基于GaN FETs的高频半桥谐振变换器分析与设计

随着Si材料半导体器件性能逐步达到瓶颈,宽禁带半导体器件(GaN、SiC)在诸多方面展现出了很好的性能,如低导通阻抗,小输入、输出电容等,这些特性使得GaN和SiC器件能够应用在更高的开关频率条件,从而提高系统的功率密度。针对基于GaN FETs构成的高频半桥谐振变换器进行设计,分析了高频条件下寄生电感参数对系统驱动电压及漏源极电压的影响,同时分析了高频条件下系统电压电流测量所需注意的事项及影响因素,为高频条件下GaN FETs的应用提供一定的帮助。

Advances in MoS_2-Based Field Effect Transistors(FETs)

This paper reviews the original achievements and advances regarding the field effect transistor(FET) fabricated from one of the most studied transition metal dichalcogenides: two-dimensional Mo S2. Not like graphene, which is highlighted by a gapless Dirac cone band structure, Monolayer Mo S2 is featured with a 1.9 e V gapped direct energy band thus facilitates convenient electronic and/or optoelectronic modulation of its physical properties in FET structure. Indeed,many Mo S2 devices based on FET architecture such as phototransistors, memory devices, and sensors have been studied and extraordinary properties such as excellent mobility, ON/OFF ratio, and sensitivity of these devices have been exhibited. However, further developments in FET device applications depend a lot on if novel physics would be involved in them. In this review, an overview on advances and developments in the Mo S2-based FETs are presented. Engineering of Mo S2-based FETs will be discussed in details for understanding contact physics, formation of gate dielectric, and doping strategies. Also reported are demonstrations of device behaviors such as low-frequency noise and photoresponse in Mo S2-based FETs, which is crucial for developing electronic and optoelectronic devices.

A comprehensive review of recent progress on enhancement-modeβ-Ga_(2)O_(3)FETs:Growth,devices and properties

Power electronic devices are of great importance in modern society.After decades of development,Si power devices have approached their material limits with only incremental improvements and large conversion losses.As the demand for electronic components with high efficiency dramatically increasing,new materials are needed for power device fabrication.Betaphase gallium oxide,an ultra-wide bandgap semiconductor,has been considered as a promising candidate,and variousβ-Ga_(2)O_(3)power devices with high breakdown voltages have been demonstrated.However,the realization of enhancement-mode(E-mode)β-Ga_(2)O_(3)field-effect transistors(FETs)is still challenging,which is a critical problem for a myriad of power electronic applications.Recently,researchers have made some progress on E-modeβ-Ga_(2)O_(3)FETs via various methods,and several novel structures have been fabricated.This article gives a review of the material growth,devices and properties of these E-modeβ-Ga_(2)O_(3)FETs.The key challenges and future directions in E-modeβ-Ga_(2)O_(3)FETs are also discussed.

Experimental investigation on the instability for NiO/β-Ga_(2)O_(3) heterojunction-gate FETs under negative bias stress

A NiO/β-Ga_(2)O_(3) heterojunction-gate field effect transistor(HJ-FET)is fabricated and it_(s)instability mechanisms are exper-imentally investigated under different gate stress voltage(V_(G,s))and stress times(t_(s)).Two different degradation mechanisms of the devices under negative bias stress(NBS)are identified.At low V_(G,s)for a short t_(s),NiO bulk traps trapping/de-trapping elec-trons are responsible for decrease/recovery of the leakage current,respectively.At higher V_(G,s)or long t_(s),the device transfer char-acteristic curves and threshold voltage(V_(TH))are almost permanently negatively shifted.This is because the interface dipoles are almost permanently ionized and neutralize the ionized charges in the space charge region(SCR)across the heterojunction inter-face,resulting in a narrowing SCR.This provides an important theoretical guide to study the reliability of NiO/β-Ga_(2)O_(3) hetero-junction devices in power electronic applications.

Design Consideration in the Development of Multi-Fin FETs for RF Applications

In this paper, we propose multi-fin FET design techniques targeted for RF applications. Overlap and underlap design configuration in a base FinFET are compared first and then multi-fin device (consisting of transistor unit up to 50) is studied to develop design limitations and to evaluate their effects on the device performance. We have also investigated the impact of the number of fins (up to 50) in multi-fin structure and resulting RF parameters. Our results show that as the number of fin increases, underlap design compromises RF performance and short channel effects. The results provide technical understanding that is necessary to realize new opportunities for RF and analog mixed-signal design with nanoscale FinFETs.

