Single-mode low threshold current multi-hole vertical-cavity surface-emitting lasers

A multi-hole vertical-cavity surface-emitting laser （VCSEL） operating in stable single mode with a low threshold current was produced by introducing multi-leaf scallop holes on the top distributed Bragg-refleetor of an oxidation- confined 850 nm VCSEL. The single-mode output power of 2.6 mW, threshold current of 0.6 mA, full width of half maximum lasing spectrum of less than 0.1 nm, side mode suppression ratio of 28.4 dB, and far-field divergence angle of about 10% are obtained. The effects of different hole depths on the optical characteristics are simulated and analysed, including far-field divergence, spectrum and lateral cavity mode. The single-mode performance of this multi-hole device is attributed to the large radiation loss from the inter hole spacing and the scattering loss at the bottom of the holes, particularly for higher order modes.

Frequency-locking and threshold current-lowering effects of a quantum cascade laser and an application in gas detection field

In this paper,the frequency-locking and threshold current-lowering effects of a quantum cascade laser are studied and achieved.Combined with cavity-enhanced absorption spectroscopy,the noninvasive detection of H_2 with a prepared concentration of 500 ppm in multiple dissolved gases is performed and evaluated.The high frequency selectivity of 0.0051 cm^-1 at an acquisition time of 1 s allows the sensitive detection of the（1-0） S（l） band of H_2 with a high accuracy of（96.53±0.29）%and shows that the detection limit to an absorption line of 4712.9046 cm^-1 is approximately（17.26±0.63） ppm at an atmospheric pressure and a temperature of 20 ℃.

Development of Surface Grating Distributed Feedback Quantum Cascade Laser for High Output Power and Low Threshold Current Density

We report on the room-temperature cascade laser （QCL） at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback （DFB） quantum optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-μm-wide and 4- mm-long laser, high wall-plug efficiency of 6% is obtained at 20℃ from a single facet producing over I W of ew output power. The threshold current density of DFB QCL is as low as 1.13kA/cm^2 at 10℃ and 1.34kA/cm2 at 30℃ in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in tile working temperature range of 20-50℃.

Two-dimensional models of threshold voltage and subthreshold current for symmetrical double-material double-gate strained Si MOSFETs

The two-dimensional models for symmetrical double-material double-gate （DM-DG） strained Si （s-Si） metal-oxide semiconductor field effect transistors （MOSFETs） are presented. The surface potential and the surface electric field ex- pressions have been obtained by solving Poisson＇s equation. The models of threshold voltage and subthreshold current are obtained based on the surface potential expression. The surface potential and the surface electric field are compared with those of single-material double-gate （SM-DG） MOSFETs. The effects of different device parameters on the threshold voltage and the subthreshold current are demonstrated. The analytical models give deep insight into the device parameters design. The analytical results obtained from the proposed models show good matching with the simulation results using DESSIS.

Effect of inhomogeneous broadening on threshold current of GaN-based green laser diodes

The inhomogeneous broadening parameter and the internal loss of green LDs are determined by experiments and theoretical fitting. It is found that the inhomogeneous broadening plays an important role on the threshold current density of green LDs. The green LD with large inhomogeneous broadening even cannot lase. Therefore, reducing inhomogeneous broadening is a key issue to improve the performance of green LDs.

Threshold Current Characteristics of Intracavity-contacted Vertical-cavity Surface-emitting Laser

Threshold current characteristics of intracavity-contacted oxide-confined vertical-cavity surface-emitting laser had been investigated in detail. Threshold current characteristics not only were depended on the size of oxide-aperture, but also were also strongly affected by the mismatch of its lasing mode and gain peak. For the same degree detuning of the gain peak and lasing mode at room temperature, the threshold current was approximately proportional to the square of the oxide-aperture diameter of above 5μm. For the same oxide-aperture device, the larger the detuning degree of the lasing mode shifted to the shorter wavelength of the gain peak at room temperature was, the lower the minimum threshold current was. The wavelengths of the lasing mode and gain peak were ±N×10nm detuning at 300K, The temperature of the minimum threshold current was changed to be about ±N×40K(N real number). The calculated results were consistent with the experimental ones.

