Another random telegraph signal

The correlation function and power spectral density are derived for a random telegraph signal of fixed amplitude where the probability of n changes of sign during an interval is governed by the Bose-Einstein distribution. The results are compared to the usual Poisson case.     

Analysis of slow traps centres in submicron MOSFETs by random telegraph signal technique

In this paper, we present a comprehensive study of slow single traps, situated inside the gate oxide of small area (W×L=0.5×0.1 μm²) metal–oxide–semiconductor (MOS) transistors. The gate oxide of the analyzed transistors, which have been used for memory-cell applications, is composed of two SiO₂ layers—a deposited high-temperature oxide (HTO) and the thermal oxide. The interface between the two gate oxides is shown to play a significant role in the channel conduction: we observed that the presence of individual traps situated inside the gate oxide, at some angstroms from the interface with the channel, is inducing discrete variations in the drain current. Using random telegraph signal (RTS) analysis, for various temperatures and gate bias, we have determined the characteristics of these single traps: the energy position within the silicon bandgap, capture cross section and the position within the gate oxide.     

SURF: A telegraph signal based uniformly distributed analog random voltage generator

The generation of uniformly distributed analog random voltages is a difficult problem, generally solved by methods using digital-to-analog conversion following a random number generator. We describe a new and easy implement system based on linear filtering of a random telegraph signal.     

The gate bias and geometry dependence of random telegraph signalamplitudes [MOSFET]

A new random telegraph signal (RTS) amplitude model based upon band bending fluctuations has been developed, in contrast to other studies of RTS noise amplitudes, which are derived from RTS fitting parameters, it is demonstrated in this work that noise amplitudes may be predicted from band bending calculations and device DC characteristics. This new model suggests that the decrease in band bending associated with slow-state trapping results in mobility degradation for low gate biases (Coulombic-scattering-limited) and an enhancement in mobility due to vertical field reductions at high gate biases (surface roughness/phonon scattering limited). The band bending formulation shows good correlation with experimental data and accurately predicts the observed dependence upon effective channel length and width     

Comment on “Channel length dependence of random telegraphsignal in sub-micron MOSFET's” [with reply]

For original paper see M.-H. Tsai, T.P. Ma and T.B. Hook, ibid., vol.15. no.12, pp.504-6 (1994). It is not possible to determine whether the fluctuations in a resistance are caused by a number or a mobility fluctuation by simply varying the magnitude of a series resistance. This is the essential claim by the authors of the original paper. The series elements are MOS channels, but since the real charge density is assumed constant, it is not material that the gates of the series connected MOST are joined together. The authors of the original paper reply to these comments     

Channel length and width dependence of hot-carrier hardness influorinated MOSFETs

A study of the interface degradation caused by channel-hot-electron (CHE) and substrate-hot-electron (SHE) injection in fluorinated MOSFETs and in unfluorinated control over a wide range of channel lengths and widths is discussed. In all cases, the fluorinated MOSFETs are more resistant to hot-electron-induced interface damage, although the beneficial effect of fluoride becomes less significant for submicrometer devices. For nonfluorinated control devices, a significant gate-size dependence of the transconductance degradation is observed after either CHE or SHE injection. In contrast, the fluorinated devices exhibit almost no gate-length dependence in the range of 0.6-10.0 μm or gate-width dependence in the range of 1.6-10.0 μm after SHE injection, in which the injected hot electrons assume much better areal uniformity than in CHE injection. However, significant gate-size dependence was observed in fluorinated devices after CHE injection, primarily due to the spatial nonuniformity of the CHE damage. The beneficial effect of F and its influence on the gate-size dependence in response to SHE injection may be attributed to the local strain relaxation near the SiO₂/Si interface where F is incorporated in the Si-O network. These results also suggest that the development of local-strain relaxed isolation technology will be important for deep-submicrometer MOSFETs     

