Investigations into the source of 1/f noise in Hg<Subscript>x</Subscript>Cd<Subscript>1−x</Subscript>Te diodes

This work is aimed at elucidating the mechanism of 1/f noise in Hg_xCd_1−xTe diodes in order to reduce 1/f noise in high-performance thermal cameras. Currently, to reach the required signal-to-noise ratio, the operating temperature of thermal cameras is 77 K. If 1/f noise could be reduced, this operating temperature could be raised without reducing the signal-to-noise ratio, allowing cheaper, smaller, and lighter cooling systems to be used. There are still some fundamental aspects of 1/f noise that are not fully understood. One aspect in particular is whether the noise is caused by mobility or number density fluctuations because both could give the conductivity fluctuations observed. This paper explores the noise coupling and current coupling between diodes on an array. It is shown that 1/f noise is present on the photons emitted from a forward-biased diode, suggesting that the rate of radiative recombination fluctuates. The results suggest that these fluctuations are due to carrier number-density fluctuations. From correlation measurements, it is shown that at least 32% of the 1/f noise in the forward-biased diode is correlated with carrier density fluctuations in Hg_xCd_1−xTe diodes.     

Critical discussion on unified 1/f noise models for MOSFETs

Recently, unified noise models, like BSIM3, have been proposed in literature to describe the 1/f noise of n- and p-type MOSFETs in all operating regimes. These models combine carrier number fluctuations and correlated mobility fluctuations. The latter are induced by the Coulomb scattering of free carriers at trapped interface charge. The unified 1/f noise models assume implicitly that the mobility, limited by Coulomb scattering, does not depend on the inversion carrier density. However, this assumption is not correct in view of theoretical calculations and recent experimental results. In this paper, we show that the correlated mobility fluctuations are negligible, if the correct dependence on inversion carrier density is taken into account for the Coulomb scattering limited mobility. Consequently, the unified 1/f noise models cannot predict the 1/f noise observed experimentally in p-type MOSFETs, except if nonphysical fitting parameters are used. This paper serves as a critical discussion on the unified 1/f noise models for MOSFETs. Here it is not our intention to propose a new 1/f noise model     

Noise modeling methodologies in the presence of mobility degradation and their equivalence

For compact modeling of the noise in devices, one of the following three methods is usually applied: 1) An equivalent circuit based approach, 2) the classical Langevin or Klaassen-Prins approach, or 3) the impedance field method. It is well known that for long-channel MOST (where mobility degradation due to a lateral field is absent), all three methods obtain the same result. But it is still not recognized how these methodologies need to be changed when the mobility starts to depend on the electric field. In this work we demonstrate how these methodologies can be adapted to incorporate mobility degradation and show that for any arbitrary mobility model /spl mu/(E) all the methods yield the same expressions for induced gate and drain noise current, which demonstrates the equivalence of the methods. We also present, for the first time, a general expression of induced gate noise which is valid for any mobility model (an expression of the drain current noise was already presented in our previous work) and some very general expressions of noise parameters that can be used for noise modeling with any kind of mobility model.     

Low-frequency noise in polysilicon emitter bipolar transistors

The low-frequency noise in polysilicon emitter bipolar transistors is investigated. Transistors with various geometries and various properties of the oxide layer at the monosilicon polysilicon interface are studied. The main 1/f noise source proved to be located in the oxide layer. This source causes both 1/f noise in the base current S_Ib and 1/f noise in the emitter series resistance S_re The magnitude of the 1/f noise source depends on the properties of the oxide layer. The 1/f noise is ascribed to barrier height fluctuations of the oxide layer resulting in transparency fluctuations for both minority and majority carriers in the emitter, giving rise to S_Ib and S _re respectively. It is also shown that a low transparency of the oxide layer also reduces the contribution of mobility fluctuations to S_Ib     

Impact of the interfacial layer on the low-frequency noise (1/f) behavior of MOSFETs with advanced gate stacks

The impact of the interfacial layer thickness on the low-frequency (LF) noise (1/f noise) behavior of n- and p-channel MOSFETs with high-/spl kappa/ gate dielectrics and metal gates is investigated. Decreasing the interfacial layer thickness from 0.8 to 0.4 nm affects the 1/f noise in two ways. 1) The mobility fluctuations mechanism becomes the main source of 1/f noise not only on pMOS devices, as usually observed, but also on nMOS devices. 2) A significant increase of the Hooge's parameter is observed for both types of MOSFETs. These experimental findings indicate that bringing the high-/spl kappa/ layer closer to the Si-SiO/sub 2/ interface enhances the 1/f noise mainly due to mobility fluctuations.     