Influence of the thickness change of the wave-guide layers on the threshold current of GaAs-based laser diode

The paper mainly deals with theoretical investigations of the effect of the thickness change of the wave- guide layers on the threshold current. It is analyzed according to the result of a numerical simulation that asks how does the shift of the active region position affect the threshold current for a single quantum well （SQW） and double quantum well （DQW） laser diode （LD） with a relatively narrow waveguide. It is found that the variation trend of threshold current and optimum position of QW are different in SQW and DQW LD with 0.2 μm-thick waveguide, which may be due to the higher variation rate of optical loss in DQW LD with the shift of the active region. It is also found that in terms of either SQW or DQW LD, the variation tendency of the threshold current with a different loss coefficient of the p-cladding layer makes little difference for the relatively narrow waveguide LD. Moreover, the variation trend of the threshold current and the optimum position of QW is almost the same in SQW and DQW LD with 0.8 μm-thick waveguide, because the optical loss is small enough and the threshold current is dominated by the optical confinement factor （OCF） in QW.

Effect of Droop Phenomenon in InGaN/GaN Blue Laser Diodes on Threshold Current

Electroluminescence （EL） and temperature-dependent photolumineseenee measurements are performed to study the internal quantum efficiency droop phenomenon of blue laser diodes （LDs） before lasing. Based on the ABC mode, the EL result demonstrates that non-radiative recombination rates of LDs with threshold current densities of 4 and 6kA/cm2 are similar, while LD with threshold current density of 4kA/cm2 exhibits a smaller auger- like recombination rate compared with the one of 6kA/cm2. The internal quantum efficiency droop is more serious for LD with higher threshold current density. temperature-dependent photoluminescence is consistent The internal quantum efficiency value estimated from with EL measurements.

Analytical model for the dispersion of sub-threshold current in organic thin-film transistors

This paper proposes an equivalent circuit model to analyze the reason for the dispersion of sub-threshold current （also known as zero-current point dispersion） in organic thin-film transistors. Based on the level 61 amorphous silicon thin-film transistor model in star-HSPICE, the results from our equivalent circuit model simulation reveal that zero-current point dispersion can be attributed to two factors： large contact resistance and small gate resistance. Furthermore, it is found that decreasing the contact resistance and increasing the gate resistance can efficiently reduce the dispersion. If the contact resistance can be controlled to 0 g2, all the zero-current points can gather together at the base point. A large gate resistance is good for constraining the dispersion of the zero-current points and gate leakage. The variances of the zero-current points are 0.0057 and nearly 0 when the gate resistances are 17 MΩ and 276 MΩ, respectively.

Model of Current Threshold for Perception in Testing Electrical Safety Performance

A generalized mathematical model of human body current threshold for perception was established and the current flowing through human body could be arbitrary cyclical waveforms.The relationship between human body current threshold for perception and current frequency, true root mean square(RMS) value and influence factor was described.A test system was established based on electroencephalogram(EEG) to study the relationship between human body current threshold for perception and current waveform, frequency and duty cycle so that the data could be obtained objectively and reliably.At least 850 groups of current threshold for perception and 16-lead EEGs were acquired.The theoretical analysis are verified by experimental data, and an amendment proposal on leakage current evaluation limits specified in International Electro-Technical Commission(IEC) standards is suggested.

Quantitative assessment of sensory functions after 3 surgical approaches for trigeminal neuralgia by current perception threshold measurement

Objective: To quantitatively identify and grade trigeminal sensory functions after 3 major surgical procedures of trigeminal neuralgia using a newly developed quantitative sensory testing technique, current perception threshold measurement (CPTM). Methods: In the current study, there were 48 trigeminal neuralgia patients without history of prior surgical treatment. These patients received one of the following 3 surgical procedures, microvascular decompression (MVD), peripheral nerve block with alcohol (PNB), or percutaneous radiofrequency thermocoagulation (PRFT). The quantitative sensory testing measurement, CPTM, and conventional qualitative sensory testing measurements were performed preoperatively and postoperatively to evaluate and grade the trigeminal sensory functions. All 3 major cutaneous sensory fiber types, large myelinated fibers (A beta), small myelinated fibers (A delta) and unmyelinated fibers(C) were allowed to quantitatively evaluate and grade by CPTM. The results of the measurements were statistically analyzed using a one-way analysis of variance (single factor). Each subject was his/her own control for comparison of the preoperative to postoperative state on the asymptomatic and symptomatic sides. Subjects were tested 48 h preoperatively and 4 weeks postoperatively. Results: PNB with alcohol and PRFT caused significant sensory dysfunction postoperatively in every fiber type, indicating damage to all fibers. On the contrary, the sensory function in all 3 fiber types was unchanged after MVD management. Conclusion: Among the 3 major surgical procedures tested, only MVD preserves sensory function in trigeminal system. CPTM is of quantitative nature on the evaluation of sensory functions of nerve

