The effect of substrate doping on the flatband and threshold voltages of a strained-Si pMOSFET

The effect of substrate doping on the flatband and threshold voltages of a strained-Si/SiGe p metal-oxide semiconductor field-effect transistor(pMOSFET) has been studied.By physically deriving the models of the flatband and threshold voltages,which have been validated by numerical simulation and experimental data,the shift in the plateau from the inversion region to the accumulation region as the substrate doping increases has been explained.The proposed model can provide a valuable reference to the designers of strained-Si devices and has been implemented in software for extracting the parameters of a strained-Si MOSFET.     

应变Si沟道nMOSFET阈值电压模型

在研究分析弛豫SiGe衬底上的应变Si 沟道nMOSFET纵向电势分布的基础上,建立了应变Si nMOSFET阈值电压模型,并利用该模型对不同的器件结构参数进行仿真,获得了阈值电压与SiGe层掺杂浓度和Ge组分的关系、阈值电压偏移量与SiGe层中Ge组分的关系、阈值电压与应变Si层掺杂浓度和厚度的关系. 分析结果表明：阈值电压随SiGe层中Ge组分的提高而降低,随着SiGe层的掺杂浓度的提高而增大;阈值电压随应变Si层的掺杂浓度的提高而增大,随应变Si层厚度增大而增大. 该模型为应变Si 器件阈值电压设计 关键词： 应变硅 阈值电压 电势分布 反型层     

应变Si NMOSFET阈值电压集约物理模型

本文采用渐变沟道近似和准二维分析的方法, 通过求解泊松方程, 建立了应变Si NMOSFET阈值电压集约物理模型. 模型同时研究了短沟道, 窄沟道, 非均匀掺杂, 漏致势垒降低等物理效应对阈值电压的影响. 采用参数提取软件提取了阈值电压相关参数, 通过将模型的计算结果和实验结果进行对比分析, 验证了本文提出的模型的正确性. 该模型为应变Si超大规模集成电路的分析和设计提供了重要的参考. 关键词： 应变Si NMOSFET 阈值电压 集约物理模型     

亚100 nm应变Si/SiGe nMOSFET阈值电压二维解析模型

本文基于二维泊松方程,建立了适用于亚100 nm应变Si/SiGe nMOSFET的阈值电压理论模型.为了保证该模型的准确性,同时考虑了器件尺寸减小所导致的物理效应,如短沟道效应,量子化效应等.通过将模型的计算结果与二维器件模拟器ISE的仿真结果进行对比分析,证明了本文提出的模型的正确性.最后,还讨论了亚100 nm器件中常规工艺对阈值电压的影响.该模型为亚100 nm小尺寸应变Si器件的分析设计提供了一定的参考. 关键词： 亚100nm 应变Si/SiGe nMOSFET 二维表面势 阈值电压     

Effects of charge and dipole on flatband voltage in an MOS device with a Gd-doped HfO_2 dielectric

Gd-doped HfO2 has drawn worldwide interest for its interesting features.It is considered to be a suitable material for N-type metal-oxide-semiconductor(MOS)devices due to a negative flatband voltage(Vfb)shift caused by the Gd doping.In this work,an anomalous positive shift was observed when Gd was doped into HfO2.The cause for such a phenomenon was systematically investigated by distinguishing the effects of different factors,such as Fermi level pinning(FLP),a dipole at the dielectric/SiO2interface,fixed interfacial charge,and bulk charge,on Vfb.It was found that the FLP and interfacial dipole could make Vfbnegatively shifted,which is in agreement with the conventional dipole theory.The increase in interfacial fixed charge resulting from Gd doping plays a major role in positive Vfbshift.     

应变Si NMOS积累区电容特性研究

积累区MOS电容线性度高且不受频率限制, 具有反型区MOS电容不可比拟的优势. 本文在研究应变Si NMOS电容C-V特性中台阶效应形成机理的基础上, 通过求解电荷分布, 建立了应变Si/SiGe NMOS积累区电容模型, 并与实验结果进行了对比, 验证了模型的正确性. 最后, 基于该模型, 研究了锗组分、应变层厚度、掺杂浓度等参数对台阶效应的影响, 为应变Si器件的制造提供了重要的指导作用. 本模型已成功用于硅基应变器件模型参数提取软件中, 为器件仿真奠定了理论基础. 关键词： 应变Si NMOS 积累区电容 台阶效应 电荷分布     

Influence of structural parameters on the immunity of short-channel effects in grooved-gate nMOSFET

This paper presents the influences of structural parameters on the immunity of short-channel effects in grooved-gate n-channel metal－oxide－semiconductor field effect transistor (nMOSFET) using the simulator PISCES-II. The zero or negative groove-junction depth is beneficial to the improvement of the threshold characters, but there exists a limited range. The doping concentration of both substrate and channel has a significant influence on the threshold characters as well as on the device transconductance. Thus, the variation in these adjustable parameters may help to optimize the device design.     

