Ge_2Sb_2Te_5相变存储单元瞬态结晶过程研究

研究了基于Ge2Sb2Te5的相变存储器单元的瞬态结晶过程,并通过高频示波器捕捉了瞬态结晶过程的电压波形,发现了在结晶过程中瞬态波形存在振荡现象,且振荡频率随时间和脉高变化具有一定规律。结晶完成后振荡现象消失,单元电阻转变为稳定的低阻,通过相变存储器的场致导电通道结晶模型很好地解释了该瞬态结晶现象。     

Ge_2Sb_2Te_5相变存储单元瞬态结晶过程研究北大核心CSCD

研究了基于Ge2Sb2Te5的相变存储器单元的瞬态结晶过程,并通过高频示波器捕捉了瞬态结晶过程的电压波形,发现了在结晶过程中瞬态波形存在振荡现象,且振荡频率随时间和脉高变化具有一定规律。结晶完成后振荡现象消失,单元电阻转变为稳定的低阻,通过相变存储器的场致导电通道结晶模型很好地解释了该瞬态结晶现象。     

Ge_2Sb_2Te_5不同晶相对相变存储单元RESET电流影响

相变存储器(Phase Change Memory,PCM)的RESET电流是决定其功耗的最重要参数。基于相变材料Ge_2Sb_2Te_5(GST)的PCM单元,不同的SET条件下晶粒表现出两种不同的晶态结构,分别为立方晶相和六方晶相。针对这两种不同晶态结构的晶粒,应用数值模拟计算,对PCM单元的RESET电流进行研究,并将模拟结果与实际测试结果对比验证。结果表明:基于立方晶粒GST的PCM单元需要的RESET电流更小。     

基于Ge_2Sb_2Te_5存储介质的相变存储器疲劳特性分析

相变存储器由于操作电压低,读取速度快,制造工艺简单且与成熟CMOS工艺兼容,被认为最有可能替代Flash成为主流非易失性存储器。相变存储介质在存储中体积变化是影响器件可靠性的一个重要因素。研究了相变存储器在疲劳测试中的电性特征,利用高分辨率透射电子扫描电镜及傅里叶转换分析方法,研究相变存储器疲劳测试后相变介质的微观结构。若底部电极与相变介质的接触存在纳米量级不平整,那么接触表面将产生大电流密度,造成过操作,产生明显的体积收缩比。可以预测在多次的写擦操作后将导致相变介质形成空洞,与底部接触电极脱附。因此,控制底部接触电极与相变介质接触形貌对器件疲劳特性有着至关重要的影响。     

溅射参数对Ge_2Sb_2Te_5薄膜光学常数的影响

研究了溅射参数对 Ge2 Sb2 Te5 薄膜的光学常数随波长变化关系的影响 ,结果表明 :(1)当溅射功率一定时 ,随溅射氩气气压的增加 Ge2 Sb2 Te5 薄膜的折射率先增大后减小 ,而消光系数先减小后增大 .(2 )当溅射氩气气压一定时 ,对于非晶态薄膜样品 ,在 5 0 0 nm波长以下 ,折射率随溅射功率的增加先增加后减小 ,消光系数则逐渐减小 ;在 5 0 0 nm以上 ,折射率随溅射功率的增加逐渐减少 ,消光系数先减小后增加 .对于晶态薄膜样品 ,在整个波长范围折射率随溅射功率的增加先减小后增加 ,消光系数则逐渐减少 .(3)薄膜样品的光学常数都随波长的变化而变化 ,在长波     

钛掺杂对Ge_2Sb_2Te_5薄膜相变特性的改善（英文）

利用椭偏光谱术与XRD对钛掺杂Ge_2Sb_2Te_5薄膜中钛元素对体系的光学性质及其微结构的影响进行了实验研究.进而对该薄膜进行变温阻抗实验表明,钛掺杂Ge_2Sb_2Te_5薄膜与未掺杂的薄膜相比具有更好的热稳定性.基于对薄膜样品的数据保持能力测试的实验数据,经阿伦纽斯外推处理可知,钛掺杂Ge_2Sb_2Te_5薄膜样品的10年数据保持温度要高于未掺杂Ge_2Sb_2Te_5薄膜样品.本文的实验结果均证实,钛掺杂Ge_2Sb_2Te_5薄膜更适合应用于相变随机存取存储器中.     

