SiC衬底上栅长70 nm fT / fmax >160 GHz的InAlN/GaN HEMTs器件

在SiC衬底上制备了InAlN/GaN 高电子迁移率晶体管（HEMTs）,并进行了表征。为提高器件性能,综合采用了多种技术,包括高电子浓度,70 nm T型栅,小的欧姆接触电阻和小源漏间距。制备的InAlN/GaN器件在栅偏压为1 V时得到的最大饱和漏电流密度为1.65 A/mm,最大峰值跨导为382 mS/mm。70 nm栅长器件的电流增益截止频率fT和最大振荡频率fmax分别为162 GHz和176 GHz。     

基于优化神经网络算法的电离层foF2预测

为了提高基于反向传输（back propagation,BP）神经网络的电离层f_oF₂预测的精度,采用了一种改进粒子群优化神经网络的方法,对BP网络的初始权值进行优化,防止出现神经网络训练中的局部最优.通过比较基于粒子群优化的神经网络预测结果与遗传算法优化的神经网络预测结果,我们发现对于BP神经网络,两种方法都有很好的性能.此外,和电离层经验模型国际参考电离层模型（international reference ionosphere 2016,IRI2016）结果进行对比,结果表明,本文提出的自适应变异粒子群（adaptive mutation particle swarm optimization,AMPSO）优化神经网络能有效提高f_oF₂的预测精度,并在低纬地区有更好的预测效果.     

fT=260 GHz and fmax=607 GHz of 100-nm-gate In0.52Al0.48As/In0.7Ga0.3As HEMTs with Gm.max=1441 mS/mm

The 100-nm T-gate InP-based InAlAs/InGaAs high electron mobility transistors (HEMTs) with the width of 2×50 μm and source-drain space of 2.4 μm are systematically investigated. High indium (In) composition of InGaAs layer was adopted to acquire the higher mobility of the channel layer. A sandwich structure was adopted to optimize the cap layers and produce a very low contact resistance. The fabricated devices exhibit extrinsic maximum transconductance G_m.max=1441 mS/mm, cutoff frequency f_T=260 GHz, and maximum oscillation frequency f_max=607 GHz. A semi-empirical model has been developed to precisely fit the low-frequency region of scattering parameters (S parameters) for InP-based HEMTs. Excellent agreement between measured and simulated S parameters demonstrates the validity of this approach.     

最高振荡频率为325GHz的InGaAs/InP双异质结双极型晶体管

A common-base four finger InGaAs/InP double heterostructure bipolar transistor（DHBT） has been designed and fabricated using triple mesa structure and planarization technology.All processes are on 3-inch wafers. The area of each emitter finger is 1×15μm².The maximum oscillation frequency(f_max) is 325 GHz and the breakdown voltage BV_CBO is 10.6 V,which are to our knowledge both the highest f_max and BV_cbo ever reported for InGaAs/InP DHBTs in China.The high speed InGaAs/InP DHBT with a high breakdown voltage is promising for submillimeter-wave and THz electronics.     

高击穿电压的InGaAs/InP双异质结双极型晶体管

利用台面工艺以及平坦化技术制作了带有复合式集电区的InGaAs/InP双异质结双极型晶体管。所有的工艺都是在3英寸圆片上进行的。发射极面积为1μm15μm的器件,电流增益截止频率为170GHz,最高振荡频率为256GHz,击穿电压为8.3V,这是国内报道的击穿电压最高的InP HBT器件。高的振荡频率以及击穿电压,使得此种类型的器件十分适用于W波段及以上频段压控振荡器（VCO）以及混频器（Mixer）的制作。     

Models for generation 1/f noise

Simple analytically solvable models are proposed exhibiting 1/f spectrum in a wide range of frequency. The signals of the models consist of pulses (point process), interevent times of which fluctuate about some average value, obeying an autoregressive process with very small damping. The power spectrum of the process can be expressed by the Hooge formula. The proposed models reveal possible origin of 1/f noise, i.e., random increments of the time intervals between pulses or interevent time of the process (Brownian motion in the time axis).     