基于0.15μm SOI工艺的耐高温短沟器件设计与实现

绝缘体上硅(Silicon on insulator,SOI)技术在200~400℃高温器件和集成电路方面有着广泛的应用前景,但对于沟道长度≤0.18μm的短沟道器件在200℃以上的高温下阈值电压漂移量达40%以上,漏电流达μA级,无法满足电路设计要求。本文研究了基于0.15μm SOI工艺的1.5 V MOS器件电特性在高温下的退化机理和抑制方法,通过增加栅氧厚度、降低阱浓度、调整轻掺杂漏离子注入工艺等优化方法,实现了一种性能良好的短沟道高温SOI CMOS器件,在25~250℃温度范围内,该器件阈值电压漂移量<30%,饱和电流漂移量<15%,漏电流<1 nA/μm。此外采用仿真的方法分析了器件在高温下的漏区电势和电场的变化规律,将栅诱导漏极泄漏电流效应与器件高温漏电流关联起来,从而定性地解释了SOI短沟道器件高温漏电流退化的机理。

AlN/β-Ga_(2)O_(3)HEMT直流特性仿真

本文利用器件仿真软件对AlN/β-Ga_(2)O_(3)高电子迁移率晶体管(HEMT)器件的直流特性进行研究。由于AlN具有很强的极化效应,在AlN/β-Ga_(2)O_(3)异质结界面处产生高浓度二维电子气(2DEG),使AlN/β-Ga_(2)O_(3)异质结基HEMT具有更加优越的器件性能。理论计算得到AlN/β-Ga_(2)O_(3)异质结界面处产生的面电荷密度为2.75×10^(13) cm^(-2)。通过分析器件的能带结构、沟道电子浓度分布,研究AlN势垒层厚度、栅极长度、栅漏间距,以及金属功函数等参数对器件转移特性和输出特性的影响。结果表明:随着AlN势垒层厚度的增大,阈值电压减小,最大跨导减小,沟道电子浓度增大使饱和漏电流增大;随着栅极长度缩短,跨导增大,当栅极长度缩短至0.1μm时,器件出现了短沟道效应,并且随着栅极长度的缩短,栅下沟道区电子浓度增大,而电子速度基本不变,导致饱和漏电流增大,导通电阻减小,并且器件的饱和特性变差;随着栅漏间距的增大,跨导增大,沟道区电子浓度不变,而电子速度略有增加,导致饱和漏电流增大;肖特基栅金属功函数的增加会增大阈值电压,不会改变器件跨导,沟道电子浓度减小导致饱和漏电流减小。上述结论为后面的器件的优化改进提供了理论依据。

石灰石粉掺量对混凝土中钢筋脱钝临界氯离子含量的影响

本工作研究了不同石灰石粉掺量(10%、20%、30%,质量分数,下同)对钢筋脱钝临界氯离子含量的影响,对混凝土试件进行干湿循环处理以加速氯离子渗透,同时采用半电池电位和电化学阻抗谱分别测定了钢筋的自腐蚀电位和腐蚀电流密度。结果表明,临界氯离子含量随着石灰石粉掺量的增加而减小,这主要是因为石灰石粉的掺入导致水泥含量降低,从而使混凝土孔隙液pH值降低。XRD分析表明石灰石粉的掺入抑制了单硫型水化硫铝酸钙(AFm)相的生成,从而降低了水化产物的氯离子结合能力。腐蚀电流密度的变化趋势服从三参数Weibull分布,其概率密度可以表征钝化膜破裂的速率,随着石灰石粉掺量的增加,钝化膜破裂速率增加。

Very low threshold operation of quantum cascade lasers

A strain-compensated InP-based quantum cascade laser（QCL） structure emitting at 4.6 μm is demonstrated,based on a two-phonon resonant design and grown by solid-source molecular beam epitaxy（MBE）.By optimizing the growth parameters,a very high quality heterostructure with the lowest threshold current densities ever reported for QCLs was fabricated.Threshold current densities as low as 0.47 kA/cm^2 in pulsed operation and 0.56 kA/cm^2 in continuous-wave（cw） operation at 293 K were achieved for this state-of-the-art QCL.A minimum power consumption of 3.65 W was measured for the QCL,uncooled,with a high-reflectivity（HR） coating on its rear facet.

