Ultra-high voltage 4H-SiC gate turn-off thyristor for low switching time

An ultra-high voltage 4H-silicon carbide(Si C) gate turn-off(GTO) thyristor for low switching time is proposed and analyzed by numerical simulation. It features a double epitaxial p-base in which an extra electrical field is induced to enhance the transportation of the electrons in the thin p-base and reduce recombination. As a result, the turn-on characteristics are improved. What is more, to obtain a low turn-off loss, an alternating p^+/n^+region formed in the backside acts as the anode in the GTO thyristor. Consequently, another path formed by the reverse-biased n^+–p junction accelerates the fast removal of excess electrons during turn-off. This work demonstrates that the turn-on time and turn-off time of the new structure are reduced to 37 ns and 783.1 ns, respectively, under a bus voltage of 8000 V and load current of 100 A/cm^2.

在双波长下识别Fe3+的一种新型可视化荧光探针的合成及性能

合成了一种新型四苯乙烯-罗丹明化合物L,通过紫外-可见吸收光谱、分子荧光光谱、裸眼和循环伏安分析法等分别研究了化合物L的聚集诱导发光性能、对金属阳离子的识别性能和电化学性能。实验结果显示:化合物L在乙醇-水的混合溶剂中表现出典型的聚集诱导发光性能;L在EtOH/H2O(V∶V,1∶1,Tris-HCl,pH=7.0)溶液中随Fe^3+的加入,化合物L的EtOH/H2O(V∶V,1∶1,Tris-HCl,pH=7.0)溶液显示出明显的颜色变化,由无色变成红色,除Al^3+、Cr^3+略微变红外,其他金属离子无明显变化,这表明化合物L可作为裸眼识别Fe3+的探针;当选用激发波长350nm时,在508nm处的荧光发射强度发生猝灭,猝灭比为87.5%,检出限为4.56×10^-6mol/L;激发波长为530nm时,在582nm处荧光发射强度呈增大趋势,较加入前增大了49.6倍,检出限可达7.4×10^-7mol/L。由此可见,L在用不同激发波长激发时,在两个不同荧光发射波长下分别实现了对Fe^3+的“turn-off”和“turn-on”识别,因此L可作为一种具有高灵敏性和专一选择性的可视化Fe^3+荧光探针。并经Jobs曲线、紫外和荧光滴定、核磁滴定、扫描电镜初步确定了探针L和Fe^3+的络合机理,探针L和Fe^3+的络合比为2∶1,整个测试在中性条件下进行,使得该类探针在生物体系或环境中有潜在的应用价值。且它的电离势为5.77eV,电离势与正电极的功函数(5.5eV)较匹配,有望开发成为空穴传输材料。电子亲合势为3.71eV,比常见的电子传输材料PBD(EA=2.82eV)的电子亲和能大,有望开发为电子传输材料,所合成的化合物也可作为一类具有潜在应用价值的光电材料。

Turn-on and turn-off voltages of an avalanche p-n junction

Characteristics of the turn-on and turn-off voltage of avalanche p-n junctions were demonstrated and studied. As opposed to existing reports, the differences between the turn-on and turn-offvoltage cannot be neglected when the size of the p-n junction is in the order of microns. The difference increases inversely with the area of a junction, exerting significant influences on characterizing some parameters of devices composed of small avalanche junctions. Theoretical analyses show that the mechanism for the difference lies in the increase effect of the threshold multiplication factor at the turn-on voltage of a junction when the area of a junction decreases. Moreover, the ＂breakdown voltage＂ in the formula of the avalanche asymptotic current is, in essence, the avalanche turn-off voltage, and consequently, the traditional expression of the avalanche asymptotic current and the gain of a Geiger mode avalanche photodiode were modified.

A SiC asymmetric cell trench MOSFET with a split gate and integrated p^(+)-poly Si/SiC heterojunction freewheeling diode

A new SiC asymmetric cell trench metal–oxide–semiconductor field effect transistor(MOSFET)with a split gate(SG)and integrated p^(+)-poly Si/SiC heterojunction freewheeling diode(SGHJD-TMOS)is investigated in this article.The SG structure of the SGHJD-TMOS structure can effectively reduce the gate-drain capacitance and reduce the high gateoxide electric field.The integrated p^(+)-poly Si/SiC heterojunction freewheeling diode substantially improves body diode characteristics and reduces switching losses without degrading the static characteristics of the device.Numerical analysis results show that,compared with the conventional asymmetric cell trench MOSFET(CA-TMOS),the high-frequency figure of merit(HF-FOM,R_(on,sp)×Q_(gd,sp))is reduced by 92.5%,and the gate-oxide electric field is reduced by 75%.In addition,the forward conduction voltage drop(V_(F))and gate-drain charge(Q_(gd))are reduced from 2.90 V and 63.5μC/cm^(2) in the CA-TMOS to 1.80 V and 26.1μC/cm^(2) in the SGHJD-TMOS,respectively.Compared with the CA-TMOS,the turn-on loss(E_(on)) and turn-off loss(E_(off)) of the SGHJD-TMOS are reduced by 21.1%and 12.2%,respectively.

LLC Resonant Converter Topologies and Industrial Applications-A Review

Owing to the advantages of high efficiency,high energy density,electrical isolation,low electromagnetic interference(EMI)and harmonic pollution,magnetic integration,wide output ranges,low voltage stress,and high operation frequency,the LLC resonant converters are widely used in various sectors of the electronics-based industries.The history and development of the LLC resonant converters are presented,their advantages are analyzed,three of the most popular LLC resonant converter topologies with detailed assessments of their strengths and drawbacks are elaborated.Furthermore,an important piece of research on the industrial applications of the LLC resonant converters is conducted,mainly including electric vehicle(EV)charging,photovoltaic systems,and light emitting diode(LED)lighting drivers and liquid crystal display(LCD)TV power supplies.Finally,the future evolution of the LLC resonant converter technology is discussed.

SERS-based mercury ion detections:principles,strategies and recent advances

Mercury ion(Hg^(2+)),known as one of the highly toxic and soluble heavy metal ions,is causing serious environmental pollution and irreversible damage to the health.It is urgent to develop some rapid and ultrasensitive methods for detecting trace mercury ions in the environment especially drink water.Surface-enhanced Raman scattering(SERS)is considered as a novel and powerful optical analysis technique since it has the significant advantages of ultra-sensitivity and high specificity.In recent years,the SERS technique and its application in the detection of Hg^(2+)have become more prevalent and compelling.This review provides an overall survey of the development of SERS-based Hg^(2+)detections and presents a summary relating to the basic principles,detection strategies,recent advances and current challenges of SERS for Hg^(2+)detections.