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Phase‐change random‐access memory (PCRAM) devices suffer from pronounced resistance drift originating from considerable structural relaxation of phase‐change materials (PCMs), which hinders current developments of high‐capacity memory and high‐parallelism computing that both need reliable multibit programming. This work realizes that compositional simplification and geometrical miniaturization of traditional GeSbTe‐like PCMs are feasible routes to suppress relaxation. While to date, the aging mechanisms of the simplest PCM, Sb, at nanoscale, have not yet been unveiled. Here, this work demonstrates that in an optimal thickness of only 4 nm, the thin Sb film can enable a precise multilevel programming with ultralow resistance drift coefficients, in a regime of ≈10−4–10−3. This advancement is mainly owed to the slightly changed Peierls distortion in Sb and the less‐distorted octahedral‐like atomic configurations across the Sb/SiO2 interfaces. This work highlights a new indispensable approach, interfacial regulation of nanoscale PCMs, for pursuing ultimately reliable resistance control in aggressively‐miniaturized PCRAM devices, to boost the storage and computing efficiencies substantially. [ABSTRACT FROM AUTHOR]

In this paper, Cu-doped GeTe materials have been investigated for high-temperature phase change memory (PCM) application. Cu incorporated in GeTe increases the crystallization temperature, crystallization active energy, and band gap significantly. The incorporated Cu has effect on refining the crystal growth and brings more number of bonds in GeTe, and has remarkable effect on improving the thermal stability of GeTe. The 10-year data retention of Cu0.06(GeTe)0.94 and Cu0.13(GeTe)0.87 are 151 °C and 185 °C, which is higher than that of GeTe. PCM device based on Cu0.06(GeTe)0.94 exhibits faster switching speed than that of GeTe. In addition, Cu0.06(GeTe)0.94 shows endurance up to 2.8 × 103 cycles with an on/off ratio of two orders of magnitude. [ABSTRACT FROM AUTHOR]

As a growth-dominated phase change material, Sb4Te (ST) has fast crystallization speed while thermal stability is very poor, which makes it unsuitable for application in phase change random access memory (PCRAM). After doping Ti, the crystallization temperature is greatly improved to 210.33 °C, which is much higher than that of conventional Ge2Sb2Te5 (∼150 °C), and the melting point is reduced to 540.27 °C. In addition, grain size of crystalline Ti-doped Sb4Te (TST) film is significantly decreased to nanoscale. Ti atom is believed to occupy the lattice site of Sb atom in TST. With good thermal stability, TST-based PCRAM cell also has fast crystallization rate of 6 ns. Furthermore, the energy consumption is also lower than that of Ge2Sb2Te5-based one. Endurance of exceeding 2E5 cycles is obtained with a resistance ratio of one order of magnitude. Therefore, Ti doping seems to be a good way to solve the contradiction between thermal stability and fast crystallization speed of Sb-Te alloys. [ABSTRACT FROM AUTHOR]

Fast and reversible phase transitions in chalcogenide phase-change materials (PCMs), in particular, Ge-Sb-Te compounds, are not only of fundamental interests but also make PCMs based random access memory a leading candidate for nonvolatile memory and neuromorphic computing devices. To RESET the memory cell, crystalline Ge-Sb-Te has to undergo phase transitions first to a liquid state and then to an amorphous state, corresponding to an abrupt change in electrical resistance. In this work, we demonstrate a progressive amorphization process in GeSb2Te4 thin films under electron beam irradiation on a transmission electron microscope (TEM). Melting is shown to be completely absent by the in situ TEM experiments. The progressive amorphization process resembles closely the cumulative crystallization process that accompanies a continuous change in electrical resistance. Our work suggests that if displacement forces can be implemented properly, it should be possible to emulate symmetric neuronal dynamics by using PCMs. [ABSTRACT FROM AUTHOR]

Superlattice-like top electrode formed alternately by TiN and W was embedded into phase-change random access memory (PCRAM) with the aim of reducing the power. Ga2Sb4Te3 film is employed as phase change layer. The minimum reset voltage of PCRAM based on superlattice-like electrode was significantly lower than that of one based on the conventional electrode. The set operation can be completed by an electric pulse as short as 5 ns. The superlattice-like-electrode-based PCRAM can be normally operated at 120 °C with endurance up to 1 × 106 cycles. The low thermal conductivity of superlattice-like electrode is responsible for the performance improvement of PCRAM. [ABSTRACT FROM AUTHOR]

The thermal stability of amorphous Sb2Te film can be significantly improved by the addition of Cu. CuSb4Te2 alloy is considered to be a potential candidate for phase change random access memory (PCRAM), as evidenced by a higher crystallization temperature, a better data retention ability, and a faster switching speed in comparison with those of Ge2Sb2Te5. A reversible switching between set and reset states can be realized by an electric pulse as short as 7 ns for CuSb4Te2-based PCRAM cell. In addition, CuSb4Te2 shows endurance up to 1.5 × 105 cycles with a resistance ratio of about two orders of magnitude. [ABSTRACT FROM AUTHOR]

