High Driving Current Selector Based on As-Implanted HfO₂ Thin Film for 3D Phase Change Memory

A large crossbar array is desirable for high-density 3D stacking phase change memory (PCM) applications, in which the leakage current is mainly decided by selector devices. Meanwhile, a large driving current is also needed to meet the Reset operation of the PCM cell. Here, we propose a selector based on a nanoscale HfO2 film via As ion implantation, which has a low threshold voltage of 1.9 V, a milliamp-scale high driving current, a large selectivity of 106, fast turn on speed, and good endurance (108 switching cycles). These excellent performances make it applicable in the high-density stacked PCM application

Improving the GeAsSe Ovonic Threshold Switching Characteristics by Carbon Buffer Layers for Ultralow Leakage Current (∼0.4 nA) and Low Drift Characteristics

Volatile Ovonic threshold switching (OTS) selectors have been regarded as the critical component of highly integrated three-dimensional (3D) cross-point array nonvolatile memory systems. However, relatively high leakage current hinders the further reduction of power consumption in the crossbar array. In addition, the threshold voltage drift phenomenon hinders the improvement of device reliability. Utilizing the buffer layer can effectively reduce the interaction between electrodes and the active layer in the cross-point architecture. Here, it manifests that leakage current can be reduced to ∼0.4 nA with a 5 nm thick amorphous carbon layer as a buffer layer in the GeAsSe-based OTS device, where the carbon layer stabilizes the composition of GeAsSe during the electrical switching cycles. It is also found that the carbon layer leads to a lower threshold voltage drift (35.6 mv/dec) and excellent endurance (>109 cycles with ∼0.4 nA ON-state current). The conduction mechanism analysis demonstrates that the inhibition of the carbon layer on drift originates from the high barrier height from delocalized states transformed into localized states. This work clearly demonstrates the role of the carbon layer and facilitates future 3D crossbar-storage technology applications

Improvement of Multilevel Memory Performance of MnTe Thin Films by Ta Doping

The pressing need for data storage in the era of big data has driven the development of new storage technologies. As a prominent contender for next-generation memory, phase-change memory can effectively increase storage density through multilevel cell operation and can be applied to neuromorphic and in-memory computing. Herein, the structure and properties of Ta-doped MnTe thin films and their inherent correlations are systematically investigated. Amorphous MnTe thin films sequentially precipitated cubic MnTe2 and hexagonal Te phases with increasing temperature, causing resistance changes. Ta doping inhibited phase segregation in the films and improved their thermal stability in the amorphous state. A phase-change memory cell based on a Ta2.8%-MnTe thin film exhibited three stable resistive states with low resistive drift coefficients. The study findings reveal the possibility of regulating the two-step phase-change process in Ta-MnTe thin films, providing insight into the design of multilevel phase-change memory

Ti–Sb–Te Alloy: A Candidate for Fast and Long-Life Phase-Change Memory

Phase-change memory (PCM) has great potential for numerous attractive applications on the premise of its high-device performances, which still need to be improved by employing a material with good overall phase-change properties. In respect to fast speed and high endurance, the Ti–Sb–Te alloy seems to be a promising candidate. Here, Ti-doped Sb₂Te₃ (TST) materials with different Ti concentrations have been systematically studied with the goal of finding the most suitable composition for PCM applications. The thermal stability of TST is improved dramatically with increasing Ti content. The small density change of T_0.32Sb₂Te₃ (2.24%), further reduced to 1.37% for T_0.56Sb₂Te₃, would greatly avoid the voids generated at phase-change layer/electrode interface in a PCM device. Meanwhile, the exponentially diminished grain size (from ∼200 nm to ∼12 nm), resulting from doping more and more Ti, enhances the adhesion between phase-change film and substrate. Tests of TST-based PCM cells have demonstrated a fast switching rate of ∼10 ns. Furthermore, because of the lower thermal conductivities of TST materials, compared with Sb₂Te₃-based PCM cells, T_0.32Sb₂Te₃-based ones exhibit lower required pulse voltages for Reset operation, which largely decreases by ∼50% for T_0.43Sb₂Te₃-based ones. Nevertheless, the operation voltages for T_0.56Sb₂Te₃-based cells dramatically increase, which may be due to the phase separation after doping excessive Ti. Finally, considering the decreased resistance ratio, Ti_<i>x</i>Sb₂Te₃ alloy with <i>x</i> around 0.43 is proved to be a highly promising candidate for fast and long-life PCM applications

Atomic-Scale Observation of Carbon Distribution in High-Performance Carbon-Doped Ge₂Sb₂Te₅ and Its Influence on Crystallization Behavior

