Defect behaviors in n-channel power VDMOSFETs during HEFS and thermal post-HEFS annealing

The results of positive/negative Fowler-Nordheim high electric field stress and thermal post-high electric field stress annealing of commercial n-channel power VDMOSFETs have been presented. They have shown that gate bias sign has an influence on the fixed trap behavior during high electric field stress, but has no influence on any defect type behavior during thermal post-high electrical field stress annealing. In addition, slow switching traps have different behavior, but fast switching traps have the same behavior during thermal post-high electrical field stress annealing and thermal post-irradiation annealing.     

Investigation polarization characteristics of vertical-cavity surface-emitting lasers

We have improved transmission line laser model to study the polarization characteristics by incorporating into spin-flip model (SFM). Theoretical studies on the influence of the Bragg reflectivity on the polarization switching of vertical-cavity surface-emitting laser (VCSEL) have been discussed in this paper. We have demonstrated that reflectivity of Bragg reflectors can be optimized to provide suitable hysteresis loops width which indicates the tolerance of the input power.     

PZT铁电薄膜纳米尺度铁电畴的场致位移特性

利用扫描力显微术的压电响应模式，并基于逆压电效应原理，研究了梯度组成的PZT铁电薄膜纳米尺度铁电畴的场致位移特性.获得了源于纳米尺度铁电畴的压电效应和电致伸缩效应贡献的场致位移回滞线，以及源于线性压电效应和电畴反转效应综合贡献的纳米尺度压电位移 场强蝶形曲线，证实了Caspari Merz理论在纳米尺度上的有效性.发现了梯度铁电薄膜存在纳米尺度印刻现象，认为该现象的内因源于薄膜中的内偏场. 关键词： PZT铁电薄膜 场致位移 纳米尺度 扫描力显微术     

Nonlinear constitutive behavior of ferroelectric materials

The ferroelectric specimen is considered as an aggregation of many randomly oriented domains. According to this mechanism, a multi-domain mechanical model is developed in this paper. Each domain is represented by one element. The applied stress and electric field are taken to be the stress and electric field in the formula of the driving force of domain switching for each element in the specimen. It means that the macroscopic switching criterion is used for calculating the volume fraction of domain switching for each element. By using the hardening relation between the driving force of domain switching and the volume fraction of domain switching calibrated, the volume fraction of domain switching for each element is calculated. Substituting the stress and electric field and the volume fraction of domain switching into the constitutive equation of ferroelectric material, one can easily get the strain and electric displacement for each element. The macroscopic behavior of the ferroelectric specimen is then directly calculated by volume averaging. Meanwhile, the nonlinear finite element analysis for the ferroelectric specimen is carried out. In the finite element simulation, the volume fraction of domain switching for each element is calculated by using the same method mentioned above. The interaction between different elements is taken into account in the finite element simulation and the local stress and electric field for each element is obtained. The macroscopic behavior of the specimen is then calculated by volume averaging. The computation results involve the electric butterfly shaped curves of axial strain versus the axial electric field and the hysteresis loops of electric displacement versus the electric field for ferroelectric specimens under the uniaxial coupled stress and electric field loading. The present theoretical prediction agrees reasonably with the experimental results. Supported by the National Natural Science Foundation of China (Grant No. 10572138)     

Thermodynamics and kinetics of switching of ferroelastic ferroelectrics at its initial stage

Thermodynamics and kinetics of switching of ferroelastic ferroelectrics (FFs) are studied at the initial (weak-metastability) stage. It is shown that in the switching of a uniaxial FF, the role of the electric field and mechanical stress simultaneously applied to the FF is analogous to that of supersaturation or supercooling of solutions and melts in the process of a conventional phase transition. The dependence of the critical size of a domain on the strength of the switching field is derived. In the space of domain sizes, the dependence of the steady flux of repolarized and redeformed nuclei on the applied field is determined and the time required for this steady flux to set in (latent time) and the time during which this flux is steady are estimated.     

基底性质对二维层状电子气感应电场的影响

采用线性化量子流体动力学模型,研究了载能粒子与二维层状电子气相互作用时的集体静电激发现象。在适当的边界条件下推导出感应电势,入射粒子所受的阻止力和侧向力的一般表达式,讨论了存在绝缘基底情况下基底介电常数对感应电势、阻止力及侧向力的影响。结果表明:当入射粒子速度较小时,基底的极化电场较弱,其介电常数的变化对感应电场几乎无影响,而当速度较高时因极化电场较强而影响很大;入射粒子距离与基底相连的电子气平面越近,基底介电常数对各物理量的影响越大。     

Light-Induced Domain Inversion in Mg-Doped near Stoichiometric Lithium Niobate Crystals

We investigate the influence of visible light on domain inversion in Mg-doped near stoichiometric lithium niobate crystals and find that the switching electric field decreases about 70% above a threshold light intensity. This effect helps us optically control domain switching and produce bulk domain structures on the micrometre scale. Finally, we introduce a model of photo-induced carriers to explain the origin of the reduction of switching electric field.     

