一种接触质量高和兼容特性好的金属-量子点-金属结构的自对准制备方法

我们报道了一种“金属-量子点-金属”结构的自对准制备方法。该方法主要包括“电子束曝光-薄膜淀积-刻蚀”工艺,具有套刻容限大、开发周期短以及可兼容多种材料等优点,尤其适用于具有类似结构的纳米器件制备。该方法中使用的牺牲层工艺和强化版图,降低了剥离工艺的难度,提升了可制备器件结构的力学强度。最后,作为应用实例,我们用该方法制备了尺寸为 255 nm × 45 nm × 30 nm（ 长 × 宽 × 高)的相变节点。     

嵌入式相变存储器的技术特点和研究现状

从2001年Intel在IEDM发表第一篇相变存储器的论文以来,相变存储器的发展十分迅猛.相变存储器由于具有非易失性、循环寿命长、元件尺寸小、功耗低、可多级存储、高速读取、抗辐射、耐高低温、抗振动、抗电子干扰和制造工艺简单等优点,被认为最有可能取代目前的FLASH和DRAM而成为未来半导体存储器主流产品.文中系统地介绍了嵌入式相变存储器的存储机理及其主要工作特点,从相变材料,器件结构,存储阵列等方面分析国内外研究现状,并讨论了器件失效与可靠性问题.     

Phase change materials and their application to random access memory technology

Phase change materials can exist in two different phases, the amorphous and the crystalline phase, which exhibit distinctly different physical properties. It is possible to repeatedly switch the state of these materials, from the amorphous phase to the crystalline phase by heating the material above its crystallization temperature, and from the crystalline to the amorphous phase by melt-quenching. Phase change materials have been utilized very successfully in all modern optical re-writable storage media such as CDs, DVDs and Blu-ray disks. Recently, they have also been applied to solid-state memory devices where their large difference in electrical resistivity is used to store information. This paper reviews the unique properties of phase change materials in particular as they are important for their application to these devices.     

相变存储器单元疲劳特性研究

本文主要研究了相变存储器存储单元的疲劳特性。随着操作次数的增多,相变存储器单元在高阻态和低祖态下的阻值逐渐的向着相反的方向变化。同时,本文还讨论了在疲劳操作下,相变单元状态改变所需的操作条件也在逐渐的改变。在最初的一定次数的疲劳操作条件下,单元的阈值电压缓慢的减小,并且在之后的操作中,阈值电压急剧增大。这是由于器件单元的界面效应以及相变区域体积变化工作作用引起的。本文对于之一现象,给出了合理的解释以及数据加以证明。     

A review of compact modeling for phase change memory

Phase change memory(PCM)attracts wide attention for the memory-centric computing and neuromorphic comput-ing.For circuit and system designs,PCM compact models are mandatory and their status are reviewed in this work.Macro mod-els and physics-based models have been proposed in different stages of the PCM technology developments.Compact model-ing of PCM is indeed more complex than the transistor modeling due to their multi-physics nature including electrical,thermal and phase transition dynamics as well as their interactions.Realizations of the PCM operations including threshold switching,set and reset programming in these models are diverse,which also differs from the perspective of circuit simulations.For the purpose of efficient and reliable designs of the PCM technology,open issues and challenges of the compact modeling are also discussed.     

Fabrication process not limited by the lithography resolution of lateral phase change memory

To improve the performance of phase change memory (PCM) and reduce the cost of fabrication, we propose a new lateral PCM structure based on the technology of angle evaporation to define the critical dimension controllable, not limited by the limitation of lithography resolution. The fabrication process is cost-effective. PCM cells featured 80 nm×100 nm were successfully demonstrated, although the resolution of the aligned used was 1 µm only. Compared with the traditional lateral PCM structure, finite element simulation results show that the new structure has better thermal stability.     

相变随机存储器材料与结构设计最新进展

介绍了相变随机存储器(PCRAM)的研究现状,包括新型相变材料、热阻层材料和器件结构等.分析了GeSb和SiSb等相变材料具有组分简单、数据保持力好、优良的存储性能等特点,介绍了PCRAM这一新型半导体存储器的基本原理、特点以及国内外有关相变材料、过渡层材料和器件结构设计等方面的研究进展,最后提出了我国发展PCRAM的几点思考.     

Crystallization kinetics of Sn40Se60 thin films for phase change memory applications

The crystallization kinetics of Sn₄₀Se₆₀ thin films has been successfully investigated using sheet resistance versus temperature measurements. Thermal evaporation was used to deposit the films on ordinary glass substrates. The crystallization temperature for Sn₄₀Se₆₀ thin film was found to be 156.6 ± 0.3 ℃. In the as-deposited state, the sheet resistance was found to be 195 MΩ, this value declined to 1560 Ω/口 upon annealing. The value of activation energy obtained from the Kissinger plot was 0.62 ± 0.07 eV. From the results obtained, Sn₄₀Se₆₀ is a promising alloy for PCM application because of its high electrical contrast, high crystallization temperature, and relatively high activation energy.     