Compact modeling of quantum confinements in nanoscale gate-all-around MOSFETs

In this work,a surface-potential based compact model focusing on the quantum confinement effects of ultimately scaled gate-all-around(GAA)MOSFET is presented.Energy quantization with sub-band formation along the radius direction of cylindrical GAAs or thickness direction of nanosheet GAAs leads to significant quantization effects.An analytical model of surface potentials is developed by solving the Poisson equation with incorporating sub-band effects.In combination with the existing transport model framework,charge-voltage and current-voltage formulations are developed based on the surface potential.The model formulations are then extensively validated using TCAD numerical simulations as well as Si data of nanosheet GAA MOSFETs.Simulations of typical circuits verify the model robustness and convergence for its applications in GAA technology.

Ionic effects on the transport characteristics of nanowire-based FETs in a liquid environment

For the development of ultra-sensitive electrical bio/chemical sensors based on nanowire field effect transistors （FETs）, the influence of the ions in the solution on the electron transport has to be understood. For this purpose we establish a simulation platform for nanowire FETs in the liquid environment by implementing the modified Poisson-Boltzmann model into Landauer transport theory. We investigate the changes of the electric potential and the transport characteristics due to the ions. The reduction of sensitivity of the sensors due to the screening effect from the electrolyte could be successfully reproduced. We also fabricated silicon nanowire Schottky-barrier FETs and our model could capture the observed reduction of the current with increasing ionic concentration. This shows that our simulation platform can be used to interpret ongoing experiments, to design nanowire FETs, and it also gives insight into controversial issues such as whether ions in the buffer solution affect the transport characteristics or not.

Modeling of cylindrical surrounding gate MOSFETs including the fringing field effects

A physically based analytical model for surface potential and threshold voltage including the fringing gate capacitances in cylindrical surround gate（CSG） MOSFETs has been developed.Based on this a subthreshold drain current model has also been derived.This model first computes the charge induced in the drain/source region due to the fringing capacitances and considers an effective charge distribution in the cylindrically extended source/drain region for the development of a simple and compact model.The fringing gate capacitances taken into account are outer fringe capacitance,inner fringe capacitance,overlap capacitance,and sidewall capacitance.The model has been verified with the data extracted from 3D TCAD simulations of CSG MOSFETs and was found to be working satisfactorily.

Investigation and statistical modeling of InAs-based double gate tunnel FETs for RF performance enhancement

In this paper,RF performance analysis of In As-based double gate（DG）tunnel field effect transistors（TFETs）is investigated in both qualitative and quantitative fashion.This investigation is carried out by varying the geometrical and doping parameters of TFETs to extract various RF parameters,unity gain cut-off frequency（f_t）,maximum oscillation frequency（f_（max））,intrinsic gain and admittance（Y）parameters.An asymmetric gate oxide is introduced in the gate-drain overlap and compared with that of DG TFETs.Higher ON-current（ION）of about 0.2 mA and less leakage current（IOFF）of 29 f A is achieved for DG TFET with gate-drain overlap.Due to increase in transconductance（g_m）,higher ft and intrinsic gain is attained for DG TFET with gate-drain overlap.Higher f_（max） of 985 GHz is obtained for drain doping of 5×10^（17）cm^（-3） because of the reduced gate-drain capacitance（C_（gd））with DG TFET with gate-drain overlap.In terms of Y-parameters,gate oxide thickness variation offers better performance due to the reduced values of Cgd.A second order numerical polynomial model is generated for all the RF responses as a function of geometrical and doping parameters.The simulation results are compared with this numerical model where the predicted values match with the simulated values.

Contact and injection engineering for low SS reconfigurable FETs and high gain complementary inverters

The newly emerged two-dimensional(2D) semiconducting materials, owning to the atomic thick nature and excellent optical and electrical properties, are considered as potential candidates to solve the bottlenecks of traditional semiconductors. However, the realization of high performance 2D semiconductorbased field-effect transistors(FETs) has been a longstanding challenge in 2D electronics, which is mainly ascribing to the presence of significant Schottky barrier(SB) at metal-semiconductor interfaces. Here, an additional contact gate is induced in 2D ambipolar FET to realize near ideal reconfigurable FET(RFET)devices without restrictions of SB. Benefitting from the consistently high doping of contact region, the effective SB height can be maintained at ultra-small value during all operation conditions, resulting in the near ideal subthreshold swing(SS) values(132 mV/decade for MoTe2 RFET and 67 mV/decade for WSe2 RFET) and the relatively high mobility(28.6 cm2/(Vs) for MoTe2 RFET and 89.8 cm2/(V s) for WSe2 RFET). Moreover, the flexible control on the doping polarity of contact region enables the remodeling and switching of the achieved unipolar FETs between p-type mode and n-type mode. Based on such reconfigurable behaviors, high gain complementary MoTe2 inverters are further realized. The findings in this work push forward the development of high-performance 2D semiconductor integrated devices and circuits.

