CTM俘获层材料选取的模拟研究

电荷陷阱存储器(CTM)由于其分离式电荷存储原理,可以使存储器件尺寸持续小尺寸化,理论上解决了传统浮栅存储器小尺寸化瓶颈的限制。基于第一性原理,从理论上对CTM材料及相关结构进行了模拟计算,采用Material Studio软件包,对多种电荷俘获材料进行改性,引入陷阱,并对其能带、状态密度、缺陷态密度等方面展开模拟研究。为CTM实验提供了非常有效的理论依据与方法,从该角度出发研究存储器是一个全新的视角,提出可以通过陷阱态密度曲线的部分积分来确定CTM的存储窗口等衡量指标。     

拼接式组合扁梁受弯性能分析

本文提出了一种拼接式组合扁梁,对其进行了受弯性能分析.组合扁梁属于内嵌式组合梁,其组成部分较为复杂,传统承载力计算公式偏保守.为便于此类梁的设计,本文在等效应力法的基础上使用等效矩形应力图法,对拼接式组合扁梁的正截面抗弯承载力公式进行推导.使用ABAQUS有限元软件对组合方法公式的准确性进行验证,并与等效应力法公式进行对比,结果表明组合公式得到的数值更为精准.在相同截面高度和用钢量下设计了一个深肋组合扁梁和一个拼接式组合扁梁,并进行了受弯性能对比;同时对不同钢强度和翼缘厚度影响下的拼接式组合扁梁抗弯承载性能进行分析.使用换算截面法对其进行了弹性刚度的计算,并和有限元进行了对比,二者吻合较好,研究结果为拼接式组合扁梁的设计和优化提供了一定参考依据.     

平行圆管空心板双向抗弯刚度的确定

平行圆管空心板横管方向抗弯刚度的取值问题尚未获得圆满解决.本文通过有限元分析,发现横管方向平均应变仍符合平截面假定;提出了两种基于数值解求其等效刚度的方法,即分别用水平位移按刚度定义计算和用竖向挠庹按挠度-刚度关系式计算,两种方法的结果得到了相互印证;继而经拟合得到了横管与顺管两个方向刚度比的经验公式,简单实用.值得指出,本文提出的等效刚度确定方法简便合理,对解决类似问题有重要的借鉴价值.     

Ultrasonic flexural vibration assisted chemical mechanical polishing for sapphire substrate

The sapphire substrates are polished by traditional chemical mechanical polishing (CMP) and ultrasonic flexural vibration (UFV) assisted CMP (UFV-CMP) respectively with different pressures. UFV-CMP combines the functions of traditional CMP and ultrasonic machining (USM) and has special characteristics, which is that ultrasonic vibrations of the rotating polishing head are in both horizontal and vertical directions. The material removal rates (MRRs) and the polished surface morphology of CMP and UFV-CMP are compared. The MRR of UFV-CMP is two times larger than that of traditional CMP. The surface roughness (root mean square, RMS) of the polished sapphire substrate of UFV-CMP is 0.83 Å measured by the atomic force microscopy (AFM), which is much better than 2.12 Å obtained using the traditional CMP. And the surface flatness of UFV-CMP is 0.12 μm, which is also better than 0.23 μm of the traditional CMP. The results show that UFV-CMP is able to improve the MRR and finished surface quality of the sapphire substrates greatly. The material removal and surface polishing mechanisms of sapphire in UFV-CMP are discussed too.     

Mechanical Strength and Tribological Properties of Diglycidyl Ether of Bisphenol-A Cured by Poly(Amide-Amidic Acid) and 4,4’-Diaminodiphenylsulfone

Diglycidyl ether of bisphenol-A (DGEBA) was cured by poly(amide-amidic acid) (PAA) and a commonly used curing agent, 4,4’-diaminodiphenylsulfone (DDS), in different molar ratios. It was found that the flexural strength, tensile strength, tribological properties, and thermal stability strongly depended on the molar ratios of PAA and DDS in the mixed curing agents. The highest flexural strength was obtained when DGEBA was cured with PAA individually. The tensile strength increased with the increase of PAA content in the mixed curing agents. The DGEBA cured with PAA containing curing agents possessed lower friction coefficient than that cured with DDS individually. The wear rate greatly decreased with the PAA content increasing in the mixed curing agent. Tribological behaviors and wear mechanisms were discussed by observing the morphology of wear debris and worn surfaces of the tested samples using scanning electron microscopy (SEM).     

