Intrinsic Limits of Electron Mobility in Modulation-Doped AlGaN/GaN 2D Electron Gas by Phonon Scattering

We theoretically present the intrinsic limits to electron mobility in the modulation-doped AIGaN/GaN two-dimensional electron gas （2DEG） due to effects including acoustic deformation potential （DP） scattering, piezoelectric scattering （PE）, and polar-optic phonon scattering （POP）. We find that DE and PE are the more significant limiting factors at intermediate temperatures of 40 K to 250 K, while POP becomes dominant as room temperature is approached. Detailed numerical results are presented for the change of electron mobility with respect to temperature and carrier density. We conclude that these three types of phonon scattering, which are generally determined by the material properties but not the technical processing, are hard limits to the 2DEG mobility.     

多晶硅薄膜晶体管Kink效应研究与建模

多晶硅薄膜晶体管(P-Si TFTs)技术在SOP(system on panel)显示应用中发挥着越来越重要的作用.随着尺寸的不断缩小,P-si TFT 的Kink效应越来越明显,对有源液晶显示矩阵和驱动电路的性能影响很大.对发生Kink效应的物理机制、二雏数值仿真及其一维解析模型进行了分析,讨论了晶粒边界、沟道长度与Kink效应的关系,提出建立适合电路仿真的一维解析模型的关键与展望.     

High-/spl kappa//metal-gate stack and its MOSFET characteristics

We show experimental evidence of surface phonon scattering in the high-/spl kappa/ dielectric being the primary cause of channel electron mobility degradation. Next, we show that midgap TiN metal-gate electrode is effective in screening phonon scattering in the high-/spl kappa/ dielectric from coupling to the channel under inversion conditions, resulting in improved channel electron mobility. We then show that other metal-gate electrodes, such as the ones with n+ and p+ work functions, are also effective in improving channel mobilities to close to those of the conventional SiO/sub 2//poly-Si stack. Finally, we demonstrate this mobility degradation recovery translates directly into high drive performance on high-/spl kappa//metal-gate CMOS transistors with desirable threshold voltages.     

New insulated-gate inverted structure AlGaAs/GaAs/n-AlGaAs HEMT ring oscillator

Inverted-structure high electron mobility transistors with insulated-gate structure, i.e. AlGaAs/GaAs/n-AlGaAs, have been successfully applied to E/D-type DCFL ring oscillators. High transconductance of 280 mS/mm was obtained at 77 K in an enhancement-mode FET with 0.8 ?m gate length. Gate leakage current was small enough even at a gate voltage of +1.4 V both at 300 K and 77 K, and a high logic swing of more than 1 V was achieved using a DCFL inverter. A 21-stage ring oscillator showed a minimum gate delay as small as 18.0 ps with power dissipation of 520 ?W/gate at 77 K.     

Range Ambiguity Resolution Based on Phase Difference for High PRF Stepped-frequency Radar

A method based on the phase difference between two adjacent range profiles is proposed to resolve the range ambiguity caused by the high Pulse repetition frequency （PRF） in stepped-frequency radar. This method does not need multiple PRFs so as to simplify the hardware implementation structure. In order to decrease the effects of target motion and noise on the phase difference, the method and process are given in the paper, and the simulations verify its validity.     

槽栅MOSHEMT研制与特性分析

An A1GaN/GaN recessed-gate MOSHEMT was fabricated on a sapphire substrate. The device, which has a gate length of 1μm and a source-drain distance of 4μm, exhibits a maximum drain current density of 684mA/mrn at Vgs = 4V with an extrinsic transconductance of 219 mS/mm. This is 24.3% higher than the transconductance of conventional A1GaN/GaN HEMTs. The cut-off frequency and the maximum frequency of oscillation are 9.2 GHz and 14.1 GHz, respectively. Furthermore, the gate leakage current is two orders of magnitude lower than for the conventional Schottky contact device.     

