深亚微米三栅FinFET短沟道效应和拐角效应计算机模拟分析

利用三维器件模拟软件,研究了深亚微米三栅FinFET的短沟道效应,并模拟了阈值电压和亚阈值摆幅随硅鳍(fin)厚度和高度的变化情况.通过优化硅鳍厚度或高度,可以有效的控制短沟道效应.在进一步对深亚微米三栅FinFET的拐角效应进行二维数值模拟的过程中,并未观察到由拐角效应引起的泄漏电流.与传统的体硅CMOS结构有所不同,拐角效应并未使得深亚微米三栅FinFET性能变差,反而提高了其电学性能.     

MESFET的源漏电压和旁栅间距对旁栅阈值电压的影响

研究了ＭＥＳＦＥＴ的源漏电压对旁栅阈值电压的影响和旁栅间距与旁栅阈值电压的关系。结果表明源漏电压的大小对旁栅阈值电压有一定的影响，旁栅阈值电压的大小与旁栅间距大致成正比。     

短沟道SiC MESFET亚阈值特性

基于器件物理分析的方法,结合沟道电势二维解析模型,分析比较了漏极引致势垒降低效应(DIBL effect)对6H-及4H-SiC MESFET沟道势垒,阈值电压,以及亚阈值电流的影响,并研究了其温度特性.研究表明DIBL效应的存在使SiC MESFET的沟道势垒最小值随栅长及温度发生变化,并带来阈值电压及亚阈值电流的变化.栅长越大,温度越高,亚阚值倾斜因子Ns越小,栅压对沟道电流的控制能力增强,最终造成亚阈值电流随栅压的变化越快.     

新型高k栅介质材料研究进展

随着半导体技术的不断发展，MOSFET（metal-oxide-semiconductor field effect transistor）的特征尺寸不断缩小，栅介质等效氧化物厚度已小至nm数量级。这时电子的直接隧穿效应将非常显著，将严重影响器件的稳定性和可靠性。因此需要寻找新型高k介质材料，能够在保持和增大栅极电容的同时，使介质层仍保持足够的物理厚度来限制隧穿效应的影响。本文综述了研究高k栅介质材料的意义；MOS栅介质的要求；主要新型高k栅介质材料的最新研究动态；展望了高k介质材料今后发展的主要趋势和需要解决的问题。     

不同栅结构的部分耗尽NMOSFET/SIMOX的总剂量辐照效应研究

研究了在改性注氧隔离(SIMOX)材料上制备的具有环栅和H型栅结构的部分耗尽NMOS晶体管在三种不同偏置状态的总剂量辐照效应.实验表明在10keV的X-射线总剂量辐照下,器件的背栅、正栅阈值电压负向漂移和漏电流都控制在较小的水平;在2Mrad(SiO2)的辐照下仍能正常工作.研究证实了无论哪种栅结构,对于背栅,PG均为最劣偏置,其次是OFF偏置,而ON偏置下器件受辐照的影响最小;而对于正栅,ON均为最劣偏置.通过拟合计算出了绝缘埋层(BOX,即埋氧)中的饱和净正电荷密度Not和空穴俘获分数α.     

总剂量辐射下的NMOS/SOI器件背栅阈值电压漂移模型

SOI(绝缘体上硅)器件在总剂量辐照下的主要性能退化是由于SOI器件的背栅阈值电压漂移引起的背沟道漏电。本文首先采用二维有限元方法,对辐射在SOI器件的埋氧层中的感生氧化物电荷进行模拟,然后分析此氧化物电荷对器件的外部电学特性的影响,建立了器件在最劣偏置下辐射引起的背栅MOSFET的阈值电压漂移模型,提取背栅MOSFET受辐射影响参数,以用于在SOI电路设计中准确的评估辐射对SOI电路的影响。模拟数据和试验数据具有很好的一致性。     

柔性非晶InGaZnO薄膜晶体管栅绝缘层的研究

采用磁控溅射方法,在聚酰亚胺薄膜上室温制备了非晶铟镓锌氧(a-IGZO)柔性薄膜晶体管(TFT)。其中,栅绝缘层选择了不同厚度比例的氧化硅(SiO_x)与氧化坦(TaO_x)薄膜的搭配,对比研究了不同栅绝缘层结构的薄膜特性以及所对应的柔性TFT器件的操作特性和偏压稳定性。实验结果表明,TaO_x的成膜速率明显高于SiO_x;随着TaO_x所占比例的增加,栅绝缘层表面粗糙度降低,介电常数显著提高。以300nm厚TaO_x搭配300nm厚SiO_x为例,栅绝缘层相对介电常数可以达到10,对应的a-IGZOTFT表现出了更高的的开态电流和更低的阈值电压,但是器件漏电流略有增加,正偏压稳定性也会有所下降。     

注氮、注氟SIMOX/NMOS器件辐射加固性能

本文对注N、注F的SIMOX/NMOSFET器件的抗辐射特性进行了研究,发现两者都能减少埋氧层及其界面的空穴陷阱,对辐射加固有所改善,特别是对大剂量辐射的加固更为明显.总体来说,在此能量下,离子注入剂量越大,加固越好.由于注入的剂量对片子本身的阈值电压有很大影响,所以选择对于器件初始特性影响较小的剂量及能量非常重要.     