Analytical models of lateral power devices with arbitrary vertical doping profiles in the drift region

By solving the 2D Poisson's equation, analytical models are proposed to calculate the surface potential and electric field distributions of lateral power devices with arbitrary vertical doping profiles. The vertical and the lateral breakdown voltages are formulized to quantify the breakdown characteristic in completely-depleted and partially-depleted cases. A new reduced surface field (RESURF) criterion which can be used in various drift doping profiles is further derived for obtaining the optimal trade-off between the breakdown voltage and the on-resistance. Based on these models and the numerical simulation, the electric field modulation mechanism and the breakdown characteristics of lateral power devices are investigated in detail for the uniform, linear, Gaussian, and some discrete doping profiles along the vertical direction in the drift region. Then, the mentioned vertical doping profiles of these devices with the same geometric parameters are optimized, and the results show that the optimal breakdown voltages and the effective drift doping concentrations of these devices are identical, which are equal to those of the uniform-doped device, respectively. The analytical results of these proposed models are in good agreement with the numerical results and the previous experimental results, confirming the validity of the models presented here.     

多晶SiGe栅量子阱pMOSFET阈值电压模型

本文基于多晶SiGe栅量子阱SiGe pMOSFET器件物理,考虑沟道反型时自由载流子对器件纵向电势的影响,通过求解泊松方程,建立了p+多晶SiGe栅量子阱沟道pMOS阈值电压和表面寄生沟道开启电压模型.应用MATLAB对该器件模型进行了数值分析,讨论了多晶Si_1-yGe_y栅Ge组分、Si_1-xGe_x量子阱沟道Ge组分、栅氧化层厚度、Si帽层厚度、沟道区掺杂浓度和 关键词： 多晶SiGe栅 寄生沟道 量子阱沟道 阈值电压     

基于双电源电压和双阈值电压的全局互连性能优化

基于双电源电压和双阈值电压技术,提出了一种优化全局互连性能的新方法.文中首先定义了一个包含互连延时、带宽和功耗等因素的品质因子用以描述全局互连特性,然后在给定延时牺牲的前提下,通过最大化品质因子求得优化的双电压数值用以节省功耗.仿真结果显示,在65 nm工艺下,针对5%,10%和20%的允许牺牲延时,所提方法相较于单电压方法可分别获得27.8%,40.3%和56.9%的功耗节省.同时发现,随着工艺进步,功耗节省更加明显.该方法可用于高性能全局互连的优化和设计. 关键词： 全局互连 双电源电压 双阈值电压 功耗     

Control of electric field in 4H-SiC UMOSFET: Physical investigation

In this paper, we show how breakdown voltage (V_BR) and the specific on-resistance (R_on) can be improved simply by controlling of the electric field in a power 4H-SiC UMOSFET. The key idea in this work is increasing the uniformity of the electric field profile by inserting a region with a graded doping density (GD region) in the drift region. The doping density of inserted region is decreased gradually from top to bottom, called Graded Doping Region UMOSFET (GDR-UMOSFET). The GD region results in a more uniform electric field profile in comparison with a conventional UMOSFET (C-UMOSFET) and a UMOSFET with an accumulation layer (AL-UMOSFET). This in turn improves breakdown voltage. Using two-dimensional two-carrier simulation, we demonstrate that the GDR-UMOSFET shows higher breakdown voltage and lower specific on-resistance. Our results show the maximum breakdown voltage of 1340 V is obtained for the GDR-UMOSFET with 10 µm drift region length, while at the same drift region length and approximated doping density, the maximum breakdown voltages of the C-UMOSFET and the AL-UMOSFET structures are 534 V and 703 V, respectively.     

Growth of High Quality Strained-Si on Ultra-Thin SiGe-on-Insulator Substrate

Ultra-thin and near-fully relaxed SiCe substrate is fabricated using a modified Ce condensation technique, and then a 25-nm-thiek biaxially tensile strained-Si with a low rms roughness is epitaxially deposited on a SiGe- on-Insulator （SGOI） substrate by ultra high vacuum chemical vapor deposition （UHVCVD）. High-Resolution cross-sectional transmission electron microscope （HR-XTEM） observations reveal that the strained-Si/SiGe layer is dislocation-free and the atoms at the interface are well aligned. Furthermore, secondary ion mass spectrometry （SIMS） results show a sharp interface between layers and a uniform distribution of Ge in the SiCe layer. One percent in-plane tensile strain in the strained-Si layer is confirmed by ultraviolet （UV） Raman spectra, and the stress maintained even after a 30-s rapid thermal annealing （RTA） process at 1000℃. According to those results, devices based on strained-Si are expected to have a better performance than the conventional ones.     