聚酰亚胺电导率随温度和电场强度的变化规律

介质深层充电对航天器安全运行构成了重大威胁.以聚酰亚胺为代表的此类聚合物绝缘介质的电导率受温度影响显著,又因为充电过程中局部产生强电场(10~7V/m量级),因此,其电导率模型需要综合考虑温度和强电场的影响,这对介质深层充电的仿真评估意义重大.已有的两类模型,不是低温区间不适用,就是没有充分考虑强电场的影响.基于跳跃电导理论,本文分析对比了现有电导率模型,提出了适用于较宽温度范围且合理考虑强电场增强效应的电导率新模型,并采用某型聚酰亚胺电导率测试数据做出验证.此外,为了提高新模型在强电场下的低温适用范围,尝试对强电场因子中的温度做变换,取得了满意的效果.参数敏感度分析表明新模型在电导率拟合与外推方面具有参数少、适用性强的优势.     

Determination of the nanoscale dielectric properties in ferroelectric lead zirconate titanate (PZT) thin films

We report on nanoscale experiments with <100 nm lateral resolution being able to differentiate the effective dielectric polarisation P_z, deposited charge density σ, surface dielectric constant ε_surface, its voltage dependence ε_surface(U), as well as the built-in electric bias voltage U_int in ferroelectric lead zirconate titanate (PZT) thin films. This is possible by combining piezoresponse force microscopy (PFM) and pull-off force spectroscopy (PFS), both methods based on scanning force microscopy (SFM). The differentiation becomes possible since both P_z and σ contribute additively in PFS, while they are subtractive in PFM, hence allowing the two contributions to be separated. ε_surface can be quantified by means of the experimental PFS data and the calculated effective penetration depth of PFM developed in a finite element modelling. Finally, U_int and ε_surface(U) are derived by an absolute matching of the P_z values measured by PFM and PFS.Our nanoscale results obtained on PZT thin films reveal values for the above specified quantities that have the same order of magnitude as those obtained from macroscopic measurements reflecting the integral response using large electrode areas. However, we stress that the data reported here reveal physical properties deduced on the nanometer scale. Furthermore, they are recorded during one single experimental investigation, using one single set-up only.     

Uniaxial pressure influence on dielectric properties of Pb(Zr0.99Ti0.01)O3 single crystals

The effect of uniaxial pressure (0–1000 bars) applied parallel to AC electric field on dielectric properties of Pb(Zr_0.99Ti_0.01)O₃ single crystals has been investigated. It was found that uniaxial pressure significantly influences these properties. With increasing pressure: (i) peak ?(T) decreases, becomes diffuse and shifts to higher temperature, (ii) the thermal hysteresis is reduced, (iii) the hump in ?(T) profile connected with antiferroelectric–intermediate phase transition vanishes, and (iv) the local anomaly in ?(T) profile connected with polar microregions existence above T_m is protruded and slightly shifts towards higher temperature. It was concluded, that applied uniaxial pressure or increasing Ti-ions content in lead zirconate titanate system induces similar effects. The results were discussed in terms of domain switching under pressure.     

Switching kinetics of ferroelastic ferroelectrics

Switching kinetics of uniaxial ferroelastic ferroelectrics (FFs) in external electric and stress fields is studied using classical theory of nucleation and growth. The stage in which the polarization and deformation reversal involves the main body of the FF and the final stage (Ostwald ripening) of the FF switching are studied with allowance for the change in the repolarization and redeformation during the phase transition. The time dependences of the repolarization and redeformation are found, and equations are derived from which the polarization current and the deformation flux, as well as their time dependence, can be calculated. The calculated main characteristics of the FF switching are compared with the experimental data for switching of Rochelle salt single crystals.     

Higher order ferroic switching induced by scanning force microscopy.

We present the observation of ferroelastoelectric switching in a ferroelectric material. It is achieved in barium titanate thin film by simultaneously applying electric field and compressive stress with the tip of a scanning force microscope. For low compressive stresses, the presented measurements reveal classical ferroelectric domain reversal, i.e., the spontaneous polarization is aligned parallel to the applied electric field. However, for high compressive stresses the direction of polarization after switching is antiparallel to the poling field, demonstrating ferroelastoelectric switching.     

Shear Stress and Dielectric Analysis of H3PO4 Doped Polyaniline Based Electrorheological Fluid

We synthesized phosphoric acid (PA) doped polyaniline (PANI) particles (PANI‐PA) and investigated their electrorheological (ER) and dielectric characteristics when they were dispersed in silicone oil. Flow curves of the PANI‐PA based ER fluid under several applied electric field strengths were analyzed using a shear stress model. We also examined ER characteristics based on the relaxation time obtained from the dielectric spectrum.     

