Current Controlled Relaxation Oscillations in Ge_2Sb_2Te_5-Based Phase Change Memory Devices

The relaxation oscillation of the phase change memory(PCM) devices based on the Ge_2Sb_2Te_5 material is investigated by applying square current pulses.The current pulses with different amplitudes could be accurately given by the independently designed current testing system.The relaxation oscillation across the PCM device could be measured using an oscilloscope.The oscillation duration decreases with time,showing an inner link with the shrinking threshold voltage V_(th).However,the relaxation oscillation would not terminate until the remaining voltage V_(on) reaches the holding voltage V_h.This demonstrates that the relaxation oscillation might be controlled by V_(on).The increasing current amplitudes could only quicken the oscillation velocity but not be able to eliminate it,which indicates that the relaxation oscillation might be an inherent behavior for the PCM cell.     

Thermal effect of Ge_2Sb_2Te_5 in phase change memory device

The properties of Raman phonons are very important due to the fact that they can availably reflect some important physical information. An abnormal Raman peak is observed at about 558 cm-1in In film composed of In/InOx core–shell structured nanoparticles, and the phonon mode stays very stable when the temperature changes. Our results indicate that this Raman scattering is attributed to the existence of incomplete indium oxide in the oxide shell.     

Phase-selective fluorescence of doped Ge_2Sb_2Te_5 phase-change memory thin films

In this Letter, new concepts of fluorescence phase-change materials and fluorescence phase-change multilevel recording are proposed. High-contrast fluorescence between the amorphous and crystalline states is achieved in nickel- or bismuth-doped Ge_2Sb_2Te_5 phase-change memory thin films. Opposite phase-selective fluorescence effects are observed when different doping ions are used. The fluorescence intensity is sensitive to the crystallization degree of the films. This characteristic can be applied in reconfigurable multi-state memory and other logic devices. It also has likely applications in display and data visualization.     

Impulse response of Ge_2Sb_2Te_5-based ultrafast photodetector integrated with SOI waveguide

The impulse response for a phase-change material Ge_2Sb_2Te_5(GST)-based photodetector integrated with a silicon-on-insulator(SOI) waveguide is simulated using finite difference time domain method. The current is calculated by solving the drift-diffusion model for short pulse(～10 fs) excitation for both of the stable phases.Full width at half-maximum values of less than 1 ps are found in the investigation. The crystalline GST has higher 3 dB bandwidth than the amorphous GST at a 1550 nm wavelength with responsivities of 21 A/W and18.5 A/W, respectively, for a 150 nm thick GST layer biased at 2 V. A broad spectrum can be utilized by tuning the device using the phase-change property of material in the near infrared region.     

Iron trichloride as oxidizer in acid slurry for chemical mechanical polishing of Ge2Sb2Te5

The effect of iron trichloride （FeC13） on chemical mechanical polishing （CMP） of Ge2Sb2Te5 （GST） film is inves- tigated in this paper. The polishing rate of GST increases from 38 nm/min to 144 nm/min when the FeC13 concentration changes from 0.01 wt% to 0.15 wt%, which is much faster than 20 nm/min for the 1 wt% H2O2-based slurry. This polish- ing rate trends are inversely correlated with the contact angle data of FeCl3-based slurry on the GST film surface. Thus, it is hypothesized that the hydrophilicity of the GST film surface is associated with the polishing rate during CMP. Atomic force microscope （AFM） and optical microscope （OM） are used to characterize the surface quality after CMP. The chemical mechanism is studied by potentiodynamic measurements such as Ecorr and Icorr to analyze chemical reaction between FeCl3 and GST surface. Finally, it is verified that slurry with FeCl3 has no influence on the electrical property of the post-CMP GST film by the resistivity-temperature （RT） tests.     