体硅FinFET三维模拟

利用三维模拟软件Davinci对体硅FinFET器件进行了详细的模拟.模拟结果显示体硅Fin-FET器件能够有效的抑止短沟道效应,具有驱动电流大、散热好、成本低等优点.为了获得好的亚阚值特性,Fin的厚度要比较薄,同时Fin的高度不能太低,以保持足够的高度来抑止短沟道效应.沟道可以采用低掺杂或未掺杂设计,从而减少沟道内杂质对载流子的散射作用和杂质涨落效应对器件性能的影响.另外,为了获得合适的器件阈值电压,体硅FinFET器件应当采用功函数在中间带隙附近的材料做栅电极,同时采用适当的功函数调节方法来获得合适的阈值电压.     

超薄SIMOX材料的Pseudo-MOSFET电学表征

介绍了一种表征SOI材料电学性质的手段,并对三种不同顶层硅厚度的SIMOX材料进行测试、提取参数,分析材料制备工艺对性能产生的影响。研究结果表明,标准SIMOX材料通过顶层硅膜氧化、腐蚀等减薄工艺制得的顶层硅厚度小于100nm的超薄SIMOX材料,其顶层硅与BOX层界面有更多的缺陷,会影响到在顶层硅膜上制得的器件的性能,引起NMOSFET的阈值电压升高、载流子迁移率降低。Pseudo-MOSFET方法能够在晶圆水平上快捷有效地表征超薄SIMOX材料的电学性质。     

Design of a pavement using piezoelectric materials

Pavement material is an important factor for creating a pedestrian and environmentally friendly walkway. Generally, kinetic energy of footstep during walking is mostly wasted, while, this energy can be harvested and converted to electrical power. This study aims to use piezoelectric materials within pavements in the form of tiles. The kinetic energy of walking is harvested through piezoelectric mechanism. The study proposed a pavement consisting of piezoelectric sensors. Flexible and green material are selected as the top layer of the pavement. The scaled prototype is fabricated according to the mechanism of walking. The pavement is tested in terms of voltage generation in different arrangements. The results show that in order to harvest the optimum energy of walking, the piezoelectric sensors need to be covered with a conductive layer such as a steel sheet. Also, it is found that covering the piezoelectric materials with a hard surface leads to load distribution over the sensors when stepping on it which subsequently, generates more voltage. Moreover, when the piezoelectric pieces are placed in an alternative arrangement, more voltage is generated. It can be concluded that the arrangement of the piezoelectric sensors and their connection to the conductive layer are important factors in harvesting the optimum walking energy. The study recommends that pavement equipped with piezoelectric material is a promising method to generate electricity when implemented in crowded areas.     

Influence of cathode voltage on electrical property and crystal structure of sputter-deposited Ag thin films

The resistivity and crystal structure of Ag thin films were investigated as a function of the cathode voltage during the Ag sputter deposition. Low emissivity (low-e) coatings with a layered construction of glass/dielectric/Ag/dielectric were deposited by magnetron sputtering. It was found that the Ag layers in the low-e coatings showed lower resistivity when lower cathode voltage was applied. Furthermore, the X-ray diffraction measurement revealed that the crystallite of the Ag layer became larger with the decrease of the cathode voltage. It can be seen from these results that the Ag deposition resulting from low cathode voltage contributes to preferred crystal growth of the Ag layer. This improvement of the Ag crystallinity can be explained by the decrease in the kinetic energy of the Ar atoms backscattered on the Ag sputter target surface.     

Surface electronic states in metal-porous silicon-silicon structures

The character of electronic states in porous silicon (PS)-Si, Pd-PS interfaces, and/or PS bulk at the formation of the metal-PS-silicon heterostructure was studied. The energy parameters were estimated using the deep-level transient spectroscopy and capacitance-voltage characteristics at the accounting of the voltage drop distribution along the structure. The analytical expression for voltage drop distribution along dielectric layer, porous layer and space charge region in silicon was obtained by solving the equation for continuity of the electrostatic induction vector. The electronic states studied were shown to manifest the quasi-continuous sub-band in the energy gap if the porous layer was 30-nm thick. Their density increased, as the energy position was being transformed to a deeper energy level of E_v+0.81 eV at the PS layer growing to 90 nm wide.     