含有Al组分阶变AlGaN过渡层的Si基AlGaN/GaN HEMT

采用一个AlN缓冲层和两个Al组分阶变的AlGaN过渡层作为中间层,在76.2mm Si衬底上外延生长出1.7μm厚无裂纹AlGaN/GaN异质结材料,利用原子力显微镜、X射线衍射、Hall效应测量和CV测量等手段对材料的结构特性和电学性能进行了表征。材料表面平整光滑,晶体质量和电学性能良好,2DEG面密度为1.12×1013cm-2,迁移率为1 208cm2/(V.s)。由该材料研制的栅长为1μm的AlGaN/GaN HEMT器件,电流增益截止频率fT达到10.4GHz,这些结果表明组分阶变AlGaN过渡层技术可用于实现高性能Si基GaN HEMT。     

Making a Higher Hit Ratio Cryptanalytic Time-Memory Trade-Off Attack on Passwords

Most of implementations of the cryptana- lyric time-memory trade-off attacks such as Hellman＇s orig- inal method, Rivest＇s distinguished points cracking and Oechslin＇s rainbow attack are also considered as an ex- haustive attack to passwords in a limited length range on a certain charset. However＇s the distributions of structures and strings making up real human memorable passwords do not appear random. Based upon these, we propose a method to generate passwords in those cryptanalytic time- memory trade-off methods. It achieves a higher hit ra- tio in attacking actual passwords and reduces search space drastically with requirement of only a little extra memory. It makes time-memory trade-off more practical. Even to attack long length passwords, the results of experiments show that our approach has a higher hit ratio compared with Oechslin＇s method. In addition, this method can be used in the distributed and parallel attack.     

分子束外延AlGaN/GaN异质结场效应晶体管材料

用自组装的氨源分子束外延 (NH3-MBE)系统和射频等离子体辅助分子束外延 (PA-MBE)系统在 C面蓝宝石衬底上外延了优质 Ga N以及 Al Ga N/Ga N二维电子气材料。Ga N膜 (1 .2 μm厚 )室温电子迁移率达3 0 0 cm2 /V· s,背景电子浓度低至 2× 1 0 1 7cm- 3。双晶 X射线衍射 (0 0 0 2 )摇摆曲线半高宽为 6arcmin。 Al Ga N/Ga N二维电子气材料最高的室温和 77K二维电子气电子迁移率分别为 73 0 cm2 /V·s和 1 2 0 0 cm2 /V· s,相应的电子面密度分别是 7.6× 1 0 1 2 cm- 2和 7.1× 1 0 1 2 cm- 2 ;用所外延的 Al Ga N/Ga N二维电子气材料制备出了性能良好的 Al Ga N/Ga N HFET(异质结场效应晶体管 ) ,室温跨导为 5 0 m S/mm(栅长 1 μm) ,截止频率达 1 3 GHz(栅长 0 .5μm)。该器件在 3 0 0°C出现明显的并联电导 ,这可能是材料中的深中心在高温被激活所致     

A Novel Generalized Simulation Technology of Aerospace TT＆C Channel

A novel generalized simulation method is proposed to simulate the dynamic transmission delay of wideband and arbitrary signal in aerospace Tracking, telemetry and command （TT＆C） channel. This method orthogonally demodulates the wideband and arbitrary Radio-frequency （RF） signal into complex baseband by a Local oscillator （LO） signal. Then the method of dynamic interpolation and delay reconstruction is proposed to ob- tain the delay reconstruction signal of complex baseband signal based on the variation rules of satellite-to-earth loca- tion. Meanwhile, the method of satellite-to-earth distance subsection and polynomial fitting is applied to obtain the delay reconstruction signal of LO signal. The simulated output signal is achieved through the synthesis of two de- lay reconstruction signals mentioned above. The proposed method can accurately simulate the variation characteris- tics of time delay and Doppler when wideband and arbi- trary RF signal transmits in channel, without knowing any priori knowledge, such as signal form, signal parameters, and so on.     

