Mobility in ultrathin SOI MOSFET and pseudo-MOSFET: Impact of the potential at both interfaces

The mobility-thickness dependence in SOI films is clarified. Measurements in fully depleted SOI MOSFETs show that the low-field mobility at the front channel decreases by thinning the Si film or by sweeping the back gate from depletion into accumulation. We demonstrate that this mobility degradation is only apparent, being related to the potential value at the surface facing the channel. This opposite-surface potential induces an intrinsic vertical field which adds to the usual gate-related field. The mobility drop simply indicates a deviation from the low-field condition which cannot be achieved. We propose an updated model for proper extraction and interpretation of the low-field mobility. Pseudo-MOSFET results reveal the existence of a similar additional vertical field in bare SOI wafers, induced by charges present on the unpassivated surface. This intrinsic field increases in thinner films and affects pseudo-MOSFET conduction. The mobility decrease measured in SOI wafers with thinner films reflects the increasing impact of the intrinsic field and does not imply any degradation in quality of film-BOX interface.     

Three-interface pseudo-MOSFET models for the characterization of SOI wafers with ultrathin film and BOX

The electrical characterization of unprocessed fully depleted silicon-on-insulator (SOI) layers relies on the pseudo-MOSFET (Ψ-MOSFET) technique. We propose three-interface models which are more appropriate for addressing the case of SOI wafers with ultrathin body and BOX (UTB²). The novel models for threshold voltage and subthreshold swing account for the channel-to-surface and channel-to-substrate coupling which are important effects, respectively, in ultrathin films and thin BOX. The influence of the density of traps at each of the three interfaces (free surface, channel/BOX and BOX/substrate) is discussed. The models are validated with experimental results from a range of SOI film thicknesses.     

AlGaAs/GaAs HBT的低频噪声

测试了AlGaAs／GaAsHBT的低频噪声，并将测试结果分解为1／f噪声、G－R噪声和白噪声，阐述了它们的产生机理，在此基础上建立了AlGaAs／GaAsHBT输入噪声电压的等效电路模型，该模型有助于AlGaAs／GaAsHBT电路的CAD。     

A comparative 1/f noise study of GeOI wafers obtained by the Ge enrichment technique and the Smart Cut technology

This paper presents an experimental investigation of Low-frequency Noise (LFN) measurements on Germanium-On-Insulator (GeOI) PMOS transistors processed on different wafers. The wafers are obtained by Ge enrichment technique and by Smart Cut™ technology. The slow oxide trap densities of back interface are used as a figure of merit to evaluate the process. The Smart Cut™ process is evaluated by studying GeOI pMOSFETs, and the enrichment process by studying Si_1−xGe_x (x = 25% and 35%) pMOSFETs. The buried oxide is used as a back gate for experimental purposes. The extracted values are of the same order of magnitude for both processes and are close to those of state of art buried oxide SiO₂/Si interfaces, demonstrating that both the Smart Cut™ and enrichment techniques produce equally good quality interfaces.     

On the geometrical dependence of low-frequency noise in SiGe HBTs

We present an investigation of the dependence of low-frequency noise on device geometry in advanced npn silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs). The devices examined in this work have fixed emitter width (W_E = 0.4 μm), but varying emitter length (0.5 μm  L_E  20.0 μm), and thus the ratio of the emitter perimeter (P_E) to the emitter area (A_E) varies widely, making it ideal for examining geometrical effects. The SPICE noise parameter A_F extracted from these devices decreases with increasing L_E. Furthermore, the low-frequency noise measured on SiGe HBTs with significantly different P_E/A_E ratios suggests a possibility that the fundamental noise source for the diffusion base current may be located at the emitter periphery. Transistors with different distances between the emitter edge and the shallow trench edge (XEC), and shallow trench edge to deep trench edge (XTC), are also investigated. The SiGe HBTs with a smaller value of XEC have higher low-frequency noise, but no significant difference is found in devices with varying XTC. Explanations of the observed noise behavior are suggested.     

Low-frequency noise in Si0.7Ge0.3 surface channel pMOSFETs with ALD HfO2/Al2O3 gate dielectrics

Low-frequency noise was characterized in Si_0.7Ge_0.3 surface channel pMOSFETs with ALD Al₂O₃/HfO₂/Al₂O₃ stacks as gate dielectrics. The influences of surface treatment prior to ALD processing and thickness of the Al₂O₃ layer at the channel interface were investigated. The noise was of the 1/f type and could be modeled as a sum of a Hooge mobility fluctuation noise component and a number fluctuation noise component. Mobility fluctuation noise dominated the 1/f noise in strong inversion, but the number fluctuation noise component, mainly originating from traps in HfO₂, also contributed closer to threshold and in weak inversion. The number fluctuation noise component was negligibly small in a device with a 2 nm thick Al₂O₃ layer at the SiGe channel interface, which reduced the average 1/f noise by a factor of two and decreased the device-to-device variations.     