Chemical mechanical planarization of Ge_2Sb_2Te_5 using IC1010 and Politex reg pads in acidic slurry

In the paper, chemical mechanical planarization(CMP) of Ge2Sb2Te5(GST) is investigated using IC1010 and Politex reg pads in acidic slurry. For the CMP with blank wafer, it is found that the removal rate(RR) of GST increases with the increase of pressure for both pads, but the RR of GST polished using IC1010 is far more than that of Politex reg. To check the surface defects, GST film is observed with an optical microscope(OM) and scanning electron microscope(SEM). For the CMP with Politex reg, many spots are observed on the surface of the blank wafer with OM, but no obvious spots are observed with SEM. With regard to the patterned wafer, a few stains are observed on the GST cell, but many residues are found on other area with OM. However, from SEM results, a few residues are observed on the GST cell, more dielectric loss is revealed about the trench structure. For the CMP with IC1010, the surface of the polished blank wafer suffers serious scratches found with both OM and SEM, which may result from a low hardness of GST, compared with those of IC1010 and abrasives. With regard to the patterned wafer, it can achieve a clean surface and almost no scratches are observed with OM, which may result from the high-hardness SiO2 film on the surface, not from the soft GST film across the whole wafer. From the SEM results, a clean interface and no residues are observed on the GST surface, and less dielectric loss is revealed. Compared with Politex reg, the patterned wafer can achieve a good performance after CMP using IC1010.     

Characteristics of Sb_6Te_4/VO_2 Multilayer Thin Films for Good Stability and Ultrafast Speed Applied in Phase Change Memory

The Sb_6Te_4/VO_2 multilayer thin films are prepared by magnetron sputtering and the potential application in phase change memory is investigated in detail. Compared with Sb_6Te_4, Sb_6Te_4/VO_2 multilayer composite thin films have higher phase change temperature and crystallization resistance, indicating better thermal stability and less power consumption. Also, Sb_6Te_4/VO_2 has a broader energy band of 1.58 eV and better data retention(125℃ for 10 y). The crystallization is suppressed by the multilayer interfaces in Sb_6Te_4/VO_2 thin film with a smaller rms surface roughness for Sb_6Te_4/VO_2 than monolayer Sb_4Te_6. The picosecond laser technology is applied to study the phase change speed. A short crystallization time of 5.21 ns is realized for the Sb_6Te_4(2 nm)/VO_2(8 nm)thin film. The Sb_6Te_4/VO_2 multilayer thin film is a potential and competitive phase change material for its good thermal stability and fast phase change speed.     

掺Sn的Ge2Sb2Te5相变存储薄膜的光学性质

提高存储密度和存取速率一直是光存储发展的方向。这对目前用于可擦重写存储的相变材料提出了越来越多的要求：它们既要对短波长有足够的响应,同时其相变速度也越快越好。因此,相变材料性能的改进十分重要,掺杂是提高相变材料性能的重要手段之一。用直流溅射法制备了掺杂不同量Sn的Ge2Sb2Te5相变薄膜,由热处理前后薄膜的X射线衍射（XRD）发现：薄膜发生了从非晶态到晶态的相变。研究了薄膜在250—900nm区域的反射光谱和透射光谱。结果表明：适当的Sn掺杂能大大增加热处理前后材料在短波长（300—405nm）的反射率衬比度,可见,通过Sn掺杂改良相变材料的短波长光存储性能是一种有效的途径。     

Optical Recording Performance of In_（47）Sb_（14）Te_（39）Phase Change Thin Films using 514．5nm Wavelength Laser Beam

ＯｐｔｉｃａｌＲｅｃｏｒｄｉｎｇＰｅｒｆｏｒｍａｎｃｅｏｆＩｎ_（４７）Ｓｂ_（１４）Ｔｅ_（３９）ＰｈａｓｅＣｈａｎｇｅＴｈｉｎＦｉｌｍｓｕｓｉｎｇ５１４．５ｎｍＷａｖｅｌｅｎｇｔｈＬａｓｅｒＢｅａｍ￥ＭＥＮＬｉｑｉｕ；ＪＩＡＮＧＦｕｓｏｎｇ；ＧＡＮ?..     