An optical sensor for hydrogen sulfide detection in open path using WMS-2f/1f technique

An optical hydrogen sulfide (H2S) sensor based on wavelength modulation spectroscopy with the second harmonic (2f) corrected by the first harmonic (1f) signal (WMS-2f/1f) is developed using a distributed feedback (DFB) laser emitting at 1.578 µm and a homemade gas cell with 1-m-long optical path length. The novel sensor is constructed by an electrical cabinet and an optical reflecting and receiving end. The DFB laser is employed for targeting a strong H2S line at 6 336.62 cm-1 in the fundamental absorption band of H2S. The sensor performance, including the minimum detection limit and the stability, can be improved by reducing the laser intensity drift and common mode noise by means of the WMS-2f/1f technique. The experimental results indicate that the linearity and response time of the sensor are 0.999 26 and 6 s (in concentration range of 15.2—45.6 mg/m3), respectively. The maximum relative deviation for continuous detection (60 min) of 30.4 mg/m3 H2S is 0.48% and the minimum detection limit obtained by Allan variance is 79 μg/m3 with optimal integration time of 32 s. The optical H2S sensor can be applied to environmental monitoring and industrial production, and it has significance for real-time online detection in many fields.     

Small-signal performance and modeling of sub-50 nm nMOSFETs with fT above 460-GHz

We have fabricated and tested the performance of sub-50 nm gate nMOSFETs to assess their suitability for mixed signal applications in the super high frequency (SHF) band, i.e. 3–30 GHz. For a 30 nm × 40 μm × 2 device, we found f_T = 465 GHz at V_ds = 2 V, V_g = 0.67 V, which is the highest cut-off frequency reported for a MOSFET produced on bulk silicon substrate so far. However, our measurements of f_max and noise figure indicate that parasitics impose limitations on SHF operation. We also present a high frequency ac model appropriate to sub-50 nm gate length nanotransistors, which incorporates the effects of the parasitics. The model accurately accounts for measurements of the S- and Y-parameters in the frequency range from 1 to 50 GHz.     

Driven Lorentz gas with 1/f noise

Nosé–Hoover mechanics is briefly introduced as an instrument for analysis of stationary nonequilibrium systems driven away from equilibrium by boundary conditions. The driven Lorentz gas – a model to which the mechanics does apply – is shortly described. Numerical simulations of this specific model revealed that the system exhibits 1/f^k noise. The explanation of the noise is given which relies on the numerically verified fact that the system approaches an ergodic strange attractor. The ergodicity of the motion on the attractor together with reduced dimensionality of the latter is shown to impose restrictions on the recurrent trajectories resulting in 1/f^k noise. Arguments are given in support of the conclusion that the exponent k is related to the dimensionality of the attractor in a rather simple way.     

On 1/f noise in semiconductor devices

Applying a thermal activation model, we show that the power index γ of low frequency noise(1/f^γ) in semiconductor structures can often be directly related to the ratio of thermal energy and a characteristic energy of the trap distribution, when there is a significant band tail or band bending. Some examples are discussed.     

On the intrinsic origin of 1/f noise

The problem of the intrinsic origin of 1/f noise is considered. Currents and signals consisting of a sequence of pulses are analyzed. It is shown that the intrinsic origin of 1/f noise is a random walk of the average time between subsequent pulses of the pulse sequence, or the interevent time. This results in the long-memory process for the pulse occurrence time and in 1/f type power spectrum of the signal.     

辐照诱生的双极性线性稳压器的1/f 噪声退化研究

研究发现辐照能使双极线性稳压器LM117的输出1/f噪声性能退化。本文在研究双极线性稳压器LM117的辐照失效机理基础上,认为LM117的内部带隙基准是其噪声性能退化的关键部件,辐照引起的带隙基准内部的双极性晶体管的基极表面复合电流的退化,导致LM117输出1/f噪声发生退化。通过对比,可以看出1/f噪声比电参数敏感,也可以用来表征LM117辐照损伤。     

Skewness and kurtosis of 1/f noise in semiconductor devices

The degree of the Gaussian nature of the white noise present in microwave low-noise devices is experimentally investigated. The chosen experimental technique consists of simultaneously digitizing four versions of the noise which are amplified by four parallel independent amplifiers. The four independent signals are then used to compute the second, and, to a good approximation, the fourth moment of the noise. The ratio of the fourth moment to the square of the second moment is the kurtosis of the noise. Gaussian processes are characterized by a kurtosis equal to 3. A deviation from this value gives an indication about the degree of non-Gaussian nature of the noise. By using this technique, the effect of the additive noise introduced by the amplifiers is strongly reduced. In our experiments, the degree of the Gaussian nature of the white noise of some microwave devices is measured in the frequency range from 100 to 500 MHz. In all the investigated devices, the kurtosis is found to be very close to 3.     