Integration of high-performance spin-orbit torque MRAM devices by 200-mm-wafer manufacturing platform

We demonstrate in-plane field-free-switching spin-orbit torque (SOT) magnetic tunnel junction (MTJ) devices that are capable of low switching current density, fast speed, high reliability, and, most importantly, manufactured uniformly by the 200-mm-wafer platform. The performance of the devices is systematically studied, including their magnetic properties, switching behaviors, endurance and data retention. The successful integration of SOT devices within the 200-mm-wafer manufacturing platform provides a feasible way to industrialize SOT MRAMs. It is expected to obtain excellent performance of the devices by further optimizing the MTJ film stacks and the corresponding fabrication processes in the future.     

自由端盖Ⅲ型宽带弯张换能器的设计

提出了一种利用多模耦合实现低频、宽带、大功率特性的新结构Ⅲ型弯张换能器。通过在压电陶瓷堆内部嵌入与凹型弯张壳体相连的弹性辅助弯曲梁结构,并用弯曲圆盘作为顶部自由端盖,增加有效工作模态。利用有限元方法对换能器进行了设计优化,分析结果显示换能器在低频段存在4个主要工作模态。根据优化结果,加工制作了换能器样机,水池实验的测试结果表明:在1.5～5.5 kHz范围内,换能器样机的发送电压响应均大于135 dB;1.5～4 kHz内的最大发送电压响应大于142 dB,响应起伏小于6 dB。研究结果表明自由端盖Ⅲ型弯张换能器不仅能够在小尺寸设计下实现大功率工作,还能获得低频宽带发射性能。     

考虑弯曲变形的端盖法兰动态密封设计方法

端盖法兰的螺栓预紧力选择是密封结构设计的重要问题。本文中通过估算端盖法兰弯曲振动的等效刚度和等效质量,建立了考虑端盖弯曲振动的法兰结构响应双弹簧分析模型,获得了与实验数据一致性较好的结构响应分析结果。总结了端盖轴向振动、弯曲振动引起的密封面位移随预紧力、端盖厚度的变化规律;并发现随预紧力增加,密封面间隙逐渐减小并趋于一个极值;端盖弯曲变形是影响该极值大小的主要因素。

     

Antibacterial and Physical Properties of PVM/MA Copolymer- Incorporated Polymethyl Methacrylate as a Novel Antimicrobial Acrylic Resin Material

Polymethyl methacrylate (PMMA), an acrylic resin used in orthodontic appliances and removable dentures for its biocompatibility and esthetics, may harbor bacteria on its surface. The present study investigated a new PMMA formula with Gantrez: an antibacterial copolymer of methyl vinyl ether and maleic acid (PVM/MA). Samples were tested for mechanical properties (surface hardness, flexural strength, water sorption, and water solubility) and effects against Streptococcus mutans. Six groups (0%-control, 5%, 10%, 15%, 20%, and 25% Gantrez) of n = 12 were fabricated for physical property tests and analyzed with one-way ANOVA and Prism 6. From these results, three groups (0%, 5%, and 10% Gantrez) were selected for antibacterial tests, and data were analyzed with one-way ANOVA and Tukey’s multiple comparison test. Adding 5% and 10% Gantrez into PMMA significantly decreased S. mutans adhesion. There was no significant difference between the control vs. 5%, 10%, 15%, and 20% Gantrez (p > 0.05) for surface hardness, the control vs. 5% Gantrez (p > 0.05) for flexural strength, and the control vs. 5 and 10% Gantrez for water sorption and water solubility. Overall, incorporating 5% Gantrez into PMMA may be a promising solution to reduce bacterial adhesion without changing the acrylic resin’s physical properties.     

Optimized operation scheme of flash-memory-based neural network online training with ultra-high endurance

With the rapid development of machine learning, the demand for high-efficient computing becomes more and more urgent. To break the bottleneck of the traditional Von Neumann architecture, computing-in-memory (CIM) has attracted increasing attention in recent years. In this work, to provide a feasible CIM solution for the large-scale neural networks (NN) requiring continuous weight updating in online training, a flash-based computing-in-memory with high endurance (10⁹ cycles) and ultra-fast programming speed is investigated. On the one hand, the proposed programming scheme of channel hot electron injection (CHEI) and hot hole injection (HHI) demonstrate high linearity, symmetric potentiation, and a depression process, which help to improve the training speed and accuracy. On the other hand, the low-damage programming scheme and memory window (MW) optimizations can suppress cell degradation effectively with improved computing accuracy. Even after 10⁹ cycles, the leakage current (I_off) of cells remains sub-10pA, ensuring the large-scale computing ability of memory. Further characterizations are done on read disturb to demonstrate its robust reliabilities. By processing CIFAR-10 tasks, it is evident that ~90% accuracy can be achieved after 10⁹ cycles in both ResNet50 and VGG16 NN. Our results suggest that flash-based CIM has great potential to overcome the limitations of traditional Von Neumann architectures and enable high-performance NN online training, which pave the way for further development of artificial intelligence (AI) accelerators.