABSTRACTWe report the demonstration of low power phase change memory (PCM) by forming thin self-assembled SiOx nanostructures between Ge2Sb2Te5 (GST) and a TiN heater layer utilizing a block copolymer (BCP) self-assembly technology. The reset current was decreased about three-fold as fill factor, which is the occupying area fraction of self-assembled SiOx nanostructures on a TiN heater layer, increased to 75.3%. The electro-thermal simulation shows the better heat efficiency due to the nano-patterned insulating oxide.

Superlattice-like GaSb/Sb2Te3 films for low-power phase change memory

The crystallization temperature of superlattice-like GaSb/Sb2Te3 films can be easily changed by the number of interfaces and thickness ratio between GaSb and Sb2Te3 layers. The reset operation can be completed by an electric pulse as short as 20 ns for the GaSb(4 nm)/Sb2Te3(6 nm)-based phase-change memory test cell. This test cell exhibited endurance up to 1.4 × 104 cycles. The thermal simulation confirmed that the improved performance of superlattice-like GaSb/Sb2Te3 films originated from the low thermal conductivity and low melting point.

Large-area, scalable fabrication of conical TiN/GST/TiN nanoarray for low-power phase change memory

We demonstrate the fabrication and phase change memory performance of a conical TiN/Ge2Sb2Te5 (GST)/TiN nanoarray prepared viablock copolymer lithography and straightforward two-step etching. The created 30 nm scale phase change memory cell (aerial array density: ∼207 Gbit inch−2) showed a threshold switching voltage of 1.1 V, a value compatible to conventional phase change memory cells. More significantly, the cell could be amorphized by a reset pulse of 1.8 V height and 100 ns width, where the reset current was 100 μA. Such a low reset current, presumably caused by nanoscale small cell dimension, is greatly beneficial for low power consumption device operation. Reversibly, the set operation was accomplished by crystallization with a set pulse of 1.2 V height, 100 ns width, and 100 ns trailing. This work provides a significant step for low power consumption and ultra-high density storage based on phase change materials.