Low-frequency noise analysis of Si/SiGe channel pMOSFETs

Low-frequency noise characteristics of 0.1 μm Si_1−xGe_x channel pMOSFETs were studied by numerical simulations in the framework of the carrier number fluctuation model as well as the correlated fluctuation in the mobility model. Simulation results predict that Si_1−xGe_x channel pMOSFETs could offer improved low-frequency noise performance as compared to the conventional bulk Si devices. This improvement in Si_1−xGe_x channel pMOSFETs could be attributed to less effective oxide trap density for noise generation due to the increasing separation of quasi-Fermi level and valence band edge at Si–SiO₂ interface by Ge-induced band offset.     

Characterization of impact of process options in Germanium-On-Insulator (GeOI) high-k & metal gate pMOSFETs by low-frequency noise

The impact of technological processes on Germanium-On-Insulator (GeOI) noise performance is studied. We present an experimental investigation of low-frequency noise (LFN) measurements carried out on (GeOI) PMOS transistors with different process splits. The front gate is composed of a SiO₂/HfO₂ stack with a TiN metal gate electrode. The result is an aggressively reduced equivalent oxide thickness (EOT) of 1.8 nm. The buried oxide is used as a back gate for experimental purposes. Front and back gate interfaces are characterized and the slow oxide trap densities are extracted. The obtained values are comprised between 5 × 10¹⁷ and 8 × 10¹⁸ cm⁻³eV⁻¹. No correlation between front interface trap density and front interface mobility is observed. We underline a strong correlation between rear interface trap density and rear interface mobility degradation. The impact of Ge film thickness is equally studied. For thin films, the measured drain-current noise spectral density shows that LFN can be described by the carrier fluctuation model from weak to strong inversion. For thicker film devices, in weak inversion the LFN can be described by the mobility fluctuation model and in strong inversion the LFN is described by the carrier fluctuation model. The α_H parameter for these devices is 1.2 × 10⁻³. These results are significant for the future development of GeOI technologies.     

LKE and BGI Lorentzian noise in strained and non-strained tri-gate SOI FinFETs with HfSiON/SiO2 gate dielectric

The LKE (Linear Kink Effect) and BGI (Back-Gate-Induced) Lorentzians present in the drain current noise spectra of fully-depleted tri-gate n- and pFinFETs, fabricated on sSOI and SOI substrates with HfSiON/SiO₂ gate dielectric are described.It is shown that the analysis of the parameters of LKE and BGI Lorentzians allows to find the values of (С_eq/m′β²), β and [j_EVB/(m′β)²] where С_eq is the body-source capacitance, m′ ≈ 1, β is the body factor and j_EVB is the density of the EVB current flowing through the gate dielectric.As a result, the following effects were observed for the first time: (i) (С_eq/m′β²) decreases with increasing gate overdrive voltage |V^∗| and depends sub-linearly on the effective fin width W_eff under strong inversion conditions; (ii) in depletion and weak inversion where (С_eq/β²) is independent of |V^∗| the proportionality (С_eq/β²) ∝ W_eff is observed for an effective width W_eff ? 0.87 μm while (С_eq/β²) becomes independent on W_eff for W_eff < 0.87 μm; (iii) the value of β for the FinFETs investigated is higher than for their planar counterparts; (iv) in spite of the fact that strain affects the barrier height at the Si/SiO₂ interface, the EVB current densities j_EVB for sSOI and SOI devices are equal; (v) the values of j_EVB for the HfSiON/SiO₂-devices are much higher than for the HfО₂/SiO₂-ones studied previously. It is also shown that the gate overdrive voltage |V^∗| at which the LKE Lorentzians start to appear is as low as 0.25 V.     

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.     

Electrical noise of laser diodes measured over a wide range of bias currents

The electrical noise of commercially available laser diodes, an index guided AlGaInP diode lasing at 635 nm (SDL3038-11) and an InGaAlP-multiquantum well diode lasing at 670 nm (SVL71B), has been investigated over a wide current range of six orders of magnitude. After increasing proportionally with current at small currents (10 nA to 10 μA), the 1/f noise tends to saturate with increasing current in the range from 10 to 100 μA. For larger operating currents, the 1/f noise increases again, and with the current proportional to I². Different noise sources were discovered below the lasing threshold current. The electrical noise at lower currents must be measured to assess the degradation of the active region of the laser diode.     