Ge2 Sb2 Te5相变薄膜光学及擦除性能研究

利用蓝绿激光对非晶态Ge2Sb2Te5 相变薄膜进行擦除性能的研究,分别用1000 ns,500 ns,100 ns,60 ns脉宽的蓝绿激光进行实验.结果表明,一定脉宽下,反射率对比度随擦除功率的增加而增大.并且,在1000 ns,500 ns,100 ns,60 ns的激光作用时间范围内,非晶态薄膜均可转变成晶态.对于脉宽为60 ns的蓝绿激光,擦除功率大于4.49 mW以后,薄膜的反射率对比度高于15％,这表明Ge2Sb2Te5相变薄膜在短脉宽、低擦除功率条件下,可具有较高的晶化速度.同时,分析了非晶态和晶态Ge2Sb2Te5相变薄膜的光谱特性,对比研究了780 nm,650 nm,514 nm和405 nm波长处的反射率和反射率对比度,提出了Ge2Sb2Te5相变薄膜用于蓝光光盘的改进方法.     

Phase transition,elastic and electronic properties of topological insulator Sb_2Te_3 under pressure: First principle study

The phase transition, elastic and electronic properties of three phases(phase Ⅰ,Ⅱ, and Ⅲ) of Sb_2Te_3 are investigated by using the generalized gradient approximation(GGA) with the PBESOL exchange–correlation functional in the framework of density-functional theory. Some basic physical parameters, such as lattice constants, bulk modulus, shear modulus,Young's modulus, Poisson's ratio, acoustic velocity, and Debye temperature Θ are calculated. The obtained lattice parameters under various pressures are consistent with experimental data. Phase transition pressures are 9.4 GPa(Ⅰ→Ⅱ) and 14.1 GPa(Ⅱ→Ⅲ), which are in agreement with the experimental results. According to calculated elastic constants, we also discuss the ductile or brittle characters and elastic anisotropies of three phases. Phases Ⅰ and Ⅲ are brittle, while phaseⅡ is ductile. Of the three phases, phaseⅡ has the most serious degree of elastic anisotropy and phase Ⅲ has the slightest one.Finally, we investigate the partial densities of states(PDOSs) of three phases and find that the three phases possess some covalent features.     

Optical and Short- wavelength Recording Properties of Ag_8In_( 14) Sb_( 55) Te_(23) Phase-change Films

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Sb_2Te_3热电薄膜的离子束溅射制备与表征

采用离子束溅射技术交替沉积Sb-Te-Sb多层薄膜后进行高真空热处理,直接制备Sb2Te3薄膜.利用X射线衍射(XRD)仪、霍尔系数测试仪、薄膜Seebeck系数测量系统对所制备的薄膜特性进行表征.XRD测量结果显示,薄膜的主要衍射峰与Sb2Te3标准衍射峰相同,在[101]/[012]晶向取向明显,存在较多的Te杂质峰;霍尔系数测试结果表明,薄膜为p型半导体薄膜,薄膜电阻率较低,其电导率接近于金属电导率,载流子浓度量级为1023cm-3,具有良好的电学性能;Seebeck系数测量结果显示,薄膜具有良好的热电性能,在不同条件下制备的薄膜的Seebeck系数在7.8—62μV/K范围;在所制备的薄膜中,退火时间为6h、退火温度为200℃的薄膜其Seebeck系数达到最大,约为62μV/K,且电阻率最小.     

Concurrent Structural and Electronic Phase Transitions in V_2O_3 Thin Films with Sharp Resistivity Change

The relationship between structural and electronic phase transitions in V_2O_3 thin films is of critical importance for understanding of the mechanism behind metal–insulator transition(MIT) and related technological applications.Despite being extensively studied, there are currently no clear consensus and picture of the relation between structural and electronic phase transitions so far. Using V_2O_3 thin films grown on γ-plane Al_2O_3 substrates,which exhibit abrupt MIT and structural phase transition, we show that the electronic phase transition occurs concurrently with the structural phase transition as revealed by the electrical transport and Raman spectra measurements. Our result provides experimental evidence for clarifying this issue, which could form the basis of theoretical studies as well as technological applications in V_2O_3.     