压印技术制备超高密度Si_2Sb_2Te_5基相变存储阵列

采用低成本、高效率的压印技术实现了高密度相变存储器(PCRAM)存储阵列的制备,开发出Si2Sb2Te5(SST)新材料的4Gbit/inch2存储阵列,存储单元面积为0.04μm2;利用SEM观测压印获得的光刻胶图形阵列以及刻蚀后的SST存储阵列,其单元外形均具有高度的一致性,且单元特征尺寸的3倍标准差均小于6nm;利用AFM研究了SST存储单元的I-V特性,阈值电压为1.56V,高、低电阻态阻值变化超过两个数量级。实验结果表明了SST新材料及压印技术在PCRAM芯片中的应用价值。     

Ag纳米线掺杂单晶SnSe热电和力学性能的研究

为探究Ag纳米线掺杂对单晶SnSe的热电和力学性能的影响,建立了一种1D-3D的复合结构体系的理论模型。基于密度泛函理论的第一性原理,计算了Ag纳米线掺杂体系的能带、态密度、载流子相对质量、声子群速度及弹性常数等。从微观特征变化研究Ag纳米线掺杂对热电转化性能和力学性能的影响。结果表明：随着Ag纳米线掺杂浓度的增大,体系的禁带宽度逐渐减小,导带有明显的提高,提高了载流子的迁移率,有利于电导率的提高;载流子相对质量呈现先上升后下降的变化趋势,且相较于未掺杂的SnSe有明显增大,材料的塞贝克系数显著提高;声子群速度逐渐减小,导热性能降低,有利于热电性能的提高;掺杂Ag纳米线的SnSe的体模量和剪切模量均比未掺杂的SnSe小,材料的可塑性和韧性逐渐加强,SnSe的力学性能得到改善。     

初始化条件对Ag_(11)In_(12)Te_(26)Sb_(51)相变光盘反射率和信噪比的影响

Ag11In12 Te2 6Sb51相变光盘的反射率对比度和信噪比受初始化条件影响很大。研究表明 ,反射率对比度基本随功率增加而增大 ,随转速增加而减小 ,不同波长处的反射率对比度相差比较大 ;信噪比随初始化功率和转速的增加都是先增大后减小 ;最佳初始化条件为 :功率为1 30 0～ 1 5 0 0 m W,转速为 3.6～ 4.8m/s。     

掺杂Ag提升TiO_2纳米薄膜光电性能研究

采用sol-gel法制备出Ag掺杂的TiO_2纳米薄膜,利用SEM、XRD、UV-Vis、XPS及电化学工作站等对其光学及光电特性进行表征,研究了掺杂浓度及退火温度对材料晶体结构、光学特性及光电性能的影响规律。结果表明:Ag的掺杂提高了材料的晶相转变温度,降低了材料禁带宽度,使吸收带边发生红移(约40 nm),有效提高薄膜对太阳光的利用效率。当Ag掺杂浓度为摩尔分数0.5%,退火温度为500℃时,材料表现出最佳的光电活性,光电流密度达0.38×10~(–3)A/cm~2,相较于纯TiO_2薄膜的光电流密度增大约41%,光电性能得到显著提升且稳定性良好。     