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。     

The total dose effects on the 1/f noise of deep submicron CMOS transistors

Using 0.18 μm CMOS transistors, the total dose effects on the 1/f noise of deep-submicron CMOS transistors are studied for the first time in mainland China. From the experimental results and the theoretic analysis, we realize that total dose radiation causes a lot of trapped positive charges in STI （shallow trench isolation） SiO2 layers, which induces a current leakage passage, increasing the 1/f noise power of CMOS transistors. In addition, we design some radiation-hardness structures on the CMOS transistors and the experimental results show that, until the total dose achieves 750 krad, the 1/f noise power of the radiation-hardness CMOS transistors remains unchanged, which proves our conclusion.     

Low-frequency noise and phase noise in MESFETS with LTG-GaAs passivation

We report measurements of the low-frequency noise and phase noise of conventional unpassivated GaAs metal semiconductor field-effect transistors (MESFETs) and of MESFETs fabricated using an overlapping-gate structure and the low-temperature grown (LTG) GaAs as a passivation layer. The noise of the LTG-GaAs passivated MESFET was found to behave quite differently from that of a conventional MESFET and to be significantly reduced at low offset frequencies. These observations are explained in terms of the surface passivating effect of the LTG-GaAs. Low-frequency noise measurements seem to support the idea that the LTG-GaAs passivation reduces the number of active traps, in particular traps with large activation emergies. These results indicate that LTG-GaAs passivation can substantially reduce the near-carrier phase noise of MESFET-based oscillators.     

The wavelet transform based processing means for 1/f noise in millimeter wave focal plane array

After briefly introducing the characteristics of 1/f noise in millimeter wave focal plane array detectors, the paper analyses the relation of wavelet transform and 1/f noise in detail, suggests the fashion of decorrelating 1/f noise using the wavelet transform and deduces the relative expressions. The results of computer simulation show good effectiveness.     

On the limitations of transimpedance amplifiers as tools for low-frequency noise characterization

An experimental set-up for the characterization of low-frequency noise on two terminal devices is reported. The experimental set-up is based on the use of the commercial transimpedance amplifier (TA) EG&G5182. This paper addresses the influence of the TA on the noise characterization process by describing the TA as a non-ideal operational amplifier with a feedback resistor. The impact of the TA finite input resistance and voltage gain is highlighted through comparison with measurements carried out on resistors and diodes.     

高k介质SOI LDMOS RTS噪声测试新方法

提出了一种基于智能温控的RTS噪声测试与分析新方法。该方法利用高k栅介质SOI LDMOS边界陷阱特性,首先建立了含有俘获时间常数、发射时间常数以及噪声幅度等参数的RTS噪声模型;然后设计了RTS噪声智能温控测试系统;最后对实测RTS噪声数据进行频谱变换,得到噪声功率谱密度并作分析。实验表明,该测试系统可以有效地获取高k栅介质SOI LDMOS的RTS噪声,具有良好的动态特性,且其本底噪声抑制率较高,较待测信号低两个数量级左右。     

噪声监测中前景噪声与背景噪声分离方法的研究

为了能够有效的区分前景噪声和背景噪声,本文搭建了一种噪声采集的系统,采用数字噪音计VC824B为噪声采集传感器,单片机作为初级处理端并将噪声数据传输给ARM主控板,再通过通讯板传输给上位机主机。本文提出了在总体噪声的数据中用声强法进行噪声分离。经过实验验证了该方法的可行性,同时为以后提供大规模的噪声采集提供了合理的硬件平台和分析方法。     

Noise Attributes of LWIR HDVIP HgCdTe Detectors

Time series and Fourier-transform data on high-density vertically integrated photodiodes (HDVIP) at 0 and 50 mV reverse bias in the dark have been studied. The detectors have a cutoff wavelength λ _c (60 K) of 10.5 μm. Examination of the detector current time series and Fourier-transform curves of these devices reveals a variety of interesting characteristics: (i) time series displaying switching between four states characteristic of random telegraph signal (RTS) noise, the noise current power spectrum having Lorentzian or double Lorentzian type characteristics, (ii) time series data exhibiting wave-like characteristics with the noise current power spectrum being 1/f ²-like at low frequencies, (iii) time series having a mean value independent of time with the noise current power spectrum being white, and (iv) time series nearly independent of time with the noise current power spectrum having 1/f characteristics. Although from a single array, the excess noise characteristics at low (mHz) frequencies were varied, most of the detectors measured fell into one of these four categories. The predominance of detectors examined had minimal excess low-frequency noise down to ~ 10 mHz. Detectors that displayed RTS noise in reverse bias were repeatable under subsequent measurement. However, when measured at zero bias, the same detectors exhibited no RTS noise, the noise current power spectrum being white in nature.     

Detection of known signals in 1/f fractal noise

Based on the whitening property of wavelet transformation for 1/f noise, this paper addresses the problem of detecting deterministic signals in the presence of 1/f fractal noise. The transfer function of whitening filter is provided as well as the condition for whitening. The receiver structure based on Karhunen-Loeve expansion and the decision rule are also given. Finally performance of the detector is analyzed.