An Sb-rich (48 at.%) Si–Sb–Te phase-change material with moderate Si content (24 at.%) is proposed for phase-change random access memory (PCRAM) applications. The real time amorphous to crystalline transformation was studied by in situ transmission electron microscopy observations and in situ resistance measurements. The results of time-dependent resistance measurements show that the \Si24\Sb48 \Te28 phase-change material has data retention of 10 years at about 382 K, suggesting a more stable amorphous state than the usual \Ge2\Sb2 \Te5 (GST) phase-change material. The reversible set –reset ability of the PCRAM cell based on the \Si24\Sb48\Te28 phase-change material is much better than that of the device employing GST. The programming cycles can reach \2.2 \times \10^4 under a set pulse of 1.5 V/1000 ns with a 30-ns falling edge and a reset pulse of 3.5 V/400 ns, whereas the resistance contrast retains a value of as large as two orders of magnitude. [ABSTRACT FROM AUTHOR]

Via in situ transmission electron microscopy, we observed on nanoscale unconventional structural evolution during two-dimensional (2D) phase transitions in a Sb 2 Te 3 /TiTe 2 phase-change heterostructure (PCH), which reduces amorphous relxation and crystallization stochasiticity to facilitate rapid and reliable memory programming. [Display omitted] Phase-change heterostructure (PCH) holds great promise for overcoming the low-precision bottleneck that limits multibit storage and parallel computing in conventional phase-change random-access memory. However, the origin of high-accuracy control of electrical resistance achieved in programming PCH memory devices has yet to be established. Via in situ transmission electron microscopy, here we unveil the unusual microscopic processes during the order–disorder phase transitions driven by electrical pulse in a Sb 2 Te 3 /TiTe 2 PCH architecture. The template-modulated phase transition is confirmed to be two-dimensional (2D) in nature. The structural transformation path and dynamics in the confined Sb 2 Te 3 sublayers are found to be profoundly changed with respect to those in bulk monolithic Sb 2 Te 3 , leading to markedly suppressed amorphous relaxation and substantially reduced crystallization stochasticity, both highly desirable for swift and accurate device operations. Our atomic-scale observations provide direct evidence of, and much-needed insight into, the working mechanisms that may enable superior 2D phase-change electronic devices. [ABSTRACT FROM AUTHOR]

Ultrafast programming speed and superb data persistency are two contradictory characteristics that need to be reconciled in the development of non-volatile cache-type phase-change random access memory (PCRAM). Scaling down the dimension of PCRAM unit cell is expected to be a feasible approach to solve this issue. Here we employ a bridge-type device using a 4 nm-thick Sb 2 Te 3 film to test this hypothesis. Thermal stability of the amorphous thin Sb 2 Te 3 film is evidently enhanced with respect to the bulky ones. The phase-change bridge device also enables the fastest crystallization speed of 1 ns. Such swift crystallization should be mainly ascribed to the enhanced heterogeneous nucleation at interfaces. Yet the aggressive geometry shrinkage may induce severe retardation in crystal growth. Tuning these two crystallization kinetic factors needs to be considered in future design of ultrafast and persistent phase-change materials for high-density PCRAM application. [ABSTRACT FROM AUTHOR]

Phase-change random access memory has been served as a bridge across the memory wall within the conventional von Neumann computing architecture, owing to its excellent non-volatility and rapid switching. Nitrogen doping in Ge 2 Sb 2 Te 5 -like phase-change materials (PCMs) was a routine method for enhancing non-volatility of amorphous phases, although sacrificing crystallization speed markedly. Here we introduced N element into Sc 0.3 Sb 2 Te 3 PCM that possesses sub-nanosecond crystallization speed, trying to cope with stability/reliability issues raised by backend thermal-budget processing. However, we observed an abnormal deterioration in thermal stability of N-doped amorphous Sc 0.3 Sb 2 Te 3 films. As compared to the undoped counterparts, they exhibit a weakened fragile-to-strong crossover in viscosity that gives rise to a higher atomic mobility at elevated temperatures while a less rigid vitreous network at low temperatures. Therefore, N doping leads to an accelerated crystal growth rate and a higher steady-state nucleation rate in heterogeneous manner, causing a faster crystallization, whereas the kinetic suffocation contributed by original Sc element as approaching room temperature must have been partially counteracted by N dopant. This acceleration in crystallization kinetics delivers N-doped Sc 0.3 Sb 2 Te 3 as a promising candidate in working memory. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Sb-rich Sb65Se6Te29 film was investigated for phase change random access memory (PCRAM) application. The crystallization temperature of the Sb65Se6Te29 film is 174°C and the crystalline activation energy is about 2.7eV. The 10-years'' failure temperature for the Sb65Se6Te29 film is about 87°C, sufficient for most consumer applications. The results of UV/visible/NIR spectrophotometer measurements show that the optical gap of the Sb65Se6Te29 film decreases as it transforms from amorphous phase to crystalline phase. Compared with the Ge2Sb2Te5 based PCRAM cell, the Sb65Se6Te29 based PCRAM cell has the advantages of lower threshold voltage and larger resistance contrast. Furthermore, as short as 10ns electrical pulse can achieve Reset operation with a Reset voltage of 2.9V. [Copyright &y& Elsevier]