Line-edge roughness induced single event transient variation in SOI Fin FETs

The impact of process induced variation on the response of SOI Fin FET to heavy ion irradiation is studied through 3-D TCAD simulation for the first time. When Fin FET biased at OFF state configuration（Vgs D0, Vds DVdd/ is struck by a heavy ion, the drain collects ionizing charges under the electric field and a current pulse（single event transient, SET） is consequently formed. The results reveal that with the presence of line-edge roughness（LER）, which is one of the major variation sources in nano-scale Fin FETs, the device-to-device variation in terms of SET is observed. In this study, three types of LER are considered： type A has symmetric fin edges, type B has irrelevant fin edges and type C has parallel fin edges. The results show that type A devices have the largest SET variation while type C devices have the smallest variation. Further, the impact of the two main LER parameters,correlation length and root mean square amplitude, on SET variation is discussed as well. The results indicate that variation may be a concern in radiation effects with the down scaling of feature size.

黑磷纳米片在重金属离子传感器中的研究进展

黑磷(BP)纳米片具有特殊的褶皱状结构从而使其具有可调的直接带隙、传输各向异性、光致发光等特性,这些独特的性质使其被广泛应用于构建金属离子传感器并在环境监测等研究领域展现了巨大的应用潜力。本文综合介绍了BP纳米片制备方法及其构建的不同类型传感器在重金属离子检测中的应用。首先,基于“自上而下”法和“自下而上”法分别介绍了不同类型的BP纳米片制备方法,并对不同制备方法的优缺点进行了归纳和总结。然后,详细阐述了BP纳米片构建的场效应晶体管(FET)传感器、电化学传感器和光化学传感器在检测重金属离子中的研究进展,对不同类型传感器的独特优势进行了分析,其中FET传感器具有优异的检出限,电化学传感器具有响应时间短、操作简单等优势,而光化学传感器则表现出更宽的检测范围。进一步,总结并指出目前BP纳米片构建的重金属离子传感器能够检测的重金属离子的种类比较有限,稳定性和选择性也有待进一步提升。最后,针对BP纳米片在构建不同类型重金属离子传感器中面临的挑战,指出BP基传感器应朝着开发低成本、高质量BP纳米片的制备方法以及BP纳米片的结构优化和功能化修饰等方面的研究方向发展。在拓展重金属离子检测应用方面,结合新技术有望使其在实际应用中有新的突破。

氧等离子处理的二硫化钼场效应晶体管表面掺杂和湿度传感研究

二维半导体过渡金属二硫属化物(transition metal dichalcogenide,TMD)具有独特的电学、光学和力学性能,在数字电路、光伏器件和能量存储等多个领域中具有巨大的应用潜力。通过表面掺杂控制TMD的电学性能为实现灵敏传感提供了有效的方法。本文开展了氧等离子体对二硫化钼(MoS_(2))掺杂特性的研究。首先,测试了MoS_(2)场效应晶体管(field-effect transistor,FET)的输运特性,发现氧等离子体处理对FET具有p型掺杂作用。随后,通过拉曼光谱研究了掺杂机制的成因,并证实了沟道表面类MoO_(3)缺陷的形成。最后,研究了经等离子体处理的晶体管的湿度传感特性,由于氧等离子体处理使得沟道对水分子的吸收中心增加,在潮湿环境下晶体管具有十分灵敏的响应特性,源漏电流值变化了约54%。这项工作不仅提供了一种调控TMD电学性能的简单方法,也展示了低维材料化学传感器的发展潜力。

螺旋断层放疗设备中千伏级X射线信号自动检测方法的探究

本文主要探讨了在螺旋管断层放疗设备中使用非物理连接方式同步X射线平板探测器、球管和高压发生器的可能性,提出了利用平板探测器内置传感器自动检测X射线信号的方法。通过简单的测试验证了平板探测器面板FET关断模式与跳跃式扫描读出模式相结合下X射线自动检测的可实现性。这种方法可以利用X射线信号的上升沿和下降沿判断X射线的发生以及计算曝光的时长。

前沿技术新型40OVSiCMOSFET用于高效三电平工业电机驱动

400VSiCMOSFET技术商用化弥补了长期存在的200V中压MOSFET与600V超级结MOSFET之间产品和技术空缺。400VSiCMOSFET技术开关损耗低、导通电阻小,非常适合三电平拓扑结构。本文简要介绍了该器件的设计理念,并研究了其在ANPC拓扑的三相交流通用工业驱动器中的性能,该驱动器工作在高达750VDC的输入电压下。

GaAs FET/pHEMT器件小信号模型电路的确定

提出了一种精确、高效的FET/pHEMT器件模型参数提取的改进方法。首先利用FET器件漏端零偏置的简化模型,测出寄生元件值,再利用正常配置时FET/pHEMT器件网络S参数,使用“剥离”技术将寄生部分全部剔除。最后利用网络导纳参数的表达式,确定了本征电路元件参数。采用了该方法的提取过程物理意义清晰,优化处理容易。对NEC器件的测试结果显示,该改进方法效率高,测试精度小于3%。

GaAs MESFET可靠性及快速评价新方法的研究

提出了一种快速评价GaAsFET可靠性寿命的新方法 .利用GaAsFET失效敏感参数的温度特性和在一定电应力下的退化特性 ,及温度斜坡法在线快速提取器件失效敏感参数的退化量与温度的关系 ,从而进一步求出器件的失效激活能等相关的可靠性物理参数 .