兼顾电缆线路效率和可靠性的载流量动态阈值研究

针对当前配电网电缆为了运行可靠性,多采用较低载流量的固定阈值方法,电缆利用率低的问题,本文提出了一种载流量动态阈值的方法。该方法从理论上研究电缆线路载流量与导体温度的关系,通过实际运行的电缆工程的实测数据量化电缆载流量与导体温度的函数关系,并测定电缆线路的基准阈值,以此实现线路的阈值动态化计算。算法应用于智能电缆测控系统的动态阈值监测功能模块,线路所得实际运行数据验证了本方法的有效性。

计及互感器融合偏差的变电站站用电剩余电流监测系统研究

稳定的站用电源系统是变电站生产设备可靠工作之本,一旦站用电系统出现问题将直接或间接地影响变电站安全。目前变电站站用电绝缘监测主要通过对变电站电源系统剩余电流实时监测实现。然而剩余电流监测方法主要面向多电流互感器融合测量场合,现有的测量系统未考虑融合过程中互感器偏差影响,致使误报警状况频出。有鉴于此,本文提出了一套计及互感器融合偏差的变电站站用电剩余电流监测系统。该系统同步采集并实时合成多通道电流互感器剩余电流数据,并利用自回归差分移动平均模型(ARIMA)对剩余电流进行时序建模与异常检测,再使用小波阈值去噪算法对修复后的剩余电流序列降噪,以实现剩余电流的高效、精准监测。为验证所提出系统的有效性,在变电站进行现场试验。结果表明,该系统能够成功识别并修复剩余电流异常值数据且去噪效果显著。修复数据最大绝对误差仅5.9 mA,与0.5S级互感器测量数据相比,去噪后数据平均绝对百分比误差与均方根误差分别降低了0.024与1.222。

Comparative Methodical Assessment of Established MOSFET Threshold Voltage Extraction Methods at 10-nm Technology Node

Threshold voltage (VTH) is the most evocative aspect of MOSFET operation. It is the crucial device constraint to model on-off transition characteristics. Precise VTH value of the device is extracted and evaluated by several estimation techniques. However, these assessed values of VTH diverge from the exact values due to various short channel effects (SCEs) and non-idealities present in the device. Numerous prevalent VTH extraction methods are discussed. All the results are verified by extensive 2-D TCAD simulation and confirmed through analytical results at 10-nm technology node. Aim of this research paper is to explore and present a comparative study of largely applied threshold extraction methods for bulk driven nano-MOSFETs especially at 10-nm technology node along with various sub 45-nm technology nodes. Application of the threshold extraction methods to implement noise analysis is briefly presented to infer the most appropriate extraction method at nanometer technology nodes.

基于亚阈值电流阵列的低成本物理不可克隆电路设计

物理不可克隆函数(PUF)能够提取出集成电路在加工过程中的工艺误差并将其转化为安全认证的密钥。由于常用于资源及功耗都受限的场合,实用化的PUF电路需要极高的硬件利用效率及较强的抗攻击性能。该文提出一种基于亚阈值电流阵列放电方案的低成本PUF电路设计方案。亚阈值电流阵列的电流具有极高的非线性特点,通过引入栅控开关和交叉耦合的结构,能够显著提升PUF电路的唯一性和稳定性。此外,通过引入亚阈值电流的设计可以极大地提高PUF的安全性,降低传统攻击手段的建模攻击。为了提升芯片的资源利用率,通过详细紧凑的版图设计和优化,该文提出的PUF单元面积仅为377.4 μm^(2),使得其特别适合物联网等低功耗低成本应用场景。仿真结果表明,该文所提亚阈值电路放电阵列PUF具有良好的唯一性和稳定性,无需校准电路的标准温度电压下唯一性为48.85%;在温度范围–20~80°C,电压变动范围为0.9~1.3V情况下,其可靠性达到了99.47%。

一种均衡阈值可调的双模式电池均衡电路

均衡电路对于提高串联电池组内部一致性、容量利用率和寿命具有重要意义。针对现有单模式均衡电路的局限性,提出了一种基于准谐振开关电容和互补三谐振LC变换器的双模式电池均衡电路,可以根据电压分布情况在任意电池至任意电池间传输模式和直接电池至电池间传输模式之间切换,且两种模式均实现了零电流开关,减少了电路损耗。为了获得最优的均衡速度,提出一种具有双阈值的均衡电路控制策略,通过对均衡阈值的调整可以获得最佳的均衡速度。分析了两种均衡模式的运行状态、均衡功率和均衡效率,并搭建了4节电池的实验样机,在不同均衡阈值下进行了均衡实验,实验结果说明均衡阈值的调整使得双模式均衡电路获得了最佳的均衡速度,实验验证了该双模式电池均衡电路的有效性。