A model for 1/f noise in diffusion current based on surfacerecombination velocity fluctuations and insulator trapping

In this paper we present a new model for low frequency 1/f noise in semiconductor diodes. The model describes noise in diffusion current due to fluctuations in surface recombination velocity. The fluctuations in surface recombination velocity are in turn caused by insulator trapping. We examine the model's predictions for 1/f noise and its dependence on device geometry, temperature, surface potential, majority carrier concentration, and trap energy. Example calculations are performed for narrow band gap HgCdTe (E_G=0.125 eV at 77 K), for which this mechanism should be relevant     

Compact Channel Noise Models for Deep-Submicron MOSFETs

In this paper, compact channel noise models valid in all regions of operation for deep-submicron MOSFETs have been developed and experimentally verified. The physics-based expressions for thermal noise and flicker noise and corner frequency constitute compact channel noise models. The carrier heating, channel-length modulation, and mobility degradation due to the lateral electric field have been incorporated in the models. The effect of the mobility and carrier number fluctuations on the flicker noise, as well as the dependence of the mobility limited by Coulomb scattering on the inversion carrier density, have been considered in the flicker noise model. The measurement results validate the proposed models.      

Noise in DMOS transistors in a BICMOS-technology

An experimental and theoretical study of the 1/f noise and the thermal noise in double-diffused MOS (DMOS) transistors in a BICMOS-technology has been carried out. By using an analytical model that consists of an enhancement MOS transistor in series with a depletion MOS transistor and a resistance, and by attributing noise sources to each device, the noise in DMOS devices is simulated accurately. Three distinct regions of operation are defined: enhancement transistor control, depletion transistor control and the linear region. In the first region, the noise is strictly determined by the enhancement transistor. It was found that the 1/f noise in this region is caused by mobility fluctuations and is very low. In the depletion transistor control region both transistors influence the total noise. Here the 1/f noise is dominated by the depletion transistor. The series resistance is only of importance in the linear region     

Oxide thickness dependent compact model of channel noise for E-mode AlGaN/GaN MOS-HEMT

In this paper, a compact channel noise model for gate recessed enhancement mode GaN based MOS-HEMT which is valid for all regions of operation is proposed. The compact noise model consists of high frequency thermal noise and low frequency flicker noise. The drain current, which is one of the most important parameters for compact noise model is developed by incorporating interface and oxide traps, mobility degradation due to vertical electric field, velocity saturation effect and self-heating effect. The flicker noise model is derived by considering mobility and carrier fluctuation due to traps present in both oxide and interface layer. The thermal noise and flicker noise models are validated by comparing the results with TCAD simulation and experimental results from literature respectively. Effect of thermal and flicker noise power spectral density (PSD) variation with different oxide thickness has also been analyzed.     

Impact of interfacial layer on low-frequency noise of HfSiON dielectric MOSFETs

Low-frequency noise measurements and analysis were performed on n-channel MOSFETs with HfSiON as the gate-dielectric material. The role of SiON interfacial-layer thickness was investigated. It was observed that these fluctuations can be described by the unified flicker-noise model that attributes noise to correlated carrier-number/mobility fluctuations due to trapping states in the gate dielectric. The model was modified to include the effect of different gate stack layers on the observed noise. The carrier-number fluctuations were found to dominate over the correlated mobility fluctuations in the measured bias range and more so at the lower gate overdrives. The noise magnitude showed a decrease with increasing SiON interfacial-layer thickness. Furthermore, an inverse-proportionality relationship was revealed between the effective oxide trap density and SiON thickness.     

Random telegraph signals in deep submicron n-MOSFET's

Random telegraph signals (RTS) in the drain current of deep-submicron n-MOSFET's are investigated at low and high lateral electric fields. RTS are explained both by number and mobility fluctuations due to single electron trapping in the gate oxide. The role of the type of the trap (acceptor or donor), the distance of the trap from the Si-SiO₂ interface, the channel electron concentration (which is set by the gate bias) and the electron mobility (which is affected by the drain voltage) is demonstrated. The effect of capture and emission on average electron mobility is demonstrated for the first time. A simple theoretical model explains the observed effect of electron heating on electron capture. The mean capture time depends on the local velocity and the nonequilibrium temperature of channel electrons near the trap. The difference between the forward and reverse modes (source and drain exchanged) provides an estimate of the effective trap location along the channel     

Evidence for 1/f noise in diffusion current due to insulator trapping and surface recombination velocity fluctuations

In this paper, we present evidence for 1/f noise in diode diffusion current due to fluctuations in surface recombination velocity caused by insulator trapping. Using a unique structure consisting of a thin HgCdTe film with a pn junction on one side and an insulated gate on the other, we demonstrate that the noise measured in the junction is a strong function of the surface potential on the opposite side of the film. We compare the results to model predictions, finding good qualitative agreement.     

Theory of 1/f noise in bipolar silicon planar transistors

A theory of 1/f low-frequency noise in silicon planar transistors is developed. It relates this noise to fluctuations in base current produced by fluctuations of occupied traps in the silicon dioxide. It is shown that the theoretical relationship of noise is consistent with experiment.     