Ionic Modulation of the Interfacial Magnetism in a Bilayer System Comprising a Heavy Metal and a Magnetic Insulator for Voltage‐Tunable Spintronic Devices

The voltage modulation of yttrium iron garnet (YIG) is of practical and theoretical significance; due to its advantages of compactness, high‐speed response, and energy efficiency, it can be used for various spintronic applications, including spin‐Hall, spin‐pumping, and spin‐Seebeck effects. In this study, a significant ferromagnetic resonance change is achieved within the YIG/Pt bilayer heterostructures uisng ionic modulation, which is accomplished by modifying the interfacial magnetism in the deposited “capping” platinum layer. With a small voltage bias of 4.5 V, a large ferromagnetic field shift of 690 Oe is achieved in heterostructures of YIG (13 nm)/Pt (3 nm)/(ionic liquid, IL)/(Au capacitor). The remarkable magnetoelectric (ME) tunability comes from the additional and voltage‐induced ferromagnetic ordering, caused by uncompensated d‐orbital electrons in the Pt metal layer. Confirmed by first‐principle calculations, this finding paves the way for novel voltage‐tunable YIG‐based spintronics.     

Biomolecule detection using a silicon nanoribbon: accumulation mode versus inversion mode

Silicon nanoribbons were fabricated using standard optical lithography from silicon on insulator material with top silicon layer thicknesses of 100, 60 and 45?nm. Electrically these work as Schottky-barrier field-effect transistors and, depending on the substrate voltage, electron or hole injection is possible. The current through the nanoribbon is extremely sensitive to charge changes at the oxidized top surface and can be used for biomolecule detection in a liquid. We?show that for detection of streptavidin molecules the response is larger in the accumulation mode than in the inversion mode, although not leading to higher detection sensitivity due to increased noise. The effect is attributed to the location in depth of the conducting channel, which for holes is closer to the screened surface charges of the biomolecules. Furthermore, the response increases for decreasing silicon thickness in both the accumulation mode and the inversion mode. The results are verified qualitatively and quantitatively through a two-dimensional simulation model on a cross section along the nanoribbon device.     

Threshold voltage calculation in ultrathin-film SOI MOSFETs using the effective potential

The success of the effective potential method of including quantum confinement effects in simulations of MOSFETs is based on the ability to calculate ahead of time the extent of the Gaussian wave packet used to describe the electron. In the calculation of the Gaussian, the inversion layer is assumed to form in a triangular potential well, from which a suitable standard deviation can be obtained. The situation in an ultrathin silicon-on-insulator (SOI) MOSFET is slightly different, in that the potential well has a triangular bottom, but there is a significant contribution to the confinement from the rectangular barriers formed by the gate oxide and the buried oxide. For this more complex potential well, it is of interest to determine the range of applicability of the effective potential model with a constant standard deviation. In this paper, we include this effective potential model in Monte Carlo calculations of the threshold voltage of ultrathin SOI MOSFETs. We find that the effective potential recovers the expected trend in threshold voltage shift with decreasing silicon thickness, down to a thickness of approximately 3 nm.     

Adhesive element modelling and weighted static shape control of composite plates with piezoelectric actuator patches

A novel finite element model is presented for static and dynamic analysis of composite plates integrated with a laminated piezoelectric layer, a host laminated composite plate and an adhesive layer between them. A new adhesive element is developed which includes both peel and shear effects in the adhesive layer based on first‐order shear deformation plate theory. The thin adhesive layer between the piezoelectric layer and the host plate is modelled by assuming that it carries constant shear and peel strains throughout its thickness. In addition, a weighted static shape control scheme for finding the optimal voltage distribution for static shape control is given. By selecting different weighting matrices, a variety of items such as displacements, slopes, curvatures, strains and even generalized forces, can be included in finding the optimal actuating voltage for static shape control. The present model is validated by comparing with those results available in the literature. The numerical results show that the weighted linear least method can give a satisfactory voltage distribution to best match the desired shape. Copyright © 2004 John Wiley & Sons, Ltd.     

Screening effect of a-C:H alignment layer in nematic liquid crystal cell

The electrical and optical characteristics of nematic liquid crystal (NLC) cells and their dependence on the thickness of an amorphous hydrogenated carbon (a-C:H) alignment layer have been studied. An increase in the a-C:H layer thickness favors enhancement of the screening of a bias voltage applied to this layer, which is manifested by an increase in the threshold voltage of the electrooptical splay effect. This is accompanied by a decrease in the initial (pretilt) director angle, which is evidence for an increase in the anchoring energy due to the field of space charge localized at the interface.     

Damage observed in silicon diodes after low energy pion irradiation

We present results of irradiation tests performed in the pion beam of the Paul Scherrer Institute. Our results confirm the prediction, that the Δ-resonance is reflected as an enhancement of the damage caused by low energy pions. At the peak of the Δ-resonance we measure a damage constant 1.5 times higher than generally adopted for neutrons and high energy protons. This result means that the lifetime of silicon detectors close to the vertex at LHC experiments will be limited by the pion background. We predict type inversion of high resistivity detectors to occur after two months of full luminosity and the depletion voltage to reach 200 V within the first four years, even if the detectors are operated at 0°C.