西峰剖面午城黄土古风化强度变化与早更新世季风环境演化

游离铁(FeD)/全铁(FeT)比值被土壤学界用来反映土壤化学风化强度,并已在风尘堆积的古环境研究中得到较好应用。然而,迄今对第四纪黄土古风化强度的研究多集中于中更新世以来的序列,只有少数剖面的分析包含午城黄土。文章基于西峰剖面661个样品的FeD和FeT分析,建立了该剖面午城黄土的古风化强度序列,并与剖面原有1·2Ma以来的序列进行对比。结果表明,早更新世古土壤的风化强度与后期相比总体较低,而黄土层的风化强度总体偏高,反映了较小的冰期-间冰期反差;古风化强度的波动总体上与深海氧同位素有较好的一致性,体现了全球冰量变化对我国北方季风环境的控制。2·6～1·6Ma期间,古土壤的平均风化强度在整个第四纪最低,指示了较弱的夏季风环境效应。从约1·6Ma开始到1·2Ma,古土壤和黄土层的风化强度均增加,并开始有较显著的约100ka周期。这些特征在深海氧同位素记录中没有表现,而与热带地区一些环境特征相吻合,从而指示了低纬过程对我国北方早更新世季风环境的显著影响。

卵裂球的完整性和生长与否对冻融胚胎移植妊娠结局的影响

目的:探讨冻融胚胎移植(FET)周期卵裂球的完整性和生长与否对妊娠结局的影响。方法:375例FET周期,其中解冻当天移植周期242例,提前解冻周期133例,根据复苏后移植卵裂球的完整性分为3组:均完整(A组,n=235)、均有破损(B组,n=21)、完整与破损混合(C组,n=119);提前解冻者根据卵裂球的生长与否分为均有生长74例(Ⅰ组)、部分有生长45例(Ⅱ组)和均无生长14例(Ⅲ组)3组。结果:375例FET周期共解冻胚胎1284个,复苏率为61.2%,每移植周期临床妊娠率30.1%,种植率18.3%;A组的继续妊娠率和种植率分别为27.7%和20.5%,明显高于B组的9.5%和8.3%(P<0.05),C组为22.7%和15.1%,低于A组,但差异无统计学意义(P>0.05)。随着移植胚胎中含完整存活胚胎数的增加(0个、1个、2个、3个),继续妊娠率呈增加趋势(9.5%、17.6%、22.3%和38.2%),移植胚胎中含3个完整胚胎的继续妊娠率明显高于含0、1个完整胚胎者(P<0.05);提前解冻的Ⅰ组继续妊娠率(37.8%)和种植率(26.1%)最高,Ⅲ组最低(7.1%和8.3%),Ⅱ组为24.4%和14.1%,组间差异均有统计学意义(P<0.05)。结论:卵裂球的完整性是影响冻融胚胎种植率的重要因素,移植前提早解冻观察复苏后胚胎有无进一步生长,有助于评价冻融胚胎的发育潜能。

特征时期黄土高原风化成壤强度的空间特征与气候梯度

文章基于15个剖面,采用土壤学使用的风化成壤强度指数(游离铁FeD/全铁FeT),对黄土高原S0,L1,S1,S4,S5-1层位的风化成壤强度的空间变化进行研究,并与磁化率反映的特征进行对比。结果表明,冰期(黄土层)和间冰期(古土壤层)的风化成壤强度均呈现由东南向西北减弱的特征,与现代季风气候的基本格局一致。然而,冰期时(以L1为代表)整个黄土高原南北气候梯度很弱,间冰期南北气候梯度远大于冰期,反映了冰期时夏季风环流对黄土高原影响很小,南北气候梯度更多体现了气候带的纬度效应。结果同时表明,间冰期时黄土高原地区风化成壤强度和南北气候梯度不具严格的对应关系。S1和S5-1指示了当时较强的夏季风环流,冬季风的影响相对亦较强,而S0和S4发育时期高原南北风化成壤强度的梯度明显减小,反映了当时黄土高原在夏季风影响的背景下,冬季风的影响亦减弱,导致南北梯度的减小。因此,黄土高原风化成壤强度的空间变化指示了冬、夏季风环流不同的消长关系,对研究高低纬度气候驱动力的相互作用具有重要意义。