Low-frequency noise spectroscopy of polycrystalline siliconthin-film transistors

Polycrystalline silicon thin-film transistor (polysilicon TFT's) characteristics are evaluated by using a low-frequency noise technique. The drain current fluctuation caused by trapping and detrapping processes at the grain boundary traps is measured as the current spectral density. Therefore, the properties of the grain boundary traps can be directly evaluated by this technique. The experimental data show a transition from 1/f behavior to a Lorentzian noise. The 1/f noise is explained with an existing model developed for monocrystalline silicon based on fluctuations of the inversion charge near the silicon-oxide interface. The Lorentzian spectrum is explained by fluctuations of the grain boundary interface charge with a model based on a Gaussian distribution of the potential barriers over the grain boundary plane. Quantitative analysis of the 1/f noise and the Lorentzian noise yield the oxide trap density and the energy distribution of the grain boundary traps within the forbidden gap     

Low frequency gate noise in a diode-connected MESFET: measurementsand modeling

The low frequency Schottky diode noise has been investigated in GaAs power MESFETs. For those devices, gate noise spectra are generally composed of 1/f and shot noise contributions. We have observed an increase by two orders of magnitude of the noise level when MESFETs are submitted to rf life-test. The increase of the 1/f noise can be explained by a modification of the gate space charge region extension. This interpretation is sustained by a reduction of the drain current transient magnitude and the inherent active trap density. A correlation is assumed between the increase of the shot noise level after rf life-test and a micro-plasma formation. Both 1/f noise and shot noise evolution might originate in a local increase of the electric field in the vicinity of the gate in drain access region. We have demonstrated that LF gate current noise is an early indicator of damage mechanisms occurring at the gate-semiconductor and passivation-semiconductor interfaces of the devices     

硅双极晶体管1／f噪声的物理机制

在低频下,1/f噪声是硅双极晶体管的主要噪声。到目前为止,一般认为,1/f噪声有二种来源:表面态的存在和体内自由载流子迁移率的涨落。这两种1/f噪声有不同的表现形式。目前还没有统一的模型来描述1/f噪声,这是由于对1/f噪声的物理机理还没有一个完整、统一的理论。本文对已见发表的1/f噪声主要研究结果作了评述。     

1/f; noise model for MOSTs biased in nonohmic region

Relations are derived for the 1/f; noise current and for the equivalent input noise voltage of a MOST biased in the nonlinear region. The experimentally obtained results are in agreement with the calculations. In addition the value of power spectrum of the noise current is related to that in the ohmic region. In the last region the 1/f; noise appears to be caused by mobility fluctuations of the charge carriers. In the nonohmic region, the noise consists of two contributions: (i) mobility fluctuations and (ii) number fluctuations in the charge carriers due to fluctuations of the effective gate voltage induced by mobility fluctuations.     

Model for the excitation of 1/f noise by high-frequency a.c. signals

A model is presented for the excitation of 1/f noise in carbon and semiconductor resistors by high-frequency a.c. signals. The model does not require special theories on 1/f noise; the observed 1/f noise is attributed, as usual, to resistance fluctuations.     

光电耦合器电流传输比的噪声表征

光电耦合器中可俘获载流子的陷阱密度是影响其电流传输比(CTR)的重要因素,并与器件可靠性有密切关系.在器件内部的多种噪声中,1/f噪声可有效地表征器件陷阱密度.本文在研究光电耦合器工作原理以及1/f噪声理论的基础上,建立了光电耦合器的CTR表征模型和1/f噪声模型.在输入电流宽范围变化的条件下,测量了器件的电学噪声和CTR变化,实验结果验证了以上模型的正确性.将CTR模型与噪声模型相结合,得到了CTR与1/f噪声之间的关系.此关系应用于对光电耦合器辐照实验结果的分析,实验结果与理论得到的结论一致.理论与实验结果表明,噪声幅值越大,电流指数越接近于2,则器件的可靠性越差,相同工作条件下CTR的老化衰减量越大,其失效率显著增大.从而证明噪声可表征光电耦合器的CTR并能准确地反映器件的可靠性.     

A nonfundamental theory of low-frequency noise in semiconductordevices

A general low-frequency noise theory based on the fluctuation in the number of carriers is presented. In this theory, the low-frequency noise is attributed to the traps within the bandgap of a semiconductor, which are the sources of the generation-recombination noise. The cumulative effect of the generation-recombination noise from each trap center generates a 1/f type noise. It is shown that in fact, 1/f noise may have any frequency dependence between 1/f⁰-1/f². If not masked by thermal noise, the low-frequency noise generated from these traps becomes 1/f² at very high frequencies. Also, if the lifetime of the carriers in the semiconductor under nonequilibrium condition is finite, at very low frequencies, the noise spectral density reaches a plateau. While this theory can be applied to any semiconductor device, only heterojunction bipolar transistors (HBTs) were considered in detail. Based on this theory, a model for low-frequency noise in the base of HBTs is derived. Frequency and current dependence of low-frequency noise are modeled. Results of the base noise measurements in AlGaAs/GaAs HBTs were found to agree with the noise theory presented here. This significant theory, for the first time, proves the possibility of the number fluctuation model as a general 1/f noise cause without a need for specific and nonrealistic carrier lifetime probability functions