A reconfigurable terahertz polarization converter based on metal–graphene hybrid metasurface

A metal-graphene hybrid metasurface polarization converter is designed in this Letter.The unit cell of the hybrid metasurface is composed of a butterfly-shaped structure whose branches are connected by multi-layer graphene sheets.The proposed device can be reconfigured from linear-to-circular polarization to cross-polarization by changing the Fermi energy of graphene.The simulation results show that for three-layer graphene,the device acts as a linear-to-circular polarization converter when EF=0 eV and switches to a cross-polarization converter when EF=0.5 eV.Compared with single-layer graphene,the device with three-layer graphene can maintain the cross-polarization conversion performance under low Fermi energy.Furthermore,two equivalent circuits in the x and y directions are developed to understand the working mechanism of the device.     

Impact of AlxGa1-xN barrier thickness and Al composition on electrical properties of ferroelectric HfZrO/Al2O3/AlGaN/GaN MFSHEMTs

Ferroelectric (FE) HfZrO/Al$_{2}$O$_{3}$ gate stack AlGaN/GaN metal-FE-semiconductor heterostructure high-electron mobility transistors (MFSHEMTs) with varying Al$_{x}$Ga$_{1-x}$N barrier thickness and Al composition are investigated and compared by TCAD simulation with non-FE HfO$_{2}$/Al$_{2}$O$_{3}$ gate stack metal-insulator-semiconductor heterostructure high-electron mobility transistors (MISHEMTs). Results show that the decrease of the two-dimensional electron gas (2DEG) density with decreasing AlGaN barrier thickness is more effectively suppressed in MFSHEMTs than that in MISHEMTs due to the enhanced FE polarization switching efficiency. The electrical characteristics of MFSHEMTs, including transconductance, subthreshold swing, and on-state current, effectively improve with decreasing AlGaN thickness in MFSHEMTs. High Al composition in AlGaN barrier layers that are under 3-nm thickness plays a great role in enhancing the 2DEG density and FE polarization in MFSHEMTs, improving the transconductance and the on-state current. The subthreshold swing and threshold voltage can be reduced by decreasing the AlGaN thickness and Al composition in MFSHEMTs, affording favorable conditions for further enhancing the device.     

一种新的磷化铟复合沟道高电子迁移率晶体管小信号物理模型

针对磷化铟(InP)复合沟道高电子迁移率晶体管(HEMT)的特点，对常规单沟道HEMT的小信号物理模型进行了修正，提出了一种新的用于复合沟道HEMT的小信号物理模型，用商用器件模拟软件ISE(integrated systems engineering)对其进行了仿真验证，对比了实测和仿真的I-V特性及转移特性曲线，重点研究了在InGaAs/InP双层沟道中考虑量子效应后的电场和电流密度随着不同栅电压的变化趋势，研究结果表明，由于在沟道中存在量子效应，在栅下靠源端低电场区域，电流主要分布在InGaAs沟道 关键词： 高电子迁移率晶体管 复合沟道 物理模型 磷化铟     

Improving breakdown voltage performance of SOI power device with folded drift region

A novel silicon-on-insulator(SOI) high breakdown voltage(BV) power device with interlaced dielectric trenches(IDT) and N/P pillars is proposed. In the studied structure, the drift region is folded by IDT embedded in the active layer,which results in an increase of length of ionization integral remarkably. The crowding phenomenon of electric field in the corner of IDT is relieved by the N/P pillars. Both traits improve two key factors of BV, the ionization integral length and electric field magnitude, and thus BV is significantly enhanced. The electric field in the dielectric layer is enhanced and a major portion of bias is borne by the oxide layer due to the accumulation of inverse charges(holes) at the corner of IDT.The average value of the lateral electric field of the proposed device reaches 60 V/μm with a 10 μm drift length, which increases by 200% in comparison to the conventional SOI LDMOS, resulting in a breakdown voltage of 607 V.     

深圳市宝安区儿童头发中微量元素含量与儿童眼病关系的研究

通过对2001～2003年深圳市宝安区独生子女(0～14岁)近20000例体检情况统计，结合测定头发中微量元素锌、铁、铜、钙、锰、硒六种元素含量，对照健康人微量元素测定，发现缺锌、缺铜、缺硒儿童较健康儿童更易患近视，这一结论与相关报道一致。     

随机边界对相对论气体玻色-爱因斯坦凝聚临界温度的影响

研究了随机边界对立方箱中相对论气体玻色-爱因斯坦凝聚临界温度的影响.在均匀分布、双模分布和高斯分布情况下,分别计算了临界温度与固定箱中的气体临界温度的比值,发现随机边界降低了系统的临界温度.相对于极端相对论情况,非相对论极限下的临界温度更低.     

基于金属圆弧孔阵列强透射的折射率传感特性

提出了一种由左右、上下对称的一大一小圆弧组成的金属圆弧孔阵列结构。利用该结构形成的法布里-珀罗腔来加强表面等离激元的耦合作用,以获得较好的强透射现象;同时研究了基于该现象的折射率传感特性。采用有限时域差分法研究了该孔阵列结构中大小圆弧孔的半径、两圆弧的圆心距和阵列周期对强透射现象的影响。研究发现,当大圆弧半径为95nm、小圆弧半径为70nm、两圆弧的圆心距为100nm、周期为425nm时,该结构具有较好的强透射现象,其灵敏度为279nm/RIU,为下一代高性能微纳米等离子体传感器的设计提供了理论参考。     

基于非对称圆形谐振腔金属-介质-金属波导结构的带阻滤波器

提出一种金属-介质-金属非对称圆形结构,该结构由两个圆形谐振腔、一个传输波导和两个耦合波导组成。利用谐振腔的局域作用加强表面等离激元的耦合作用,获得较大的透射率。采用有限时域差分方法研究了圆形谐振腔半径、个数和两圆腔中心距离对强透射特性的影响。结果表明,当非对称圆形谐振腔的半径为100nm、两圆间距为200nm时,该结构具有较高的透射率。通过优化主要参数,所设计结构的平均阻带宽度为1000nm,工作范围可增大到2500nm。     

Broadband asymmetric transmission for linearly and circularly polarization based on sand-clock structured metamaterial

We proposed a sandwich structure to realize broadband asymmetric transmission(AT) for both linearly and circularly polarized waves in the near infrared spectral region. The structure composes of a silica substrate and two sand-clock-like gold layers on the opposite sides of the substrate. Due to the surface plasmons of gold, the structure shows that the AT parameters of linearly and circularly polarized waves can reach 0.436 and 0.403, respectively. Meanwhile, a broadband property is presented for the AT parameter is over 0.3 between 320 THz and 340 THz. The structure realizes a diode-like AT for linearly wave in forward and circularly wave in backward, respectively. The magnetic dipoles excited by current in the two gold layers contribute to the broadband AT. The current density in top and bottom metallic layers illustrates the mechanism of the polarization conversion for broadband AT in detail.     

New SOI power device with multi-region high-concentration fixed interface charge and the model of breakdown voltage

A new SOI power device with multi-region high-concentration fixed charge(MHFC) is reported. The MHFC is formed through implanting Cs or I ion into the buried oxide layer(BOX), by which the high-concentration dynamic electrons and holes are induced at the top and bottom interfaces of BOX. The inversion holes can enhance the vertical electric field and raise the breakdown voltage since the drain bias is mainly generated from the BOX. A model of breakdown voltage is developed, from which the optimal spacing has also been obtained. The numerical results indicate that the breakdown voltage of device proposed is increased by 287% in comparison to that of conventional LDMOS.