基于GMR及TMR效应的磁随机存储器的最新应用开发

介绍了巨磁电阻（GMR）及隧道磁电阻（TMR）效应,讨论了计算机磁随机存储器（MRAM）的最新应用开发。     

Preparation of (Pb0.88La0.12)TiO3 thin films for dynamic random access memory by low pressure-metalorganic chemical vapor deposition

La-modified lead titanate (PLT) thin films were prepared by hot-wall type low pressure-metalorganic chemical vapor deposition method. Pb(dpm)₂, La(dpm)₃, and titanium tetraisopropoxide were used as source materials. The films were deposited at 500°C under the low pressure of 1000 mTorr and then annealed at 650°C for 10 min in oxygen ambient. Sputter-deposited platinum electrodes and 180 nm thick PLT thin films were employed to form MIM capacitors with the best combination of high charge storage density (26.7 μC/cm² at 3V) and low leakage current density (1.5 × 10^-7 A/cm² at 3V). The measured dielectric constant and dielectric loss were 1000∼1200 and 0.06∼0.07 at zero bias and 100 kHz, respectively.     

Improving the data retention of phase change memory by using a doping element in selected Ge_2Sb_2Te_5

The crystallization characteristics of a ubiquitous T-shaped phase change memory(PCM) cell, under SET current pulse and very small disturb current pulse, have been investigated by finite element modelling. As analyzed in this paper, the crystallization region under SET current pulse presents first on the corner of the bottom electron contact(BEC) and then promptly forms a filament shunting down the amorphous phase to achieve the low-resistance state, whereas the tiny disturb current pulse accelerates crystallization at the axis of symmetry in the phase change material. According to the different crystallization paths, a new structure of phase change material layer is proposed to improve the data retention for PCM without impeding SET operation.This structure only requires one or two additional process steps to dope nitrogen element in the center region of phase change material layer to increase the crystallization temperature in this confined region. The electrical-thermal characteristics of PCM cells with incremental doped radius have been analyzed and the best performance is presented when the doped radius is equal to the radius of the BEC.     

Flexible and transparent ReRAM with GZO memory layer and GZO-electrodes on large PEN sheet

Fabrication of flexible transparent resistive random access memory (FT-ReRAM) which consists of Ga doped ZnO (GZO) film not only as a memory layer but also as electrodes on the large Poly Ethylene Naphthalate sheet was attained by introducing RF plasma assist DC magnetron sputtering method. The averaged transmittance in the visible region (400-800 nm) was 66%. The memory effect was studied by using conducting atomic force microscope. It was suggested that the increase of Joule heating and oxygen vacancy density enhances memory effect, which is consistent with the redox model which has been proposed as the switching mechanism for conventional ReRAM. Stable and repeatable bi-polar resistive switching by application of the low voltage less than 2 V and low current less than 100 μA was confirmed in the FT-GZO-ReRAM. Reset switching, which is a switching from the low to the high resistance states, in GZO-ReRAM was confirmed to be smooth and continuous, which will enable a multilevel application. It was suggested that the smooth and continuous reset was brought about by Ga-doping.     

菱形NiFe薄膜单元的自发磁化及剩磁状态的研究

利用微磁学方法系统研究了纳米尺度的NiFe薄膜菱形单元的自发磁化状态及剩磁状态。研究结果表明,在不同的尺寸下,菱形单元将有不同的自发磁化状态及剩磁状态。在单元的长宽尺寸小于某个临界尺寸时,菱形单元结构呈现单畴态。同时还分析了菱形NiFe单元作为磁性随机存储器(MRAM)存储单元时的要求。     

Fabrication of high density nano-pillar type phase change memory devices using flexible AAO shaped template

In this study, the high density nano-pillar type phase change memory was fabricated using duplicating nano-patterns of the anodic alumina oxide (AAO) by nanoimprint process. The high density nano-hole array of AAO template was transferred to the flexible PVC polymer template using hot embossing method. To use the flexible AAO shaped template for UV-NIL, the high density nano-pillar type Ge₂Sb₂Te₅ patterns were fabricated, and the electrical properties of the device were evaluated by conducting atomic force microscopy, connected electrical measurement system. To use the flexible AAO shaped template for UV-NIL, high density GST pattern could be fabricated even on the flexible polyimide (PI) substrate.     

