Total Dose Radiation Tolerance of Phase Change Memory Cell with GeSbTe Alloy

Phase change memory （PCM） cell array is fabricated by a standard complementary metal-oxide-semiconductor process and the subsequent special fabrication technique. A chalcogenide Ge2Sb2Te5 film in thickness 50hm deposited by rf magnetron sputtering is used as storage medium for the PCM cell. Large snap-back effect is observed in current-voltage characteristics, indicating the phase transition from an amorphous state （higher resistance state） to the crystalline state （lower resistance state）. The resistance of amorphous state is two orders of magnitude larger than that of the crystalline state from the resistance measurement, and the threshold current needed for phase transition of our fabricated PCM cell array is very low （only several μA）. An x-ray total dose radiation test is carried out on the PCM cell array and the results show that this kind of PCM cell has excellent total dose radiation tolerance with total dose up to 2 ×10^6 rad（Si）, which makes it attractive for space-based applications.     

Quantum—Confined Stark Effect of Vertically Stacked Self—Assembled Quantum Discs

We study the electronic energy levels and probability distribution of vertically stacked self-assembled InAs quantum discs system in the presence of a vertically applied electric field. This field is found to increase the splitting between the symmetric and antisymmetric levels for the same angular momentum. The field along the direction from one disc to another affects the electronic energy levels similarly as that in the opposite direction because the two discs are identical. It is obvious from our calculation that the probability of finding an electron in one disc becomes larger when the field points from this disc to the other one.     

Optical spectra and Exciton State in Vertically Stacked Self—Assembled Quantum Discs

We study the oscillator strengths of the optical transitions of the vertically stacked self-assembled InAs quantum discs.The oscillator strengths change evidently when the two quantum discs are far apart from each other.A vertically applied electric field affects the oscillator strengths severely.while the oscillator strengths change slowly as the radius of one disc increases.We also studied the excitonic energy of the system.including the Coulomb interaction.The excitonic energy increases with the increasing radius of one disc.but decreases as a vertically applied electric field increases.     

Single Crystal Si Layers on Glass Fabricated by Hydrophilic Fusion Bonding and Smart-Cut Technology

A single crystal Si thin film on a glass substrate has been obtained successfully by hydrophilic fusion bonding and the smart-cut technology. Tensile strength testing shows that the bonded interface has strong adhesion and the bonding strength is about 8.7MPa. Crystallinity and microstructure of the samples have been characterized by transmission electron microscopy (TEM). Electrical properties have also been investigated by Hall measurements and four-point probe. The mobility of the transferred Si layer on glass is about 122cm^2//V.s. The results show that the single-crystal silicon layer transferred onto glass by direct bonding keeps good quality for the applications of integrated circuits, transducers, and fiat panel display.     

一种新型的三维半解析数值算法

在三维空间,结合有限元线法与有限层法的思想,构造了一种新型的半解析数值算法,数值结果表明该方法具有较高的精度,切实可行。     

负载型催化剂制备的聚丙烯等规度分布

负载型Ziesler－Natta催化剂中存在许多活性中心［'3，为了解其本质，需对其各自产生的聚合物进行分离，以往采用的溶剂抽提法［'－'j只能将聚合物大致分级．最近，升温淋洗分级法（TREF）已被运用于聚丙烯的分级卜，'，其原理是根据聚合物的结晶度分级D'，影响聚丙烯结晶性的主要因素是等规度，而分子量到达一定程度后其影响较小，故通过TREF分级可得到聚丙烯的等规度分布．TREF法的淋洗温度可控，故分级效果较好．该法在分级前需对样品进行等温结晶处理，以消除抽提法由于样品未必充分结晶而带来的误差．本文用TREF法对不同催化…     

生物特异性功能高分子

模仿天然生物活性高分子关键作用点的化学组成，在高分子链上接上各种官能团或化学残基，制备具有与该天然高分子相似生物活性的高分子，即生物特异性功能高分子。本文主要介绍拟肝素高分子和似粘连 蛋白高分子两种生物特异性功能高分子。     

材料参数拟合方法对弹靶侵彻仿真的影响

弹靶侵彻仿真中材料参数对计算结果有着至关重要的影响。为寻求一套适用于弹靶侵彻仿真计算的材料参数拟合方法,借助前期开展的靶板材料动态力学性能试验、靶板材料断裂试验,通过不同拟合方法依次得到不同的JC本构模型及失效模型参数,依据试验建立有限元计算模型,将数值计算结果与试验结果进行对比。结果表明:(1)对于同一材料的力学性能试验,采用不同的拟合方法可得到不同的JC本构、JC失效参数,二者会对弹靶仿真结果造成一定影响;(2)在不考虑温度软化项的前提下,采用高应变率作为参考应变率进行拟合能更加准确地表征材料在高应变率下的应力-应变关系,更加适用于弹靶侵彻强瞬态、高应变率作用过程仿真;(3)对于同一JC本构模型,采用平均应力三轴度拟合的JC失效模型较采用初始应力三轴度拟合的JC失效模型所得战斗部剩余速度计算结果偏小,仅采用拉伸试件结果拟合的JC失效模型较采用扭转、拉伸试件结果拟合的JC失效模型所得战斗部剩余速度计算结果偏小。     

Reactive Ion Etching as Cleaning Method Post Chemical Mechanical Polishing for Phase Change Memory Device

In order to improve nano-scale phase change memory performance, a super-clean interface should be obtained after chemical mechanical polishing （CMP） of Ge2Sb2Te5 phase change films. We use reactive ion etching （RIE） as the cleaning method. The cleaning effect is analysed by scanning electron microscopy and an energy dispersive spectrometer. The results show that particle residue on the surface has been removed. Meanwhile, Ge2Sb2Te5 material stoichiometric content ratios are unchanged. After the top electrode is deposited, currentvoltage characteristics test demonstrates that the set threshold voltage is reduced from 13 V to 2.7V and the threshold current from 0.1 mA to 0.025 mA. Furthermore, we analyse the RIE cleaning principle and compare it with the ultrasonic method.     

Decaying solitary waves propagating in one-dimensional damped granular chain

We numerically investigate the nonlinear waves propagating in a one-dimensional particle chain when the damping effect is taken into account. It is found that decaying solitary waves exist, in which the amplitude of the wave decreases exponentially as time increases. Meanwhile, the velocity of the solitary wave also slows down as time goes. This result implies that the damping coefficient is an important parameter in such a nonlinear system. Theoretical analysis has also been done by the reductive perturbation method. The result indicates that the nonlinear waves propagating in such a system can be described by the damped KdV equation.