Effects of Thickness and Temperature on Thermoelectric Properties of Bi_2Te_3-Based Thin Films

Bi_2Te_3 thin films and GeTe/B_2Te_3 superlattices of different thicknesses are prepared on the silicon dioxide substrates by magnetron sputtering technique and thermally annealed at 573 K for 30 min. Thermoelectric(TE)measurements indicate that optimal thickness and thickness ratio improve the TE performance of Bi_2Te_3 thin films and GeTe/B_2Te_3 superlattices, respectively. High TE performances with figure-of-merit(ZT) values as high as 1.32 and 1.56 are achieved at 443 K for 30 nm and 50 nm Bi_2Te_3 thin films, respectively. These ZT values are higher than those of p-type Bi_2Te_3 alloys as reported. Relatively high ZT of the GeTe/B_2Te_3 superlattices at 300-380 K were 0.62-0.76. The achieved high ZT value may be attributed to the unique nano-and microstructures of the films,which increase phonon scattering and reduce thermal conductivity. The results indicate that Bi_2Te_3-based thin films can serve as high-performance materials for applications in TE devices.     

BaNb_xTi_(1-x)O_3薄膜的电学性质及结构相变(英文)

我们利用激光分子束外延设备(L MBE)在MgO上外延生长了一系列BaNbxTi1-xO3(0 相似文献   

Time-dependent evolution process of Sb_2Te_3 from nanoplates to nanorods and their Raman scattering properties

High-quality Sb_2Te_3 nanostructures are synthesized by a simple hydrothermal method. The morphologies of the nanostructures change from hexagonal nanoplates to nanorods with the extension of growth time. Secondary nucleation is the dominant factor responsible for the change of the morphologies. Structural analyses indicate that all the obtained nanostructures are well crystallized. IR-active phonons are mainly observed in the Raman spectra of the nanoplates and nanorods. The slight deviations are observed in the Raman modes between the nanoplates and nanorods, which could originate from confinement effect in the nanostructures.     

纳秒单脉冲激光诱导AgInSbTe薄膜的相变特性

利用磁控溅射法在K9玻璃基底上制备了Ag8In14Sb55Te23(AIST)纳米薄膜,并利用激光抽运-探测技术测量了薄膜的时间分辨反射率变化特性。研究结果表明,在合适能量密度的单脉冲纳秒激光脉冲作用下,AIST薄膜可以快速从沉积非晶态转化为晶态结构,晶化过程包含中间熔化态。在较低能量密度范围内,反射率变化量和晶化时间都随能量密度变化呈线性增加趋势。     

PbI2厚膜的结构、形貌与光谱性质研究

毫米级厚度碘化铅(PbI2)膜是制造下一代阵列高能辐射探测器的关键材料。采用近空间升华法制备了PbI2厚膜,研究升华源温度对制备样品晶体结构、表面形貌及光谱性质的影响。结果表明,随着源温度的升高,样品厚度由1 000μm下降到220μm。X射线衍射测试表明,厚膜为沿(002)晶面择优取向生长的六方相多晶结构,其晶粒尺寸、位错密度及生长应力与源温度密切相关。扫描电子显微镜测试显示,样品由六方片状颗粒堆积而成,其颗粒直径约为248μm,厚约32.7μm,有明显的层状结构。解谱拟合发现,样品的拉曼光谱有147,169,217和210cm-1等4个散射峰,前三个峰对应于4H晶型PbI2晶体的纵光学波振动模式,210cm-1来源于衬底SnO2的相关振动模式。随源温度的升高,147cm-1拉曼峰有明显变化,其峰强高于225℃时出现大幅度的下降,峰形展宽。在340nm光激发下,样品的室温光致发光谱在2.25,2.57和2.64eV附近出现弱的发光峰,来源于与缺陷和激子相关的复合。综合结构表征与光谱测试结果,200℃时沉积的PbI2厚膜具有最佳的结晶质量,其厚度约为659μm。     

薄膜沉积过程中TiO_2的金红石相向锐钛矿相转变

用ＲＦ磁控放电方法以纯金属钛做靶材在氩氧混合气体中制备了ＴｉＯ２薄膜,Ｒａｍａｎ光谱测量表明,在２Ｐａ工作气压下制备的ＴｉＯ２薄膜为锐钛矿结构,而在０２Ｐａ工作气压下制备的是金红石结构。工作气压的改变引起了ＴｉＯ２薄膜沉积中的相转变。