沟道电场分布对AlN/GaN HFETs极化库仑场散射的影响

Based on the measured capacitance–voltage(C–V) curves and current–voltage(I–V) curves for the prepared differently-sized Al N/Ga N heterostructure field-effect transistors(HFETs), the I–V characteristics of the Al N/Ga N HFETs were simulated using the quasi-two-dimensional(quasi-2D) model. By analyzing the variation in the electron mobility for the two-dimensional electron gas(2DEG) with the channel electric field, it is found that the different polarization charge distribution generated by the different channel electric field distribution can result in different polarization Coulomb field(PCF) scattering. The 2DEG electron mobility difference is mostly caused by the PCF scattering which can reach up to 899.6 cm2/(V s)(sample a), 1307.4 cm2/(V s)(sample b),1561.7 cm2/(V s)(sample c) and 678.1 cm2/(V s)(sample d), respectively. When the 2DEG sheet density is modulated by the drain–source bias, the electron mobility for samples a, b and c appear to peak with the variation of the 2DEG sheet density, but for sample d, no peak appears and the electron mobility rises with the increase in the2 DEG sheet density.     

L-MBE法制备以ZnO为沟道层的薄膜晶体管

采用激光分子束外延法(L-MBE)在SiNx/Si(111)衬底上制备了高质量的ZnO薄膜,用X射线衍射(XRD)和原子力显微镜(AFM)对薄膜的晶体结构、表面形貌进行了表征,结果表明ZnO薄膜有高度的c轴择优取向,薄膜表面平整致密.并以ZnO薄膜为沟道层制作了薄膜晶体管(ZnO-TFT),该晶体管工作在n沟道增强模式,阈值电压为17.5V,电子的场迁移率达到1.05cm2/(V·s).     

3D Freehand Tracking Based on Relevancy Among Local Motion Models

A novel 3D freehand tracking algorithm based on relevancy among local motion models is put forward. Firstly, a specification of the Cognitive and behavioral model （CBM） called PAMT is proposed. Secondly we regard PAMT as a data structure upon which freehand tracking algorithm is designed, and we describe the PAMT in detail. Lastly, the experimental results are provided. The proposed algorithm is tested in a virtual assembly platform and two other application systems. The highlights of this paper are as follows： （1） A new cognitive and behavioral model, called PAMT, is presented; （2） The PAMT is explained with cognitive model; （3） Focus on describing ＇Attractor in PAMT with the relevancy among local motion models; （4） Shows us how the PAMT is shaped and used to design the 3D freehand tracker. One of the advantages of PAMT and RLMM model is that it is easier to explore some of the complex correlations among the variables of the 3D hand model. Our experimental results show that, compared with the particle filter and the annealed particle filter, our algorithm effectively reduces dimensionality and can track 3D hand in real-time.     

单电子晶体管的制备、集成与电路研究

我们制备出了高温Si单电子晶体管,研究了单电子晶体管的集成原理,实现了14个单电子晶体管的串联集成和2个单电子晶体管的并联集成。同时也研究了单电子晶体管与传统高迁移率晶体管的集成和技术,发现可用单个电子来调控传统晶体管的栅对源漏极电流的控制能力（跨导）,利用单电子晶体管的集成方法,建立了对电荷超敏感的探测技术（包括超敏感的库尔计）,实现了单电子存储器中的单电子过程的探测,并设计了一种新型的多值存储器。     

High-voltage MIS-gated GaN transistors

Transistors with a high electron mobility based on AlGaN/GaN epitaxial heterostructures are promising component types for creating high-power electronic devices of the next generation. This is due both to a high charge-carrier mobility in the transistor channel and a high electric durability of the material making it possible to achieve high breakdown voltages. For use in power switching devices, normally off GaN transistors operating in the enrichment mode are required. To create normally off GaN transistors, the subgate region on the basis of p-GaN doped with magnesium is more often used. However, optimization of the p-GaN epitaxial-layer thickness and doping level makes it possible to achieve a threshold voltage close to V _th = +2 V for the on-mode of GaN transistors. In this study, it is shown that the use of a subgate MIS (metal–insulator–semiconductor) structure involved in p-GaN transistors results in an increase in the threshold voltage for the on-mode to V _th = +6.8 V, which depends on the subgate-insulator thickness in a wide range. In addition, it is established that the use of the MIS structure results in a decrease in the initial transistor current and the gate current in the on mode, which enables us to decrease the energy losses when controlling powerful GaN transistors.     