松下MicroP2存储卡和摄像机高低码流记录的应用实践

本文就电视新闻采访中使用的P2格式高清摄像机存储卡的安全性问题提出有一定参考价值的建议,并结合松下公司最新推出的 MicroP2存储卡在实际应用当中的体会与读者交流分享。     

Evaluation of binary and ternary melts for the low temperature liquid phase epitaxial growth of silicon

Liquid-phase-epitaxy allows the growth of good quality layers at low temperature, although this advantage is yet to be fully exploited for silicon. Silicon solubility was investigated in a range of binary and ternary metal alloys to identify suitable low temperature combinations. Gold based alloys were determined to be the most suitable for the growth of lightly doped layers, with Au-Bi and Au-Pb alloys giving high silicon solubilities at temperatures below 400° C. Liquid-phase-epitaxy of silicon was demonstrated over the 380–450° C range from such alloys.     

A new extension method of retention time for memory cell on dynamic random access memory

Demands have been placed on dynamic random access memory (DRAM) to not only increase memory capacity and data transfer speed but also to reduce operating and standby currents. When a system uses DRAM, the restricted data retention time necessitates a refresh operation because each bit of the DRAM is stored as an amount of electrical charge in a storage capacitor. Power consumption for the refresh operation increases in proportion to memory capacity. A new method is proposed to reduce the refresh power consumption dynamically, when full memory capacity is not required, by effectively extending the memory cell retention time. Conversion from 1 cell/bit to 2^N cells/bit reduces the variation of retention times among memory cells. The proposed method reduces the frequency of disturbance and power consumption by two orders of magnitude. Furthermore, the conversion itself can be realized very simply from the structure of the DRAM array circuit, while maintaining all conventional functions and operations in the full array access mode.     

Capacitors with an Equivalent Oxide Thickness of <0.5 nm for Nanoscale Electronic Semiconductor Memory

The recent progress in the metal‐insulator‐metal (MIM) capacitor technology is reviewed in terms of the materials and processes mostly for dynamic random access memory (DRAM) applications. As TiN/ZrO₂‐Al₂O₃‐ZrO₂/TiN (ZAZ) type DRAM capacitors approach their technical limits, there has been renewed interest in the perovskite SrTiO₃, which has a dielectric constant of >100, even at a thickness ～10 nm. However, there are many technical challenges to overcome before this type of MIM capacitor can be used in mass‐production compatible processes despite the large advancements in atomic layer deposition (ALD) technology over the past decade. In the mean time, rutile structure TiO₂ and Al‐doped TiO₂ films might find space to fill the gap between ZAZ and SrTiO₃ MIM capacitors due to their exceptionally high dielectric constant among binary oxides. Achieving a uniform and dense rutile structure is the key technology for the TiO₂‐based dielectrics, which depends on having a dense, uniform and smooth RuO₂ layer as bottom electrode. Although the Ru (and RuO₂) layers grown by ALD using metal‐organic precursors are promising, recent technological breakthroughs using the RuO₄ precursor made a thin, uniform, and denser Ru and RuO₂ layer on a TiN electrode. A minimum equivalent oxide thickness as small as 0.45 nm with a low enough leakage current was confirmed, even in laboratory scale experiments. The bulk dielectric constant of ALD SrTiO₃ films, grown at 370 °C, was ～150 even with thicknesses ≤15 nm. The recent development of novel group II precursors made it possible to increase the growth rate largely while leaving the electrical properties of the ALD SrTiO₃ film intact. This is an important advancement toward the commercial applications of these MIM capacitors to DRAM as well as to other fields, where an extremely high capacitor density and three‐dimensional structures are necessary.     

甚低频横跨极区传播相位的观测与研究

对甚低频横跨极区传播相位观测数据进行了分析与研究,得出了甚低频跨极区传播相位的日、季变化的主要特征及规律:(1)在夏至前后的一段时间内,传播相位日变化往往呈现"驼峰"形状;(2)昼夜间的传播相位差季节变化明显;(3)传播相位的随机起伏大.     

侧墙技术在相变存储器中的应用

从相变存储器(phase change random access memory,PCRAM)的基本结构和工作原理出发,首先介绍了PCRAM的技术优势、面临的技术挑战、常用的解决策略以及存在的相应问题;接着阐述了在微电子加工中广泛应用的关键工艺——侧墙技术,并将其在PCRAM中的应用成果进行了分类;然后从加热电极的制备、相变材料限制结构的制备、新相变材料的制备与表征和器件间互联等4个方面展开叙述;最后展望了该技术在相变存储领域应用发展的趋势。侧墙技术因其具备自对准的特点,制备工艺可控性好,制备精度不依赖于光刻精度,在纳米技术飞速发展的今天,侧墙技术将会在更高精度上发挥其作用。