Phase change memory (PCM) has great potential for the next-generation nonvolatile memory technology, in which Ge2Sb2Te5 (GST) alloy is commonly used. However, poor thermal stability and short device lifetime of GST-based PCM are still the major obstacles. Here, we demonstrate 128 Mb carbon-doped GST (CGST) PCM chips with excellent thermal stability, reduced reset current (0.6 mA), and longer cycle lifetimes (>108 cycles). For the first time, we use the atom probe tomography (APT) technique to investigate the carbon distribution in CGST. APT results reveal the formation of Ge–C, Sb–C, and Te–C bonds in the as-deposited CGST, which leads to the remarkably improved thermal stability of CGST. Moreover, these C-based bonds will break in the recrystallization process and form nanometer-scale carbon clusters in crystalline CGST. Crystalline growth simulation shows that these carbon clusters can also inhibit the growth of the grains, which is responsible for the slower operation speed of the CGST cell compared to that of GST cell. Importantly, owing to the significant inhibition of long-range thermal and electro migrations of Ge, Sb, and Te atoms by carbon clusters, CGST-based chips can achieve a long lifetime

Atomic-Scale Observation of Carbon Distribution in High-Performance Carbon-Doped Ge₂Sb₂Te₅ and Its Influence on Crystallization Behavior

Phase change memory (PCM) has great potential for the next-generation nonvolatile memory technology, in which Ge2Sb2Te5 (GST) alloy is commonly used. However, poor thermal stability and short device lifetime of GST-based PCM are still the major obstacles. Here, we demonstrate 128 Mb carbon-doped GST (CGST) PCM chips with excellent thermal stability, reduced reset current (0.6 mA), and longer cycle lifetimes (>108 cycles). For the first time, we use the atom probe tomography (APT) technique to investigate the carbon distribution in CGST. APT results reveal the formation of Ge–C, Sb–C, and Te–C bonds in the as-deposited CGST, which leads to the remarkably improved thermal stability of CGST. Moreover, these C-based bonds will break in the recrystallization process and form nanometer-scale carbon clusters in crystalline CGST. Crystalline growth simulation shows that these carbon clusters can also inhibit the growth of the grains, which is responsible for the slower operation speed of the CGST cell compared to that of GST cell. Importantly, owing to the significant inhibition of long-range thermal and electro migrations of Ge, Sb, and Te atoms by carbon clusters, CGST-based chips can achieve a long lifetime

Hybrid integration of deterministic quantum dots-based single-photon sources with CMOS-compatible silicon carbide photonics

Thin film 4H-silicon carbide (4H-SiC) is emerging as a contender for realizing large-scale optical quantum circuits due to its high CMOS technology compatibility and large optical nonlinearities. Though, challenges remain in producing wafer-scale 4H-SiC thin film on insulator (4H-SiCOI) for dense integration of photonic circuits, and in efficient coupling of deterministic quantum emitters that are essential for scalable quantum photonics. Here we demonstrate hybrid integration of self-assembled InGaAs quantum dots (QDs) based single-photon sources (SPSs) with wafer-scale 4H-SiC photonic chips prepared by ion slicing technique. By designing a bilayer vertical coupler, we realize generation and highly efficient routing of single-photon emission in the hybrid quantum photonic chip. Furthermore, we realize a chip-integrated beamsplitter operation for triggered single photons through fabricating a 1x2 multi-mode interferometer (MMI) with a symmetric power splitting ratio of 50:50. The successful demonstration of heterogeneously integrating QDs-based SPSs on 4H-SiC photonic chip prepared by ion slicing technique constitutes an important step toward CMOS-compatible, fast reconfigurable quantum photonic circuits with deterministic SPSs

Visible and Near-infrared Microdisk Resonators on a 4H-Silicon-Carbide-on-Insulator Platform

Wavelength-sized microdisk resonators were fabricated on a single crystalline 4H-silicon-carbide-oninsulator platform (4H-SiCOI). By carrying out microphotoluminescence measurements at room temperature, we show that the microdisk resonators support whispering-gallery modes (WGMs) with quality factors up to $5.25 \times 10^3$ and mode volumes down to $2.69 \times(\lambda /n)^3$ at the visible and near-infrared wavelengths. Moreover, the demonstrated wavelength-sized microdisk resonators exhibit WGMs whose resonant wavelengths compatible with the zero-phonon lines of spin defects in 4H-SiCOI, making them a promising candidate for applications in cavity quantum electrodynamics and integrated quantum photonic circuits