Millimeter-wave low-noise high electron mobility transistors

High electron mobility transistors (HEMT's) have been fabricated which demonstrate excellent millimeter-wave performance. A maximum extrinsic transconductance as high as 430 mS/mm, corresponding to an intrinsic transconductance of 580 mS/mm, was observed in these transistors. A unity current gain cutoff frequency fTas high as 80 GHz and a maximum frequency of oscillationf_{max}of 120 GHz were projected for these HEMT's. At 40 GHz, a minimum noise figure of 2.1 dB with an associated gain of 7.0 dB has also been measured. These are the highestf_{T}, f_{max}, and the best noise performance reported to date. The results clearly demonstrate the potential of HEMT's for millimeter-wave low-noise applications.     

0.1 μm Schottky-collector AlAs/GaAs resonant tunneling diodes

The Schottky-collector resonant tunneling diode (RTD) is an RTD with the normal N+ collector and ohmic contact replaced by a Schottky contact, thereby eliminating the associated parasitic resistance. With submicron Schottky contact dimensions, the remaining components of the parasitic series resistance can be greatly reduced, resulting in an increased maximum frequency of oscillation, f_max. AlAs/GaAs Schottky-collector RTDs were fabricated using 0.1 μm T-gate technology developed for high electron mobility transistors. From their measured dc and microwave parameters, and including the effect of the quantum well lifetime, f_max=900 GHz is computed     

Low ballistic mobility in submicron HEMTs

Ballistic effects in short channel high electron mobility transistors (HEMTs) greatly reduce the field effect mobility compared to that in long gate structures. This reduction is related to a finite electron acceleration time in the channel under the device gate. As an example, the field effect mobility at room temperature in 0.15-μm gate AlGaAs/GaAs HEMTs cannot exceed 3000 cm²/V-s. These predictions are consistent with the values of the field effect mobility extracted from the measured AlGaAs/GaAs HEMT current-voltage characteristics     

Effect of surface passivation by SiN/SiO2 of AlGaN/GaN high-electron mobility transistors on Si substrate by deep level transient spectroscopy method

Device performance and defects in AlGaN/GaN high-electron mobility transistors have been correlated. The effect of SiN/SiO₂ passivation of the surface of AlGaN/GaN high-electron mobility transistors on Si substrates is reported on DC characteristics. Deep level transient spectroscopy (DLTS) measurements were performed on the device after the passivation by a (50/100 nm) SiN/SiO₂ film. The DLTS spectra from these measurements showed the existence of the same electron trap on the surface of the device.     

最大振荡频率640 GHz的70 nm栅长InAs PHEMTs器件

由于高的电子迁移率和二维电子气浓度,InP基赝配高电子迁移率晶体管（PHEMTs）器件成为制作太赫兹器件最有前途的三端器件之一。为提高器件的工作频率,采用InAs复合沟道,使得二维电子气的电子迁移率达到13000 cm2/（Vs）。成功研制出70 nm栅长的InP基赝配高电子迁移率晶体管,器件采用双指,总栅宽为30 m,源漏间距为2 m。为降低器件的寄生电容,设计T型栅的栅根高度达到210 nm。器件的最大漏端电流为1440 mA/mm （VGS=0.4 V）,最大峰值跨导为2230 mS/mm。截止频率fT和最大振荡频率fmax分别为280 GHz和640 GHz。这些性能显示该器件适于毫米波和太赫兹波应用。