Pyroelectric and photoelectric responses of capacitors based on thin PZT films

The influence of 0.63-μm laser radiation and an external electric field on the photo-and pyroelectric response of thin ferroelectric Pb(Zr_0.54Ti_0.46)O₃ (PZT) films is studied at various temperatures. The films are grown by RF magnetron sputtering of a PZT ceramic target on platinum-coated substrates. It is found that the photosensitivity of PZT films increases after switching of the applied static electric field, as well as after an increase in temperature.     

Comparison between post-irradiation annealing and post-high electric field stress annealing of n-channel power VDMOSFETs

The behavior of the defects created in the gate oxide and at the Si/SiO₂ interface of n-channel power vertical double-diffused metal-oxide-semiconductor field-effect transistors (VDMOSFETs) by irradiation and positive high electric field stress have been investigated. Interface traps exhibit the same behavior after both types of stress, while there are significant differences in post-stress responses of the charge trapped in the oxide, consisting of fixed and switching component.     

横向电场对平面织构胆甾相液晶螺距及反射特性的影响

阐述一种理论模型,讨论共面转换（IPS）模式下横向电场对平面织构胆甾相液晶螺距及扭曲角的影响．利用琼斯矩阵法计算了光正入射情况下未加电场时胆甾相液晶的反射谱．在上述模型基础上,计算了施加电场后胆甾相液晶的反射峰值波长以及反射带宽随场强的变化关系．探讨了忽略锚定与强锚定两种边界条件下横向电场对平面织构胆甾相液晶螺距及反射特性的影响．所得结论在理论上证实：共面转换模式下电场可以调谐胆甾相液晶的反射光颜色,从而为基于电控螺距原理的胆甾相液晶反射式彩色显示方案提供了理论上的依据． 关键词： 胆甾相液晶 电控螺距 共面转换 琼斯矩阵法     

In situ neutron diffraction studies of a commercial, soft lead zirconate titanate ceramic: response to electric fields and mechanical stress

Structural changes in commercial lead zirconate titanate (PZT) ceramics (EC-65) under the application of electric fields and mechanical stress were measured using neutron diffraction instruments at the Australian Nuclear Science and Technology Organisation (ANSTO) and the Oak Ridge National Laboratory (ORNL). The structural changes during electric-field application were measured on the WOMBAT beamline at ANSTO and include non-180° domain switching, lattice strains and field-induced phase transformations. Using time-resolved data acquisition capabilities, lattice strains were measured under cyclic electric fields at times as short as 30 μs. Structural changes including the (002) and (200) lattice strains and non-180° domain switching were measured during uniaxial mechanical compression on the NRSF2 instrument at ORNL. Contraction of the crystallographic polarization axis, (002), and reorientation of non-180° domains occur at lowest stresses, followed by (200) elastic strains at higher stresses.     

正对电极结构碳化硅光导开关的电路模型

利用SilvacoTCAD软件,在532 nm激光辐照下,对正对电极结构6H-SiC光导开关（SiC-PCSS）瞬态电流电场的分布及不同光功率下的伏安特性进行了仿真。结果表明:载流子速率在强场下达到饱和,并且电流电场在主要电流区域沿垂直于激光辐照方向均匀分布。提出SiC-PCSS电路模型的建模依据,可以近似条件化简得到PCSS电阻一般表达式的解,建立SiC-PCSS载流子迁移率随电场变化的PSpice模型,分析讨论了外电路参数对SiC-PCSS导通过程的影响。该模型模拟结果与已有实验结果吻合良好。     

Numerical and analytical investigations for the SOI LDMOS with alternated high-k dielectric and step doped silicon pillars

This paper presents a new silicon-on-insulator(SOI) lateral-double-diffused metal-oxide-semiconductor transistor(LDMOST) device with alternated high-k dielectric and step doped silicon pillars(HKSD device). Due to the modulation of step doping technology and high-k dielectric on the electric field and doped profile of each zone, the HKSD device shows a greater performance. The analytical models of the potential, electric field, optimal breakdown voltage, and optimal doped profile are derived. The analytical results and the simulated results are basically consistent, which confirms the proposed model suitable for the HKSD device. The potential and electric field modulation mechanism are investigated based on the simulation and analytical models. Furthermore, the influence of the parameters on the breakdown voltage(BV) and specific on-resistance(R_on,sp) are obtained. The results indicate that the HKSD device has a higher BV and lower R_on,sp compared to the SD device and HK device.     

Temperature-electric field hysteresis loop of multicaloric effects in PbZr0.8Ti0.2O3 thin films

The Multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin films is investigated with the application of sine wave electric field, dc electric field and stress using a phase field method combined with the thermodynamic analysis. The simulation results show that the adiabatic temperature change-electric field curve presents a shape of butterfly in the presence of the sine wave electric field. In order to detect the effect of the sine wave electric field, the multicaloric effect and the domain structures under the direct electric field and the sine wave electric field are compared. It is found that the domain switching behaviors are quite different under the different applied electric fields. And the negative multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin film is attribute to the domain switching under the external field.