超薄埋氧SOI nMOSFET器件硅膜内RTN研究

本文主要研究在超薄埋氧SOI器件内,位于硅薄膜内的单点缺陷造成的随机电报噪声(RTN)。通过低频噪声测试和时域测试,硅薄膜内单点缺陷RTN得到了识别和分析。RTN的相对幅值dID/ID与前栅、背栅、源漏电压的关系得到了具体的分析。实验结果显示,交换源漏电极位置时,不同单点缺陷的dID/ID与VDS的相关性会呈现一致性或者非一致性。这是由于单点缺陷在源漏方向的位置不同所致。文中还做了进一步的仿真研究,对这一点进行验证和解释。     

Effects of quantization on random telegraph signals observed in deep-submicron MOSFETs

Random telegraph signals (RTS) have been investigated in the drain to source voltage of W_eff×L_eff=1.37×0.17 μm² medium-doped drain (MDD) n-type MOSFETs. The emission (τ_e) and capture (τ_c) times of the probed trap were studied as a function of gate voltage as well as substrate voltage. The small size and high doping density of the n-MOSFETs studied create a strong electric field in the MOSFET inversion layer, which makes the surface conduction band split into discrete energy levels. Therefore, modified expressions of τ_e and τ_c including the influence of bulk bias (V_SB), which changes the degree of quantization, are presented. The trap position in the oxide with respect to the Si–SiO₂ interface, and the trap energy, were calculated from the gate voltage dependence of the emission and capture times under different bulk bias conditions. The behavior of the emission and capture times predicted by the two-dimensional (2D) surface quantization effects is in qualitative agreement with the experimental results. The RTS amplitude (ΔV_DS/V_DS) shows a positive dependence on V_SB. The coefficient α for screened oxide charge scattering was calculated at different gate voltages and bulk bias from the RTS amplitude. In addition, the theoretical calculation of the scattering coefficient α, using a 2D surface mobility fluctuation model, was presented, which shows a good agreement with the experimental data.     

Random telegraph signal noise instabilities in lattice-mismatched InGaAs/InP photodiodes

Spontaneous and induced instabilities in the character of Random Telegraph Signal (RTS) noise are studied in photodetector arrays, fabricated on lattice-mismatched InGaAs/InP heterostructures. The disappearance and reappearance of the RTS noise as well as abrupt changes in the RTS noise amplitude and pulse complexity are investigated as a function of voltage and temperature. The RTS noise instabilities are explained in terms of structural transformation of complex multistable crystalline defects.     

Random telegraph signal currents and low-frequency noise injunction field effect transistors

The detailed study of random telegraph signal (RTS) currents and low-frequency (LF) noise in semiconductor devices in recent years has confirmed their cause and effect relationship. In this paper we describe the physical mechanisms responsible for RTS currents in any device. The methods for calculating the amplitudes and characteristic times of the RTS currents produced by traps with known electrical characteristics and locations are described. The noise spectra in junction field effect transistors (JFET's) resulting from traps in the silicon or the oxide are derived as a function of basic device parameters, operating conditions and temperature. Experimental results verifying the predictions of the models are presented     

Quantization in multisensor random signal detection

Optimum detection schemes based on quantized data are of great interest in radar and sonar applications. The design and properties of multisensor schemes are considered here for detection of weak random signals in additive, possibly non-Gaussian, noise. Signal-to-noise ratios are assumed unknown and the signals at the different sensors may be statistically dependent. Analytical expressions describing the best way to fuse the quantized observations for cases with any given observation sample size are provided. The best schemes for originally quantizing the observations are also studied for the case of asymptotically large observation sample sizes. These schemes are shown to minimize the mean-squared error between the best weak-signal test statistic based on unquantized observations and the best weak-signal test statistic based on quantized observations (under signal absent). Numerical results indicate it is sometimes best for each quantizer to use different size alphabets when a quantizer is located at each sensor     

A differential equation related to a random telegraph wave problem--Computer calculation of series solution

A method is developed for calculating the probability density functionp(y)of the output of anRCfilter when the input is a particular kind of random telegraph wave. The method makes use of a computer to determine the numerical values of the coefficients in two series solutions, one of which contains a logarithm, of a fourth-order linear differential equation. The constants of integration are determined from the boundary conditions by a procedure that involves a summation of the series. Representative values and curves ofp(y)are presented, and the generality of the computer method is discussed briefly,     