生长温度对Ge2Sb2Te5薄膜的相变行为以及微观结构的影响

采用射频磁控溅射方法,分别在玻璃和具有本征氧化层的Si（100）基片上制备了Ge2Sb2Te5相变薄膜。利用X射线衍射仪、扫描电镜（SEM）、原子力显微镜（AFM）、紫外分光光度计等对薄膜进行了表征,研究了不同生长温度（室温～300℃）的Ge2Sb2Te5薄膜的表面形貌和结晶特性。分析结果表明：室温沉积的薄膜为非晶态;沉积温度为100℃～250℃时,薄膜转变为晶粒尺度约14nm的面心立方结构;300℃～350℃沉积的薄膜有少量的六方相出现。薄膜表面粗糙度随着沉积温度的升高逐渐递增,且薄膜的反射率变化与表面粗糙度有直接的关系。     

Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics

The operation of a single class of optical materials in both a volatile and nonvolatile manner is becoming increasingly important in many applications. This is particularly true in the newly emerging field of photonic neuromorphic computing, where it is desirable to have both volatile (short‐term transient) and nonvolatile (long‐term static) memory operation, for instance, to mimic the behavior of biological neurons and synapses. The search for such materials thus far have focused on phase change materials where typically two different types are required for the two different operational regimes. In this paper, a tunable volatile/nonvolatile response is demonstrated in a photonic phase‐change memory cell based on the commonly employed nonvolatile material Ge₂Sb₂Te₅ (GST). A time‐dependent, multiphysics simulation framework is developed to corroborate the experimental results, allowing us to spatially resolve the recrystallization dynamics within the memory cell. It is then demonstrated that this unique approach to photonic memory enables both data storage with tunable volatility and detection of coincident events between two pulse trains on an integrated chip. Finally, improved efficiency and all‐optical routing with controlled volatility are demonstrated in a ring resonator. These crucial results show that volatility is intrinsically tunable in normally nonvolatile GST which can be used in both regimes interchangeably.     

Si2Sb2Te5 phase change material studied by an atomic force microscope nano-tip

The Si2Sb2Te5 phase change material has been studied by applying a nano-tip (30 nm in diameter) on an atomic force microscopy system. Memory switching from a high resistance state to a low resistance state has been achieved, with a resistance change of about 1000 times. In a typical Ⅰ-Ⅴ curve, the current increases significantly after the voltage exceeds～4.3 V. The phase transformation of a Si2Sb2Te5 film was studied in situ by means of in situ X-ray diffraction and temperature dependent resistance measurements. The thermal stability of Si2Sb2Te5 and Ge2Sb2Te5 was characterized and compared as well.     

利用原子力显微镜纳米针研究Si2Sb2Te5 相变材料性能

The Si2Sb2Te5 phase change material has been studied by applying a nano-tip（30 nm in diameter） on an atomic force microscopy system.Memory switching from a high resistance state to a low resistance state has been achieved,with a resistance change of about 1000 times.In a typical I-V curve,the current increases significantly after the voltage exceeds～4.3 V.The phase transformation of a Si2Sb2Te5 film was studied in situ by means of in situ X-ray diffraction and temperature dependent resistance measurements.The thermal stability of Si2Sb2Te5 and Ge2Sb2Te5 was characterized and compared as well.     

钛掺杂对Ge2Sb2Te5薄膜相变特性的改善

利用椭偏光谱术与XRD对钛掺杂Ge2Sb2Te5薄膜中钛元素对体系的光学性质及其微结构的影响进行了实验研究。进而对该薄膜进行的变温阻抗实验表明,钛掺杂Ge2Sb2Te5薄膜与未掺杂的薄膜相比具有更好的热稳定性。基于对薄膜样品的数据保持能力测试的实验数据,经阿伦纽斯外推处理可知,钛掺杂Ge2Sb2Te5薄膜样品的10年数据保持温度要高于未掺杂Ge2Sb2Te5薄膜样品。本文的实验结果均证实,钛掺杂Ge2Sb2Te5薄膜更适合应用于相变随机存取存储器中。     

硫系相变材料Ge1Sb2Te4和Ge2Sb2Te5薄膜相变速度及电学输运性质研究

利用磁控溅射方法制备了Ge1Sb2Te4和Ge2Sb2Te5两种相变存贮材料的薄膜.原位X射线衍射(XRD)的结果表明,随着退火温度的升高,Ge1Sb2Te4和Ge2Sb2Te5薄膜都逐步晶化,材料结构发生了从非晶态到面心立方结构、再到六角密堆结构的转变.由衍射峰的半宽高可以看出,在达到第一次相变温度后,Ge2Sb2T...     