1/f Noise separated from white noise with wavelet denoising

The low-frequency noise in the devices often appears to be a superposition of 1/f noise and white noise, which are induced by different physical mechanisms or microscopic defects. The separation of the two noises is necessary especially in the characterization of quality and reliability by means of noise measurement. The traditional separation method is usually used in frequency domain with limited frequency range, and the estimated value of exponent index γ for 1/f^γ noise has considerable error when the ratio of 1/f noise and white noise is smaller than 20 dB. In this paper, based on wavelet denoising theory, a new method is proposed to separate 1/f^γ noise from white noise in time domain and can be used to estimate γ values with much better accuracy even if the ratio of 1/f noise to white noise in low enough.     

Origin of 1/f noise in lateral PNP bipolar transistors

1/f noise was measured on lateral bipolar PNP transistors over a temperature range of 220<T<450 K. Noise power spectral density measurements were performed simultaneously across two resistors connected in series with base and collector. The equivalent base current noise source S_IB has two dominant components. One is S_IBE that is between the base and the emitter, in parallel with r_π. The other is S_IBC coming from the surface recombination current at the neutral base, between the base and the collector. The extracted S_IB exhibited a near square law dependence on base current I_B. The noise remained nearly constant when the temperature was below 310 K. However, it presented strong temperature dependence when the temperature was beyond 310 K. Two different models are proposed for the noise in different temperature regions. For the high temperature region, the surface recombination velocity fluctuation model is proposed, which indicates that the noise is coming from the fluctuations in the surface recombination velocity at the neutral base surface. The tunneling assistant trapping model is responsible for the low temperature region, where the noise source is the carrier trapping–detrapping by the defects in the spacer oxide covering the surface of the depletion layer.     

一种氮化镓高迁移率晶体管的栅电流噪声模型

This work presents a theoretical and experimental study on the gate current 1/f noise in Al Ga N/Ga N HEMTs. Based on the carrier number fluctuation in the two-dimensional electron gas channel of Al Ga N/Ga N HEMTs, a gate current 1/f noise model containing a trap-assisted tunneling current and a space charge limited current is built. The simulation results are in good agreement with the experiment. Experiments show that, if Vg Vx, gate current 1/f noise comes from not only the trap-assisted tunneling RTS, but also the space charge limited current RTS. This indicates that the gate current 1/f noise of the Ga N-based HEMTs device is sensitive to the interaction of defects and the piezoelectric relaxation. It provides a useful characterization tool for deeper information about the defects and their evolution in Al Ga N/Ga N HEMTs.     

Degradation of 1/f noise in short channel MOSFETs due to halo angle induced VT non-uniformity and extra trap states at interface

The impact of halo implantation angle on the low-frequency noise of short channel n-MOSFET is reported. The low-frequency noise is degraded with larger tilt angle for the same implant dose and energy. The higher dose/energy of the halo implant with larger tilt angle further enhances the degradation of low-frequency noise. The larger halo angle introduces non-uniform doping distribution and creates the non-uniform threshold voltage along the channel. Additional traps can be created near the oxide/semiconductor interface due to boron pileup due to larger tilt angle. A quantitative analysis supported by experimental results confirm that the degradation of 1/f noise is due to the combined effect of non-uniformity in threshold voltage along the channel and the creation of extra trap charges near the oxide-semiconductor interface (near-interfacial charges).     

太阳活动低年(2005—2007)期间中国低纬地区电离层foF2变化特性

利用2005—2007年广州、海口和重庆三个台站的f_oF₂数据,研究了f_oF₂日变化、季节变化和f_oF₂随太阳活动的变化规律,以及空间天气事件如磁暴对f_oF₂的影响.结果发现:f_oF₂的日变化规律体现在日出前出现最小值,海口和广州两站在14:00—16:00出现最大值,重庆站在12:00—14:00出现最大值;春秋季f_oF₂均值高于夏冬季节,春季高于秋季,冬季高于夏季（重庆站不明显）;从2005年开始,临频值整体下降,与太阳黑子数呈现正的线性关系;在2005-08-24开始的磁暴期间在磁暴的主相发生f_oF₂的正向扰动,在磁暴发生的第二天f_oF₂整体呈现负向扰动.综合以上信息可知,我国低纬地区可以划分为赤道异常区和非赤道异常区,两个地区f_oF₂有所相似但仍有不同,应结合太阳活动具体分析.