Characterization of oxide traps in 0.15 μm MOSFETs using random telegraph signals

Random telegraph signals (RTS) have been used to characterize oxide traps of W×L=0.97×0.15 μm² medium-doped drain n-MOSFETs. RTS have been measured in the linear and saturation regions of operation, both in forward and reverse modes where the drain and source are reversed. The contribution of mobility fluctuations as well as number fluctuations to the amplitude of RTS has been investigated. The scattering coefficient due to screened Coulomb scattering effect is computed from the measured data as a function of channel carrier density. The depth of the position of the trap in the oxide from Si–SiO₂ interface is calculated utilizing the dependence of the emission and capture times on the gate voltage. In addition, the position of the trap along the channel with respect to the source is obtained using the difference in the drain voltage dependence of the capture and emission times between the forward and reverse modes. Knowing the location of the trap in the oxide and along the channel, the energy associated with the trap can be extracted accurately from the data. This technique allows one to evaluate the trap energy at the point where the trap is located without any assumptions about the location of the trap or the need for variable temperature measurements. The probed trap was found to be an acceptor type center (repulsive for an n-MOSFET) located at about 27 Å deep the oxide, half-way between drain and source with an energy of E_Cox−E_T=3.04 eV, slightly above the conduction band edge.     

随机信号雷达抗干扰性能分析

研究了采用带限高斯白噪声波形的随机信号雷达在噪声和欺骗干扰环境下的工作性能.通过研究接收机输入/输出信噪比关系和检测性能,分析了随机信号波形抗噪声干扰的性能;采用仿真方法,分析了抗欺骗干扰性能.仿真和分析结果表明,随机信号波形比线性调频脉冲压缩波形具有更好的抗欺骗干扰能力.     

Temperature dependence of diffusion length in MCT epitaxial layers

The temperature dependence of the minority charge carriers diffusion length in the active photosensitive layer of a matrix photodetector based on MCT heteroepitaxial structure grown by molecular beam epitaxy is studied.     

Channel length independent subthreshold characteristics insubmicron MOSFETs

This work reports an anomalous subthreshold characteristic of the MOSFET for the first time. It is observed that the subthreshold characteristic does not change as the channel length decreases. The cause of channel length independent subthreshold characteristics is identified as the localized pileup of channel dopants near the source and drain ends of the channel. The low surface potential of this pileup region limits the subthreshold current of MOSFET. As a result, the ratio of on-current to off-current for this MOSFET increases as the channel length is reduced, which is an important parameter for low-voltage operation. It is found that a MOSFET with channel length independent subthreshold characteristic is more suitable for low-voltage operation     

Quantum-mechanical linear filtering of random signal sequences

The problem of estimating a member of a scalar random signal sequence with quantum-mechanical measurements is considered. The minimum variance linear estimator based on an optimal present quantum measurement and optimal linear processing of past measurements is found. When the average optimal measurement without postprocessing, for a fixed signal, is linear in the random signal and the signal sequence is pairwise Gaussian, the optimal processing separates: the optimal measurement is the same as the optimal measurement without regard to past data, and the past and present data are processed classically. The results are illustrated by considering the estimator of the real amplitude of a laser signal received in a single-mode cavity along with thermal noise; when the random signal sequence satisfies a linear recursion, the estimate can be computed recursively. For a one-step memory signal sequence it is shown that the optimal observable generally differs from the optimal observable disregarding the past; the optimal measurement can be computed recursively.     

Dose-rate dependence of optically stimulated luminescence signal

Optically stimulated luminescence (OSL) is the luminescence emitted from a semiconductor during its exposure to light. The OSL intensity is a function of the total dose absorbed by the sample. The dose-rate dependence of the OSL signal of the semiconductor CaS doped Ce and Sm was studied by numerical simulation and experiments.Based on a one-trap/one-center model, the whole OSL process was represented by a series of differential equations.The dose-rate properties of the materials were acquired theoretically by solving the equations. Good coherence was achieved between numerical simulation and experiments, both of which showed that the OSL signal was independent of dose rate. This result validates that when using OSL as a dosimetry technique, the dose-rate effect can be neglected.