The Roles of the Ge‐Te Core Network and the Sb‐Te Pseudo Network During Rapid Nucleation‐Dominated Crystallization of Amorphous Ge2Sb2Te5

Ge₂Sb₂Te₅ (GST) has demonstrated its outstanding importance among rapid phase‐change (PC) materials, being applied for optical and electrical data storage for over three decades. The mechanism of nanosecond phase change in GST, which is vital for its application, has long been disputed: various, quite diverse scenarios have been proposed on the basis of various experimental and theoretical approaches. Nevertheless, one central question still remains unanswered: why is amorphous GST stable at room temperature for long time while it can rapidly transform to the crystalline phase at high temperature? Here it is revealed for the first time, by modelling the amorphous structure based on synchrotron radiation anomalous X‐ray scattering data, that germanium and tellurium atoms form a “core” Ge‐Te network with ring formation. It is also suggested that the Ge‐Te network can stabilize the amorphous phase at room temperature and can persist in the crystalline phase. On the other hand, antimony does not contribute to ring formation but constitutes a “pseudo” network with tellurium, in which the characteristic Sb–Te distance is somewhat longer than the covalent Sb–Te bond distance. This suggests that the Sb‐Te pseudo network may act as a precursor to forming critical nuclei during the crystallization process. The findings conclude that the Ge‐Te core network is responsible for the outstanding stability and rapid phase change of the amorphous phase while the Sb‐Te pseudo network is responsible for triggering critical nucleation.     

Ge2Sb2Te5的电化学特性及化学机械抛光

从电化学角度研究了Ge2Sb2Te5薄膜在化学机械抛光液中的作用，以及不同的pH值和H2O2浓度下的电化学特性. 采用Solartron SI1287电化学设备测试了Ge2Sb2Te5薄膜在溶液中的开路电位和动电位扫描. 开路电位结果表明：Ge2Sb2Te5在pH值为10的抛光液中表现出钝化行为；而抛光液的pH值为11时，开始向活化转变；当pH值为12时，薄膜处于活化状态. 在动电位扫描过程中，不同的pH值和H2O2浓度下，薄膜的扫描曲线形状相似，表明薄膜腐蚀具有相同的反应机理. 自制碱性抛光液，对Ge2Sb2Te5薄膜进行化学机械抛光，用SEM和EDS对抛光后的结构进行分析. 结果表明，通过CMP实现了Ge2Sb2Te5填充结构.     

制备条件对Ge2Sb2Te5薄膜电学性能的影响

研究了磁控溅射制备Ge2Sb2Te5薄膜时，制备条件诸如功率、气压等对薄膜性能的影响. 主要通过测量薄膜方块电阻随退火温度的变化情况，探索Ge2Sb2Te5薄膜的成长机理. 实验结果表明，不同溅射功率下制备的薄膜经不同温度退火后方块电阻没有明显的区别，而随着溅射气压的上升，薄膜方块电阻随退火温度的增加，下降的速率增加，意味着由面心立方结构转变为六方结构所需的结晶温度降低     

Single Pulse Laser‐Induced Phase Transitions of PLD‐Deposited Ge2Sb2Te5 Films

Phase transformations between amorphous and crystallized states are induced by irradiation with a single nanosecond laser pulse in Ge₂Sb₂Te₅ films grown by pulsed laser deposition. By adjusting the laser fluence, the two different phases are obtained and can be distinguished by their different optical reflectivity. The effect of laser fluence on the crystalline nature of the films is studied in detail. Large structural differences between the laser‐irradiated and thermally annealed films are revealed, due to the high heating rate and short duration of the laser pulse. X‐ray reflectivity measurements show a density increase of 3.58% upon laser‐induced crystallization.