Mobility-independent doping in crystalline rubrene field-effect transistors

We report doping effects in an organic semiconductor, crystalline rubrene. Oxygen-related states are introduced (removed) by annealing in oxygen (vacuum), at an elevated temperature. Room temperature stability is found in the resulting effects: (1) about two orders of magnitude increase in carrier density at equilibrium, (2) significant modification of threshold voltages, and (3) an unchanged field-effect mobility in the on-current state. Density of states data are modeled as tunneling from the valence band in the channel region into deep-level acceptors in the adjacent region. These oxygen acceptors are the likely dopant species.     

On the effects of NBTI degradation in p-MOSFET devices

This paper presents the effects of interface trap concentration and threshold voltage shift on NBTI degradation in p-MOSFETs. To explore the degradation mechanisms, transistors having an EOT of 1.1 nm and 5 nm were simulated by applying various stress conditions. The NBTI degradation mechanism was studied by varying the gate voltage, temperature and substrate doping level. The simulations show NBTI degradation in terms of the threshold voltage shift, ΔV_th and number of interface traps, ΔN_it. The simulation results show an improved degradation trend in terms of ΔV_th and ΔN_it when the substrate doping level is increased.     

Electric field induced metal–insulator transition in VO2 thin film based on FTO/VO2/FTO structure

A VO₂ thin film has been prepared using a DC magnetron sputtering method and annealing on an F-doped SnO₂ (FTO) conductive glass substrate. The FTO/VO₂/FTO structure was fabricated using photolithography and a chemical etching process. The temperature dependence of the I–V hysteresis loop for the FTO/VO₂/FTO structure has been analyzed. The threshold voltage decreases with increasing temperature, with a value of 9.2 V at 20 °C. The maximum transmission modulation value of the FTO/VO₂/FTO structure is 31.4% under various temperatures and voltages. Optical modulation can be realized in the structure by applying an electric field.     

Analytical modeling and simulation of subthreshold characteristics of back-gated SSGOI and SSOI MOSFETs: A comparative study

The Silicon–Germanium-on-Insulator (SGOI) and Silicon-on-Insulator (SOI) based MOS structures are spearheading the strained-Si technology. The present work compares the subthreshold characteristics of two short-channel back-gated (BG) strained-Si-on-SGOI (SSGOI) and BG strained-Si-on-Insulator (SSOI) MOSFETs, and provides some solutions to overcome the degradation in subthreshold characteristics with the unrelenting downscaling of the devices. Subthreshold behaviors of the MOS structures are based on surface potential model which is determined by solving the 2D Poisson's equation with suitable boundary conditions by evanescent mode analysis for both of the MOS structures. The closed form expressions for threshold voltage, subthreshold current and subthreshold swing have been derived for symmetrical as well as independent gate operation (IGO). In addition, the Electrostatic integrity (EI) factors for SSOI and SSGOI MOS structures have been estimated and compared with Double-Gate (DG) MOSFET. The numerical simulation results, obtained by ATLAS?, a 2D device simulator from Silvaco, have been used to assess the validity of the models.     

Two-dimensional analytical models for asymmetric fully depleted double-gate strained silicon MOSFETs

This paper develops the simple and accurate two-dimensional analytical models for new asymmetric double-gate fully depleted strained-Si MOSFET. The models mainly include the analytical equations of the surface potential, surface electric field and threshold voltage, which are derived by solving two dimensional Poisson equation in strained-Si layer. The models are verified by numerical simulation. Besides offering the physical insight into device physics in the model, the new structure also provides the basic designing guidance for further immunity of short channel effect and drain-induced barrier-lowering of CMOS-based devices in nanometre scale.     

Effects of doping and free carriers on the refractive index of direct-gap semiconductors

A model for the doping and current dependence of the refractive index of direct-gap semiconductors has been developed and applied to GaAs in order to explain certain properties of single heterostructure injection lasers. The model involves the concept of an effective energy gap which takes account of the effects of doping and free carriers via the Burstein shift, the exchange interaction, and the average screened Coulomb potential of the impurities. This effective gap, together with empirical results for the energy dependence of the refractive index, facilitates the calculation of refractive index changes with doping and current. Numerical results are given for GaAs, and the model is applied particularly to the substrate and active regions of single heterostructure injection lasers. In these devices the refractive index values are particularly important in determining the dielectric waveguide properties. With the aid of our model, this feature can be discussed in detail, with special reference to the breakdown of the waveguide effect which occurs (a) for substrate doping levels below a critical value, and (b) for currents well above threshold ('saturation').